Improve JBL's?

[joetech]

I have a pair of JBL L-88s that I've had for 33 years. They are the 2ways that could be 'upgraded' to 3ways like the L-100 studio models. I've never seen the need and now the kit is no longer available. For years I drove these with a Heathkit 15w/ch amp. Worked great.
I recently had a chance to buy a HK3380 for a price I couldn't refuse. I also finally talked the wife into letting me move these speakers to where they really belong. The difference is amazing. Soundstage is really there and no need for any subwoofer with these babys. The Cleveland Orchestra's new home is in my livingroom.
Years ago I built a few speakers and I have been thinking of building some again for my daughter who in college. (No use letting a 33 year old Heathkit amp go to waste). Looking over the internet I see some things have changed. Mostly crossovers are getting more sophisicated and software design and simulation is really impressive.
As far as the JBLs go...
Their xover is just a L-pad and a cap and resistor. Could I improve thinks with a more advanced xover? I know the old adage 'If it ain't broke, don't fix it' But I was just wondering if anyone has any experience in this area?

 

[Pyrrho]

A sophistocated crossover is designed for specific drivers in a specific cabinet. With your speakers, you would need it designed for those specific speakers in those specific cabinets, or it would likely be worse than leaving things alone. My advice is, unless you are a speaker designer, leave them as they are, because you are more likely to make them worse than better. Additionally, sometimes, drivers are so well matched that a simple crossover is exactly what is needed for best performance.

Also, you may wish to go listen to some new speakers, as there have been some interesting developments in the past 33 years. Please don't take this the wrong way; JBL made many fine speakers long ago, and I am not suggesting that everything made today will be better than what you now have. In fact, I think I prefer what JBL made back then to what they are making now, but there are other brands, and (for the benefit of those who disagree with this assessment of JBL), it could be that my memory of them is not entirely accurate, and I have not listened to every model in JBL's current lineup. Perhaps they have some new gems that I am missing out on.

Anyway, since you are contemplating replacing the crossovers in your current speakers, presumably you want better sound than what you are currently getting. For that, I recommend new speakers.

 

[j_garcia]

I agree entirely with Pyrrho. Redesigning a crossover can be a chore, and the gains minimal. Without equipment to measure your results, you are basically left with blindly guessing, and if you aren't a hobbiest who designs speakers in their spare time, that could be a lot of trial and error.

 

[Swerd]

I have a pair of JBL L-88s that I've had for 33 years. They are the 2ways that could be 'upgraded' to 3ways like the L-100 studio models. I've never seen the need and now the kit is no longer available. For years I drove these with a Heathkit 15w/ch amp. Worked great.
I recently had a chance to buy a HK3380 for a price I couldn't refuse. I also finally talked the wife into letting me move these speakers to where they really belong. The difference is amazing. Soundstage is really there and no need for any subwoofer with these babys. The Cleveland Orchestra's new home is in my livingroom.
Years ago I built a few speakers and I have been thinking of building some again for my daughter who in college. (No use letting a 33 year old Heathkit amp go to waste). Looking over the internet I see some things have changed. Mostly crossovers are getting more sophisicated and software design and simulation is really impressive.
As far as the JBLs go...
Their xover is just a L-pad and a cap and resistor. Could I improve thinks with a more advanced xover? I know the old adage 'If it ain't broke, don't fix it' But I was just wondering if anyone has any experience in this area?

Yes, the gear and software to measure speaker performance and and design crossovers has become commonplace for amateurs with some money and the willingness to learn. It has made crossover design more of a science and less of an art than it used to be.

If you are interested, you should go to the Madisound DIY speaker building forum http://www.madisound.com/cgi-bin/discuss.cgi and ask who might be interested in measuring your L-88s and designing a new crossover for them. You might also inquire about replacing the tweeter. Depending on where you live, you might find someone local.

I have been toying with the same idea for a 33 year-old pair of L-100s that I have. Here is what I've learned so far. A Danish DIY speaker designer named Troels Gravesen has a page in his web site devoted to restoring vintage speakers http://www.troelsgravesen.dk/vintage.htm. If you scroll down, you'll see entries for the JBL L-26, which he is in the process of restoring. Is the L-26 like the L-88?

If you scroll down a little further, he shows frequency response curves that he measured for the L-100 woofer (JBL 123A, in red) and the tweeter (LE25, in blue). The JBL 12" woofers are very good, probably better than anything available today. They are sensitive and smooth out to 6 kHz! The midrange and the tweeter are another story. I believe most if not all of the shrill sound associated with the L-100 is due to the uneven performance of the mid. I'm waiting for Troels to get around to measuring the midrange, and designing, if possible, a network that smooths it out some. An alternative would be a suitable replacement.

Like your speakers, the L-100 crossovers are quite simple. The woofer has no low-pass filter at all! The vented cabinet is tuned to 27 Hz. The midrange has only a cap and a variable L-pad that high-passes at 1.5 kHz without any low-pass filter. The tweeter has a cap and another variable L-pad that highpasses at 6 kHz.

 

[joetech]

Swerd: Thanks for the info on the Danish guy. Very interesting. The L-26 has the same tweeter but uses the 123A woofer. I have gone to some local audiophile showrooms and listened to some Definitive Tech and paradym and Polk and some MacIntosh speakers. Still don't see a good reason to buy anything new. Mine sound especially good when I consider they're paid for.
I was wondering if maybe upgrading the Cap with the newer poly caps at 1% (keeping the same value) would make a noticable difference? Wouldn't cost all that much to find out I suppose.

 

[Swerd]

The L-26 has the same tweeter but uses the 123A woofer. I have gone to some local audiophile showrooms and listened to some Definitive Tech and paradym and Polk and some MacIntosh speakers. Still don't see a good reason to buy anything new.

As Gravensen showed, a properly designed crossover made a large difference with the old L-26 drivers. Did you see the part where he compared the freq-response curves of the old minimal crossover, and with his design? The difference was not subtle. Try looking for someone who has the measuring gear to help you. There are DIY builders who love to do designs for others in your situation.

I was wondering if maybe upgrading the Cap with the newer poly caps at 1% (keeping the same value) would make a noticable difference? Wouldn't cost all that much to find out I suppose.

Unless the old cap is no longer delivering it's rated value (some old non-polar electrolytic caps drift in capacitance value with age), or has fallen completely apart as Gravensen showed in his L-26 page, I don't think replacing a cap will change anything audible. Considering the age, you might try it. Don't buy anything more expensive than an inexpensive poly cap such as Dayton (Parts Express) or Bennic (Madisound).

In the few years that I have followed DIY speaker building, I've heard all the talk about "upgrading caps" and have decided that, like exotic speaker cables, there is nothing to it. About 2 years ago I was at a DIY speaker builder's meet in the Washington, DC area, where a capacitor blind listening test was done comparing cheaps caps to exotic caps. Among about 40 people who were all amateur DIY speakers builders, some with extensive experience and ability, no one could tell the difference between cheap electrolytic caps, inexpensive polypropylene caps, and the exotic high-priced caps. The real audible benefits come with good crossover designs, not with expensive parts.