Subwoofers: A Complete Guide

Subwoofers are speakers, just intended for lower frequencies. Many think they're not speakers, but they are and as such I will refer to them as speakers often in this text.

What is impedance and how does it affect me?

Impedance is the resistance that a circuit provides to electrons passing through it. (it's actually the opposite of the conductivity. It's the classic argument that there is no dark just absence of light, no cold but absence of heat...etc. But shut up and just listen). Impedance is measured in ohms, which is represented by the symbol Omega. Google it if you don't know what it looks like, since you'll probably want to know. The less impedance, the more easily electricity can flow through.

What that means in the real world is that power output of a specific amplifier is different at different resistances.

An amp will have a rating of say "75Watts RMS @ 4 ohms, 150W RMS @ 2 ohms". As you can see, with less resistance the amp could flow more electricity. The only problem is, the more electricity it flows the hotter it gets. Don't run your amp at a lower impedance than it was designed for, or you can kiss it goodbye!

Car audio stuff is generally 2 or 4 ohms. Home audio is usually 8 but sometimes 6.

RMS? What's that?

RMS is the continuous power output of an amp, or continuous power handling of a speaker. In wattage, RMS is the REAL info that you want. Coupled with ohms (your impedance again folks) it tells you pretty much which amp you should buy for which speakers.

Such measurements as MAX will only tell you what it's putting out at a peak. These measurements are pretty worthless to amateurs like you and I. What? Yes, I'm an amateur. The world of audio is very very complicated and I'm only at an understanding of the tip of the iceburg.

RMS isn't the only thing you want to take into effect while purchasing a sub. Sensitivity will also affect it. A sub that takes slightly more power with lower sensitivity might be just as loud as a sub with higher sensitivity and lower RMS wattage.

Crossovers are your friends

When you're installing speakers, crossovers are awesome. They make sure that your highs only receive high signals, your mids only receive mid signals and your lows only receive low signals. A crossover is an electronic component, and how it works is beyond the scope of this essay. Just imagine it cutting the high parts of the music off and hiding them from the subwoofer.

This is good, because speakers only appreciate producing certain frequencies of sound. A subwoofers acoustic range is going to be very low because it was MADE to produce LOW sounds. A high (tweeter) would be pretty pissed if it had to produce bass and would destroy itself very rapidly.

Playing mids or highs through a sub isn't necessarily going to hurt it very much, but it'll sound like utter garbage.

I want a car audio subwoofer system, what should I do?

Generally I pick out a speaker first. You can start with an amp, because they're the most expensive part. Either way, lets start.

Subs:
You should decide on if you want one or two, and what size you want. The bigger you go, the slower they are. If you like techno, then you want a punchier bass. Go with something like a 10 inch sub. If you like rap then you probably want something deep and LOUD. Go with 12 or 15 inches. Keep in mind the more subs you buy, the bigger an amplifier you need to purchase. I have two 12 inchers, and they're not bad for techno but I really LOVE them when listening to drum and bass or rap. Nothing like a free back massage.

Since this is a beginner guide, I'm not going to cover all the crazy hookup methods you could do with dual voice coils, series parallel configurations using 2 channels on amps, etc.

Pick out a nice single or dual voice coil sub. Older kicker comps can be purchased for cheap and hit pretty nicely. They do require a bit more power though, so be careful. I've owned eclipse, sony xplods and several kickers.

The sub will be rated with an impedance, an RMS wattage and a MAX wattage.

Grab one thats not too high in the RMS category, because the higher you go the more expensive amplifiers will be. 150W or so is a good starting point.

Ignore MAX, as it's pointless.

If you go with a 2 ohm sub it'll be easier to get an amp that is powerful enough, but there will be more distortion. Believe me, you probably would NEVER know, unless you're some kind of audiophile and then..why are you reading this guide?

Paper subs suck and you should avoid them. Plastic or kevlar coned subs are pretty nice. This is what you're aiming for with your beginner system. Aluminum subs are nice, but expensive so you probably won't be getting one of them for your first system. Try to get a sub with a rubber surround. Dual voice coils are cool, but definitely not necessary at this point.

Sensitivity tells you how much loudness you'll get out of it. It's not something to worry about too much, as long as you grab a decent name brand sub.

Frequency response tells how low (and high) the sub will play. The bigger it is, the lower the frequency response. Don't worry too much, as most subs you buy will do just fine.

