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Old 02-18-2009, 02:54 AM   #1
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-=The Car Audio Basics=-

I have been reading a few posts on here talking about what capacitors actually do and don't do so here is an in depth explanation

All right here is a myth:


"Capacitors will help my lights stop dimming"

alright to address this lets look at why they dim. When your system is playing your amplifier is using amperage to make wattage. You can figure out how much amperage is being use by using this formula.

http://www.the12volt.com/ohm/ohmslaw.asp

I(amperage) = P(wattage) / (.75 * E(voltage))

so say your amplifier makes 1000 watts of RMS power @ 14.4 then the amplifier roughly should be drawing 93 amps of current. now say that you have a stock 1992 Nissan 240sx w/ the stock 80 Amp alternator in it. You will be drawing more power from the car than the alternator will make.

The amplifier will try to pull as close to the 93 amps of current needed to make the 1000 watts of power. as Amperage available drops voltage drops as well. Amperage and Voltage are correlated together. The voltage drop is what causes your headlights to dim.

Now a capacitor, or stiffening cap, will try to keep voltage stable. As voltage drops it releases power to bring it back up. But as stated above the voltage dropped because of amperage drop and a capacitor can not restore amperage.

The true fix to this problem is to get an alternator to make sure that your amperage does not drop below the required amount. Also when you are purchasing an upgraded alternator also understand that the car normally requires 50-75% of the amperage that the stock alternator makes.

So if your amp draws 93 amps of current and you start out with 80 amps then you should try to get at least a 175 amp alternator.

Do not think that a capacitor will fix your lights dimming.. a capacitor can not replace lost amperage.. only a alternator can..




Next Myth:

"This 1 farad cap will make my amplifier hit harder"

While this is partly true there is a big flaw in how most look at it.

P(wattage)=E(voltage) * I(amperage)

so of course if your voltage drops then your power drops.. but your voltage only drops when your amperage drops. Again as stated above the way to fix this issue is to buy an upgraded alternator


The reality of why a capacitor is good:

http://www.caraudiohelp.com/newslett...citor_myth.htm

Quote:
Why Does a Car Audio Power Capacitor Work?

A car audio power cap works by storing large amounts of electrical power which it can then deliver to power hungry components when called upon to do so. They have an advantage over typical lead acid storage batteries because they have very low internal resistance. This allows them to deliver large amounts of power (current) very quickly. Much faster than a car's charging system can deliver that same amount of current.

Car audio power amplifiers have can have very large current demands. This is dependent on the music being played through the amplifier. Typically these currents are only needed in short bursts during transient peaks (cannon shot, bass drum strike, etc.). If the amplifier tries to pull this current from the electrical system directly it may cause a drop in voltage called a sag. This sag is equivalent to a voltage drop in the system and the size of the drop depends on the resistance of the wire from the source (battery) to the amplifier.


They are used to try to keep the voltage in to your amplifier stable which keep power output stable.. this means your music you are listening to will not fluctuate or change volume randomly.. but make sure you have the proper charging system to back it up or a capacitor will do you no good..

I hope this helps explain what a cap really does. If you have any other questions feel free to PM me any time about anything car audio related. Thanks!
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Old 02-18-2009, 03:00 AM   #2
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woah great read dude
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Old 02-18-2009, 03:02 AM   #3
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woah great read dude
thx
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Old 02-18-2009, 03:04 AM   #4
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actually i am gonna start doing more of this stuff to try to break the car audio segment down.. hopefully to help people realize that making something in your car sound good isn't magic.. its just basic physics
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Old 02-18-2009, 03:07 AM   #5
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wow great stuff
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Old 02-18-2009, 03:09 AM   #6
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Wow, detailed, info-filled thread. I like..
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Old 02-18-2009, 03:20 AM   #7
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Old 02-18-2009, 03:21 AM   #8
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i never really put to much thought into the first part because ive always had big alternators. but i know what post you are talking about in the second, one, and i was just trying got say it in lam ins terms
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Old 02-18-2009, 03:34 AM   #9
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i never really put to much thought into the first part because ive always had big alternators. but i know what post you are talking about in the second, one, and i was just trying got say it in lam ins terms
oh man.. don't worry this was no attack at anyone.. just trying to get the details out there to try to help everyone learn ya know
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Old 02-18-2009, 10:31 AM   #10
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im taking physics 2 now and cant event read another post my head hurts
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Old 02-18-2009, 10:41 AM   #11
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I(amperage) = P(wattage) / (.75 * E(voltage))
WRONG!
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Old 02-18-2009, 11:25 AM   #12
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WRONG!
lol i knew someone would catch me.. you are right i am wrong but i am using .75 as a average number to calculate the efficiency of an amplifier..

of course there is no way to calculate efficiency but on average amplifiers that run subwoofers are around that range.. so its close.. but i didn't feel like going into detail on that
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Old 02-18-2009, 12:13 PM   #13
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good post. shows you know a good sum of knowledge. props.
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Old 02-18-2009, 12:17 PM   #14
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good post. shows you know a good sum of knowledge. props.
he knows physics lol, I have those formulas on in the back of the calculator I have for sale lol.
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Old 02-18-2009, 12:24 PM   #15
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very nice write up
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Old 02-18-2009, 12:25 PM   #16
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Class A

