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View Full Version : 8 ohm to 16 ohm.



chopss
03-10-2014, 04:29 PM
Hello. Need some tech help please. I have a pair of JBL LE15A woofers which one of needed a recone. I took the opportunity to have both reconed to 16 ohms for use with tube amps. My question regards the crossover. It is the JBL LX13. Will I need to modify these to work with the newly 16ohm driver? The HF is a 16 ohm 806A/811. Or, is there another crossover I should look for. Thanks for your help.

NickH
03-10-2014, 07:24 PM
You want the drivers impedance to match the design impedance of the cross over. If the driver impedance is to low it will increase the frequency it crosses over the drivers. But I know jbl was a bit funny on the impedance rating system so measure the dcr of the voice coil. The other thing to do is feed it a sign wave of your cross over frequency through a 8 ohm resistor. Make sure your only feeding the driver 1 volt at the voice coil. Then measure the voltage drop across the 8 ohm resistor. Using ohms law you can now calculate the impedance via dividing your voltage over your current. You get your current number by measuring the voltage drop across the 8 ohm resistor and calculating the voltages reading by the resistance of the resistor.

if you want to go one step further you can take readings at set increments from 20 hertz to say 1khz. You can the calculate a rudimentary impedance versus frequency plot. Then the know exactly what ps going on at any given frequency. You could even use this info to design your own crossover network. But only if you own an inductance capacitance meter.

On a simpler note great plains audio sells a crossover that would work for you. I believe the le15 likes to be crossed over low, like 500hz.

Hope I wasn't to complicated and long winded.

Nick

chopss
03-11-2014, 04:10 PM
Thanks for your input. The LX13 crosses over at 800hz which probably is above what would be ideal. I'll look into the GPA networks also.

NickH
03-11-2014, 04:25 PM
The spec spec sheet says 600hz and below for the le15. I just checked GPA's ebay page and there's no crossovers that low. But I would call them.

Mannermusic
03-12-2014, 02:39 PM
The spec spec sheet says 600hz and below for the le15. I just checked GPA's ebay page and there's no crossovers that low. But I would call them.

Hi Nick - Just to add to all the above: Have used the LE15A for 750 years in various configurations and found, as you say, it "ain't so hot" above 500-600 Hz, fuzzy definition in the mid range (needs a nice 10" mid). However, it WILL work reasonably well to 700-800 Hz depending what kind of material you are listening to. Really shines below 300 Hz! Another option is an active crossover - really helps. The old Luxman 2003 tube job used to be the just the ticket - also would handle the impedance problem. Choice of 6db or 12db and can be adjusted to any frequency. Hard to find, unfortunately - old. Mike

chopss
03-12-2014, 05:52 PM
Thanks for responding. Yes, I have heard the LE is not ideal that high. Makes me wonder why they made a kit around it with LX13 xover. GPA replied, rather curtly, that they don't work on xovers. Is there a JBL xover I should be shopping for? I also have an Emminence 800hz xover I could Frankenstein. Thanks, Mike.

Mannermusic
03-13-2014, 09:30 AM
Thanks for responding. Yes, I have heard the LE is not ideal that high. Makes me wonder why they made a kit around it with LX13 xover. GPA replied, rather curtly, that they don't work on xovers. Is there a JBL xover I should be shopping for? I also have an Emminence 800hz xover I could Frankenstein. Thanks, Mike.

Yes, Eminence has a regular line of "all purpose" crossovers for professional or other use. Their engineering lab, as I recall is in Kentucky - they sell everything from speakers to software. Established, professional outfit. You could do worse than trying one of their crossovers since you are doing a "Frankenstein" experiment; no std. crossover available. A starting point - as you say, you can do some math, etc., see Nick's method above. Develop a custom crossover. Not easy, takes time, but can be done. Just thinking out loud, depends how involved you want to get.

chopss
03-21-2014, 02:01 PM
Well, I got the woofers back today. Reconed with 2235 cone They sound pretty darn amazing. It may get a little shallow in the midbass area, but not to bad. Thanks for all of your help. Also, break in music is James Brown "Get up off That Thing".

Mr. Widget
03-21-2014, 04:26 PM
Well, I got the woofers back today. Reconed with 2235 cone They sound pretty darn amazing. It may get a little shallow in the midbass area, but not to bad. Thanks for all of your help. Also, break in music is James Brown "Get up off That Thing".I hope I am mistaken. Are you saying you had a service center put 2235H kits into a pair of LE15A frames?


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chopss
03-23-2014, 09:16 AM
Yes, that's what they did.

Mr. Widget
03-23-2014, 10:02 AM
Yes, that's what they did.Maybe you misinderstood what theyve done? If they removed your LE15A cones and popped in JBL 2235H kits, you should demand your money back and find a more competent firm.

Here's the thing, there are two fundamental woofer designs, those with underhung coils and those with overhung coils. The LE15A is an underhung design with a massive top plate and very short coil, the overhung 2235H uses a much thinner top plate and a very long coil. Any recone shop with even the most simplistic understanding of their trade should never confuse the two.

With your current configuration you will experience greater distortion at moderate levels and very low frequecies at higher levels will slam the bottom of the coil against the back of the motor structure since it is too long for the gap. This will cause an audible popping noise and eventually damage the coil.


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Earl K
03-23-2014, 12:02 PM
Hello. Need some tech help please. I have a pair of JBL LE15A woofers which one of needed a recone. I took the opportunity to have both reconed to 16 ohms for use with tube amps. My question regards the crossover. It is the JBL LX13. Will I need to modify these to work with the newly 16ohm driver? The HF is a 16 ohm 806A/811. Or, is there another crossover I should look for. Thanks for your help.

Mr. Widget,

Here's the first post again ( with added emphasis ) .

I truly can't explain all the disconnect that's gone on with the OP ( since there is no-such-thing as a bona-fide, JBL-made, 2235 cone kit that is 16 ohms ) .

:)

speakerdave
03-23-2014, 02:24 PM
Maybe they had residual stock of the (appropriate) 2215 kit, and OP has confused the numbers.

Mr. Widget
03-23-2014, 03:07 PM
Maybe they had residual stock of the (appropriate) 2215 kit, and OP has confused the numbers.I hope that's what's going on.


Widget