Dumb speaker question

[Regis]

I'm refurbishing the $20 garage sale JBL L-110's. The woofers need new foam surrounds, which isn't a problem. I've got the mid's covered with an Ebay purchase for $40 (the magnet on the one unit was loose enough to rattle). The tweeters are another story. The one-inch domes have been pushed in very hard and the 033's are very expensive to re-diaghram at $100 apeice. They're hard to find on Ebay too. My dumb question is, can I replace the tweeters with any similar 8 ohm tweeter? Parts Express has some really nice units for far cheaper from Davis Accoustics and Morel. I just have to rework the old face plate to get them to fit in the larger hole on the L-110's. Any thoughts?

[roddyama]

There should be no reason that you wouldn't be able to replace the 033 with another driver. I couldn't remember if you had the owners manual so this will linkyou to it. You'll see that the 033 takes over at 4kHz and up and it has a sensitivity of 90db/Wm. The replacement will need to match these specs.

[usekgb]

Here's a link to the Technical Service Manual:
JBL L-110 Technical Manual
BTW, many modern tweeters won't play well with your vintage JBL drivers. There's just something about those old JBL drivers that had a certain magic to them. They weren't always the most accurate things in the world, but they sure sounded great. Good luck with your project.

Cheers,
Zach

[roddyama]

Good one Zach.

It appears there is some equalization happening with L4 and C5. If you do get replacements of a different kind, you might think about disconnecting those 2 components to start with. It will ultimately depend on how well behaved the new tweeter is in the xover region.

[sreten]

L4 and C5 is just your standard R,L,C series tweeter resonance
compensator, with the resistance built into the inductor.

With a ferrofluid tweeter it should be removed.

For a tweeter with an appreciable impedance rise at resonance
C5 should be rescaled to match the tweeters resonant frequency.

No time now, I'll post the formula's tonight.

sreten.

[Regis]

Rodd and Zach,
Thanks so much for the great advice. If I go with a ferrofluid tweeter, I'll definitely disconnect L4 and C5. The link was very helpful as I have a dead mid-range output in one of the speakers and doing a side-by-side (good x-over to bad x-over) comparison, I found R2 open. The schematic verified that, yep, R2 is in the mid range section. Very cool.

Let me pose another question, as Zach said the old JBL drivers were really good. Actually, I'm bidding on a pair of JBL LE-20 tweeters, which are probably older technology (and hopefully, sound as good). My question is, would these work with the N110 X-0ver? Secondly, just where do you guys find these cool technical manuals? I can't find it on the JBL website. If I have to pay more than $25-$30 for the pair, then I'm going to go with the Morels or something with similiar performance and disconnect the L4/C5 combo.

Thanks for your insight all!

[roddyama]

Originally posted by Regis
Let me pose another question, as Zach said the old JBL drivers were really good. Actually, I'm bidding on a pair of JBL LE-20 tweeters, which are probably older technology (and hopefully, sound as good). My question is, would these work with the N110 X-0ver?

The LE20 was mainly used in 2-way speakers although it did see some use in 3-way speakers as well (L100), just not as much. You would loose the high end extension of the 033's and I doubt the LE20's are as smooth as the 033's.

Originally posted by Regis
Secondly, just where do you guys find these cool technical manuals? I can't find it on the JBL website. If I have to pay more than $25-$30 for the pair, then I'm going to go with the Morels or something with similiar performance and disconnect the L4/C5 combo.

I found the L110A manual here at the JBL Home web site. Zach must have a password or something to get to the service pdfs. because I've tried through the web site and couldn't.

[usekgb]

The LE-20 tweeters should work OK, but will have a different tonal character than the 033's. Don't get me wrong though, the LE-20 is a wonderful tweeter from yesteryear. I would love to have a pair to go with my LE5-2's and my 126A's. As for the manuals, I'm a "certified" JBL pro and consumer repair tech. I've got access to pretty much any manual JBL ever put up.

Cheers,
Zach

[sreten]

1.0mH and18uF.

At resonance impedances are equal so 2*pi*f*L=1/2*pi*f*C

F^2=1 / 4 *pi^2 * L * C, F = 1.2kHz.

So to adjust to another resonant frequency you need to set f to
the new frequency and find C with the 1mH value. This is not the
perfectly ideal way to do it but its the most sensible IMO.

for example for 1KHz , C = 25uF so add 6.8uf in parallel to C4.

some other points to consider :

As its a first order tweeter crossover it is important values are
readjusted if the resonant frequencies are different, though as
said before for well damped ferrofluid tweeters compensation
is not necessary, given the parallel section of the L-pad.

Allthough sensistivity is 89dB per watt you really want a few
more dB than this from the tweeter to make the Lpad adjuster
be around midway under 'flat ' operation.

sreten.

[Regis]

Thanks Sreten for the formula! I'll follow it if I'm not going to go with the "pretty much compatible" LE-20 tweets. This site has been an education for sure!