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Understanding Car Audio 

 

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 Post subject: Understanding Car Audio
Posted: Sat Mar 03, 2007 3:42 am 
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Hey guys just cruising another forum and thought that some people could use this when thinking about making sub boxes,porting etc. So here you go.




this site is excellent for understanding all aspects of car audio from wiring, to speakers, heaunits, box's ect... clcik the links down the right side of the page

This site is similar to the above but covers thing more technicaly.. This site also.. but a bit technical and over kill, some may find it interesting

also theses tutorials will help even more

how to wire your subs??? SVC and DVC.. and how to get what ohm load from your amp, click here

also click here for info on how to make box's, ports, bracing etc...


and heres a basic run down on terms, abbrivations and deffinitions etc..

General Information
*Terminology:
Impedance - The resistance of a load
Ohms - Main unit for Impedance
Watts - Main unit for Power
Amps - Main unit for Current
WRMS - Watts Root Mean Square (see below)
Hertz - Unit of measure of frequency
Frequency response (Hz) - It identifies the speaker bandwidth, the limits within which it can be used with a linear response
Decibel - Unit of measure of sound pressure
HU - Head Unit
AMP - Amplifier
THD (Total Harmonic Distortion) - Measured additional noise or interference induced into the system by the power supplies
DVC – Dual Voice Coil
SVC – Single Voice Coil
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Amplifiers
Calculating WRMS:
From Max Power - Max Power / (Square Root 2)
Bridged Mode for a single 4 ohm speaker - 2*(AMP Power in WRMS @ 2 ohm):
#Eg. 2 Channel Amp; Power: 50WRMS/channel with 4 ohm load, 70WRMS/channel with 2 ohm load .:. Bridged WRMS = 2* 70 wrms = 140 wrms. Therefore the 4 ohm speaker is receiving 140 WRMS of power
Parallel Mode with 2 equal speakers of x ohm - Power = [Power @ (x/2) ohms]/2
#Eg. Mono block Amp; Power: 200 WRMS with 4 ohm load, 350 WRMS with 2 ohm load. .:. Parallel WRMS = 350 WRMS/2 = 175 RMS. Therefore, each 4 ohm sub would be receiving 175 WRMS of power
Series Mode with n speakers at x ohm - ?
*Terminology:
Stereo -A stereo system has two independent signals, each driven into its own separate speaker
Mono - A mono system sends the SAME signal to ALL of the speakers
Max. Power - The maximum power an amplifier can produce with no load
WRMS (Nominal Power) - The power that the speaker is actually receiving from the amplifier at a continuous rate
Bridging - Connecting the -ve from one channel and the +ve from a second channel to drive a single speaker with more power due to each channel seeing 2 ohm resistance. This does NOT mean that there is a resistance of 2 ohm in total, just that each channel see half the total resistance.
Parallel - Running two speakers off the one channel, in result halving the impedance
Clipping - When the volume is turned up past what the amplifier can deliver and distorts
Overload Protection - A protection circuit that eliminates component failure from impedance loads that are to low by shutting off the amplifier
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Speakers
*Terminology:
Power Handling - The power that a speaker can receive for short moments (Max) or for continuous programs (Nominal).
Efficiency (dB): Reference efficiency value of a speaker; it is measured in decibels and at a distance of one meter, with 2.83 Volts in the input
Tweeter - Speaker specialised in reproducing high frequencies
Midrange - Speaker specialised in reproducing mid frequencies
Woofer - Speaker specialised in reproducing low and mid frequencies
Xmax (mm) - Mobile voice coil excursion, in one direction
Voice coil - Wire (usually copper) winding around a cylindrical former that is glued with the speaker membrane. Alternate current passing through mobile voice coil generates a magnetic field that interacts with the one occurring into the gap; the vibrations that derive from this are sent to the membrane, generating sound
Speaker Size - The dimensions of the speaker given in terms of inches
Coaxials - A speaker which produces all three frequencies in one unit
Components/Splits - A set of speakers which seperates into 2 or 3 lone speakers, which is combined with a crossover so that each speaker only reproduces its specific frequency
Crossover - Filter used to separate frequencies to their appropriate speakers
*Resistance Calculations:
Speakers in Series = R1 + R2 + ... + Rn
Speakers in Parallel = [R1^-1 + R2^-1 + ... + Rn^-1]^-1
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Speaker Enclosures
*Terminology:
Sealed - Airtight enclosure suited to general applications
Ported - Enclosure with ports which can be tuned to certain frequencies to change SQ and SPL characteristics
Isobaric - Two speakers placed in an array as to act as one speaker in an enclosure design that requires half the air space that a single driver requires
Bandpass - Bandpass boxes are a special type of ported box designed for maximum bass. The woofer is mounted inside a dual-chambered box (one chamber sealed, the other ported), with the sound waves emerging from the ported side. The sound that comes out of the port is extra loud within a narrow frequency range
Dipole Passive Radiator - A sealed box with 2 subs running out of phase

Infinite Baffle - Infinite baffle enclosures are the simplest from a design concept. The principle of IB design is the seperation of the front output of the woofer from the rear output of the woofers. One of the advantages of this design is the low resonant frequency of the IB system. This low RF allowes the system to have a very good low frequency extension. Another advantage of an IB design is the little amount of boot space needed for this application. For this reason IB designs are popular in cars where the boot space is small but there is a need for big bass...

