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coherent_guy
11-21-2006, 08:16 PM
Hi folks, I have a pair of LE85's with 2370A horns arriving soon (my first ones) and I've been trying to locate an impedance vs frequency graph for the LE85/2420 driver. That would be for selecting component values for a crossover. I have been unsuccessful in locating this information. Is that because the impedance is dependent on the horn used with the driver? I'm new to using compression drivers and trying to learn the ropes, any suggestions would be appreciated, Thanks!

Zilch
11-21-2006, 08:47 PM
Different horns introduce different anomalies in the basic impedance curve, yes.

If peaks occur in the crossover region, you may want to deal with them.

I'll measure a few LE85s on 2370As for you to compare sometime over the next couple of days.

Consider purchasing Woofer Tester II for these pursuits. :thmbsup:

Robh3606
11-21-2006, 09:35 PM
Hello Coherent Guy

I would measure the DCR on them to see what you get. There is no guarantee that they still have the original diaphragms in them. They could have 8 ohm diaphragms in them as opposed to the original 16 ohms. The 2370's are a modern Biradial that approximates the dispersion pattern of the 2308 lense used in the classic large format monitors but are much more uniform with their high frequency coverage than the horn/lense combo. With no HF comp they will roll off above 5K or so but you can drop a small value cap in series to improve that a bit.

http://www.lansingheritage.org/images/jbl/specs/pro-comp/2370/page1.jpg

Rob:)

coherent_guy
11-22-2006, 06:35 AM
Zilch, I greatly appreciate your efforts performing and posting those measurements. I read Mr. Widget's thread on Horn/Driver comparisons, and about the only thing it did not have were impedance measurements for the LE85, although that was not the purpose of his study.

Robh, thanks for your suggestions, I sure hope I get readings on my meter other than "40Meg" flashing, meaning open! Along those lines, in searching for replacement diaphragms, I see that JBL replacements cost more than I paid for the drivers and horns combined (O.C. Speakers, D16R2421). What recommendations would you make for replacements? I found some made by Radian for much less, but I hate to bastardize these LE85's :D But if they're good, so be it.

Thanks again :applaud:

Robh3606
11-22-2006, 10:19 AM
I see that JBL replacements cost more than I paid for the drivers and horns combined (O.C. Speakers, D16R2421). What recommendations would you make for replacements?

Yes they are expensive, one reason to be very careful with what you put into the drivers. With any luck yours will be OK. I have only used JBL diaphrams so I can't really comment on the Radians. You may want to ask in the High Efficiency forum at Audio Asylum. There are lot of guys there many of whom have had first hand experience with them. Some of the guys here may have as well and when they read this I am sure they will share their experiences.

Rob:)

toddalin
11-22-2006, 05:34 PM
Hi folks, I have a pair of LE85's with 2370A horns arriving soon (my first ones) and I've been trying to locate an impedance vs frequency graph for the LE85/2420 driver. That would be for selecting component values for a crossover. I have been unsuccessful in locating this information. Is that because the impedance is dependent on the horn used with the driver? I'm new to using compression drivers and trying to learn the ropes, any suggestions would be appreciated, Thanks!

You could forgo all of that testing and just build the "keeper" crossovers documented on this site. Works great with the LE85!

Robh3606
11-22-2006, 08:06 PM
You could forgo all of that testing and just build the "keeper" crossovers documented on this site. Works great with the LE85!

Depends on the horn. The "keeper" could work fine or be a dead end. There is no plug and play with this stuff. Be a good idea for Zilch to give it a whirl but there are no quarantee it will work with a 2370.

Rob:)

Zilch
11-22-2006, 08:31 PM
You could forgo all of that testing and just build the "keeper" crossovers documented on this site. Works great with the LE85!Well, THAT's a premature skid to a finish line, Todd!! :p

From the diversity of solutions detailed in these forums, it's easy to appreciate a variety of approaches to successful projects.

Regarding coherent guy's own, we don't know the specific application objective, two or three (or more) way, companion drivers, cabinet design, etc.

There may in fact be no purpose other than learning how this stuff functions, itself a substantial undertaking.

I've got to support working with the fundamentals as a good way to get somewhere worthwhile with any of these endeavors. :thmbsup:

[I know, I know, "Shut up and go do the impedance curves, Zilchster...."

Zilch
11-22-2006, 11:42 PM
#4 & #5 are a Thanksgiving "Bonus." :)

coherent_guy
11-23-2006, 12:22 AM
Fantastic!! All these graphs are amazing and just what I wanted, and then some, to say the least! :applaud: Thanks so much, I had no impedance graphs, and I was not happy with the FR graphs JBL provided in their literature. I wanted to get in a quick thank you before I lose myself in studying them, and then come back with a million question. I also need to thank and reply to all you others, but not right now... what stinks is I still don't have the drivers and horns yet! Supposedly Friday or Saturday...

