Xref: utzoo rec.audio:5569 sci.electronics:2608
Path: utzoo!utgpu!water!watmath!clyde!att-cb!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!uw-beaver!tektronix!reed!psu-cs!qiclab!al
From: al@qiclab.UUCP (Al Peterman)
Newsgroups: rec.audio,sci.electronics
Subject: Re: Position Feedback On Woofers?
Summary: Do you like good tight Bass?
Message-ID: <1085@qiclab.UUCP>
Date: 26 Mar 88 15:30:03 GMT
References: <3388@briar.Philips.Com>
Reply-To: al@qiclab.UUCP (Al Peterman)
Organization: Qic Laboratories, Portland, Oregon.
Lines: 50

In article <3388@briar.Philips.Com> ams@philabs.Philips.Com (M. Ali Shaik) writes:
>
>Does any of you know anything about woofers/ sub-woofers incorporating
>position feedback? (I believe Velodyne & Infinity make them).
>What are the merits/demerits? Is there any merit at all in doing it?
>
>uunet!philabs!ams

   It is interesting to have this question come from Phillips, since one of the
best early speakers with feedback was the Phillips RH series in 1974-1981.
They incorporated a feedback circuit on the bass cone and were internally
biamped.  Good speakers.

    I own 3 sets of speakers with "feedback".  I like lots of tight accurate
bass, and feel that the extra circuitry is defineatly worth the cost.  I have
a set of LWE 1's and a set of LWE 6's (I used to have a set of LWE 3's) as
well as a set of Infinity RS 2.5's.  The Infinity's use the "Watkins dual
drive" bass cone, which hooks up a second voice coil that is wired through
a massive crossover to passively correct the drive to the first voice coil.

    The LWE's (Lewis W. Erath) were a very good speaker from the early 70's
that actually sampled the signal across the bass cone, compared it with the
input signal, and then sent the signal back to the amplifier.  At the amp
the feedback signal is tied into the amplifiers negative feedback line and
corrects for speaker errors.  The sound is great, but the problem of hooking
up to different amps caused to company to die in 1976.  They had engineered
many "clip kits" to hook up to the most popular amps/receivers of that era,
and there was a "design protocol" to allow engineering a hookup to other amps.
CM labs took over their speakers, and continued them, even having "feedback"
speakers outputs on their amps.  I believe CM labs died in 1982 or so.

   Despite the difficulties, it is hard to believe how good tight controlled
bass sounds.  As an added plus, it is very difficult to overdrive feedback
controlled speakers, since they tend to control their cone position from
excessive motions.  I know of an engineer, Robin Wernick, who has designed 
and uses a system similar to the LWE idea, except it mixes the correction
signal into the line inputs to the power amp.  Due to time constants, and
line and amps speeds he limits the feedback bandwidth to the under 200 Hz
range, so effectively it is a bass feedback.

BTW - Have you noticed that Phillips is "entering" the US market under
their own name?  Have they forgotten they made and sold here some nice
products in the 70's, including the speakers, receivers, tape decks and
one of the nicest simple turntables ever made, the GA-212.  "Entering"??

-- 
Alan L. Peterman     Aero Air  Hillsboro, OR   (503)-640-3711 wk
                                               (503)-684-1984 hm
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