Need help ID'ing Audax/Polydax driver

Hi, I am attempting to rejuvenate an older pair of Watson Labs speakers

(http://www.dayton-wright.com/WATSON-7_.html)

that use Polydax/Audax drivers.

I am missing one of the 8" (210mm) drivers and am looking around to see if anyone might have one available to sell to me. Unfortunately, no stamp or label information is present on the driver so I am unable to identify the driver. So, I have taken a couple of pictures in hopes that someone might be able to identify it visually for me. The pictures are below and/or attached:

http://www.flickr.com/photos/pneumonic/3215982798/

http://www.flickr.com/photos/pneumonic/3215132655/


Further, I have been told that I might look into a replacement Audax driver for it. The model of this replacement driver is “hm210g0”

If anyone happens to have either the original driver in the picture or the replacement, and wishes to sell it, you have an interested buyer here.

I can be reached via PM or by email pneumonic at rogers dot com.

Thanks

***** EDIT: I have been told it is a Bextreme cone with inverted surround. Stamp lettering on back of magnet appears to start with HD20 B25 ......

That is exactly what it it - an HD20B25H#.

20 = cone diameter in CM
B = bextrene
25 = voice coil diameter
H# - voice coil indicator; if # = 2 it's 2 layer, 4 = 4 layer.

The spec sheets are out there online somewhere, maybe on Audax' site in the historical info portion. I do recall it had a rather low efficiency as well as a low resonant frequency (27 hz).

Unfortunately, I haven't any to spare. I have 4 of them in my Mariah LS-2s, and three of them had to be rejuvenated with new Flexlead where the mice ate it. They sound very, very smooth IMO. Good luck on the replacement!

bakes said:

That is exactly what it it - an HD20B25H#.

20 = cone diameter in CM
B = bextrene
25 = voice coil diameter
H# - voice coil indicator; if # = 2 it's 2 layer, 4 = 4 layer.

The spec sheets are out there online somewhere, maybe on Audax' site in the historical info portion. I do recall it had a rather low efficiency as well as a low resonant frequency (27 hz).

Unfortunately, I haven't any to spare. I have 4 of them in my Mariah LS-2s, and three of them had to be rejuvenated with new Flexlead where the mice ate it. They sound very, very smooth IMO. Good luck on the replacement!

Click to expand...

Spot on!

The tweeter looks like it is probably the standard Audax 1" soft dome HD100??? forget the number. Some have rectangular faceplates, some round.

Audax 8" Bextrene units are used in old Tangent speakers from the 70s, listening to a pair now, RS2 also used in RS4

Many thanks, gentlemen.

I may have found myself a pair ............

Nice amp Radfordman. Brings back fond memories.

They are a very nice sounding unit.

Can be seen here in my Tangent RS2

http://www.audiokarma.org/forums/showthread.php?p=2403122#post2403122

Great that you may have found some.

Let me know if you can't source these woofers. A guy I work with may have a pair stashed away. I can certainly check...

Regards,
Gordon.

The pair I'm looking into are being pulled from a pair of Angstrom speakers and are local so I'm keeping all of my extremities crossed.

Gordan, thanks for the offer. If the ones in the Angstrom's aren't right I may take you up on your offer if you don't mind.

Radfordman, I had a STA 25 that served me faithfully for 5 years. One of the nicest sounding tube power amps I have ever listened too.

Pneumonic said:

Radfordman, I had a STA 25 that served me faithfully for 5 years. One of the nicest sounding tube power amps I have ever listened too.

Click to expand...

Agreed, had mine 35+ years! have not found anything better (solid state or tube), not for the lack of trying!!

It was bought second hand, has never needed any repair. I have recently (just for fun) replaced the original Mullard EL34s with KT77. The Mullards are still fine and in storage.

Incidentally, I built speakers for the UK Sales Director of Audax (Long time ago). These were for his home, driven by Quad 33/303. The speakers had that 8" Bextrene Audax +very large Audax soft dome mid +Audax 1" soft dome tweeter.

Radfordman said:

Agreed, had mine 35+ years! have not found anything better (solid state or tube), not for the lack of trying!!

It was bought second hand, has never needed any repair. I have recently (just for fun) replaced the original Mullard EL34s with KT77. The Mullards are still fine and in storage.

Incidentally, I built speakers for the UK Sales Director of Audax (Long time ago). These were for his home, driven by Quad 33/303. The speakers had that 8" Bextrene Audax +very large Audax soft dome mid +Audax 1" soft dome tweeter.

Click to expand...

Your Radford story is one I have heard repeated countless times now. I traded mine for some Classe DR gear many moons ago and have always considered going back. Most likely will some day.

The Watson Labs speakers that this Audax driver is going into sound quite spectacular when they are right. The guy who designed these is the Wright in Dayton Wright and the guy responsible for Stabilant 22. He's got some pretty radical design theories including the gas-linearized-compliance woofer system in the Watson Labs speakers I am having rebuilt.

