General Car Audio FAQs

One of the members here saw this info that I posted on another forum and asked that I post it here as well. Hopefully it will help some of you in your search for audio nirvana and if you have any questions please feel free to ask!

BTW, after re-reading this tonight I edited some info to hopefully make it easier to understand and in some cases I added to it.

disclaimer: I am not some "Audio Guru", rather just a car audio fanatic that likes to experiment and learn why things are as they are as well as pass on what I have learned! The following is based MOSTLY on my actual experience and knowledge (unless I mention it wasn't in which case I'll provide references )! In some cases it will be my opinion and my opinion may be worth exactly what you paid for it! This in NO way is meant to sound like it is the "Holy Grail" rather just to pass on some info that hopefully helps some of my fellow car audio fanatics get the most out of this hobby. In any case, "I cannot hear what you can hear and you cannot hear what I can hear so your results may vary".

I get a LOT of calls from the great members here and recently a lot of the same questions have been asked pretty often so I thought I'd take a few minutes to post my thoughts/experiences on some of them in one place . BTW, please note that I'm not trying to discourage anyone from calling me for help because I'm always willing to help if I can and I really do answer the phone!


Q: "I kept the factory headunit and replaced my factory speakers but the new ones don't sound much better (or in extreme cases they actually sound worse)

A: A lot of the factory headunits have built in "non defeatable processing" to compensate for the "less than stellar quality" speakers so this can happen."
They can also have "volume dependant" equalization which alters the response to keep from blowing the speakers (typically the bass will be reduced at higher volumes). A device such as the JL Cleansweep will dramatically improve the quality of sound in the situation where you want to keep your factory head unit.


Q: Are aftermarket headunits "better" than factory headunits?

A: Not necessarily. Aftermarket headunits typically will have more features however in some cases the the OEM factory specs will require tolerances that are tighter than those for some aftermarket units (this info is from a friend that is an engineer for Ford).


Q: Do I need to separate my power wire from my speaker wire and interconnects?

A: This is a myth that has been around a long time. I believe it came from cases where people ran the wires together and got induced noise. They would then separate the wires and the noise would go away so they figured it was the wires next to each other that caused the problem. This can be dispelled quite easily if you look at it this way-it takes a positive and negative connection to complete a circuit, correct? The ground wire from your vehicles battery is connected to the chassis/body correct? So if that's the case no matter where you run the speaker wire/interconnects they will always be "on top of the power wire" per se, correct? . This is not to say that there cannot be noise induced with the wires next each other rather that the problem was most likely caused by a bad cable, something electronic the wire was near or what I call a "hot spot" on the vehicle where the wire was and when said wire was moved "away from the power wire" the noise went away.
BTW, I've run all the wires together in the countless number of systems I have installed over the years and have never had a noise problem in any of them.


Q: Is sound deadening my vehicle worth it?

A: IMO yes, but it also depends on what "level" of sound quality you are looking for and what it is worth to you. Personally I am always looking to get the "most" out of my sound system so I go overboard however for some people the "point of diminishing returns" comes before the cost/time of deadening.


Q: What are the "best" speakers out there?

A: There is no "best" for everybody and every application since as I mentioned, I cannot hear what you can hear and you cannot hear what I can hear! Since speakers are what actually make the sound I ALWAYS make them the first priority in my sound system or any system I build. The best bet in finding speakers that work best for you is to listen to them yourself however I know that is not always possible so you'll have to rely on the ears of others/reviews and hope they have similar tastes to yours. And don't forget, a "good" speaker installed properly will sound better than a "great" speaker installed improperly"


Q: Should I use "rear fill"?

A: As with most things, car audio is all about "personal preference". If you like sound "all around you" or are concerned with the rear passengers use rear fill! If you are looking for "competition type" soundstage/imaging I'd say not to use rear fill as it will be more difficult to maintain a coherent front stage. An easy way to find if you like rear fill is to fade your headunit all the way to the front and if you like it like that don't spend any money on the rear! If you do prefer rear fill, the front speakers will still be doing the majority of "the work" (or should be ) so I typically suggest spending the "lions share" on the "best" speakers within your budget for the front and using a pair of mids only in the rear. Also, if you are using the rears for "ambient fill" only (and not 5.1 surround etc) you won't need much power to them. When I install systems with rear fill speaker I usually run them off of the headunit and I typically don't use tweeters as they can "pull" the sound towards the rear (but again, if that's what you like then do it!).


