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View Full Version : Mismatch of speakers and crossovers, LX-5 crossover, 16 ohm HF + 8 ohm LF = stop?



donsof
12-04-2013, 10:01 AM
Hi all,

I need a little help, and here is my background. I can wire a house, a car, built a Hafler DH220 kit amp once, and can design and build lots of mechanical things, but I am no JBL expert. It seems all this talk about vintage HIFI, JBL classic speakers, and watching the value of this stuff on the secondary market, makes me lust after the sound. Or at least I want a JBL experience!

I bring home stray stuff, and play with it, and try to improve restore and make it nice. Then rotate the collection after a year or two. My latest stray dog find, was a clean but tired JBL LE-15A woofer, LE85 HF driver, LX-5 crossover, all 16 ohm. I went to try the components out in a home brew cabinet, and the woofer had no action. I took it to the best local speaker guy I could find, and he did a recone on it. He used an 8 ohm recone kit numbered 2235 (maybe JBL kit?) with a DCR of 3.6-3.7 now. (old 16 ohm checked 8.9 or so)

So now that I have it home, I want to play it, without screwing up something. Reading all this stuff on old JBL components, has led me to read for hours and hours on wiring polarity, impedance, cross-overs, and lets just say I tried to answer my own questions and learn, but sometimes you need good help.

So can I run this setup with an 8 ohm LE-15A, the 16 ohm LX-5 crossover, and 16 ohm LE-85 HF driver?
This is question 1... will this mismatch cause problems that are costly?
or are the problems sonic only?
or will there be a problem?
The recone guy thought the 16 ohm, LE-85 HF driver, would be OK on the crossover network.

Polarity confusion...
Originally the LE-15A had reverse polarity, where red was actually negative, when tested with a 9 volt battery, for excursion direction. Now its still the same way as original. (Old JBL standard right)
The recone guy didn't know about this old JBL reverse polarity standard.
When asked how the HF should be wired out of the crossover, he said the polarity of the HF driver doesn't matter as its behind the network, and blind.
I see where there are people running the outer two wires, at the output lineup on the crossover, to the red terminals on the HF and LF speakers.
So should I hook up my amp's red output wire to the LX-5 crossover black input side?
I even went into the LX-5 schematic, and looked this over.
It seems like past advice on the forum is to do it this way.
I am unsure about the top row on this LX-5 crossover, as all the lugs are black?
Why would they not make this clear is beyond me.

Next step...
Reading things here, leads me to believe my mismatch of stuff might make go looking for a 8 ohm crossover, and put an 8 ohm diaphragm in the LE-85 HF setup?

If I were to run this setup, as stated above, would I hurt anything or would the woofer just play louder than before?

Can you hurt an amp, or speaker, if you have a 16 ohm C-36 on one channel and a 8 ohm C-36 on another channel of your stereo?

thanks Don from Davenport Iowa

fpitas
12-04-2013, 11:03 AM
Connecting the 8 ohm woofer to the 16 ohm rated crossover probably won't hurt anything, but the crossover won't work as intended. I'm not sure how to fix that either, other than redesigning the crossover. Probably the best approach is to get an 8 ohm crossover, and an 8 ohm diaphragm.

donsof
12-05-2013, 10:02 PM
After my best effort to sort out everything that may go wrong, and how to wire the LX-5 crossover.
I have this theory in mind to hook up the components.
I am going to proceed with a 8 ohm LF woofer and the 16 ohm HF driver.
Can anyone tell me if this is the wrong method.
Also keep in mind I will probably put another speaker on the opposite channel to run with the JBL stuff.
Like any of 10 other speakers I have around, all 8 ohm.

thanks for all the help! Don


60831

Mr. Widget
12-06-2013, 08:11 AM
I bring home stray stuff, and play with it, and try to improve restore and make it nice. Then rotate the collection after a year or two. My latest stray dog find, was a clean but tired JBL LE-15A woofer, LE85 HF driver, LX-5 crossover, all 16 ohm. I went to try the components out in a home brew cabinet, and the woofer had no action. I took it to the best local speaker guy I could find, and he did a recone on it. He used an 8 ohm recone kit numbered 2235 (maybe JBL kit?) with a DCR of 3.6-3.7 now. (old 16 ohm checked 8.9 or so)If he did use a 2235 kit or an aftermarket 2235 kit in a LE15A speaker, you've got way bigger problems than impedance mismatch.