Class A amplifying devices operate over the whole of the input cycle such that the output signal is an exact scaled-up replica of the input with no clipping. Class A amplifiers are the usual means of implementing small-signal amplifiers. They are not very efficient; a theoretical maximum of 50% is obtainable with inductive output coupling and only 25% with capacitive coupling.
Quote:
Class B amplifiers only amplify half of the input wave cycle. As such they create a large amount of distortion, but their efficiency is greatly improved and is much better than Class A. Class B has a maximum theoretical efficiency of 78.5% (i.e., π/4). This is because the amplifying element is switched off altogether half of the time, and so cannot dissipate power. A single Class B element is rarely found in practice, though it can be used in RF power amplifier where the distortion levels are less important. However Class C is more commonly used for this.
Image:Electronic Amplifier Class B fixed.png
and class D is even more effecient.. but using the efficiency of .75 kinda give an average
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Old 02-18-2009, 12:43 PM   #17
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-=The Car Audio Basics=-

Alright guys I am going to change up how i was gonna do this originally.. i want to know what questions you guys have about how cars electrical systems work. More towards the car audio side but i will try to any questions revolving around 12 volt power if i can.. if i don't know the answer i will let you know.. but i can try to find out for you..

Also if think something i am saying wrong then i am fine with that but please let me know how.. the way you learn is by questioning what you know at all times.. eventually you will find out whether your truly correct or not.

I have been in the car audio industry for the last 8 years.. so i am not saying i am an expert but i want to try to help anyone i can.. so start throwing out the questions
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Last edited by Bubbles; 02-26-2009 at 11:20 PM.
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Old 02-18-2009, 12:49 PM   #18
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im really glad that this site is getting more info like this

hopefully this trend will continue and this site will be as (or even more) informative as NICO or other sites like that



keep up the good work man!


i appreciate it
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Old 02-18-2009, 02:04 PM   #19
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im really glad that this site is getting more info like this

hopefully this trend will continue and this site will be as (or even more) informative as NICO or other sites like that



keep up the good work man!


i appreciate it
http://www.houston240sx.com/forums/s...ad.php?t=34504

thats the plan.. working on it now
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Old 02-26-2009, 11:20 PM   #20
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bump for update.. please read above
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Old 02-26-2009, 11:48 PM   #21
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do you only mess around with the electrical side of car audio, or
do you design any enclosures aswell?

ive had aset of alpine type e 10's for like 6 or 7 years now. had then installed for a year or so and just held on to them for all this time.

they are not in a box now and was thinkng about hookin them up recently.
what type of box would you sugguest?
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Old 02-27-2009, 12:22 AM   #22
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i am wise because i know i know nothing-socrates

do you only mess around with the electrical side of car audio, or
do you design any enclosures aswell?

ive had aset of alpine type e 10's for like 6 or 7 years now. had then installed for a year or so and just held on to them for all this time.

they are not in a box now and was thinkng about hookin them up recently.
what type of box would you sugguest?
they like sealed.. depending on what year they are made if i remember correctly they were around .65 cu ft sealed..

also go to walmart and pick up pillow stuffing.. its called poly fill or Dacron.. there are a bunch of names for it.. stuff the box almost full with it and it will help make the woofer sound pretty good..
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Old 03-01-2009, 07:34 PM   #23
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yea that is right inline with what i wanted to do .
for a long time when i was making boxes (in highshcool of course)
i always wanted to toy with the 'waveguide' theme that bose uses...
any experience with that??

i used to know a good way to get the harm freq of the vehicle and that would give you an idea of how to tune the box better.
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Old 03-01-2009, 07:56 PM   #24
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Going to Sticky this because it can come in handy, especially with you adding any info into 12v power sources. This should help out with people looking to find clean ways of installing gauges and running power and ground sources. Thanks Bubbles.
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Old 03-02-2009, 02:34 AM   #25
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yea that is right inline with what i wanted to do .
for a long time when i was making boxes (in highshcool of course)
i always wanted to toy with the 'waveguide' theme that bose uses...
any experience with that??

i used to know a good way to get the harm freq of the vehicle and that would give you an idea of how to tune the box better.
Yes i have actually.. the science behind the design is pretty cool but has a few flaws.. (other than bose using crappy 10cent speakers in the design) lol

the way it works is that the speaker is in a really long tube.. basically lower end frequency's need a long distance to actually "unfold" so that they can play at their full volume.. that is why you can hear loud bass from far away because the farther away it gets from the car the louder it gets to a point..

this is how they can get low bass out of a 3-4 inch speaker.. all speakers can play that low depending on the size but its harder to get them to play lower frequencies loud enough to hear



its basically a really long tuned ported box.. it works real well when all of the speakers are done this way and can be tuned together.. problem in a car is that you can do this with the subwoofers but not the speakers in your door..

when you put a speaker in a long tube like that there is a delay called "group delay" which is basically a few millisecond delay where the air movement of the speaker is bouncing back and forth at each fold in the tube.. this causes the sound of the woofer to be delayed compared to the rest of you speaker system..

on rap music this is normally not a big deal because the boom of the sub normally doesn't correlate to the rest of the music..

but when you listening to music with a bass guitar or something similar where the bass is used to follow the beat of the song you will hear it as if it was half a step off..

it can actually sound really weird.. if you listened to this all the time in your car.. you would just get use to it and think that is how the song is.. but as soon as you heard the same song on another stereo system you would notice the difference..

so in a car application it doesn't really work.. normally a well built vented box in a car works very well.. if built correctly you will have a very efficient, accurate box that will stay in time with your music
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