Thiel CS3.5 Replacement Drivers and Ohm

[mitchalee]

I recently bought Thiel CS3.5 loudspeakers as part of a lot. The drivers are all original. Both woofers are OK. Both mids are dead open. One tweeter is dead open. The other seems to work. Both woofers and the possibly OK tweeter measure as 4 ohms. I know the woofers are OK. And the tweeter seems OK. I know the original CS3.5 were 4 ohm speakers. Here's my puzzle: why does everyone recommend 8 ohm replacement mids and tweeters for these speakers? Are you sure the original mids and tweets were 8 ohms?

Tomorrow I will re-test the tweeter and re-measure it with a digital meter at my shop. But the junk meter I have at home says 4 ohms.

I know that one can use a 4 ohm woofer with any mid or tweet one wants and then just match with crossover design. The woofer will set the measured resistence of the whole system. However my experience is that it is generally cleaner and simpler to stay with matching drivers. So I am surprised that Thiel chose to mix and match. Am I missing something?

 

[RossW]

The original drivers were 8 ohm, you're measuring DC resistance not AC impedance. The D28 tweeter ranges from ~5-10ohms depending on frequency.

Tweeters are easy, the D28 was pretty common. The mids are tough. The recommended replacements are pricey and the originals were unique to the CS3.5. They do show up on eBay occasionally and they usually don't sell for too much (I think I paid $50 for my spare a couple years ago).

Do you have the bass EQ?

 

[mitchalee]

The original drivers were 8 ohm, you're measuring DC resistance not AC impedance. The D28 tweeter ranges from ~5-10ohms depending on frequency.

Tweeters are easy, the D28 was pretty common. The mids are tough. The recommended replacements are pricey and the originals were unique to the CS3.5. They do show up on eBay occasionally and they usually don't sell for too much (I think I paid $50 for my spare a couple years ago).

Do you have the bass EQ?

Yes. I have the EQ unit. Have not tested yet. Some people seems to think it subtly degrades the high end. I am skeptical about this. But noticed right away that the bass was too loud above 60 hz and too soft below that without it. So I will give it a test myself since I proabably would not listen to them much with the bass as is. Supposidly they are nearly flat to about 25 with the EQ.

With respect to the ohms, thanks a million! That does seem to be the conventional wisdom and what I expected. Except that almost always the DC resistence measures about 1.5 ohms lower than the manufacturers rating. So in my limited experience an 8 ohm driver would generally give 6 to 7 ohms resistance. I have encountered exceptions, but not many. This was just my experience and assumed that the exceptions were due to a lot more going into impedance than simple resistance.

But after measuring the whole CS3.5 system as 4 ohms, the woofers as 4, and the one working tweeter as 4.9 (I was expecting 3 or so), I was, and frankly still am, just a bit baffled. But as you say, I was just using a standard multimeter set to a 200 ohm range. So if I had a way to measure AC impedance, then I would get something closer to 8 at some standard frequency? This is where being short on theory bites me, I guess! Thanks again!

 

[mitchalee]

The original drivers were 8 ohm, you're measuring DC resistance not AC impedance. The D28 tweeter ranges from ~5-10ohms depending on frequency.

Tweeters are easy, the D28 was pretty common. The mids are tough. The recommended replacements are pricey and the originals were unique to the CS3.5. They do show up on eBay occasionally and they usually don't sell for too much (I think I paid $50 for my spare a couple years ago).

Do you have the bass EQ?

Yes, see above.

Tweeters Original DynAudio D-28 AF D2806 2A Made in Denmark; Replacements Usher 9930 or 9950, Dayton RS28F, MDT33, Morel MDT32S, Eton 25SD-1

Mids OriginalScanspeak 13M 8521 and 13M 3808; Replacements Scanspeak Discovery 10F/8414G-10, Scanspeak Discovery 12W/4524G, Scan-Speak 13M Midrange Replacement

Madisound:
Morel MDT32S $112.00 each = $224.00
Scanspeak Discovery 12W/8524G $64.90 each = $129.80
Subtotal: $353.80

or

Madisound:
Morel MDT32S $112.00 each = $224.00
Scan-Speak 13M Midrange Replacement $210.00 each = $420.00
Subtotal: $644.00

Or perhaps for mids Scanspeak 10F/8424G, Scanspeak Discovery 10F/8414G-10, WaveCor WF120BD03, . . .