The LE15A and the 2235 are two different design topologies. The LE15A is an underhung design and the 2235H is an overhung design. This refers to their voicecoil length. If you start to drive a woofer mismatched in this way the speaker will have much higher distortion than it should and the voicecoil will bottom out loudly smacking against the back plate with only moderate power applied.

As for your impedance question, it is more complicated than the simple theory suggests, but in simple terms if you use a crossover designed for 16 ohms with a 8 ohm driver, you will shift the crossover frequency down one full octave, meaning a 16 ohm crossover with 8 ohm drivers will shift from the designed 500Hz to 250 Hz.


Widget

fpitas
12-06-2013, 12:16 PM
After my best effort to sort out everything that may go wrong, and how to wire the LX-5 crossover.
I have this theory in mind to hook up the components.
I am going to proceed with a 8 ohm LF woofer and the 16 ohm HF driver.
Can anyone tell me if this is the wrong method.
Also keep in mind I will probably put another speaker on the opposite channel to run with the JBL stuff.
Like any of 10 other speakers I have around, all 8 ohm.

thanks for all the help! Don


60831

Well, since you put it that way; yes, it is most definitely the wrong method.

donsof
12-06-2013, 03:21 PM
Thanks again, so I should have asked him to put in a 16ohm recone kit then. I would then build a system all 16 ohm, and I wished I knew better before the recone. At least I only made the mistake on one speaker. The recone guy services all the local guitar/music stores, but doesn't know everything about systems.

What 16 ohm kit would you guys buy for an LE-15A?

I plan to get another and maybe put together a C40 type system.

The old Lansalloy surround was stiff, and the spider actually made croaking noises. It just wasn't free enough to pump waves. My HF driver is fine and the crossover was working.
I will buy another LE-15, LX-5 and an LE-85 if anyone has an orphan.

email ssguy66 at y a h o o dot c o m

Mr. Widget
12-06-2013, 03:25 PM
It must be a LE15 kit, original was about 10 ohms...(At different points in time they were labeled either 8 ohms or 16 ohms) The impedance is not the biggest deal, the correct cone and coil are.


Widget

donsof
12-07-2013, 09:46 AM
Mr Widget...
Thank you for being patient with me, and my endless questions and fussing!
I am a machinist by trade and can go into details for days on end.

I have to say this... a few years ago, one would have looked at worn old cores, and just toss them out into the landfill. Now with all the choices of finding recone kits online, and recone guys online and ebay, it has done a great service to people trying to keep these things running. It does leave us with many options, and I am sorting through who to go to, for the cones next time around. Any of 3-5 guys on ebay sell kits. I kind of got some good help from simply speakers, so I am open to suggestions for a recone supplier. I plan to make a pair with this setup.

Do you guys go direct to JBL pro audio, for the cone kits?
I will confer with my recone guy on where he got the cone kit used, and report back.

This is a very specialized knowledge base, and I thank all here for your insight.

Don

Mr. Widget
12-07-2013, 02:03 PM
I would ask the reconer if he used an actual JBL 2235H kit or an aftermarket kit... either way, if he doesn't correct you and tell you it is a kit for a LE15A, you need to find someone else. Any decent repair shop should know the difference between an overhung and underhung woofer.

Ideally you would use a JBL factory authorized shop who would use an actual JBL kit. This will be expensive. If you aren't up for a several hundred dollar expense, sell the woofers as is explaining what they are and look for some working woofers.


Widget

donsof
12-08-2013, 01:04 PM
Maybe this will help all the members here, and be a future reference.
I kept the original LE-15A cone and voice coil.
Below are the pictures of it.

When Widget says "The LE15A is an underhung design" do you mean that the coils are placed near the end of the voice coil paper? Or is it under hung, because its only .30" inches long, compared to the 2235H coil having a longer .750" coil length?

I looked over the specs on the 2235H and clipped this from JBL's site
http://www.jblpro.com/pages/components/2235h.htm

"The (2235h) 100 mm (4in) diameter voice coil benefits from new adhesive technology and optimized coil-former construction of aluminum, plastic and high temperature paper for increased power capacity. The 19 mm (3/4 in) length of the voice coil allows increased linear excursion capability and the extension of usable frequency response to 20 Hz in equalized alignments and subwoofer applications."

From this I gather that the model 2235H coil wire, is wound around the coil paper nearly .45" longer than original LE-15A of .30-.32" on the original cone. See my pic of the original cone.

