There is no general answer. Speaker design is much more complicated.
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Does a lot of damping material have any negative effects in a closed box?
- Thread starter test1223
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I suspect some DIYers stuff to the point of reducing box volume. I've never seen anyone actually measuring this stuff (pun intended) other than Nousaine, and Dickason in his books.
@test1223, your posted video has not stated where the initial tuning measured Qtc for the smaller box. For the larger box, he shows a small shift in Qts and likely it is not audible. His varying amount of polyfill is also much less than amounts done by previously established tests. So this affects his measurements results too.
As for the model from audio judgement, am not sure of its source and only have some of the reference material he cites. As you had asked where the model would account for damping material, I was simply pointing it out. The enclosure compliance would include the absorption loss (Qa) and heat ratio (gamma). Have not found the exact formula, but @kimmosto would know as he includes Qa in VituixCAD’s model. In any case, these are models and are only meant to approximate reality. Have not seen the research behind them. I do know Bassbox developers put considerable effort into adding damping factors into their model though.
In any case, as the models show, there are a lot of variables. Some variables are more significant than others but along the way, the test conditions matter. So am not surprised when general conclusions break down over less significant factors. However, sometimes when small factors are pushed beyond their expected range, there can be larger impacts than a model may provide. I gather how audible they are is also why you initially created this thread. Extreme overstuffing is already well documented as a tipping point for enclosure behavior. Whether your experience fits the more extreme case or a expected case is not clear as you have only specified your conditions subjectively.
As for the model from audio judgement, am not sure of its source and only have some of the reference material he cites. As you had asked where the model would account for damping material, I was simply pointing it out. The enclosure compliance would include the absorption loss (Qa) and heat ratio (gamma). Have not found the exact formula, but @kimmosto would know as he includes Qa in VituixCAD’s model. In any case, these are models and are only meant to approximate reality. Have not seen the research behind them. I do know Bassbox developers put considerable effort into adding damping factors into their model though.
In any case, as the models show, there are a lot of variables. Some variables are more significant than others but along the way, the test conditions matter. So am not surprised when general conclusions break down over less significant factors. However, sometimes when small factors are pushed beyond their expected range, there can be larger impacts than a model may provide. I gather how audible they are is also why you initially created this thread. Extreme overstuffing is already well documented as a tipping point for enclosure behavior. Whether your experience fits the more extreme case or a expected case is not clear as you have only specified your conditions subjectively.
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From pure experience about stuffing an 3 way speaker ported, in witch the mids had his own enclosure inside the box...overstuffing the box and the mids box killed the sound.
What killed mean...I do not know exactly but the sound was bad at the ears. The sound became "lifeless" like in compressed, non resonant and to controlled with decreased apparent volume and impact. The general impressions was that you need increasing the sound volume and the speaker sound still was annoying, flat.compressed and artificial.
What killed mean...I do not know exactly but the sound was bad at the ears. The sound became "lifeless" like in compressed, non resonant and to controlled with decreased apparent volume and impact. The general impressions was that you need increasing the sound volume and the speaker sound still was annoying, flat.compressed and artificial.
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ernestcarl
Major Contributor
These both have smaller cabinets, so damping is not going to do much. Would at least do some Sonic barrier on the back panel in either case. There is this somewhat larger version...
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Dayton Audio 8" Reference Series HO Subwoofer and Cabinet Bundle 300 WattsAbout the CabinetThis particular cabinet is designed specifically for the Dayton Audio 8" Reference Series High Output subwoofer, but works for any subwoofer with an overall diameter of 8-1/2" or less, and a cutout...www.parts-express.com
Gives you a little more room to work with and has better cabinet bracing....
Would find out what they recommend for good fasteners (likely t-nuts and bolts).
This is clearly lower cost kit of the bunch and would not do unless budget is an issue.
Thanks. Ahhh, it looks like they do specify or suggest damping on the larger sized box. My bad. I did not look at those closely as I thought they would be simply too large (from not having enough of the right sized longer clamps on hand). Hmmn, I think I should get more clamps first to spare myself the headache...
FWIW, I discovered that gluing polyurethane egg crate foam inside the walls of my woofer boxes seemed to help the knock test. Seems to be most effective when the glue covers the entire area, rather than a few spots.
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I built 4x of those 8" Dayton Ultimax subs a year ago (Quad 8" subs for my office), although I made my own custom sealed boxes and did not use their kit. I didn't cover it in my thread, but did use poly fill in them and I agree with your comment that the damping did not do much at all in such a small box. I don't recall how much I used in them in the end, but I could tell very little if any difference at all between various volumes of fill other than at the extremes. I still ended up using a "full but not packed" amount in them since I had it on hand, but it wasn't any kind of difference maker.These both have smaller cabinets, so damping is not going to do much. Would at least do some Sonic barrier on the back panel in either case. There is this somewhat larger version...
Home
Dayton Audio 8" Reference Series HO Subwoofer and Cabinet Bundle 300 WattsAbout the CabinetThis particular cabinet is designed specifically for the Dayton Audio 8" Reference Series High Output subwoofer, but works for any subwoofer with an overall diameter of 8-1/2" or less, and a cutout...www.parts-express.com
Gives you a little more room to work with and has better cabinet bracing....
Would find out what they recommend for good fasteners (likely t-nuts and bolts).
