How do you test tweeters to see if diaphragms are damaged ?

[Mr Wizard]

Hello.

I have a pair of JBL 4612OKs.
They took a pretty good shot of high volume amplifier wattage for brief second.
After the sudden burst, the 2404H-1 Ultra-High Frequency Transducers sound a little less crisp, less fidelity.
The pair of JBL 4612OKs just sound a little more bassy.
The woofers seem to be working fine.
The amp wattage is 35 wattage into 8 ohms.
Volume control was set at half when the speakers took the burst.

How do you test the tweeters to see if diaphragms are damaged ?

Thanks,

Mr Wizard

[sguttag]

Run a frequency sweep. The tones should be clean/crisp (nothing rough sounding or buzzing). The JBL test on that driver (2404) is a 1.0V sine wave swept from 1KHz - 20KHz.

[Mr Wizard]

What type of test equipment do I need to perform a frequency sweep.
Is there some type of computer software and microphone that will visually plot a graph of the tweeter's frequencies?

[Earl K]

What type of test equipment do I need to perform a frequency sweep.
Is there some type of computer software and microphone that will visually plot a graph of the tweeter's frequencies?

Test software & USB Test mic :


Room EQ Wizard

( click the microphone pic )



Compare your results to;

[Mr Wizard]

Earl K,

Thank You for the information.
The graph that you posted, is that what the microphone picked up of the 2404H and 2404h-1 ?
Is there a procedure that I can follow to perform that test?

Thanks,

Mr Wizard

[Mr. Widget]

I made that measurement back in 2005 by the looks of it... time flies!

Yes, Zilch had quite a driver collection and brought these over along with others and we measured them on and off axis. These are on axis measurements at 2m from mic tip to the front of the drivers. They were located mid point (~60” from the floor) in a 10’ high room about 3.5-4m from any other reflective surface or wall and the mic was also about 3.5-4m away from any walls or reflective surfaces. The drivers were located in as close to free space on a small baffle as we could arrange.

As can be seen from the plot, the system used was Clio using their MLS measurement software and a calibrated mic. The system was accurate to better than 0.5dB. There are many lower cost options today. They will likely be a little less accurate, but then my Clio system would also be less accurate without the required recalibration if I were to use it today too.



Widget

[Mr Wizard]

Mr. Widget

I take it that when the test were done, the diaphragms were fairly new genuine JBL diaphragms.
Is there instruction somewhere, on how to do the test ?

I have fourteen 4612OK's and two 4612B's that need to be tested.

For the 2404H-1, JBL Pro service said the replacement diaphragms part# is D16R2405
He said the D8R075 (orig.) diaphragms are no longer available.
I thought that, to turn a 2404H into a 2404H-1 a 2402's D8R075 diaphragm was used in the 2404H because of the lower 3 kHz crossover point. Isn't the D16R2405 diaphragm for the 2405 which has crossover point of 7 kHz and up ?

As for the pair of 4612OK's in question, I think one or both of the 2404H-1's metal portion of the diaphragm may have been slightly misshapen. Just a guess though.

[Mr. Widget]

Some of the drivers were brand new others were not. We tested quite a few drivers and compared various versions. We tried to post the most representative units we could.

Many of the answers you are looking for are buried in this thread:

http://www.audioheritage.org/vbullet...or-Comparisons

As for testing procedure, that came from reading on-line materials, testing manuals, and trial and error. Honestly it has been so long since I have been actively involved in DIY and testing that I would have to dig through a ton of notes to get back up to speed. From looking through the first few posts I see that these measurements were taken at 1m not 2m as I had thought. Most measurements I took back then were at 2m.


Widget

[Mr Wizard]

Widget,

I will check out the link that you provided.

Thank You for the help,

Wiz

[Mr. Widget]

It starts out with useful info, veers off course and then gets back in track later on.

The thread is fairly long but if you are patient you will find it is sprinkled with useful data throughout.


Widget