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

  • From: "J Silverman" <greentron@xxxxxxxxxxxxxxxx>
  • To: <techassist@xxxxxxxxxxxxx>
  • Date: Fri, 15 Feb 2002 15:53:22 -0500

I made the post only because I have seen so many questions about measuring
speaker impedance wiith an ohm meter. The question displays a fundamental
misunderstanding of the meaning of the "speaker ohms" and of transducer
theory. For a simple speaker with a voice coil, the DC resistance represents
a power dissipating component that just generates heat and makes no
contribution to acoustic power delivered to the air. The significance of the
DC resistance to the overall performance varies with  the complex impedance
presented by the speaker dynamics and the acoustical load, which is in turn
affected by the enclosure and the proximity of absorbing and reflecting
surfaces and frequency. If the "speaker ohms" is representative of the
average equivalent  dynamic resistance over the useful range of the properly
installed speaker, and the DC resistance is a significant percentage of the
dynamic resistance, the speaker cannot have high efficiency.
Jerry Silverman
Greentron Inc
4 Newland Ave
Greenville SC 29609
864 232 3889
Fax 271 2080
mailto:greentron@xxxxxxx
----- Original Message -----
From: "OrpheusComputing.com Repair" <techassist@xxxxxxxxxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Friday, February 15, 2002 3:12 AM
Subject: [TechAssist] Re: Acoustic Research speakers AR93Q, repairopinions
please


>
> "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
> http://tech-assist.org
> techassist@xxxxxxxxxxxxx
> 4orpheus@xxxxxxxxxxxxx  (alternates)
> orpheuscomputing@xxxxxxxxx
> (PLEASE include our previous correspondence
> if replying to this email!!)
>
>
> ----- 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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>
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