Snell Type A Tweeters

[Guest Bluzmaster]

Hey there -

Presently working on some abused Type A's. Can anyone confirm the original tweeters used in these?

The general consensus is the Audax HD 12X9D25. My confusion is whether these were 4 ohm (as I've been told by pretty reliable sources elsewhere) or 8 ohm.

The Audax website archives do not show a 4 ohm version of the 12X9D25.

Before I take the puchasing-plunge and buy the recommended equivalent replacements, I need to confirm the ohms. Perhaps another owner out there could test theirs w/ a VOM and tell me whether DC resistance comes up 6.x or 3.x ohms.

Recommended equivalents are the Audax TW025A0 (but the TW025A10 is the 4 ohm) or the TW025K, buit the 'K looks like only available in 8 ohms.

Getting just a bit convoluted.

Thanks,

B

[Pete B]

Hey there -

Presently working on some abused Type A's. Can anyone confirm the original tweeters used in these?

The general consensus is the Audax HD 12X9D25. My confusion is whether these were 4 ohm (as I've been told by pretty reliable sources elsewhere) or 8 ohm.

The Audax website archives do not show a 4 ohm version of the 12X9D25.

Before I take the puchasing-plunge and buy the recommended equivalent replacements, I need to confirm the ohms. Perhaps another owner out there could test theirs w/ a VOM and tell me whether DC resistance comes up 6.x or 3.x ohms.

Recommended equivalents are the Audax TW025A0 (but the TW025A10 is the 4 ohm) or the TW025K, buit the 'K looks like only available in 8 ohms.

Getting just a bit convoluted.

Thanks,

B

I agree that it would be good if someone could confirm the exact model number

and impedance or DC resistance for the tweeter.

It looks to me based on the crossover schematic that the tweeter was probably 4 ohm,

this is an educated guess. That Audax tweeter was very popular and came in many

variations. The 12X9 referred to the rectangular face plate, it was also available in

the round 100D25 version, in both 8 and 4 ohm versions. This then evolved into

the 100D25HR that had different motor geometry and higher efficiency, and then

again into the TWO25A0 and A2 which I believe changed the motor geometry

again, and used a catenary shaped dome. Some of these were available with

ferro fluid so there were many variants. I've actually got a long write up about

this, and I don't remember the exact details at the moment.

Fs of the 12X9D25 was 800 Hz +/-120 Hz, the later TWO25A2 was 900 Hz.

The early Spica TC-50s used the 100D25 in 4 ohm. I have the later revised version

of the TC-50s that use the DTW100T25 in 4 ohm. I believe that the 4 ohm replacement

domes from the TWO line will fit the DTW100T25 driver but not the earlier 100D25, I

have a pair here from Madisound, the part number for the dome alone is RWO25A2.

You can buy the latest TWO25A0 8 ohm tweeter, the 4 was not available last I checked

and install the 4 ohm domes to get a 4 ohm driver.

It is really not the same driver as the old 12X9D25 -- just a caution.

See the reference here to the Spica TC-50 on the Madisound Retrofit page, they

claim that the new tweeter is a replacement, but it is not exact as I understand it:

http://www.madisound.com/services/retrofits.php

I'm considering this low cost driver as a possible replacement also:

http://www.madisound.com/catalog/product_i...c18a8973cfb3b62

[Pete B]

Here's a link to some data on the modern 4 ohm version:

http://www.madisound.com/pdf/printcatalog/audaxcatalog.pdf

Many of these drivers were out of production about a year ago

or so, then I heard a few months ago that they were back in

production. This is stated at that link "Audax is now produced

by AAC of France" I don't know any details about this.

[Guest Bluzmaster]

RE: The 12X9D25 sensitivity rating.

One thing that's bothering me is that I have not yet found any specs for the 4 ohm version of the 12X9D25. (the info on the Audax site refers only to the 8 ohm).

The 8 ohm 12X9D25's E = 89dB. Tweeters we have been discussing as "equivalent" show 3 - 4 dB greater E. Kind of throws the balance of the system off a bit, don't you think?

I would feel much more comfortable if we could find someone to post the specs on the 4 ohm 12X9D25.

[Pete B]

RE: The 12X9D25 sensitivity rating.

One thing that's bothering me is that I have not yet found any specs for the 4 ohm version of the 12X9D25. (the info on the Audax site refers only to the 8 ohm).

The 8 ohm 12X9D25's E = 89dB. Tweeters we have been discussing as "equivalent" show 3 - 4 dB greater E. Kind of throws the balance of the system off a bit, don't you think?

I would feel much more comfortable if we could find someone to post the specs on the 4 ohm 12X9D25.

This is a familiar discussion, the SPICA TC-50 guys are constantly asking for this,

as the tweeters do often fail. I have two Audax data books, one has the old

12X9D25 and many variants, however data is provided only for the 8 ohm version.

I've never seen data for the 4 ohm versions.

Here's an Audax archive: http://www.hautparleur.fr/

Here's the 8 ohm data sheet: http://www.hautparleur.fr/_audax/hd12x9d25.jpg

You can find my discussion of the early SPICA TC-50 tweeter (same driver as the Snell

but with a round face plate), and the 8 ohm data sheet here:

http://members.aol.com/basconsultants/sptc50_drv.htm

[Pete B]

I posted this on a SPICA forum, which is based on emails where I tried to help a

TC-50 owner replace the domes on the early HD100D25 4 ohm. I've learned more

since writing this and I don't believe that the current replacement domes are

correct for the early HD100D25:

I've been following and using Audax/Polydax tweeters for probably more than 20 years and recently pulled out my old literature to answer a few questions about replacement domes for the TC-50 tweeter. It would help if anyone on the list has noted the tweeter part number for the new or old versions of the TC-50 and could post them here. Measured DC resistance would help also.