One of the main disadvantages of this application is the REDUCED MECHANICAL POWER HANDLING of the speaker. This is due to the fact that the enclosure is actually the whole boot volume and the air in the boot is not able 2 help the mechanical suspension system of the woofer, for this reason not all woofers are suited for IB applications.

It is a common misconception that IB enclosures are the easiest to construct, this is not true as maximizing performance in this type of enclosure is quite difficult and time consuming. Maximizing the performance in a IB system you must minimize leaks and maximize the sturdiness of the baffle....

Ok, so in short an IB enclosure is putting a sub in the parcel tray and using the boot as one big enclosure and attempting to seperate all the air either side of the tray, same principal is used when placing a sub in the ski-port in some sedans and using the back seats/parcle tray as the dividing wall and the boot as the enclosure.

Also this type of enclosure means u cant feed buckets of power 2 the sub cos its not being helped by the box and will be worked 2 hard if u do apply 2 much power.

You will be surprised how many installs come out of brisbane car sound like this, if u feel air leaking from around the plate ur sub is fixed 2 then this is the "box" that u have got... *Written by 'Ferdie'
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Head Units
*Terminology:
'Loud' Button - To prevent overloading on speakers i.e push into clipping, try and adjust system gain levels to prevent its use
Power Rating ( 45 x 4 etc.) - This is the Max Power of the HU, not the WRMS. However, this usually equates to only approx. 13 WRMS from each channel
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SPL and SQ
*Terminology:
SPL - Sound Pressure Level, measured in dB
SQ - Sound Quality, measured by a pair of judges
-----------------------------------------------------------------------------------------------
Display Units
*Terminology:
LCD - Liquid Crystal Display
-----------------------------------------------------------------------------------------------
Wiring Guide
*Terminology:
AWG (Gauge) - American Wire Gauge; Used to describe the size of a wire in relation to its current carrying ability. Smaller the AWG, Higher the current carrying ability
Earth/Ground Wire - The wire which is earthed to the chassis via direct contact; Drains excess electrons to create an equal balance in the system
Power (Memory) Wire - The wire running directly from the battery to the source unit i.e HU, AMP; providing the main source of power. Called memory wire in reference to its ability to provide power to the HU so that stored data is not lost when the car is switched off
Accessory Wire - The wire which only supplies power to the source unit when the ignition is turned over to ACC i.e car turned 'ON'
Speaker Wire - The wire which sends power and signal to a speaker
RCA Outputs - Dual wires which are specifically for sending signal to an amplifier, as they do not have a high enough output current to drive a speaker
Internal Wire Resistance - The resistance of the actual metal which the wire is made out of, usually small in relativity
*Guide to choosing what gauge wire:
AWG___Maximum Rated Current
00___ 400 amps
0___ 325 amps
1___ 250 amps
2___ 200 amps
4___ 125 amps
6___ 80 amps
8___ 50 amps
10___ 30 amps
12___ 20 amps
14___ 15 amps
16___ 7.5 amps
-----------------------------------------------------------------------------------------------
FREQUENTLY ASKED QUESTIONS (FAQ'S)

Q: Is it safe to overpower a sub or speaker? Eg. 700W amp on a 400 W sub...
A: Yes, as a matter of fact, it is a lot more beneficial for the subs performance and safety that you use a overpowered amp and adjust the gain settings to suit your listening levels. Underpowering a sub, then pushing it to its limits (high volumes) can be harmful to both sub and amp due to clipping (see above)

-----------------------------------------------------------------------------------------------[/quote]

Power wire sizing..
work out what size wire you need to power your amp.. then use the fuse required.. making sure the fuse is also big enough for the amp(s) draw

general rule

if your amp has two 30amp on bored fuses then its gonna be drawing 60amps (30x2=60) so use a fuse of about 70amps (a little higher then the amps draw) then u should use wire that can safly pass that much...

REMEMBER: the fuse on your power supply wire is there to protect the power wire NOT the amp.. so this fuse needs to be as close to the batery as posable (within 18" of the possitive terminal).. so mounting it in the boot so u can show off your wikid cool fuse if compleatly pointless and very dangerous.. as the wire from the battery all the way through the car to the boot is totally unprotected... shorting this can cause your car to burn to the ground.

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Posted: Sun Mar 04, 2007 2:29 pm 
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Good work dude alot of helpful info there...might see If i can right up some stuff and have aaron add it too his doco...the amplifier calculating WRMS isnt 100% correct but a good guide to base everything off as you have to take into account the amplifies efficiency...

but all in all I think alot of beginners/novices to car audio will have alo of initial questions answered right there.

 

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Posted: Sun Mar 04, 2007 3:17 pm 
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thanks mate, thought it may answer a lot of questions , if people took the time to read it.

 

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• F*** McDonalds... I'll make you go Mmmmmm...
• F*** SubWay... I'll give you a foot long
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