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Discussion Starter · #1 · (Edited)
I posted this in the subwoofer forum but didn't get much traction. The sub is a commercial one but the mods are DIY. I had always heard to put fill in a sealed sub, but for a ported one, not so much.

https://www.avsforum.com/threads/re...&share_fid=47413&share_type=t&link_source=app

Results from adding poly fill batting to a ported sub


 

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Discussion Starter · #3 ·
link doesn't work:

Oops! We ran into some problems.
Sent from my SM-G991U using Tapatalk
 

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That result is very surprising; I can only think of reasons LF output would be reduced, not increased.

Are you sure the before/after measurement technique was consistent?

How hard would it be to remove the batting to see if you get back to the before measurement?

Though that would risk your happiness with the current state of affairs, real or not.

You decide - the red pill or the blue pill? :)
 

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I'll be curious to see what happens in a PR enclosure. Less air flow issues than ported, I'm guessing it may actually help.
 

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I'll be curious to see what happens in a PR enclosure. Less air flow issues than ported, I'm guessing it may actually help.
Help what?

Damping is by definition dissipative, so can only lower efficiency.

As the Data-Bass results show, it will help tame unwanted internal reflections/resonances.
 

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It sure looks like there was enough to detune it, assuming the measurements are accurate, but I would have expected less of an effect, as well. Another win for practice over theory.:)
 

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I'd just get some peal-n-stick 1/2" open cell foam rubber and some 3/4" open cell foam rubber with the mass loaded vinyl. There's also closed cell foam rubber. I used a combination of the 3 in my subs.
 

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I'd just get some peal-n-stick 1/2" open cell foam rubber and some 3/4" open cell foam rubber with the mass loaded vinyl. There's also closed cell foam rubber. I used a combination of the 3 in my subs.
umm... don't put mlv in you sub... ever...

no need to add mass... if you do, add a brace, mdf is heavy.
 

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Discussion Starter · #14 ·
That result is very surprising; I can only think of reasons LF output would be reduced, not increased.

Are you sure the before/after measurement technique was consistent?

How hard would it be to remove the batting to see if you get back to the before measurement?

Though that would risk your happiness with the current state of affairs, real or not.

You decide - the red pill or the blue pill? :)
Yes, I re-ran each test twice to ensure repeatability. Got consistent results.

I did not go back to baseline and re-test.

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umm... don't put mlv in you sub... ever...

no need to add mass... if you do, add a brace, mdf is heavy.
Both of my sub enclosures are Baltic birch plywood with 2, 4" Precision Ports at the bottom of the frt baffle. I only put in 2 ea. 7" x 13" pieces of open cell foam rubber with mlv about 1/8" from the bottom then about 1/8" of open cell foam rubber below it, at the bottom of the enclosure below each port, with no sound deadening within 4" of each port inlet. Anyway, I listened to the 1st one I built without any sound deadening. With it the bass sounded better/cleaner after installing the S.D. I used about 60% open cell foam rubber and 40% 3/8" closed cell foam rubber from Second Skin Audio.
 

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Both of my sub enclosures are Baltic birch plywood with 2, 4" Precision Ports at the bottom of the frt baffle. I only put in 2 ea. 7" x 13" pieces of open cell foam rubber with mlv about 1/8" from the bottom then about 1/8" of open cell foam rubber below it, at the bottom of the enclosure below each port, with no sound deadening within 4" of each port inlet. Anyway, I listened to the 1st one I built without any sound deadening. With it the bass sounded better/cleaner after installing the S.D. I used about 60% open cell foam rubber and 40% 3/8" closed cell foam rubber from Second Skin Audio.
not saying it won’t work…. No offense intended…

there are just way cheaper and easier ways to deal with treating an enclosure…. Structural resonances are easy to deal with via braces when building (since this is the DIY section…)

sound resonances are easily dealt with by using $2 wal mart pillows, or more expensive ecocore….