Zilch
11-23-2006, 01:37 AM
O.K., just one more for the holiday, then, since this is set up:

I gave #4712 a bit of passive boost to flatten the HF (cyan). It's apparent 2370A doesn't support response above 15 kHz. I believe that's confirmed in the data sheet.

It sounds fine. Pushing frequencies above that any harder, tho, and it starts sounding nasty. (I'm crossed at 800 Hz on the bottom here.)

By contrast, I put a 2344A horn on that same driver and crossover and easily produced extension to 20 kHz (orange).

I don't know what your design objectives are, but these are the VHF limits according to this and my prior experience with 2370A....

Zilch
11-23-2006, 02:26 AM
Regarding Radian and JBL's 2421 diaphragms, I found them both different enough from the originals as to warrant filter modifications.

If your LE85s have red wax seals intact, then verify that they are operating correctly and use them. They're the sweetest sounding of the alternatives, but their lifetime is finite at high SPL, depending somewhat upon prior use and environmental exposure.

Otherwise, choose your diaphragm and design around it. You're going to need some test and measurement gear to accomplish this; under $500 investment will get you by....

coherent_guy
11-25-2006, 10:25 AM
I've had a problem with my posts disappearing, after logging in, writing them, and when I click preview it tells me I'm not logged in, and I loose it. I've done that several times over the past several days. I guess I'm taking to long. Trying again later... :banghead:

4313B
11-25-2006, 10:29 AM
Yep. It's best to always make sure you do a Ctrl-A followed by a Ctrl-C while in the editor before you hit that Submit Reply button. ;)

Personally I don't bother, preferring to play the "lottery". My posts are often acerbic and fraught with useless filler.
This time-out "feature" saves the forum from having to suffer my posts since I never bother with a second attempt.



P.S. Do you have that "Remember Me?" box checked? If not check it and see if that helps.

coherent_guy
11-26-2006, 02:20 PM
Well I finally received one of them, how do boxes mailed at the same time get separated? (Giskard, I think my habit of doing <Ctrl> n to open a new window after logging in is not appreciated by the software here, whatever... but the :blah: factor is true as you say) Like I said I've never even seen one of these in the flesh before, except I do own 2402's, so I have a million questions. It's an LE85, serial # 56712, and looked pretty darn good on the outside. Can you tell approx. how old it is by the S.N.? That model was made, what, from the 60's up to the 80's? I started to remove the rear cover, which I then noticed was on cockeyed, and found the screws to be bent. Reminds me of what I think when I see the DVD's my kids rent, (all scratched up) what do people do to get these things in that condition? Not gonna find exact replacements for those screws anytime soon, I thought. OK, off came the cover (oops, forgot, no red wax, but you knew that...) and out comes the foam bits, not much as there was not much left. I know enough not to touch, not that it really mattered. (interested in pics of this?) So what is done with that foam, how important is it, how is it replaced, etc.? The diaphragm looked perfect. Not a diamond surround, more like V's at an angle. The plastic ring around it is black, with no markings at all. Do I even dare ask who made that? Forgot again, the LE85 is marked 8 Ohms, and the DCR was 6.7 ohms. The wires from the input terminals had ring lugs on one end, spades on the other. One wire had been pinched under the cover and flattened in one spot, but no copper was visible. Serviced by Joes Garage I guess... Time to make new ones. The screws holding the diaphragm were not tight at all, how tight should they be? I did not remove the diaphragm. I found some screws to keep that cover on though they don't fit in the recessed holes in the cover. I then examined the other end, and found a gasket, which was glued into place. The horn (2370A) was not attached, they came in a box on Friday, this driver on Saturday. Looked similar to automotive gasket material, gray and stiff. I removed it with a putty knife in one piece (mostly). One horn has a gasket on it, the other does not. How important is the gasket, and what else can be used besides official ones? So I cleaned the LE85 up as best I could but it was in good shape appearance wise. I have not applied a signal to it yet. One reason I wanted to see an impedance curve was so I could figure out the proper value for a simple X-over capacitor and inductor, just for safety's sake when experimenting with it. I have an active X-over with variable frequency settings, but I'm not sure I want to run it straight from the amp output with just that in line. I read in the forum a recommendation of a 20mFd capacitor be used for protection, but I did not verify if that was for 8 or 16 ohm diaphragms in general. I'll check that, but does that sound correct?
That's enough for now, I imagine you have other things to do with your time than to answer newbie questions, but if you feel so inclined, I am very grateful. I'll post later with my intent and goals as Zilch mentioned (why is he Zilch, he ought to be Santa with all his posting gifts on this forum... among others) I have enough other transducers around to be dangerous, but I lack enclosures and crossovers at this point. Thanks folks, Be Well!