Audax HD3P

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hammerworks

Member
Joined 2007
#1
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.
 
#2
Hi,
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.
 
#4
Hello,
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,
gianmaria
 
#5
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?
 
#7
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.
 
#8
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.
 
#9
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.
Cheers.
 
#12
Hi Hammerworks,

Just seen your post on reflating the HD-3P and an amazed - and impressed. I never thought of that.
At Hi-Fi World magazine we produced World Audio Design kit loudspeakers using this tweeter, back in the 1990s and sold large quantities, even though they cost £100 each then! Few commercial loudspeakers ever used the HD-3P because of its price. Unfortunately, readers regularly contact us about their 'deflating tweeters', often in despair because it had a unique sound. It is probably one of the purest, sweetest and easiest yet accurate (under measurement) tweeters ever. However, it only reached down to 6kHz (4k later I recall) and the front face plate was so large it was always more than a wavelength from the midrange, so phase matching was never ideal. We asked Audax to fit our own smaller plate, but they were not interested, even on an order for 50 pairs.
Can you let me know about the fix please? You can e-mail me at publisher@hi-fiworld.co.uk (it is an open, public address). If you want to keep it secret for commercial reasons, just let me know.
On a related issue I see Audax drivers still being sold and wonder whether they are old stock or new manufacture. It looks like someone bought the Audax tooling, looking at the remaining inert website. I am awaiting replies from some French contacts and will let this forum know if I can dig up anything interesting. Audax made a great range of drivers but were hopeless to deal with at the time.

Noel Keywood, publisher, Hi-Fi World magazine
 
#13
hello every one
I am a new comer on Diyaudio forum. I found the forum looking for a method to repair my Leedh ICA loudspeakers.
Hi Hammerworks I am interested by your method to reflate the HD-3P. Please would you mind sending me your method as I don't want to change my equipment. Thank you for your help.
Best regards
Dom
 
#16
Audax hd3p

Hi all,
I just joined this forum, not as fanatic engineer but as a fanatic high-end Belgian music lover since...50 years and having tried many music reproduction systems. At present and since 10 years I play the legendary black laquered Leedh Nacza loudspeaker system which contains the HD3P's. They still perform extremely well and I never had any problem of the kind described. Moving soon to an appartement due to retirement I may have to sell them but, very sadly so !
Virgilius
 
#19
Hi Hammerworks. I built the Hi-Fi world loudspeaker KLS Gold II using the HD-3P only to have them deflate on me. I subsequently found a pair on ebay to replace them, only to find they eventually went flat as well. Now I have four deflated tweeers, and would really appreciate finding out about the reflation method you use. My email is sdroyd@yahoo.co.uk
 
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