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Imbalanced JBL L96s, anyone?

diddlebunk

diddlebunk

Member
I recently picked up a nice set of L96s with sequential serial numbers. The cabinets and the drivers were in good cosmetic condition, but when I got them home I noticed that one of the woofers would rattle when there was deep bass, so I took them to my speaker tech, who corrected a misaligned voice coil in the woofer and replaced the surrounds of both woofers for good measure.

After I returned home with them and hooked them up, with the pots of both speakers set flat, I found that one of the speakers had more "presence" in the mids and highs, throwing the imaging off-center. I swapped the speakers and found that the emphasis followed one of the speakers. I called the tech to report the issue and he said that this sometimes happens, therefore the high and mid frequency adjustment pots can be adjusted to correct the irregularity.

I adjusted the "underperforming" speakers to go +1 on high freq. and +3 on the mid freq., while the stronger set I left flat, and the image is now centered (I used familiar stereo and mono recordings for subjective testing) — but I'm still feeling a little OCD about this.

To the experienced JBL heads here, how common is this issue? My instinct is to expect that setting the pots flat would be sufficient to ensure that the two speakers are matched. Though these are not clinically precise monitors, they seem high performance enough that it's unlikely that such a wide variance between their settings and calibrations is normal.

Does it seem like I might have an issue with my drivers? How can I actually go about testing whether the frequency response of either speaker is "flat" so that I know for a fact that they are matched?

I'm the type of listener who loves tone defeat and doesn't like EQing or playing with frequency bands, particularly when the settings differ from speaker to speaker. I dig the sound of this L96 set, but I'd love to really "dial them in" more or less precisely.

Any advice would be appreciated!
 
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Hello diddlebunk, never had that much deviation on my sets. By chance is the one speaker cabinet that has the problem also the one the woofer was in. If so your Lpads are probably intermittent from maybe being over driven. Not letting all the signal pass. Other possibility different mid as there are many various models of LE5's. Yours should be marked LE5-12 could be a different model if not marked. Do a DCR reading on the coils to see how close they are to spec. With no power take a large flat blade screw driver and work both Lpads in complete rotation back and forth. If you feel any heavy grainy resistance when moving first try and clean the Lpads. If the Lpads are bad you will need a hair dryer and flat blade putty knife to carefully remove the foilcal to access the screws.
These screws hold the Lpad assembly to the baffle board. Once removed you can get at them to clean or replace. Hope this helps and keep us informed:rockon:
 
The first thing I would do is check the drivers using a multi meter. This will measure the DC resistance (which is different than impedance) of each driver. You can view the minimum/maximum acceptable values here: https://servlib.com/jbl/audio/l-96-delta.html But it's also informative just to know if the DC resistance is different between the left and right drivers.

The pots can be a bit finicky also. These are the same pots my L150 uses. There was one occasion where the mid mostly dropped out on one of my L150s and after investigating it turned out to be the trim pot that was the problem. Working it back and forth a dozen or so times cleared up the issue, for now.
 
Thanks, guys. The pots have been worked back and forth a bunch, by the tech while he had them and by me when I got them back. The pots aren't scratchy at all, FWIW. That's not to say that they aren't the culprit; they weren't disassembled and cleaned while he had them.

The imbalance isn't intermittent, otherwise I expect that the image wouldn't be stable one way or another. I've had other speaker issues where one or another of the drivers kicks in and out or becomes intermittently more lively, and that's not occurring here. If the pots on both are set flat, one of the speakers is just less "there" than the other one. With one of the sets adjusted rather aggressively, the image is centered and stays there. They both play, but the stereo image definitely leans to one side when both are set flat, which isn't right.

After testing the drivers, what steps should I take if I find that the DC resistance differs between the left and the right? Is there an adjustment that would remedy that, or would I just need to replace the driver if that were the case?

Similarly, what should I do on the off-chance that the quieter mid happens to be a different model of LE5? Would I have to source an LE5-12 to substitute in its place?
 
diddlebunk said:
<<snip>> I called the tech to report the issue and he said that this sometimes happens, therefore the high and mid frequency adjustment pots can be adjusted to correct the irregularity.<<snip>
Click to expand...

This doesn't "sometimes happen", this indicates a problem and if a Tech told me this I would be finished talking to him.

Wow.
 
diddlebunk said:
Similarly, what should I do on the off-chance that the quieter mid happens to be a different model of LE5? Would I have to source an LE5-12 to substitute in its place?
Click to expand...

Just in case you didn't notice when you looked at the spec sheet, LE5-6, LE5-8, LE5-10, and LE5-12 are all acoustically equivalent and interchangeable. LE5-8 and LE5-12 have a silver front faceplate while the LE5-6 and LE5-10 have a black front faceplate, but that difference is cosmetic only. Having any of those 4 in there would be okay, and you could expand your search for a replacement (if necessary) to include those models. Just avoid the others, like LE5-2, LE5-9, etc, that are not the same.
 

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SaturationPt said:
This doesn't "sometimes happen", this indicates a problem and if a Tech told me this I would be finished talking to him.
Click to expand...

I hear you loud and clear. Unfortunately there just aren't many decent techs to choose from out here, and he's a well-reputed JBL service technician. In fairness to him, this wasn't an issue that I had identified when I dropped them off. They were new to me, and the woofer issue drew my immediate attention. I described the midrange problem to him after I got them back home, and he may have just tried to rationalize it dismissively. I hadn't yet centered the image with some pretty substantial frequency adjustments, so I didn't share those details with him.

In any event, I appreciate all of the guidance here. I haven't yet pulled the drivers to compare but will do so and follow up once I learn more about what's going on. Noted on the other LE5 models per the JBL spec sheet. The drivers in these speakers all look identical from the front, I'll be surprised if that ends up being the issue. It may have to do with the pots or something else.

When I figure it out, I'll be sure to circle back and close the loop. It's always satisfying when these threads reach a OP conclusion, as opposed to being left with no closure.
 
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