Another L100T problem

[wu6fiend]

I have a pair of L100Ts. The day I first got them, after about an hour of high volume (+2 dB), the coil and cone separated. Got that fixed. The speaker guy said it wasn't the amplifer, it was a result of bad adhesive (that had glass fibers in it) they used, he could tell by the color. My amp is a nearly new HK AVR630.

Today I was playing with a new turntable I just bought, and playing the L100Ts with my Akai AM-73 amplifier. All of a sudden one of the woofers started vibrating violently, coupled with a loud humming noise. I immediately reduced the volume, and the speaker seems undamaged. I've owned the amp since new, and its never given me any trouble.

I'm starting to wonder if these speakers just can't stand being driven hard. Maybe I need to reconsider my love of vintage audio.:(

Are these speakers simply old and fragile?

[doodlebug]

I'm assuming that this is a problem only with use of the TT, correct? If so, then this really isn't a JBL problem at all, IMHO.

If the woofer motion and howling was volume-related, then I'd suggest you were experiencing acoustic feedback. This happens when the turntable vibrates from the sound pressures set up by speakers being pushed hard enough to overcome the inertia of the TT's mass, specifcally the arm. This is then fed back through the cartridge and into the system, setting up a positive feedback loop.

I'd suggest you start finding other placement options for the speakers and/or the turntable. Isolation is your friend at this point.

Cheers,

David

[Paul D]

From my experience, JBL's can be driven harder than most brands of speakers! Even the older ones seem to handle much more power than they are rated for if the right amp is used. I have found that the more powerful the amp the better. If you are using an amp that does'nt have a high damping factor, you might have a problem with lack of control because JBL uses heavy cones. I have only noticed this with 15" & 18" woofers so I dought this is your problem. Try isolating your turntable before making any other change.

[wu6fiend]

Thanks guys! I've discovered that this turntable (Pioneer PL88-FS) is very sensitive to any vibration, and I must have had it much too close to the L100Ts (it was in my office, just trying things out). That description of acoustic feedback exactly describes what happened. I'm feeling a little more confident in the L100Ts now.