My response was not technical, there was no math in it at all. If I'd wanted to get "technical" I could have done so. It was simply a correction to an incorrect statement, technicaly or not, with the reason why being stated. And he should "eat my hat".
This is the article I was thinking of in post #4. Just realised I hadn't posted it.
http://www.nousaine.com/pdfs/Box%20Stuffing.pdf
No, that was the point, that the difference was modest and had limits. Continuing to increase the density of the stuffing material does not bring a proportional increase in effective enclosure volume (and in TN's test it reaches a knee and then decreases), which was the OP's idea;
No, I'm not Tom Nousaine incognito, but pretty much everything in his article you linked on stuffing small boxes I've already covered here previously.
I'm getting the feeling reading these posts that many here need to purchase a copy of Vance Dickason's Loudspeaker Design Cookbook. He's got an even more thorough theoretical and emperical study of box stuffing in it. It's the current 'bible' on loudspeaker design and construction. In addition to more stuffing info, you'll get a derth of information on loudspeakers.
It should be obvious that it's not benefitial to replace all air in a box with solid material - that's a simple volume decrease 😉
But what are we discussing here? Absorption, dampening or virtual volume increase?
Best, Markus
Awesome. I added it in because I intended to when I wrote post 4, but didn't have time to find it then, and found a note to myself to add it, so I did.
I took it to be both absorption and virtual volume increase. As it was not specified that it was for sub only, absorption for rear wave control in MB/MF and VVI for LF.
Yes they are. But I have the feeling that some people here don't see the whole picture.
Best, Markus
Thats usually the case.
The only point that I would make is that this is not a significant issue in speaker design, it's actually rather insignificant. Just put a "good" amount (not too much, not too little) of decent absorption material in the box and be done with it. Obsessing about the fiber length and stuffing density just aren't that important.
No they are not.
There are three things to consider.
1 Generation of standing waves inside the enclosure. The shape of the enclosure impacts on this one. The closer to a sphere you get to the more random the standing waves. At the opposite end we have the cube, this will make one big standing wave impacting on your frequency response.
2 Sound absorbtion/damping. Takes in acoustic energy and transforms it to heat thus 'dampining' standing waves.
3. Volume increases. This is a different effect using different materials. Here open cell foam is the clear winner. However it won't make much difference to lower bass energy.
Remember we are only considering the energy output of the driver. That is bass energy for bass enclosures or mid energy for mid drivers. You can consider all three separate as the design/materials required to help in all three instances are much different. Yes it can make a huge difference. Controlling this acoustic energy gives, 'tighter' 'faster' bass.
Terry
foam is not manufactured with the precision of a silicon wafer. some cells are open and some are closed.
the proportion of one relative to another will depend on the type of foam. the size of an average opening will vary as well.
i just mentioned two extremes because i thought it was obvious that you can also have everything in between.
that's it Brett, now you're going DOWN. i hope the take home message for you will be that Borat is always right.
even though i welcome everybody to question what i write i strongly recommend that before criticizing my posts you READ THEM first.
now comes your education. fasten your seat belt.
effective box volume increase comes from thermodynamics. when a gas ( such as air ) is compressed it doesn't just have its pressure but also its temperature go up.
we do not really think about the heat component when we think speakers but its there and its important. this heating due to compression is what allows air conditioners and refrigerators to work and why the most important part of them is called COMPRESSOR.
the increase in temperature however results in ADDITIONAL increase in pressure. this is how internal combustion engines work - the power to move your car comes form the pressure increase which is caused by temperature increase from combustion.
in supercharging and turbocharging such temperature increase is undesirable and a device known as INTERCOOLER is used to extract heat out of the air in the intake allowing more air to be packed into the cylinders as cooler air doesn't resist compression as much.
this is exactly how stuffing works to increase box volume - it acts as an intercooler. well not exactly - it really acts as a thermal mass. while turbochargers always compress air speakers compress it 50% of the time and rarefy it the other 50% of the time. when air is compressed stuffing stores the heat and when air is rarefied it releases it back. the net effect is the same as with intercooler - more air can get packed into the same volume effectively increasing box size.
now there is a limit to this. at best you can remove 100% of pressure due to temperature increase ( by completely clamping the temperature with the thermal mass of the fibers ) but you will still have all of the pressure increase that simply comes from more gas occupying the same space. therefore once the thermal mass of stuffing is sufficient to clamp the temperature you get no further box volume increase from adding more.
UNFORTUNATELY FOR YOU THAT IS NOT WHAT I WAS TALKING ABOUT
i was talking about increase in absorption of standing wave resonant energy in the box which is subject to a completely different mechanisms namely viscosity and/or turbulence. this has ZERO to do with the thermodynamic issues discussed above and is NOT subject to the same limits.
and i have SPECIFICALLY stated in this very thread that i consider box volume increase to be merely a SIDE EFFECT of stuffing while damping is the GOAL.
why ?
because box volume can simply be increased ( get ready for it ! ) by increasing the box size ! ! ! is this shocking ? on the other hand damping of standing wave resonant energy is NOT improved by increasing box size therefore it is NECESSARY to stuff the box for the damping of standing waves but NOT necessary to stuff it for effective volume gain.
if you look at commercial speakers from serious makers they NEVER use stuffing to increase box volume - only to increase absorption. how do i know their REASONS ? very simple ! because they will stuff the midrange enclosure before they stuff the woofer enclosure - and guess which one needs the extra volume ?
i hope this answers your questions.
excellent question.
a lot of confusion in audio comes from the fact that a single word like DAMPING is used to describe multiple unrelated physical phenomena.
there is at least 3 different kinds of damping in a speaker box:
1 - electromechanical damping that defines speaker Q and is primarily accomplished by speaker motor switching into generator mode. stuffing while having an effect here should NOT be regarded as means of achieving the desired level of this type of damping.
2 - cabinet damping which can be tested by knuckle test and is primarily due to the glue in MDF
3 - internal standing waves damping that is accomplished by foam and stuffing and is primarily due to viscosity of air on a small scale when passing through fine openings. this is the same mechanism that provides damping in automotive shock absorbers.
i thought it was clear that i was talking about number 3 but apparently it wasn't.
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