A few more numbers slightly more scientific. To get your attention, may I say it is a fun day when what you absolutely knew does not test that way.
OK, I have a small 4L test box of 3/4 MDF. I have a modified Dayton RS 150 laying around. ( not the good one from the other test. ) My scale is a Weight Watchers, so not accurate, but will do the job. I used WT-II to plot the impedance which gives me Fs and Qts. I will give the numbers, and you can make your own chart. I stuffed until it seemed impractical. ( except the cotton, I only had so much. )
Empty box. Fs 84.96 and Qts 1.108. Yes, the box is way too small.
3 Oz fit to the box and driver 1.5 Lb open cell foam 78.48 Hz, .9217
Craft polyester 2 oz: 82.19 Hz, .9721 4 oz: 80.21 Hz, .9427 That was all I could stuff in.
Cotton 4 Oz: 79.91, .9813 6 Oz 78.78, .9274 THat is all I had. Pretty well stuffed, but it could take a little more
Wool 2 Oz: 81.42, .9875 4 ozs: 79.30, .9568, 6 oz: 78.49, .9244 8 oz: 78.78, .9067
Bonded Dacron "Acoustastuff" 4 oz: 81.57 1.006, 6 oz: 80.67 .9902 8 oz: 79.67 .9588 10 oz: 79.22 .9452
Fiberglass batt 2 oz: 79.82 .9513 4 oz: 78.34 .8587 6 oz 78.05Hz, .7738
WTF, fiberglass wins by a sliver. ( pun intended
) This is counter to what "experts" have said in how much better polyfill is. It is also not very good information for the speciality fill makers, except FG is nasty and dangerous any never use it in a ported box where it can pump fibers out. (remember the Dynaco tuned port!)
Wool still has an edge over the cotton and daycron. I would probably not use the fiberglass for half a Hz, but the difference in Qts is quite significant. I will do frequency response to verify the Q. If I were a manufacturing company, it would be really tempting to use die-cut foam as that is the best way to assure placement and consistency. I am about where I was the first time, roughly 5 Hz.
Note the Daycron is heavy and the polyester very springy and light.
Converting to fill per cubic foot for the best of each: ( remember, scale inaccuracy)
Foam was fixed at 19 oz
Polyester, 26 oz
Cotton 40 or so ( maybe a bit more if I had it)
Wool at 40 oz
Dacron Acoustastuff a full 66 oz
Fiberglass at 40 oz per cubic foot.
I bet those numbers are higher than people are used to. Only the wool could be stuffed in to where it started to decline. If stuffing through a driver hole, you could force in a bit more, but the best results were pretty darn packed.
OK, I have a small 4L test box of 3/4 MDF. I have a modified Dayton RS 150 laying around. ( not the good one from the other test. ) My scale is a Weight Watchers, so not accurate, but will do the job. I used WT-II to plot the impedance which gives me Fs and Qts. I will give the numbers, and you can make your own chart. I stuffed until it seemed impractical. ( except the cotton, I only had so much. )
Empty box. Fs 84.96 and Qts 1.108. Yes, the box is way too small.
3 Oz fit to the box and driver 1.5 Lb open cell foam 78.48 Hz, .9217
Craft polyester 2 oz: 82.19 Hz, .9721 4 oz: 80.21 Hz, .9427 That was all I could stuff in.
Cotton 4 Oz: 79.91, .9813 6 Oz 78.78, .9274 THat is all I had. Pretty well stuffed, but it could take a little more
Wool 2 Oz: 81.42, .9875 4 ozs: 79.30, .9568, 6 oz: 78.49, .9244 8 oz: 78.78, .9067
Bonded Dacron "Acoustastuff" 4 oz: 81.57 1.006, 6 oz: 80.67 .9902 8 oz: 79.67 .9588 10 oz: 79.22 .9452
Fiberglass batt 2 oz: 79.82 .9513 4 oz: 78.34 .8587 6 oz 78.05Hz, .7738
WTF, fiberglass wins by a sliver. ( pun intended
) This is counter to what "experts" have said in how much better polyfill is. It is also not very good information for the speciality fill makers, except FG is nasty and dangerous any never use it in a ported box where it can pump fibers out. (remember the Dynaco tuned port!)Wool still has an edge over the cotton and daycron. I would probably not use the fiberglass for half a Hz, but the difference in Qts is quite significant. I will do frequency response to verify the Q. If I were a manufacturing company, it would be really tempting to use die-cut foam as that is the best way to assure placement and consistency. I am about where I was the first time, roughly 5 Hz.
Note the Daycron is heavy and the polyester very springy and light.
Converting to fill per cubic foot for the best of each: ( remember, scale inaccuracy)
Foam was fixed at 19 oz
Polyester, 26 oz
Cotton 40 or so ( maybe a bit more if I had it)
Wool at 40 oz
Dacron Acoustastuff a full 66 oz
Fiberglass at 40 oz per cubic foot.
