Rec-audio-car-archive-name: FAQ/part3 Version: 4.33 Last-modified: 13 May 1998 4 Subwoofers ***************** This section describes some elements necessary for understanding subwoofers - how they operate, how to build proper enclosures, how to pick the right driver for you, and how to have a computer do some of the work for you. 4.1 What are "Thiele/Small parameters?" [CD, RDP] ==================================================== These are a group of parameters outlined by A. N. Thiele, and later R. H. Small, which can completely describe the electrical and mechanical characteristics of a mid and low frequency driver operating in its pistonic region. These parameters are crucial for designing a quality subwoofer enclosure, be it for reference quality reproduction or for booming. `Fs' Driver free air resonance, in Hz. This is the point at which driver impedance is maximum. `Fc' System resonance (usually for sealed box systems), in Hz `Fb' Enclosure resonance (usually for reflex systems), in Hz `F3' -3 dB cutoff frequency, in Hz `Vas' "Equivalent volume of compliance", this is a volume of air whose compliance is the same as a driver's acoustical compliance Cms (q.v.), in cubic meters `D' Effective diameter of driver, in meters `Sd' Effective piston radiating area of driver in square meters `Xmax' Maximum peak linear excursion of driver, in meters `Vd' Maximum linear volume of displacement of the driver (product of Sd times Xmax), in cubic meters. `Re' Driver DC resistance (voice coil, mainly), in ohms `Rg' Amplifier source resistance (includes leads, crossover, etc.), in ohms `Qms' The driver's Q at resonance (Fs), due to mechanical losses; dimensionless `Qes' The driver's Q at resonance (Fs), due to electrical losses; dimensionless `Qts' The driver's Q at resonance (Fs), due to all losses; dimensionless `Qmc' The system's Q at resonance (Fc), due to mechanical losses; dimensionless `Qec' The system's Q at resonance (Fc), due to electrical losses; dimensionless `Qtc' The system's Q at resonance (Fc), due to all losses; dimensionless `Ql' The system's Q at Fb, due to leakage losses; dimensionless `Qa' The system's Q at Fb, due to absorption losses; dimensionless `Qp' The system's Q at Fb, due to port losses (turbulence, viscosity, etc.); dimensionless `n0' The reference efficiency of the system (eta sub 0) dimensionless, usually expressed as a percentage `Cms' The driver's mechanical compliance (reciprocal of stiffness), in m/N `Mms' The driver's effective mechanical mass (including air load), in kg `Rms' The driver's mechanical losses, in kg/s `Cas' Acoustical equivalent of Cms `Mas' Acoustical equivalent of Mms `Ras' Acoustical equivalent of Rms `Cmes' The electrical capacitive equivalent of Mms, in farads `Lces' The electrical inductive equivalent of Cms, in henries `Res' The electrical resistive equivalent of Rms, in ohms `B' Magnetic flux density in gap, in Tesla `l' Length of wire immersed in magnetic field, in meters `Bl' Electro-magnetic force factor, can be expressed in Tesla-meters or, preferably, in meters/Newton `Pa' Acoustical power `Pe' Electrical power `c' Propagation velocity of sound at STP, approx. 342 m/s `p' Density of air at STP 1.18 kg/m^3 (rho) 4.2 How does speaker sensitivity affect real world SPL? Will a higher sensitivity give me a larger SPL? [MS] ======================================================================== When it comes to mids and highs, efficiency (sensitivity) is a fairly good indicator of output differences at the same power level. When it comes to subwoofer performance, the driver's sensitivity is irrelevant unless you are also specifying a box volume. An efficient sub requires a larger box to achieve equivalent extension to a less efficient sub. In a small box, the less efficient sub will actually be LOUDER at low frequencies at the SAME POWER as the more efficient sub. Linear excursion is a very good indicator of ultimate output capability (given sufficient power to drive the speaker to that point.) To make sound you must move air; therefore, the more air you move, the more sound you make. When comparing two speakers of equal surface area, the one with greater excursion capability will play louder given sufficient power. 4.3 What are the enclosure types available? [JLD, JG] ======================================================== Only the order of the enclosure itself is shown here. The addition of a crossover network increases the order of the system by the order of the crossover. Example: If a First-Order, 6dB/Oct. crossover (single inductor in series with the speaker) is used with a Fourth Order enclosure, the total system is a fifth order. Note: Air volumes and ratios shown here may not be to scale. This is designed to provide order information only. First Order Infinite-Baffle or Free-Air | | / / || || \ \ | | Second Order Second Order Acoustic- or Air-Suspension Isobaric* Acoustic-Suspension or Sealed (Compound Loaded) _______________________ _______________________ | | | _____| | / | / / | / | / / | || | || || | || | || || | \ | \ \ | \ | \____\ |_______________________| |_______________________| Fourth Order Fourth Order Fourth Order Bass-Reflex or Passive Radiator Isobaric* Vented or Ported Bass-Reflex Bass-Reflex _______________ _______________ _______________ | | | | | ____ | | / | / | / / | / | / | / / | || | || | || || | || | || | || || | \ | \ | \ \ | \ | \ | \____\ | | | | | | | | | / | | | | | / | | | ____| | | | ____| | | | | | ____ | \ | ____ | | | \ | | |_______________| |_______________| |_______________| Fourth Order Fourth Order Single-Reflex Bandpass Isobaric* Single-Reflex Bandpass _________________ ____ _______________________ ____ | | | | | | | | | | | / | | | | / \ | | | | / | | / \ | | || | | || || | | || | | || || | | \ | | \ / | | \ | | \ / | |_________|_______________| |_______________|_______________| Fourth Order Fourth Order Three Chamber Three Chamber Isobaric* Single-Reflex Bandpass Single-Reflex Bandpass ____________ ____________ ______________ ______________ | | | | | | | | | | | | | / | | \ | | / \ | | / \ | | / \ | | / \ / \ | | || || | | || || || || | | || || | | || || || || | | \ / | | \ / \ / | | \ / | | \ / \ / | |______|_____________|______| |_______|_______________|_______| Fifth Order = Fourth Order Enclosure + First Order Crossover = Third Order Enclosure + Second Order Crossover, etc. Sixth Order Sixth Order Dual-Reflex Bandpass Isobaric* Dual-Reflex Bandpass ____ _____________ ____ ____ ____________ ____ | | | | | | | | | | | | | | | | | / | | | | | | / \ | | | | | | / | | | | / \ | | || | | || || | | || | | || || | | \ | | \ / | | \ | | \ / | |_______________|_____________| |______________|_____________| Sixth Order Three Chamber Quasi-Sixth Order Dual-Reflex Bandpass Series-Tuned Bandpass _ _________ _________ _ _________________ ____ | | | | | | | | | | | | | | | | | | / | | \ | | | | / | | | | / \ | | / | | || || | | || | | || || | | || | | \ / | | \ | | \ / | | \ | |________|_____________|________| | ____| | | | | ____ | | | | |___________|_____________| Seventh Order = Sixth Order Enclosure + First Order Crossover, etc. Quasi-Eighth Order Series-Tuned Dual-Reflex Eighth Order Bandpass Triple-Reflex Bandpass _ _______________ _ ____________ _____________ | | | | | | | | | | | | | | / | | | | | | | | / | | | | || | | | | || | | | | \ | |____ _____________ ____| | \ | | | | | | | | | ____| | | | | / | | | | | | / | | ____ | | || | |_____________|___________| | || | | \ | | \ | |______________|______________| * Isobaric or Coupled Pair (Iso-group) Variations: A variety of configurations may be used in the isobaric loading of any order enclosure. Physical and acoustic restrictions may make one loading configuration preferable to another in a particular enclosure. Composite or Push-Pull Compound or Piggy-Back or Face-to-Face Loading or Tunnel Loading _________________ ___________________________ | | | ____| | / \ | / / | / \ | / / | """ || || """ | """ || || """ | """ || || """ | """ || || """ | \ / | \ \ | \ / | \___\ |_________________| |___________________________| Back-to-Back Loading Planar Loading _________________________ ___________________________ | _________| | | | | \ / | / | | \ / | / | | """ || || """ | || """ | | """ || || """ | || """ | | / \ | \ | | /_______\ | \ | |_________________________| |________________________| | | | / | / | || """ | || """ | \ | """ indicates direction of \ | """ simultaneous cone movement. |__| 4.4 Which enclosure type is right for me? [IDB, DK] ====================================================== This answer is not designed to tell you exactly what kind of enclosure to build, but rather to give an idea of the advantages and disadvantages to the simple configurations (Infinite baffle [1st order], Sealed [2nd order], Ported [4th order] and basic bandpass). Building and designing more complicated systems (order #4) is not for the light at heart. 4.4.1 Infinite Baffle ("free-air") ----------------------------------- * Advantages... - No box necessary! - This means it's usually cheaper to design and implement in your system * Disadvantages... - Requires that a good seal be obtained between front and rear of driver. In a car, this can be quite difficult and may require the installer to remove trim panels to plug any holes that would let energy "bleed through". - The responsibility for damping cone motion rests solely on the driver's suspension. As fatigue sets in, this becomes a critical issue in infinite baffle set-ups. - Less efficient in the sub-bass region than above mentioned enclosures. - Potentially more expensive drivers than good boxable woofer - The suspension must be extremely hearty and long-lasting to withstand high power applications. 