Thinking about your stereo system for your car... ok.
What's it for?
What do you want? There are two main branches of car audio:
- SQ ("Sound quality") - what it says on the tin
- SPL ("Sound Pressure Level") - Bass. Lots of it. This is right now known as VBA ("Violent Bass Air") on one well-respected SQ-focussed website.
There's a third, kinda hybrid: SQL ("SQ Loud") - which implies serious volume levels whilst retaining quality.
To get SQ, there's a lot of work involved. It's probably just as much as in SPL: there, you'll spend days redesigning your box to fit another sub or reinforce or add another couple of kilowatts. It might sound like the easy option, but if you're doing it properly, it isn't! These guys win and lose competitions on 0.1dB (most normal people can only hear 1-2dB difference, we'll go through dB as a measurement in a minute) - so every little part is important.
Attention to detail is what will get you far with SQ, but you can start simply. Where do we start, though?
Fundamentals
Let's start with bass, since that's seemingly what everyone wants. If you want volume, you need air moved. Especially with regard to Bass. Ever youtubed for "hair trick"? Go do it, then come back.
So, how was it for you? Did the earth move? Some of the brits managed that recently.. definitely on the richter scale.
How d'you think those boys do that? It's with air. Lots of it.
That means lots of power at low frequency (physics 101 should tell you about the length of waves and the fact that to reproduce them, the cone of the speaker driver moves forwards and backwards) combined with a very large magnet and coil system on the back end to cope with the heat involved and the amount of air you want to shift. Remember, the signal excites a coil - and that, reacting to the magnet, moves the cone of the loudspeaker driver. More movement = louder sounds. Faster movement = higher frequencies. Bigger membranes (the cones) find it harder to move fast enough to reproduce higher frequencies. You remember "the only substitute for displacement is more displacement"? It's true about membranes, too.
Drivers, beaming and physics 102
Coming back to the other speaker drivers: each speaker driver has a range where it works best. Think about that faster movement - it's much easier for a smaller, lighter membrane to vibrate quickly than a big, heavy one. Size matters, too: there's something called 'beaming' by the physics nerds which basically breaks down (with the above statement) to "big speakers for low frequencies, smaller ones for higher", and "the higher the frequency, the more a smaller speaker actually has a chance of spreading the sound over a large area".
Quick test: on a sound sytem with a tweeter, put some music or some static (you know, that hiss you get between radio stations) on. Start directly in front of the tweeter. Now move so that you're close to the side of the tweeter. There's less "air", high frequencies now, no? Try moving directly behind the speaker. That's almost the same? Should be. Now, the thing is that different tweeters are designed for different things. There are crazy people out there using tweeters that were originally made for seriously expensive home speakers in their car. They're kinda nuts, but it can make for really good results, if you know what you're doing. Those frequencies where the speaker starts "beaming", if you're interested, are around 2500Hz for a 6" driver and 13kHz for a 1" tweeter. However: those numbers are theory. You want the best sound in your car, with your kit: you need to try different positions and angles.
When you go look at frequency responses of home drivers, then you'll see most of the time that they'll include 0, 30 and 60 degrees. Off-axis (so it's not directly facing you) is the 30 or 60 degree response; some drivers are built to work well in specific locations. Ignore the manufacturer's recommendations if you feel the need, but - as stated - they are there for a reason and though you might get different results, they do provide a starting point. Flat is "good", depending; you'll see that some tweeters seem to work really well at 30 degrees, they're flat, but others are flat only at 0.
The same thing applies to subwoofer boxes; JL might recommend 1.2cuft, but 1.1 might work for you and anyway, there are manufacturing tolerances that you can't do anything about. They are normally 5-10%... working accurately is good, but you can take it to the point where the effort isn't worth the extra you'll get out of it. So, get within 5-10% and you should be OK. You might want to make it better, though.. this is all part of the bug.
