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hammerworks 6th July 2007 02:09 PM

Audax HD3P
Hi everybody. I've got a big problem that I'm hoping someone here will be able to help with...I'm the proud owner of a pair of Audax HD3P tweeters which have been slowly deflating over the last couple of years.
Last week I dismantled one to see how it goes together and hopefully fix the leak. While I was cleaning off some adhesive from the gold dome, I knicked the membrane. Now I have one HD3P.
Going by a thread posted last year, there appears to be a few members with deflated HD3P's in their bottom drawer and if anyone wants to free up some storage space, I'd love to purchase one of those little beauties from you.

AndrewT 6th July 2007 02:53 PM

if you had not damaged the piezo would you have been able to re-pressurise the dome?

Have you any idea of the voltage (ac or dc) the piezo can take?

I was enquiring about high voltage direct drive rather than through the air cored transformer.
But, I got no info on what operating voltage they can take.

hammerworks 7th July 2007 03:46 AM

Hi Andrew.

I reckon I can re-pressurise the piezo sac and I'll be having a go at my remaining tweeter this week.
As far as the voltage tolerance of the piezo material...I've no idea.

gianmaria 8th February 2010 08:17 PM

can you please come back with the way you inflate the gas in the HD3P again? I have a pair of these but very low sounding due to the gas leakage (how I also read in other forums).

Anyone can help with advices, please?

I would really like to restore them....

Thank you,

Dr_EM 8th February 2010 10:00 PM

A very curious tweeter, can anyone explain how it works? What is the function of the inflated sack, it somehow helps couple the piezo element to the surrounding air more effectively? Does it just rest/press against the element?

hammerworks 16th February 2010 10:37 PM

Hi Gianmaria. If you pm me with your e-mail address, i'll send all the details on how to re-inflate these beautiful tweeters.

jerome69 17th February 2010 06:24 PM

In France, this tweeter HD3P seems difficult to find. I have always heard, this tweeter is very fragile.
Great if you have a solution to inflate this fragile tweeter :)

I see here, the designer Gilles Millot gave this company address MOCA-AUDIO. This company proposes to inflate the HD3P or as a replacement this tweeter. A magnesium dome like the SEAS T29MF001. It seems to have the same diameter than the HD3P. You should redesign the crossover. I also understand they can sell and install a system to inflate the HD3P periodically.

My opinion is to change the tweeter if you cannot find a solution. Excellent tweeter exists at good price, cheaper than repair.

hammerworks 18th February 2010 12:07 AM

To the best of my knowledge, the piezo crystals are ground to a dust and bonded to one side a mylar film. They react when an electrical charge is passed through/over them by physically contracting, the mylar being inert doesn't move, so the laminate bends. When the charge is stopped, the laminate resumes it's original size and shape. When a varying charge from an audio amplifier is used, the piezo film flexes at different rates and generates sound waves.
There is plenty of info on the web at places like Wikipedia, etc.

hammerworks 18th February 2010 12:30 AM

Hi Jerome, I have managed to re-inflate my HD3P's and they sound better than when they were new, probably because they were a couple of years from the factory by the time I bought them. They've been running for a couple of years since I repaired them and no sign of sagging.
Before I did this though, I tried repacing them with a pair of Bohlender Graebener Neo 3's; nice but nowhere near the clean sound of the HD3P.
BTW, is there any way of reading the MOCA-AUDIO web site in English. My French stopped at year 8 high school.

jerome69 18th February 2010 06:28 AM


This is a very good news if you can re-inflate them.

You can use google translator ;)

Translation on the fly


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