4.4.2 Sealed Box ----------------- * Advantages... - Small enclosure volumes - Shallow (12 dB/Octave) roll off on low end - Excellent power handling at extremely low frequencies - Excellent transient response/ group delay characteristics - Easy to build and design - Forgiving of design and construction errors * Disadvantages... - Not particularly efficient - Marginal power handling in upper bass frequencies - Increased distortion in upper bass over ported design - When using high power and small box, magnet structure is not in an ideal cooling environment 4.4.3 Ported Box ----------------- * Advantages... - 3-4 dB more efficient overall than sealed design - Handles upper bass frequencies better with less distortion - Magnet is in good cooling environment - When properly designed, a ported box will slaughter a sealed in terms of low frequency extension * Disadvantages... - Size (not so critical outside the mobile environment) - Woofer unloads below Fb - More difficult to design/ can result in boomy, nasty sounding bass if misaligned 4.4.4 Bandpass Box ------------------- * Advantages... - When properly designed and implemented, can provide superior LF extension and efficiency. - Cone motion is controlled more and therefore mechanical powerhandling is increased. - Cones are physically protedcted from contents of trunk flying around. - Output is easily channeled directly into the interior of sedans. * Disadvantages... - Difficult to build (not recommended for newbies), and very sensitive to misalignment due to calculation or construction errors. - Their characteristic filtering often masks any distortion that occurs as a result of amplifier clipping or overexcursion and thus will give the user no warning that the driver is over-stressed and about to fail. - Need substantial mid-bass reinforcement to make up for narrow bandwidths in efficient alignments. - Transisient response is largely dependant upon the alignment chosen....wider bandwidths will result in sloppier performance, narrower bandwidths (and thus higher effiencies) result in better transient performance. - They can oft times be quite large. 4.5 How do I build an enclosure? [AO] ======================================== These instructions are for building a first order (sealed) subwoofer enclosure. Builing ported or bandpass boxes is more difficult, and those designs are less forgiving of mistakes. These instructions apply for all box designs, but be sure of the measurements before you make your cut. Building your own enclosure can save you a lot of money, but only if you don't need to buy all of your materials twice because of mistakes! You will need: *Wood* I only use MDF (Medium Density Fiberboard), but others have reported success uisng other hardwoods like birch and oak. Do not use plywood - it's far to flexible and porous. Use a minimum of 3/4" wood - flexing sub enclosures lose precious energy! *Screws* For one inch wood use #8 2 inch wood screws. For 3/4 inch wood use #8 1 3/4 inch screws. Double grip Drywall screws also work well. *Adhesive* I use "Liquid Nails" which comes in a caulk tube or a bucket, but any paste type of adhesive will work. Spray adhesives will not work. *Silicone sealant* White, brown, clear, caulk tube, or squeeze bottle, it doesn't matter. Make sure you don't get silicone lubricant (which comes in a spray can)! *Terminals/Terminal Cup* To allow easy connections from your amp. Besides these materials you will need several tools: *Table saw or radial arm saw* I use a radial arm saw, just because it's a little easier and accurate, but a table saw will work also. You can use a circular saw, but be very careful to make your cuts straight. *Jig saw* For cutting your speaker hole. *Drill* You will also need a 1/8" drill bit, a screwdriver bit, and a countersinking bit. *Pencil* To mark your cuts, make notes, etc. *Measuring tape* *Safety Goggles* *Face Mask* Breathing MDF dust has not been proven to cause health-related problems, but hang around with with a few installers at your local shop for an afternoon and you'll see why you need a face mask. :-) Start by marking the cuts you need to make on your wood. Double check your math, and your measurements. Use the table or radial arm saw to cut your wood. When you're done you should have six pieces of wood which fit together tightly to form a box. At this point you will need to trace the cut out for your subwoofer onto the front of the box. Remember that if you have a 10 inch subwoofer you do NOT want a 10 inch cutout. The 10 inch measurement is from the outside of the mounting ring. The actual cutout diameter should be with your instructions. Transfer the proper sized circle onto the sub box and cut it out with the jig saw. If you have trouble starting cuts with a jig saw, drill a 1/2" hole in the wood inside the circle. You can drop your blade into the hole and then cut out to the edge of the circle and around. After you have cut out your mounting hole you will need to cut out a square on one of the sides for your terminal cup. Transfer the proper size rectangle onto the wood and cut it out with the jig saw. Now you are ready to start assembling the enclosure. Choose one of the ends, and one of the sides. Apply a bead of ahesive along the edge of the end piece. Affix it to the edge of the bottom piece. Flip it over (have a friend hold the other end and hold the end in place,) and screw the edge to the end. Use one screw at each corner and then one more screw about every 8 inches. Drill a pilot hole with your 1/8" drill bit, then drill a countersink with your countersinking bit. Finally, drive the screw in. Make sure that you don't strip the hole. Repeat the above procedure with the other end. You should now have the two ends connected to one side. Affix the other three sides the same way. Finally, you'll want to seal the insides of the box with silicone. Apply a bead of silicone across all the inside edges and around the terminal strip. Allow the box to dry over night and then place your speaker into the hole. Screw it down and you're done! 4.6 What driver should I use? ================================ 4.7 Is there any computer software available to help me choose an enclosure and a driver? [JSC, MH, DK] ==================================================================== Various enclosure design software is available via ftp from `ftp://ftp.uu.net/usenet/rec.audio.high-end/Software'. The most popular program there is Perfect Box, which is in the file `perf.uu' (or `perf.zip'). Note that NO program can tell you what enclosure is best for YOUR car! The program does not take into consideration your space limitations, the type of car you drive, the type and number of midbass drivers you use, your musical preferences and the goals you have for your system. Many people follow (blindly) what a computer program says is "optimal," and end up unhappy with the results. Therefore, it is always a good idea to discuss a design you think looks good with a qualified installer or (even better) with the manufacturer. For an overview of many programs and devices available for enclosure design, obtain the file `sahfsd01.doc' at the ftp.uu.net archive. The filename stands for "Software and Hardware for Speaker Design", and was added to the archive in June 1994 by an anonymous contributor. 4.8 What is an "aperiodic membrane?" [CD, DK] ================================================ An "aperiodic membrane" is one part of a type of subwoofer enclosure. It is an air-permeable sheet which has frequency-dependent acoustical resistance properties. The original design goes back to Naim, for use in home systems, but has been applied by several individuals and companies in car audio. The completed system will be aperiodic, which means it will prove to be over-damped with a Q well below 0.7. In contrast, the most commonly used sealed enclosures have Qtc's in the range of 0.8 to 1.1 which are considered, by definition, to be underdamped. When improperly used, a high-Q system may have poor transient response, nasty peaks in frequency response, and high rates of roll-off. Aperiodic systems will feature excellent Aperiodic systems are characterized by better transient response, flatter frequency response and somewhat extended low frequency response. Another benefit of the system is that you can pretty much choose whichever driver you'd like to use, as long as they are big. The Thiele/Small parameters (which would normally determine what kind of box would be used) are taken into consideration by the membrane designers so that the response is extended and overdamped, regardless of the characteristics of the driver. Physically, the aperiodic membrane isn't for every car. It requires sealing the trunk from the passenger compartment in an air-tight manner, as well as sealing the trunk from the outside for best results. The drivers are then mounted into the baffle between the passenger compartment and the trunk, as would be standard in an infinite-baffle/free-air set-up. The aperiodic membrane is then placed either in front of the driver or behind the driver, depending on the type. When mounting behind the driver, the membrane is used as the rear-wall of a very small box which the driver sits in (as in Richard Clark's infamous Buick Grand National). So, in short, it's not suitable for trucks, jeeps, R/V's, or hatchbacks. You should probably only get an aperiodic membrane if you've got money to burn, lots of amplifier power, some big subs, a sedan, a desire for trunk space, and no wish to boom. If your tastes lean towards bass-heavy booming, as opposed to well-recorded acoustic instruments, you're not going to be pleased with the result. 