Help with 4" driver impedance plots

Dear all,

I just updated my impedance measuring SW and now I get impedance plots that are not entirely smooth like they used to be. The new SW does have better resolution and maybe that is the case or the set of driver cores I’m trying to change diaphragms in are no good.

I’m swapping in two brand new D16R2451SL diaphragms in two used 2451J standard cores. I don’t know how many times I have had them a part to clean and check for rubbing.

There is no noise audible when sweeping them with a tone generator 200Hz to 10kHz, but the curves looks like they are rubbing above 1Khz. The first resonance is fine (below 1Khz) but the seconds is edgy like there is a resonance somewhere. I I can’t hear anything when sweeping them. Maybe that is how they are supposed to look but I did not seen that with the older system. It’s driving me nuts as I have spent many hours on this. I have swapped the diaphragms between the cores and both behave the same.

No visible damages to the cores and no corrosion. Gaps cleaned VERY thoroughly several times.

Is there someone here that has an impedance plot with good resolution of a known good or new JBL 4" driver without horn load as a reference, it would be much appreciated if you could post a picture here or send via PM.

Preferable from an 1,5” driver ie, 2447, 2450SL, 2451 or 2452 and if it has an SL diaphragms that is even better.

Kind regards and thank you

//Rob

I'll assume that you're running the latest DATS version ( V3 ) .

Here's a thread to read, over at TechTalk

:)

Quote:

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Originally Posted by sebackman

<snip>

Is there someone here that has an impedance plot with good resolution of a known good or new JBL 4" driver without horn load as a reference, it would be much appreciated if you could post a picture here or send via PM.

<snip>
//Rob

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A driver "without hornload" still is loaded by the plug of air within the throat. To get rid of it, a terminated tube is used.

Can that explain your weird resonances? If you cannot hear what you see on the impedance plot, then what is happening happens above your hearing capabilities (10+ kHz).

Ruediger

This is a 476Mg on the M2 Don't have any plots without a horn. Hope this helps

Rob:)

Hi,

Thank you for feedback.

Earl K, that is exactely my problem, I have gone from V2 to V3 and data is completely out the door.

Too bad they did not specify how they solved it. I can't find any settings in the SW that would alter the results in that manner.

Ruediger, I have tried to put on various horns with the same result. Must be the measuring rig that is wrong. By the way do you have any idea how one could do a DIY "terminated tube"?

I will have new go at it tonight.

Kind regards and thank you
//Rob