Searched with google but cannot find any mention of the IE40 damping material - are you aware if it's still available or know of a similar product to use instead?
Thanks
Thanks
I wonder though, how much bracing would be preferred?
I made 3 versions, where version 1 is the most simple, small one; v2 the horizontal one is wider; and v3 where the horizontal brace almost goes almost all the way to the back panel and the back brace-finger stretches further forward too.
I guess my question is, how much surface area is wanted? As big as possible brace + as wide as posible fingers?
Or would a brace like v3 won't dampen as much, but only stiffen the panels?
Also, I removed the vertical ones because of the reasons mr. GedLee told.
I made 3 versions, where version 1 is the most simple, small one; v2 the horizontal one is wider; and v3 where the horizontal brace almost goes almost all the way to the back panel and the back brace-finger stretches further forward too.
I guess my question is, how much surface area is wanted? As big as possible brace + as wide as posible fingers?
Or would a brace like v3 won't dampen as much, but only stiffen the panels?
Also, I removed the vertical ones because of the reasons mr. GedLee told.
Attachments
Last edited:
There is no objective data, alas, only my subjective. But with decades of experience in noise control, I know what works, what doesn't, etc. I went by long trails of trying different things and what I ended up with is what I have described. Nothing objective, and as I have said before, I tried to get actual radiated data and could not do so.
As to your point about stiffness, a fixed rod is way too stiff, there is no motion and yes this will raise the panel resonates in frequency, but it will not damp them. Only by adding some damping in the members themselves. Some stiffness is lost, some damping gained - I'll take the damping.
As to your point about stiffness, a fixed rod is way too stiff, there is no motion and yes this will raise the panel resonates in frequency, but it will not damp them. Only by adding some damping in the members themselves. Some stiffness is lost, some damping gained - I'll take the damping.
Thinking about it, rigid braces would work to prevent a mode from being excited. But that energy doesn't disappear... knocking on cabinets as I have progressively braced them subjectively showed rising pitch as I added bracing - energy shifting up in frequency. But not really any decrease in the noise generated by my rapping.
Perhaps the key in Earl's scheme is to leave that first mode available? Allow energy to excite the mode (don't make the brace too stiff, don't make it too large in other dimensions as it then becomes a stiff brace in that direction) and then provide a quick path to convert that energy to heat.
Mr. Lee's comments seem to be converging toward this. Perhaps this is the implied position, but I thought I'd state it explicitly (and provoke his response) for those of us trying to understand what he has done.
Perhaps one day when I have run out of other things to keep me busy I'll make a series of otherwise identical boxes braced (or damped or decoupled) in a variety of different ways for measurement and subjective evaluation. That would be fun...
Perhaps the key in Earl's scheme is to leave that first mode available? Allow energy to excite the mode (don't make the brace too stiff, don't make it too large in other dimensions as it then becomes a stiff brace in that direction) and then provide a quick path to convert that energy to heat.
Mr. Lee's comments seem to be converging toward this. Perhaps this is the implied position, but I thought I'd state it explicitly (and provoke his response) for those of us trying to understand what he has done.
Perhaps one day when I have run out of other things to keep me busy I'll make a series of otherwise identical boxes braced (or damped or decoupled) in a variety of different ways for measurement and subjective evaluation. That would be fun...
Modes are always excited, the question is always, to what degree. As the modes in the enclosure are shifted upwards with stiffness they are excited less, that's true, but they tend to radiate more - that's bad. IMO damping is the key, not stiffness.
And I think that it needs repeating: they is no objective data to support any of these more extreme techniques (perhaps that is the point that someone was trying to make and I agree.) hence it seems logical to me to do what is pragmatic and leave alone the ideal. Unless one can show that the "ideal" is really audible. (And that, I suggest, would be an extremely difficult task.)
The knuckle test is, to me, not very relevant. It's the lower frequencies that make it out to the surface of the enclosure as radiatable motion. The way to test a box would be to put a long tube on a big driver (say a 10" tube on a 10" woofer, about ten feet long, hopefully in another room. Port this tube into the box and measure the sound radiation. You would have to do this in full 3D as the box will radiate in all directions. This still does not tell you if this sound is significant to the directly radiated sound, but it would still be good for comparative purposes.
