Best Stuffing for Speakers Tested - Unexpected Results

[@IBuildIt]

"Best" is a relative term. All three work, but if you prefer to use polyfil it'll get the job done. You just need to use more of it than the other two. And I'm only looking at the ability of the stuffing to damp the interior of the box from the perspective of that one panel. The real difference between these is probably low enough that it really doesn't matter. With that said, when compared by weight, fiberglass and rockwool nose out the polyfil by a small margin. My preference for fiberglass mostly came from almost always having some on hand. I like to use what I have and tend to be realistic about the differences between materials. Even if there is an audible difference, a difference doesn't necessarily mean one is better than the other. Moving on to direct panel damping, rubber damping was almost useless and doubling the panel thickness is effective but mostly down low. Double layer CLD is effective across the tested frequency range. I would consider that to be something worth doing if you are looking for peak performance. Like I said in the video, it can be combined with stuffing to make it even more effective. Important to put all of this in perspective. These differences are relatively insignificant when compared with other much more important design considerations when build a speaker. Driver selection, box design (volume, alignment) and crossover design are orders of magnitude more important to how the speaker will sound. I do these tests to demonstrate just how small the difference actually is between these and how little they will affect the sound.

[@joruss]

What would be the effect if you'd put acoustic foam on the panels inside walls?

[@FOH3663]

@@joruss In this accelerometer test, most likely nothing would change.

[@olivieroli9750]

Helo look this ! kzbin.info/www/bejne/fHmWnqCIgc9-rrc

[@wwlittlejOfficial]

This is all wrong. The whole idea of stuffing a box was not the dampening effects, it's the ability to cancel waves and make the box appear "bigger" if I am thinking correctly. I don't have the math in front of me, but I've seen this test done here: kzbin.info/www/bejne/oZSXcqmcpNKXf7M

[@josephnunnally8734]

Mineral wool or you call rock wool is nasty to work with but it works great insulating 500 to 600 degree pipe

[@ChonkTek]

I did some tests 25 years ago with an SPL meter, two 12" subwoofers in a sealed enclosure (trunk tire well enclosure) and various amounts of polyfill. I did individual frequency plots on a graph, 1Hz intervals. I found that adding polyfill decreased peaks and extended lows. There was a threshold where overall I started to lose some amplitude on all frequencies if I stuffed the enclosure too much. It was a great experiment to prove to myself that spikey response in a subwoofer can be tamed some.

[@keytrackmusicreviews]

That's really cool, and I've seen your results repeated elsewhere on YT. Adding polyfill does have a point of diminishing returns, but until then it will reduce bass resonance.

[@iggynub]

That's essentially lowering the Q by slowing the air, thus the driver appears to have more internal volume to work with. Up to 40% of the internal volume is effective, if i recall. Check with ChatGPT/Bing/Bard.

[@chadridsdale9970]

I just found your Channel last night. My goodness do I appreciate what / how you are testing. I have a few projects that im procrastinating on and now im glad I did. Thank you

[@patrickthunnus]

I found it odd that the various stuffings weren't directly behind the woofer. I always thought the role of any stuffing was to absorb/diffuse the rearward wave of the cone and flatten the impedance curve, kinda like how the vintage dynaco speakers did with their aperiodic design. Every acoustic suspension speaker I've ever opened up had the stuffing directly behind the woofer.

[@chicotruco]

so this test is wrong, rigth?

[@imfrom210texas]

@@chicotruco no, this test is fine. That's another test for you to make a video on

[@edjackson4389]

I've opened some older ones (from the 60's) that had wool material on the sides bottom and top, but nothing on the back wall. When I added rock wool to the rear wall it hurt the bass performances alot. So, I decided the people who designed them knew what they were doing and returned them back to stock. The bass came back. Not sure why

[@jacksonsystemslimited]

No not nessescarily. Not directly any way.

[@ChonkTek]

The Dynaco A35 is an interesting sealed design where the woofer chamber was greatly filled with mineral wool, and then a slot in a wall divided that chamber from another chamber which was empty!