4.9 Can I use my subs in the winter? [MS] ============================================ The following applies to all speakers in extremely cold conditions, but the question most often occurs in reference to subwoofers. The suspension of the speakers will stiffen considerably at very cold temperatures (lower than 30 degrees F). So will certain cone materials which may become more brittle. If a very cold speaker is played very hard there is a small potential for damage because more stress is placed on the cone's neck. The likelihood of damage is minimal for well-constructed and well-designed automotive speakers, however. Thermally, the danger is minimal because the ambient temperature and the coil temperature are so low that it is highly unlikely that a coil will overheat and burn, despite limited movement and ventilation. At temperatures between +20 degrees F and 0 degrees F, it is a good idea to play the system at a moderate level until the car's heater has warmed the vehicle interior. As the speakers warm up, they will play louder and lower signifying that their suspensions are warming up and returning to nominal compliance. If the temperature is extremely cold (less than 0 degrees F), you should avoid playing the system at all until the vehicle interior is warm. This is to avoid stress fractures in the surround material (especially with rubber surrounds). 4.10 How can I carpet my enclosure? [AO] ========================================== What you will need: * Adhesive (3M Super 77 or Super 90 is excellent.) * Carpet. * A good sharp pair of scissors. * A razor sharp utility knife. Buy a BOX of blades, they go dull fast. * Solvent to clean up excess adhesive. Before you start, find a large, clean, flat surface on which to set the box as you carpet it. Start by unrolling the carpet onto the surface, smoothing it out so that its flat, and setting the box on top of it edgewise. Also, make sure that you remove the speaker, any ports and terminal cups from the box. The instructions on how to carpet the box are as follows: 1. Place the box such that it is centered on the carpet lengthwise, and one edge of the box is about one inch from the edge of the carpet. 2. Roll the box back so that the side of the box that was previously done faces forward, and the carpet beneath it is exposed. Coat both the box and carpet with adhesive, but do NOT apply the carpet to the box - the adhesive needs a few minutes to set up (follow the instructions from your adhesive to find out how long you should wait). 3. After the adhesive has set up, roll the box back into position. Wait a few more minutes for the adhesive to bond. 4. Now coat the side of the box adjacent to the remaining carpet (the side facing backwards) and the carpet next to it with adhesive, let the adhesive set up, and roll the side you just coated onto the coated carpet. Repeat this until three sides of the box are carpeted. 5. Before carpeting the next side, the 1 inch of carpet sticking over the edge must be removed. To do this, rotate the box so that the first side that was carpeted is up. Pull the carpet sticking over the edge down towards the uncarpeted edge and cut it off with the knife, flush with the uncarpeted side of the box. You will have to run the knife nearly parallel to the uncarpeted side to get a perfect cut. 6. This done, spray the remaining side and carpet, and roll the box onto it. Shear off the remaining carpet sticking out from all edges with the scissors leaving a 1 inch border everywhere. 7. Clean up the ends of the box so that the carpet is flush with the sides of the box as in step 4. 8. Next cut off the remaining 1 inch flap of carpet (located at the point where you began carpeting). This is the tricky part, as you don't want to be able to see this seam. Again, pull the flap down over the edge of the box, but this time cut it at roughly a 45 degree angle. If you are successful you shouldn't be able to see the wood under the seam, but will probably see the white of the adhesive and the back of the carpet. 9. Soak some of the solvent onto a rag and use this to scrub the edge you just cut off. It should dissolve the adhesive and the carpet backing somewhat, causing the carpet on the edge to become fuzzy. Keep scrubbing the edge until you can no longer see the seam. 10. Now carpet the ends of the box. Cut two pieces of carpet slightly larger than the ends of the box and lay one of them flat on the surface. Spray the carpet and one end of the box with adhesive, and set the end of the box on the carpet, so the box stands on end. 11. After the adhesive has dried sufficiently cut off the remaining border of the carpet as in 7 and 8. 12. Repeat step 9 and 10 for the other end of the box. Congratulations! You've just carpeted your box! 4.11 Are large magnets always better than small magnets? [ST] =============================================================== Magnet *size* is meaningless! Every speaker will have an optimal BL ((see Section 4.1),) product, the field strength in the air gap multiplied by the length of the voicecoil wire in the field. If the BL product is too low, the speaker is electrically not very well damped (which will result in a woofer with a high Qts). A bump in frequency response and a level drop in midband efficiency may be the result. If the BL product is too high, the speaker is electrically overdamped (Low Qts woofer). A very high midband efficiency, but the driver starts to roll of early. An high BL product can be achieved in a number of ways: increase field strength; or increase wire length in magnetic gap. The increase in field strength is limited; so some manufacturers use very thin wire for the voice coil, as such they can achieve a high BL product with a low field strength (cheap magnet). Or they use an 8 layer voice coil... needless to say that electrical powerhandling will decrease enormously. Long stroke woofers, having only a part of the voice coil in the air gap, need a very high field strength to achieve a high BL product. Often this means a big magnet as well... Use magnet size as an indication, but as nothing more than that. 5 Installation ******************* This section describes how to do what you want once you know what it is you want to do. 5.1 Where should I buy the components I want? [JSC] ====================================================== Most of the time, you will either buy from a local dealer, or from a mail-order house. Buying from a local dealer can be good because you get to deal directly with a person: you can show them your car, ask specific questions, haggle prices, get quick service when there are problems, get deals on installation, etc. But there can also be advantages to buying mail-order: generally cheaper prices, sometimes better service, etc. In either case, you should always check prices before you buy, inquire about warranty service, and ask about trial periods. 5.2 What mail-order companies are out there? [JSC, JM, MM, IDB] ================================================================== *Crutchfield* - 800/955-3000 1 Crutchfield Park, Charlottesville, VA 22906 USA * Advantages: - Great customer service - Generally knowledgeable sales and tech support personnel - Custom mounting kits, wiring harnesses, etc. free of charge. * Disadvantages: - limited product line - generally higher prices than local shops *J.C. Whitney* - 312/431-6102 1917-19 Archer Avenue, P.O. Box 8410, Chicago, IL 60680 USA * Advantages: - Lots of "miscellaneous" items - 10kW amps for $19.99 * Disadvantages: - 10kW amps that really only put out 1mW and break after first 10 minutes of use. *Parts Express* - 800/338-0531 340 E. First St., Dayton, OH 45402 USA * Advantages: - Large selection of electronics supplies at respectable prices. - Showroom prices said to be better than catalog prices. * Disadvantages: - Also carries some of the same quality-level components as J.C. Whitney. *Classic Research/Z-Box* - 520/571-0171 5070 E. 22nd St., Tucson, AZ 85711 USA * Advantages: - Creates custom door panels with car audio in mind. * Disadvantages: - Only services expensive sports and luxury cars. *MCM Electronics* - 800/543-4330 650 Congress Park Drive, Centerville, OH 45459-4072 USA * Advantages: - Sells lots of decently priced trinkets (fuses, fuse holders, wire, etc.) - Has excellent service and available technical support. * Disadvantages: - ? There are many other mail-order houses that can be found in the back of magazines, such as S.B.H. Enterprises, Speed and Sound and Smile Electronics, but people seem to have mixed feelings about these companies. The prices are very low, often due to the fact that these companies are not factory authorized - this means that there could be problems getting the unit serviced by the manufacturer should it break. To get around this, these mail order houses will often provide their own service departments, to repair defective units. Generally, it is advised to be careful when dealing with any mail order companies, to protect yourself. There are also a number advertisements for mail order houses (such as Apex Audio & Electronics or Insider's Audio) that offer special deals or free equipment if you buy their expensive catalog or pay a membership fee. While these ads may be enticing, keep in mind that they are often *too good to be true*! Usually you have to buy a large amount of equipment before you qualify for the "bonus" or the prices are very high for most equipment. 