I didn't get to see the workings of the new cone in the speaker right now, as I wasn't there when it was installed. I am only going off the markings on the cone, to assume its a 2235 cone. Its not marked with the H suffix, and the 2235 is written in silver pen. Other markings on this cone are "4 37 114" in stencil.
I can attach a picture if needed. Is it possible the H suffix on 2235H changes anything... and is there a non H version?

Would someone also tell me if the hookup on the crossover was done correctly?
It seems rather important to get the polarity correct, or do I have it correct with regards to amp positive and speaker positive? See the earlier post pictures.

thanks Don

6084760848

Mr. Widget
12-08-2013, 03:07 PM
Yes, the coil height for the LE15 is much shorter and the top plate much thicker than the 2235H. The H means the driver uses a ferrite magnet. The factory never made an alnico 2235, so they are all H's from the factory. You can put the 2235 kit in quite a few JBL frames, both ferrite and alnico, just not the LE15.


I have no idea about your wiring... Phase is extremely trivial compared to putting the an overhung kit in an underhung woofer though.

Check this out: http://en.wikipedia.org/wiki/Voice_coil


Widget

toxcrusadr
12-13-2013, 08:51 AM
I will try to pitch in here on the crossover phasing question. I don't know a darn thing about these particular crossovers, but in general, two adjacent drivers (mid/tweet or mid/woof) are wired either in phase or out of phase in order to get the flattest curve at the crossover point. If the two drivers are in phase, they can make a peak or a dip when their contributions are added together. It's specific to each system of drivers and crossover. This may not help you much with this particular gear, so hopefully people more knowledgeable than me will help out on that. You can't damage anything by reversing the polarity of one or the other, so one way is to try it and see what sounds good, and/or construct a response curve using a db meter and a tone generator or a test tone CD.

First post. Hi folks. :p

Mr. Widget
12-13-2013, 08:55 AM
First post. Hi folks. :pWelcome aboard!

And along the lines of your post, the the "correct" phase may change if you change horns with a longer or shorter geometry pushing the driver further behind the woofer or bringing it more in line with it.


Widget

donsof
12-16-2013, 06:48 PM
Well thanks everyone for giving me help on what I am doing right and wrong.
Here is an update.
I was basically building a test stand for these found components, the LE-15A, LX-5, and LE-85.
My test stand took the form of an old Marantz LS20 cabinet, with some reworking.
I just needed to see if this stuff is worth owning or using.

Well this thing lit my ears up!
I am now JBL hooked, and can't believe the sound I have been missing all these years.
I thought my home stuff was good enough for years, but this marks a new direction for me.
The LE-15A with whatever the cone is???? seems pretty good. The recone guy mentioned the voice coil gap was extremely tight, so maybe he did have the wrong cone, but got it through his test bench anyway.

Once hooked up, the 8 ohm LF woofer, was probably at a slightly lower output than the 16ohm HF driver.
I compensated right away by turning the crossover gain down (min.) on the HF section.
It also seemed like the bass was a little low, so I just adjusted the amplifier bass output up some. So maybe there is a hole in the crossover transition, like predicted.

I did hook it up with amp positive to the black terminal, and outside posts to both speaker red posts, (like in the above picture).

I played the unit for hours in my garage, and was amazed at how good it did sound, even with these things wrong. It makes me wonder just how good its gonna be, when I actually get the similar system running with proper cabinets, ohm matches, and crossover matches.
I had on one of my favorite bands "Royal Crown Revue" on, and it felt like I was at a live show.

I could see myself happy with a mint C50SM system, as I like the smallest box footprint possible.
I wonder if I would be just as happy with a C36-38 type tall boy system? (with these components)
Would you veteran's think a system like the 4430 or L200 would rival or best a C50SM setup?

I wish I would have been more knowledgeable before the recone, as I would have went with a 16 ohm LF cone.
Can anyone tell me if all the alinco frames like the D130, 130-A, 130-B, and even the D130-F are the same?
I ask because if you are reconing oldies, its not really a true LE-15A anymore?
Is the basic woofer frame and magnet the same for all?

Its pretty confusing reading all the options in the JBL line without having someone to bounce an idea off of.
I will be hunting up a tallboy cabinet, or build, buy, or restore a 2 way system, like my test bench.

Also, after reading into the crossover options and specs, I found something interesting.
It looks like a 3110A crossover would be a good choice for the mismatch system I setup, as it seems compatible with an 8ohm LF woofer, and 16 ohm HF driver.
It crosses over at 800HZ, so is that a better choice for me right now?

Its funny how little money I have in this heap, and yet its barking out loud and true!

thanks again... Don