Le85

[yggdrasil]

Today I have 8ohms. At least I think I do, because it says so on the back of the LE85.

The crossovers are calculated with 8 ohms. There is also the fact that there is an L-pad attenuator between the crossovers and drivers.

Meaning:
12db band-pass crossover, 1200Hz and 7000Hz -> L-pad attenuator 8ohms -> LE85 8ohms.

The dia's on e-bay are 16ohms.

What will happen?

[Mr. Widget]

If you have an original JBL aluminum diaphragm with a smooth surround it is a nominal 12-16 ohm driver regardless of what the nameplate says. If it is an aluminum diaphragm with diamond pattern or JBL titanium diaphragm with diamond pattern it can be either 8 ohm or 16 ohm. If it is an aftermarket diaphragm you have ?


If you are using JBL networks that were designed for the LE85 they are designed for the 12-16ohm impedance. If you are using custom made networks that were designed for a nominal 8 ohm load and you put a proper LE85 (2420) diaphragm in it you will want to adjust the network.

Widget

[Alex Lancaster]

Widget, You must be thinking of a 375/2440 when You say "smooth surround"; All the L85/2420´s I have seen had the tangential lines on the surround.

[Mr. Widget]

Damn! You are right... it has been a long time... actually no, I helped Infredible replace his 2420s a few months ago, OK my brain is getting soft.

Yes I had a mental image of the 4" diaphragms as I wrote that. The 1.75" diaphragms have a radial pattern of angled tangential lines for the original aluminum version and then in the 80's when they discovered the diamond surround they changed it and the impedance.



Widget

[yggdrasil]

Yesterday evening I opened the speakers, took out the cables from the LE85's. They ohmed out at 10,6Ohms..

That explains a lot..... E.g. odd response when adjusting the attenuators.

As a quick and crude attempt to fix the fact that both the attenuator and band-pass filter are designed for 8Ohms I added a 16Ohms resistor in parallell with the driver.

What does this do with sound quality? Is it a way to go around the problem of finding 16Ohm attenuators?

[Mr. Widget]

http://www.partsexpress.com/

have 100 watt 16 ohm L-pads at very reasonable prices. You may not need 100 watt pads, but they tend to be better built all around. I would suggest you order a pair. Shipping will no doubt be more than the parts, but they are small and the entire order should be relatively painless.

Widget

[yggdrasil]

Thanks Widget.


I'll order more than just the pair. There will be other projects later on. Think I will move the upper crossover frequency too if I can get some Aluminum diaphragms.