5.3 What tools should I have in order to do a good installation? [JSC] =================================================================== *Electrical tape* Make sure you get some that can withstand extreme temperature ranges. *Wire cutters/strippers and crimpers* Get a big pair with stripper holes precut for individual wire sizes. *Angled screwdrivers* Makes taking dash and rear deck speakers out a lot easier. *Multiple size screwdrivers, both flathead and Phillips.* Magnetic screwdrivers can be a big help when trying to get screws into (or out of) tight spaces. *Various wrenches, pliers, and socket sets* The specific sizes you need will depend on your vehicle. *Metal drill and saw* You'll need these if you need to modify your vehicle for new speaker cutouts or to accommodate a new head unit. *Hot glue gun* Good for putting carpeting or door panel trim back in place after modifications. *Razor knife* Helps for detailed modifications of door panels or carpeting, especially when installing new speakers. *Wire* (see Section 2.3). *Soldering Iron* Makes excellent connections, but can be messy if not careful. *Shrink wrap or flex tubing* Good for protecting wire, especially in the engine compartment. *Multimeter* Helps to diagnose installations. *Extra hardware* Screws, nuts, bolts, connectors, etc. *Fuse puller and extra fuses.* In addition to the fuses for your stereo system, check your car's fusebox to find the various sizes you'll need. Also, you can use needle-nosed pliers to pull fuses. *Wire ties* Helps to tuck wire away in otherwise exposed areas. *Small light source* A flashlight will do - you just want something that you can poke around the innards of your car with. *Tape measure* 5.4 Where should I mount my speakers? ======================================== 5.5 What is "rear fill", and how do I effectively use it? [HK, JSC] ====================================================================== "Rear fill" refers to the presence of depth and ambience in music. A properly designed system using two channels will reproduce original rear fill on the source without rear high frequency drivers. Since recordings are made in two channels, that is all you will need to reproduce it. What is captured at the recording session (coincident pair mics, Blumlein mic patterns, etc.) by a two channel mic array will capture the so called rear fill or ambience. Many of the winning IASCA vehicles have no rear high frequency drivers. Also a lot of this has to do with system tuning. If rear high frequency drivers are added, however, the power level of the rear fill speakers should be lower than that of the front speakers, or else you will lose your front-primary staging, which is not what you want (when was the last time you went to a concert and stood backwards?). The proper amount of amplification for rear fill speakers is the point where you can just barely detect their presence while sitting in the front seat. Separates are not a requirement for rear fill; in fact, you may be better of with a pair of coaxial speakers, as separates may throw off your staging. 5.6 How do I set the gains on my amp? [JSC] ============================================== The best way to do this is with a test tone and an oscilloscope (*Note Oscilloscope::.) Since most people have neither item, the following will work approximately as well. 1. Disconnect all signal inputs to the amp 2. Turn all sensitivity adjustments as low as possible 3. Turn head unit on to around 90% volume (not 100% or else you'll have head unit distortion in there - unless you've got a good head unit) with some music with which you're familiar, and with EQ controls set to normal listening positions 4. Plug in one channel's input to the amp 5. Slowly turn that channel's gain up until you just start to notice distortion on the output 6. Turn it down just a wee little bit 7. Disconnect current input 8. Repeat steps 4-7 with each input on your amp 9. Turn off head unit 10. Plug in all amp inputs, and you're done If by some chance you do have an oscilloscope (and preferably a test disc), you do essentially the same thing as above, except that you stop turning the gains up when you see clipping on the outputs of the amplifier. Note that if you are paralleling multiple speakers on a single amp output, you need to set the gains with all of the speakers in place, since they will be affecting the power and distortion characteristics of the channel as a whole. 5.7 How do I select proper crossover points and slopes? [DK] =============================================================== Basically, this requires a degree of patience. The subwoofer should be started off at about 100Hz and adjusted until you are happy with the sound. Keep in mind that the higher the crossover point, the more power the driver on the high-pass will be able to handle but raising excessively may cause the low-pass driver to sound raspy or unnatural. The idea here is to first make rough selections to protect the drivers and then to fine tune crossover point selections to achieve optimum fidelity. It's all a matter of what sounds good to you after that, but remember that even *minute* changes in crossover frequency can make dramatic differences in the way your system sounds and images. As a rule, subs should be crossed over no higher than 120Hz, a 6 1/2 mid should be able to handle about 90 Hz, a 5 1/4" should be okay with about 100Hz, a 4" - about 500Hz, and tweeters vary from about 3500-5000Hz. These points all assume the use of a 12dB/octave crossover ... if you have a steeper roll-off a lower crossover point may be chosen. Remember, these are not hard and fast rules but rather a rule of thumb to help you get started (and so you don't blow up all your speakers when you are setting your gains!). 5.8 How do I flatten my system's frequency response curve? [IDB, DK] =================================================================== First, you'll need a good quality equalizer - either a 2/3 octave (15-band) or 1/3 ocatve (30 band) equalizer or a quasi- parametric equalizer such as PPI's PAR 224 that allows you to choose the center frequency and bandwidth (Q) of each knob on the EQ. This will allow adjustments to very specific frequency ranges. Next, you'll need to get a hold of an RTA (Real Time Analyzer), which is an expensive peice of equipment that good shops will usually have. The shops can then equalize the system by making a measurement with the RTA, and varying the levels on the equalizer in order to make the overall response curve flat. Unfortunately, most shops will not do this for free, since proper equalization can take anywhere from a half hour to many many hours. Another method involves buying an SPL meter (available from Radio Shack for between $32 and $60) and a test disc (Autosound 2000 makes one that runs about $25) that plays discreet frequency ranges - in 1/3 octave groups. Then, moving through the range of frequencies, SPL measurements can be taken at each range, and you can plot out a "response" curve. You'll be able to see what frequency ranges need to be boosted and which need to be cut. This process will be time consuming (more so than an RTA, which can analyze the entire frequency spectrum simultaneously), but should be much less expensive than having it professionally done. One last note: While a smooth curve will get the most points at an auto sound competition, you must NOT rely only on the RTA to tell you what sounds good. Use the RTA to get a good start, and then use your (better, use someone experienced in tuning systems) ears to do the fine-tuning. 5.9 How do I wire speakers "in series" and "in parallel?" [IDB] ================================================================== Wiring speakers in series involves connecting at least two speakers so that the first speaker's positive lead is connected to the amplifier's positive terminal, and the negative lead is connected to the positive lead of the second speaker. If there is a third speaker, its positive lead will be connected to the second speaker's negative lead ... and so on. The last speaker in the chain will have its negative lead connected to the amplifier's negative terminal. Speakers that are wired in parallel are all connected to the positive and negative terminals of the amplifier. So, when two speakers are wired in parallel, you'll connect each speaker's positive lead to the amplifier's positive terminal, and you'll connect each speaker's negative lead to the amplifier's negative terminal. Be careful when wiring multiple speakers in parallel or series so that you do not exceed your amplifier's rating. To calculate the effective impedance of a number of speakers, use the following formuals: Series Connections: Z(t) = Z(1) + Z(2) + Z(3) + ... + Z(n) That is, add up all of the impedances for each speaker to get the total impedance. For example, with 3 4-ohm speaker in series, the total impedance is 4 + 4 + 4 = 12 ohms. Parallel Connections: 1/Z(t) = 1/Z(1) + 1/Z(2) + 1/Z(3) + ... + 1/Z(n) That is, add up the inverse of the impedance of each speaker and invert the sum to get the total impedance. For example, with 3 4-ohm speakers in parallel, the total impedance is 1 / ( 1/4 + 1/4 + 1/4) = 1 / (3/4) = 1.33 ohms. 5.10 Are there any alternatives for Dynamat? It's too expensive! [MM, PK] ======================================================================= In this question, "Dynamat" refers to all commercial products that are marketed expressly for reducing ambient noise in the car. Dynamat, Stinger RoadKill, *et al.