Replacing tweeter pairs in old JBL62 bookshelf speakers

[Doc Morgan]

Hey, guys...I have a sticky problem. I was given a pair of old JBL62 speakers with one burned out tweeter to repair. I've looked high and low for the things. These are 67259-01 tweeters, 8 0hm nominal with 5.2 ohm DCR.
I am finding 67259-02 tweeters, but these are 4 ohm tweeters. Should I throw up my hands and quit? What are the ramifications of using the 4 ohm units in lieu of the 8 ohm ones. I can imagine that it screws up the crossover frequency, but I am not a speaker guy so I need some advice.

 

[moamps]

I think you asked the question in a completely wrong place, so there was no reaction.
My opinion is that you can use a driver with a nominal impedance of 4 ohms instead of a driver with a nominal impedance of 8 ohms. There are some problems here, you will probably need to insert some kind of resistive attenuator at the input of the crossover for the tweeter, because the volume of the woofer and tweeter will be unequal. Of course, the impedance of the speaker will not be linear in frequency, but this will not be a problem if it will be driven by a solid state amplifier. Good luck.

 

[Flatpicker]

If it were me, I'd probably replace the bad one with a 4 ohm version and start adding some resistance in series with the 4 ohm tweeter until you get it to a level that matches the working 8 ohm one. I'm guessing it won't take much resistance - maybe as little as 2 or 3 ohms, but you'll just have to try and see. If you get them close and/or end up liking the 4 ohm better, then just buy a pair and modify them both with the same parts.

If you want to spend some more money to get an improved crossover and (hopefully) sound, run it by Danny at GR Research and see what he recommends, as he does a lot of speaker mods.

https://gr-research.com/

 

[Doc Morgan]

Thank you very kindly, Flatpicker. I was musing that perhaps a series resistor would do the trick. I am replacing both tweeters on the old JBL62 speaker pair. Since this speaker pair will be used in my client's home, and will not be used for critical listening or monitoring, I am not overly concerned about the series resistance's effect on the crossover. Thank you for your time and for your advice.
Doc Morgan

 

[cyrano]

Have you checked the broken tweeter internally to see if it can't be repaired? I've saved some because only the thin wire between the solder lug and the coil was broken.

 

[Doc Morgan]

Yes. Unfortunately, the voice coil was actually heated until it seized and the coil lead to one of the terminals simply vanished. One can only imagine what sort of signal was fed to the speaker in order to cause that amount of damage; the entire tweeter had that unmistakable "burned varnish" odor.
Thank you for your input. It is much appreciated.

 

[soapfoot]

Check on the Lansing Heritage forum. Someone there will likely be able to help you out.

One thing that has been true at various times in JBL history... the exact same driver would be marked with different impedances for different systems, despite the voice coil being exactly the same!

I'm not sure whether this could've been true with your specific tweeter, but it's worth measuring the DCR of the good one

 

[Doc Morgan]

Thanks, soapfoot. I did notice, when reading the technical literature on the speakers, that the tolerances in the dc resistance for that particular tweeter were amazingly large. One supposes that the inductive reactance enters the equation as a greater factor at some frequency, and increases as the frequency increases. So, I reasoned that there may not be an appreciable difference between the "4 ohm" and "8 ohm" tweeters. Time will tell; I am going to measure the remaining original speaker using a pink noise source and audio spectrum analyzer, and compare it with the other speaker containing one of the "4 ohm" tweeters. Should be enlightening, regardless of the measured results.
Lansing Heritage forum? I'll definitely check that out.

Doc

 

[Disco Volante]

Ah but these are not exotic drivers. The LF driver looks like the LX-series units. You can probably source a replacement diaphragm somewhere, the cheaper JBL drivers are mostly made in France and a lot of the diaphragms are interchangeable. Seems like they would redesign the fascia every other year. Try speakerrepairshop.nl, I get most of my parts there.

The lower impedance of the 4 ohm version would make the series cap a tad too large, but like the other posters have indicated I'd try it and see what works. Perhaps a small resistance directly in series with the driver would take you there.
It'd be fun if would post your measurements;-)

Happy tinkering
Viggo

 

[Doc Morgan]

Thank you, Vigo. I infer from your comment about the drivers not being "exotic," that in your experience (as well as in mine) the aforesaid JBL62 speakers are adequate for reproducing music, but nothing special in terms of accuracy. I should have liked to replace the diaphragm, but I'm an old guy now and don't have good control of my fine motor skills when using my hands...in fact (in the words of one of my friends), when doing small finicky work, I "shake like a puppy trying to pass a bologna rind." Since said friend is the one for whom I am repairing a vintage stereo system, I shall not dispute the accuracy of his hyperbolic simile. I shall take under advisement sharing my measurements, and thank you for that suggestion.
Regards,

Doc

 

[Disco Volante]

Yes, you got my point exactly;-)
Most speaker drivers benefit from better cabinet work and some crossover attention. I'd say the same applies for your JBL 62. Budget drivers well treated can be quite enjoyable.
If you were on the European side of the pond, I could have helped you out, I can still TIG-weld and replace diaphragms;-)
Make sure to replace the cheap electrolytics in the crossover with some decent poly ones of the right value (assuming you can still handle a solder pen)...
It might well be worth the trouble experimenting a bit with different values and measuring/listening in between. I'm guessing you're in for an enjoyable experience;-)

Have fun,
Viggo