Audax HD-3P DIY Re-gassing Part II

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#1 Audax HD-3P DIY Re-gassing Part II

Post by JohnG »

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

Post by Greg »

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

Post by pre65 »

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.
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
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#4 Re: Audax HD-3P DIY Re-gassing Part II

Post by JohnG »

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

Post by JohnG »

It has been almost Three Years since I started this Thread.

I used the WAD KLS 3 Speakers with Pumped Up HD-3P's during 2017 and for part of 2018,
they even got an appearance at a Owston, where 'Steve s', Nick and a couple of others had a listen on the Sunday.
Shortly after this the KLS 3 were to have a little extra work done following a advice and were stripped of their Drivers.
This did not materialise and the Drivers were put in storage.

I then returned to my Quad 57's that progressed into creating a Stacked Array.
Following this I also ended up with a Dedicated Listening Room in the home and worked with the Room Acoustics getting to a place that to the ear allowed for a very attractive presentation from the Stacked Array.

Fast forward to Late 2020,
I had a system issue I was trying to understand and put a Two Way Cabinet Speaker into use.
These were the antithesis of the Quads, coloured, obscure and very much wanting in their overall performance.
But! I thoroughly enjoyed them, and they remained in use until the weekend past.
It was like being in Pub with a Band Playing and I was sitting next to a PA Speaker enjoying the show, and I forgot the HiFi thing and just rolled with the music.

On the weekend Past I could not stop myself, I had to try out the KLS 3 in the Dedicated Room and compare them to the Two Ways that had done so well to offer simple pleasures.

Plenty of Head Scratching and Room Rearrangements taking place to try and recollect the hiding places used for the Speakers Parts and dig out the Cabinets that were concealed inside my DIY Bass Traps.

On Sunday Afternoon all the needed pieces were in one place to complete the reassembly.

When I was unboxing the HD-P3 I was struck with the knowledge I would need to re-inflate them, and the Bloody Kit used in the past was buried in a cupboard I had made the Door inaccessible, as it was now concealed behind the Room Treatments and 57 Stacked array.
I had a 'B**ls to this Moment' and nearly Jacked in for the day.

Then there was the surprise, there was not a Wrinkly Grape Gold Foil on the HD-3P when unboxed but a Gold Foil that was showing surface tension.
The second Gold Foil was looking identical.
I then had to check the Surface Tension of the Foil, nothing scientific, but I was sure I would not attempt to put more inflation pressure into the Tweeter when I did the Work previously.

I thought I would leave the final analysis for the level of inflation to the listening experience that was envisaged.

I am wanting at anything EE, and used a Soldering Iron for possibly the first time in 25+ Years and it was maybe my third or Fourth Time ever using the tool, '
'or was I the Tool :lol: '

The Speakers work, they have been in use since Sunday.
The HD-3P seems to be on the money with the Frequency, I am extremely impressed with the Presentation.

I tuned the Port to lean up the Bass a little and let it be less woolly and this served the Mid's and Highs in a Upward Improvement.

I then changed the Mounting Methods and this also moved the whole performance of the Speaker in a Upward Improvement.

I am in a Honeymoon Period, but can't contain my expressing of my satisfaction with the KLS 3 Speakers, now resident in the Listening Room, where they have made their Debut.
In this environment they are Keepers I am already sending out invites for the New Freedoms that are soon to be given.

Do they surpass the Stacked Array ? It doesn't matter they have blown me away, and I feel confident that the guests being lined up will find a Smile for them as well.

The added Bonus being that the Method I used for the re-inflation of the HD-3P has lasted for a period of approx' Two Years was not expected, but is very much welcomed surprise,
especially when I don't know how to predict when a need might arise to re-inflate them again
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