* all have similar pricing, so this question is intended to give non-standard options. There is a material known as "Ice Guard," which is used by roofing contractors. It is similar to Dynamat, both in thickness and density. It is self-adhesive on one side, and seems to work very well. Unfortunately, it is sold only in large quantities (225 ft^2 rolls), and runs about $70 for this much. Perhaps a few people could get together for a roll, or it might be possible to get scraps from a roofing contractor. MCM Electronics (see Section 5.2), sells a product called "Sound Deadening Pads" (part #60-2010) which cost $0.90 for each 10" x 10" square. 5.11 How many devices can I attach to my remote turn-on lead? [IDB] ======================================================================= The remote turn-on lead that most head units will not provide very much current (usually 250-300mA), so there is a limit to the number of components you can activate with it. Generally, it is safe to hook up two devices to the lead without having to worry about problems. However, if you'll be activating more components, then you should probably use a relay. 5.12 How do I wire a relay in my system? [IDB] ================================================ There are two types of relays that are commonly used in 12-volt automotive applications: Single-pole Double Throw (SPDT) relays, which have 5 pins, and Single Pole, Single Throw (SPST) relays, which have 4 pins. Depending on the application, you can use either of these; for remote turn-on leads (see Section 5.11), an SPST relay is fine, SPDT relays are often used in alarm installations. Make sure that you get a 12-volt relay - this specifies the voltage required to make the relay "switch." The connections on the two types of relays look like this: SPST SPDT ===================== ===================== (87) (87) +---------+ +---------+ | --- | | --- | | | | | (86) | | | | (85) (86) | | --- | | (87a - center) | | | | (85 - right) | | | | | | +---------+ +---------+ (30) (30) Pins 85 and 86 connect to the coil which causes the relay to switch. On both relays, pins 30 and 87 are normally disconnected. When the relay is activated (switched) pin 30 and 87 are then in contact. The difference with the SPDT relay is that in the "normal" state, pins 30 and 87a are in contact. To hook up a relay (either kind) for a remote turn on, make the following connections: *Pin 30* +12 Volts (Battery +) *Pin 87* Amplifiers' remote turn-on terminal *Pin 86* Head unit remote turn-on lead *Pin 85* Ground *Pin 87a* No connection (SPDT only) 5.13 How do I design my own passive crossovers? [JSC, JR] =========================================================== A "first order high pass crossover" is simply a capacitor placed inline with the driver. A "first order low pass crossover" is an inductor inline with the driver. These roles can be reversed under certain circumstances: a capacitor in parallel with a driver will act as a low pass filter, while an inductor in parallel with a driver will act as a high pass filter. However, a parallel device should not be the first element in a set; for example, using only a capacitor in parallel to a driver will cause the amplifier to see a short circuit above the cutoff frequency. Thus, a series device should always be the first element in a crossover. When like combinations are used, the order increases: a capacitor in series followed by an inductor in parallel is a "second order high pass crossover". An inductor in series followed by a capacitor in parallel is a "second order low pass crossover". To calculate the correct values of capacitors and inductors to use, you need to know the nominal impedance Z of the circuit in ohms and the desired crossover point F in hertz. The needed capacitance in farads is then 1/(2 * pi * f * Z). The needed inductance in henries is Z/(2 * pi * f). For example, if the desired crossover point is 200Hz for a 4 ohm driver, you need a 198.9 x 10^-6 F (or 199uF) capacitor for a high pass first order filter, or a 3.18 x 10^-3 H (or 3.18mH) inductor for a low pass first order filter. To build a second order passive crossover, calculate the same initial values for the capacitance and inductance, and then decide whether you want a Linkwitz-Riley, Butterworth, or Bessel filter. An L-R filter matches the attenuation slopes so that both -3dB points are at the same frequency, so that the system response is flat at the crossover frequency. A Butterworth filter matches the slopes so that there is a peak at the crossover frequency, and a Bessel filter is in between the two. For an L-R filter, halve the capacitance and double the inductance. For a Butterworth filter, multiply the capacitance by 1/sqrt(2) and the inductance by sqrt(2). For a Bessel filter, multiply the capacitance by 1/sqrt(3) and the inductance by sqrt(3). You should realize, too, that crossovers induce a phase shift in the signal of 90 degrees per order. In a second order filter, then, this can be corrected by simply reversing the polarity of one of the drivers, since they would otherwise be 180 degrees out of phase with respect to each other. In any case with any crossover, though, you should always experiment with the polarity of the drivers to achieve the best total system response. One other thing to consider when designing passive crossovers is the fact that most passive crossovers are designed based on the speakers' nominal impedance. This value is NOT constant, as it varies with frequency. Therefore, the crossover will not work as it has been designed. To combat this problem, a Zobel circuit (also known as an "Impedance Stabilization Network") should be used. This consists of a capacitor and resistor in series with one another, in parallel with the speaker, e.g., ________ __ + o----| |----o-----o + | | / INPUT | Xover | R1 | |/ | | C1 | |\ - o----|________|----o-----o - |__| \ To calculate these values, R1 = Re (in ohms) x 1.25, and C1 = (Lces in henries / Re^2) * 10^6. See 4.1 for definitions of Re and Lces. R1 will be in ohms, and C1 will be in uF (micro- farads). As an example, an Orion XTR10 single voice coil woofer has Re = 3.67 ohms and Lces = 0.78 mH. So, R1 = 3.67 * 1.25 = 4.6 ohms. C1 = ( 7.8E-4 / 3.67^2 ) * 10^6 = 57.9 uF (be careful with units - 0.78 mH = 7.8E-4 H) As with the definition of crossover slopes, the above definition of the phase shift associated with a crossover is also an approximation. This will be addressed in future revisions of this document. 5.14 How do I build my own passive crossovers? [JSC] ====================================================== This section assumes that you have a basic understanding of how to solder, so the actual assembly of the crossover is not discussed. Rather, tips on choosing the proper types of capacitors and inductors are given here. To obtain low insertion losses, the inductors should have very low resistance, perhaps as low as 0.1 to 0.2 ohms. Also, be sure to select capacitors with proper voltage ratings. The maximum voltage in the circuit will be less than the square root of the product of the maximum power in the circuit and the nominal impedance of the driver. For example, a 4 ohm woofer being given 100W peak will see a maximum voltage of sqrt(100*4) = sqrt(400) = 20V. Make sure that the capacitors are bipolar, too, since speaker signals are AC signals. If you cannot find bipolar capacitors, you can use two polar capacitors in parallel and in opposite polarity (+ to - and - to +). However, there are some possible problems with this approach: the forward voltage rating will probably not be equal to the reverse voltage rating, and there could be a reverse capacitance as well. Both problems could adversely affect your circuit if you decide to use opposite polarity capacitors in parallel. 5.15 Can I split the single pre-amp output from my head unit to drive two amplifiers with a Y-cable? [IDB] ======================================================================= [This section was written by someone who wishes to remain anonymous, but I will field any questions on the subject -IDB] Yes. When two loads are connected in parallel (such as with a Y-cable) they get the same voltage as each other. They do NOT get the same voltage as if only one load was connected because the head-unit has an internal resistance (typically around 600 ohms). So, given that the amp has a typical input impedance of around 10k ohms then we get something like this: ----------------------------- ---------------------------- HEAD UNIT ________ | | AMP | ______| |_________Vamp___________ | | | R(head)| | | | | _ | __|__ |________| | | __|___ |__| - _ | / \ | | | | | -___|__ | Vi | | | |R(amp)| | _- | \_____/ | | |______| __| _- | |_______________________________|________| - | | | | ----------------------------- ---------------------------- for the single amp situation. Please realize that the R(head) and R(amp) are internal to the head unit and amplifier and in fact are not deliberately added resistors but are characteristic of the real world circuits (non-ideal) in the head-unit and amplifier (and eq's, etc.). These numbers are typical, check your specific equipment for its particular specs. the worst case situation is a high source output impedance and low load input impedance. So, assuming a typical head unit and single amp the voltage seen at the amp (Vamp) is given by (Ohms law/Kirkov's law/1st year EE/high school electonics technology class/etc.): R(amp) Vamp1 = Vi * ------------------ R(amp) + R(head) Vamp1 = Vi * 0.94 Now, putting two amps in parallel from the original signal, R(amp) is effectively halved while R(head) is unchanged. Using the same voltage divider formula we get: 10000/2 Vamp2 = Vi * --------------------- 10000/2 + 600 Vamp2 = Vi * 0.89 So, for an Alpine 4V preout, Vi in the diagram (the open circuit head unit line level output) is 4V. Thus Vamp1 = 3.76V and Vamp2 = 3.56V. With two amplifiers' inputs connected in parallel, the voltage is reduced from 3.76V to 3.56V or approximately 5%, not a big deal. If you had a more typical 1V preout you would get Vamp1 = 0.95V and Vamp2 = .89V, also not a noticeable drop. This is also why this is slightly more susceptible to noise than a direct one-to-one connection. If the noise level inserted due to cabling was 0.1V per cable then the noise level in the signal reaching each of the two amps would be a slightly higher percent of the signal level but not doubled. (this is also why the 4V head unit is favoured over the 1V unit for noise immunity: 0.1V noise / 3.76V or 3% is much less than 0.1V noise / 0.95V or 10% even in a one to one connection). 