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Subject: Re: E36 audio (death of the Blau thread :) Content-Type: text

From: Bob Hazelwood <>

I am suprised that more people STILL do not know what is going on in BMW
audio systems. Heck, until the dreaded DSP came along they really
haven't changed much in years!

First. The head unit does not "suck". In "objective" terms, the response
range, dynamic range, FM tuner capability etc of the BMW head unit is
comparable to some of the better aftermarket units. I've had quite a few
units on the test bench as the result of my previous two jobs (VP
Product management as a/d/s/ and Product and Marketing Manager for
Mobile Audio at JBL).  The characteristic which can give you the wrong
impression if you don't take it into account when adding upgrades, is
that the BMW head unit is equalized. There is a bass boost which varies
with level, and the top end is rolled off. This is the cause of the big
change you hear with a new head aftermarket unit while keeping the BMW
amp and speakers. If you know this going into an upgrade exercise, you
can compensate for it in the system design and get superb results using
the factory head unit/CD changer. Output voltage is most definitely NOT
.2V as stated. Actual clipping occurs at around 5V., ( I measured 5.25V
on the bench on the Pioneer unit from my E34. I have measured similar
output from various Alpine heads from E36's) so I would call it a
nominal 4V unit (making allowances for low battery voltage under some
conditions). So there is plenty of available output voltage to put into
an aftermarket amp with low noise and high fidelity. At the same time,
even if it wasn't this high, the output voltage has little or no effect
on the sound quality other than the level of background hiss. All it
effects is where you have your input sensitivity controls set on the
amp. With a high voltage head unit, you can keep the input gain controls
turned down, making the amp less susceptable to noise pickup. Issues
such as frequency response, distortion, separation etc. have absolutely
nothing whatsoever to do with the head unit's output voltage. Matt
correctly in that the BMW head unit reduces bass at high levels. More
specifically it does not "cut" bass, but reduces bass "boost". This
helps save speakers at high volumes, and if you calibrate the amplifier
adjustments of add-on equipment well, it can work in your favor by
adding a very useful loudness compensation, where bass is boosted at low
levels to compensate for road-noise masking and the ear's reduced
sensitivity to bass at low levels.

Second. There is no crossover in the BMW head unit!(at least in the USA).
The crossover is in the BMW amp. It is a passive crossover at the output
of the four-channel amp. There is nothing high-tech about this, it's a
regular old passive crossover made from run-of-the-mill capacitors and
inductors. They are just located inside the amp chassis instead of
between the amp and the loudspeakers. And no, it's not ten 25W channels.
The amp is four channel, and by Hi-Fi standards puts out 15W/channel.
Yep, that's all folks. The crossover for each corner of the car is at
the output of each channel, and divides the spectrum appropriately for
the drivers on that channel. The only problem with this set-up is that
you don't have a powered full range output to drive aftermarket speakers
that you can get to with without tearing the amp apart and making an
internal connection. This pretty much forces you to replace the amp as
part of a speaker replacement just so you can get a full-range signal.
The E39 DSP system is another animal all together, which is beyond
anything you probably want to consider upgrading. Its possible, but not

So, the bottom line is that if you find that audio performance is
important to your vehicle enjoyment, there are alternatives to having to
gut the entire system which can give superb results IF you know the
quirks of the BMW system going in. If you treat it like the system in a
Honda or Chebbie when you try to upgrade your system, you'll be

Best regards,
Bob Hazelwood
Product Manager, Cambridge Soundworks
'93 525i 5-sp. Sharked, BL/ss'd, H&R + Bilsteins
a/d/s/ 335is front, A5is rear, 310rs sub, P2110 sub amp, P840 main amp,
Factory Pioneer head unit and CD
BMW CCA (Boston)

> Date: Sun, 27 Jun 1999 16:39:28 EDT
> From:
> Subject: Re: E36 audio (death of the Blau thread :)
> Puzzled John writes:
>  << 1. Can the head unit's 0.2 v output (rather than 0.5 v or whatever)
> really be the first cause of the distortion? The dynamic range of
> audio is many orders of magnitude - if I remember correctly you can
> just barely perceive a doubling of voltage.>>
> My apologies, but that example was only used to illustrate the deficiencies
> of the stock head unit. Almost every Alpine head runs at a full 4v, which is
> significant and very noticeable improvement from the 1.8v of most lower line
> units. True, there are many other factors, but I thought the 2000% jump was a
> good example.
>  <<2. How can the BMW head unit have crossovers when it only has four
> outputs: left and right front, and left and right rear? At least, I
> assume the U.S. head unit is that way. The European RDS units are!>>
> The US crossovers are such that they attenuate high and low frequencies in
> exactly the opposite of what many aftermarket systems do; by pulling bass off
> the high volumes, you increase the life of cheesy paper speakers.
> << 3. Is having no crossovers and individual channels from the main
> amplifier to each loudspeaker really such a bad thing? That would
> avoid the losses and decreased damping introduced by the passive
> crossover networks I am familiar with, as well as the greater
> variance, cost and bulk of an LC network. (I can't find any
> inductors wound with better than 5% tolerance in the one catalog I
> am looking at.) >>
> In terms of a factory amp, it's not such a bad thing. However, it requires
> that the other components work well with it (which they don't) which leads to
> the need for them to work well with aftermarket stuff (which they don't). The
> passive crossovers are not the preferred way to do it, so I can see how the
> losses might seem severe. H/L crossovers, or an active system (very trick)
> would be the way to go. Instead of using a simple high/low pass filter like
> most aftermarket amps, the BMW amp sends out 10 different 25 watt signals.
> That's absurd!! Who wants their tweeters getting as much power as their
> woofers? If it was just 60watts x 4, then crossovers on the component
> speakers could dole out the power and signal properly.
> Oh well.
> - -Matt