Improving upon vintage JBL's

I bought my first pair of JBL's in 1976, the L26's. They were 10" 2-way's with orange grill cloth. I loved those speakers, they were a huge improvement over my hand-me-down Knight 12" 3-way's. I sold the L26's along with my Dynaco SCA_80 and Thorens Turntable just before joining the Navy. My next pair of JBL's were the L88's which I still have. Again, a world of difference between these and the thrift store Utah 12" 3-ways (same drivers as the previously mentioned Knights) that I had been using while in college.

In the late 90's, I came across a pair of JBL Signature C38 cabinets. The original JBL drivers had been replaced with a pair of 12" Stephens TruSonic Full Range Drivers, no tweeters or crossovers. After doing a little research on the internet and some time searching ebay, I found a pair of D123's which are the recommended drivers for these cabinets. After installing the drivers and powering up my Dynaco Stereo 70, PAS-3 and Thorens TD160 w/ Shure V15 cartridge and spinning some vintage Blue Note vinyl, I was thoroughly disappointed. The sound as I remember was flat, lacking bass and treble. After some searching on ebay, I found the JBL recommended tweeters and crossovers, the LE20's and LX2's. There was a slight improvement in the upper mid range but still not nearly as musical as my L88's.

I've searched the forums in this website as well as the library but haven't found any information regarding DYI tweaking of these speakers. Does anyone have any suggestions for improving these high quality but somewhat dated sounding speakers? Can the cabinets be modified to improve the sound? Should I sell the drivers and install new ones in the cabinets?

The one thing that attracted me to JBL, aside from their reputation of quality, was the aesthetic quality of the enclosures. The C38 cabinets are true mid-century beauties and look great in my living room but I would like to use them for more than just side tables.

IMHO, the best load in the C38 would be the 001 with the 15" 130A and the LE175DLH driver. I'm assuming your cabinets have the adapters to fit the 12-inch you're using. Removing it allows the 15-incher to fit. The C38 is a bit small to optimize the 130A but it works better than the 123. You could always add an 075 for extended top-end. The problem is you'll spend a ton of money populating these with that vintage system that will still be outperformed by many more modern systems at way less expense. You'll have to determine what makes sense for you. Heck, just the correct crossovers will cost you more than a pair of L7s!

A lot of folks here like the D123 and might have better ideas for you that won't cost the same arm-and-a-leg.

Hi brian, I own JBL d123's. When equalized,they can sound great,except the high end. They roll off at 7k about 12 db an octive. Try to find a pair of great JBL 077 or 2405 tweeters, use them from 7k up, and equalize the system. You now have great sound- RUDY

I like BMWCCA's post. In other words, it's a major engineering project. How are your engineering development chops? Nothing is a "bolt-in," everything takes money and hours of test and development and requires at least a few tools and basic electronics education/savvy. At best, you end up with something that sounds "pretty good" but, you cannot get to that final level without the equipment and smarts that the JBL lab guys have. So, have fun, but it's a hobby. For most of us DIY lunatics, learning is a major component - not so much perfection . . . which is impossible.

Why not simply sub the L88 woofers in place of the D123s? Reversible, free...

Thanks for all of your replies.

BMWCCA,
I agree, the cost of obtaining those drivers wouldn't make it worthwhile.

rudy sesztak,
what type of equalizer do you use?

Mannermusic,
I have no real engineering skills. I'm a designer/woodworker and am handy with a soldering iron but I agree that learning is half of the fun.

clmrt,
2 problems, one is that the L88's have awesome cabinets. They are the NOVA's which have mahogany grills with a circular opening around the woofer. The little lady thinks they are "groovy". The other problem is that the 123A's aren't as efficient as the D123's.

The C38's have been around a while, they are listed in the 1959 as well as the 1970 catalog so JBL must have sold a bunch. There must be someone who has tweaked these for better performance. I'm wondering if the D123's are just getting old and maybe not as flexible as they use to be. I can certainly say that about me self.

Quote:

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Originally Posted by bran kulez

The C38's have been around a while, they are listed in the 1959 as well as the 1970 catalog so JBL must have sold a bunch. There must be someone who has tweaked these for better performance. I'm wondering if the D123's are just getting old and maybe not as flexible as they use to be. I can certainly say that about me self.

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If you look at those old listings you'll find the load you have was the cheapest way to buy a loaded C38. It cost almost double to get the C35/37 which really allowed the larger systems to maximize their performance and the best speaker load available was nearly three-times the cost of the D123. You might just be getting exactly what $170 bought you in the late '60s. Don't blame the cabinet. :dont-know:

http://www.lansingheritage.org/image...1967/chart.jpg

I'm not saying that the cabinets are to blame, I'm sure there many variables involved in designing a speaker system. Regarding your point about price, the C38 cabinet with a D123, LE20 and LX2 (system 032 according to the attached chart) was $222.00. The same drivers in the C35 or C37 enclosures are $279.00 and $285.00 respectively. System 001 in the C36 cabinet was $360.00. Even the lowest priced system $440.00 (220 x 2) was not cheap in 1967. Anyway, I'm still thinking that someone must have tweaked these and came up with satisfying results .

My point was you kept calling yours C38s as if the entire line in that cabinet was deficient. What you have isn't ever going to be very magical. I'm not saying they were inexpensive, but I am saying yours was the lowest-level load there was. Even the C38 was simply a compromise for those where WAF wouldn't allow the C37.

BTW, that is $93 for the cabinet and $72 for the D123 for a total per-side of $171, plus the un-priced adapter needed to plug that 15-inch hole. Heck, the C37 cost 70% more than the C36. The 030 load cost 3.7 times what the D123 cost. It was ALL about saving money. You're just not going to squeeze blood out of that turnip. :dont-know:

Quote:

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Originally Posted by bran kulez

I'm not saying that the cabinets are to blame, I'm sure there many variables involved in designing a speaker system. Regarding your point about price, the C38 cabinet with a D123, LE20 and LX2 (system 032 according to the attached chart) was $222.00. The same drivers in the C35 or C37 enclosures are $279.00 and $285.00 respectively. System 001 in the C36 cabinet was $360.00. Even the lowest priced system $440.00 (220 x 2) was not cheap in 1967. Anyway, I'm still thinking that someone must have tweaked these and came up with satisfying results .

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Thank you for your input BMWCCA.

Yes, you are correct, $93.00 for the cabinet, and $72.00 for the D123 PLUS the tweeters and crossovers.

Anyway, I'm not looking for "magic" just some direction from SOMEONE who maybe has tweaked these. That's all.

"2 problems, one is that the L88's have awesome cabinets. They are the NOVA's which have mahogany grills with a circular opening around the woofer. The little lady thinks they are "groovy"."

I have a pair of L88 NOVAs with the porthole grill. Never quite thought of them as "groovy" though. <G>

That said, even though my L88's cabinets have seen (much) better days, I would find it very hard to take some woodworking tools to modify their original cabinet. They're certainly not the end all and be all of speaker engineering technology, but having worked in manufacturing, I admire whoever got that cabinet and grill past the accountants.