I've worked as a sound engineer for a while now, and bad staging in cars (unfortunately including my own...) is a major bugbear of mine!!!
Lets look at the average sound set up in a mini:
Under the seats most people fit 6x9's the reasons against them have already been covered for parcel shelf fitting, but under the seats is a very bad place for speakers. Mainly as most of the speaker boards point down towards the floor in my experience and that is silly! What it does is bounce the sound off the floor and into a random pattern towards your ears, completely diffracting the stereo image the music's producer spent so long getting right!!!
Then, we move onto the rear shelf speakers, rear speakers as has been said tend to be a bit fuzzy in ears due to them facing the wrong way! But on top of that I often see minis with them pointing at the back window... Surprisingly this does the same as a board pointing at the floor/back seats.
Front speakers I've seen mounted in several ways, but for now, we'll assume they are in the door pockets. Most aftermarket and home build door pods point the sound straight at your shins! As above with the back shelf etc
Hear we can see a rough guide (yes the angles look wrong and aren't accurate, so please take them as a very quickly cobbled together paint picture, to very roughly demonstrate the principle,) to the path the sound takes from the average install:
As you can see, the sound has no clear path to the centre, where a stereo image is centered. it's one of the reasons a film always sounds better at a cinema than it does on your home surround sound as nobody ever gets the picture right lol. The front speakers that are aimed at your shins actually cancel certain frequencies out of each other as they both point directly at each other!!! I have this in my golf at the minute and its damned annoying. (i'm just too skint to do owt about it!)
The best designed builds tilt the speakers towards the top centre of the car, as thus;
As you can see i've ignored the back seat passengers, as they don't matter, they'll always mangle the stereo image no matter how hard you try in a mini lol there just isn't the space!
So we have in that picture, the tweeters at the front on top of the dash or attached to the A pillars, either or it doesn't really matter, Door pods with 6.5" (or mid bass woofers,) speakers pointing directly at a point in the car in between the front seats and level with the headrests, Then the pods in the rear bins with smaller speakers doing similar, only a little further back so as not to muddy the sound. They are usually a lot lower in level than the front.
Under the back seat we have a small 6-8", (ten if you can get on in, i haven't tried lol,) for the mid/lows and a 12" in the boot. I would usually suggest a sealed enclosure for the little 'un and a ported for the big. That gives you hard bass drops and tight, punchy mid bass. I find bass guitars and deep voices pop from sealed 8"'s really nicely!
So I'm sure you're about to ask "but if theres only you in ther car you'll get mostly the left in your ear anyway so it's all irrelevant!" and, I shall say, "thats what the balance control on the stereo is for!!!"
A few early 00's sony head units came with a one touch sound stage button, that could boost the volume to the side opposite the driver so it balanced the sound out. But i'm guessing they dropped it becuase nobody knew what it was for!!!!! On a poor build you'll find that you actually need to boost the side you're on as you mostly hear the left. In a well designed system the speakers on your side will be pointing at your head so will need the volume cutting a bit to even it all out!!!
Ideally you want the fader set to about 4/5 to the front to keep the levell of the backs at a background. The main problem with doing this is a lot of headunits only have front and rear amp pre-outs meaning you're sub will go quite with the back!!! To combat this always make sure the headunit has a seperate subwoofer amplifier out, as it saves you having to buy line level controls to distribute the signals! Any questions, feel free to ask!!!
I forgot to mention about surfacings lol. A lot of spl Installers fit fabric over the hard plastic/metal surfaces of a car. this isn't just aesthetic! It softens impact of the sound waves, and reduces distortion or fragmentation of frequencies you get from hard surfaces such as glass or metal. Insulating the floors etc has already been covered, so just remember that the aim is to place the sound where you want it BEFORE it has to reflect off anything. this isn't always possible and when you're in the car you are generally in the way!
Edited by Crowson_punk, 21 June 2010 - 09:48 AM.