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Polydax / Audax HD 12x9 D25 Tweeter Replacement

David_NC

David_NC

Super Member
I recently rediscovered my pair of 3D Acoustics 3D6 speakers when I was last in NC. This is a smallish 2-way bookshelf that really impressed me, so I shipped them back to CA. They worked fine when shipped, but today, I fired them up, and one has no highs. Removing the tweeter and testing for continuity shows an open coil. I was hoping it was a bad cap.
So, I need a to replace a tweeter. As the title says, it's a Polydax HD 12x9 D25, shown below:
Vintage-Polydax-Audax-Tweeter-HD-12-X.jpg

I'm not finding any online anywhere. Other than keeping an eye on eBay, I'm curious if there are any comparable tweeters that I can use. If I went this route, I'd change both so they'd match. Any thoughts, suggestions, or ideas would be appreciated.
 
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Falcon Acoustics. You going to need 2 so they match.

Screenshot_20210611-205402_Samsung Internet.jpg

They came off like 3 dbs hotter the the original I had. Very close sounding though. However the one good tweeter I had left comparing it against could of been damaged / chunky ferrofuild and maybe bad doping on the cloth. Alot of factors.
I would recommend them as replacement though.
 
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You don't need to buy the square plate version from Falcon. You can certainly buy the round plates and swap the face plate as well. Might be a tad cheaper too.
 
David_NC,
I have a pair of these same Polydax. I got them at an auto swap, they just looked cool so I picked them up, made in France. I’ll send you a PM.
Mark
 
I can't remember the difference between the round and square. However I don't think they interchange as with ease as mentioned above. As I recall the diaphragm is glued to the faceplate plus soldered to the terminals. I remember going through a old polydax catalog in French and the specs being different. I could be wrong.
 
Audi0 said:
I can't remember the difference between the round and square. However I don't think they interchange as with ease as mentioned above. As I recall the diaphragm is glued to the faceplate plus soldered to the terminals. I remember going through a old polydax catalog in French and the specs being different. I could be wrong.
Click to expand...
I think the same dome works for both, but once it’s attached to the faceplate, it’s pretty much there. I don’t think I could remove it without damage.
 
Looks like the TW025A_ have somewhat higher resonance frequencies (in range 1100 to 1200 Hz) than the HD 12x9 D 25 (800Hz +/- 120Hz) and voice coil inductance seems to be lower. Not sure whether it makes a difference in your application but it's worth noting that there are differences. "Direct replacement" presumably refers to dimensions and mounting considerations. Sensitivity spec is 1dB higher for TW025A_.

Specs for the HD 12x9 D 25 are here.
 
audiotemp said:
Looks like the TW025A_ have somewhat higher resonance frequencies (in range 1100 to 1200 Hz) than the HD 12x9 D 25 (800Hz +/- 120Hz) and voice coil inductance seems to be lower. Not sure whether it makes a difference in your application but it's worth noting that there are differences. "Direct replacement" presumably refers to dimensions and mounting considerations. Sensitivity spec is 1dB higher for TW025A_.

Specs for the HD 12x9 D 25 are here.
Click to expand...
I ordered two TW025A1's and installed one to replace the dead HD D25. As predicted, they do not sound alike; the one with the original tweeter sounds much better. It sounds like a smooth, well-designed 2-way sealed speaker, which it is. I initially thought the one with the new TW025A1 was fine, but its level is too high, likely due to the sensitivity, impedance, and other differences.
This leads me to my next question - how do I get the new tweeter to work properly with this speaker? I suppose I could try resistors in series with the tweeter, but I'd have no clue where to even begin. Any suggestions would be appreciated.
 
Leave the old one in. And make a attenuator circuit on the back of the tweeter with resistors. Then take steps in slight increments and match with the old one. Playing mono music. So channels are the same. When done just glue the resistors to back of tweeter with hot glue. And reinsert tweeter. Then Copy resistor setup with other speaker.

As a note I kind of knew these replacement come off hot. Like way hotter then the 3db mentioned. I had the same issue. 9db or 6 db hotter. (According to the generic calculator) I didn't want to type that as it may start an argument.


calculator here this is for keeping the same load presented to crossover while lowering dbs.

http://www.sengpielaudio.com/calculator-Lpad.htm
 
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Audi0 said:
Leave the old one in. And make a attenuator circuit on the back of the tweeter with resistors. Then take steps in slight increments and match with the old one. Playing mono music. So channels are the same. When done just glue the resistors to back of tweeter with hot glue. And reinsert tweeter. Then Copy resistor setup with other speaker.

As a note I kind of knew these replacement come off hot. Like way hotter then the 3db mentioned. I had the same issue. 9db or 6 db hotter. (According to the generic calculator) I didn't want to type that as it may start an argument.


calculator here this is for keeping the same load presented to crossover while lowering dbs.

http://www.sengpielaudio.com/calculator-Lpad.htm
Click to expand...
Thanks for the link. That's pretty much what I'm planning. What wattage rating on the resistors would I need? I know the tweeters aren't receiving the full input power of the amp, but I bet they'd still need to be rated over the 1/4 to 1/2 watt of the ones that I have on hand. I suppose I could try whatever I have to get the levels good and then buy some with the appropriate wattage rating, once I know what it is.
Re your side note: they def are hot. It's funny, but I initially thought the speaker with the new tweeter sounded better. It does have more detail, but that often seems to be the case with boosted highs. It didn't take a couple minutes of listening for the highs to start bothering my ears. These speakers, with proper / properly adjusted tweeters, are very nice and sort of remind me of smaller ADS speakers... not surprising due to their East Coast heritage, I suppose (New Hampshire). Currently, the accentuated highs on the one remind me of how most horn speakers cause me ear pain.
Once I get them straightened out, I'll post pics, etc. In the meantime, here's a link to the same ones: https://audiokarma.org/forums/index...ics-three-piece-speaker-system-3d610b.499822/
Thanks.
 
Audi0 said:
Leave the old one in. And make a attenuator circuit on the back of the tweeter with resistors. Then take steps in slight increments and match with the old one. Playing mono music. So channels are the same. When done just glue the resistors to back of tweeter with hot glue. And reinsert tweeter. Then Copy resistor setup with other speaker.

As a note I kind of knew these replacement come off hot. Like way hotter then the 3db mentioned. I had the same issue. 9db or 6 db hotter. (According to the generic calculator) I didn't want to type that as it may start an argument.


calculator here this is for keeping the same load presented to crossover while lowering dbs.

http://www.sengpielaudio.com/calculator-Lpad.htm
Click to expand...
I just completed the L-pad as directed by the calculator in the link:
IMG_1416.jpg
I used 4 ohm resistors, with 2 in series to equal the 8 ohms. It was a bit confusing at first until I broke it down in my mind. The 8 ohms in parallel simply drops the tweeter to 4 ohms, and the 4 ohm resistor in series brings it back to 8 while attenuating it... at least that's how I interpreted it! At any rate, it worked just fine the first time. I went with 6dB of attenuation, as this tweeter was very bright. Now, they sound very close, with the new tweeter plus modifications maybe being just a bit better. Thanks for the suggestion and link!
 
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