if foam was placed in a vacuum it could carry a wave all by itself.
all it takes for a wave is mass and elasticity. air has it but also the foam itself has it.
perhaps what needs to be measured is speed of sound in the foam itself ( when the foam is in vacuum ).
the actual wave is then a superposition of air wave ( in immobilized foam ) and foam wave ( in vacuum ) with a certain degree of coupling between the two !
the only useful model would have to be built on this foundation. it would then be able to correctly predict all effects.
all it takes for a wave is mass and elasticity. air has it but also the foam itself has it.
perhaps what needs to be measured is speed of sound in the foam itself ( when the foam is in vacuum ).
the actual wave is then a superposition of air wave ( in immobilized foam ) and foam wave ( in vacuum ) with a certain degree of coupling between the two !
the only useful model would have to be built on this foundation. it would then be able to correctly predict all effects.
Yup that would be a good analytical method, perhaps just by subtracting the resultant wave from the original, sine or otherwise, would give you a pretty good idea of the characteristics. That is, although its possibly not the easiest method around. Maybe an improvement though.
yes sorry. my bad.
I agree this may be partially true, although i cant see it working for a small volume box say 5litres. maybe if you had a 100litre box then it would be quite possible.
again quite possibly, in a large volume.
I agree. as the foam doesnt have a uniform density due to the aerated structure, the nearest approximation would be to do exactly that. I expect it would be more accurate than current methods.
I have just read this thread completely, and I like to give the open cell foam a try. What i could not find however, is the recommended PPI for the foam (I will be using it in a midbass enclosure covering 100Hz - 1Khz)
I have read Earl uses his "scrap", which comes (I think) from the fabrication of his well known foam plugs (which use 30 PPI foam I think).
Earl, if you are still following this thread, could you please confirm this? As this foam is quite expensive, I do not want to buy all available sorts to see what works…
I have read Earl uses his "scrap", which comes (I think) from the fabrication of his well known foam plugs (which use 30 PPI foam I think).
Earl, if you are still following this thread, could you please confirm this? As this foam is quite expensive, I do not want to buy all available sorts to see what works…
Yes, too dense will "turn the corner" and have a negative effect. Too open and you are not getting as much effect as you could. For a waveguide I tested a wide range and 30 PPI was the optimum. For use inside, I suspect that this is too open. I can almost guarantee it, because I was looking for low loss at 10 kHz. At 100 Hz, this would equate to almost nothing. I would go to 50 ppi just on principle. I would suspect that 80 PPi might be the optimum, but its hard to say.
Wim, Take a look at the foam used in outdoor and nautical furniture. Some of that is obviously reticulated because the water just goes right through. What the PPI is, I don't know.
Sorry to be dragging up old threads but this interested me and I want to understand.
If a speaker moves in a sinusoidal fashion then the forward air flow = reverse air flow (in magnitude) at the surface of the cone.
The definition of power = pressure drop x flow = flow^2 x impedance in the equivalent circuit.
So if the impedances are different in the front and rear circuits, as they clearly are in a loudspeaker system (enclosure vs room) then the power delivered in each hemisphere differs by the ratio of the impedances, which will generally be quite significant. The only case where they will be the same is an infinite baffle system into open space on each side.
I hope this isnt too techy but I think this is what happens. Air flows front/back are equal but neither pressures nor powers are.
A little update on my progress...
I got several qoutes for 75ppi open cell foam (Bulpren S 31 062), but this stuff is too expensive for me (more then 200 euro to fill the entire speaker, per speaker!).
So I filled the inner volume with 30 PPI filterfoam (can be got quite cheap at the local pond shop) and I lined the side walls with 5cm Basotect (an open cell melamine foam of 200 PPI that can be got quite cheap here)
The enclosure has the following inner dimensions: 420 x 316 x 658 (D x W x H) and is loaded with an AE speakers TD12M and a CD horn (Geddes 12”).
I measured the impedance of the TD12M installed in the filled enclosure, and to my eyes it looks very well-behaved (see the scale on zoomed chart), so I would think the damping material has done a decent job. Does anyone know above what point an irregularity in the impedance becomes significant? I seen examples with peaks of 3 ohms and more, so I would think 0.26 ohm (my highest peak) would count as insignificant…
I got several qoutes for 75ppi open cell foam (Bulpren S 31 062), but this stuff is too expensive for me (more then 200 euro to fill the entire speaker, per speaker!).
So I filled the inner volume with 30 PPI filterfoam (can be got quite cheap at the local pond shop) and I lined the side walls with 5cm Basotect (an open cell melamine foam of 200 PPI that can be got quite cheap here)
The enclosure has the following inner dimensions: 420 x 316 x 658 (D x W x H) and is loaded with an AE speakers TD12M and a CD horn (Geddes 12”).
I measured the impedance of the TD12M installed in the filled enclosure, and to my eyes it looks very well-behaved (see the scale on zoomed chart), so I would think the damping material has done a decent job. Does anyone know above what point an irregularity in the impedance becomes significant? I seen examples with peaks of 3 ohms and more, so I would think 0.26 ohm (my highest peak) would count as insignificant…
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Why do you think not the entire innner volume is filled?
Because the weed was smoked is the long listening hours building and testing listening equipment which was bought with the money which was supposed to be stuffed in the box just as the weed
Kef has another approach to getting more volume out of a given box. It's called ACE technology. It's used in their >$100,000 flagship loudspeaker, the Muon.
Read more about it here
ACE Technology[/QUOTE]
Gallo also claims to use a proprietary fiber stuffing that extends the low-frequency response up to two octaves...
Read more about it here
ACE Technology[/QUOTE]
Gallo also claims to use a proprietary fiber stuffing that extends the low-frequency response up to two octaves...
closest I could find...
Anthony Gallo Acoustics Classico CL-3 Loudspeaker (TAS 224) | The Absolute Sound
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