5.16 How do I determine a speaker's polarity? [IDB] ===================================================== If you have a speaker and the terminals are no longer marked, you can do a simple test to determine which terminal is positive (+) and which is negative (-). This test is useful for midrange/midbass/subwoofers, but not for tweeters. Use a 1.5V battery (AA, C, D) and connect the (+) terminal on the battery to one terminal of the speaker, and connect the (-) terminal to the other terminal of the speaker. If the cone moves OUT, then the battery is connected "properly," i. e., the (+) terminal of the battery is connected to the (+) terminal of the speaker, and the (-) terminal of the battery is connected to the (-) terminal of the speaker. If, however, the cone moves IN, the battery has been connected "backwards," i. e., the (+) terminal of the battery is connected to the (-) terminal of the speaker, and the (-) terminal of the battery is connected to the (+) terminal of the speaker. 5.17 How can I use an oscilloscope to set the gains in my system? [AO] =================================================================== This section assumes you are already familiar with your oscilloscope and will not go into setting it up. If you haven't already, spend a few minutes with your scope's manual. You'll need a test disc with a variety of test tones. I use the official IASCA test disc, but there are some of the "Bass Discs" that have test tones as well. You do NOT want to use sweeps, only pure tones. There is an AutoSound 2000 disc (#101?) which has a signal which is unclipped for 20 seconds, clipped for 5, and then unclipped for the last 5 seconds. I have never used the AutoSound 2000 discs, but know them to have excellent recommendations (as well as all the test tones you could ever need). Viewing this track on your scope's display could be useful if you've never seen clipping on an oscilloscope display before. You start by finding the clipping level of your head unit. Many of the better head units will not clip the pre-amp outputs, even at full volume, but it's always better safe than sorry. Disconnect the RCA's from your head unit. Pop in your test disc and skip to the track with a 1 KHz tone. If your CD player has a repeat function, set it to repeat just this track. That way you won't have to skip back at the end of the tone. Set your bass, treble, fader, and balance all to center. Turn the volume all the way up. Probe your right and left front (and rear if you have them) one at a time. Your scope should show a wave, either a sine wave or a clipped sine wave. If you have a standard pure sine wave then all is good, and you're ready to proceed. If you have a clipped wave then you need to turn down the volume, one click at a time untill you see a perfect sine wave on your scope's display. Rember this point, as this is the highest you can EVER turn up your head unit. After you set the level for one of your outputs the rest should be the same, but check them all just to be sure. The results will be the same if you leave the RCA's pugged into the head unit and disconnect them at the other end (from your amp/EQ/processor/whatever) but unless you have a remote control you'll be running back and forth to change the volume. If your headunit has subwoofer pre-amp outputs you'll need to test them using a different tone. I usually test subwoofer outputs at a level midway between the crossover points. For example, if your subwoofer outputs are crossed over at 80Hz then you would want to use a 40Hz test tone. Other than that the procedure for testing subwoofer pre-outputs is the same as testing front or rear outputs. Once you've found the clipping level of your head unit it's time to proceed down the signal chain. If you are using an EQ, preamp, DSP, or other processor (NOT including crossovers) test them next. Leave your EQ set the way you usually use it. Hook up the processor and probe all the outputs of your processors in the same method as you did your head unit. You should probe each of the outputs using tones that match the bands of your EQ. For example, if you have a 9 band EQ with bands at 50/100/200/400/800/1.5k/3k/6k/12kHz you would probe your EQ 9 times, once with a 50 Hz test tone, once with a 100 Hz test tone, and so on. If your EQ also includes a crossover you'll need to follow the crossover procedure. If any of these processors are clipping you will probably need to turn down your headunit's volume control or make any adjustments on that unit that you can. For example, if you are testing an EQ and you have any bands excessivley boosted, try bringing down that band first. That may be causing your clipping. To test your crossover you need to probe each output using a test tone that is midway between the high and low pass. For example, a channel which is crossed over between 100 Hz and 20 KHz (like a front channel) would be tested at 9950 Hz. Since you'll be hard pressed to find a 9975 Hz test tone on your CD use the 10Khz tone. For a rear channel crossed over with a lowpass of 3500 Hz you would use a 1750 Hz tone. As you again would have problems finding a 1750 Hz tone on a CD use a 2 KHz tone. For a subwoofer channel lowpassed at 70 Hz you would use a 35 Hz tone. This one you may find on your CD, if not use 30 Hz or 40 Hz. Assuming your crossover has level settings you will want to turn the level for whatever channel you're testing all the way up and probe the output. Assuming the output is clipping, back the level down slowly untill you see a perfect wave on your scope. Now it's time to check your amp's outputs. Hook up your amps and play the same test tones you were using on the crossover. Disconnect the speakers and then turn the gains all the way up. Probe the first channel's output. Adjust the gain the same way you did your crossover. Back the gain down slowly untill your wave isn't clipping anymore. Voila! You are done. You have just effectively eliminated clipping from your system. If you turn your bass or treble up, or boost up a channel on your EQ you may introduce some clipping. After major EQ work you may want to redo this procedure, starting at the EQ. 5.18 Why are kickpanels such a popular location for mounting speakers? [ES] ======================================================================== There is a lot more to mounting speakers in the kick panels than just equalizing the path length difference (PLD). Two of which are: on-axis response, and angling for pattern control. On-axis response refers to the fact that most speakers sound best when listened to on-axis, or as close to on-axis as possible. Second, after mounting your speakers in the kick panels you can then angle the speakers to take advantage of their off-axis response to use output level to overcome any PLD that is still present. The pattern control I am mentioning is one of the ways a horn loaded compression driver works very well, they not only use amplitude to overcome any PLD that is still present they minimize early reflections that can destroy imaging staging and spectral balance. PLD can be improved more than marginally when you consider the stock locations in a lot of vehicles, or the locations most installers choose. Measure the PLD betwwen tweeters when mounted high in the dash or at the front corner at the top of the door and you will notice its probably on the order of 24". This mounting setup requires a lot of amplitude adjustment to correct the problems induced by this difference. The nearer tweeter is out phase from the opposite side and is arriving much sooner and with much greater amplitude due to the fact is not as far away. When all these factors are added together, it is very difficult for even the most flexible DSP unit to correct. On top of that, not many people or installers have access to the necessary tools to properly set up time delays using a DSP - TEF, MLSSA or other very expensive time domain measuring equipment are required to do the job properly. There will always be trade offs involved and deciding which trade offs to take can be very hard. A small dropout due to phase cancellation will probably not be noticed by most people but most people will quickly notice when a vehicle is not imaging properly, and if you can move the problem to higher frequency where we determine localization more from amplitude rather than phase differences, it will be much easier to deal with. Also, if you minimize the time/phase difference it will be much easier to correct with amplitude. Some people complain that kickpanel mounting gives a low sound stage. However, keep in mind that when any stereo system is imaging properly the point sources can no longer be localized. When our brains can no longer localize the point sources it will then hear things at eye level. 