JBL L65 - Replacement Woofers

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Bsteele

New Member
I just picked up a pair of JBL L65 for dirt cheap.

Everything is working. All original except the woofers.

The woofers have each been replaced with a JBL GT122 (4 ohms, 140 watts RMS).

In my research, I found that the original woofers are 126A (8 ohms, unknown wattage).

I’m not very experienced with all of this stuff. It’s fun though!

I tested the resistance of the entire speaker using the rear terminals and a voltmeter. I got ~4ohms. So I have set my amp to 4ohms.

(I may have tested incorrectly, please let me know if you think something isn’t adding up.)

The speakers work and sound pretty good.

My question:

Since the replacement woofer has a different resistance (4 vs 8 ohms), is this an issue/threat to the other components in the speaker? I don’t want to damage the crossover, tweeter, or mid range driver.

Also, what happens to a speaker like this when the woofer has half the resistance than the original? Will the tweeter and midrange driver sound louder/quieter?

If I need to find an 8ohm woofer, any suggestions? Other than the originals of course.

Thank you for your help. Been lurking here for some time. I’m excited to contribute more.
 

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They are what many will call "frankenspeakers", likely won't sound anything like the originals. If the 077 tweeters are original with the original (blue) diaphragms, they are likely worth more than the entire speaker at this point. Therefore, no harm in playing with them, provided you don't damage the 077 tweeters.

Those are BTW L65A models it appears from the photo.

A woofer with a 4Ohm impedance will require roughly twice the current at the same voltage output from the amplifier, over the original 8Ohm woofer. This means that the wattage (power) is roughly double at the same volume-knob setting for your LF, and it will likely be overpowering the sound output from the midrange and tweeter, a significant deviation from the original design. Possibly, if a series resistance is added to the woofer it can be tamed, but a series resistor (especially a wirewound of adequate power rating) will introduce its own problems (delay / phase shift).

Beyond that, there are specs that can tell you if the woofer is correct for the cabinet volume and porting/design but as that is I believe designed to be a car subwoofer, it is probably just the cheapest 12" driver from JBL the previous owner could find, likely a horrible mismatch.

Best of luck, and if you strike out on an original spec woofer, at least you have a very desirable pair of tweeters to move you toward the next find.

Welcome to AK.
 
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I tested a "score" recently and got 5.1 ohms on both speakers. The end result when at home proved one tweeter dead. It's not a perfect hobby. And some perfect results can result in a crap listening experience in your particular space. Let your ears be the final test. Educate you're ears.
 
Yours will not have the 126A, being that your speakers are L65A or L65B (the port is on top of the baffle in the L65 original version).l65 variants.gif

DC Resistance at the cabinet terminals will tell you little to nothing, as DC will not pass through the capacitors in the crossover. 4Ohms will not work in that speaker.

As you'll note in the schematics, without the woofer the only way I know to tell whether yours is an A (AlNiCo woofer) or B (Ferrite woofer) is the value of L4. If you can find "N65A" or "N65B" on the crossover that will tell you also, but I don't recall if it is on the artwork of that board. If there is an A or B on the foilcal after the serial number that will also tell you.

<edit> There is a Lansing Legacy forum here also, where you might get more specific and accurate information regarding JBL speakers. If you want this moved, click on the REPORT at the bottom left and ask to have it moved.
 
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The problem with using a 4 ohm woofer instead of an 8 ohm woofer is that the crossover frequency for the woofer is affected. The JBL has a first order filter for the woofer. Halving the driver impedance will half the crossover frequency, so there will be a hole in the frequency response. I suggest finding the correct woofer.
 
You are all brilliant and so helpful. Thanks for taking the time to respond so thoroughly.

The speakers are indeed L65A. Great catch.

I will be on the lookout for the original woofers. If not, I’ll be putting these up for sale as is.
 
Before you decide to put them for sale as-is, and I'm going to wince a little typing this, check JBL 077 prices and if they're in good condition with the blue diaphragms, I'd say they're firewood with saleable mids and tweeters.
 
SaturationPt said:
Before you decide to put them for sale as-is, and I'm going to wince a little typing this, check JBL 077 prices and if they're in good condition with the blue diaphragms, I'd say they're firewood with saleable mids and tweeters.
Click to expand...

I’m sorry, do you mean that the entire intact speakers won’t sell easily, but parted out, the tweeters, mids and diaphragms will?

I notice the 077s are worth quite a bit on their own.

I do have the original blue diaphragms too. They’re dirty and need a good cleaning. Hopefully I can get them looking neat again.
 
