I've used plasticine (permanently soft modeling clay) on the frames of cheap drivers. Works great.
with acoustic guitar the enclosure resonces are desired effect, thats why thin plywood is used. If we pull 6 strings over concerete slab there wont be much sound coming from that 'quitar'. In a loudspeaker only the cone is suppose to move, everything else is distortion. But there has to be a story when marketing strange, uber over priced crap like Ongaku and Gaku On triod amps from Japan (Audio Notes main business), the quitar story and Russian plywood might sell some speakers to some very rich people who have no clue
Personally I think this was a matter of marketing too. I didn't see anything of a technical nature that impressed me as ingenious nor was my brief exposure to two AN systems in any way memorable. PQ seemed almost annoyed that I asked him to play a disc I had brought along with me. I don't understand the logic behind his explanation for the way his products speaker cabinets are designed either. Someone must like them, they're awfully expensive for what you get IMO.
These guys take both of those concepts to an artform.
speaker | ECLIPSE TD series speaker
One with the other will have a deloterious affect on DDR.
dave
Harwood goes into it in his study. He was measuring cabinet walls with a very close figure 8 mic (with frequency compensation). Based on a variety of cabinets and their listening tests he came up with a threshold curve (fig. 12) In general he found that resonances needed to be 30 dB down from 400 Hz and up. Level could rise about 6dB per Octave below 400 without being audible. For the cabinets he measured most of the troublesome resonances were in the 200 to 700 Hz range.
http://www.bbc.co.uk/rd/pubs/reports/1977-03.pdf
David S.
Nice! More BBC R&D:
http://downloads.bbc.co.uk/rd/pubs/reports/rpt60s_70to96.pdf
A few gems, but 95% TV/Radio related
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I have to agree with many people here, who also disagree partly with eachother, and probably partly with myself!
from a material POV we want low mass, high rigidity and high damping. a compromise is the only way. Adding mass may not lower F1 amplitude linearly, but the force required to move/vibrate that mass at anything other than the fundamental will increase. the natural resonance will exist in all materials, except perhaps a composite/amalgam. however resonant decay time will increase with increased mass, assuming all else equal. Id expect the amplitude (which IFAIK IS SPL, unless weve started measureing sound POWER...) to reduce somewhat, leaving longer decay to deal with. with adequate damping this is far easier to deal with than an undamped fundamental accompanied by many harmonics, some spurious.
huge levels of bracing are appealing in some ways, but its a bit like whipping the horse at the end of a race. Either we have 10 ton concrete boxes or a box so stiff it could withstand a bomb blast. both are pointless. the forces within the box do not demand such overexertion. a WELL BRACED, ADEQUATELY mass damped/CLDamped/OM damped box will suffice, and a great deal easier to achieve. hollow sand filled walls work great, if you allow the sand to settle with some bass playing, and then top up the panels after a time. mind you plaster of paris/plasterboard lath works great in the centre of a sandwhich too!
from a material POV we want low mass, high rigidity and high damping. a compromise is the only way. Adding mass may not lower F1 amplitude linearly, but the force required to move/vibrate that mass at anything other than the fundamental will increase. the natural resonance will exist in all materials, except perhaps a composite/amalgam. however resonant decay time will increase with increased mass, assuming all else equal. Id expect the amplitude (which IFAIK IS SPL, unless weve started measureing sound POWER...) to reduce somewhat, leaving longer decay to deal with. with adequate damping this is far easier to deal with than an undamped fundamental accompanied by many harmonics, some spurious.
huge levels of bracing are appealing in some ways, but its a bit like whipping the horse at the end of a race. Either we have 10 ton concrete boxes or a box so stiff it could withstand a bomb blast. both are pointless. the forces within the box do not demand such overexertion. a WELL BRACED, ADEQUATELY mass damped/CLDamped/OM damped box will suffice, and a great deal easier to achieve. hollow sand filled walls work great, if you allow the sand to settle with some bass playing, and then top up the panels after a time. mind you plaster of paris/plasterboard lath works great in the centre of a sandwhich too!
A friend of mine made a cabinet out of a composite wood material made from a cardboard honeycomb, like a hollow core door. Apparently it is used for dance floors. I think the joints were probably the weakest part of the structure. Once braced, though, it was quite a dead enclosure.
Hello,
It is not about agreement or disagreement. It is about understanding and application of materials.
No one has said a thing about Q as it relates to dampening of the panels of the enclosure.