5.19 How can I build custom kickpanels? [MB] ============================================== Building custom kickpanels for your car is a fairly advanced task, and requires knowledge (and experience) in working with fiberglass. Auto Sound & Security published an article in the August 1996 issue that covered the basics of working with fiberglass. This is kick panels in a nutshell. It takes about 2 days to do this right, although it is possible to do overnight (a LONG night) in one vehicle. Step 1: Cover base area with plastic & duct tape. Step 2: Lay fiberglass over the entire area. Don't worry about getting the pieces cut to the exact size and shape, you will trim them later. Step 3: Build the baffles for your speakers. Step 4: After the fiberglass has cured, set the baffles (with the speakers properly mounted into the panels and use a backstrap to secure the baffle to the panels. Now, spend some time listening to the car and aim the baffles until you get the best image and stage in the car. Note: Take your time aiming the speakers - once you fix the baffles, you won't be able to readjust the speakers. You may want to spend a few days listening to different positions to determine what sounds best. Step 5: Remove the speakers from the baffle and fill from behind with self-expanding insulation foam. This will allow you to mold the baffle into the rest of the car. Step 6: After the foam has hardened, sand it to the shape you want the panel to have. Step 7: Lay fiberglass over the foam to form the top panel of the kick panel. Step 8: After the fiberglass has hardened, sand the surface smooth. This may require the use of a little bondo to get things perfect. Step 9: Remove the foam by grinding it out from the inside of the kickpanel. Step 10: Cover the panels with carpet, vinyl, leather, fleckstone or other substance of your choice. Step 11: Install the kick panels in the car. Step 12: Install the speakers in the panels. Step 13: Make speaker baffles from Plexiglas, and grilles. Step 14: Enjoy. 5.20 What's worse for a speaker, too much or too little power? [IDB] ====================================================================== Problems occur (in everyday operation) when distortion is fed to a speaker. This occurs MUCH more often when you are dealing with an underpowered system - typically the owner will turn up the volume too much or set the amplifier gains too high to try and get more volume from the system. These introduce distortion to the signal - this will destroy *any* speaker. ((see Section 5.21).) When a speaker is overpowered, however, it is not nearly as common to have these kind of problems, so speakers aren't blown as much. Of course, it is certainly possible to destroy a speaker (thermally) by overpowering it, but you'll have a pretty hard time doing this on your own, especially with standard car audio amplifiers. 5.21 Why is distortion harmful to my speakers? [RK] ===================================================== Distortion is hard on speakers for two reasons. Reason 1: Distortion causes the power spectrum to shift upwards in frequency. A bass note, when distorted, will have lots of high frequency energy. This will cause mid-ranges and tweeters to fry, if the amplifier is operating full range. It doesn't harm woofers, necessarily. Reason 2: Distortion causes the average power to be much higher. Typically, a music signal that never clips has an average power level of 1/4 the peak power level for even the most compressed speed metal or pop. More dynamic music will be 1/8 the peak level or less on average. When you clip the amp hard, the average output moves up to the full-rated output of the amp or more. The peak to average ratio can be less than 2 to 1, with the peaks being at double the rated power of the amp, and the average being at the rated power of the amp or higher. Thermally, the speaker can handle the average power being 1/4 the rated power of the amp (little to no clipping), but it will have a much harder time with the average power being the amp's rated power or more (massive clipping). As you might expect, this is pretty hard on the amp, too. For transients, most speakers can handle a ton of power. But for long term signals, the power handling is much less. 6 Competition ****************** This section describes the competition branch of the car audio world - what it is, and how to get involved. 6.1 What is IASCA, and how do I get involved? [JSC, HK, IDB] =============================================================== IASCA is the International Auto Sound Challenge Association, a sanctioning body for car audio competitions held throughout the world. Competitors earn points at each competition, and those that perform the best each year can advance to the finals. Prizes (trophies, ribbons, and sometimes cash) are usually given out to the top competitors in each class at every competition. IASCA memberships can be purchased at your local car audio retailer, if they are an IASCA member. You can call IASCA at 602/437-4678 to get a list of IASCA shops in your area. 6.2 What is USAC, and how do I get involved? [HK] ==================================================== USAC is another sanctioning body, similar to IASCA. However, USAC places greater emphasis on SPL measurements than IASCA. 6.3 What are the competitions like? [HK, CD, IDB] ==================================================== [HK writes:] They are much like loud car shows: a lot of cars parked with their hoods/doors/trunks open showing their audio systems. There are two types of judging styles: 1) drive through - where competitors drive their own vehicles to judging stations to be judged, and 2) walk-arounds - where the teams of judges will walk around the event site and judge vehicles that fit within their judging assignments. Typically SPL is done first with the mic stand in the driver's seat and the competitor in the passenger side adjusting only the volume. Hearing protection must be worn. After SPL measurements are completed, RTA measurements are performed by playing pink noise. When the volume level is within the specified "window" around 90db-110db, the RTA judge will signal you out, and at that point you must exit the vehicle for the actual scoring measurements. The next area for judging should be sound quality where two judges will sit in your car and judge the sound quality based on IASCA's reference CD/tape. The next area is installation judging where the competitor has 5 minutes to explain and show the installation of his/her vehicle. It is very useful to have a picture book/album of photos of the installation that may not be visible to prove that items not visible do exist. When that is completed, the competitor can park the vehicle and show spectators the vehicle. These procedures may differ from show to show, and at the regional/final levels they are very strict in what can and can't be done, e.g. a judge will make sure no adjustments are made after SPL until after sound quality judging is over, ear protection, etc. [CD writes:] Most involve a lot of waiting around. Thus, they are perfect for meeting other people interested in car audio, and seeing some installations which may give you some ideas. They're also perfect for listening to some cars that sound a lot better and a lot worse than your own. In IASCA competition, the cars are judged on: * Installation Quality (187 pts possible) - Wiring (40 pts) - Source Units (15 pts) - Amplifiers (25 pts) - Speakers (25 pts) - Other Devices (25 pts) - Overall Creativity (30 pts) - Attention to Show Details (20 pts) - Security and Convenience Features (7 pts) * Sound Quality (248 pts possible) - Tonal Accuracy and Spectral Balance (100 pts) - Soundstage and Ambience (65 pts) - Imaging (50 pts) - Sound Linearity (30 pts) - Ergonomics (+/- 3 pts) - Noise Adjustment (up to -20 pts) * Frequency Response - RTA (40 pts maximum) * Sound Pressure Level - SPL (1 point per dB) 6.4 Should I compete? [CD] ============================= You should compete if: a. You have an ok sounding stereo b. You have an ok installation (i.e. no amps/changers sliding around in the trunk) c. You'd like some pros to comment on your system d. Your feelings won't get hurt if you don't get first place e. You've been to a contest and talked to competitors about it f. You've read the rulebook g. You've listened to a test disc in your car, and understand what the sound quality judges are listening for You can compete even if you don't do all of the above, but the recommendations will help you understand and gain the most from competing. 