If you're just running a component set or coaxial set from the head unit, quit worrying about it too much, but moving your tweeter around (try maybe putting them at the bottom of the windscreen, facing one another in the a-pillars!) may mean that suddenly jay-zee is standing, rappin' 'bout dat s*** directly in front of you. Your car may be different, YMMV: if you don't test, you won't know.
Now, about L-Pads... L-Pads are there to reduce the output of your tweeters, that much is true. However: why are you using loudness? You shouldn't need it. Turn the gain up a little on your sub; swap the phase (that's the + and - to you) on one of the midbasses, dampen the doors (see below).
The crossovers... what are they? that's where this L-Pad is. It's that little box you got with the speakers. Simply speaking, it splits the signal from the amplifier into different parts for the drivers. The tweeter will be blown if you feed it too much signal or too low-a signal; the midbass won't care much.
Overheating of crossovers is virtually impossible unless you ignore completely the "maximum power:200 Watts". At which point, we come to another point: watts.
Watt?
Yes, James Watt. Limey, back in the 18th Century did some funky stuff wit steam. The unit of power is named after him.
What's important is that you think about matching power of amplifier with the power your speakers can take. You can probably go +10-15-20% over what the speakers say (so that's one-tenth more) - for example, 50W speakers with 60W amp is probably OK. It's easier to blow speakers by pushing too much power through a straining amplifier (think about that European Ford using a four-pot: the vee-six won't drink much more juice, sounds better and doesn't have to work as hard to keep the acceleration up) than by feeding them too much power. Don't go over the top, it is very possible to fry speakers. If you run your amps with the gain turned to 11, don't be surprised if you need new drivers very quickly. You can still blow that V6 - it takes more effort or neglect, but it's still possible.
About watts and deebeez: the relationship between the two is logarithmic, as is dB and Volume. Perceived volume is another story (search for "Fletcher Munson curves"), but to get double the volume *in theory* - needs ten times the power. Really. Most of the time you'll see (if you measure) around 1-3W going into speakers in a system that's running at a small room "medium-loud" - you can still talk over it, but it's hard. So why run 500W into bass? Because Bass needs more energy (we talked about that earlier) and then you've also got enough in reserve when you want to crank it. This also gets called "headroom". There are guys that run several hundred watts into midbass, a kilowatt into subwoofers.. and that's still SQ, though heading rapidly towards SQL.
If you're foolish enough to try a three-way (so that means a midbass, midrange and tweeter) system up front, have fun trying to set it up. Two way is much easier, and if you've positioned the drivers correctly, then it should sound pretty good.
Crossovers
There are different ways to cross over. One is a bridge, then there's a ferry... Think of the crossover as a boat which transfers sound from one driver to another. There's the fast ferry, the not quite so fast one which goes a strange way round, the medium-speed one which runs backwards and the guy with the outboard motor who insists on arriving at right-angles. Those are four different ways of splitting the sound: 24, 18, 12 and 6 deeBeez per Octave. Octave? Octave = doubling of frequency. 24db/Octave (the nerds call it fourth order) means the sound gets split quickly between the two. 6db (the guy with the outboard!) is slower, more gradual. The right-angle stuff is to do with phase (remember the + - thing earlier?) and it means that 24dB is pretty useful. However, if you're going to implement it in hardware (so that means in the crossover box), you need lots of components. Too expensive for many, so they just do 12dB/Octave (2nd order for the geeks). This is the "medium-speed boat that runs backwards" - i.e the phase is turned round. Now, this is why your midbasses might sound better with the + and - swapped. It might be that your midbass is good - try it on the sub and the tweet too. Especially on the sub, one way will sound "muddy", the other tight. Pick which one you want and run with it... L-Pads work by making sure some of the "cargo" (sound) you load on to the boat to go across the river stays in the river as heat.
You could also run "active" (above, with the little box between your speakers, defines "passive"); this uses an active crossover BEFORE the amplifier. Downside? you need lots of amplifier channels: instead of three - one for the sub and one for front left and front right, you need five - front left high and low, front right high and low, sub or more.
