Speaker Damping

[DON]

I have several pairs of Polk speakers and used to visit the "Club Polk" forum often. One of the favorite mods of most members there was to install damping material to the inside of the speaker enclosures and to the backs of the metal cones of the drivers. The favorite is a product called Dynamat. Some actually used Mortite or modeling clay. I've not seen any posts here that discussed this mod/tweek. Would any of the "Classic Speakers" on this forum benefit from this type of treatment? I'm not suggesting that this would improve the sound of these speakers but I would like to hear some opinions. Thanks. Don

[JKent]

I have several pairs of Polk speakers and used to visit the "Club Polk" forum often. One of the favorite mods of most members there was to install damping material to the inside of the speaker enclosures and to the backs of the metal cones of the drivers. The favorite is a product called Dynamat. Some actually used Mortite or modeling clay. I've not seen any posts here that discussed this mod/tweek. Would any of the "Classic Speakers" on this forum benefit from this type of treatment? I'm not suggesting that this would improve the sound of these speakers but I would like to hear some opinions. Thanks. Don

Along those lines, IIRC some people used an asphalt-based roofing product that was supposedly as good as Dynamat but cheaper. Never found it in Home Despot or Lowes.

Kent

[Carlspeak]

I think the OP is referring to two different issues. The application of damping (Dynamat, etc..) to the inside walls of cabinets is done to attenuate midrange reflections from reverberating to the back of the speaker cone, thus addint distortion.

The application of mortite or modelling clay is typically done to the backside of woofers and midrange drivers to attenuate frame resonances. Stamped metal frames are particularly prone to this issue as they are not as rigid as cast frames.

[DON]

I think the OP is referring to two different issues. The application of damping (Dynamat, etc..) to the inside walls of cabinets is done to attenuate midrange reflections from reverberating to the back of the speaker cone, thus addint distortion.

The application of mortite or modelling clay is typically done to the backside of woofers and midrange drivers to attenuate frame resonances. Stamped metal frames are particularly prone to this issue as they are not as rigid as cast frames.

Carl do you have any experience with this and is it worthwhile on ARs or Advents. It's said to make a huge difference in bass response. I've heard people refer to the "knock" test......knocking on the speaker enclosures to get an idea of how solid they are. The only speakers I have that pass the knock test are my B&Ws and my Velodyne sub.

[Carlspeak]

Carl do you have any experience with this and is it worthwhile on ARs or Advents. It's said to make a huge difference in bass response. I've heard people refer to the "knock" test......knocking on the speaker enclosures to get an idea of how solid they are. The only speakers I have that pass the knock test are my B&Ws and my Velodyne sub.

AR cabinets are generally pretty well braced.

OTOH, Advent cabinets are not. I do add braces to them when doing resto's. One front to back just above the woofer hole and sometimes a stiffener rib glued and screwed down each side panel.

[JKent]

AR cabinets are generally pretty well braced. OTOH, Advent cabinets are not. I do add braces to them when doing resto's. One front to back just above the woofer hole and sometimes a stiffener rib glued and screwed down each side panel.

That's good to know Carl. I have some OLAs awaiting restoration.

Question: Does the decreased internal volume caused by bracing cause a problem? And if so, is that negative offset my the improved stiffness due to the bracing?

Kent

[Carlspeak]

That's good to know Carl. I have some OLAs awaiting restoration.

Question: Does the decreased internal volume caused by bracing cause a problem? And if so, is that negative offset my the improved stiffness due to the bracing?

Kent

Download the attachment at post #12 for details of my Advent improvements that included the bracing.

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=2895&st=0&p=67529&hl=improvement&fromsearch=1entry67529

Also check out post #18 of that same thread where I show actual NLA cabinet resonace measurement results and what bracing did to mitigate it.

[JKent]

Thanks Carl. I had missed that post and it answered another question: Should I re-use the foam blocks or substitute FG? And if so, how much?

Your pdf answered those questions.

Kent

[DON]

Thanks Carl. I have also read that thread but it has wandered to a part of my brain that becomes more and more cluttered making finding and retrieving more difficult the older I get. So to sum it up replacing foam with fg and bracing improves the perceived sound.??

Have you performed tests comparing the sound before and after recapping?

Which Advent has the greater potential OLA, NLA, 5012 or 25th anniversary.

[Carlspeak]

Thanks Carl. I have also read that thread but it has wandered to a part of my brain that becomes more and more cluttered making finding and retrieving more difficult the older I get. So to sum it up replacing foam with fg and bracing improves the perceived sound.??

Have you performed tests comparing the sound before and after recapping?

Which Advent has the greater potential OLA, NLA, 5012 or 25th anniversary.

Regarding the bracing, yes. The other post at the link I gave has cabinet resonance tests graphs as attachments. There was measureable improvement in resonance reduction. Regarding the lowering of FC and flattening of the impedance curves, those improvements are best judged by simple listening tests. I've had no complaints from the customers for whom I did the work. I am most familiar with the OLA and NLA speakers - not so much with the latter two you listed. Both OLA and NLA can benefit from bracing and FG.

You may also want to consider Pete Basel's BSC or my shelving network. Both attenuate the mid and high frequencies down so they are more level with the bass.

See this link for more info.... http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6053&st=0&p=85598&hl=shelving&fromsearch=1entry85598

[dynaco_dan]

I have several pairs of Polk speakers and used to visit the "Club Polk" forum often. One of the favorite mods of most members there was to install damping material to the inside of the speaker enclosures and to the backs of the metal cones of the drivers. The favorite is a product called Dynamat. Some actually used Mortite or modeling clay. I've not seen any posts here that discussed this mod/tweek. Would any of the "Classic Speakers" on this forum benefit from this type of treatment? I'm not suggesting that this would improve the sound of these speakers but I would like to hear some opinions. Thanks. Don

Hi Don

Many moons ago I read once that someone used car undercoat to completely coat the inside of their enclosure and the woofer frame to lessen vibration resonance.

Another was to apply a coating of plastercene(?), maybe modeling clay equal, about 1/4" thick to the inside cabinet walls and woofer frame.

Another was coating the butt edges and corners with same to eliminate sharp edges and change to radiussed edges.

Another was to build up the existing insulation behind the woofer.

An article I have from England shows a sketch for using long and short fiber wool and the mounting method using a screen to support different areas in the enclosure.

Maybe Carl would be able to measure any improvements.

I don't think we human beings would hear much or any improvement if any.

Sometimes we hear the impossible when we do something or spend money.