Does stuffing a vented enclosure give an apparent increase in volume the same way it does for a sealed enclosure. If so, is the increase the same as for a sealed enclosure?
I would say no. The primary purpose of stuffing in a vented cabinet is attenuation of internal reflections, not cabinet size enhancement.
OTOH, I have worked on some speakers with PR's that are stuffed like a AS.
OTOH, I have worked on some speakers with PR's that are stuffed like a AS.
I think it may not be quite as effective in increasing the box size, but it's fairly effective in reducing the efficacy of the port.
To answer your question, yes, the apparent volume increase is the same whether the box is vented or sealed. It is a compliance increase that makes the box look a little larger and would push both the vent frequency or the closed box resonance downwards. The "adiabatic to isothermal" conversion can give a theoretical 40% compliance increase. In practice I remember more like 20% max. and also a little mass loading.
The others are right that vent Q will be effected and that may be a bigger factor in defining bottom end response.
David S.
The others are right that vent Q will be effected and that may be a bigger factor in defining bottom end response.
David S.
if you know your woofer T/S parameters you may use a box simulator i.e. Unibox to see the effects of more or less dampening:
UniBox - Unified Box Model for Loudspeaker Design - Kristian Ougaard 😉
Although I haven't tried simulating it, I was under the impression that any stuffing (of the sort usually seen in closed boxes) added to a vented box will always cause a net reduction in bass, since the loss in bass response caused by damping the high Q vent resonance will outweigh any small gain that might occur from the apparent size of the cabinet volume increase.
Certainly that has been the case on the boxes I have measured, but I'm not sure if its universal or only occurs with "typical" alignments. Anyone know for sure ?
see what i dont quite understand.. is yes it does add some acostical volume. but it has physical mass and volume itself. so in a vented enclosure tuned to say 30hz. if you lightly dampened the cabinet with foam. the foam apparently adds to the volume, while also having a volume of its own, doesnt quite make sence. i would have thought for a vented speaker you could crush your dampining into a cube and mesure its volume, and then include that in the final box volume, but if it adds this so called vomule itself is what it adds equal to what it takes up? it is a baffaling subject, and one i still dont have a answer to
Thats a hard question to answer on a theoretical basis. You'd have to run the experiment to see if you can optimize in practice. My impression was that you can thickly line a cabinet but leave plenty of open volume around the port and center of the cab and not impact vent Q too badly. Still, I don't have the empirical evidence to prove it.
Pete_B did a nice study a year or so ago (might have been at classic speakers) where he went through a series of sealed box stuffing densities. Initially the woofer resonance and 3dB point went down as he increased stuffing quantity. Eventually the density got to be too much and the resonance went back up. Not exactly a vented box but somewhat similar.
Doesn't Vance's book experiment with this some?
David
Pete_B did a nice study a year or so ago (might have been at classic speakers) where he went through a series of sealed box stuffing densities. Initially the woofer resonance and 3dB point went down as he increased stuffing quantity. Eventually the density got to be too much and the resonance went back up. Not exactly a vented box but somewhat similar.
Doesn't Vance's book experiment with this some?
David
it just sounds stupid to me, how can stuffing a box up with fibers that take up half of it atully make the box seem larger to the woofer, when there physically far less of a box than before. it defies physics, im curious to know
thats what i was planning to do, but do i make the box volume say 80l tuned to 30hz then add the padding, or do i make it 80 with 10l to spare for the volume of the padding?
for my ataul box of 80.5l tuned to 24ish hz i was simply planning to make the box 90l to allow for the driver and the padding, its just if i get it wrong the driver may wind up tuned tooo looow
the other option is to abandon stuffing altogether as i am using 25mm mdf and my port has 2 90degree twists at both ends.
for my ataul box of 80.5l tuned to 24ish hz i was simply planning to make the box 90l to allow for the driver and the padding, its just if i get it wrong the driver may wind up tuned tooo looow
the other option is to abandon stuffing altogether as i am using 25mm mdf and my port has 2 90degree twists at both ends.
In simulation on a vented box, adding stuffing increases F3 and decreases bass response.
In simulation on a closed box, removing stuffing decreases F3 and increases bass response. Hope this helps.
In simulation on a closed box, removing stuffing decreases F3 and increases bass response. Hope this helps.
im guessing f3 is tuning frequency.. so i need to allow volume for the stuffing then
so incresing the -3db point do you mean, lowering it down from say 30-28 or raising it up from say 30-33?
that little pfb from earlyer on in the topic says adding stuffing tunes the port lower, thus decresing bass output
Hi,
Independent of the physical volume of the foam or fibres, stuffing and
foam lining increases the effective volume of the box, foam lining a little.
For stuffing a vented box its best to keep it away from the port end.
e.g. stuffing behind the driver but not the port is a halfway house.
rgds, sreten.
Good reference. Elliot is getting a little bit of extension with a modest loss of bass level from the foam lined case.
David