I just spent 3 hours putting on and taking off that sticky roofing felt stuff that comes in 6" rolls from the DIY outlets. The sound of my speakers, which was lively and naturel went muffled, dead and foggy. Vocals, which were airy and lifelike sounded like somebody singing inside a hessian sack. Pulling the bloody stuff off is a nightmare. Fortunately I only did one speaker and not both, and listened to the results - music from one side, muffled sounds from the other. I just wanted to let off steam after a wasted afternoon. I HATE SOUND DAMPING PANELS!!!!!!!!!!!
I really like it and use it in all my designs. But I take a tip from the experience of ProAc 2.5 builders (I'm one!). The conventional wisdom there is to apply damping to all walls except the baffle, and that more (thickness) is not better. Double thickness or all walls damped resulted in a negative review similar to this one.
I think it is all about finding the right amount of damping for a specific design. Proac spec is 5mm I believe; I think I used about 3mm there and 2mm in another project.
I think it is all about finding the right amount of damping for a specific design. Proac spec is 5mm I believe; I think I used about 3mm there and 2mm in another project.
I only apply regular fibreglass stuffing, no damping mat. on the panels. But i usually build "layer constraint" boxes with good internal bracing to make them as non resonant as possible - with good results imho, as i am not treating the speaker as a musical instrument whose resonant body enhances the produced sound.
My dissatisfaction with sound damping panels is that I was brought up by marketing to believe the idea that you can improve the sound by sticking some viscous damping stuff onto a panel. These things aren't marketed to be used where they serve a useful purpose - as a sandwich between layers of harder materials - they are marketed to 'stick on' to things. In just about all my experience with audio separates, turntables, speakers etc, these panels made the sound thick and unlovely when simply 'stuck on' to a surface. Yet the voice in the head goes - better put a sound deadening something on that surface. This is a pathetic misconception - products should carry a warning "the sound of your hi-fi may go down as well as up". I've really had it with sticking things onto panels - the solution lies elsewhere and the audio public is being deluded into thinking that such simplistic ideas actually guarantee some sort of improvement. They don't - the physics is considerably more complex, as more experienced speaker builders than me already know and practice.
Long answer:
I think it largely depends on the panel in question. Remember that the goal is to push the panel resonance high enough to effectively eliminate its audibility. From what I've read, that number is typically 1khz. Adding mass to the panels is going to LOWER its resonant frequency, not raise it.
BUT... in cases where there is excessive resonance (like in my most recent 2-ways which only use .5" MDF), the high mass sheets can damp this resonance well enough that although the resonant frequency may be falling, the added mass causes the panels to become less excited from the resonance. If you use sufficient matierials and adequate brace your enclosures in the first place, there should be no need to add mass later on.
Short answer: It depends.
I think it largely depends on the panel in question. Remember that the goal is to push the panel resonance high enough to effectively eliminate its audibility. From what I've read, that number is typically 1khz. Adding mass to the panels is going to LOWER its resonant frequency, not raise it.
BUT... in cases where there is excessive resonance (like in my most recent 2-ways which only use .5" MDF), the high mass sheets can damp this resonance well enough that although the resonant frequency may be falling, the added mass causes the panels to become less excited from the resonance. If you use sufficient matierials and adequate brace your enclosures in the first place, there should be no need to add mass later on.
Short answer: It depends.
I think it also depends on the thickness of the panels you stick them to. The BBC idea with the Bitumen pads was to use a thin wall and then mass load it to get the resonance down.
I'm not sure what benefit damping thicker panels would have.
I notice that one supplier is definitely NOT recommending the Deflex panels any more.
Colin
I'm not sure what benefit damping thicker panels would have.
I notice that one supplier is definitely NOT recommending the Deflex panels any more.
Colin
Well - I could certainly do with some help here. I made 20 litre enclosures for a (nearly) fullrange 5" alu cone speaker (Monacor 130AL). construction was:
Front panel - aluminium channel, 6mm front, 10mm sides, vertical.
Sides - bolted onto front panel - 47mm, made from 3 sheets contiboard with bitumen roofing felt in between sheets.
Back - same
Top and bottom - TBA (now one sheet contiboard - needs something better, maybe thick alu or even concrete slab)
enclosure is 25w, 40d, 40h in cm. The back is actually sloping.
Weight is 16 kilo.
Now, the enclosure is rigid and heavy, and yet fairly light to a knuckle test - not soggy. Sticking on the bitumen pads made the sides go down in resonance, and that ruined the voicing. I haven't yet scraped the stuff off the back - it probably has less effect there since it's a small panel (150mm or 6" wide) .
