Why does duntech put adhesive backed felt on the bass drivers?

jkess114

Member
2013-02-06 2:59 pm
Sreten-

I don't mean "around" the bass drivers, I mean glued to the dust cap of the driver.

Tinitus, are you saying, John Dunlavy found the speakers sounded better with the dustcap damped? That must be it. The weight of the speaker couldn't change that much with the felt.
 
Sreten-

I don't mean "around" the bass drivers, I mean glued to the dust cap of the driver.

Tinitus, are you saying, John Dunlavy found the speakers sounded better with the dustcap damped? That must be it. The weight of the speaker couldn't change that much with the felt.

I plugged the hole in the fibre glass coned speakers in my TQWP's and that definitely improved them.
 

tinitus

Ex-Moderator R.I.P.
2005-11-24 1:47 am
Tinitus, are you saying, John Dunlavy found the speakers sounded better with the dustcap damped? That must be it.

oh it works alright
tried it, and other similar things
with selfadhesive it has a bad habbit of coming loose :D

but worse the way he plasters all kinds of material onto the baffle, around driver etc
it has just as much bad sideeefcts as it has good
there are better ways to build good speakers

but as I said, the fact that he still does it is a clear indication that there must be something wrong with those speakers, and thats about all there is to it
he wouldn't do if they were good
good speakers would sound worse doing that
 

ScottG

Member
2003-02-04 12:23 am
US
..but as I said, the fact that he still does it is a clear indication that there must be something wrong with those speakers, and thats about all there is to it
he wouldn't do if they were good

He doesn't do "it" anymore - he's dead. ;)

Many if not most drivers could use some modification to improve certain characteristics. Sometimes damping. Sometimes higher freq. absorption from cone reflections. Sometimes added-mass to lower resonant freq. for a design. Etc..

The baffle modification adding felt *surrounding* the drivers is a way to deal with diffraction and reflections for a stepped baffle.

Dunlavey was big on time-aligned 1st order designs. His use of both modifiers is just a way to achieve this. Note that on some of his later designs under his own name, rather than Duntech, the mids were not modified - Vifa (as opposed to Dynaudio) were producing more wide-band linear drivers for him at that time.
 

ScottG

Member
2003-02-04 12:23 am
US
but is it possible he didn't have the new modern speaker PC software tools :confused:

He had modern enough tools.

It was just a design choice - in search of a semi-point source time-aligned system with minimal group delay. He was fanatical for near perfect square-wave production.

He could have gone with separate cabinets that had lower diffraction, but he wanted that quasi point-source radiation pattern AND he needed the added volume for his sealed-only design. (..it was also a passive crossover.)

Under these sorts of constraints it's a pretty logical outcome. As the original poster has questioned however, perhaps the least likely conclusion was the use of felt on the bass drivers. I think that was more a case of getting the drivers with the distortion performance in a sealed design (and low freq. extension) that he wanted - while excepting some top-end break-up that he could deal with as a modification.


I've personally heard both the earlier Duntech Sovereigns and several of the latter Dunlavy's.

NONE of the latter designs sounded as clear or provided more tangible imaging than the Duntech's. Considering the designs were so similar I'd chalk-it-up to the more expensive Dynaudio drivers - particularly the treble from the Esotar. (..I've heard the Esotar in other designs as well with the same sort of performance.) This of course is despite the fact that Dynaudio drivers were LESS linear than the Vifa's.

On the other hand the Duntech's were a bit more "plodding" in rhythm from what I remember from the Dunlavy's.

I could never get over the MTM low order arrangement however. The vertical polars had audible combing issues for me.
 
I think the felt was added to the cone to mechanically dampen break-up effects on the large dust caps. The location of the felt is the clue - it's usually a button placed in the center of the dust cap itself, which is the location where breakup of a dome-shaped structure would be the worst.

Damping adds mass, true, but not that much.

I have also seen these drivers (the Dynaudios) used in designs by other manufacturers (see Abbingdon Music Research) with felt treatments applied to the outer edge of the cone, just before the surround, but not that much. In every case, it's still for the purpose of damping uncontrolled mechanical resonances. Poly is excellent at shedding excess energy from resonance, but the felt takes that behavior even further.
 
Ex-employee of Duntech posting again. ScottG and Taterworks are on the money.

The felt on the drivers, yes I am pretty sure it was to reduce the nasties that came from the, at the time high tech plastic, cones. Because, as mentioned earlier, Dunlavy loved to use 1st order crossovers, to avoid phase issues, on his quest to produce amazing square wave pulses and really flat frequency sweeps he would critically dampen the drivers and get about 12db per octave rolloff and I assume that this use of felt would have contributed to the reduction of some undesirable multiple order harmonics that could have come from the cones because the drivers were not wired to higher order filters.

The use of the felt on the baffle, again, on the money, diffraction distortion would have been in abundance on a "naked" baffle which was as stepped as the Sovereigns. Again all this for producing great square wave pulses. There is no practical way to radius to reduce diffraction distortion that would be as efficient as using that felt.

If you are able to test the speakers do it with and without the felt and even just move the felt around slightly and see what happens to your response. The felt placement and design is no accident I can assure you. I do think it looks a little rough though I have to say, but at the end of the day the result is worth it.

The Dynaudio Esotar? When I was there, up to 1987, it was not in use although there were some samples in the factory. Dunlavy considered them too expensive to use in the Sovereign. If you think about it, he had already made an amazing speaker and it was held in regard, changing the tweeter was a significant change to something so good. I am also pretty sure that the tweeter was a Scanspeak unit and not a Vifa, although they may be one in the same now, I am pretty sure they were not back then. Dynaudio tweeters were used in the Crown Prince and the Little Duchess though. Funny enough the Crown Prince used a Scanspeak cone midrange and Dynaudio Bass units and Tweeters the Little Duchess, a two way system, was the only one at the time that used only Dynaudio drivers exclusively.
 
NONE of the latter designs sounded as clear or provided more tangible imaging than the Duntech's. Considering the designs were so similar I'd chalk-it-up to the more expensive Dynaudio drivers - particularly the treble from the Esotar. (..I've heard the Esotar in other designs as well with the same sort of performance.) This of course is despite the fact that Dynaudio drivers were LESS linear than the Vifa's.

I disagree with this. The Duntech's were great sounding speakers, but I don't think they were in the same category as the SC-V and SC-VI. Hence why these speakers made it into so many studios including mine. By the time John got around to making these speakers, he had refined the design pretty darn well. His later tweaks and upgrades even further refined the sound of these speakers.
 
The use of the felt on the baffle, again, on the money, diffraction distortion would have been in abundance on a "naked" baffle which was as stepped as the Sovereigns. Again all this for producing great square wave pulses. There is no practical way to radius to reduce diffraction distortion that would be as efficient as using that felt.

If you are able to test the speakers do it with and without the felt and even just move the felt around slightly and see what happens to your response. The felt placement and design is no accident I can assure you. I do think it looks a little rough though I have to say, but at the end of the day the result is worth it.
It's easy to see the improvement that felt makes on stepped baffles. For those who haven't seen it, there's a set of pictures and measurements at my audioXpress article.

felt_vs_nofelt_2.gif


Dave