i think you got this one 180 degrees out of phase.
light stuffing is what one would use for box volume increase.
dense foam is what one would use for bass energy absorption.
but at least we agree that the two effects are separate and unrelated.
box volume increase would require maximum surface of material in contact with air as well as materially be maximally dispersed through the air. in other words heat transfer is what is to be maximized here. think of the design of radiators in your car and air conditioner - that is what is needed here.
bass energy absorption is on the other hand related not to radiators but to suspension components such as shocks and struts. here we want not to maximize heat transfer but to restrict the passage of the fluid ( air ) to openings of a sufficiently small scale that the medium ( air ) begins to exhibit sufficient viscosity.
the difference between a more viscous fluid and less viscous one is in the size of the opening that it takes to produce resistance. on a large enough scale very viscous substances like mud can act as if they are completely liquid and flow freely ( mudslide ). on a small enough scale very fluid substances like air can be highly viscous and provide significant drag (air filter).
this is where you have to recognize that all foam is not the same. just because foam is open cell doesn't mean all openings are same size.
Hmmm if you intend to make a lot of people not take anything you say seriously then this is probably one of the quickest ways to do so 😉
Having read Brett's original post #4 I think that it is a stretch to say he was criticising your post!
Whilst I will agree with the first part of this (ie intercooling allows more air to be packed in) The primary reason for wanting to do this is not that it is easier to compress (the opposite is the case), but that it means that there is more oxygen per cc of air (due to the fact that cold air has higher density) which allows more fuel to be added per cylinder charge. The result is that there is more fuel and more oxygen to burn resulting in more energy expended and hence more power.
Tony.
Hey all, thanks everybody for there input, the more information the merrier
I am currently using "Acoustic Foam/egg crate" from Clark Rubber (expensive) that i think is 35mm... After reading this thread i tried looking for the exact details but found almost none... I can only assume its open cell?? Has anybody used it?
I have the top/sides and back wall lined top to bottom, no the front, is this enough/too much??
Should I be only lining directly behind the drivers with the foam?
Should i add some of the bag of cheap Jaycar "poly-fill?" to the bottom of the box.
Also with the foam in place and my 80mm port curving into the center of my boxes i have about a 10mm gap around the port for the pressure to pass from the drivers at the top to the bottom of the box past the port in the middle? Is this an issue?
Cheers all 🙂
Dean
I am currently using "Acoustic Foam/egg crate" from Clark Rubber (expensive) that i think is 35mm... After reading this thread i tried looking for the exact details but found almost none... I can only assume its open cell?? Has anybody used it?
I have the top/sides and back wall lined top to bottom, no the front, is this enough/too much??
Should I be only lining directly behind the drivers with the foam?
Should i add some of the bag of cheap Jaycar "poly-fill?" to the bottom of the box.
Also with the foam in place and my 80mm port curving into the center of my boxes i have about a 10mm gap around the port for the pressure to pass from the drivers at the top to the bottom of the box past the port in the middle? Is this an issue?
Cheers all 🙂
Dean
Agreed again. Borat seems to be making a mountain out of a molehill. Of course, without any conclusive test data in support of his claim regarding the primary purpose of stuffing to damping standing waves.
And so the debate will go on and on and on.......Also, simply making a box larger to solve the box vol. increase issue isn't always an option when the all-critical WAF is taken into account in a new design.
I my case, where I work mostly with boxes that already exist, gaining a few hz in bass response with the judicious use of proper stuffing type and technique is always welcome by customers.
I'm not sure about the type of foam you used, but what you've done with it seems quite correct for the type of speaker you have.
Don't forget, you are the final judge of how well your speakers sound. Give them a good, critical listen over an extended period. If you don't tire of them and find yourself going back and listening to those favorite tracks, I'd say you succeded with your design and construction.
Hi Dean,
Yes I have a roll of that clark rubber stuff. I put it on the floor between the speaker and the mic when I take measurements... It was one of the types of foam I tested in my boxes (test results earlier in this thread, though I can't say for certain whether the eggcrate foam in the graph was indeed the clark rubber stuff or some other that I had from packing materials). It is ok but not as good as the special stuff I eventually purchased (certainly it's a lot better than nothing). Having two layers of it on the back wall helps as well 🙂
I don't know if it is open or closed cell, I would assume open, but could well be wrong 🙂
Try putting in some polyfill as well, if you don't find it offensive (shouldn't if you don't overdo it) it certainly will not do any harm.
Tony.
Just because you always want to be right doesn't mean you are always right. Loudspeakers and car engines are different, although they both produce noise 🙂
You seriously should read a good book to get a better understanding of the basic principles in speaker building. Someone already mentioned Vance Dickason's "Loudspeaker Cookbook". It's an excellent start.
Best, Markus
not your average bulletproof logic
From Borat:
From Borat:
Borat, Which is it? Does "stuffed box only" mean sealed? Are you saying a sealed box works better than vented?
Wow! Lots of chest pounding and sword rattling going on here.
I am curiuos why I just get a "No!" without the honor of a diatribe.