[@noahnovotny2100]

To me, using fill is never something I do to “fix” cabinet wall resonances. It’s only to help reduce standing waves or port resonances within the enclosures. I have tried many types: polyfill, pink insulation, Dacron, rock wool, demin, etc. The way I test is with impedance sweeps. I have found that lining the walls with 1.5” fiberglass is the best in midbass speakers. I put cheese cloth type material over it in ported boxes for piece of mind. Putting filling in the cabinet like you did dampens the airflow to the port which reduces output. I think that’s why people say overstuffing boxes will get weak bass. In subwoofers I use 3 inch pink insulation because it does the best job of “increasing” box size. Again, I only line the panels and adhere it with spray adhesive or hot glue. It works best with slot ports because you can get large even coverage. Getting a 30% increase in theoretical box size is common in common shaped enclosures. Whether or not that box volume gives an output increase or just changes the port tuning is still up for debate in my lab. To fix cabinet resonances, bracing is the only thing I’ve found that truly makes a significant enough difference for me do it. I know your measurements show that it doesn’t help at higher frequencies, but my cabinets really never have any resonances that high other than ports. Honestly I’m not sure why your getting such high peaks on yours. Maybe I just don’t notice them as much as the low 100-400hz ones.

[@zukispur5493]

Hello mate. Ive got a pair of celestion ditton 44 mk 2 (with the passive radiator) what filling should I use? Thanks in advance.

[@noahnovotny2100]

@@zukispur5493 if you think you are having problems with cabinet resonances you should consider putting some additional bracing instead of just adding filling. If you are trying to get rid of standing waves or internal resonances then I’d start with a 1.5 inch thick insulation, rockwool or fiberglass should both work. Since they are sealed with passive radiators you shouldn’t need to worry about dusting.

[@zukispur5493]

@@noahnovotny2100 some bracing with inch and half rock wool it is then. Cheers mate I appreciate your swift reply

[@paulthetubew]

Very interesting! what software were you using for the test? The damping material used is usually to control the resonance and other box parameters without regard to panel vibrations. Speaker enclosures can be viewed as filter networks, particularly for vented enclosures (such as Butterworth alignments.) However, controlling resonances will indirectly control the amount of energy available at any frequency to flex panels. You might consider using a measurement microphone to measure the acoustic radiation from a panel as opposed to the contact sensor on the panel. You might consider a box made of mdf instead of plywood. Mdf is a good material for do it yourself enthusiasts has high density and greater acoustic losses. Internal bracing is also effective in reducing any panel vibrations. Of course if you really want to eliminate you can build enclosures out of concrete, which I did for a customer in the mid 1970s. Wharfedale had speakers, which you poured sand into a sandwich construction enclosure in the 1960s. A speaker box has 6 surfaces, the most important is the baffle which is aimed at the listener, any radiation from top, sides, and rear are radiating into the room and contributing to reflected and not direct sound. The bottom of the speaker if sitting directly on a floor is coupled to that radiating 'panel', which changes the sound. That can be modified in a number of ways, a layer of material such as Vibrathane, a large mass (concrete), speaker spikes, or a combination of these.Keep up the good work! - Paul - former speaker designer.

[@myturkishlife1777]

I have always been a fan of the "CLD" technique, have glued thicker MDF panels with silicone inside factory speaker enclosures many times always given good solid results. Great video👍

[@BMRStudio]

Glass and rock wool slowly decomposes by the time, because of the mechanical vibrations from the sound. This glass dust particles make huge damages in the coil and spider area. We had this issue with old Telefunken TLX 2, 3, Kenwood trio LS, Pioneer and RCF speakers. Sometimes beyond unrepairable.

[@briantruck2284]

Wow Thanks for information !! Never would've thought 💭

[@briantruck2284]

Fiberglass is like sandpaper

[@toecutterjenkins]

Would be Interesting to see a test of "no rez " a product made for this purpose. I was also told vinyl floor tile with foam glued to it would work well.

