Audax HD-3P DIY Re-gassing Part II

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Audax HD-3P DIY Re-gassing Part II

Post by JohnG » Sat Apr 15, 2017 1:26 pm

Wifey Awoke "Hoo Rah"
After a little search through Wifey Domain it appeared, a multi pack of PTFE tape, to the words " I never put that there"
I was back on track.
Step 1,
Removed slot head screws from air inlet, I then cleaned the air seal residue from earlier attempt.
I replaced the screw back into the hole leaving the countersink exposed so I could wrap a small amount of the PTFE tape around it, about
10- 20mm in total length, leave the initial length longer and trim when done.
Apply a little pressure to PTFE tape by tightening the screw a little.
Step 3,
I wanted a better control of the re-gas procedure to get a better pressure behind the diaphragm, so I put this method into practice.
The tweeter had a sticky soft foam disc set behind it in the enclosure, I took the soft foam and folded it in half. I then used a scissor to cut a
small hole in the centre, two little mirror image "V" cuts allowed a hole about 10mm to be achieved.
I put the foam pad on the back of the tweeter with the air inlet screw sitting exposed in the scissor cut hole.
I then took the tweeter out to my car.
Step 4,
I plugged in my 12V tyre air compressor, I placed the hose nozzle onto the foam covering the hole and air inlet to create a air seal.
Whilst watching the Gold Peizo Diaphragm, I switched on the compressor. The re-gas is immediate, less than a second in time.
Pull the nozzle away from the foam. Add a little more pressure to air intake screw.
Check the Gold Peizo Diaphragm for tension, I chose a taught skin with a quick to reset reaction when pressed.
To achieve this you may have to apply the nozzle to foam and air intake a few times, applying a little extra tightening to the screw after
each air intake.
When the desired tension is achieved on the diaphragm surface, fully tighten the air intake screw.
The second tweeter will be a breeze, just be sure to check each tweeter has a similar surface tension.

I encourage all those who watched there hard earned outlay for the HD-3P evapourate, follow these steps and new life will be breathed into
this Very Good Tweeter.

Oasis are filling the house with their tunes, and it sounds great where ever you are, my Ridgeback Dogs have stole the listening sofa.

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Re: Audax HD-3P DIY Re-gassing Part II

Post by Greg » Sat Apr 15, 2017 6:16 pm

I'm not sure why you have started a new thread on the same topic.

What you are doing is interesting but you are covering ground that a number of others before you have already done. Reading on the internet I conclude that the most you can expect to achieve is a temporary solution. You need to ask why the pressurised diaphragm lost it's pressure in the first place. You have not sealed a leak. You are just repressurising a leaky chamber. Success has been recorded as variable from a week to more than two years retained inflation.

What was used to originally pressure the diaphragm? You are using air. It is unclear what Audax originally used, preferring the foo marketing mystery of it being something special. It has later been suggested that it was nitrogen which is a reasonable assumption as this could explain an osmotic transfer of the gas through the membrane. All so called repairs I know of use air.

You then need to consider what is the optimum pressure to inflate the diaphragm to. I don't think Audax' original spec is known. What you will find is the higher the pressure, the greater the SPL of the tweeter and this is important because the SPL needs to be correct to ensure a balanced sound with the other drivers and between stereo speakers.

A member here, Brian experimented with trying this repair but gave up in the end because of the ongoing need to constantly recharge the diaphragm. You could as you suggest incorporate a facility to easily top up with air as and when required, but how long this would work for is debatable. Even who used to offer this type of solution would not guarantee it, stating it might maintain pressure for two years but equally it might not last beyond a fortnight.

I don't want to be the spoiler of your fun, but the conclusion of many is that it is a waste of time because the original Audax design was fundamentally flawed and the real solution is to replace the tweeter which just needs a tweak to the crossover. Several different tweeters have been used for this and to get similar performance, but at a price, surely the Seas Millennium is the way to go. I have heard this tweeter and it has a remarkable liquid clarity. Were it to go into WAD KLS3's, they are speakers of sufficient quality IMO (when correctly built) to justify the the £400 outlay. Alternatively you could use, as in the original Mk1 KLS3, the Audax TW025M1 for about £80. A copy of the filter required, designed by our own Scottmoose can be found here. ... php?t=7414

Anyway, all the very best with your experiments.

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Re: Audax HD-3P DIY Re-gassing Part II

Post by pre65 » Sat Apr 15, 2017 6:26 pm

To me, the mere use of the word "gas" would suggest something other than air.

But if you like how they sound after the procedure then just enjoy.
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)

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Re: Audax HD-3P DIY Re-gassing Part II

Post by JohnG » Sat Apr 15, 2017 9:40 pm

This was very easy to achieve, speakers picked up Friday, the pondering of a replacement set of tweeters at £400, got me thinking about previous read articles on the repair of the HD-3P.
Much of the comments raised I agree with, there are uncertainties, as to the cause of the problem
and the longevity of a repair.
The Owner of Moca Audio, was a Audax Engineer
I believe, he refills the tweeter with air, and the self refill if required by the user of the modified tweeter is done using air.
There is not any clear instruction supplied on how to apply the correct diaphragm surface tension.
I have been listening today with my family and to our untrained ears it sounds very good, my daughter thinks the vocals are very similar to the ESL57. I was mainly tuning the bass to the room, I have got a clean cut off now by reducing the port diameter.
I have never seen comprehensive instructions on how to achieve a refill the deflated diaphragm, so these will help with any individual who has a curiosity, and wish to work with a HD-3P.
The two articles relate to two separate operations, the moderators can combine both posts if they see the need.

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