This is clearly lower cost kit of the bunch and would not do unless budget is an issue.
ernestcarl
Major Contributor
I need to read more about this... There does seem to be such a thing as "overdamped"
"The damping ratio is a system parameter, denoted by ζ ("zeta"), that can vary from undamped (ζ = 0), underdamped (ζ < 1) through critically damped (ζ = 1) to overdamped (ζ > 1)."
Damping - Wikipedia
How much damping one personally likes (psychoacoustics) even with EQ leveling much of the measured results is still going to take some experimentation.
I need to read more about this... There does seem to be such a thing as "overdamped"
"The damping ratio is a system parameter, denoted by ζ ("zeta"), that can vary from undamped (ζ = 0), underdamped (ζ < 1) through critically damped (ζ = 1) to overdamped (ζ > 1)."
Damping - Wikipedia
en.wikipedia.org
How much damping one personally likes (psychoacoustics) even with EQ leveling much of the measured results is still going to take some experimentation.
It may take some personal experimentation to turn into something you hear, but damping factor has long been studied in speaker design. It is just discussed as the quality factor Q. As the wikipedia article explains, they are simply related as the damping factor = 1/(2Q).
Note you will see quality factor defined in various contexts. For post #33, it is Qtc for the quality factor of a closed box speaker. Post #33 in this thread is a depiction of Qtc. For a speaker driver, Qts is quality factor at free air resonance. While both are quality factors, they are in different conditions and so the values have different meaningful ranges. These are important distinctions in audio as the solo letter Q is used as the quality factor for a simple resonance. In this case, the quality factor is most simply the resonant frequency divided by its bandwidth.
Hope this helps!
p.s. I hope these definitions will help others better comprehend quality factor and why context is key. For example, while did not specifically call out earlier, am pretty DIY Audio Guy mixes Qtc and Qts. His measurements are showing Qts but his context is a closed box system (rather than a free air) and so is really Qtc.
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Davide
Senior Member
I'll take advantage of the thread to ask a similar question.
If I have a ported speaker and in addition to closing the port (because bass reinforcement is not necessary) I add a lot of damping material inside, what effect I obtain?
Is it possible to reduce internal resonances and the leakage of reflections from the cone in this way?
Or I alter something else?
If I have a ported speaker and in addition to closing the port (because bass reinforcement is not necessary) I add a lot of damping material inside, what effect I obtain?
Is it possible to reduce internal resonances and the leakage of reflections from the cone in this way?
Or I alter something else?
You'll certainly lower the total Q of the bass driver, which will affect its frequency response. Whether that's good or bad depends on a lot of things.
Davide
Senior Member
Altering the FR doesn't worry me as I can theoretically compensate with eq. I'm just wondering if increasing damping material has a positive effect on cabinet resonances and cone leakage.
Anecdotally, I've noticed the box sounds less resonant to the Knock Test once I glue egg-crate foam over all the surfaces, using plenty of glue over the whole area. As for cone re-radiation, it stands to reason that reducing box modes will reduce that, too. See the link in post #9 for some interesting measurements.
ernestcarl
Major Contributor
It should, up to a point... I've experimented increasing the amount of damping material in some of my own speakers and it reduced some upper bass and low-mid resonance smearing which can be seen in the spectrograms.
To measure is to know.
Lacking equipment to measure, if you know the woofer specs, contemporary simulation software can offer some indication. If the vented bass sounds bad, then sealing the port can help but, as posted earlier, is often not a optimal closed box. In this case, adding damping is the wrong approach.
Davide
Senior Member
Thanks for your answers.
I took measurements between open and closed port and the differences in FR were clear. The port closed is smoother and clearly has less boost at the bottom.
There was also less jaggedness in the decay.
However, as regards the absorption of internal reflections and leakage, I believe that a more accurate measurement system and a dedicated environment are needed... that's why I'm trying to understand on a theoretical level what the story is like.
I took measurements between open and closed port and the differences in FR were clear. The port closed is smoother and clearly has less boost at the bottom.
There was also less jaggedness in the decay.
However, as regards the absorption of internal reflections and leakage, I believe that a more accurate measurement system and a dedicated environment are needed... that's why I'm trying to understand on a theoretical level what the story is like.
DanielT
Major Contributor
It may have already been brought up in the thread, but try to really pushing in with as much force as possible damping material in the speaker. With A LOT OF VIOLENCE, really squeeze so much that the speaker box seems like it's going to crack.
Preferably with high density on the material.You will notice the magic of trolling away bass. Poof ...and bass disappeared.
Regarding low bass. Subwoofers should not have any filling at all. Filling only reduces the sensitivity of the subwoofer.
Filling/stuffing in Subwoofer?
Hi I am grateful if anyone could sort this out; Is there any point in having filling in a Subwoofer? The question based on the assumption of an otherwise well-constructed Subwoffer, with , for example,cross braces in the box and with steep LP filter, for example 24 dB, crossover frequency 80 Hz...
audiosciencereview.com
If you want to know about radiation from the cone, place the mic as close to the cone as possible and sweep frequency. As shown in the link above, you'll see odd glitches where box modes affect things.
But smooths out box modes that might show up in the stopband before the filter has rolled a lot. That of course depends on the crossover and box. I'm willing to take a small efficiency hit.
DanielT
Major Contributor
With a steep filter of at least 24dB, most of the higher frequency (plus resonances) above 80-100 Hz, if you put the crossover point there, should be cut off. Terroretically, it should work that way, but then that so-called reality comes in, so well. It probably depends on a lot of different factors, circumstances.
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