I read a passage in the dead cabinet thread about stiffness being crucial where low energy storage is a requirement. What does everyone think about low energy storage enclosure requirements. I have performed a search and there seems to be a lot of conflicting opinions out there.
Dan
PS: I am particularly linterested in the effects on a sealed low frequency enclosure
Dan
PS: I am particularly linterested in the effects on a sealed low frequency enclosure
I haven't read anything on this subject but Moving Mass = stored energy, so reduce the movement of the panels. A wild guess here but maybe enclosure Q also correlates with stored energy. Low Q = low stored energy... maybe.
ding said:
Energy storage has to do with how long the resonances in a cabinet continue to ring after the initial stimulus. The longer the ringing, the greater the energy storage.
There are basically two approaches you can take in dealing with it. Either you can move the resonances up or down in frequency so that they're not excited by the particular driver in the first place, or you can employ resistive losses to damp existing resonances which more effectively turns mechanical energy into heat.
It's not surprising that you found conflicting opinions as some folks feel that the cabinet should be inert and not contribute anything to the sound coming from the drivers themselves and others feel that the cabinet should contribute significantly, much like the body of a violin or piano contribute to the vibrations of its strings.
If you want more accurate, objective performance, you'd go with the latter. If you want something more subjectively pleasing you might opt for the latter, though there's no guarantee that you yourself will be subjectively pleased by the result. It all boils down to individual tastes, preferences and philosophies.
se
Circlotron said:
Not too wild a guess. It does relate to stored energy, but in a different context. The Q of an enclosure relates to the resonance of the cavity of air it encloses (i.e. its Helmholz frequency). A bit different matter from the mechanical resonances of the material enclosure itself.
se
Another way to look at the problem is by modeling the air volume and cabinet as springs. I'm of course assuming a sealed cabinet here. The major benefit of a sealed cabinet, found lacking in most other designs, is the added transient response. This is a result of the air acting like a fairly linear spring, which becomes more non-linear the greater the excursion, i.e. greater excursion=greater distortion. For the response of the enclosure to behave more like the perfect model, you want to minimize the effect of other springs in the system, because when you have two springs modeled in series (like here), the net result is an overall spring constant lower than both, which translates into a performance loss. Basically, the more rigid the enclosure, the less it will behave like a spring. In theory.
-Joe
-Joe
Clayton's port.
A thought just popped into my mind, and that is if the enclosure sides did flex a bit then at very low frequencies they would simply respond to the air pressure in the box, so when the cone moves inward, the box "puffs up" and the panels flex out. But when the panels reach their resonance they might be vibrating opposite to the speaker cone, much the same way as a passive radiator cone does. This would in a way be a good thing perhaps. You could even have a reflex box that doesn't actually have a port but is sealed! It would get trickier if the panel resonance is different to the box volume resonance (which it probably is). Would probably work best with a cube shaped box that has all panels the same size so have similar resonances and all flex in the same mode.
A thought just popped into my mind, and that is if the enclosure sides did flex a bit then at very low frequencies they would simply respond to the air pressure in the box, so when the cone moves inward, the box "puffs up" and the panels flex out. But when the panels reach their resonance they might be vibrating opposite to the speaker cone, much the same way as a passive radiator cone does. This would in a way be a good thing perhaps. You could even have a reflex box that doesn't actually have a port but is sealed! It would get trickier if the panel resonance is different to the box volume resonance (which it probably is). Would probably work best with a cube shaped box that has all panels the same size so have similar resonances and all flex in the same mode.
Re: Clayton's port.
A cube probably isn't the best idea because of the internal standing waves.
How about having a rigid cabinet with just one wall that flexes. You could mount a thin plywood panel inside one wall or make an entire wall out of the plywood.
You would have to tune it with the size and thickness of the plywood. You could possibly use a thin plywood wall and tune it by adding weight (plastecine or similar).
This one wouldn't come with a guarantee. Might be fun to experiment with though.
Steve
Circlotron said:
A cube probably isn't the best idea because of the internal standing waves.
How about having a rigid cabinet with just one wall that flexes. You could mount a thin plywood panel inside one wall or make an entire wall out of the plywood.
