Audax HD3P Repair

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Warning: Proceed at our own risk. Audax recommends Moca Audio for this repair.

I was able to repressurize my HD3P. 18 hours and counting the dome has maintained pressure .

To recap. There is an access port in the back of the tweeter behind the label. There is something that acting like a check valve inside the tweeter. I inflated the tweeter with a desoldering tool, the dome will hold pressure for a few seconds and then slowly deflate. I plugged the opening before it deflated with some blu-tak. I plan to use some tape to reinforce the blu-tak.

I am also considering using a syringe. Plug the hole with the blu-tak with syringe in place, reflate then remove syringe quickly closing opening. I will let you know.

Still looking into a miniature needle valve. Hopefully, this will allow me to set a specific PSI. However, the tweeter dome seems extremely delicate that 1 or 2 PSI seems alot. Using the desoldering tool method the tweeter will release some pressure as you inflate the dome. Pressure-relief valve? I'll keep you informed of new developments.

This thread started here: What has been the most detailed driver you have worked with?

[pinkmouse]

Have you done any SPL measurements? That might be the best way to get the correct pressure.

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Not yet. Within the next few days. Still monitoring if the tweeters will stay inflated. I have test results from the factory to compare with. Hopefully, it will perform as intended.

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HD3P HM100z0.jpg

Got around to working on these last weekend. Here are some FR graphs for the Audax HD3P and HM100Z0. I don't have specific PSI data but higher pressures attenuate 6k to 10k. Shown in the graph the red line has the higher pressure. SPL is OK as shown by the HM100z0(blue line) which is 93db@8ohm and the HD3P is 90db@4ohm. The drivers have been in storage for so long that it requires break-in. Hopefully in a few weeks time I'll get better readings.

I'm putting this system together using linear phase crossover. The idea being driver spacing is a non issue or at least its effects minimized. I have them installed in a test box and so far the results are very promising. Not having heard the HM100Z0 in awhile. I have to add that its a very nice blend of accuracy and musicality.

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Step Audax_HDA_HD3P.jpg

So far... so good. 7k, 51 taps. HD3P running direct with its network.

No conclusions on the issue of driver spacing when using FIR based linear crossovers. Given the 6k crossover point and well behaved nature of these drivers at the selected frequency. Same results could possibly be garnered with a passive... bessel?

Compared a MP 2nd order butterworth with a FIR LP. Again, with these drivers both where listenable. The difference is more "air" with MP. LP sounded recessed and dull in comparison. LP was less impressive on first listen, deeper soundstage and solid imaging. MP imaging and soundstaging was less precise. As if the room more "live." Extended listening started revealing the timbre and "voice" of the instruments with FIR LP. The subtle ebb and flow of the music as you get immersed into the performance. It does not sound like a fullrange but the results are similar. Been on steady diet of strings and brass.

Trying the same setup with JX92S and OX at 3-4k. Same general impressions except the timbre and tone from the instruments. Which I can only attribute to the HD3P which is best described as an electrostatic point source monopole.

Edit: Measured 1 meter. Audax HM210Z0 HM100Z0 HD3P.

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FR Audax HM100Z0_HD3P.png
Step Audax HM100Z0_HD3P.png

Testing HM100Z0 and HD3P only. The following was HM100Z0 FIR LP 6.5k 19 taps. HD3P on its network. All measurement taken at 1 meter.

Mic is from my LAUD kit from Bill Waslo, maybe I need a new one. Getting the same general FR from other drivers. Or... I may need to use a different gas for pressurizing the tweeter. Need to test with an IR thermometer. Or... passive components, capacitor, resistor, transformer issues? Bypassed the cap with a .01uf no change.

FR 0_90 Audax HM100Z0_HD3P.png

FR taken at 0 to 90 degrees at equal increments. Drivers are spaced at 4.25 inches c-c.

Spectral Waterfall Audax HM100Z0_HD3P.png
Spectral Sonogram HM100Z0_HD3P.png

HM100Z0 resonance at 5k, on the to do list. Drivers still test box. New enclosure in the works.