Don't bother with rear speakers unless you really, really need them. Why? Well, if you're going for SQ, you're going for something called a soundstage - essentially, you should be able to hear the instruments in different spaces on the dashboard. It may be good, it may be not so good - doesn't really matter, but any attempt at this will be hampered if you are using more speakers in the rear. Don't need them? turn 'em off. Passengers? add them back in again.
Running active has another advantage that you can trim the power ratings: 500W sub, 180W per midbass, 30W per tweeter. Then you can turn the amps down and up as you want - and therefore trim the sound some without resorting to an equaliser.
Power
Coming back to power, there's something else: power ratings and power requirements.
You *could* take as a rule that you need twice the bass power... and that would generally be pretty effective. But why? Well, those short waves that make up tweeter sounds don't need very much push. And your hearing is more effective at higher frequencies. So: halve the power.
Power ratings are also fun. If I remember right, there's a CIAA power rating. This is pretty realistic. RMS ratings can be and are abused. THD means distortion (if something's being rated at 1% THD, it's already distorting and would be audible to someone who is listening!) - if you want to hear distortion, try listening to Madonna's "Voices", the last track on Candy Shop, on a real system. You'll hear that the bass is overdone. They should have backed off, but they didn't, so now it's on the CD. And it's this distortion that will blow speakers / subs easily.
Selecting components
Before you select your components, think about a couple of things:
- space
- what you want. Do you want BASS, bass that goes "thump" or "p p p" or "buuu buuu buuu" for the same music? The easiest way to work this out is to listen to some systems and go read. There are lots of audio sites on the web - remember, though, that if something works well in the home, that doesn't mean it will be good in the car and viceversa.
For your main components, think about the space you have. You'll maybe need to take your doors apart, you might need adapters, rings or you might need to rebuild half of your door to make your driver fit. You'll also have to put that amp somewhere: where? It needs power and cables both from the head unit and to the loudspeakers.
Please also don't just twist wires together. Use connectors, at the very least tape, and always use fuses, at least between the battery and the amplifier(s). Make sure that you budget something for cables - high powered amplifiers use lots of juice and that means thick cables and big fuses. If it's a longer run between your amplifier and battery, you'll need an even bigger cable. Check it, there are lots of tables on the web. The first fuse should be less than a foot away from the battery!
Source unit / Head unit
Sources are as important as anything else; they feed the signal into the chain. Any chain is only as good as its weakest link; work out your budget and run to that. You can upgrade later if the bug really bites, but spending similar amounts on your source unit, amps, speakers and then some for cables would seem reasonable.
Sources can be iPod players (but you'll want to turn your EQ off!), CD players, MP3 capable CD players, radio, DVD players, carPCs... Most normal portable audio equipment has a headphone output and with a simple cable, you could plug this into your amplifier. However, then you've only got whatever that equipment has - so it's generally not too good an idea. What to look for in a source? That it fits budget, that it looks good to you, that it has the features you need. Reputable makes are a good idea.
You don't need to worry too much about features like equalisation, time alignment or high power output ("Pre-out 4V"), but they will help later if you feel the need to tune things, which you probably will. EQ is more important than TA, which is again more important than high power output.
"Deadheads" have no onboard amplifiers; Some units require their own power supply and some can control processing boxes, which is very nice if you want / need to do that and have the budget to match. Your call.
Amplifiers
Amplifiers are another story. Power is good; be very skeptical about high power ratings from very small boxes. There are lots of good and not-so good amplifier manufacturers out there. Be wary of advertising highlighting "damping factor", simply because by the time you've added a couple of metres of speaker cable between the amp and the speaker, any huge damping factor simply won't exist any more.
Signal to noise ratios ("S/N") are more important on both your head unit and amplifier; 90+dB is very good. You remember that cheap mini-system you had as a kid? When you turned it up, it just hissed, didn't it, without any signal? That's the sign of a poor S/N ratio. Higher is better.
Power ratings were discussed earlier.