[@thomasschafer7268]

No rez ist wie bo dum 800 viel zu teuer. Schweissbahn auf Bitumen 4-6 mm dick bedämpfen auch gut bassreflex gehäuse

[@chadridsdale9970]

​@@thomasschafer7268agreed no res is very expensive to get shipped to Canada

[@trevorbartram5473]

Two great videos, thanks! The preferred CLD method in UK DIY years ago was bituminous felt panels (a thick roofing product) covering all box internal surfaces. I built the Wireless World Tabor DIY design using Audax drivers using this technique in the late 70s. I had many comments regarding their excellent sound quality. When it comes to bracing, the matrix method first introduced by B&W and, later, used by Paradigm is beyond the capabilities of most DIYers. It is used in my present speakers Paradigm Studio Monitor 30s purchased twenty years ago that I have never felt the need to replace. However, I must admit I'm tempted by the KEF LS50 Metas with their use of a sculptured disc to absorb high frequency energy within the box, truly revolutionary and a tribute to British engineering.

[@l0zerth]

It was great that you tested a wide variety of materials, but it should be compared by volume, as well as weight. Another material i haven't seen used much that i plan on trying my own tests when i get the chance is closed cell foam, not sure if any of you have had any experience with that.

[@joshua43214]

My understanding is that stuffing mainly reduces reflections from coming out through the speaker cone, and any damping properties are secondary. It would be interesting to see this with a different box design. What would be even more interesting would be a double walled box with sand fill. This is supposed to do wonders for resonance. I would be most interested in seeing it with a big driver in a big box, vs a small driver in a small box. At what frequency does the sand stop doing anything? Thanks, I enjoy the content.

[@preddy09]

A small amount of stuffing/carpet especially on the inside back wall helps break up standing waves. But the primary reason for lots of polyfill type stuffing is to act as an air spring....i.e slow the speed of sound down a bit. This has the effect of making the box look bigger to the speaker But this is only if a small amount of stuffing is used and packed in a "fluffy" manner. If the box is packed too much it will have the opposite effect and actually increase the sound speed and make the box look smaller. Plus all this packing comes at the cost of some damping and efficiency loss.

[@davej3487]

I build my encloser from 3/4 inch (19mm) Burch ply. It had a slight buzzy ring. So, cut the front baffle off, put a heaver mid brace inside. Then used 'Flex-Seal' brush on rubber on all surfaces inside and out. Then I lined the inside back and sides with a scrap piece of "Mohawk" Berber carpet but no other filling. So much better. I do not have all the 'Wiz-Bang' test gear but to these damaged Tinnitus ears, it sounds so much better. I have ear damage that shows up as a 20 dB White Noise shusssss all day and night.

[@BischBaschBosch]

Interesting series mate. Used to work as a Q&R for Bowers & Wilkins many moons ago in one of my brief career deviations. Materials, material density, isolation and insulation is something that can be talked about without end. As is shape and compartmentalisation. Whether you want a speaker characteristic or a flat response etc. All about marginal gains at a certain level. For DIY'ers, I think your info is sound. Good stiff box, braced and plenty of fixings as you've done. Also driver sensitivity matching as best you can which I think you've touched on. Acoustic loose fill stuffing (looks like cotton wool) is effective and cheap alternative to the stuffing options you've shown. Particularly good around internal bracing.

[@jacobclark89]

How can they use fiberglass with vented enclosures , just imagine all the tiny glass particles you are breathing . 😥🖐🔊😡

[@SuperMcgenius]

When you brace in the middle of the box you up with two panels of the same resonant frequency, this is why asymmetrical bracing and trapezoid boxes will generally give you a better performance. Mass does work but is best with Multiple techniques of dissimilar Materials that will not exasperate resident modes. Enjoy the hobby. 😀

[@southern_merican]

You are correct it would help him if he moved his brace off center

[@curtchase3730]

I'd like to see the results of just gluing acoustic foam to all surfaces of the inside of the box. Use the type that studios have on the walls. The 1 inch thick stuff with the triangle cuts.