Q: Will I blow my speakers if I "under" power them?

A: Another one of those myths I keep seeing repeated all the time but I believe it is just because some have not actually had this explained before. This one came from people blowing speakers while using amps that were rated less than what the speaker(s) could handle and blaming it on "under" powering. A very simple answer that dispels this myth is "if that were the case, every time you turned the volume down you would blow the speakers"! Let's say you had a speaker rated at 200 watts rms and your amp produced 100 watts rms. When an amp goes into "heavy" clipping it can "theoretically" produce twice its rated power so you could "theoretically" send 200 watts to that speaker when clipping the amp. This will NOT blow the speaker (sans a defective speaker or inaccurate rating) since the speaker is capable of handling that amount of power and it doesn't "know" if that power is from a "clipped" source. Now let's say you have a 200 watt rms speaker and a 150 watt rms amp. Under heavy clipping this amp could "theoretically" produce 300 watts which can blow a speaker rated at 200 watts rms since that is more power than the speaker is rated to handle. In these cases people would state "I blew the speaker because I was under powering it when in fact as you can see by the example they actually overpowered it.

BTW, clipping is murder on tweeters due to the increase in high frequency content (this is what happens during clipping and not that myth you may have heard about "DC current" or the speaker "stopping" due to the wave being cut off etc ) so the above does not apply! (part of this was based on info I received from several audio engineers as well as testing I did on my own after learning about it and if you'd like more detailed info I have it ).


Q: Amp "A" has .05% THD and amp "B" has .0005 THD. Does this mean amp "B" will "sound" better?

A: If you can hear the difference between .05 and .0005 you must be superman! Here's a little test you can take to determine just how much distortion a human is capable of hearing and you may be surprised at how much you can't hear.
http://www.klippel.de/aura/default.html


Q: Why do the same speakers sound "better" when the salesman switches to certain headunits or amps on the soundboard?

A: Have you ever heard the salesman say "this amp is better for bass" or "if you like brighter highs you need this particular headunit" or "this one is better for vocals" etc etc? I have and used to wonder about it until we did some experimenting using numerous mid level/high end headunits/amps at one of my car audio meets some time ago. The major finding was that MANY headunits/amps had "built in processing" even when the EQ was set on flat! The headunits usually had certain frequencies boosted or cut which emphasized or de-emphasized a certain part of the music and some of the amps had similar processing going on (check out the review of the new Rockford amps in Car Audio and Electronics this month and you'll see what I'm talking about). Also, most people equate "increased output" with "increased SQ" so an amp/headunit adjusted to put out a bit more power could easily be perceived as "sounding better". I think it would be extremely difficult to keep all of the headunits and amps on a sound board the same in output/frequency response and even if they could I can't imagine it would be beneficial for the salesperson since then they couldn't say stuff like "this amp/headunit sounds better than that one which is why it costs more" etc (as an electrical engineer friend of mine always says, "if it measures the same it will sound the same". ) BTW, there were several other "variances" in the amps/headunits however one thing we noticed with the "higher end" units we tested was that the channels were more evenly matched and most did not have "EQ curves" built in.


(Continued below due to excessive amount of characters! )

 

Continued.......

Q: Can I use my steering wheel controls with a device such as the JL Cleansweep?

A: You can still use the cd/tuner controls however you must use an external volume knob because the headunit volume knob is set at a specific position when you run the software that "flattens" the response of the factory headunit and if you change this position at the headunit you can induce the "factory equalization" thereby negating the benefit of flattening the response.


Q: If my amp already has a fuse do I still need a fuse on the power wire near the battery?

A: Yes!!! The fuse at the battery keeps your truck from burning up in case of a short! . General guidelines state you should put the fuse within a foot or so of the battery and in any case it must go before the wire passes through ANY metal (make sure to use a rubber/plastic grommet at that point).


Q: How do I know what size wire and fuse I need?