This is a summary of some email discussions that I recently had:

I don't believe that the RWO25 types that you, Madisound, and I mention are exact replacements for early (Those with the Polydax HD100D25 4 ohm) TC-50s, however, I do believe that they fit but will result in a brighter sound with their higher efficiency.

I spoke to Tom Moran some time back who has a TC-50 page and his system (serial #5413) uses the Polydax HD100D25 4 ohm, and he tells me that the DC resistance measures 3.1 ohms. They made many different versions of this basic tweeter, large and small magnet, round and square faceplate, with ferrofluid and without, 4 and 8 ohm.

The 12X9D25 is the square face plate version and I expect that it is an exact replacement, if it's truly 4 ohm, check the magnet size and if it's the same you could probably just swap face plates. I'd be curious to know the DC resistance of both your old and new tweeters.

To confuse things even further there was an HD100D25HR with a 2mm long voice coil and gap height rather than 3mm in the non HR version. The moving mass is lower and voice coil DC resistance slightly lower 5.5 vs 5.8 ohms resulting in higher efficiency (up by 2.5 dB). Fs is 900 as compared to 800 Hz for the non HR version. I don't know if any TC-50s used the 4 ohm HR version.

The Vandersteens that I have use an 8 ohm, 12X9 version, with Ferro Fluid. They add FF to the end of the model number when ferro fluid is used. Ferro fluid is easy to remove if the ones you get happen to have it.

If you have to swap the new domes into your old tweeters I'd take a close look at the old and new domes side by side. Is the dome shape the same, the voice coil length, diameter, and position on the former the same? Measure the DC resistance, is it the same +/- 5 to 10 percent? If the tweeters in your TC-50s are the RWO25A0 version then if the 12X9 domes fit you'll be "making" an HD100D25 type tweeter which has lower efficiency.

I happened to come across my old polydax/Audax literature after I made the web page and while the TW025A0 looks very much like the HD100D25 it has a "catenary" shaped dome, a 1.6 mm long 2 layer voice coil with a 3mm high gap, Fs = 900 Hz, no Ferro fluid, and 91 dB efficiency. I've seen talk of SPICA going to a tweeter with a 2 layer voice coil in later models and perhaps this is the one with the 4 ohm coil of course, all of the other tweeters I mentioned above have a 1 layer voice coil.

These 2 layer and the HR tweeter versions are more efficient so a resistive pad should be added if they are used in older TC-50s.

People on the Spica list mention a new woofer in the 1988 version, I wonder if that's the one that also used the newer RWO25AO tweeter with the 2 layer voice coil?

---------------------------

This last question was based on a statement on the Madisound pages where they claim that

the latest tweeter is an exact replacement which is incorrect. I now own the newer TC-50,

the tweeter model number is DTW100T25F 4* (measured DC resistance is 3.14 ohms) and

it is not exactly the same as the latest TW025A2 tweeter with the catenary dome.

I have replacement domes for the TW025A2 and the DC resistance measures 3.6 ohms for

both.

[Pete B]

Another potential 4 ohm solution, note that this has shorting rings for lower

distortion, a feature usually found in much more expensive drivers:

http://www.madisound.com/catalog/product_i...roducts_id=8300

[Guest Bluzmaster]

Pete -

Those look great. I've never seen a tweeter w/ such low Fs and high power handling. It doesn't state what material the dome is. Do you know?

B

[Guest Bluzmaster]

O.K. I checked them out. They have fabric domes. But who are these guys?

Company debut at the Winter 2008 CES in Las Vegas! You want me to be the guinea pig?

[Pete B]

O.K. I checked them out. They have fabric domes. But who are these guys?

Company debut at the Winter 2008 CES in Las Vegas! You want me to be the guinea pig?

I spoke to a gentleman at Madisound about this SB company. Ex ScanSpeak designer,

fabrication at a top plant in India. I dislike seeing jobs lost overseas but I must say that

the price of some drivers in small quantities is getting to be rediculous. I did not like the

fact that Usher for example copied the look of Scan Speak drivers and have avoided

them for this reason as good as they are.

I try out a lot of drivers, so go ahead they should work just fine. You really do not

want a lower Fs, rather it should be as close as possible. You could remove the dome,

if you have steady hands, and plug the pole vent to raise Fs.

[Pete B]

I spoke to a gentleman at Madisound about this SB company. Ex ScanSpeak designer,

fabrication at a top plant in India. I dislike seeing jobs lost overseas but I must say that

the price of some drivers in small quantities is getting to be rediculous. I did not like the

fact that Usher for example copied the look of Scan Speak drivers and have avoided

them for this reason as good as they are.

I try out a lot of drivers, so go ahead they should work just fine. You really do not

want a lower Fs, rather it should be as close as possible. You could remove the dome,

if you have steady hands, and plug the pole vent to raise Fs.

Zaph tested this driver and the distortion performance is quite poor in my opinion,

the driver has potential but they've got to fix this issue:

http://www.zaphaudio.com/tweetermishmash/

I can't suggest this driver at this time.

[Carlspeak]

I'm working on a pair of Model A's and measured the DC resistance of the midrange and tweeter with my DMM. Got 4.5 ohm on the tweeter and 5.6 on the midrange. However, following the measurements, I removed the midrange from the cabinet and found a 2 ohm resistor wired in series. I can't say with certainty if this was an original part. The back of the magnet was marked by hand with a marker and no MFG. info.

Also attempted to remove the tweeter but found it was glued in and didn't want to risk damage to the delicate hardboard baffle.

FWIW...