I bet those numbers are higher than people are used to. Only the wool could be stuffed in to where it started to decline. If stuffing through a driver hole, you could force in a bit more, but the best results were pretty darn packed.
Totally disagree. This is a test to see when all other things remain the same, what is the effect on ONE change. That is how we do science. Would the shape of the box improve the response? Maybe. Would it change what the fill material does relative to others? No. I am testing to answer a question, not optimize a speaker.
Same box, same driver, same test rig, same scale, same procedure. If I was going to write a paper for review, I would probably do it all 10 times with different test equipment and different drivers, on different days with different people doing the test. I am not, so it is what it is.
Driver technology has advanced considerably since that article. It may not be an issue anymore with the ultra high quality drive units now available to the diy crowd.
BP changes quite a bit, and the voice coil heating can change the temp several degrees. Is this enough to push the cone out of the gap? Actually yes. I did too good a job sealing a pair of Ditton 44's on a hot day with low BP. When it cooled off and fair weather cam in, the woofers were set back viablely. I had a pair of tweeters rise out of a dashboard in Colorado. The leak should be very small. A pin prick fixed the tweeters. A #60 drill is fine for woofers. That big honking 18 inch sub in the 8 cubic foot box, yea, I would not worry about it.
A few more numbers slightly more scientific.
WTF, fiberglass wins by a sliver. ( pun intended
QUOTE]
Ever so slightly more scientific. 4L seems the size for desktop computer speakers, if that.
FG wins is NOT counter to what 'experts' have said. Did you read the O'Hanlon/KK studies?
Your scale up /cu. ft. numbers aren't practicle, indicating the test box size is too small.
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They do not scale because the classic Acoustic Research closed box stuffing optimized FG amount averaged about 1 lb/cu. ft., not 2.5 lbs/cu. ft. as your scale up numbers would suggest.
Speaker box stuffing study - Page 2 - Acoustic Research - The Classic Speaker Pages Discussion Forums
Also, you seem to have overlooked one other interesting result of your latest stuffing study. Note how much more FG reduced Q in comparison to all the other fibers you tested. Did you also notice how the impedance also dropped?
Foam blocks were used in production of New Large Advents in the 70's. It is suspected Advent switched from FG to foam due to OSHA concerns. I removed the foam and replaced with FG and got improved results. Read post #12 and download the attached paper (>800 downloads) at the link below...
http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=2895&hl=stuffing
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So not only does fiberglass lower the box fundamental resonance, it is the only fill that is heading towards critical damping (Q = 0.707). Still abhor handling the stuff.
From your data it seems only wool has an optimum fill amount. For all the others the more fill the lower Fs and Qts. That seems to be counter to widely help theories. Your results seem to suggest it is impossible to stuff sufficient fill to effectively reduce the box volume. For such a tiny box too. Hmmm.
TVRgeek, I had a hard time reading your results so I have reformatted them here. I hope you don't mind
Empty box.
Fs=84.96 Qts= 1.11.
1.5 Lb open cell foam
3 Oz (fit to the box and driver) : Fs=78.5 Hz, Q=0.92
Craft polyester
2 oz: Fs=82.2 Hz, Q=0.97
4 oz: Fs=80.2 Hz, Q=0.94
Cotton
4 oz: Fs=79.9, Q=0.98
6 Oz Fs=78.8, Q=0.93
Wool
2 oz: Fs=81.4, Q=0.99
4 oz: Fs=79.3, Q=0.96,
6 oz: Fs=78.5, Q=0.92
8 oz: Fs=78.8, Q=0.91
Bonded Dacron "Acoustastuff"
4 oz: Fs=81.6 Q=1
6 oz: Fs=80.7 Q=0.99
8 oz: Fs=79.7 Q=0.96
10 oz: Fs=79.2 Q=0.95
Fiberglass batt
2 oz: Fs=79.8 Q=.095
4 oz: Fs=78.3 Q=.086
6 oz Fs=78.1 Q=0.77
Empty box.
Fs=84.96 Qts= 1.11.
1.5 Lb open cell foam
3 Oz (fit to the box and driver) : Fs=78.5 Hz, Q=0.92
Craft polyester
2 oz: Fs=82.2 Hz, Q=0.97
4 oz: Fs=80.2 Hz, Q=0.94
Cotton
4 oz: Fs=79.9, Q=0.98
6 Oz Fs=78.8, Q=0.93
Wool
2 oz: Fs=81.4, Q=0.99
4 oz: Fs=79.3, Q=0.96,
6 oz: Fs=78.5, Q=0.92
8 oz: Fs=78.8, Q=0.91
Bonded Dacron "Acoustastuff"
4 oz: Fs=81.6 Q=1
6 oz: Fs=80.7 Q=0.99
8 oz: Fs=79.7 Q=0.96
10 oz: Fs=79.2 Q=0.95
Fiberglass batt
2 oz: Fs=79.8 Q=.095
4 oz: Fs=78.3 Q=.086
6 oz Fs=78.1 Q=0.77
For people that hate fibreglass, there is a new product called earthwool which is fibreglass without the use of fomaldehyde. It does not irritate the skin like regular fibreglass batting does.