You would have to tune it with the size and thickness of the plywood. You could possibly use a thin plywood wall and tune it by adding weight (plastecine or similar).
This one wouldn't come with a guarantee. Might be fun to experiment with though.
Steve
An alternative would be to have fixed, rigid panels and the plywood sheet like a partition inside.
This would be an example of a "diaphragmatic absorber" of the sort sometimes used in a room to dampen room resonances.
Again, no guarantees but if you've got the time, some wood and a couple of bass drivers (I suspect that cheaper would be better for this) you might get some interesting results. The main thing is that you could learn a lot in the process.
Steve
This would be an example of a "diaphragmatic absorber" of the sort sometimes used in a room to dampen room resonances.
Again, no guarantees but if you've got the time, some wood and a couple of bass drivers (I suspect that cheaper would be better for this) you might get some interesting results. The main thing is that you could learn a lot in the process.
Steve
dead enclosures
Umm,
Just IMO and IME there are a couple of things to remeber.
The walls resonate and this is mostly due to the fact that they are clamped flat rectangles and thus have bending modes.
Curved surfaces don't have strong bending modes but enclosures using them are rare.
Materials that are rigid, have low storage are not usually available to DIYers. You may be able to find soame rigid foam core laminates.
If you want to deaden the output of typical MDF or chipboard cab's, at reasonable cost in rectangular enclosures, there are lots of ways to do this: cross bracing, vertical strip bracing, and dual walls filled with sand.
A cheap but slow method is to glue several layers of thin hardboard or mdf together under pressure (use blocks or sand bags overnite) using a water based contact adhesivewater based - for each enclosure wall.
Glued and later pinned to each wall this will stiffen the walls notably, and provides some sheer force and constrained layer damping.
You can also include a layer of lead sheet in there, sometimes you can pick this up at builders recyclers. This is most valuable on the front baffle and rear.
Layers of mineral loaded bitumen or one of the acoustic absorbent sheets can also be used over the mdf.
One of the unsung and yet very effective methods is to use modelling clay, of the oil/wax base type with lead shot mixed in AFTER you have heated the clay up.
Once mixed, pieces can be formed while still warm and sticky and layered on to all the resonant surfaces and is very effective on driver frames. Makes the box heavy though.
I would guess that this method is likely to be the most economical and it is VERY effective and lasts forever.
In large box for a Sub say I would also cross brace in both dimensions but not at the center of the panels.
A very useful tool (esp. for positioning braces) is a stethoscope, along with a block of wood, hand sized and about two inches thick, to give you a dead reference when you are listening to the cabinet.
Timbo
Umm,
Just IMO and IME there are a couple of things to remeber.
The walls resonate and this is mostly due to the fact that they are clamped flat rectangles and thus have bending modes.
Curved surfaces don't have strong bending modes but enclosures using them are rare.
Materials that are rigid, have low storage are not usually available to DIYers. You may be able to find soame rigid foam core laminates.
If you want to deaden the output of typical MDF or chipboard cab's, at reasonable cost in rectangular enclosures, there are lots of ways to do this: cross bracing, vertical strip bracing, and dual walls filled with sand.
A cheap but slow method is to glue several layers of thin hardboard or mdf together under pressure (use blocks or sand bags overnite) using a water based contact adhesivewater based - for each enclosure wall.
Glued and later pinned to each wall this will stiffen the walls notably, and provides some sheer force and constrained layer damping.
You can also include a layer of lead sheet in there, sometimes you can pick this up at builders recyclers. This is most valuable on the front baffle and rear.
Layers of mineral loaded bitumen or one of the acoustic absorbent sheets can also be used over the mdf.
One of the unsung and yet very effective methods is to use modelling clay, of the oil/wax base type with lead shot mixed in AFTER you have heated the clay up.
Once mixed, pieces can be formed while still warm and sticky and layered on to all the resonant surfaces and is very effective on driver frames. Makes the box heavy though.
I would guess that this method is likely to be the most economical and it is VERY effective and lasts forever.
In large box for a Sub say I would also cross brace in both dimensions but not at the center of the panels.
A very useful tool (esp. for positioning braces) is a stethoscope, along with a block of wood, hand sized and about two inches thick, to give you a dead reference when you are listening to the cabinet.
Timbo
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