[@Subsonic-g2n]

I would have put the stuffing right behind the woofer. Also, try lining the inside with No-Rez dampening material as a comparison to an empty box - I would,bet that this alone would make a huge difference. The rubber lining you placed was way too thin to make a difference. The CLD method sounds interesting by sandwiching silicone in between the wood, but you have also effectively doubled the thickness of the wood. I would be interested to see if glueing the two pieces of wood was just as effective than the silicone. Interesting tests, thank you for posting!

[@thomaslutro5560]

Any thoughts on bracing asymmetrically? I'd like to see you test with an accellerometer attached right over the brace and on each of the panel sections created. Even summing those three (amplitude and phase) would be a very interesting excercise. I'm building speakers right now, an planning to use some of the leftover materials for asymmetricaly placed braces, lots of polyfill (almost getting a rash from just thinking of glass- or rock wool). and possibly adding glued/stapled on bitumen and heavy felt. The mains will be an active cardioid solution with front and rear drivers in a common volume, rear inverted and delayed to mimick an output more similar to a theoretical U-baffle.

[@EdwardT9]

Nice test! Another option is the CLD with thinner panels that’s about the same thickness as a 19mm MDF. I bet the CLD wins. The old speaker books and articles always showed better performance from fiberglass vs poly stuffing, and the really old articles from the UK mention sheep’s wool as the best stuffing. Also, what about the speaker output due to the stuffing? I thought the speaker output is smoothed out because the stuffing damps out the interior acoustic resonances.

[@IBuildIt]

The CLD has the most potential, for sure. Probably a combination of panel thickness and stiffness and size to arrive at the best result, but by then it might be deep into the rabbit hole and the time would be better spent doing something that produces more net gains. I would like to get some wool to try, though.

[@brendanloconnell]

Some very high end speakers use CLD with a thin metal layer sandwiched between plywood.

[@stevenholt5484]

If you use sheep's wool you might get some ba ba baaing above 1K! Well, bad joke of the day.

[@RennieAsh]

@@stevenholt5484 the bass will sound wooly

[@БояровАндрей]

Троелс же использует войлок ( у стены) + слой синтепона , они в паре работают на СЧ и НЧ, в блок НЧ битумная автоантивибра ещё нужна на стены.

[@Sigmatechnica]

I'd love to see how natural wool performs as a filler, i dont like useing fiberglass espexialy in ported speakers, all those vibrations are going to start blowing out fibers of the stuff at some point

[@KravchenkoAudioPerth]

A well presented video. I like the control of parameters in one way. Having done quite a lot of work recently on exactly this type of internal dampening there are a few things to add. You have to keep something equal in the comparisons and that has to be in order for there to be a valid test of properties. Mass may not have been the best choice to create equality. Your explanation of how a fibrous panel can dampen internal energy from the air pressure created by the driver is spot on. Perhaps a more equal test of the different fibres would have been equal volume. With the Polyester fibres there was great contact with the box walls, and the glass fibers were in great contact with the box walls. The mineral wool was not. When you look up in the specs from each company that makes the insulation panels you'll find that Rockwool has a broader sound absorption than fiberglass when measured in thickness. I'm talking normal North American stud wall cavity thicknesses. Carpenter to Carpenter ( :) ) you know what I mean. Rockwool seems to have the edge due to what you referred to as the problem with Polyester Fibre. Mass. Rockwool is indeed heavy stuff. When in intimate contact with the cabinet walls it changes the cabinet wall behaviours. Again spot on is the attention to the resonant peaks at 350, 680, and 1.8 kilohertz. There is an approximate numerical relationship to these. They could be harmonics. And I'd love to see a impedance and phase plot to see their relationships. I'd be willing to bet that they are indeed harmonics. And this is the box singing along with the woofer. Note how some of the harmonics are actually louder than the signal. Nice demonstration of the panel bracing. That is a DIY loudspeaker myth as large as thick panels. Slaying the dragons one by one. Just because everyone is doing it does not mean that it is the best thing to do. Last thought. Placement of your absorber is also a variable. You had a resonant cavity behind the woofer without any absorber present.

