How close it is reasonable to expect two 2451SL driver to measure if they both had new diaphragms?
As the phasing plug is glued they will most likely not be identical. But how close is acceptable over 8 kHz. They are mostly close below that.
Kind regards
//Rob
The solution to the problem changes the problem.
-And always remember that all of your equipment was made by the lowest bidder
Plus or minus 2dB would be my hope, closer would be ideal.
If you can’t get that, can you use DSP?
Widget
Agree with Mr Widget that seems to be about right. Actual driver matches can be almost 1db over most of the range.
Rob
"I could be arguing in my spare time"
Here is where I'm at right now.
I will tear them apart for the 125th time and try all diaphragm in both driver cores to see if I can get a better match.
There is no rub and impedance is much closer so it can potentially be the cores...
Is this acceptable? OBS, scale is only 2db per line.
Disregard the fact that there is a dip at 10k as it is an measurement artefakt from the 4367 on the table, but it should be the same for both drivers I guess.
3ms window, no smoothing and only 50 cm out. Maybe it is not so bad up there above 10 kHz?
I have similar differences in brand new 4" drivers and D2's but here I do have the luxury of being very picky and it is a nightmare to remove them from the 4367 cabinets, so once in the they stay in... For a while at least. :-)
All input much appreciated.
Kind regards
//Rob
The solution to the problem changes the problem.
-And always remember that all of your equipment was made by the lowest bidder
Those are better matched than brand new JBLs from the factory.
Widget
Hello Rob;
In my opinion if you could get them any closer it would be pure luck. The 12k and over is a total wild card with these drivers.
I would say you are done. Well done.
Barry.
If we knew what the hell we were doing, we wouldn't call it research would we.
Have you looked at the impedance plots.
At any rate of you are using active/ dsp EQ these differences can be trimmed out.
What you have is like a 1/2 or 1/3 db variation. Small changes in Dirac mic positions product larger variations.
I wouldn't worry about the differences above 10K. That is where I see most of the differences between drivers. Bellow they look really good.
Rob
"I could be arguing in my spare time"
I had an issue with some new diaphragms in a 2451 core one time. I tried numerous times aligning them with the same results. I finally got them aligned to the other pair by changing the torque sequence of the diaphragm. The misalignment was much worse than this case. Thanks,Scott
I had a similar experience with installing new diaphragm on a similar core. The prevailing opinion was that the centering pin eliminated the need for a more careful installation (with adjustments). The prevailing opinion was WRONG. The install required both carful torquing and some shimming. With the "poor" install, the symptoms were high 3rd harmonic distortion at the low end and attenuation of the output at the upper end of the spectrum.
Great feedback. Thank you.
After putting in much time and effort into the 4367N clones I will try to get one step further. We did get 4 brand new in box 2451SL's and with the 4 cores I have we should be able to get two really well matched pairs (6 visible in picture + some D2's). I have swapped out the odd round HLA plug for standard push cable connectors. Seem to have been standard on some JBL factory drivers at the time. These were unopened boxes. Quite remarkable to find unopened boxes after som many years.
When you shim the diaphragms how did you do that and how did you get the dia to seal towards the core?
Have a nice weekend, when it arrives
//Rob
The solution to the problem changes the problem.
-And always remember that all of your equipment was made by the lowest bidder
After a gazillion iterations of cores, diaphragms, cleaning and realigning, I think we have winner.
Two NOS 2451SL cores compared on the 4367 wave guide, 3ms window but NO smoothing. OBS the scale is 2db :-)
I think the ear is about 1/6 or 1/3 smoothing and when applying 1/12 smoothing here the differences are not visible anymore.
Some payback for many frustrating hours in the workshop.
Time to finish up the 4367M's.
Have a great weekend, I know I will
The solution to the problem changes the problem.
-And always remember that all of your equipment was made by the lowest bidder
Bravo!
That is beautiful! No "consecutive serial numbered" NOS drivers will ever be that close.
Widget
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