I don’t know how much open cell foam you need for any given frequency of treatment…. None of the testing tables I use measure it, only more traditional box stuffing materials and acoustic panels materials
 

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Everything old is new again. Tom Nousaine, RIP, published a decent experiment on this back in the '90s. Fortunately, the internet never forgets: GlassWolf's Pages

I believe Dickason's LDC also covers this phenomena pretty well. And Ken Kantor, founder of NHT, did some extensive research, including testing various materials, that he shared with the DIY community back in the day. Dating back to the '90s, I've always stuck with good old fashioned fiberglass insulation batts as I recall it has shown measurable, though not huge, advantages over other commonly used stuffing materials. I've always been a little skeptical of using stuffing with a cover, such as whole pillows, as opposed to directly exposing the fibers, but I've never seen anyone try to directly test for impact.

As it pertains to the OP's Klipsch measurements. I would think the slight increase in low end output is primarily due to lowering the tuning frequency a bit. As Nousaine's testing showed, you can drop Fb quite a bit. OP, you could confirm if you ever decide to repeat the experiment by close micing the driver and/or port to find the min/max output during your sweeps. And as long as you're experimenting, play with the amount of stuffing used as Nousaine did, until you get to the point of diminishing returns...just keep a clear path between the driver and port.
 

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Everything old is new again. Tom Nousaine, RIP, published a decent experiment on this back in the '90s. Fortunately, the internet never forgets: GlassWolf's Pages

I believe Dickason's LDC also covers this phenomena pretty well. And Ken Kantor, founder of NHT, did some extensive research, including testing various materials, that he shared with the DIY community back in the day. Dating back to the '90s, I've always stuck with good old fashioned fiberglass insulation batts as I recall it has shown measurable, though not huge, advantages over other commonly used stuffing materials. I've always been a little skeptical of using stuffing with a cover, such as whole pillows, as opposed to directly exposing the fibers, but I've never seen anyone try to directly test for impact.

As it pertains to the OP's Klipsch measurements. I would think the slight increase in low end output is primarily due to lowering the tuning frequency a bit. As Nousaine's testing showed, you can drop Fb quite a bit. OP, you could confirm if you ever decide to repeat the experiment by close micing the driver and/or port to find the min/max output during your sweeps. And as long as you're experimenting, play with the amount of stuffing used as Nousaine did, until you get to the point of diminishing returns...just keep a clear path between the driver and port.
YES!

I've been hammering this concept out over and over, this is not new material. Couple points; haven't seen it with a PR sub, I have one a couple feet away from me (old sunfire driver/PR put in a cheap PE 1cuft flatpack), and just did an impedance sweep of it "empty box" (no stuffing). Driver tuning ~26hz. Will add some poly and see what we get. Will post if worth posting.

Fiberglass is the best material.... unless.... you have a ported sub, then you may want to consider if you want the potential for fiberglass exiting the port(s). I'd pass then, and settle for boring but safe polyfil.

Again, yes, what is old is new. This stuff was well understood 50 years ago, it's just forgotten these days and brought back up/questioned. In the days of DATS/Woofer Tester/etc there is no excuse, stuff is easy to measure.

As to the dude gaining 5dB, or thereabouts, 946% chance it's a measurement anomaly unless you really dropped the tune that much. 2.5 dB is the better part of twice the power. I do see some extreme low end gain typically, but it's usually fractions of a dB, the slope changes nicely, the q of the box drops, and the fs of the box drops, overall a worthwhile thing to do unless you give zero cares to anything except SPL. Distribution, box size, and -this is a new one- box size relative to driver Vd, seem to matter. Sealed is a no-brainer, stuff small sealed heavier than large sealed but stuff 'em all. I use fiberglass on those usually. Ported isn't something I've messed with and measured, but it's just so easy to do. I wouldn't use pillows. PR's, I'm about to do small box PR's and will do with Ishmael when complete. Prob use 10lbs per box or close to it for those big girls.

Chris
 
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