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#1
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tweeter damage?
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? |
#2
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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! |
#3
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"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. |
#4
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"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 |
#5
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"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 |
#6
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"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. |
#7
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"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. |
#8
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"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 |
#9
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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! |
#10
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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. |
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