About “resonant decay time will increase with increased mass, assuming all else equal”. In addition to reduced amplitude added mass will lower the resonant frequency, the “decay time” or more importantly the number of cycles to damp is entirely dependent on Q.
DT
All just for fun!
This seems to be where most are getting away from what theory tells us. Higher mass means a higher reactive force. Q at resonance is the ratio of reactance to resistance (damping). All other things being equal, higher mass means higer Q and longer number of cycles to decay.
Secondly, mass becomes irrelevant at resonance (and each panel will have multiple frequencies of resonance). That is the definition of resonance: a frequency where a positive reactance (mass) is exactly equalled and cancelled by the negative reactance of stiffness. At that frequency, no matter how massive, there is no "work" in pushing the mass. The only work consumed is in the losses. So bridges can swing, buildings can sway, kids on a swing (or heavy adults) can literally swing, as long as we overcome the frictional losses.
"All other things being equal" is a little confusing as we vary cabinet construction. The easiest change is to modify thicknes, by doubling up on cabinet walls or just buying the thicker stuff. This generally pushes the resonances up. Mass per square foot goes up with thickness but stiffness generally goes up with the cube of thickness. Double cabinet thickness and most of the resonances will double in frequency. Damping is a bulk material property and doesn't appear to change.
I'm wondering about ways to increase mass per unit area without raising stiffness. This would push resonances down rather than up. What if we used a fairly thin cabinet surface and then added many disconnected chunks of mass? Imagine 1/2" or less plywood with dozens of squares of lead filling the surface. If the chunks of lead have small gaps (and a compliant connection to the plywood?) then the stiffness they add could be minimal. Lead shot in a lossy goop layer?
Any other ideas about adding mass without adding stiffness?
David S.
Bricks, sand etc. as ballast internally - though it feels as if they'd not be damping much used like that.
This reminds me of when I added some paving slabs to my hi-fi rack. At first I liked the over the top bass but I soon tired of it and was refreshed to hear a more tuneful sound after removing them. I guess what I did was shift the resonance down and give it a long decay time.
This point "All other things being equal, higher mass means higer Q and longer number of cycles to decay" seems to be quite counter-intuitive to a lot of people but not to me after my rack experiment! I now feel I know why heavy metal and glass hi-fi racks sound so bad - compared to wooden ones, for example.
edit: obviously the science guys on here won't entertain the notion that resonance can affect the performance of electronic equipment. I think it's heresy on here.
This reminds me of when I added some paving slabs to my hi-fi rack. At first I liked the over the top bass but I soon tired of it and was refreshed to hear a more tuneful sound after removing them. I guess what I did was shift the resonance down and give it a long decay time.
This point "All other things being equal, higher mass means higer Q and longer number of cycles to decay" seems to be quite counter-intuitive to a lot of people but not to me after my rack experiment! I now feel I know why heavy metal and glass hi-fi racks sound so bad - compared to wooden ones, for example.
edit: obviously the science guys on here won't entertain the notion that resonance can affect the performance of electronic equipment. I think it's heresy on here.
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i agree...i dont see the misunderstanding....higher mass will increase Q, reduce freq, and as a result broadband excitation of the panel will reduce. resonant Q increases, decay time too. harmonic structure of the panel vibration may also be shifted, more towards resonance. If the freq is easy to damp(at a useful freq) then this would surely be easier to damp with a minimal mass of material.
eg i have some granite placemats, i bought for an experiment with a 4" woofer 2way. held by the corner, they ring like a dinner plate. But when glued rigidly, and with bracing added (even just mdf) I am sure it would be high enough to damp. the only problem i have atn is that the fundamental of the 6mm thick placemat is probably in the 100-200 hz range, maybe lower, but the harmonics are alot higher. I figured, maybe daftly, that since the fundamental is so much less audible, then damping all the higher harmonics would work, as long as i braced it enough to move the fundamental up.
I am torn between building one with very rigid corners, and internal panel damping, and one simply using silicone sealer to glue together and no internal damping.
the problem is how to define the -ve reactance, as in an LC tank, then define the level of loss, by adding a resistance in parallel. the analogy being, the closer we can get the -ve reactance to inversely equal the +ve one, then the more damping 'resistance' we need to prevent oscillation of many cycle at a very high Q.