Any opinions?

 

[RossW]

For the tweeters I'd hold out for originals, especially since you only need one and they're a standard part. There are several on eBay right now although they all seem to be dented and pricey so patience may be rewarded in this regard.

For the mids the picture is a bit murkier. Since you need 2 anyway a substitute may be the way to go (it took me years to get my hands on a single spare original mid). Rob Gillum (former Thiel employee) suggests the 10F/8424G, although you'll have to rig together a trim ring to make it fit properly. I believe the 12W/4524G is a bit more of a drop-in physically although from what I've read it's not as good of a sonic substitute.

The EQ is definitely a tradeoff, it helps low frequency extension enormously, but it does take a bit of sparkle off the top end. I like to put it in the tape loop so that I can choose whether or not to use it on the fly.

Good luck!

 

[Ffastfreddy]

I got some very very nice Scan Speak 13m "replacements" from Madisound. They cost plenty but really suit with no crossover mods and bolt right in. They are pricey. Note, the Thiel plastic wave guides will need to be modified to fit over them.... that is, if you can get them separated in one piece as they are glued to the mids. Or, you could just leave them off.
The bottom line is they are a great sounding and satisfying solution for a tough to find replacement. I have no affiliation with Madisound other than being a satisfied customer. JMHO
Note: Dynaudio specs for the D28 AF tweeter show DC Resistance should be 5.3 ohms.

 

[Ffastfreddy]

Yes, see above.

Tweeters Original DynAudio D-28 AF D2806 2A Made in Denmark; Replacements Usher 9930 or 9950, Dayton RS28F, MDT33, Morel MDT32S, Eton 25SD-1

Mids OriginalScanspeak 13M 8521 and 13M 3808; Replacements Scanspeak Discovery 10F/8414G-10, Scanspeak Discovery 12W/4524G, Scan-Speak 13M Midrange Replacement

Madisound:
Morel MDT32S $112.00 each = $224.00
Scanspeak Discovery 12W/8524G $64.90 each = $129.80
Subtotal: $353.80

or

Madisound:
Morel MDT32S $112.00 each = $224.00
Scan-Speak 13M Midrange Replacement $210.00 each = $420.00
Subtotal: $644.00

Or perhaps for mids Scanspeak 10F/8424G, Scanspeak Discovery 10F/8414G-10, WaveCor WF120BD03, . . .

Any opinions?

The Morel MDT32S do not fit the Thiel CS 3.5. The face plate is perfect but they are too deep to fit in the enclosed recess. I suppose you could space them out with a "doughnut" but...

 

[mitchalee]

The Morel MDT32S do not fit the Thiel CS 3.5. The face plate is perfect but they are too deep to fit in the enclosed recess. I suppose you could space them out with a "doughnut" but...

Too late. I ordered them. Will have to improvise. Will take a look at the innerds, again. Can't recall exactly how deep the space behind the tweet was and what was there. My preference would be to avoid building the tweets out since it could raise hell with the sound unless I chaged the tilt back a bit to compensate, but that might get the mid off. In any case, there is probably a best compromise postion. And it may be that I can shave the innnerds a bit with no ill effects.

Had the same problem with Design Acoustics PS10 woofers. The originals are just like the mids with with a larger cone, so they are very shallow. No replacement that matched the specs would fit. Eventually gave up an added a shallow modern subwoofer that could not be more different than the original! But the volume was right and it gave me solid bass down to 25. The original woofer faded out between 55 and 35 and had a slight boom at about 120. Oddly, the imaging was just a hair off afterward. I never expected this from a woofer replacement. But otherwise the sound was more accurate and convincing. Tradeoffs!

 

[mitchalee]

For the tweeters I'd hold out for originals, especially since you only need one and they're a standard part. There are several on eBay right now although they all seem to be dented and pricey so patience may be rewarded in this regard.

For the mids the picture is a bit murkier. Since you need 2 anyway a substitute may be the way to go (it took me years to get my hands on a single spare original mid). Rob Gillum (former Thiel employee) suggests the 10F/8424G, although you'll have to rig together a trim ring to make it fit properly. I believe the 12W/4524G is a bit more of a drop-in physically although from what I've read it's not as good of a sonic substitute.

The EQ is definitely a tradeoff, it helps low frequency extension enormously, but it does take a bit of sparkle off the top end. I like to put it in the tape loop so that I can choose whether or not to use it on the fly.