A: The power wire size is determined by the capacity needed for any equipment connected to it. The fuse size is determined by the capacity of the wire. It is OK to use a fuse smaller than required for the capacity of the wire but it is NEVER OK to use a fuse larger than the capacity of the wire. On the other side, it is OK to use a wire size larger than needed but it is NOT OK to use a wire smaller than required for the determined capacity. Here's a chart to help you determine the correct wire size:
http://www.the12volt.com/info/recwirsz.asp


Q: How long can my ground wire be?

A: The size of the ground wire is determined by the capacity of said wire. As long as the ground wire has at least the same capacity as the positive wire you can run it all the way back to the battery if you want (that's how we do it in boats and other situations where you cannot get a good ground elsewhere ). BTW, this of course is assuming you already have a properly sized positive wire to start with.


Almost forgot, I actually prefer a circuit breaker instead of fuses.


Again this is not meant to sound like the "Holy Grail" (check my disclaimer above ), I'm just passing along some experiences in hopes it will help others since I have been hearing these questions a lot lately. You may or may not agree with my "opinions" on certain things and that's cool however before disputing anything else please ask yourself "Do I have any solid proof to dispute that or am I just "repeating" something I heard/read?" If you do have solid proof please pass it along as I am always willing to learn something new myself!

Lunch time is over and I gotta get back to work but I'll check back later to field any questions/provide references or add more as I think about it.

 

Great post and I love your enclosures, some of the best on the market. I felt I had to comment about one of your Q&As. One of my first systems had tremendous alternator whine going through the speakers. I relocated the RCA cable to the other side and problem solved so I'm a firm believer in the "Keep Em Separated" philosophy.

 

Thanks!
I can understand how that situation would make you a believer in that philosophy (I used to believe in it as well ) however if you had moved all of the wires (including the power wire) to the other side the noise would have still gone away and maybe you'd have joined me on "the other side" (wow that was weak! )

BTW, I mentioned above that I have never had any noise problems in a vehicle with all of the wires bundled together however that wasn't quite correct. I have had noise however I just moved the entire bundle of wires and the noise went away.

 

Another one I have been asked quite a lot lately...

Q. Do I really need baffles/adapters to install new speakers or can I just screw them to the metal of the door?

A. The proper baffle is more than just an easy way to mount aftermarket speakers and this goes along with my comment above that "a good" speaker installed properly will sound better than a "great" speaker installed improperly". Since the front speaker is a 6x9 and most replace it with a 6.5" the baffle serves to separate the front speaker wave from the back speaker wave in order to avoid cancellation (you must also seal all large holes in the door frame). It also provides a solid mounting surface which helps keep the "energy" from transferring to the door causing unwanted resonance that will degrade the sound of your new speakers (applying "mass loading" material around the baffle also helps "de-couple" the speaker from the door). BTW, the thin plastic adapters you see available are a convenient way to mount speakers however you will not receive the above benefits as you need a "dense" material baffle if you really want to get the most from your speakers.

 

what can i do to add to improve the sound while keeping the factory stereo. I have a Double cab with very limited space behind the back seat.
Thank you

 

Thanks and you're welcome!

Several guys suggested I post the following from another thread concerning choosing speakers so here it is with a couple of edits!

 

heres a dilema of mine have a single dick player and purchased a 6 cd model jbl upgrade but the wiring is not compat. only 1 of the 4 harnesses working is there possibly a harness kit that would convert these others. Thanks for any and all suggestions

 

I'm not familiar with that however if you start a new thread maybe someone can help you out!

 

I had wish I had this information in 2001, when I started messing with car stereos. Great information.

 

I just installed a 12 behind my back seat and the area under the back window has a slight vibration will dyna mat take care of this problem thanks in advance

 

Next time, please post your question in a seperate thread. This helps you get better responses.

As to your question, it's very dependent. Some vehicles are inherently more resistant to rattles than others, so removing ALL rattles might be a wild goose chase. I suppose you could remove the rear window and put stick-on strip caulk around the edges where the metal meets (note that this is pure theory, I haven't taken the rear window off). This would be the cheapest option by far.