I recently purchsed a small quantity and it is indeed low irritant. You can rub it on your skin without any side effect
I recently purchsed a small quantity and it is indeed low irritant. You can rub it on your skin without any side effect
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Quite a bit, by my reckoning.
Not sure about the connection between KK and FG? How didn't fiberglass work? Lowering resonance is fine but the more important attribute is reduction of internal resonances, not shown in these tests. We should also distinguish between Q dropping with resonance (fs/Qt should be constant) or real increases in mechanical loss (lower Qm) that may or may not be desirable.
David S
thanks again TVRgeek for the interesting results! I find it particularly interesting that the foam performed equally to 6oz of wool. I expected it to be less effective. Food for thought indeed. Thanks again.
Perhaps with the FG there is something else occurring-a compounded effect?
Perhaps with the FG there is something else occurring-a compounded effect?
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Earthwool is among a large host of Brand names given to a product developed by a German company (Germany has one of the world's most stringent environmental concious countries) named Knauf.
It's still fiberglass with a cellulose binder and thus should have acoustical performance similar to traditional OC type binded with Formaldehyde.
Earthwool is still required to be labeled with warnings (see MSDS at link below).
Material Safety Data Sheets (MSDS)
The bottom line here, for me at least, is while Earthwool's earthy/crunchy marketing name should attract new business, the product is still fiberglass. When handling it, one should wear a mask and covering over hands/arms, etc. as recomended in the MSDS. Personally, OCFG doesn't irritate me. So, I only wear a mask when stuffing and un-stuffing speakers. I've read on many audio forums though that FG has gotten a pretty bad rap - like it was another asbestos. It's not.
It's still fiberglass with a cellulose binder and thus should have acoustical performance similar to traditional OC type binded with Formaldehyde.
Earthwool is still required to be labeled with warnings (see MSDS at link below).
Material Safety Data Sheets (MSDS)
The bottom line here, for me at least, is while Earthwool's earthy/crunchy marketing name should attract new business, the product is still fiberglass. When handling it, one should wear a mask and covering over hands/arms, etc. as recomended in the MSDS. Personally, OCFG doesn't irritate me. So, I only wear a mask when stuffing and un-stuffing speakers. I've read on many audio forums though that FG has gotten a pretty bad rap - like it was another asbestos. It's not.
Please share with us the details of where/how you learned FG doesn't work.
IMHO, KK has probably forgotten more about speaker technology than most of us will ever know.
My sentiments, exactly. With no disrespect to the effort the OP did in his experiments, tuning for Fs might be better done by properly sizing the box instead of using stuffing as a crutch (assuming, of course, that one is designing from scratch, and not trying to modify an existing speaker). Better to oversize the box and tune by reducing volume.
So if the box is tuned to the correct volume, the important question is which material sounds better; i.e., which damps internal resonances and/or absorbs reflections better? Secondarily, which is more practical/cost effective to use.
Fiberglass is a PITA, both in handling and breathing. But it is cheap, and only needs to be done once.
Wool is very expensive, and needs moth treatment, and is not readily available at a local store.
Cotton and Acoustistuff fall somewhere in between in cost, and are easy to handle.
No scientific studies to link to, but over the years, my impression is that the subjective order of preference has been, from best to worse,
1) Wool
2) Cotton
3) Fiberglass
Not sure where Acoustistuff fits in wrt cotton, but probably higher than fiberglass.
Pooge,
On what are you basing your rankings of the three materials. To just say that without giving a reason could just be a random choice based on what material you like to handle. I have used both fiberglass and poly fibers but think that the fiberglass required less stuffing to achieve the same results. I agree that there is much more to this than what can be used to retune a box. I think that with all the information on Thiel Small parameters there isn't much reason to build the wrong sized cabinet in the first place. The information on the gas filled enclosure is of more interest to me because with that we can reduce a box size for packaging reasons. I intend to look much deeper into this, there is much more to know and the interaction of this gas with air and the formation of acid concerns me.
On what are you basing your rankings of the three materials. To just say that without giving a reason could just be a random choice based on what material you like to handle. I have used both fiberglass and poly fibers but think that the fiberglass required less stuffing to achieve the same results. I agree that there is much more to this than what can be used to retune a box. I think that with all the information on Thiel Small parameters there isn't much reason to build the wrong sized cabinet in the first place. The information on the gas filled enclosure is of more interest to me because with that we can reduce a box size for packaging reasons. I intend to look much deeper into this, there is much more to know and the interaction of this gas with air and the formation of acid concerns me.
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