Pneumonic said:

Your Radford story is one I have heard repeated countless times now. I traded mine for some Classe DR gear many moons ago and have always considered going back. Most likely will some day.

The Watson Labs speakers that this Audax driver is going into sound quite spectacular when they are right. The guy who designed these is the Wright in Dayton Wright and the guy responsible for Stabilant 22. He's got some pretty radical design theories including the gas-linearized-compliance woofer system in the Watson Labs speakers I am having rebuilt.

Click to expand...

Cool that you found a pair! :thmbsp: My only advice is to check whether they are H2 cp9s or H2 cp12s (it may say on the basket) - they have different T/S parameters; not vastly different, but you might notice a difference. Didn't find a spec sheet for the 4 layer coil one, so maybe my memory is playing tricks and these were the names of the different versions. Here's a jpeg of the spec sheet:

bakes said:

That is exactly what it it - an HD20B25H#.

20 = cone diameter in CM
B = bextrene
25 = voice coil diameter
H# - voice coil indicator; if # = 2 it's 2 layer, 4 = 4 layer.

The spec sheets are out there online somewhere, maybe on Audax' site in the historical info portion. I do recall it had a rather low efficiency as well as a low resonant frequency (27 hz).

Unfortunately, I haven't any to spare. I have 4 of them in my Mariah LS-2s, and three of them had to be rejuvenated with new Flexlead where the mice ate it. They sound very, very smooth IMO. Good luck on the replacement!

Click to expand...

Exactly!! Nice visual ID, and yes, the model number is clearly visible on the back of the magnet. If you are searching for them, especially on Ebay, do an international or worldwide search for Audax (French name), Sonaudax (British name), and Polydax (US distribution) IIRC. These came in a number of variants besides layers, also different ohmages as well. This model was incorporated in the DIY Tabor speaker which I think was part of the impetus for the Tangent line (commercialized version so to speak).

The tweeter bears a visual relationship to the Audax HD12X9D25 1" silk soft dome that was so prevalent in the late 70's and early 80's British speakers. However, I think I can see a little bit of a horn-like loading structure around it. So would think it is related to the 1 or 1.25" dome tweeter with integrated horn from either Dynaudio or Morel. I think a similar tweeter was used on the Fried Beta satellite speaker. A very stout and fast tweeter IIRC.

OP, can you get us a pic front and back of the tweeter and of the mid driver? Thanks, interesting speakers you're trying to work up there!!

Bart

HI Bakes,

I've got the same Polydax catalog from way, way back too but its also buried in storage boxes along with my Dalesford bextrene driver catalogs. Used to get speaker information from Madisound (Wisconsin), Meniscus (Michigan), and JustSpeakers (San Francisco)/A&S speakers (Denver). I knew the owner of JustSpeakers when he was getting started - walked into his older home where he was running his business and saw just stacks of raw Audax boxed drivers - that's where I bought my Tabor parts and started my DIY habits.

here's a net pdf copy of a 2000 parts catalog from long time but recently closed supplier Falcon Acoustics from England. The proprietor, Malcom Jones, was a true engineer with crossovers and designed and implemented most of KEF's crossovers from their beginning through the KEF 104aB series. He then left to found Falcon to build custom inductors for the speaker industry. You'll see the Tabor parts listed alongside networks 19-20. The --C9 or C12 designation was the length of the voice coil in mm. which changed the voice coil weight, inductance and consequently the Thiele-Small (TS) parameters of the driver.

Probably more than you ever wanted to know about drivers!!

http://diyaudio.co.kr/wwwboard1/data/board3/falcon.pdf

Regards,

Bart

Wow, thanks bakes and Bart. Much appreciated.

I've got info on the two drivers. They were taken from a pair of Angstrom's.

The one is stamped HD20B25H 8 CP12 .... there is an omega (ohm) symbol after the 8 indicating impedance value no doubt.

Below it is printed CN 106TN

The other one is printed only as HD20B25H 8 with an omega (ohm) symbol after the 8. No other label information is discernible.

Both have "Made in France" Polydax labels on them.

Unfortunately, I believe the existing driver that I have has a 4 ohm stamp on it. I won't want to use one 8 ohm speaker with a 4 ohm one so can I simply use these two newly acquired 8 ohm units and be alright? Or will the crossover need to be re-worked by going to 8 ohm drivers instead of 4?

..... Bart, I will get you some better pictures tomorrow sometime. In the meantime here are a couple more that I had already taken. Probably not what you are after ........

**** Note in the bass woofer picture the Melmac lunch plate that is glued to the cone in order to add mass. ***

Here is designer Mike Wright's philosophy on the woofer system in this Watson Labs design.

