[TechAssist] Re: Acoustic Research speakers AR93Q, repairopinions please

  • From: "OrpheusComputing.com Repair" <techassist@xxxxxxxxxxxxxxxxxxxx>
  • To: <techassist@xxxxxxxxxxxxx>
  • Date: Fri, 15 Feb 2002 02:12:10 -0600

"Speaker ohms" are electrically and mechanically (or
acoustically) induced ohms, depending on when they are
measured, and are a function of the T/S parameters.  When
measured during operation, they can rise to great levels as
the driver reaches it's Fs (fs=resonance, which is part of
the T/S parameters).  What is stamped on the magnets of most
drivers is the 'nominal' impedance.  An 8 ohm speaker can
have a graphical impedance curve of 2 or even below, up to
over 50 ohms depending on frequency and other T/S parameter
characteristics.  If a speaker had 0 ohms at rest, it would
be shorted and would blow out the amp.  Even if it
(hypothetically) was not shorted, it would still blow an amp
due to having no load.  (Of course if it read infinity that
would mean it's also blown but as in the voice coil being
open).  If a driver could be zero ohms (and wasn't blown),
the crossover network would not work because it is a function
of capacitive and inductive reactance and resistance.  The
exception is non-electromagnetic induction drivers, i.e.
electrostatic drivers or piezo electric drivers (tweeters &
mid's).  (In the case of the latter, it has no voice coil or
magnet, and is seen by the input signal as a purely
capacitive device, and reaches over 30K ohms at lower
frequencies [and exponentially rising as frequency decreases]
hence the lack of the need for a crossover network for those
type drivers).

While it can be 'generally' correct at times, It's not
necessarily true that the higher the impedance, the less
efficient a driver is.  There are (for example) some 4 ohm
drivers that are only 85db/SPL @1w/1m, and some 8 ohm drivers
that can be over 100db/SPL @1w/1m.  :-)
-Clint

God Bless Us All
Clint Hamilton, Owner
http://OrpheusComputing.com
http://ComputerHardware-ConsumerElectronics.com
sales@xxxxxxxxxxxxxxxxxxxx
Fax: 209-882-9602
TechAssist Administration
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----- Original Message -----
From: "J Silverman" <greentron@xxxxxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Thursday, February 14, 2002 12:17 PM
Subject: [TechAssist] Re: Acoustic Research speakers AR93Q,
repairopinions please



Speaker ohms are acoustically induced ohms, not ohm meter
ohms. Obviously
the total ohms, acoustic plus wire resistance is greater than
the ohm meter
reading. An ideal speaker would measure zero ohms with an ohm
meter. The
higher the meter ohms, the less efficient the speaker.
Jerry Silverman
Greentron Inc
4 Newland Ave
Greenville SC 29609
864 232 3889
Fax 271 2080
mailto:greentron@xxxxxxx
----- Original Message -----
From: "Gary McCartney" <number63@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Wednesday, February 13, 2002 9:36 PM
Subject: [TechAssist] Re: Acoustic Research speakers AR93Q,
repairopinions
please


>
> Thanks Ed. Now that you mention Cathray, I just received
their moving
> special flyer in the mail today. Looks like they're moving
closer to me.
> That is good. As for the speakers, I'm not sure how the
originals are
> rated, such as power, input impedance, etc. My measurement
of 8.6 ohm
> across the woofer doesn't really make sense to me. Usually
8 ohm
> speakers that I measure, show about 6.2 ohm on my meter.
Does this mean
> these woofers and midranges are 10 ohm impedance? Also,
would the cross
> over frequencies match up if I replace with third party
parts? If I can
> get the specs from somewhere, then yes I would go for
replacement parts,
> as long as they are good quality. I can ask Cathray for
their opinion.
> Maybe they've sold parts for replacements in Acoustic
Research in the
> past, but then again they may just sell me anything to get
a sale. How
> do you find them in that regard?
>
> Also checked the site you mentioned but can';t seem to load
the pages
> properly. Maybe later.
>
>
> Gary McCartney
>
> McCartney Electronics
> 7134 Fife Rd, RR 7
> Guelph Ontario Canada N1H 6J4
> Fax: (519)821-1530
> email: number63@xxxxxxxxxxxxx
>
>
>
>
> Edward Gaidies wrote:
> >
> > Gary;
> > Just to mention, Cathray is having a moving sale, (on
speakers).
> > If you are changing them as a set, Cathray has a good
supply of
speakers,
> > such  as Crown, etc. I believe that Acoustic Research is
no longer in
> > business, and what I can remember, they were not a high
end speaker, the
> > type that Hi-Fi aficionados would purchase.
> > I'm sure if they are replaced in pairs, they would do
quite nicely.
> >
> > -Ed-
> >
> > teltek@xxxxxxxxxxxx
> >
> > >
> > > I have this pair of speakers come into the shop with
foam surrounds
> > > desintegrated in all the woofers and midranges. They
belong to a
doctor
> > > who has given me the go ahead at $400.00 CDN
> > > guest-imate.
> > > I actually gave the price of $400.00 hoping to scare
him off because I
> > > don't really feel like doing the job.(I'm not a speaker
expert).
Didn't
> > > expect him to say that he thought that was a fair price
to repair and
> > > that the speakers are worth $1000.00 CDN.
> > >
> > > Ok, so now the problem. Are original parts available
for these, and
what
> > > cost? If not available, what are replacement options in
keeping these
> > > sounding like original?
> > >
> > > The woofers are pn: 200035 (need 4 of them) and
midranges are pn:
200036
> > > (need 2 of them)
> > >
> > > All speakers are 8". The woofers measure 8.6 ohm on my
meter, or 4.3
ohm
> > > -2 in parallel. The midrange measures 8.6 ohm. I
measure 5.4 ohm
across
> > > the input terminals of the complete encloser.
> > >
> > > I have posted a web page to show the speakers and the
cross over
network
> > > schematic.
> > >
> > > http://www.number63.ca/speakers/speakers.html
> > >
> > >
> > > Another option: installing new surrounds. I have
attempted this one
> > > other time and it was a flop. The surround I got was
just a generic so
> > > maybe that is why. I think I would want proper
surrounds to fit these
> > > speakers if I attempt it again. Any pointers in doing
this?
> > > Are the surrounds available?
> > >
> > >
> > >
> > >
> > > Thanks for any suggestions in how to go about repairing
these the best
> > > way.
> >
> > --
> > From: Ed Gaidies
> > teltek@xxxxxxxxxxx
> > Tel-Tek Electronics
> >
> > ------------------------------------------
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