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Old 17th December 2009, 10:51 PM   #1
jpnoll is offline jpnoll  United States
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Question JBL 2206 possible problem:

Hi gang,

I just bought 2 JBL 2206's off eHAY and I did an Impedance test on them today and noticed when I looked at the waveform on the o-scope that the negative portion of the sinewave had what looked like: "back-emf", and it was on both speakers ans was almost identical on each.

Does anyone know what this anomoly is? Will it affect the performance of the speaker? Do they need reconing/recoiling?

James
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Old 21st December 2009, 09:21 PM   #2
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I may be because of the test gear having a high impedance, an amp will have very low z out effectively shorting the back emf...??? (perhaps you could test again with a low R across the speaker?)
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 22nd December 2009, 05:26 AM   #3
jpnoll is offline jpnoll  United States
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PeteMcK,

Hmmm, thats possible, but I tested another set of speakers and it didnt do it to them. I was thinking it was the "hang-up" from the ferro-fluid that JBL uses to "slow-down" a speakers velocity to prevent it from smashing the bottom of the coil channel. Got any thoughts or experience with that?
As for adding a resistor in parallel across the speaker (zobel network portion) it would throw off the measurements I am looking for mainly the drop across the voice coil. Vsource-Vdrop=Vr-currentlimit.

Rcurrent-limit tp#1
---\/\/\/\/\/\------------------| /
|---/
600 hz sig |---\
-------------------------------| \
tp#2

Vsource=1.0 v a.c @600 hz
Vdrop=Vsource-Vtp1Tp2
IRcurrent=Vdrop/Rcurrent (10 ohms)
Z=Vdrop/IRcurrent

so as you can see any resistor placed across the speaker changes the Z factor and I cannot get a true impedance figure.

James
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Old 26th December 2009, 12:22 AM   #4
SteveW is offline SteveW  United States
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Interesting. I assume you are driving the 1v source from the output of a solid state amp?

Can you post a picture of the waveform?

Also, assuming you are testing in a free air environment?

As PeteMcK suggested, it may not matter.

However, it's interesting. I have a pair of 2206H's I picked up on eBay myself and test gear. Off work on vacation for two weeks - maybe I'll set them up and sweep em' to compare notes.

Let me know if you're interested.

I'm planning on using them in custom front horn loaded low/mid enclosures in a 4-way system with active crossover.

Good rationale on the ferro fluid excursion damping theory. If they were damaged it may be the cause - cuz at that power level they should have minimum excursion at 600hz. I've bought a few pieces of junk on eBay over the years myself.
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Last edited by SteveW; 26th December 2009 at 12:31 AM.
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Old 26th December 2009, 05:12 AM   #5
jpnoll is offline jpnoll  United States
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Smile Reply to Possible 2206 problem

Well all, I have VERY good news regarding this "possible" problem. It is not a problem after all. I put the 2206's into a 3.5 cu ft trap cab and used a Seleniom 2K Xover with an eminence horn driver and horn and ...WOW!!!

The sound is far better than my brand new stock JBL JRX 115's I just bought.

BTW, if any of you have any of these speakers (JBL JRX 115s), there is a tweeter mod that is necessary. Replace the mexican tweeter driver with a selenium D220Ti. The difference is supposed to be incredible!

See this YouTube Link:

YouTube - Brian Hot Rods his JBL JRX-115 Top Cabs (Horn Driver)

Note: The driver he mentions is no longer available, but the replacement is the Selenium D220Ti.

I wish you ALL a merry and blessed Christmas and a happy new year AND lots of great sounding speakers!

James
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