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guitdoc
06-16-2009, 10:24 AM
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?

grumpy
06-16-2009, 10:26 AM
spinning records? (sounds like you're describing low frequency feedback).

might have a read here regarding power:
http://www.lansingheritage.org/images/jbl/specs/home-speakers/1973-l100/page6.jpg

guitdoc
06-16-2009, 10:47 AM
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.

BMWCCA
06-16-2009, 10:52 AM
Got a rumble filter on your pre-amp? Tried it with a clean source like a CD player?

grumpy
06-16-2009, 10:52 AM
... 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)

guitdoc
06-16-2009, 11:04 AM
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)

badman
06-17-2009, 08:50 AM
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.

4313B
06-17-2009, 09:20 AM
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.Actually it is just the opposite. The 123A could use more mass as well as motor strength.

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.

BMWCCA
06-17-2009, 09:53 AM
Actually it is just the opposite. The 123A could use more mass as well as motor strength. Zilch plugs? :dont-know

duaneage
06-17-2009, 10:10 AM
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.

4313B
06-17-2009, 10:38 AM
Zilch plugs? :dont-knowYep!

guitdoc
06-17-2009, 11:47 AM
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.

Mannermusic
06-18-2009, 06:44 AM
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 :blah:

midlife
06-18-2009, 08:41 AM
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? :bouncy:

robertbartsch
06-18-2009, 09:46 AM
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...

BMWCCA
06-18-2009, 10:16 AM
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. Are you guys all using old turntables or something?

I can play even my L96s at high volume and I can't tell the LE10H cone is moving unless I give it a burst like the big kick in Al DiMeola's Embrace, and even that's just a quick movement with no flutter or flop. None of my stuff from 6.5" to 18" seems to have that problem. I remember in college how boring it was when my friends wanted to see the D130s move to watch how something that big produced such a sound, Watching them with a flashlight through the C37's black grille cloth proved kind of boring after a while as they barely moved. :dont-know

Robh3606
06-18-2009, 10:30 AM
I was wondering the same thing. I used to beat the hell out of my L100 with an old Dynaco St-400. Telarc cannons you name it. Never did they just flop around even with the cannon shots which had to unload them. Sure sounds like a feedback or tonearm issue to me.

Rob:)

Fangio
06-18-2009, 11:00 AM
As it is, the 123A is a closed box driver.

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.
Slightly OT, sorry but I wonder if the same could be said from a certain 15" driver too.

It's the LE15B, also with accordian surrounds, and I have a pair (http://s268.photobucket.com/albums/jj35/MacFangio/JBL_LE15B/) sitting here doing nothing. Would closing the port help to improve the bass in, lets say a L200, C50 or 4503 type enclosure? :hmm: (http://s268.photobucket.com/albums/jj35/MacFangio/JBL_LE15B/)

4313B
06-18-2009, 11:22 AM
You'd have to run the TS parameters on them and post them.

#2 (http://audioheritage.org/vbulletin/showpost.php?p=36408&postcount=2)

Zilch
06-18-2009, 11:49 AM
Early S7 (LE15(A)) Olympus was closed box.

Seems easy enough to measure Fs and Qes to calculate EBP.

I have measured LE15B in L200 with the ports closed; the results are posted here somewhere, along with those of several other drivers in the same session.... :yes:

mech986
06-18-2009, 12:23 PM
I was wondering the same thing. I used to beat the hell out of my L100 with an old Dynaco St-400. Telarc cannons you name it. Never did they just flop around even with the cannon shots which had to unload them. Sure sounds like a feedback or tonearm issue to me.

Rob:)

You may have hit on another parameter even for the L100 - use of a strong, big SS amp with plenty of damping factor. Recall that the L100 was designed in the early infancy of big SS power amps. As amps got better, their output impedence went way down, increasing the damping factors, which usually leads to better woofer control near or below resonance. Also, with appropriate high pass filtering, efficiency is improved while avoiding the muddy low bass.

OP might want to try another amp and see what happens.

Bart

Old curmudgeon
06-19-2009, 07:35 AM
You may have hit on another parameter even for the L100 - use of a strong, big SS amp with plenty of damping factor. Recall that the L100 was designed in the early infancy of big SS power amps. As amps got better, their output impedence went way down, increasing the damping factors, which usually leads to better woofer control near or below resonance. Also, with appropriate high pass filtering, efficiency is improved while avoiding the muddy low bass.



This might explain why the combination of JBL L-100s, 4310s, 4311s or 4312s with large vintage Crown Amplifiers such as the DC300AII, Power Line Four or PS-400s sound good.

There may be better JBLs (and I'm sure someone will make this point :blah:) or amplifiers that some think are better, but THIS particular combination seems to work well.

mike
06-19-2009, 07:06 PM
I would have to agree that it is probably the turntable rumble and lack of damping factor. If you are using a tube amp you will notice a lot of cone movement because of the lack of damping factor.

Those L100 woofers have some unique qualities and seem to last forever.

Mike