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Path: utzoo!watmath!watdcsu!herbie
From: herbie@watdcsu.UUCP (Herb Chong [DCS])
Newsgroups: net.audio
Subject: Re: A-B CD comments
Message-ID: <1284@watdcsu.UUCP>
Date: Mon, 22-Apr-85 10:26:36 EST
Article-I.D.: watdcsu.1284
Posted: Mon Apr 22 10:26:36 1985
Date-Received: Tue, 23-Apr-85 06:09:12 EST
References: <260@moncol.UUCP> <3612@alice.UUCP>
Reply-To: herbie@watdcsu.UUCP (Herb Chong [DCS])
Organization: U of Waterloo
Lines: 47
Summary: 

In article <3612@alice.UUCP> ark@alice.UUCP (Andrew Koenig) writes:
>> The BOSE tends to be very forgiving of suboptimal sources, and might
>> lack the resolution to differentiate between the players.
>
>I would like to see your evidence for this claim.

for starters, by its very design, the Bose 901's are nonlinear phase
transducers.  the primary sound is from the rear speakers which reflect
off of the walls and back into the listening area.  great cancellations
occur between the back sound wave and the one from the front speaker.
there are 8 drivers in the back.  even if each were an ideal point
source, the combined is anything but, and after reflecting off of
uncontrolled wall surfaces with absorption curves that can be wildly
different between setups, flat freqency response can't be guaranteed
even with equalization.  which brings up another point, the supplied
equalizer.  the drivers in the 901's are 5 inches nominal diameter.
equalization must be supplied to bring up the low end and the high end
to get flat response.  this also means that the 5" drivers are being used
well above 10K.  yes, plenty of boost will even allow a 10" woofer
to play a 15K tone decently, but how much power do you have to supply
when the natural roll-off of the driver is 6dB/octave above 5K?  so you put
high power voice-coils in, as Bose did, which increases mass, which 
decreases the natural roll-off frequency.  fortunately, he uses a sophisticated
ducting system to achieve decent low frequency response without equalization,
but then massive phase shifts are produced, and the air from the ducts
are such high velocity that you can sometimes hear them whistling (depends
upon how much other frequencies are being reproduced at the same time).

the direct/reflecting principle is very interesting and has some theoretical
advantages, but they are hardly ever realized in practice.  the equalizer
removes some of the variables, but using electrostatic elements and
properly designed conventional woofer would have been better from the
point of view of reduced driver mass and little or no equalization
in the high frequencies.  of course, electrostatic elements have a whole
set of problems of their own, but they are more appropriate for another
discussion.  the type of drivers that Omar Bose should have used given
his design requirements were horrendously expensive back when he started
and notoriously unreliable.  quads were about the only option.

Herb Chong...

I'm user-friendly -- I don't byte, I nybble....

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