From: cal@gsbux1.uchicago.edu (Cal Lott)
Subject: Re: Clipping questions
Organization: University of Chicago Computing Organizations
Date: Thu, 31 Dec 1992 04:59:56 GMT

lstowell@pyrnova.mis.pyramid.com (Lon Stowell) writes:
>In article <1992Dec29.210924.21212@midway.uchicago.edu> cal@gsbux1.uchicago.edu (Cal Lott) writes:
>>
>>	What I am specifically unclear on is the relationship of the
>>amplifier to the speaker that it is driving when clipping occurs. Can
>>one realistically say that it is either the amp or the speaker that is
>>"clipping"? It would seem to be more reasonable to say that the entire
>>system is clipping, but that would not help in determining which
>>component is the weak link in the chain.
>
>   The amplifier is clipping INTO THAT SPEAKER LOAD....whose fault
>   it is is a matter of personal opinion.   

	True, but still not helpful in determining what should be
changed in the particular system.

>>	Is there an audible difference between the ugly noise a system
>>makes when it runs out of power to properly drive the speakers and the
>>ugly noise a system makes when the speakers are being overdriven?
>
>   Usually an overdriven speaker becomes audible when the bass is
>   overdriven....this is usually a truly horrid mechanical rattling
>   sound.  Some rare wimpy midranges (and some verrrrrry pricey
>   panel speakers) will exhibit signs of overdriving in the
>   midrange.  On a cone speaker, overdriven midrange tends to be
>   brassy, harsh (usually...your mileage may vary) or even honky.

	Well, the rattling sound was actually coming from the
speaker's 6-1/2" passive radiator, as far as I could tell. The
overall sound was not harsh, and there were no other unpleasant
sounds other than a nasty thumping sound.

>>	So what is causing my sister's system to clip, folks? Any
>>ideas would be appreciated. It's not a real problem-- just something
>>that I am curious about.
>
>    Did the amp clip, or did the Polks start making rattling noises?
>    It also could be defective power supply in the amp......

	Well, it would seem that this defective power supply 
would have also evidenced itself with the previous set of
speakers. (A truly miserable set of Fishers.) These speakers
actually produced more (not better) bass than the Polks, but
did not demonstrate the same clipping behavior.

>    If the amp, check for excessive bass boost or bass
>    boost+loudness control on.  Its pretty common to boost the bass
>    too much on a pair of small speakers to make it sound better.

	The 5-band equalizer was set to flat, and the
interconnects were Monster Cable with gold binding posts. I
don't think that cabling and/or excessive equalization were
the signifgant factor(s) here.

	The more likely suspects, after the discussion both
here and in email, seem to be a combination of several
factors:

    -1)	Poor speaker design. The passive radiators in the
S6's seem to be problematic. This pair of speakers is
actually the second pair to be used in this system: one of
the speakers in the first pair had a passive radiator that
exhibited a similar "thump" at any volume level. These were
returned as defective.

    -2)	Program material with boatloads of low bass. This
is not a problem, but rather a factor that exposes (1)
above. I think that the S6 may have cabinet resonance
problems at certain frequencies that can cause excessive
excursion of the passive radiators.

    -3)	A really bad amplifier. I don't know how this
piece of crap can perform on the low end of the scale.
It could be feeding the speakers a load of garbage that
might exacerbate the resonance problems by inducing
further distortion in the signal.

	I really doubt that the S6's in general have a
resonance problem. This line was specifically engineered
to *reduce* standing waves in the cabinets. Unless they
are lying outrageously to their dealers and in their
advertisements, Polk has spent a great deal of time
carefully engineering their new line. They are not a
"component every year" company like many other popular
names in low to mid-fi equipment, and they *only* make
speakers. I think that they would have caught such a
serious problem in their preproduction stage.

	I *do* think that it is possible that they have
put out a bad batch of speakers, however, and that my
sister (and the local dealer) could have been stuck with
some rotten apples.

	So, does this idea sound reasonable to anyone,
or am I totally out in left field? Does anybody have
some information or anecdotes about Polk speakers that
could shed light on my theory above?

	If anybody is still awake after plowing through
all this, I would welcome your thoughts. I need to come
to a decision on whether or not I should get my sister
to return her speakers and insist on a good pair, or a
set from a different manufacturer. (Polk offers a five-
year warranty, BTW.)

					-Cal
--
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Cal Lott          "Oh, I see-- I thought 'no' meant 'spoon'!" --Dan
Email me, baby!   cal@gsbux1.uchicago.edu   cjl1@midway.uchicago.edu
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Newsgroups: rec.audio