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LuigiCartino
05-04-2009, 12:46 PM
Hi, has anybody info on the travel of the 2108 midlow speaker? Mine seem to have only 8 mm of travel. I bought them two years ago and they were already reconed. So I do not have any comparison.
Any clue?

Thanks!

speakerdave
05-04-2009, 01:10 PM
For linear response the excursion will be a lot less than 8mm unless that's a peak to peak distance, though I would still be skeptical of that number. The voice coil depth is .17 inch in a gap the depth of the top plate. I believe its an underhung design. It's meant to play upper bass and lower midrange--not actually a woofer per se. It was used in the L212 down to 70 Hz, but not at punishing volume.



Hi, has anybody info on the travel of the 2108 midlow speaker? Mine seem to have only 8 mm of travel. I bought them two years ago and they were already reconed. So I do not have any comparison.
Any clue?

Thanks!

LuigiCartino
05-05-2009, 04:23 AM
Hi, thanks for your quick repons. I did the check manually. Not with brutal force though... ;-)) So my estimation seems to be a bit high.
Your 0.17 inch is less than half a centimeter (as a European JBL fan, I am used to ISO...) and that could be close to the truth.
This gives me some confident having bought the right speaker set.
I will upload some photos soon. Thanks again!



For linear response the excursion will be a lot less than 8mm unless that's a peak to peak distance, though I would still be skeptical of that number. The voice coil depth is .17 inch in a gap the depth of the top plate. I believe its an underhung design. It's meant to play upper bass and lower midrange--not actually a woofer per se. It was used in the L212 down to 70 Hz, but not at punishing volume.

Earl K
05-05-2009, 04:41 AM
Hi Luigi,

JBL publishes the TS parameters for their old & new drivers . These parameters include the drivers' Xmax rating ( "travel" in your vernacular ) .

Here's a link to the latest JBL Publication of TS Parameters (http://www.jblproservice.com/pdf/Thiele%20Small%20Parameters/Theile%20Parameters.pdf) .

>< cheers :)

speakerdave
05-06-2009, 12:40 PM
Hi, thanks for your quick repons. I did the check manually. Not with brutal force though... ;-)) So my estimation seems to be a bit high.
Your 0.17 inch is less than half a centimeter (as a European JBL fan, I am used to ISO...) and that could be close to the truth.
This gives me some confident having bought the right speaker set.
I will upload some photos soon. Thanks again!

Looking at an Alnico 2108 frame, I think the plate thickness is about 13/32, which is about .41 in. Subtracting the .17 coil depth leaves about .24. That divided by 2 yields .12 one way excursion with the coil remaining fully withiin the gap. That's about 3.5mm in each direction, and would seem about right to me.

4313B
05-07-2009, 05:47 PM
Many JBL's used a .280 top plate, I'm pretty sure the 112/2108 was one of them but I don't currently have any to measure. I could have sworn I posted all that many years ago.

I do know that the 112/2108 worked just fine down to ~ 70 Hz in the L212 system without any over excursion issues.

Robh3606
05-07-2009, 07:50 PM
On the 112A I have I am measuring about .350 on the top plate. It's thicker than the 108H from the L250.

Rob:)

speakerdave
05-07-2009, 08:00 PM
On the 112A I have I am measuring about .350 on the top plate. It's thicker than the 108H from the L250.

Rob:)

There's a touch more. It's let into the frame a little, I think.

4313B
05-08-2009, 07:01 AM
I find that hard to believe...

4313B
05-08-2009, 10:50 AM
On the 112A I have I am measuring about .350 on the top plate. It's thicker than the 108H from the L250.

Rob:)


I find that hard to believe...The 3 models only had the .280 and .350. The 112 family used the .350.

speakerdave
05-08-2009, 05:10 PM
It is not let in and it's .350.

4313B
05-09-2009, 07:11 AM
Yeah, it's too bad alot of the data on those old drivers was lost.

I do know that the 112/2108 worked just fine down to ~ 70 Hz in the L212 system without any over excursion issues.~ -9 dB at ~ 70 Hz for clarification. The B212 was also ~ -9 dB at ~ 70 Hz making for a rather nice crossover transition in a typical living room.