Now that you have your sub, you'll need a box.

Sub boxes and why cats like to hide in them.

Yes, cats like to hide in sub boxes that have no subs in them. It's amusing I know, but back on topic.

A sub box will typically be of three types. sealed, ported or bandpass. Each type has advantages and disadvantages.
Sealed boxes tend to be the punchiest and the cleanest sounding, and are my personal favorite for their ease of construction and good clean sound. They're also rather deep sounding. They provide the best protection for your sub against damage. They're simple, constructed of an air tight chamber which has the right volume of air for your sub (taking into account the amount of air the sub itself will displace when placed into the box, you can find these specs in the subwoofers owners manual.) I suggest going with one of these. Kicker, my favorite sub company, also recommends using a sealed box.
Ported boxes are "tuned" so that they sound best at and around a certain frequency. This is done by adjusting the size of the ports, the size of the box..etc. These don't provide the protection for your sub that a sealed box would. They can sound better and louder than a sealed box, but only if you do a VERY VERY good job building one. I say stay away if you're a sub newbie (unless you buy a pre-matched sub and box combo which will be decent.)

Bandpass is interesting because it combines the elements of sealed and ported into one. Bandpass boxes are ok, I've never really gotten into them. They require tuning just like a ported box. If you purchase a pre matched sub and bandpass box combo, then you'll do fine. I wouldn't attempt this without being far more knowledgable than I am at building boxes and matching subs.

When you buy a sealed box, make sure that it's of decent construction and is air-tight. Caulk should be used at all wood joints. Boxes are generally made out of 3/4" medium density fiberboard and covered in carpet. Air leaks mean your sub isn't going to hit nearly as hard as it could be, and it's also going to be more prone to damaging itself at high volumes.

The right size box which is air tight will ensure that you get every last drop of sound out of it. Filling your box with NO MORE than 50% polyfil (the stuff they put in couch pillows...grab it at the wal-mart arts and crafts section) will make your sub THINK it's in a bigger box giving you better sound, and also dampen rattling that may occur.

Box size can vary also, my kickers can be used in a box sized 1.0 Cubic foot, to 4.0 cubic feet. The bigger you can manage, the better. Just make sure your box is somewhere in the range of your subs specification.

Amplifiers, try not to catch them on fire.

Purchasing an amp is directly dependant on your sub purchase. (or vice versa).

Try to buy one that has a built in low pass crossover. That'll make things so much easier on yourself.

Remember that when you purchase an amp, it's RMS has to be equal or less of your subs at the same impedance (ohms) rating .

If your sub is 150W @ 2 ohms, purchase an amplifier that produces 150W @ 2 ohms. OR purchase a TWO channel amplifier that produces 150W @ 2 ohms BRIDGED. Most amps can only operate in FOUR ohm bridged mode.

If you have two subs, get a two channel amp which produces enough RMS wattage for one sub on each channel. This will simplify your wiring job and make everything work nice n easy for you.

For instance, you have two subs which are 150W RMS @ 2 ohms. Purchase an amplifier which is rated "150W RMS x 2 @ 2 ohms". This means 150watts, times two channels, at 2 ohms per channel.

An amp will have a specific distortion level, the lower the better. MOSFET chips are good.

There are different classes of amps. Class D is very good for subs, and efficient. You DON'T NEED it, especially for a beginner system. The classes are beyond the scope of this guide.

A convenient feature of an amp would be a remote bass control. These are typically a +12 to +18 DB gain, which you adjust with a knob. It's nice to have as you can quickly and easily turn your subs up or down, to adjust for differences in types of music etc.

Rockford Fosgates amps have treated me well in the past. In fact I've had three. Two of which I blew up being a moron. The one I have now is gonna last me a good long while. They include a remote bass control, have a good distortion level, and sound nice. They're not too expensive either, so check them out. The ONLY gripe I have is that the GAIN on them are tiny knobs you have to turn with a screwdriver. Quite annoying.

You don't have to buy one that has the same RMS as your sub. For example, each one of my kicker subs will operate on 50 to 400watts RMS. I ran them each on 200 for about a year and a half and they sounded good and hit decently hard. Enough to make old ladies shake their fingers at me, and have my friends announce gleefully that they could hear me coming for a minute or two. At 400, they make me feel like I got out of a concert afterwards, and I end up saying "WHAT" when everyones words muddle together.