6.5 What class am I in? [HK, JSC] ==================================== This section is mainly geared toward IASCA. [HK,JSC write:] There are three classes: novice, amateur, and pro. The novice class is intended to be an unintimidating level where beginners can start out; however, a competitor may only be in the novice class for one year, at which time he is automatically moved to the amateur class. Most competitors stay in the amateur class indefinitely, unless they become affiliated with a car audio shop or manufacturer, at which point they are moved into the pro class. [CD writes:] Are you or were you employed by a car audio manufacturer or dealer? *Yes:* You compete in pro *No:* Is this your first year of competing? *Yes:* You compete in novice for the first year *No:* You compete in amateur Note that modifying your amplifiers, buying your equipment below retail, or being sponsored by a manufacturer or dealer will get you kicked into pro. Also note that any home built active gear in the signal path (e.g. custom built equalizers, crossovers, or noise gates) will get you kicked out of novice. Once you know what group you are, you next need to know what power category you are in. Add up the 4-ohm non-bridged rating of all your amplifiers, including your head unit if your head unit is powering speakers (rather than exclusively feeding amplifiers). Then, find the category you fit into: Novice 1-150 151-300 301-600 601+ Amateur 1-150 151-300 301-600 601+ Pro 1-150 151-300 301-600 601+ Expert 1-600 601+ Thus, if you had a Rockford Punch 4040 (20Wx4) and a Punch 60ix (30Wx2), with a head unit that put out 6Wx2 (powering, perhaps, a center channel) you're in the 151-300 class. It does not matter if your amps are bridged down to .002 ohms; it's only the 4ohm rating that counts. If you no longer used your head unit to power speakers, you would be in the 1-150 class. Competition is usually most vicious in the 151-300 and 301-600 categories at typical contests. 6.6 Where can I find out when these Sound-Offs are? [IDB] ============================================================= The best way to get the most current list is to call either of the sanctioning bodies (IASCA or USAC). They can be reached at 602/437-4678 or 601/939-7828, respectively. You can also visit the Official IASCA and USAC pages on the web at the following URLs: IASCA - `http://www.mobileaudio.com/iasca' USAC - `http://www.soundoff.org' 7 Literature ***************** This section describes various literature which you can read to brush up on your car audio skills, or to keep current, or to see other people's installations, or whatever else you'd like. 7.1 What magazines are good for car audio enthusiasts? [JSC, MI, NML, JR] =================================================================== Car Audio and Electronics $19.95/year P.O. Box 50267 (12 issues) Boulder, CO 80323-0267 800/243-6400 CarAudio@ix.netcom.com Car Stereo Review $17.94/year P.O. Box 57316 (6 issues) Boulder, CO 80323-7316 303/447-9330 Auto Sound and Security $28.95/year P.O. Box 70015 (12 issues) Anaheim, CA 92825-0015 714/572-2255 Car Sound Buyer's Guide $17.95/year 939 Port Washington Blvd. (Quarterly) Port Washington, NY 11050 516/944-5940 carsound@aol.com Car Hi-Fi #23.60/year Freepost (8 issues) TK660 081 943 5943 Leicester KE87 4AW Bilstereo Forlags AB Skr ?? Box 230 84 (? Issues) 104 35 Stockholm 08-34 29 70 Sverige (Sweden) bilstereo@public.se 7.2 Are there any newsletters I can read? [IDB] ================================================== Unfortunately, AutoSound 2000 Tech Briefs is no longer in publication, and as a result, there are no more newsletters currrently in publication. 7.3 What books can I read? [JSC, JW, TT] =========================================== *Loudspeaker Design Cookbook* by Vance Dickason Published by Audio Amateur Press ISBN 0-9624191-7-6 $25-$30 *Designing, Building and Testing Your Own Speaker System* by David Weems Published by McGraw Hill ISBN 0-8306-3374-X $16.95 *Killer Car Stereo on a Budget* by Daniel L. Ferguson Published by Audio Amateur Press ISBN 0-9624191-0-9 $19.95 7.4 Can I contact any manufacturers on-line? [IDB] ===================================================== Yes, there are a number of manufacturers who have started to use the Internet and can offer advice for component selection, installation and advice. A list of these manufacturers is available on the WWW, at the URL: `http://www.mobileaudio.com/intdir' 8 Credits ************** [JSC] Jeffrey S. Curtis "curtis@anl.gov" [JLD] Jason Lee Davis "jdavis@paris.cc.tx.us" [MI] Matt Ion "matt@ship.net" [JW] Jerry Williamson "jerry.williamson@amd.com" [CD] Cal Demaine "demaine@terranet.ab.ca" [MO] Mark Obsniuk "Mark_Obsniuk@sfu.ca" [HK] Harry Kimura "hkimura@ball.com" [RDP] Dick Pierce "DPierce@world.std.com" [BG] Brian Gentry "brian@eel.ufl.edu" [JM] Jeff Meyers "meyers@tellabs.com" [MH] Marvin Herbold "11mherbold@gallua.gallaudet.edu" [TT] Trevor Tompkins "tt17+@andrew.cmu.edu" [MM] Matthew E. Meiser "meiser@dris.com" [NML] N. M. Lines "csznml@scs.leeds.ac.uk" [IDB] Ian D. Bjorhovde "ianbjor@mobileaudio.com" [JG] John Graley "maufd@csv.warwick.ac.uk" [DK] Dan Kreft "bigdan@kreft.net" [JR] Jason A. Reiser "jreiser@escape.com" [PW] P. Wilson "scratchy.mi.net!ccbbs!pwilson" [JGr] Jerry Grooms "grooms@denali.cc.uky.edu" [PK] P. Kaufmann "pkauf@gnn.com" [MS] Manville Smith "msmith@jlaudio.com" [LC] Ligeng Cao "ligeng@wam.umd.edu" [AO] Andrew C. Ohnstad "andysaudio@cybermail.net" [MB] Michael Brennan "M1Brennan@aol.com" [RK] Russell Kinder "russmax@cowboy.net" [MHa] Mike Harmon "mikeharmon@usa.net" [ST] Steven Tolleneer "Steven.Tolleneer@ping.be" [JD] John Durbin "durbinj@concentric.net" 9 Changes ************** This section keeps a running log of the changes to this document. + $Log: rac-faq.texi,v $ + Revision 4.33 1998/05/13 06:56:34 ianbjor + Updated for May 1998 distribution. + + Revision 4.32 1998/05/13 06:47:28 ianbjor + Updated totals for IASCA scoresheets to use current (1998) scores. + (see Section 6.3). + + Revision 4.31 1998/05/13 06:39:40 ianbjor + Added information about turn off thump, and how to get rid of it. + (see Section 2.2). + + Revision 4.30 1998/05/13 06:22:15 ianbjor + Added section about Magnet Size. + (see Section 4.11). + + Revision 4.29 1998/04/10 07:10:26 ianbjor + Updated for April 1998 distribution. + + Revision 4.28 1998/03/08 08:35:55 ianbjor + Updated for March 1998 distribution. + + Revision 4.27 1998/03/08 08:24:37 ianbjor + Added new section about carpeting enclosures. + See (see Section 4.10). + + Revision 4.26 1998/03/08 08:06:58 ianbjor + Finally added information about how to build an enclosure. + See (see Section 4.5). + + Revision 4.25 1998/03/08 07:34:18 ianbjor + Added Mike Harmon's updated and expanded section about bridging. + See (see Section 3.5). + + Revision 4.24 1998/02/09 08:29:13 ianbjor + Clarified symbol notation for Impedance (using 'Z' instead of 'I'). + (see Section 5.9). + + Revision 4.23 1998/02/09 02:22:24 ianbjor + Updated for February 1998 distribution. + + Revision 4.22 1998/02/09 02:18:32 ianbjor + Added section about how distortion destroys speakers. + (see Section 5.21). + + Revision 4.21 1998/02/09 01:41:34 ianbjor + Added information about using too much or too little power with + speakers. + (see Section 5.20). + + Revision 4.20 1998/01/06 15:51:02 ianbjor + Updated for January 1998 distribution. + + Revision 4.19 1997/12/09 08:06:21 ianbjor + Updated for December 1997 distribution. + + Revision 4.18 1997/12/09 06:43:00 ianbjor + Added section describing why kickpanels are a popular mounting + location. + (see Section 5.18). + + Revision 4.17 1997/12/09 06:14:35 ianbjor + Added section on building Kick panels. + (see Section 5.19). + + Revision 4.16 1997/11/17 09:12:55 ianbjor + Removed useless reference in stiffening capacitor section. + (see Section 2.9). + + Revision 4.15 1997/11/16 17:26:05 ianbjor + Small changes in introductory text. + + Revision 4.14 1997/11/13 10:41:29 ianbjor + Updated for November 1997 distribution. + + Revision 4.13 1997/11/13 10:38:42 ianbjor + Fixed typo and incorrect logic in noise troubleshooting logic. + (see Section 2.1). + + Revision 4.12 1997/10/06 23:04:13 ianbjor + Updated for October 1997 distribution. + + Revision 4.11 1997/09/07 20:18:21 ianbjor + Fixed omission in section on setting gains with an Oscilloscope. + (see Section 5.17). + + Revision 4.10 1997/09/07 00:44:05 ianbjor + Updated for September 1997 distribution. + + Revision 4.9 1997/09/06 01:07:08 ianbjor + Added section on setting gains with an oscilloscope. + (see Section 5.17). + + Revision 4.8 1997/09/06 00:31:15 ianbjor + Fixed Changes Section to include complete 4.x history. + + Revision 4.7 1997/09/06 00:24:46 ianbjor + Added Changes section. + (see Section 9). + + Revision 4.6 1997/09/06 00:02:41 ianbjor + Added section descirbing how to determin speaker polarity. + (see Section 5.16). + + Revision 4.5 1997/09/05 22:22:20 ianbjor + Added section about Line Drivers. + (see Section 3.30). + + Revision 4.4 1997/09/05 20:38:42 ianbjor + Added section covering speaker sensitivity and the resulting SPL. + (see Section 4.2). + + Revision 4.3 1997/09/05 20:27:59 ianbjor + Added section about using subwoofers in the winter. + (see Section 4.9). + + Revision 4.2 1997/09/05 18:18:25 ianbjor + Fixed minor wording error in crossover design section. + (see Section 5.13). + + Revision 4.1 1997/08/06 22:40:25 ianbjor + Updated for August 1997 distribution. + + Revision 4.0 1997/07/11 08:12:32 ianbjor + Updated FAQ to Texinfo format. -- Ian D. Bjorhovde || READ THE FAQs BEFORE YOU ASQs! ianbjor@mobileaudio.com || ----------------------------------- rec.audio.car FAQ Maintainer || http://www.mobileaudio.com/rac-faq/ http://www.mobileaudio.com || http://tutorials.jlaudio.com/