2450J

[sa660]

People,
I am planing to used 2450J without horns for testing the imunity to vibration to a electronic board. I have no horns available and I am wondering what is the safe frequency for low cut off.
Hoping to be around 1000Hz.

Thanks,

[Earl K]

Hi Richard

- 1000hz is too low to provide the necessary 1/2 wave loading ( for the @ 2.75" deep throat found in JBLs' large format drivers ).

- 2500hz would just barely provide the proper 1/2 wave loading ( but only in the "x" axis or depth of the horn ,,, & not the "y" axis or mouth area ).

- I wouldn't do noise tesing at high SPL levels without an additional horn , such as ; the 2311 or the Selenium HL14-50 .

- No matter which horn is used , you should filter the noise with at the very least, a 24db per octave hipass-filter ( appropriately set to the cutoff frequency of the chosen horn )


regards

[sa660]

I was thinking about such value.
Let say to be safe I use a crossover @3Khz and 12db.
It may be cheaper to get a horn like 2350 etc...

[Baron030]

Hi Richard
I know this is going to sound crazy. But, instead of using the 2450J driver alone for this application. What about attaching a length of PVC pipe to the driver. I know that I have seen it somewhere in a technical paper, that JBL uses a pipe to test their compression drivers. So, my guess is that a pipe could provide the necessary air load on the driver's diaphragm, so that it will operate normally.
And I sure that the sound at the end of the pipe would be a lot more concentrated then it would be at the mouth of a large horn.

Maybe someone here has a strong physics background, and could provide some additional information about this crazy idea. Or at least have some fun explaining why, this crazy idea just will not work.

[sa660]

This is another good point
Thank you.

[Mike Caldwell]

Hello
If your just needing high frequency energy for vibration testing I would find
a phenolic diaphragm driver. With proper loading they will operate at lower frequencies and still go out to around 6000hz. A JBL 2482 or a clone would work.
A non JBL phenolic diaphragm driver could be had for what the 2450 replacement diaphragm would cost.

Mike Caldwell