Can Polyfill "fix" a small box: Bass in a Small Space 

Ports are the bass cabinet honking at a low bass frequency. I prefer bigger sealed box drivers ,voice coils larger and dedicated sub amplifier (s), few short cuts to the desired (Your) system I may have to start or be an apprentice on a channel to help maturing audiophile diy.

I am retired,master photographer, 2nd class fcc,72, IBM ,Atlantic steel, designer, composite materials, gave it all away(lol,take nothing never look back, eyes forward on Him. I built my first car stereo in 1968, with horn tweeters, so I could hear gospel songs with windows down.

I'm experimenting with the lawn fabric and shelf liner for unique covers. Or reducing pressure comb effect.

Why ask us if you should do and spl test in the car Of course do this test, and even go as far as having a friend see if he thinks box A B C was louder not tell8ng him what is what

@@UPsideDOWNworld321 still waiting on this video to get 200,000 views before I give that a try.

If I can get enough views on this video then I will be able to do more tests.

@@DIYAudioGuy 😂😂😂

Spot on. I'm focused on SQ at home and in my vehicle. I have a background in pro recording, ears spoiled by reference monitors for years- I only care about accuracy at this point. Losing 10db all around is fine by me if I gain accuracy as a result... clean amplification is cheap these days. Those crisp transients, damped internal reflections are worth it.

​@@lllllllllllllllllllll1lll1 Same for me for decades; at home particularly in my 2-CH room, my vehicles. I like things louder than friends & family for sure, but definitely prefer tight responses and accurate (to me) reproduction. 👍

polyfill will do nothing for resonances, it has no mass.

Interesting, perhaps I'll need to build some bandpass enclosures and see what happens.

Slowing the movement of air makes driver think it's in a bigger box. That is one reason why stuffing is used. In ideal use would be to tweak a little bit too small enclosure size into more favourable. This comment is before watching the video, I'll be back if something changes my mind.

Unpopular opinion- drivers don’t “think”.

@@robtaylor8907 Yes, just words we use. They don't "think" or "believe", they are working according to their specs considering surroundings.

@@robtaylor8907 sheesh ...mine do. I just trained a couple of 18's to clean my garage😂

Cool

I remember my mother saying "Am I going nuts? Where did that pillow go?" - "Not so great" is being nice about it : )

I added stuffing when I made a cabinet for my bass woofer out of an old beat up Kustom brand cabinet that had one blown speaker out of the two, so I bought a book from RadioShack and as I started to understand the concepts, I became intimidated by the math, and the fact that I had no specs on the 15" woofer, so I used fiberglass lining and stuffed it with poly fill, both RadioShack products, and it sounded pretty good in a manageable package. I would love to make a special cabinet with the modern updates and the goal of making tight bass with no irritating peaks.

Does poly work in ported enclosures? Great tutorial by the way 😎

Yes, poly works to improve sound quality in ported enclosures. The goal of the poly is to smooth out sound quality rather than increase volume. For example, Kicker includes poly sheet inside their pre-fab combo units of a sub + ported enclosure@@anthonysandoval965

This was not a sound quality test, it was a frequency response test. My goal was see if the polyfill would improve low end extension. I conclude that it did not.

@@DIYAudioGuy I just did a polyfil test today. Im building some medium size 3-way stand mounted speakers. 8" woofers with 10" passives. I have them mocked up for testing, so I added 1.5lbs of polyfil to one and left the other empty. I see why people think it adds lower extention. It's actually damping down the upper bass(120-200hz) which allows my ears to hear the lower bass notes more clearly. The empty box sounds much more "boxy" (for lack of a better term) at higher volumes than the stuffed one which sounds more natural.

Some people say it works, others don't.

You bought a $300+ 10 inch Low Profile subwoofer that only handles 600w and then did a hack job of building a sealed box for it. Then instead of reassessing the situation, like buying a prefab or contacting a local box builder or re-designing, you think shoving polyfill in it is not only the bees knees, but a mighty fine job? Just for reference, a Skar ZVX 15" 1500w RMS woofer costs about $350, this is a competition level subwoofer. You got played by Sundown. Then you played yourself. Then a handful of morons upvoted you. What a world.