[@IBuildIt]

Thanks Mark :) Hard to equally portion compressible material by volume and I think that would be less of a fair comparison because the rockwool is much denser than the other two. It would be the clear winner, just like a heavyweight fighter would easily beat lightweights of the same age in the same ring. And I don't see the empty space as a variable, since it was empty for all three.

[@KravchenkoAudioPerth]

@@IBuildIt I agree with you assessment that the heavier product wins. Hands down. But isn't that the goal in DIY audio? To take the state of the engineering art farther. DAmn the torpedoes versus cost and time involved. And be willing to intelligently apply these gains in our own creations. This is done for the companies that I design for. Apply the best of what is out there and connect the dots on the stuff that is either not published or simply becomes intuitive with greater experience. Keep these videos coming. You have a good handle on this stuff. Much better than I have seen from many people on KZbin or otherwise.

[@IBuildIt]

As you have had some considerable exposure to audio forums, you'll agree with me when I say that what you say is best, might be completely rejected by someone else. Putting a denser stuffing into a cabinet might yield objectively better measured results, but it might not sound as good to someone who compares it to a less densely stuffed box. So I think the best I can do here with these tests it to try to show the apples to apples comparisons and the effects they have.

[@KravchenkoAudioPerth]

@@IBuildIt Oh do I agree with this. I post nearly nothing on forums. For good reason. So many arm chair quarterbacks it sickening.

[@TheAndreasKL]

@@IBuildIt You should be able to find information of the density of the different materials. If you have that, then you could easily weigh out the 3 to the match the volume ;)

[@mythos5809]

Very informative. Thank you. Would like to have seen result of using rubberized lead damping panels. also in CLD between plywood and mdf. Just curious.

[@TonicofSonic]

I have much success with dynamat. Make sure you have a roller and get it on tight. Many speakers simply will not have enough room for getting the dynamat properly installed. I put sound barrier on top on it. Only helps poorly braced boxes that have low frequency resonances, mine being 300hz specifically.

[@kennethnielsen3864]

Thanks for sharing your thoughts and ideas.

[@mpikas]

This is an interesting test, but I was always under the impression a thin layer of stuffing attached to the walls was dampening, but stuffing in the enclosure is tuning for a enclosure that is slightly too small for the speaker, the stuffing slows down the waves in the box causing it to act bigger. That said, I'm not sure how much sense that makes since a solid should conduct sound faster than air, but the explanation has aways been that you're preventing a direct path, kind of how insulation prevents a direct path for heat to escape by capturing some air volume. Not sure I buy either explanation, but you can audibly hear the difference in the speaker most of the time. FWIW, I've always been team fiberglass even though it seems like polyfill is preferred everywhere. I've typically used 'glass for my own stuff that I didn't care as much about and poly when it was supposed to match some spec or someone else's standard.

[@yvesboutin5604]

Sound waves are pressure waves moving through a medium like air, water, wood, plastics and any other material that exist. Some materials like rubber, foam or cork are good at damping pressure waves because of their elasticity. This mean they absorb and redirect that energy, transforming it into heat (yes, that's right, heat). The proportion in sound to heat ratio is quite low, but enough to slow down the sound waves and lower the cabinet rebound sound, particularly in the midrange. With some crossover artifacts like a notch filter, it help the speaker sound balanced without killing the dynamics.

[@2gnospam]

Sorry for the late comment as I just found this video. For this setup given the simple single speaker, you could take acoustic measurements close to the speaker (say 6" or so), and the room dynamics would be insignificant. Therefore you could quantify the speaker acoustic output (albeit only from the driver) with measurements for each setup and see which changes (if any) happen to the sound from the driver. Just saying a vibration is insignificant could be strengthened with actual measurements.

