I installed NOS Wharfedale Diamond 7 Anniversary Edition bookshelves. These
are small ported designs with a silk dome tweeter, rated at 100wpc, with the
usual music power caveats. The amplifier is a 48 wpc Sugden A48, a
relatively soft clipping MOSFET design. The music was mixed jazz/classical,
played at perhaps 85 dB max as measured on a Radio Shack SPL meter from 8
feet away.

After several hours of intermittent listening, both tweeters developed a
scratching noise, while continuing to produce mildly distorted output. The
woofers are fine.

One speaker exhibited the tweeter noise about an hour before the other. As
it developed, it could be produced on demand by thumping the top of the
cabinet while music was playing. A little while later, the noise became a
reliable problem without the need for a hand thump.

It's embarassing to think I might have destroyed two speakers. In my
defense, the music appeared clean, without obvious clipping. No hard rock or
electronic music was played, so I should have been able to identify clipping
artifacts.

What kind of damage would be expected of these tweeters? Adhesive failure?
Overheating?

In article ,

Robert Morein wrote:
I installed NOS Wharfedale Diamond 7 Anniversary Edition bookshelves. These
are small ported designs with a silk dome tweeter, rated at 100wpc, with the
usual music power caveats. The amplifier is a 48 wpc Sugden A48, a
relatively soft clipping MOSFET design. The music was mixed jazz/classical,
played at perhaps 85 dB max as measured on a Radio Shack SPL meter from 8
feet away.

After several hours of intermittent listening, both tweeters developed a
scratching noise, while continuing to produce mildly distorted output. The
woofers are fine.

One speaker exhibited the tweeter noise about an hour before the other. As
it developed, it could be produced on demand by thumping the top of the
cabinet while music was playing. A little while later, the noise became a
reliable problem without the need for a hand thump.

It's embarassing to think I might have destroyed two speakers. In my
defense, the music appeared clean, without obvious clipping. No hard rock or
electronic music was played, so I should have been able to identify clipping
artifacts.

What kind of damage would be expected of these tweeters? Adhesive failure?
Overheating?

One possibility is that you might have a stability problem in the amp
or preamp or signal source, leading to a high-frequency oscillation.
This might have produced enough of a high-amplitude ultrasonic signal
through the amp to overheat the tweeter voice coils.

Another possibility is that the tweeters were in fact defective
out-of-the-box, or had been exposed to some environmental condition
(excessive heat? solvent vapors?) which attacked the tweeter's
materials.



--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Dave Platt" wrote in message
...
In article ,

Robert Morein wrote:
I installed NOS Wharfedale Diamond 7 Anniversary Edition bookshelves.
These
are small ported designs with a silk dome tweeter, rated at 100wpc, with
the
usual music power caveats. The amplifier is a 48 wpc Sugden A48, a
relatively soft clipping MOSFET design. The music was mixed
jazz/classical,
played at perhaps 85 dB max as measured on a Radio Shack SPL meter from 8
feet away.

After several hours of intermittent listening, both tweeters developed a
scratching noise, while continuing to produce mildly distorted output.
The
woofers are fine.

One speaker exhibited the tweeter noise about an hour before the other.
As
it developed, it could be produced on demand by thumping the top of the
cabinet while music was playing. A little while later, the noise became a
reliable problem without the need for a hand thump.

It's embarassing to think I might have destroyed two speakers. In my
defense, the music appeared clean, without obvious clipping. No hard rock
or
electronic music was played, so I should have been able to identify
clipping
artifacts.

What kind of damage would be expected of these tweeters? Adhesive
failure?
Overheating?

One possibility is that you might have a stability problem in the amp
or preamp or signal source, leading to a high-frequency oscillation.
This might have produced enough of a high-amplitude ultrasonic signal
through the amp to overheat the tweeter voice coils.

Yes, though it would be surprising if the same stability problem occurred on
both channels. With their small magnet structures, the speakers are not
difficult loads, the cables are short, and the Sugden has a terrific
reputation, and does actually sound quite nice.

Another possibility is that the tweeters were in fact defective
out-of-the-box, or had been exposed to some environmental condition
(excessive heat? solvent vapors?) which attacked the tweeter's
materials.

It seems unlikely that the environment of the assembled speaker was ever
severe. It contains a fine finish and delicate fabrics, all of which appear
to be in new condition.

However, your speculation that the tweeters materials were damaged, or the
related possibility that they were defective, coincides with my own
suspicion. Still, I have a lingering fear that somehow, I damaged the
speakers. If so, it's my first time.

"Robert Morein" wrote in message

What kind of damage would be expected of these tweeters? Adhesive failure?
Overheating?

Lacquer cooked to 'bubbling', probably blackened, and rubbing on the
magnets.
Time discrepancy probably related to the average signal level over time per
channel. Get new tweeters, and a 100W amp.

geoff

"Robert Morein" wrote in message
...
I installed NOS Wharfedale Diamond 7 Anniversary Edition bookshelves. These
are small ported designs with a silk dome tweeter, rated at 100wpc, with
the
usual music power caveats. The amplifier is a 48 wpc Sugden A48, a
relatively soft clipping MOSFET design.

May have been clipping - one can't always hear that. Or possibly the design
has inadequate tweeters, or too low crossover point, or they are defective -
physically falling apart inside (least likely).

geoff

"Robert Morein" wrote in message


I installed NOS Wharfedale Diamond 7 Anniversary Edition bookshelves.
These are small ported designs with a silk dome tweeter, rated at
100wpc, with the usual music power caveats. The amplifier is a 48 wpc
Sugden A48, a relatively soft clipping MOSFET design. The music was
mixed jazz/classical, played at perhaps 85 dB max as measured on a
Radio Shack SPL meter from 8 feet away.