I then tend to think its far easier to increase the resistance in series with the material, if you like. by some means i have yet to fully explore.
im not disagreeing...lol
eg i have some granite placemats, i bought for an experiment with a 4" woofer 2way. held by the corner, they ring like a dinner plate. But when glued rigidly, and with bracing added (even just mdf) I am sure it would be high enough to damp. the only problem i have atn is that the fundamental of the 6mm thick placemat is probably in the 100-200 hz range, maybe lower, but the harmonics are alot higher. I figured, maybe daftly, that since the fundamental is so much less audible, then damping all the higher harmonics would work, as long as i braced it enough to move the fundamental up.
I am torn between building one with very rigid corners, and internal panel damping, and one simply using silicone sealer to glue together and no internal damping.
the problem is how to define the -ve reactance, as in an LC tank, then define the level of loss, by adding a resistance in parallel. the analogy being, the closer we can get the -ve reactance to inversely equal the +ve one, then the more damping 'resistance' we need to prevent oscillation of many cycle at a very high Q.
I then tend to think its far easier to increase the resistance in series with the material, if you like. by some means i have yet to fully explore.
im not disagreeing...lol
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From an audibility point of view, I do think that shifting a resonance down in frequency and up in Q seems a bad move. If you consider how music is hoped to decay in a listening space - equally at all frequencies and not too quickly, not too slowly - then the idea of reducing ringing at most frequencies only to hear ringing at one or two distinct points goes against this. Colouration, as with room modes, will be heard. I don't see what's wrong with allowing a certain amount of resonance, as long as it is low Q / broadband. This is surely what the "box as an instrument" guys are getting at and I think they are maybe getting a little more efficiency from the speaker by doing this, and avoiding that "dull hi-fi sound".
I think this is another interesting and valid approach, even if it is counter-intuitive.
Harwood describes a defective cabinet where the corner battens were half connected. The resonance profile was distinctly better.
Rubber corners?
David
I'd advocate lower frequency but not higher Q. Harwood found resonances progressively less audible below 400Hz. I'd still want the damping to be as high as possible and I think that attaching flexible mass would likely add a damping component as well.
I'm not in that camp. Cabinet contribution can never be a flat and useful output. We need to reduce it, especially the resonant peaks. If the box is an instrument, does all your music sound like a cello, an acoustic guitar, a piano case? Bad idea.
David
Hello,
When Linkwitz was building closed boxed he used “tar and wool”. The tar was 3 parts Henry 107 plus 1 part sand. The goop is applied in layers to the inside of the cabinet panels. This stuff is really a mess and will get on everything until it is dry.
More mass in the form of chunks (tiles 6x6 or so) of ½ inch thick concrete Wounderboard can be set in the goop bed and coated with more tar goop.
This application is added mass and dampening only. The panels and bracing provide the required structural strength and stiffness.
107 ? Asphalt Emulsion | Henry.com
DT
All just for fun!
When Linkwitz was building closed boxed he used “tar and wool”. The tar was 3 parts Henry 107 plus 1 part sand. The goop is applied in layers to the inside of the cabinet panels. This stuff is really a mess and will get on everything until it is dry.
More mass in the form of chunks (tiles 6x6 or so) of ½ inch thick concrete Wounderboard can be set in the goop bed and coated with more tar goop.
This application is added mass and dampening only. The panels and bracing provide the required structural strength and stiffness.
107 ? Asphalt Emulsion | Henry.com
DT
All just for fun!
I've heard good things about porcelain times/floor tiles (we joked about that a few pages back). I wonder if there is an easy waterbased goop that stays forever soft? We once made something using a curable product that was rubbery and typically used by dentists for molds of teeth. At KEF we used a 2 part called Polyoll for filling 104/2 heads.
David
p.s. The Henry stuff looks like it might fill the bill.
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Tar stinks. Linoleum has about the same mass, doesn't ring, has negligible stiffness, and is a lot easier to use. Just glue it on with something flexible.
Or, use the stuff for car panel damping. It has a sort of solidish tar-like layer and is topped with a thin piece of what looks like roof flashing metal, so it's a constrained layer. Auto parts places have it. The downside is it's rather thick
I personally think there's an awful lot of overkill in some of the proposals I've read here.
Or, use the stuff for car panel damping. It has a sort of solidish tar-like layer and is topped with a thin piece of what looks like roof flashing metal, so it's a constrained layer. Auto parts places have it. The downside is it's rather thick
I personally think there's an awful lot of overkill in some of the proposals I've read here.
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