Bsteele said:
I’m sorry, do you mean that the entire intact speakers won’t sell easily, but parted out, the tweeters, mids and diaphragms will?

I notice the 077s are worth quite a bit on their own.

I do have the original blue diaphragms too. They’re dirty and need a good cleaning. Hopefully I can get them looking neat again.
Click to expand...

My mistake. I thought “diaphragm” was referring to the blue grill.

I see now that inside some 077s, there is a blue thingy called a diaphragm.
 
They will sell, but without the correct woofers I think it will be a hard sell. Since the mids and tweeters are easier to ship however, they can be sent anywhere and will likely bring more money faster.

I watch evilbay for pairs of good 077s (as spares for my L300As) and they come along occasionally, for a good high price. Singles are easier to find (matched is to me and many people important as it will affect imaging).

I'm a bit of a vintage JBL fan, but was disappointed in the L65A right out of the box, mostly the midrange presentation. They were an improvement over the L65. Grilles in good shape, I see you have the fairly rare navy blue, are also valuable, even the crossovers might be worth something.

Back to the vintage JBL fan part though, I have never "parted out" a set of speakers, even though a pair of used L100As I bought years ago were a good candidate (scratched cabinets, blown midrange, bad trimpot, etc.) It's just so hard to find the correct 122A woofers.

Look into the tweeters and you will see either a sky-blue (original) or gold (not original) glint looking back at you.
 
Very insightful. Thank you so much.

I see that I do in fact have the blue 077s.

I’m actually more into thrifting than audiophile stuff. My dad is the hobbyist. I will let him enjoy these speakers for what they are before I part the speakers out and put them on the market.

Perhaps I can reach out to you when that time comes. I appreciate all the help!
 
4 vs 8 ohm, as a fix so the crossover works better, try adding a 4 ohm resistor on the + connection of the 4 ohm woofer.
The system may sound better with the woofer presenting a 8 ohm load.
 
geiman said:
4 vs 8 ohm, as a fix so the crossover works better, try adding a 4 ohm resistor on the + connection of the 4 ohm woofer.
The system may sound better with the woofer presenting a 8 ohm load.
Click to expand...

This is not a good solution. Such a resister in series with the woofer will be dissipating half of the power to the speaker and will attenuate the woofer by 3dB. Depending upon the listening level, the resistor will need to be at least 50 watts, which is big, expensive, and will get hot. The attenuation of the woofer will reduce the bass and emphasize the highs from the tweeter.

It would be much better to find the proper woofer and use it. If the specs of the current woofer warrant its use in the cabinet, then the next best option is to replace the inline inductor with one that has 1/2 the inductance.
 
Also keep your eyes opened for a pair of 128H’s as JBL lists then as a last resort replacement for all the L65 series
 
RTally said:
This is not a good solution. Such a resister in series with the woofer will be dissipating half of the power to the speaker and will attenuate the woofer by 3dB. Depending upon the listening level, the resistor will need to be at least 50 watts, which is big, expensive, and will get hot. The attenuation of the woofer will reduce the bass and emphasize the highs from the tweeter.

It would be much better to find the proper woofer and use it. If the specs of the current woofer warrant its use in the cabinet, then the next best option is to replace the inline inductor with one that has 1/2 the inductance.
Click to expand...
Got to disagree there. It's better to do the resistor than run a 4 ohm woofer.
As you say, an 8 ohm woofer is the best solution but the resistor does not need to be 50w rated. It would never be played at a 50 RMS level anyway.
 
But since the 4Ohm woofer of that size is likely a wirewound, there will be frequency-dependent delay and other changes. I have to feel that it's just a "Band-Aid", find a correct 8 Ohm woofer is a much better solution.
 
Thanks for all the input. On Friday, I contacted every person within my province that I could find who might have an appropriate pair of woofers (122A/128H). No luck.

Then I saw a new posting online for a pair of L150s nearby. Great price. Posted less than 30 minutes prior. Everything original except for the tweeters. 128H had just been refoamed.

I grabbed them. Instant manifestation, if you’re a hippy like me.

I spoke with the seller. She said she was going to throw them out but something told her to post them online that evening.

Took the 128Hs out of the L150 and into the L65As. Sounds amazing!

The GT122s that came with the L65As were actually not 4 ohm! They were 4+4 ohm. So they could have been wired up to be 8 ohms. But whoever installed them didn’t even do that.

I also realized that they probably put the GT122s in because they had the number 122 in there. Maybe they thought the number meant it was close enough.

Anyway, it’s been a fun journey with JBL. I see why there’s a cult like following around these speakers.

Now I have to figure out what to do with the L150s with aftermarket tweeters and no woofers.
 
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