[@VioletGiraffe]

Thank you for these tests, very interesting. I had the same idea as CLD, but I want to use vibration dampening materials from the car audio industry, they come in sheets with adhesive pre-applied, quite convenient to use and specifically designed for this task.

[@lolaa2200]

You may try to drill holes in the Inside of the panel in a Helmholtz resonator pattern that you compute to act around the most offending frequency. About the same as your acoustic panels just inside the speaker box

[@ptmmatssc13]

I have used Dynamat and acoustic foam panels. Both did better than filling the cabinet.

[@wyup]

So you used a combination of both? Can you point to those products?

[@deoncruywagen5191]

Another thing to try is to put a cavity between two panels and fill it with sand. This should be even more effective than the CLD. One more experiment to try is to mount the woofer compliantly to the box. Add a ring of soft material between the woofer and the box. I read a study years ago and that had a big effect.

[@hotrodsurplus]

I'm open to the idea that I'm all wet, but from my understanding CLD requires a decoupling surface like foam to isolate the mass-loaded material from the panel. That's what prevents energy from transferring from one surface to another. Applying it with silicone just bonds the mass to the panel.

[@onewheelup]

well what about a thicker rubber speaker gasket,rubber is used to stop vibration but would it show results with your test ? which i really enjoyed thank you,im one of those people that never go overkill on bracing and using double walls on enclosures,i cringe in using a double baffle in fact i use 3/4 mdf but when i go to put my double piece on i actually just use 1/2 mdf.my bracing is kinda like well whats right above your head ? if your sitting in your house look up,in the attic theres 2x6's vertical so i use a couple pieces of light weight pine not treated pine 2x4's and put them vertical under the baffle with screws on each side of the box and screws going into the 2x4 from the top.thats just me.ive never cut picture frame shaped bracing,to me it looks like it would interfere with back waves.

[@rogerdavis2056]

Great video, for years in car audio I used to put carpet padding on all sides of the inside of the box! Except the subwoofer side, Thanks for the video.

[@Epic501]

Would love to see a further dive into different CLD methods, when you said CLD I was expecting a solid rubber layer not caulked silicon, interesting!

[@FinsleysCustomCarAudio]

I used 2” foam padding inside a ported box. Stapled it to walls. Lost out on higher notes but gained down low on lower hz music.

[@dmaifred]

Thumbnail looks like you are stuffing raw chicken into speaker ;)

[@cliveclapham6451]

That exactly wot l thought, 🤭

[@dmaifred]

PS love yah John . Been watching for at least 8 yrs? Need more orig 90s rock shirts I kept recognising shirts I got at concerts during early 90s

[@brentspellmeyer8943]

Adding braces basically changes the internal volume because your adding material inside thus changes tuning frequency especially in ported box.

[@By_Rant_Or_Ruin]

I remember responding to this but nope. Firstly great work. Accepting the use of fiber fills, I have Used activated carbon or sand or glass bits in woven cloth bags to keep the glass from rattling. The glass didn't do anything. It isn't porous so no sound absorption just deflection and a ton of weight. The sand made a dead speaker - oops. The carbon was best for low frequencies and I could isolate it in bags. But it was very expensive because I have not looked into what chemical is used with the charcoal to produce the very porous cavities of "activated" carbon. I noticed you left parts of the wood exposed when applying the rubber which seemed counter productive to me. I can't help but think that spraying the entire inside of the cube with rubber spray would be more thorough? But like you have shown, thickness of panels and an isolated speaker would also fix some resonance. Again, great video. Thank you for the time and hard work.

[@noahkatz9616]

Since as you say the advantage of fiberglass and rockwool is the higher density, I'm puzzled as to why you would disadvantage them by putting in the same weight as polyfill and not the same volume.

[@lohikarhu734]

hi John... pretty late to the party...i wondered if you have tried slower sweep rates, or, indeed, how your sweep rates run? in spectrum analysis, to fast a frequency sweep kind of "aliases" into the results, and, depending on the Q of the resonant system, you can easily sweep right past a peak... anyway, what do i know 'bout speakers!

