BMW 318ti/Compact List #74 - Friday, August 1, 1997 Re[2]: Some ?'s...audio (long)

by George Derbin <George_Derbin_at_ccmail.bms.com>

Subject: Re[2]: Some ?'s...audio (long) From: George_Derbin_at_ccmail.bms.com (George Derbin) Date: Thu, 31 Jul 1997 23:34:50 -0400

Derek,

Thanks for the info. Got a few points to add. You said "It does not give a huge amount of sound, but it is a lot louder and clearer than the stock unit was." Ok louder is a perceived term. Unfortunately you are still at the mercy of the factory amp. If it only can produce 10 watts a channel, no matter what your head unit can produce you still are only going to get 10 watts of clean power a channel. You can provide a 'hotter' signal to the step down input of the factory amp which will make the same position on the dial SEEM louder. But in terms of the point at which major distortion kicks it, it will be the same. Most high level inputs of amps will lower the signal to match what would be coming from "normal" low level RCA inputs, now designs differ but I doubt the factory did anything out of the normal with the OE amp. Now if you had a very skillful installer who cared, he/she could match the input of the factory amp with your new headunit better than the original setup. This would result in less distortion of the head unit at high volume, which in turn means less distortion to be amplified by the factory amp. Moral here, garbage given to the factory amp (garbage = distortion) means MEGA garbage after amplification. I would bet what you have is a cleaner source signal, which allows you to drive the factory amp at a higher level, to get the same distortion. As far as the power of the head unit, I believe it really doesn't matter. The resisters that your installer put on the unit, just trim some of the wattage going to the factory amp anyway. Besides in all of my reading I have only seen one or two amplified head units that actually delivered, in a real world setting, what they claimed. This is what happens, your headunit makes a low level signal from, say, the CD, it passes it on to the amp stage of the headunit which boosts it. That high level signal is sent to the factory amp's high level input which cuts the signal back down, which is passed on to the factory's amp stage which gives the wattage needed to drive your OE speakers.

Now throw in the fact that your system is now not having to produce the power hungry bass frequencies (your subs do that). That power which used to produce the bass now can be given more evenly to the other frequencies. Which in turn allows the overall level of the higher frequencies to be higher...i.e. louder. Your sub amp covers the bass well enough, and the pure size of the subs allows more of the audio frequency to be heard. The human ear is much more sensitive to highs and lows then to mids. Therefore if you were to increase the amount of lows produced, i.e. extend the frequency response, you would effectively increase your perception of loudness at a non linear rate to a non extended frequency response.

As far as your subs go. Not everyone has the room, nor the expenses to invest in sub as you did. You went pretty far to get some boom. But for me, for example, TWO 12" subs in a bandpass takes too much room away from my cargo. Remember different strokes for different bimmers. I suggested tubes as a quick and inexpensive way to add bass. I wasn't trying to make a system that could be heard three car lengths away from the car. Remember I said Bass Hounds hate tubes, for good reason, but I cautioned that if you were a bass hound your should just rip out the old system and open up your wallet. You can't get something for nothing, quality is expensive, as you know. I was shooting for cost effectiveness and practicality, not for ultimate sounds. Realize how many different products are out there, anyone one of which would make a nice addition to/over the stock factory system we have.

I applaud anyone who sinks the kinda cash you have in your system, IMHO it is worth it. But I like music, YMMV.

Regards,
G.M. Derbin
'97 Jet Black Sport 5spd