"Only the woofer/subwoofer were not bipolar. These relied in the use of SF6 (sulfur hexafluoride) gas (which is inert), to increase the virtual volume of the enclosure. As SF6 is an 'ideal gas', it operates as an 'isothermal' spring, thus avoiding the problems with 'acoustic-suspension' loudspeakers that operated partially as an isothermal and partially as an adiabatic system. Some designers seemed to lave little knowledge of Boyles Law or the Laws of Thermodynamics.

In effect, the use of SF6, increases the virtual volume of the enclosure by a factor of 27! As can be appreciated, this both lowers the distortion as well as permitting a lower resonant frequency of the woofer.

But to use this, a larger cone mass is needed and the suspension has to be much more compliant. This bring up the problem of 'gyratory-moments-of-inerta' if the woofer cone is to remain stable during its excursions. The usual concentration of mass near the voice coil does not accomplish this.

What is needed is to shift the effective cone mass farther away from the cone's center-of-mass. Doing this increases the gyratory-moments-of-inerta and the cone is more stable. Wright used a near-flat plate on the front of the cone - with most of this plate's mass around the rim! He added an EPDM foam-elastomer as a damping element on the front of the disk."

BTW, here is some interesting technical reading on Wright's speaker design philosophies for those so inclined.

http://www.dayton-wright.com/Watson-Credo.html


-Kerry

Not sure if its been mentioned, but there are at least two different size magnets fitted to the old Audax 8" Bextrene units. My first set of Tangent RS4 had big magnets, the second set small. Both my pairs of Tangent RS2 have the smaller magnet.

Beware of very early 8" Audax with white surrounds (where foams would be). The white surrounds can shrink a lot affecting the performance, in bad cases pulling the coil off centre.

Similar problem with white surround Spendor BC1, B&W DM4 bass units.

Well I have a pair of 2 way speakers that where built in Canada that use Polydax (Audax) tweeters HD12X9D25A tweeters and a pair of 8" Polydax (audax) woofers. The label on the woofer that I looked at is hard to read but this is what I thought it said 20625J4C12. I believe that it should read 20b25J4C12, what I thought was a 6 most likely is a B.

No name on the speaker anywhere, crossover board is labelled Mirage. Not badly built but the bass is too loud compared to the tweeter, I believe that a better crossover design would help. I did like the sound of them just the problem of excess bass.

Is the Vas of the driver 39.5l as it is hard to read the data sheet.

What are the value's on your crossover and it's design.

Presently I am away from home so this is all I can tell you at this time.

Hi happyears,

Your speakers echo the trend in GB for those drivers. I might guess the Mirage speakers were ported and the woofer you have have mounting "ears" extending from the frame circumference like the OP's woofers. Likely then the drivers, if Bextrene, are very similar. If you guys measure the magnet diameter and height, we can then determine if the magnet spec is the H or J and which is small or larger (my vague recollection is the H is larger and the J is smaller).

Before you do anything about the imbalance, you might want to review your crossover too and then take a snap of it for us. My bet is there are Non-polarized (NP) electrolytic caps there and it very likely they need to be replaced after all these years. That alone may help a lot since tweeters usually are much more sensitive and can provide a lot more output per watt than the heavy and heavily damped bextrene cones (as good as they are at providing some very good quality sound, they usually were fairly inefficient). Also, if there was any type of L-pad (usually not), that would also need cleaning. One other thing to look for is the attachments of the wire to the tweeters and crossover - many of them used some for of faston connector (spade type) and these may have corroded, come loose, or just plain to make good contact, despite how they look. Refasten with a lot wiggling or remove, cut off 1/2 inch, restrip and resolder. That may help.

Regards,

Bart

The Tangent RS2 (small magnet Bextrene Audax 8" + KEF T27) I find to be very nice speakers.

I have a boxed brand new pair of the bigger magnet Audax 8" Bextrene, can't remember if they are 2 or 4 layer coils. I bought them years ago for the Tangent RS4

Thanks for the continued advice, fellas.

I did buy the three 8" woofers and have included a picture of one of them. I may also have a line on some 4 ohm ones as well.

I also have included some other pictures, including x'over picture, Bart. I see a bunch of electrolytic caps in that x'over.

The tweeters are Polydax and stamped HD12X9D25.

I can snap additional pictures to include if anyone wishes.


-Kerry

......... for some reason my other uploads (crossover and upward firing tweet) have failed.

I'll play around and see what I can do.

Pneumonic said:

Thanks for the continued advice, fellas.

I did buy the three 8" woofers and have included a picture of one of them. I may also have a line on some 4 ohm ones as well.

I also have included some other pictures, including x'over picture, Bart. I see a bunch of electrolytic caps in that x'over.

The tweeters are Polydax and stamped HD12X9D25.

I can snap additional pictures to include if anyone wishes.


-Kerry

Click to expand...

With Poyldax on them, they are later production than ones with Audax on, that may be a good thing as they will not be as old.

Any more pics would be interesting.