Good point!

@@DIYAudioGuy I also wonder if it would be more apparent if the box was bigger. Like if you put it in a "regular" sized box.

@@beakerwsw One of the boxes I used was a midsize box, same size that the manufacturer recommended. It's perfectly normal to put a 10-in subwoofer in an enclosure that is just under a cubic foot.

@@beakerwsw I think the box size is irrelevant. Manufacturers as well as DIY installers are constrained to the confines of a vehicle so box size is often limited to the space available. What we're trying to test here is the best use of the space we have. For SPL, clearly polyfill is a waste of money (and we see that in SPL lanes where builders rarely bother to fill their boxes) but for SQ installs using stealth boxes where you are going to level-match your subwoofer and midbass drivers at a particular crossover frequency, let's say 70-80Hz, it's pretty clear from these charts that you'll get way more low bass below that frequency with any amount of polyfill. Anyway, as I said before this just proves that polyfill does what people claim and the engineers at major manufacturers know what they are doing when they fill their boxes. Thanks again @DIY Audio Guy for taking the time. Your title and conclusion might have been clickbait, but your data was very useful.

Thank you, I appreciate that.

That's a real good point.

Hot melt to tac wire then liquid nails for no rattle or shift.

That is the goal.

I would love to do some AB listening tests.

@@DIYAudioGuy After I moved on from entry level subs sheer output was never a goal it was always sq.

Nothing wrong with that.

Yes, I just wrote a comment about the benefit of damping being to reduce cabinet resonances. Then I saw this comment said essentially the same thing that I said, so I removed my comment.

@@Roger_Gadd - I wrote something similar, then accidentally deleted it, then wrote it a second time. Here is a repost of my explanation. "This should not be how insulation in speakers is used. People make this mistake all the time. Insulation should be used to address standing waves and to absorb energy which can cause reflections on the driver, as well as absorb the energy to prevent it from setting the enclosure into a resonating state, which can effect sound quality and have a constant frequency being put off that is not part of the music. If you are doing it to make the enclosure "sound bigger," buy a different driver, one more suited to fit in the size that you intend to have the driver installed. That might mean saving up more. But you will be happier in the long run. Now, for sub frequencies, constrained layer damping is one of the best ways to stop the energy in the enclosure, with 2# MLV being able to drop the dB of the sub frequency range by up to 19dB (varies over the range). That makes it an excellent candidate if trying to address cabinet resonances while not trying to increase the enclosure size. If instead you want to go the insulation route, for subs, you MUST use 3.5" or thicker insulation, line the entire cabinet, and it should be denim, rockwool, or fiberglass. Polyfill, also called PET insulation, also called Dacron and Acousti-stuf (specific version with crimped polyester fibers that do inscrease its effects on frequencies) and other similar names, does practically nothing at the relevant FR for subs. As such, the use of poly outside of mids/woofers should stop. This can be seen in effectiveness charts in the loudspeaker design cookbook p.45 et seq. Insulation helps to smooth the frequency response of the speaker. It should not be used to gain low end extension. Instead, if it is used properly, you can have smoother bass. Look up Bobgolds website for absorption coefficient. This will show the only way to hit 125Hz or less is to use at least 4" insulation. With going deep, you may want 5.5" - 6". And there goes exploding the size of the enclosure. To do this experiment properly, it requires two boxes, both built to have the open space being the same volume in the end. That means the final open volume in the speaker enclosures must be the same, but one built with the extra thick insulation and one without it at all. Then, you are not trying to change the Q of the driver, instead you are trying to absorb the energy before it can effect the enclosure. Surely 4"-6" insulation is not practical as it greatly increases the size of the enclosure. But, it takes that to make insulation effective at smoothing at lower frequencies. Lowe's carries (although out right now) 3.5" and 5.5" UltraTouch Denim insulation which is a decent price. For Rockwool, you can get 3x 2'x4'x4" insulation for $65. That would be the thinnest I would recommend to have an effect on sub frequencies. At 0.15 absorption coefficiant, or 15%, this is negligible on performance. As such, anything showing 50% at 125Hz will be less than that by the time you reach 40Hz, or even 20Hz. That means you will need something reading near or at a coefficient of 1 at 125Hz if you have any hope to damp low frequencies. Hence the 3.5" being the minimum to consider, and 5"+ preferred for very low frequency damping. This was the second time I typed this, so lost some things, but I think this is enough to start with. I put no links because YT likes to delete my posts when I link things. So, hope you can find things I referenced."

