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Old 4th March 2014, 03:58 AM   #21
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so when I fill a sealed enclosure with loosely packed acoustic fluff, (other then preventing reflections which is for a different thread. ) the fluff ads dampening by being heavier then air aging inertia? is that correct?

I can picture an overly "springy" enclosure, that is to small would sound like. but how does a overly dampened box behave/sound in the real world and why?

laplace ; your quite a good teacher and really appreciate your explanations :-) thanks
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Old 4th March 2014, 04:18 AM   #22
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Quote:
Originally Posted by laplace View Post
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Very nice.

I'm not an expert in any which way, but I've always considered the driver "Q" on similar terms as xo "Q". It is the total value of how a driver or xo will behave at a specified frequency, under certain conditions. To get an even response: You can calculate a sealed box for a driver with low qts, but this would just make the driver roll off way above it's resonant frequency (fs), so it is inefficient. You can calculate a reflex box for a high qts driver, but this would result in a fb (frequency of box) normally much much lower than the drivers fs, potentially causing phase issues and possibly destruction because the driver will move at a different rate at different frequencies than it is designed for.
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Old 4th March 2014, 10:46 AM   #23
laplace is offline laplace  Australia
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Originally Posted by ubza1234 View Post
so when I fill a sealed enclosure with loosely packed acoustic fluff, (other then preventing reflections which is for a different thread. ) the fluff ads dampening by being heavier then air aging inertia? is that correct?

I can picture an overly "springy" enclosure, that is to small would sound like. but how does a overly dampened box behave/sound in the real world and why?

laplace ; your quite a good teacher and really appreciate your explanations :-) thanks
Glad to be able to help somewhat...

Yes, adding stuffing increases the density of the "air" in the box and therefore increases damping without changing the springiness very much. It means you can use a smaller box without it becoming boomy due to being too springy.

An overdamped box will sound dull and flat, like beating on wet cardboard instead of a drum. It might sound a bit "soggy" or "flappy" if that makes any sense. There might be a lot of cone movement and not much sound if the box is too big.
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Old 4th March 2014, 11:22 AM   #24
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Always assumed that adding stuffing increased the resistance the air has to move through. Many more fibers to slow down and create tiny fluctuations in the air's movement, making it move slower as an end result. If anything you *reduce* the volume of air whilst adding stuffing?
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Old 4th March 2014, 11:29 AM   #25
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It's both: the fibre vibrates with the air (denser moving mass) and the air suffers viscous drag in its coupling to the fibre; both result in a damping effect.

Yes the air volume is smaller of course, but the damping effect increases much faster (stuffing is what, hundreds of times denser than air?) than the compliance falls due to lost volume, so the Q falls with addition of stuffing.
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Old 4th March 2014, 12:52 PM   #26
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So rockwool is better than nylon-polyamide because it is denser? Makes sense to me at least.
Increased resistance because of increased weight, and therefore a difference in inertia. Or something.

Last edited by KaffiMann; 4th March 2014 at 12:56 PM.
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Old 4th March 2014, 04:44 PM   #27
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Ideally the "stuffing" should be thermodynamically connected to the air, not mechanically connected.
If the "stuffing" is so dense that it moves with the air within the box it is too dense and is not doing the job that it is supposed to.
It is then an outright damper.
Stuffing should increase the apparent volume of the "Air" (box volume)

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Old 4th March 2014, 07:26 PM   #28
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Stuffing within an enclosure has two functions, One: To increase the apparent volume that the driver "sees", whereby we can reduce the actual dimensions of the enclosure (10-18%).
Second, quite likely a more important benefit, to "kill" frequencies that emanate from the rear of the cone....these frequencies wind up bouncing off the inner back wall of the enclosure, come forward & set the cone in motion.....the driver trying to act like a microphone..........this winds up fouling things up as you can imagine.
The practical "test" when your building these enclosures, once built & you've stuffed it full..........You simply talk into your enclosure, yell, sing "scales" into the hole where you would mount your driver. You should hear no resonance, no reflected sound whatsoever........it is an odd thing not hearing anything when you do this....one half expects to hear SOMETHING? It is a "sound sponge", nothing to hear, it is strange.




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Last edited by Richard Ellis; 4th March 2014 at 07:29 PM. Reason: typo
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Old 4th March 2014, 07:31 PM   #29
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Quote:
Originally Posted by Shadydave View Post
Ideally the "stuffing" should be thermodynamically connected to the air, not mechanically connected.
excellent point
Quote:
If the "stuffing" is so dense that it moves with the air within the box it is too dense and is not doing the job that it is supposed to.
It is then an outright damper.
...
Dave
This is an issue I'm finding rather difficult to achieve with my mltl using conventional stuffing. bjorno posted up a suggestion on using Ikea pillow fill, declumped and fluffed per directions (prefer the word "Guidance" and still shifting is an issue, adds distortion, audible close in. What doesn't shift are microfiber towels. Have yet to slice up some to control in a more refined way. In that configuration is ~12oz for a Vb of 27.5L. Flow is much improved yet far overdampened.
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Old 4th March 2014, 09:37 PM   #30
laplace is offline laplace  Australia
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Originally Posted by KaffiMann View Post
So rockwool is better than nylon-polyamide because it is denser? Makes sense to me at least.
Increased resistance because of increased weight, and therefore a difference in inertia. Or something.
Better performance from the greater mass, yes, and the fibres are probably finer too so you get more resistive drag on air motion.

However, the crumbling and presence of irritating particles that are a hazard to your lungs are a pretty big drawback...
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