I have some L100A speakers that seem to be in good shape that have a problem in the low end. The woofers seem to move excesively even at moderate volumes along with a low end warble. The surrounds feel nice and firm when not in use and I cant detect any voice coil problems. Is this common with this model? Also, what is the power rating for these?
spinning records? (sounds like you're describing low frequency feedback).
might have a read here regarding power:
http://www.lansingheritage.org/image...l100/page6.jpg
Yeah,mostly records,but other speakers dont react the same. I have the low end attenuated down with mids and highs up a pinch and they still seem to be very jittery on the bottom.
Got a rumble filter on your pre-amp? Tried it with a clean source like a CD player?
". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers
... if it goes away with CD or radio as the source, you're probably seeing the ability of the
L100 to output more energy than other speakers, at a frequency that's reaching your
turntable. Turntable dust cover is closed? and turntable is mounted on a heavy or
isolated platform? Infra-sonic filter on (if available)?
(yeah... what Beemer said)
I'll try setting the turntable on a heavy chunk of flagstone and maybe switch my McIntosh MX110 that doesnt have a rumble filter with my HK Citation preamp that has multiple phono settings. I'd really like to hear what the JBLs can sound like. I really miss my late 60's Rectilinear IIIs (somehow they got toasted while I was out of town)
The vented cabs are tuned too high. This creates the "Whump" bass the L100s are known for, but also acts as a near acoustic short-circuit below tuning. Essentially, the drivers are not getting any restoring force from the cabinet, so they're 'flapping in the breeze'.
The woofer is dramatically overpowered for the enclosure. The cone mass could be halved and the motor strength likewise and it'd be a better match for the enclosure. As they are, a high pass filter at 50Hz would be well-advised.
But, thems some fantastic woofers, with more motor on them and low frequency extension than many modern subwoofers.
Actually it is just the opposite. The 123A could use more mass as well as motor strength.Originally Posted by badman
As it is, the 123A is a closed box driver. The problem is that JBL didn't have much to do with Thiele and Small way back then and they were into vented boxes so pretty much anything went into a vented box. It wasn't until guys like Keele and Gander showed up to the party that things started normalizing a bit.
Zilch plugs? :dont-know
". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers
Cork off the vents and see a dramatic improvement. The 123 drivers are very durable but mismatched in the vented enclosure. As a side benefit the midbass will be a lot cleaner and less boomy.
Further improvement could be made by adding a 1 mh coil in series with the woofer to provide a low pass filter for the driver. My complaint with the L100 is they didn't have proper crossover networks and this leads to driver failure as well as a nasal sound quality.
But they made JBL a lot of money and earned huge market share in the day.
Why buy used when you can build your own?
Yep!
Hey. thanks for all the input. It makes sense to block the vent as the woofers seem to move way to easily. I'll give that a try first just to see what happens. Maybe between that and isolating the turntable better will do the trick. And if anyone knows of a reasonably priced x=over kit that might work better tha stock ,let me know. Thanks again.
There's a bunch of stuff in the data base on L100 X-over upgrades - but I like the comments above best. KISS! FWIW, I installed a pair of refurbished L112/L96 crossovers in a pair of 4312 "monitors" (same basic system as L100) which was a nice improvement in woofer control especially and smoothness generally - cleaner, clearer overall sound. But, it ain't exactly easy or inexpensive and takes some engineering. Plug the port! Mike
I have some L65s that seem to have the same symptoms. Woofer cones that seem to be too free moving as compared to my other JBLs. A little muddy on the bottom, etc. Of course I realise different drivers have different characteristics. Weak magnets, aging xovers, the suspension ring apears to be fine? Just not sure, maybe my listening is not accute enough to reconcile speaker differences?
IMO, these systems do best with at least 200WPc.
I have not noticed my 123s flapping around but I should check them, I suppose. Anyway, they sound much better with a large amp...
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