If you're using an aftermarket head unit, you will want an amplifier with line-level inputs. If you're using a stock head unit, then you want one with speaker level inputs. Many amps have both. Line level inputs are better, but then again so are aftermarket head units. If you MUST have an amp with just line levels and you're using a stock unit, there are ways to convert your speaker level inputs to line levels, but I will not discuss them here.

Wiring kits:

You're going to need a wiring kit to hook up your new amplifier. Purchase one on ebay, as the in store ones are ridiculously priced. Get one that has an 8 gauge power and ground wire, an in-line fuse of between 40 and 60 amps or so, and preferably includes an RCA (phono plug) cable for hooking your line-level output from your head unit to your amplifier. It should also include a nice blue cord for the remote turn on, usually some small amount of mounting materials (zip ties, etc.) and some speaker wire for your subs to hook to the amp.

Physical Installation

This parts pretty simple. Wire the sub to the box by attaching the + to the + on the inside of the box, and the - to the - inside the box. Crimp on style quick disconnects work pretty well for this with some kinds of terminal plates on boxes.

As a general rule, RED is + and BLACK is -. Just remember that and you'll do fine.

Often times manufacturers distinguish positive and negative speaker cables by putting a white stripe on the positive lead.
Make sure that you hook up your speaker so that it's positive to positive, and negative to negative. FAILURE to do so will cause the speaker to be out of phase, meaning it's going IN when it should be going OUT. This will result in POOR performance, and you will definitely not be pleased with the output.

Place the sub into the circular hole on the box, and make sure the gasket is under it. If theres no gasket, a small strip of hot glue works alright. You could also use a bead of silicone RTV sealant. Some subs with a rubber coated basket don't really require this, but it's good to make sure everythings 100% air tight.

THE BEST WAY to attach your sub to the box is using machine screws and T-Nuts. T nuts are nuts which are hammered into the box from underneath. They look like they have little spikes on them. You want to place the sub EXACTLY where you want it, then drill holes in the box for each hole on the basket of the sub. Then remove the sub, and hammer in the T-nuts from the underneath. Make sure you do this right, or you'll be pissed when your T-nuts fall down and you can't get your sub tight. It's happened to all of us. If you are lazy or ghetto, course thread wood screws will work ok but will get annoying if you end up taking your sub out of the box, and if you overtighten them expect to be turning your sub and making new holes in the box.
If the T-nuts fail completely, it's possible to put wood screws in at an angle to the original hole, in order to get some wood to grip. Lets hope it doesn't go that far.

Many people attach the amp to the back of the box. Most amps prefer to be mounted vertically. Be sure that wherever you mount it, it will not be stifled for air. The amp relies on air to cool it, and without cooling it will go into protection mode. (and may never come back out of it, after burning out)

Some people mount them on the back of the seats, I find mounting them on the box makes it the easiest. If I want to remove the subs, all I do is unhook the amp and take the box out. All in one package, easy and simple.

Holding the box in place becomes a question. Some people use bungee cords, some leave it and hope for the best, some screw it down, some wedge it in. It depends on your individual set up. Mine is held in with bungee cords, again, so I can easily remove it.

Wiring up your car, don't catch this on fire either

Whenever you do this kind of stuff, I suggest unhooking the battery.
Each car will be different, but pretty similar.

Start with whatever you'd like.

I start with the power. Attach it to your battery harness under the hood. Don't have the fuse in yet. Your fuse holder can be mounted somewhere in the engine compartment, or left hanging if you're lazy. It's usually best to have the fuse in the engine compartment rather than the other way around, but you can do it the other way if you want. Hook the other end up to your amps power (+B).

For the ground, you want it to be on bare metal. Find a bolt that is connected to the metal of your car, in the trunk. It should be something that doesn't move around. Sand down a small area under where the head of the bolt is, to get the paint off. Paint doesn't conduct electricity! Attach your ground here. Remember for grounds, the shorter the better. Just don't make it so small that you can't get it to attach to your amp! Now connect the ground to the amp.

You will want to attach the remote (REM) to your head unit. (CD player, deck, whatever you call it). Almost all aftermarket units have a wire which is referred to as REM. I believe it's blue, but don't quote me on that. It'll either be written on the wire, on a tag attached to the wire, or on a wiring guide thats on the bottom or top of the head unit itself. Very few lack all three, and it can be found in the owners manual.