After several hours of intermittent listening, both tweeters
developed a scratching noise, while continuing to produce mildly
distorted output. The woofers are fine.

That would seem to be rubbing voice coils, probably due to cooked voice
coils.

One speaker exhibited the tweeter noise about an hour before the
other. As it developed, it could be produced on demand by thumping
the top of the cabinet while music was playing. A little while later,
the noise became a reliable problem without the need for a hand thump.

Still sounds like rubbing voice coils.

It's embarassing to think I might have destroyed two speakers.

I think you had help.

In my
defense, the music appeared clean, without obvious clipping. No hard
rock or electronic music was played, so I should have been able to
identify clipping artifacts.

The idea that clipping kills tweeters has been effectively deconstructed
many times.

What kind of damage would be expected of these tweeters?

Nicely simmered voice coils. The glues and varnishes used to insulate the
wire, and hold the wire in shape, forms bubbles that rub the pole pieces, if
carefully simmered.

Adhesive failure?

Due to overheating.

Overheating?

Possibly due to a defective power amp. It might be interesting to throw a
scope across the speaker terminals and look for the thickening of the trace
that is characteristic of amp oscillation.

"Arny Krueger" wrote in message
...
"Robert Morein" wrote in message


Arny, Geoff, nice posts.
All these are possibilities. I have the following additional info to
provide:
The tweeters use a 2nd order crossover and do not have ferrofluid. Thus the
possibility of cooked adhesives, which both of you suggested, seems likely.

The amplifier has now driven MB Quarts and Kef RDM1 up to 92 dB with
exemplary fidelity, and no tweeter failures. Both these speakers use higher
order crossovers and more robust tweeters. The Sugden A48 MkIII is not a
marginal piece -- it would be unlikely for both channels to oscillate.

"Dave Platt" wrote in message
...
In article ,

Robert Morein wrote:
I installed NOS Wharfedale Diamond 7 Anniversary Edition bookshelves.
These
are small ported designs with a silk dome tweeter, rated at 100wpc, with
the
usual music power caveats. The amplifier is a 48 wpc Sugden A48, a
relatively soft clipping MOSFET design. The music was mixed
jazz/classical,
played at perhaps 85 dB max as measured on a Radio Shack SPL meter from 8
feet away.

After several hours of intermittent listening, both tweeters developed a
scratching noise, while continuing to produce mildly distorted output. The
woofers are fine.

One speaker exhibited the tweeter noise about an hour before the other. As
it developed, it could be produced on demand by thumping the top of the
cabinet while music was playing. A little while later, the noise became a
reliable problem without the need for a hand thump.

It's embarassing to think I might have destroyed two speakers. In my
defense, the music appeared clean, without obvious clipping. No hard rock
or
electronic music was played, so I should have been able to identify
clipping
artifacts.

What kind of damage would be expected of these tweeters? Adhesive failure?
Overheating?

One possibility is that you might have a stability problem in the amp
or preamp or signal source, leading to a high-frequency oscillation.
This might have produced enough of a high-amplitude ultrasonic signal
through the amp to overheat the tweeter voice coils.


Yup, had that same thing happen in a large live sound rig. HF amp developed
an oscillation and it took out all the HF horns. Expensive thing to have
happen.
now we put a low pass filter on the input of the horns..

Doug

In article 31rmd.237941$%k.214885@pd7tw2no,
Doug Schultz wrote:

One possibility is that you might have a stability problem in the amp
or preamp or signal source, leading to a high-frequency oscillation.
This might have produced enough of a high-amplitude ultrasonic signal
through the amp to overheat the tweeter voice coils.


Yup, had that same thing happen in a large live sound rig. HF amp developed
an oscillation and it took out all the HF horns. Expensive thing to have
happen.
now we put a low pass filter on the input of the horns..

Hmmm. If I recall correctly (it's been a few years since I looked at
the books) it's common for speaker drivers to have a rising impedance
at higher frequencies. Some speaker designers add an impedance
compensation network in parallel with the driver (often a resistor and
capacitor in series) to flatten out the impedance, making it easier
for a crossover circuit to be designed to give the system a flat
treble response.

It's possible, I suppose, that the speakers in question have such an
impedance compensation network, and that this network
"overcompensates" at very high frequencies... making the speaker's
impedance one which has a low R and a low but negative X at high
frequencies (i.e. the speaker "looks like" a capacitor at high
frequencies). There are some amps (IIRC, the old Naim amps were
notorious) which are distinctly unstable and prone to oscillate when
used to drive capacitive loads.

It's also possible that the CD player was "running berserk" and
pushing a lot of ultrasonic garbage into the amp... possibly this
player has ineffective or defective anti-image filters? Or, the
preamp stage might have been oscillating, or picking up a strong local
RF signal, or ... ?

In any case, the only way that the original poster will be able to
tell whether there was a stability/oscillation or ultrasonic-noise
problem, is to hook the damaged speakers back up to the amp, turn on
music from the original CD player at a representative volume, and look
at the amp's output using a fast 'scope. Trying to deduce the cause
of the problem by theory and logic is all well and good, but
experimental investigation will be needed to determine the actual
facts and conditions of operation.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

It's also possible that the CD player was "running berserk" and
pushing a lot of ultrasonic garbage into the amp... possibly this
player has ineffective or defective anti-image filters? Or, the
preamp stage might have been oscillating, or picking up a strong local
RF signal, or ... ?

This is something which happened to me also with my system, my Shanling CDT100 burned out my Tweeters on my Celsetions and Kef's at moderate volume too..I binned the Shanling and now have an old Meridian CD Player.