It may help with that, but I'm no longer convinced by the argument that polyfill will improve low frequency extension.

This could be another test - how does polyfill effect irregularities or random spikes? How flat is the curve in the + or - 3db range with and without polyfill?

@@ramonbmovies there are an infant number of variations that can be tested. One person can't do them all.

@@DIYAudioGuy I would have to agree... I have never used polyfill for that application. Predictions modeled in software you can see the effect of fill in your box really does correspond with the measurements you took. Negligible changes in the lowest range with some reduced overall output.

I do similarly. I often use some Ultra-Touch Denim insulation on the walls torn in half thickness-wise in strategic locations, then lightly stuff with Polyfill just to help reduce the echos and sound bouncing around inside the cabinet. Similar to sounds echoing inside an empty room in a house... If you can hear an echo, that sound wave can interact with the rear of the driver cone and create additional, non-musical sounds. I don't think I've ever used it to try and make an enclosure 'appear' larger to a woofer or sub.

Glad I could help!

I hope to do more in the future!

No need for research and development, it's already been done, just study the actual research from actual, researchers ,Thiel/Small , Butterworth, ect.

Right, this stuffing works best in a box that's already been designed correctly. Trying to stuff a box to make it bigger is an exercise in futility.

You always have good information.

So it's totally worth it to get a pillow or two and stuff my new sealed subs. I just bought dual 15" HO driver from Parts Express and the Denovo sealed enclosure. Havent built them yet. To get the best performance, I should use polyfil and a lot of it right?

That's the topic for another video.

Have rebuilt a pair of Realistic MACH1a series; famous/infamous vintage 1970s horn based 3-ways. Completely taken apart, I actually spray sealed the internal plastic horns (Twt & Mid) and added a high(!) volume (didn't weigh) of fiberfill in the interior cabinet and compared Left (with) to Right (w/out) as I rebuilt. The filled cabinet, w/ the light rubberized spray around the mid-high horns, we're audibly improved to me, so I completed project w/ replicating remaining Right CH speaker.

Thanks for watching!

A lot of people use it, does everybody use it because that is just what everybody does, or does it actually work? The tests I did do not tell us anything about sound quality.

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Good question!

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Thank you!

@@DIYAudioGuy wow you sure got popular Justin, look at this other fake account trying to be you 😅

Interesting, I've never really thought of the shape of the box as being that important.

@@DIYAudioGuy it's typically more important for frequencies a bit higher, but I do believe it plays a role in frequencies as low as these too. We've just started a thread in 14.4v talk discord about it, it's been very interesting

Glad it was helpful!

I hope to do a few more tests. Since I'm going against conventional wisdom, I'll need a lot of data to back that up.

Hehehe nice!

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I think that is exactly why people believe polyfill works. It makes the upper frequencies, the stuff from 60 up to 100 Hertz, quieter. So they compensate by turning up the volume and thus gives the impression of improved low frequency extension.

@@DIYAudioGuy so what I think your saying is that poly fill does not ADD low end, it dampens high end (relative to this specific application ofc) but in the world of cheap wattage the net effect for the user is that they can add a little more volume and the net response in their experience is in fact added low end correct? Because in the end whether it mutes the mid and high range of the driver or truly adds to the low end is kind of semantics. If you can simply bump your subwoofer output by one and get a flatter frequently response that allows the total system to play lower overall and less peaky you're getting exactly what you want out of the polyfill aren't you? You're getting a cheap addition to an enclosure you're stuck with that allows you to play lower in the frequency range!

