So i have noticed that many who are new to the world of car audio, ask the same exact questions. So in an attempt to cut down on some of these posts, i figured we should start a thread with the most commonly asked noob questions.
feel free to add here guys if you think of anything else....
ALSO: These answers are meant to be a good starting point for understanding some basic principles in car audio. They are in no way the definitive answer to every single application, just more of a generality to help those just starting out.
My subwoofer is rated at xxx watts rms & xxx watts peak, how much power should i give it?
For the sake of generalities, and a large amount of equipment that is out there, peak rating is pretty much useless. It has become more of a marketing tool to make said equipment seem more appealing to the buyer. There subs out there that can handle alot more than rated RMS power, but if you are just starting out in car audio, RMS rating is a good bench mark to use when thinking of powering your subs. Once you become more knowledgeable, then i would start to consider running more than RMS safe, but, if you are new, i would not recommend exceeding it.
What impedance (ohm load) should i run my system at?
This is a very subjective topic, with a mariad of opinions. I will say this though... As you lower your impedance, the strain on your electrical system as well as your amp increases. At the same time, your amp's THD (Total Harmonic Distortion) will increase, diminishing sound quality. On the large majority of amps, this will not even be noticeable until you get into very low impedances (1 ohm and below). The amount of THD increase can be as small as >.1%, or can be much greater, just depends on the amp. You also want to take what your amp is rated at into consideration. The large majority of mono block amps are rated at 1 ohm, but on the flipside, if you are running a 2 channel amp bridged, the large majority of those are rated at only 2ohmx1... What this really translates to, is that running your amp at lower than rated impedance can be dangerous. Also, even if your amp is rated at lower ohm loads, if you do not have the proper electrical upgrades to back it up, it can also be dangerous. The biggest point i'm trying to make here, is if you don't have the electrical to back it up, or arent sure, wire to a higher impedance... otherwise the magick blue smoke fairy may come for a visit (AKA you might fry your amp).
How do i wire my subs to a different impedance?
I could make a long drawn out thread about this, but instead, i will link you to a great wiring wizard, that will show you exactly how to do it.
Subwoofer Wiring Diagrams
Why is setting my gains properly so important?
This is a very Long and Arduous topic. The simplest answer is this... mis matching your gains can lead to a clipped signal, which in turn can lead to problems... from a distorted signal all the way up to frying your VC's (voice coils on your subs). If you really want the nitty gritty of it, check out this great write up...
The WHY of gain setting
I set my gains by ear because blah blah blah/ How do i set my gains properly?
I dont care who tells you that you can properly set your gains by ear/that it doesnt matter... He is a dirty, stinking, liar. Truth of the matter is, a clipped signal occurs WAY before the distortion is audible to the human ear. That is why using the proper tools to set your gain is so important. You can not hear any difference, but yet be running an extremely clipped signal to your subs. You will need a few things to porperly set gains will be a DMM (digita mutimeter), a test tone generator or CD, and basic math skills. (an o-scope is preferable to a DMM, but you can still do with just a DMM)
You will need to know a few basics of Ohm's law... which defines the relationship between power, current, voltage and resistance. The most basic principle to understand, is that all the variables are relative to each other, meaning if you change on of the variables (power, current, voltage, or resistance), it will directly affect the others.
This is the equation to remember: Voltage = sqrt(power x resistance) ----- voltage equals the square root of power times resistance.
You will take this formula, and use the specs from your amp for the variables...
I.E. if you have an amp that runs 300 watts @ 2 ohms, it will look like this....
V = sqrt(300 x 2)
Voltage = 24.49 - this is your magic number. this will be the amount of AC voltage you will look for when setting your gain.
*You also want to make sure you use the impedance (ohm load) that you will have it wired to in your equation.*
Take your DMM, set it to AC voltage, then place the test leads on the output terminals.
Take your tone generator or cd, and set it to 50 hz.
*The vast majority of HU's (head units) out there will clip their signal when at very high outputs, the majority of which will start at around 3/4 full volume*
Set all you setting on your HU to 0/flat, and turn it up to 3/4 of full volume.
Starting with your gain turned all the way down, start turning it clockwise, until you reach the voltage you found in the formentioned equation.... this is where you will set your gain at... no higher.
The rest of your setting are like this... the LPF is the upper limit of frequency you want your subs to hit, the subsonic is the lower... and bass boost shouldn't be used in most situations.
For your mid/high amp, you will do the same, only you will use a 1khz tone instead
*This is a very general and simple way to safely set your gains... There are better/more in depth methods, but this is the simplest*
Here is a good chart for those who are not math inclined
What is the big 3, how do i do it, and why is it so important?
The big 3 is an essential step when upgrading your electrical. Main reason being, when auto manufacturers designed your electrical system, it was never designed for high amperage duties (such as large amplifiers), so the stock wiring in between your alternator and battery is garunteed to be very small, and insufficent for high power applications. This can lead to a "choke point" in your electrical system. You can have all the 1/0 runs from your battery to your amp you want, but unless you do your big 3, it really wont do any good. Your electrical system is only as strong as it's weakest point, which is usually right at your alternator.
To accomplish the Big 3, you will want to use a minimum of 4 Ga wire (although 1/0 much better)... and you will want to match the size wire you use to the rest of your install (if you run 1/0 from your battery to amp, but only use 4ga on your big 3, your still creating a choke point).
You can either straight up replace stock wiring, or just add to it.. and on the majority of newer model cars, you'll want to add to it, and leave the stock (due to their wiring harnesses being interconnected).
The wires your going to replace/add are from alternator to battery, battery to chassis, and battery to engine block. Alternators for the large part are self grounding, which is why you wont need to run a ground.
For a much more in depth write up on Big 3, check this out...
Official CarAudio.com Big 3 Thread
What size capacitor should i use to keep up with my amp?
The simple answer is none. A capacitor is completely useless in 99% of installs. The smaller farad capacitors have no benifit for voltage drop, and can actually cause a choke point in your electrical, causing voltage drop when not installed properly. They are useful in certain, more advanced installs... but that has nothing to do with voltage drop for which they have been marketed over the last 5-10 years. If you are really experiencing alot of voltage drop, refer to the last question about big 3, and consider upgrading your alternator, battery, or even adding an extra "helper" battery in the rear.
If you want more info on capacitors, and how they are useless in the majority of installs, here's a really good read....
If i fuse in between batteries/alt and batteries, what should the fuse be rated at?
You will want to fuse according to the wire, not the batteries... This also varies for each brand of wire... so there is no real "magic number" for all 1/0 ga, or 4 ga... you will want to check with the manufacturer of the wire for what amperage it is rated at, and fuse it at that rating.
Another, much more in depth writed up...
Dual battery wiring tutorial (and why)
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