Anyway attach the remote (blue generally) wire to there, and then connect it to the remote on the amp. This will tell your amp to turn on ONLY when the head unit is powered up. The remote is generally a +5 volt. You can wire it to a switch if you want, but thats pretty pointless unless you run the radio with the car off very often and the subs are gonna drain the battery. If you are using a stock head unit, you can wire this up some other way, although I'm not sure the best method. Theres plenty of car audio forums online which will be happy to help you figure it out.

Wire your subs + to the + on the amp, and the - to the - on the amp. Doing this wrong will put your sub out of phase again, so do it right. Make sure your amp crossover is set to low pass (LP).

Attach your line level inputs from the head unit to the amplifier. They're color coded so how could you mix them up? You should use the one that says "NON-FADER OUT", or "SUB". If you've only got one, don't worry about it.

If you're using a stock head unit then you hook up your speaker level inputs. Left and right, and each one has positive and negative. It depends on your amp which is which is which...so have fun.

If you've got one, hook the remote gain control up in the front and then to the amp. Pretty simple.

While you're doing all this, you should try and hide the wires. Each car has a hole in the firewall (behind the engine, separating the engine compartment from the passenger compartment. Usually this hole is occupied by a rubber grommet. Once you find it, make a small hole in it with a tool that you undoubtably have lying about. Then push the power through that hole, and pull it out the other side. This usually comes out under the dash, possible under the carpeting thats under the dash. Hide the wire under carpet, behind trim etc. I won't go into taking apart the interior of your car, because that'll take forever. Each wire should be hidden for a clean install, however watch that you don't put them in places where people will constantly be stepping on them, where a door is going to close on them all the time, where a seat will roll over them..etc. DO NOT run the power and RCA line level inputs next to each other. This will cause interference.

Now double check and make sure everythings hooked up right.

Plug your battery back in, and put the fuse in your fuse holder. Did anything explode? Is your house burning down? If so, go call the fire department. If not, check the amp. Make sure it's not smoking or anything. The power and ground should never touch. If they do, then murder/suicide right now.

Since you're still reading I'm going to assume that your flesh is not being melted off by a raging inferno. Go ahead and turn the car on. Turn on your head unit. The amp should light up. If it does, then good. If it doesn't, turn off the car and double check all wiring.

Tuning your new system

OK since everything is going awesomely, because you are smart and you're following this guide, turn on your car. Turn on the head unit and find a good reliable example of the music you're going to listen to most.

My suggestions for tuning your system are as follows: Bass -6(As low as possible) Mid 0, or +1, High +4 (out of +- 6, yours may be different.) Speaker savers are passive crossovers and can be purchased at best buy and wired in. Ask them which one to buy. Since your subs are going to be providing the bass from now on, no reason to pound your cars mids and highs with the low when your subs are going to be doing a MUCH better job.

Even with the speaker savers, you can still have bass getting through. Turning it down saves the tiny wires in your cars harness, and the little amp in your head unit from trying to reproduce such sounds in the first place. It'll help with light dimming, etc, and just overall make everything sound better. Tune the mid and high to your musical liking.

Now turn the music up to about 80% maximum level. The extra 20% will come into effect when you have a CD with a low recording level, or a bad radio signal or whatever.

Make sure that your remote bass control is turned up to maximum. (if you have one) Go to the amp and turn the gain knob (or screw) until you hear the sub start to clip. You will know that it's clipping because it'll sound like crap. A good clean hitting sub will pound, and a clip sounds like distortion, almost like the sub is hitting something. It's almost like a click.

Once it clips, turn it back down a bit until you can't hear any more clipping. Running your subs and amp into clipping is bad for them.

The gain is adjusting the sensitivity of the amp to how much voltage your line level input is giving you. Basically, if your line level input is 2volts, you want the gain to be adjusted for 2 volts. Thats a little more info than you really need, but many people are confused by it.

Make sure you're not clipping, try a few different basslines. Once that is set, go ahead and turn your system back down.
Thats it! You've done it, and hopefully didn't break too many (audio components/fingers/parent's hopes and dreams) in the process!

Now go out there and annoy the crap outta everyone else at stop lights!