And I'm not saying that my test is going to settle the debate. Hopefully more people will make some videos showing off some more tests.

I'll just have to wait and see if this video gets enough views to justify more testing. Give it a like and a share so that the algorithm will show it some love.

Or maybe you just think you do, it could be the placebo effect. I'm not aware of anyone that has posted the results of large-scale a/b testing on RU-vid. There might be an academic study showing this.

I agree, that's the same exact reason why I use it...and that's also my exact explanation of what I hear using it too. It changes from a more "hollow box" sound to a more smoother sound.

@@DIYAudioGuy The placebo effect can definitely be the answer. However the speaker cone isn’t impenetrable. Any sounds bouncing around inside the box could reverberate through the front of the cone. Using polyfil (or any type of dampening material) will reduce the effect substantially. If you look inside any speaker made by a reputable brand they will always have something inside. I could definitely be wrong, but I’d bet you could measure the difference on a spectrum analyzer. I’d imagine the “hollow” sound will include some harmonics that are not found in the original music, giving it the “hollow” sound I think I hear. All that being said, placebo effect can also definitely still be at play here. Love your videos man. 👍

@@poopandfartjokes ^^^This^^^ - Bingo!!!

Anything you put in the box to break up standing waves and cut down reflections will improve sound quality. The only thing this test shows is that you don't actually improve low end extension by adding polyfill to a box that is to small to begin with.

That's the problem with these kind of rabbit holes, a lot of people want more detailed tests, but when you start making the more detailed test people stop watching. I think I said toward the end of the video that if this video got a quarter million views that I would do more testing. So I'm sticking to that.

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I'm glad it worked for you.

I definitely prefer the quilt batting to the loose fill.

I'm not at all surprised to learn that Villchur did not find anything more than a 10% difference.

@@DIYAudioGuy In my experience (granted, I haven't built a speaker in 20+ years) it did more to clean up midrange in two-way speakers than it did to improve bass. And fiberglass, though a pain to deal with, is way better than polyfill.

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Thanks for the sub!

You mean this stuff: amzn.to/3jzFtor

@@DIYAudioGuy yes exactly!

Great tip!

Good question, I have no idea.

Reducing Internal Standing Waves Flattens out the Bottom End so there are no 'Notched' Losses or Gains.

I welcome disagreement. Thanks for sharing your experiences.

+1 for this! I have added fill to many small sealed boxes and it improves the sound greatly. Some boxes that have size limitations need the help. This analysis is very interesting, but it doesn't show what matters....how it sounds.

@@alejandronunez9796 Yes, the age old question. and the Survey says....... it's purely Subjective. My 60 year old ears do not hear what my 25 year old ears did. Everyone has their own 'Frequency Curve' . Some people hear better dynamic range... some higher frequencies.... and my Cat hates everything associated with my obnoxious Audio Systems.

There's probably very little difference between polyfill and fiberglass, both from a standpoint of fibers floating around and from a standpoint of dampening the enclosure.

I would call kicker tech support, they provide excellent customer service.

@@DIYAudioGuy Good idea, thanks.

The key thing to remember about the test in this video I was focused on one very specific hypothesis, or rather I was attempting to verify or bust one very specific myth. I have been told for decades that if my box is too small I can add polyfill and make the box behave as if it were larger. My results indicate that this is 100% BS. If you build the box wrong there's no magic trick to fixing it. How does the stuffing impact sound quality? I did not test that, I did not measure that. The thing to remember is that polyfill, rockwool, fiberglass batting, jute, eggshell foam are all used for the same reason. You're trying to break up the standing waves and you're trying to keep reflections from coming back through the cone. I think that these things work for that purpose, and I will continue to believe that until I'm able to prove that they don't.