 

I want to clarify something here that I believe is wrong:

Underpowering a speaker CAN blow it. Lets take an aftermarket speaker that can handle 100wrms. A stock headunit can put out roughly 15wrms, or possibly 20-30wpeak (no one cares about peak, it's all about RMS). What the original poster didn't mention was Distortion. Distortion is an audible form of clipping.

Clipping is a distortion in the sine wave of an audio signal.

Normal Sine wave:


Clipped Sine Wave:




As you can see, the regular rounded Sine wave has turned into a Square wave. In a sence, you are trying to produce more power than what the amp can handle. You're not really producing more power, it just seems that way to your ears.

The gain on an amp is NOT a volume control. It is meant to match the RCA output voltage of your head unit to your amplifier. Typically it is adjusted using a DMM, or an Occiliscope if you have one avaliable.

Anywhoo, back to what I was talking about. Once you start clipping the signal to your speakers, you start forcing the speaker to act irradically.

That's why people blow aftermarket speakers off of a stock headunit. If it's not loud enough for you, get an external amplifier and run them off of that.

A good rule to follow is once you start to hear crackling or distortion, turn it down.

Well, I re-read the original statement, and I somewhat agree wtih it. I wanted to give visual examples. Technically, underpowering doesn't blow speakers, it's the clipping that does. Underpowering leads people to turn it up which leads to clipping which leads to a blown speaker.


I miss car audio.. I need to get back into it.

 

You may believe it is incorrect however here is a little more info on the subject from Manville Smith of JL Audio and a few other renowned audio engineers that may help you out.

 

a little more.....

 

Lots of good info Mr. Marv. You say you're not an audio guru, but you sure sound like one bro. LOL. Good read.

Love Manvilles rants as well!!!! Good guy!!

 

A quick note on the issue of separating power and signal/speaker wires.

The idea that this is necessary probably originates from home audio, where it is necessary because power cables on a home system are carrying A/C and therefore producing an oscilating 60Hz EMF which is capable of inducing a "hum" into speaker or component signal wires when the two are intertwined or routed in proximity for significant lengths.

In car audio the power wiring is carrying a DC power supply (there can be a little oscillation in voltage depending on the quality of rectifier in your alternator, but the current never reverses), and therefore produce a constant (and much smaller since the voltage is so much lower) EMF which physically can't create noise in the signal lines. When car systems do encounter induced noise, odds are that the source is actually the ignition coils which can create a lot of EM/RF noise as a side effect of what they do, and depends a lot on how well they are shielded and where in the engine bay they're located and if the plug wires aren't well shielded. A steel firewall should usually protect the HU and interconnects from coil noise, and this should rarely be an issue for most street cars, and since the 2nd gen Tacos have the coils right on the plugs, there's no worry about unshielded plug wires.

If you're really paranoid about niose and don't care about possibly wasting a few bucks, you could always use coax RCA cables (usually used for HT digital or composite video hookups) as interconnects, as coax cable is theoretically immune from induced noise (as with anything else, no application is perfect to the theorey).

 

Have you really never experienced alternator whine? It's just plain awful. I think that a god set of shielded RCA's helps in most instances but I think it's also important that the source is shielded from this interference as well. I've yet to figure out how to manage that but maybe one day I will.

I've always found that when you increase the load on the electrical system the noise gets louder. For instance, if you hear the whine and you turn on your headlights, roll the windows down, or do something else electrical; it will get much much louder. Any idea why that is?

 

There is the potential for EM noise coming off the alternator, and power window motors will make a little bit as well, and halogen headlight lamps could make some RF, but the worst I've ever encoutered has been RF noise coming off the ignition system while attempting to tune in a weak AM signal in an RX8.

It kind of makes sense that noise coming from the electrical systems could get louder when something's put in use as that would increase the current through parts of the wiring, but the potential for DC wiring to create noise in the first place is pretty limited. YMMV, and how truly "DC" the system acts can be dependent on what type/quality of rectifier is built into the alternator (might need an oscilloscope to check this, since the frequency would likely be too high to spot with a VM/DMM); might be possible to mitigate or negate this effect by wiring a capacitor across the alternator leads, but consult with a mechanic before doing this since a sizable cap charged to 12-14 volts can store dangerous amounts of energy and doesn't look any different when charged as opposed to discharged.