Here are the impedance plots of the three drivers all mounted on the same horn. They are all definitely 8 ohm drivers.
Widget
Here are the impedance plots of the three drivers all mounted on the same horn. They are all definitely 8 ohm drivers.
Widget
Thanks for that info!
Well it seems that the larger backcap reduce distortion. But we should wait for the JBL inspection on Zilchs drivers.
Personally I think it's a shame that we have new JBL drivers here and can't be sure if they are according spec!
Very Interesting,
Thanks guys, for all the effort put into this !
- I would have loved to see a distortion plot generated for the heavier diaphragmed 2430. I would think it should have a bit less 3rd Harmonic than the 2431 or 2435.
( Would also have loved to see how the Altec 288-8K measures up in the distortion department )
- My initial guess would be that the higher distortion specs (for the 2431 & 2435 ) are due to the lack of aquaplas on their light-weight diaphragms / an underdamped situation, perhaps . ( Just showing my personal bias again for proper mechanical dampening )Well it seems that the larger backcap reduce distortion.
Widget - I thought when you ran the distortion curves for the 2431 that they weren't plotted at the same -30 offset. In the plots you posted, the 2431 distortion curves don't look as bad as I remembered them looking during the tests...Originally Posted by Mr. Widget
John
The 2435's were purchased on eBay, provenance indeterminate. The were used, but the price was right, especially if JBL's 5-year warranty applies....Personally I think it's a shame that we have new JBL drivers here and can't be sure if they are according spec!
They look pretty nasty below 800 Hz there. They were buzzin' at the lower frequencies. In retrospect, I think we should start at 500 Hz, not 100 Hz, with power tests on compression drivers. It does not seem to have harmed them, tho....
There's supposed to be one on the way for testing. I'll follow up on that....
No, that's what we ran... it must have been the shock of seeing all that green on the monitor that made it seem even worse. The fact is second harmonic distortion is much harder to hear so a bit of it isn't a problem. Third harmonic distortion sounds definitely wrong and should be as far down as possible. On most of the plots I have seen third harmonic distortion is well below second, but here on the 2431 it is about the same as the second and on the 2435 it is even higher than the second in places. Typically manufacturers only raise their distortion curves by 20dB, so these curves will "look" worse than other published curves.
Two points here. The 2431 driver and the 435Be are "new" drivers that were shipped from JBL. The 2435 was an eBay purchase so the fact that it's higher distortion is rather suspect.
Widget
"They look pretty nasty below 800 Hz there. They were buzzin' at the lower frequencies. In retrospect, I think we should start at 500 Hz, not 100 Hz, with power tests on compression drivers. It does not seem to have harmed them, tho...."
With the cap we had on them they were -3dB at ~400Hz and we were feeding them milliwatts. I am quite sure it was safe. I think these particular drivers are not meant to be used at those lower frequencies and hence the distortion.
That is what we were doing after all... seeing how they perform at lower frequencies.
Widget
Yeah, some members wanna use them on BIG horns!
Perspective: 2425/6/7, LE85, 2420, etc. diaphragms are 1.75" diameter. These are 3".
Maybe I open up that 2431H and make sure everything is tight in there....
might the buzzing sound simply be a misaligned diaphragm voice coil (vs. actual
mechanical damage)? the procedures for installing new diaphragms suggest that some
"5lb alignment tool" tweaking is the norm. Mostly curious, as diaphragms I've installed
have passed through the suggested sweep without issue thus far (properly cleaned and
gaps checked, etc...), but I don't have experience with newer JBL compression drivers.
If I followed right (no guarantee there), JBL is or will be looking at the unit in question?
It would be nice if they also provided a diagnosis of the "failure".
-grumpy
edit: or just being used outside design/intended range...as suggested.
These are also not general purpose drivers like the LE85(2420) and 2425/2426. The 435Be was specifically designed for the H9800 horn in the K2-S9800 system and these others were designed to be compact and lightweight in specific PA arrays. Just because they have 3" diaphragms doesn't mean that they will perform as well as the general purpose drivers outside of their design range.Yeah, some members wanna use them on BIG horns!
Perspective: 2425/6/7, LE85, 2420, etc. diaphragms are 1.75" diameter. These are 3".
I think we need to send in the 2431 and 2435s to JBL and have them look at them before we can come to any conclusions.
Widget
2435HPL's went back to JBL today.
[Wishin', hopin', n' a-prayin'....]
Yeah, let the waiting begin..2435HPL's went back to JBL today.
[Wishin', hopin', n' a-prayin'....]
Sorry Zilch couldn't resist
Dear Mr. Widget and zilch,
Superbe jobs and very thanks for all precous times test for evaluation driver and horn...
the manys responses test and THD curve is expose many critical information...
thanks again...
for more deterministic test it is interesting to expose test response in many angle ??? ( 0°, 15° and 30° )
this test is expose a important aspect of quality of driver...
2--- it is interesting to expose more parameters experiences: rectangle pulse, distance mic etc...
Thanks for all big works and give at this communauty...
To All,
Only a PWT load will provide a rational means for measuring driver performance. Otherwise, what is being measured is a combined driver/horn response dominated by horn artifacts at the frequency extremes; i.e.:
1) When the test signal frequency approaches horn [fc], the driver becomes un-loaded while at the same time the horn mouth becomes acoustically small and the intensity of the resulting back-waves that impinge on the diaphragm is increased. This leads to erratic diaphragm excursions even though the drive signal may be relatively small.
2) On axis response and power response are different animals. In the former, beaming of horn output hides roll-off at the upper end; so, here again horn influence is masking driver capabilities.
Regards,
WHG
True.
However what we were attempting to do was compare the 435Be with it's large back cap with these similar drivers. We chose this particular horn because it has a [fc] below 500Hz which is well below the frequency range we were interested in. I would agree that a plane wave tube would be ideal, but since we don't have one, and a home brewed PWT would only add to the questions, I am quite happy with the results of our comparisons. Once we have verified drivers to test we should be able to come to some reasonable conclusions. These will be relative conclusions between these drivers, not idealized conclusions.
Widget
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