@@DIYAudioGuy the different materials absorb different frequencies though. This I know from setting up a recording studio. 1.5" fiberglass is much more effective in taming mid frequencies than eggcrate foam. For bass traps you need even thicker and denser materials. I suspect the same is true in sub enclosures.

Yes, but the extra volume would be very small. If your speaker cut out had a 9.5" diameter you would only gain 141 cubic inches with a 2" ring. That is only .082 cubic feet.

If the goal is to break up standing waves and dampen second and third order harmonics then I think maybe some stuffing might be okay.

@@DIYAudioGuy I need to play with it some more. Its the closest I've ever had my live guitar rig sounding like it sounds in my studio control room, so I'm pretty happy. Maybe I'll hear something I don't like and need to fix it, but so far, loving it. If I build another, I'd like to make it slanted so its more aimed at where it matters, but not sure how to calculate the new dimensions, so I'll stick it on a speaker stand to tilt it. Oh, and next time I will build ONE! Not the insane dual I have now, its way more than loud enough if I unplug one of the speakers

It has a different texture and consistency.

@@DIYAudioGuy acusta stuff is just over baked pollyfill

Here is the video where I built the boxes. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-BicefelesIA.html

I have not tested it myself. But conventional wisdom says it works.

I've done this, made the bass tighter, clearly less boomy...

The standard recommendation is 1 lb per cuft. As you can see form the video when you weigh it out 1 lb per cuft means cramming a ton of polyfill in the box.

Not really sure.

@@DIYAudioGuy What I can give you for reference is that the exhaust filter looks like a foil version of polyfill. it looks a bit like carpeted flooring they put out of the box.

Right, not much of a difference when measured but people tend to prefer the sound.

I can't say for sure.

Thank you!

You are far too kind.

These test show that placing a sub in a box that is to small is a bad idea and that polyfill does not fix that problem. Consider using an 8 instead of a 10.

I would not recommend doing any of that. If you don't have a subwoofer I would recommend getting one.

I currently have 2 polk audio 10 inch subs hitting at 100 watts and I have a Yamaha rx-a800 advantage avr and a Yamaha S-701 amplifier that I'm using for my 2 front towers and I also have 2 polk monitor 40 series 2s all bi amped and I have 2 book shelfs for my center channel I wired them in a daisy chained and it sounds great but I'm looking for a deeper richer sounding version of the system. So if you say it's not a good idea then I won't do anything to them I'm thinking about adding 4 more book shelfs 2 for my front heights in both corners and 2 in the back aiming down into the room. The one thing that I have noticed is that the book shelves with the 5 1/2 inch drivers sound so evenly matched and blended with the towers that have 6 1/2 drivers and I have all this set up as a 5.2 surround system

@@MadeinAMERICA369 Stop throwing money at it. Make sure you have everything set up correctly, and experiment with speaker placement. You've got to be careful when you're running two subwoofers they might be canceling each other out. A good place to start would be to just unhook everything except for the right and left speaker and just listen to it in stereo.

You created an Aperiodic enclosure. Its a cross between ported and sealed. An Aperiodic enclosure is one in which the woofer breathes through a resistive membrane to control it's cone characteristics. In laymen's terms, it makes a woofer in a tiny enclosure act as if it were in a large, sealed enclosure. Since you had ported stuffing made it more sealed lowering SPL slightly, tightening up the bass, and extending the low end.

I've never thought about like that before.

I think you're probably right.

Ported vs. sealed tuning is very different.

That's what happens when you cut out the higher frequencies, you get the impression that the lower frequencies are louder even though they're not.

@@DIYAudioGuy I don't want my subs playing high frequencies. Also, if you're cutting out the high end then you're theoretically adding to the low end. Your results showed this.

That's a good question.

Fiberglass batting was also popular. I have pulled apart a few 70's era home speakers and found the walls lined with yellow fiberglass, the itchy stuff.

@@chrishuyler3580 Ahh yes I forgot about that itchy fiberglass! I’ve been in a few of those (regretted it for awhile! Lol) fiberglass filled speakers too 🔊 😬

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