Glossary:

Line Level Input - A low voltage, low wattage input which is specifically for hooking up amplifiers and isn't meant to drive speakers.

RMS - constant wattage provided to a speaker at a certain resistance
Ohms - measure of resistance of a circuit.

Head unit - CD player, tape deck, radio, whatever it is that you're listening to music through.
Amplifier - Device that powers speakers.

Cone - Part of a speaker which moves to drive air producing sound.
Basket - metal framing of a subwoofer.

Gain - an adjustment allowing for different line level inputs to be used. Adjusts sensitivity.

Clipping - Refers to when an audio signal has it's top and bottom "cut off", resulting in a choppy signal. Clipping can quickly result in speaker and amplifier damage.

Grommet - A rubber protector used to allow wires to pass by a sharp metal surface without harm.

RTV silicone - Common sealant used in automotive purposes to make gaskets. Comes in tubes.

Gasket - A strip of material which serves to make a seal between two surfaces. By being softer than the materials, it will conform to their individual surfaces, creating a seal around the edges.

Q & A

Why shouldn't I use a home audio sub in my car/car audio sub in my house?

Well first of all, the impedances are all wrong. Home audio is generally 8 ohms, sometimes 6. Car audio is usually 2 or 4. Using a car audio sub with a home audio amplifier will probably burn out the amp in short order.

Using a home audio sub in a car won't hurt anything, it'll just be coercing less power from the amp. Thus, you'll need a more powerful amp to make the power requirements. Most amps aren't rated for 8 ohms.

Good home audio subs often times have a built in amplifier. This will require a power inverter.

Home audio stuff won't "hit" like car audio stuff will. It's not really made for that. Home audio is generally softer, often times they have paper cones, and are generally intended for movies and regular volume music, not you crazy kids. (tee hee)
Using a car audio sub in a house is a bad idea too. Being 2 or 4 ohms, most amplifiers will be very ANGRY with you for hooking them up, and will soon show their displeasure by overheating and dying.

Assuming that you have a car audio sub that matches the impedance of your home audio system, and it also matches the power requirements, be my guest. At that point, theres not all that much difference except that your car audio sub will probably be of better construction.

Another thing is aesthetics. A car audio box is not going to match the drapes, or the carpet, you may find your cat using it as a scratching post, and people will oggle it suspiciously. Likewise, a home audio sub placed in the trunk of a car is going to get some strange looks when you pop your trunk.

I found a sub + box + amp package at XXXXXX store! Should I get it?

Is this your first subwoofer system? Does the kit look to be of good construction? Is the amp decently matched to the subs?
If you answered yes to these questions, then sure! It's not going to be the best thing in the world, but it will also save you a lot of the hassle of hooking up all this stuff. I build my own boxes, wire my subs in crazy ways (with 2 voice coils on each sub, and a two channel amp theres quite a few different configurations to try to find the best hookup) and play with gain settings. Of course, I also spent quite a bit on amps and speakers.

My brother in law got a "Dual" brand bandpass box, with pre-installed Dual subs, and a Dua amp. I hooked it up for him, and was pleasantly suprised to find that it didn't sound half bad. It was no competition for my system of course, but it would get dirty looks from old folks whenever you asked it to. For the money he spent, it was a pretty decent system and would shake the car up enough to be fun. This is probably on par with a sytem you'll build your first time around. Check out sales at Circuit City and Best Buy. Those places can also install stuff for you, but since you're cool you can just do it yourself with the help of my handy guide!

What brands should I buy/avoid?

It depends on your price range. I like kicker subs, as they're reasonably priced and hit pretty hard. The subs are constructed well, and I've only blown up one in my lifetime, and I believe it was a factory mess up.

Amps, I go with Rockford Fosgate. Again, decently priced, sound good and have nice features like the remote bass control.
Good stuff: Kenwood, Alpine, Rockford Fosgate (amps), JBL, Adire, Eclipse, Kicker, Pioneer (speakers and head units), MTX, Boss,

OK stuff: Sony, Pioneer subs, Lightning audio, Dual
Meh: PYLE, no-name stuff.

The best way is to read reviews and do research, talk to other people online about brands.

You didn't really tell me much about home audio stuff!

Considering the amount you know about CAR subwoofers now, apply your knowledge to the home. It's basically the same, except sometimes the amplifiers are built INTO the subwoofer. I'm sure you'll figure it out.