JBL LE15A Weird Impedance Curve - Need advice

Hi all,
I'm using a pair of LE15A with LE85A, which sounds OK to me. Yet I had the drivers checked; one has a highish voice coil resistance of 9ohms yet has the expected impedance curve when checked against a frequency sweep, with resonance peak @ 29Hz and a slow rise above 1kHz. The other driver has the expected static 6 ohms voice coil resistance, but when tested does not show any sign of the expected 29Hz resonance in the impedance curve!!
When tested in free space, they have almost perfectly similar spl/frequency curves!! The technicians I have talked to here (Belgium) are puzzled and don't know what to do besides a complete re-cone. I don't want that has the cones and surround are in perfect conditions; and I can't find NOS LE15A replacements part that easily.

As I said, I can't hear a difference, but I am asking this since I blew a HK Citation 22 driving these, while my trusty Jadis tubed DA-30 integrated can drive them without any harm for hours.... We're all wondering what the heck is going on, if anyone has a clue, I would appreciate.

Thanks for your help,

Hello,

I had a similar problem with a 2245 woofer and asked more or less the same question here in this forum.
Strangely enough nobody seems to know the reason for a woofer having no free air resonance peak anymore.
I had my speaker sent to a german repair repair shop.
My speaker turned out to have a partly shorted voice coil. There must have been a rubbing that scratched off the outer isolation from the wire on one spot thereby shorting about half of the turns on the coil.
Thus the DC resistance was lower than normal and BL-factor was effectively much lower than it should.
Seemingly BL decreased so much that there was almost no back-EMF left in the coil to induce the usual impedance peak.
Be aware that in my case the still intact turns of the overhung coil were all outside the gap with low measurement excursions !!
I guess this might be the fault in your case as well. If your alnico magnet was decharged to a very low level impedance might measure similar but then spl (in midband > 100 Hz) should also be much lower than a normal woofer of this type.
So you better have your voice coil(s) checked !

greetings

Franz

Franz could be right!

The right DC resistance of a LE15A should measure 7,6 to 9,2 Ohms according to the JBL Field Manual.

Thanks for your answers, that's what I origianlly thought, but the guy who checked the driver says that the voice coil was looking OK, no apparent rubbing - the mystery goes on... If I get a solution to this, I'll post it later. The frustrating part is being worried to blow the power amp on these again.

Cheers,