And I think that it needs repeating: they is no objective data to support any of these more extreme techniques (perhaps that is the point that someone was trying to make and I agree.) hence it seems logical to me to do what is pragmatic and leave alone the ideal. Unless one can show that the "ideal" is really audible. (And that, I suggest, would be an extremely difficult task.)
The knuckle test is, to me, not very relevant. It's the lower frequencies that make it out to the surface of the enclosure as radiatable motion. The way to test a box would be to put a long tube on a big driver (say a 10" tube on a 10" woofer, about ten feet long, hopefully in another room. Port this tube into the box and measure the sound radiation. You would have to do this in full 3D as the box will radiate in all directions. This still does not tell you if this sound is significant to the directly radiated sound, but it would still be good for comparative purposes.
CLD Strategies
Earl is outlining one strategy for "CLD," which is to dampen the panels with damped braces. Keep in mind that Earl is using his internal braced damping technique on speaker panels which have a high level of internal damping due to the properties of the cabinet materials that he uses. Applying this method to wooden speaker panels would likely be helped by this method, but you likely will end up at a different place than Earl.
Another way would be to use the fixed braces (not dampened) which increases the frequency of the vibrations. Then CLD panels (box within a box with dampening material inbetween) can be used to dissipate the high frequencies since CLD works better at higher frequencies.
I recall another discussion like this where I think that it was concluded that for subwoofer boxes, you would be best served to use braces to cause the box resonance frequencies to be above the frequencies reproduced by the speaker. On the other hand, for midrange and higher frequencies, you would be best served to design the box resonance frequencies to be below the frequencies being reproduced by the speaker. This helps to avoid causing panel resonances. This is a challenge when using wood materials.
I think that using speaker panel material which has significant internal damping properties is the best strategy for midrange and higher frequencies. One guy (krk971) started to make speakers out of foam core and I think that one reason why this works well is because of the damping qualities of the material, and it likely resonates at lower frequencies. For handling bass in his wide range speakers, he has stiffened his boxes with cardboard, which also has high internal damping properties.
I made some front waveguides out of conventional cardboard which works great at higher frequencies, but the cardboard seems to be too flimsy for reinforcing the midbass, not to mention too flimsy for supporting itself. I am still working on a more permanent solution.
All this is very interesting stuff, and a lot of the research done on this has been done by commercial industries which may or may not have applicability to speakers depending on the situation.
Retsel
Earl is outlining one strategy for "CLD," which is to dampen the panels with damped braces. Keep in mind that Earl is using his internal braced damping technique on speaker panels which have a high level of internal damping due to the properties of the cabinet materials that he uses. Applying this method to wooden speaker panels would likely be helped by this method, but you likely will end up at a different place than Earl.
Another way would be to use the fixed braces (not dampened) which increases the frequency of the vibrations. Then CLD panels (box within a box with dampening material inbetween) can be used to dissipate the high frequencies since CLD works better at higher frequencies.
I recall another discussion like this where I think that it was concluded that for subwoofer boxes, you would be best served to use braces to cause the box resonance frequencies to be above the frequencies reproduced by the speaker. On the other hand, for midrange and higher frequencies, you would be best served to design the box resonance frequencies to be below the frequencies being reproduced by the speaker. This helps to avoid causing panel resonances. This is a challenge when using wood materials.
I think that using speaker panel material which has significant internal damping properties is the best strategy for midrange and higher frequencies. One guy (krk971) started to make speakers out of foam core and I think that one reason why this works well is because of the damping qualities of the material, and it likely resonates at lower frequencies. For handling bass in his wide range speakers, he has stiffened his boxes with cardboard, which also has high internal damping properties.
I made some front waveguides out of conventional cardboard which works great at higher frequencies, but the cardboard seems to be too flimsy for reinforcing the midbass, not to mention too flimsy for supporting itself. I am still working on a more permanent solution.
All this is very interesting stuff, and a lot of the research done on this has been done by commercial industries which may or may not have applicability to speakers depending on the situation.
Retsel
And I should remind all that I use(d) first and foremost CLD damped baffle and back panel, which combined have about 60% of the total surface area. So yes, my main panels have very high internal damping as well.
Yes that is what tends to happen: the modes are raised higher in frequency but remain just as loud. Most DIYers assume that because the cabinet is stiffer and harder to deflect it will be quieter but at higher frequencies the cabinet needs to move less to be equally loud (e.g. tweeter deflection vs woofer deflection). One of the old BBC publications from the 70s had some measurements showing the failure of thicker panels to quieten cabinet radiation but many DIYers still seem to favour overly thick walls (baffle stiffness is different as mentioned above).