Good luck!

Exactly. I found several original tweets but they all seemed to have been ridden hard and put away wet. Also the one I have would need the dome replaced. I could probably straighten it out with a rubber cement and q-tip trick. But it would never be quite right, only look better.

 

[mitchalee]

Will try to remember to get back with results. I just lucked out getting these. Paid $1750 for a lot of about 20 loudspeakers from Apogee to AR to some really old highend oddities from the 60s and 70s. My period! And basically the Thiel were just thrown in as an afterthought because of condition to seal the deal! Adding to my collection of Klipsch, Design Acoustics D-12, ADC, Acutex, Electro-Voice, Heil, Sansui, Polk Monitor 7, MIrage SM3, and so on and so forth. And, yes, I am divorced!!!

 

[lukiedog]

Tweeters:

Why don't you try repairing the voice coils on the D28AF? Should cost all of $4 for the pair:

https://www.aliexpress.us/item/2251832644296681.html?spm=a2g0o.productlist.main.1.6b5f1462tEVuA8&algo_pvid=4bde48d1-7a53-4c85-9b0d-cedc1e70120d&algo_exp_id=4bde48d1-7a53-4c85-9b0d-cedc1e70120d-0&pdp_npi=3@dis!USD!3.78!2.95!!!!!@210217c716815986167601970d0750!64952123850!sea!US!0&curPageLogUid=9KAtTpOU5MLk

Note the wires come out in different directions, there are other 25.4mm voice coils that look the same, but the wires come out off the coil in the same direction, that is incorrect. You can see that on your pair.

Mid:

For the mids, the best thing to do is get the 10F8424G. You can buy bare and make your own mounting plate or buy the ones from madisound ready to go with the aluminum adapter. Pricey, but quite simply the only solution at this point. Mids do come up on eBay and I happen to have received 8 of them in a row that are seized up or otherwise not working. Tired of wasting my time trying to obtain the original 13M8521, they are all trashed by now.

Woofers:

Bulletproof, never heard of any of them going bad, though there was an initial batch on the first CS3.5s that came bad from the factory, but those should all have been removed by now.

The MDT-32s is a nice tweeter, you can make yourself an Affordable Accuracy Monitor designed by Dennis Murphy if you can put together the crossover. First rate speaker.

 

[lukiedog]

Here are some ideas for tweeter substitution. The D28/2 was used by Thiel late in the CS3.5 without crossover modification, it is the best sub if it can be found, otherwise, the ones listed here as subs for D28/2 itself. These are sonically similar tweeters, they would still need to fit the hole. The CS3.5 has a chamber for the tweeter that limits its depth, which can sometimes present a problem.

You might also want to do a visual inspection of the crossover boards, make sure nothing has blown up, happens.

 

[nerdorama]

After seeing this thread, I stumbled onto this one. Thought it might interest.

https://audiokarma.org/forums/index...dio-d28-rebuild-service-all-varieties.916591/

 

[lukiedog]

The MDT-32s don't hold up very well over time, in my experience. I got a batch of used ones that tested very poorly on DATS, flat impedance curve with the peak shifted out towards 2000Hz. Apparently, this is a sign of degraded ferrofluid, so that service that would also replace the fluid is not a bad idea.

 

[Basspig]

I'm in the same boat here.. friend gave me a pair of CS3.5s. And it looks like both mids are not producing any sound.
I think a cap shorted in the crossover, because bass frequencies were reaching the tweeters. If I put my finger on the domes, while bass was playing, I could feel vibration of the tweeter domes. Perhaps the mids got the same full bandwidth signal and that fried them. Oddly the tweeters mostly survived, though the one on the right is sometimes intermittent.
Frankly there's so much overlap in the woofer high response and tweeter low response that I never really noticed anything wrong with the sound.

 

[paulram]

If I put my finger on the domes, while bass was playing, I could feel vibration of the tweeter domes.

I am experiencing the same on my D28afs and thought maybe that was normal. I believe the crossover point is 3k on the Thiel 3.5 and I find they vibrate too much .This has always bothered me. KIndly let me know what you find out.

 

[Basspig]

The crossover must have a rather gradual slope for it to be sending any significant power to the tweeters with upper bass range signals. The tweeter on the right channel has become intermittent as a result. I can see arcing at the voice coil lead wires if I turn off the lights.