Tip: Class D or "digital" amps work using something called "PWM". Basically, they supply a high voltage, but only for a short period of time; Volume is changed by mixing the amount of time the signal is off with the time the signal is on. If it's on only half the time, you get half volume, that kind of thing. Because this is done with some electronic "trickery"
, it's possible that there are noises in the output signal. You can't normally hear this in the bass region, but you might in the tweeter zone. That's a decision you need to make after listening.
Speaker drivers
The arguably most important part.
First: check the space you have. Many cars are "standard" - 6.5" or 5.25", some are different. Making something fit that wasn't supposed to be there is difficult and time-consuming. It may also not work properly.
Unless you're really prepared to make stuff and adapt and test, buying something that was set up for the space you have is probably a good option. There are various decent manufacturers; a certain amount of "you get what you pay for" is also true here.
Co-axial speakers have the tweeter mounted in the middle of the bass driver. Components generally comprise a tweeter, woofer and crossover box; active components leave the crossover out.
Subwoofers are another story for themselves. Smaller woofers (6"-8"-10") tend to be slightly faster in response, but if you want depth and volume, you will need either several or one big one. There are also different technologies in use; Aliantes are flat, XBL^2 extends the usable distance the cone can travel and a big "inner-tube" like surround is sometimes used too. Check the specifications that the manufacturer has on their website (and if they don't, walking away is a good option), and listen / talk to others about their experiences.
You will want to think about the Thiele-Small parameters if you want to build your own box; otherwise, the recommendations are a good guide to just how much space they'll take up in your trunk. Bigger subs generally want bigger boxes. This may well constrain (along with the amplifier power you want to use) which subs you have to choose from. That and the application.
Different boxes sound different: sealed ones don't drop so well, but are faster; ported are louder but slower to react. Bandpass boxes do that - allow certain frequencies out - and so they have a very limited range. Passive radiators can be used instead of ports. Since Sub box building could take up another three pages, it's easier to recommend reading. Search for "WinISD
" or "BassBoxPro" and that should give you an idea.
After installation
If you have resonances in the car, it's because it isn't damped properly (key words: butyl, mass, Dynamat - if you're poor or cheap, peel'n'seal or flashing tape, but don't expect it to stay stuck for any length of time), not because it's not possible to get real bass in a car.
Your damping will drop the resonant frequency of the panels in the car, down away from the 50Hz your sub will produce; If you add mass, too (lead sheet, "Mass loaded vinyl"), you'll make it difficult for the panel to be excited by the sound. Fewer resonances not just from your speakers, but clearer bass and - guess what? - less road noise. Huh? Well, if the subs and midbasses quit agitating panels instead of air, you'll get clearer and louder sound, no? There's less energy being wasted as buzzes and more being dedicated to thumping you in the chest.
But where's that thump? Depends. There's a couple of charts on the interwebz - this is a good one
http://www.independentrecording.net/irn ... isplay.htm - that explain what different frequencies can do for you. If you want punch, you'll need a clear midbass.
Now, to go back to the speaker thing: Generally, if your sub doesn't directly vibrate the floor directly next to it, then you shouldn't be able to locate it if it's only playing below 80Hz like it should be (that means a crossover point, preferably 4th order, or 24dB/Octave at 80Hz). Your Midbasses in the door should be in a position to take over at that point: If you also cross those at 80Hz, it might work for you. It might not. You might need to swap the + and - on ONE speaker driver to make it sound better. You did pay attention when connecting them, didn't you?
Most people can't locate sound below around 150Hz, some can. Keep lower than this for a sub otherwise you'll hear it's in the trunk - same thing applies if something buzzes every time the bass hits, it attracts attention.
There's something else called cabin gain that you might also want to take note of. Bit more physics: the length of your car determines what waves fit. Anything that can't fit basically creates pressure instead of sound. It means that, depending on the size of the vehicle, anything lower than 50-55Hz will be auto-magically amplified. This is why a subwoofer might sound thin in your lounge, but it's great in your automobile.
Upgrading
never ending story ....
remember, it's your system. Unless you're going to a show to be graded, if it sounds good to you, then it's probably OK. And it's you that has to listen!