So i can either leave the box with no internal damping, or go for some foam, long haired wool or carpet felt. the next step is trying out varying amounts of each.
Finally, I'll have to decide whether IB or ported, and whether port should come out on front, back or a bigger tuned pipe under it
Ideas? What would you do at this point?
Front panel - aluminium channel, 6mm front, 10mm sides, vertical.
Sides - bolted onto front panel - 47mm, made from 3 sheets contiboard with bitumen roofing felt in between sheets.
Back - same
Top and bottom - TBA (now one sheet contiboard - needs something better, maybe thick alu or even concrete slab)
enclosure is 25w, 40d, 40h in cm. The back is actually sloping.
Weight is 16 kilo.
Now, the enclosure is rigid and heavy, and yet fairly light to a knuckle test - not soggy. Sticking on the bitumen pads made the sides go down in resonance, and that ruined the voicing. I haven't yet scraped the stuff off the back - it probably has less effect there since it's a small panel (150mm or 6" wide) .
So i can either leave the box with no internal damping, or go for some foam, long haired wool or carpet felt. the next step is trying out varying amounts of each.
Finally, I'll have to decide whether IB or ported, and whether port should come out on front, back or a bigger tuned pipe under it
Ideas? What would you do at this point?
Update - scraped the last of the bitumen pads off. Sounds better. these things are a pain to remove. finally deduced that the best way to pull them off is to slice them into strips and pull hard - a whole panel adheres too much but strips come off. Seems like fortuiitously the pads have mega adhesion onto the Contiboard (white laminate faced particle board) that I used
I'd be interested to know what kind of solvent dissolves + removes bitumen - anyone?
Well - currently without any damping inside. I have to say this sounds the most detailed so far, best on vocals and most treble. this has restored my good humour - the sound finally improved. I also bolted down the speaker unit with bigger dia bolts, and that was good. Widened the tuned port dia. That was better too. The trials of building speakers!
I'd be interested to know what kind of solvent dissolves + removes bitumen - anyone?
Well - currently without any damping inside. I have to say this sounds the most detailed so far, best on vocals and most treble. this has restored my good humour - the sound finally improved. I also bolted down the speaker unit with bigger dia bolts, and that was good. Widened the tuned port dia. That was better too. The trials of building speakers!
Jim85IROC said:
Good one...
I tend towards thin, stiff materials (plywood) with a high lvel of proper bracing (shelf braces may be easy & look impressive, but aren't the best way to do it). I stay away from damping pads (althou the stick-on stuff for car doors and such can make a big difference on the cover of your CD player 7 such.
You have to be careful adding mass... i had a quite nice sounding set of little pyramidal boxes (LS3/5A size) made of 1/2" HDF... after adding a 1/4" cherry "veneer" they looked way better, but didn't sound as good... it had lowered the wall resonances enuff that they were being excited and coloring up the sound.
I'll be doing some bracing retrofits to them soon.
dave
I tend towards thin, stiff materials (plywood) with a high lvel of proper bracing (shelf braces may be easy & look impressive, but aren't the best way to do it). >>
What do you recommend for braces?
also, does anybody know the laminated sheets about 2 inches thick made by some guy in the North of England, also used for hifi platforms? They are made by many thin sheets of ply interposed with layers of some white plastic corrugation which is filled with white glue - the whole thing is then pressed together to dry in a large industrial press. The stuff sounded really excellent at the London HiFi show last year. I can't remember the name and details - maybe it was **** lam or something. Anyone know?
What do you recommend for braces?
also, does anybody know the laminated sheets about 2 inches thick made by some guy in the North of England, also used for hifi platforms? They are made by many thin sheets of ply interposed with layers of some white plastic corrugation which is filled with white glue - the whole thing is then pressed together to dry in a large industrial press. The stuff sounded really excellent at the London HiFi show last year. I can't remember the name and details - maybe it was **** lam or something. Anyone know?
theoracle said:
Steve just glues up the layers of machined MDF
Andy Graddon has the best compilation of translam projects
http://users.tpg.com.au/users/gradds/curved/curved sided loudspeakers.htm
A buddy of mine who built a very goos small production speaker in the 70s & 80s did a lot of investigation into panel materials & ended up with a lamination of something like 7 layers of thin MDF/HDF-like material (3-4mm?) pressed together using a special glue.
These kinds of approaches invariably seem to lead to better results... it is all -- in essence -- specialty built plywood.
dave
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