In the scheme above the bracing has negligible stiffness because the weak damping material is deformed not the stiff wood. It adds mass though which will tend to lower the frequency of the modes which move the bracing (some modes will be missed as mentioned earlier). It also adds damping which is the point but whether it effectively damps the one or two modes that need damping is somewhat of an open question.
How will you determine the sound radiated by the cabinet? A knuckle rap test can give you the frequencies of the main modes and their damping which is useful information but it won't tell you the mode shape, the strength of each mode when driven by the drivers nor the radiation pattern for each mode.
In industry measured sound radiation from a physical cabinet is typically determined by measuring the deflection/velocity/acceleration at a great many points over the complete surface of the cabinet with a vibrometer, solving the boundary surface integral to get the pressure over the surface and then integrating to get the pressure at any points of interest such as the listening location. There's a hint of info here on this old blog. Not surprisingly detailed information on commercial speakers is omitted but this is what measured cabinet radiation looks like.
Of course what the larger companies in industry tend to do when sufficiently interested in sound radiation from cabinets is not measure it but simulate it using 3D BEM and FEM software. Example here which I think was posted earlier. I still have it on my todo list to finish off and post some simulations I did a while ago.
I think of it this way. Take a plate and hang it normal to gravity, clamped at the edge. Now picture a mass hanging at the center in a vat of thick fluid. This, if the mass and fluid viscosity are set correctly will kill the sound in that plate. So even with zero stiffness the effect is good. But the stiffness will depend on thickness and shear modulus of the damping layer, both of which are variables, so the stiffness could be made significant if this is deemed to be good. In my estimation the stiffness will however be a negligible factor in the effect - meaning that it doesn't really matter what it is.
One could adjust the mass and stiffness of the damper together to get a tuned damper at whatever frequency one wanted. This is a common technique in noise control. Think of the damped engine mount. They have hanging masses on them to absorb the vibrations. Same idea.
Last edited:
I have been following this thread as I have two speaker projects I plan on completing this year. My only other previous experience has been the .53x Karlson foamboard by XRK971.
The first one is an OB by Dick Olsher using SAL and Augie speakers. Would a thicker, laminated baffle along with the two side supports be beneficial. The design is based on the Visaton OB kit no longer made. Panels were 19mm MDF.
The second is the FAST by XRK971 posted here on DIYA. Interior damping materials are used along with a single brace in the middle connecting the sides of the box. Following the posts of Lee and others it would appear the damped cross bracing would be beneficial.
Just seeking thoughts from the more experienced builders.
Tnx
David
The first one is an OB by Dick Olsher using SAL and Augie speakers. Would a thicker, laminated baffle along with the two side supports be beneficial. The design is based on the Visaton OB kit no longer made. Panels were 19mm MDF.
The second is the FAST by XRK971 posted here on DIYA. Interior damping materials are used along with a single brace in the middle connecting the sides of the box. Following the posts of Lee and others it would appear the damped cross bracing would be beneficial.
Just seeking thoughts from the more experienced builders.
Tnx
David
I have found an possible worthy alternative for a IE40 rubber. At least the specifications are comparative.
It's the VytaFlex 40 VytaFlex™ 40 Product Information | Smooth-On, Inc.
It's also affordable at €23 for 1 kg and €133 for 7 kg.
I also got recommended to use the Ure-Fil 11 URE-FIL™ 11 Product Information | Smooth-On, Inc., which makes it more viscous. That way it can be more easily applied to a plywood, without it running all over the place
It's the VytaFlex 40 VytaFlex™ 40 Product Information | Smooth-On, Inc.
It's also affordable at €23 for 1 kg and €133 for 7 kg.
I also got recommended to use the Ure-Fil 11 URE-FIL™ 11 Product Information | Smooth-On, Inc., which makes it more viscous. That way it can be more easily applied to a plywood, without it running all over the place
If the shore is not very important, then what properties do you look at?
I thought visco-elastic meant the vibrations will be converted to heat instead of bouncing back.
I think I don't grasp the desired properties from the dampening layer..
If it is a significantly viscoelastic material rather than mainly an elastic one then the harder the material the greater the damping force. However, if it was significantly viscoelastic it would be reasonable to expect the damping coefficient (or equivalent) to be mentioned in the datasheet.