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
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
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.
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
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.
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.
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.
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)
Dave
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)
Dave
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.
____________________________________________________Rick..........
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.
____________________________________________________Rick..........
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excellent point
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.
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...
It's not a matter of cancelling. The force on the cone is the sum of the spring-force due to the box pressure increasing, and the resistive damping force. Adding damping increases the resistive damping force, which lowers Q and makes the system ring less. It does not reduce or cancel out the spring force, it changes the ratio of the two forces.
I like just having a very thin sheet of felt surrounding the rear of the driver to make sure it's all neat'n'tidy.
I also tried stuffing a t-tqwt with ikea pillows, ended up using a single layer of 2cm thick wool felt in the bottom part, much cleaner sound.
"As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications." - eminence.com I don't understand why a high Qtc is suitable for an infinite baffle. Seems to me it would ring like a bell!
I always had the idea that sealed subs sound "better" or "tighter" or "flatter".
Until I got a proper sub with a light cone (unlike car subs that have heavy, plastic cones). Built both a ported and a sealed sub, and man the ported one sounds sooo nice. I obviously built it to be flat, not boomy as many people think they are.
So yes, it's all about the driver.
Until I got a proper sub with a light cone (unlike car subs that have heavy, plastic cones). Built both a ported and a sealed sub, and man the ported one sounds sooo nice. I obviously built it to be flat, not boomy as many people think they are.
So yes, it's all about the driver.
The most help I've ever seen on this topic....leading to others' insightful elementary contributions.
Belated thank you Cal.
The resulting Qtc from putting a driver in an enclosure will always be higher than Qts.
The smaller the enclosure the higher the Qtc will be. This is because the smaller the box, the stiffer the air "spring" pushing back on the cone. (think about it, a big box = lots of air = easier to compress a few cm). The stiffer the air spring, the less damping, and the more it tends to keep vibrating (aka ringing).
A higher Qtc will tend to ring more than a lower Qtc.
You don't usually want this, so if a speaker has a high Qts, you want a very large or even infinite box to avoid ending up with an unpleasantly high Qtc.
The smaller the enclosure the higher the Qtc will be. This is because the smaller the box, the stiffer the air "spring" pushing back on the cone. (think about it, a big box = lots of air = easier to compress a few cm). The stiffer the air spring, the less damping, and the more it tends to keep vibrating (aka ringing).
A higher Qtc will tend to ring more than a lower Qtc.
You don't usually want this, so if a speaker has a high Qts, you want a very large or even infinite box to avoid ending up with an unpleasantly high Qtc.
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