Borat does have a few things wrong, mostly about foam. There are the two extremes of all cells open and all cells closed, that is true, as he said, but depending on which end of the scale you are targeting the foam is made differently. And yes, the cell size is variable, but a good manufacturer can control this to a very tight range of sizes.
Closed cell foam is the oldest and yes even in this type of foam some cell walls collapse, but the vast amjority of them are still in tack. This makes sound waves not penetrate very well and so the absorption is lower due to the lack of air flow. This type of foam is good for thermal insulation for the same reason.
Open cell foam is processed with another step wearby the gas left inside of each cell is flamable and a flame is sent through the brick blowing or burning out the cell walls. This results in the vast majority of cells being open. Sound waves readly penetrate this kind of foam and hence flow resistance develops and the foam acts as a good sound absorber - also know as damping when this is converted into the mechanical domain. This type of foam is a poor thermal barrier.
The cell size is highly variable in production from hundres of cells per in^2 to only ten or twenty. The variance on the cell sizes tends to be quite small.
I am curiuos why I just get a "No!" without the honor of a diatribe.
Borat does have a few things wrong, mostly about foam. There are the two extremes of all cells open and all cells closed, that is true, as he said, but depending on which end of the scale you are targeting the foam is made differently. And yes, the cell size is variable, but a good manufacturer can control this to a very tight range of sizes.
Closed cell foam is the oldest and yes even in this type of foam some cell walls collapse, but the vast amjority of them are still in tack. This makes sound waves not penetrate very well and so the absorption is lower due to the lack of air flow. This type of foam is good for thermal insulation for the same reason.
Open cell foam is processed with another step wearby the gas left inside of each cell is flamable and a flame is sent through the brick blowing or burning out the cell walls. This results in the vast majority of cells being open. Sound waves readly penetrate this kind of foam and hence flow resistance develops and the foam acts as a good sound absorber - also know as damping when this is converted into the mechanical domain. This type of foam is a poor thermal barrier.
The cell size is highly variable in production from hundres of cells per in^2 to only ten or twenty. The variance on the cell sizes tends to be quite small.
Well, Trolls don't respond to everything. You have to feed them correctly to get best results.
In the test cell I mentioned in my article I did test several types of foam and confirmed what Earl has stated, closed cell types of foam reflect most of the sound incident upon them and do a poor job of absorbing it, whereas acoustic foams do actually absorb sound, and different grades have different absorption spectra.
Ideally a scheme designed to absorb sound inside such an enclosure should have a material with graded acoustic impedance, i.e. higher impedance nearer the walls, an exponential increase from nearly zero at the driver to the wall impedance at the wall is probably optimum.
Rcw.
Ideally a scheme designed to absorb sound inside such an enclosure should have a material with graded acoustic impedance, i.e. higher impedance nearer the walls, an exponential increase from nearly zero at the driver to the wall impedance at the wall is probably optimum.
Rcw.
Thanks for this, it was interesting reading. I mostly agree, especially with the "like-minded" posters all coming to a common set of beliefs and "common sense" that is completly wrong. But I think it wise to be careful about how things are handled as we don't actually want to drive away someone with true expertise. Borat is obviously knowledgable, but just as obvious to me, slightly over-extending his knowledge base. Best to be careful in this kind of position.
i think the discussion was about Transmission lines. his argument was that his superior skills made his TL ( which was stuffed ) sound much better than most speakers ( which aren't stuffed ).
and my argument was that he should now try building regular speakers and STUFF THEM.
i don't think sealed vs ported came up but since you ask sealed is better ( for midrange quality ) while for bass it depends on what you are looking for.
generally speaking though sealed is a cost-no-object approach while vented is a price/performance approach. all else being the same for the same output a sealed speaker will cost more but sound better. i mean something like 18" sealed subwoofer vs 12" ported subwoofer. this is why virtually no commercial speakers are sealed - they are too cheap to do it.
there are certainly benefits to using ports. that's why virtually all commercial speakers use them. but most of these benefits have to do with the bottom line, not ultimate fidelity.
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that's what i always say myself.
such a scheme should result in best sound but not in a smallest box.
for a smallest box the material should fill the box almost uniformly i think.
in fact a box with such a gradient would not be a sealed box any more. it would probably behave more like an aperiodic box vented into a second chamber. and some of the volume of the box should in fact count towards that second box.
that was some interesting information about foam. i didn't know they burned out the walls.
are you implying that this technology ( sending a flame through ) cannot produce small openings ?
i tried breathing through Auralex foam and it wasn't really working. it would barely pass any air. yet it is probably classified as open cell foam because it is marketed for controlling room reflections.
so it seems they CAN make small openings after all ? or maybe a mix of closed and open cells ?
do you know the foam i am talking about ?
Auralex Acoustics - Acoustic foam bass trap products.
it says there ( on the mega LENRD page ) that it is effective to below 50 hz.
this is the one i used:
Amazon.com: "Auralex 12X12CFFGR 12 CornerFill; 1- 12x12x24 Pieces in Forest Green; Covers 2 Linear Feet": Musical Instruments
its just a slab 1 foot by 1 foot by 2 feet. mine was purple though.
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