AOH :: CARAUD-3.FAQ
Frequently Asked Questions About Car Audio, Part 3
|
Archive-name: car-audio/part3
Rec-audio-car-archive-name: FAQ/part3
Version: 3.1
Last-modified: 5 September 95
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,
viscousity, etc.); dimensionless
n0 The reference efficiency of the system (eta sub 0)
dimensionless, usually expressed as %
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 (rho) density of air at STP 1.18 kg/m^3
4.2 What are the enclosure types available? [JLD, JG]
Only the order of the enclosure First Order
itself is shown here. The addition Infinite-Baffle or Free-Air
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.
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. |__|
4.3 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.
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
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
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
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.
4.4 How do I build an enclosure?
4.5 What driver should I use?
4.6 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.uu.net in the /usenet/rec.audio.high-end/Software
directory. 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 waht 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.
4.7 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.
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 602/571-0171
5070 E. 22nd St.
Tucson, AZ 85711
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
Advantages: sells lots of decently priced trinkets (fuses, fuse
holders, wire, etc.) and 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.
5.3 What tools should I have in order to do a good installation? [JSC]
Electrical tape - lots of it. 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, depending 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.
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.
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. 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 crossedover 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.
5.10 Are there any alternatives for Dynamat? It's too expensive! [MM]
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.
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.
A relay is a device that can handle a large amount of current
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 (137 pts possible)
Attention to Show Details (12pts)
Source Unit Installation (15pts)
Amplifier Installation (30pts)
Speaker Installation (30pts)
Other Devices (20pts)
Overall Creativity (30pts)
Sound Quality (230 pts possible)
Tonal Accuracy and Spectral Balance (60pts)
Soundstage and Ambience (55pts)
Imaging (50pts)
Sound Linearity (45pts)
Ergonomics (10pts) **
Noise (10pts) **
Frequency Response - RTA (40pts)
Sound Pressure Level (SPL) ***
** The 1995 IASCA rules for both ergonomics and noise state that
the competitor will begin with the full points and have points
deducted for each problem, which is to be noted on the
scoresheet.
*** There are two formats for 1995 IASCA competition: SoundQ
and SoundQ Plus. In SoundQ, all areas listed are judged except
for SPL; SoundQ Plus adds the SPL measurement, and the
competitor's final score is determined by their SoundQ score
plus 1 point per dB above 100dB. For example, if a competitor
scored 250 in SoundQ and had a 128dB reading, their SoundQ
Plus score would be (250 + 28) = 278.
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. There is also a
WWW site with a list of soundoffs, URL:
http://www.nsma.arizona.edu/~ianbjor/caraudio/soundoff.html
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
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
Car Hi-Fi #23.60/year
Freepost (8 issues)
TK660 081 943 5943
Leicester
KE87 4AW
7.2 Are there any newsletters I can read? [MO,HK]
Autosound 2000 Tech Briefs $50.00/year
2563 Eric Lane, Ste D (12 issues)
Burlington, NC 27215 800/795-1830
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.nsma.arizona.edu/~ianbjor/caraudio/direct.html
8 Credits
[JSC] Jeffrey S. Curtis (curtis@anl.gov)
[JLD] Jason Lee Davis (jdavis@wizard.etsu.edu)
[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 (meiserme@nextwork.rose-hulman.edu)
[NML] N. M. Lines (csznml@scs.leeds.ac.uk)
[IDB] Ian D. Bjorhovde (ianbjor@nsma.arizona.edu)
[JG] John Graley (maufd@csv.warwick.ac.uk)
[DK] Dan Kreft (jlaudio@nwu.edu)
[JR] Jason A. Reiser (jreiser@skidmore.EDU)
[PW] P. Wilson (?) (scratchy.mi.net!ccbbs!pwilson)
[JGr] Jery Grooms (grooms@denali.cc.uky.edu)
--
Ian D. Bjorhovde UofA Div. of Neural Systems, Memory & Aging
ianbjor@NSMA.Arizona.EDU UNIX Systems Administrator
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