[@Colin-From-Corby-yy4vb]

Good effort, but I can't understand why you didn't put the fillings behind the woofer section, because by filling just half the speaker cabinet with sound deadening material would allow sound waves to bounce around quite happily in the bare cabinet woofer section ! Another option would be egg box foam placed on all sides of the cabinet, or even 1/2" felt pads stuck to all internal panels, maybe try those suggestions next time round 😊

[@marisbarkans9251]

Hey i was wondering can i use the same principles as soundproofing a wall and eliminateing echoes by using like cone stryctures in all typses of hights to absorb the resonant frequencies or will that make the speaker sound dead? i am not experimenting with saw dust with pva. i made a speaker and i need a thicker front panel its a bluethooth portable 200w speaker so theres not much space. to be honest i would need to remake it cause the 100w sub is way to much for the thickness of that boerd but i was wondering if i could make a putty and just make the wood thicker that way. the first small plate i made isnt dry yet after some 15h but it looks like the adhesion is greeat and it seems to stay somewhat plastic and moldable maybe when it dries it will harden but right now if i can use the spike type of structure this would be amazing material to do it with.

[@sudd3660]

great video, i always seek to improve my cabinet designs. i have not done much testing, but i do like to use things that have weight to it, when a 20 liter box has 1 kilo of bitumen or a kilo of damping stuffing then things are having an effect. i use "recycled textile fiber", its pretty heavy and packs in pretty nicely(for sealed box only)

[@felixm.8910]

Now here in Germany we have a product called 'Reckhorn ABX'. It is a 2-2.5 mm thick sheet of butyl, covered with aluminium. It has a weight of 2.5kg/m². I would be really, interested in what that does to a panel. It has a relatively high density, so it doesn't take away a lot of volume, but also dampens really well.

[@thomasschafer7268]

Nehm Bitumen schweissbahn das ist billiger.

[@MorRobots]

What about an equal volume(m^3, not amplitude) test? Also it would be interesting to see some difrent laminations and even more complex bracing setups.

[@bigbirdwpg]

I always thought that the purpose of stuffing was more to dampen that hollow sound you get in an empty box as opposed to damping the resonance of the panels.

[@stefanweilhartner4415]

yes, you can damp the standing waves/resonances, but just a tiny bit. the best way is to put boards horizontally and vertically inside that partially reflect a wave. also using layers of light and heavy dampening create reflections between them. many different reflections result in shifting the energy from a single strong/loud resonances to many different smaller resonances.

[@castletown999]

I built speakers in my youth but never had access to the tools available now, so I have no experience with them. That said, I have a feeling you are scanning the frequency range way too fast. In my experience resonances take a while to build up. It makes sense right? Like if you push a kid on a swing it takes multiple cycles before the resonant amplitude builds up. You are not spending enough time at any given frequency for a panel resonance to build. (IMHO). So. Have you ever tried scanning much slower? I would be fascinated to see if that makes any difference.

[@DonnieMulligan]

I have also used vinyl floor tile to line the cabinet interior, along with foam, and insulation. I believe a combination of materials might be effective too. Sorbothane and Desadamp are two other products but are definitely more expensive. Did you try testing the woofers output to see if there was any change to the frequency response?

[@Aswaguespack]

I have used combinations of “dissimilar” materials of various density in a few speakers I have experimented with and the results were satisfying from an auditory standpoint. I used polyfill along with rockwool and strips of Noico sound deadening mats. Overkill? Possibly but I was satisfied with the improvement in response. The cabinet was deadened substantially and the Noico helped greatly in that regards

[@scottwallace1689]

Thanks for this really good video. Do you have details of the accelerometer you used, and what method it uses to connect to your computer, etc? I would like to try to replicate your experiment method to help with some speakers I'm building. Happy if you have an affiliate link you'd like to share. Thanks again.

[@donepearce]

I don't understand why you think that the stuffing is intended to damp the panels. It is an air damper, preventing cavity resonance in the box.

[@Coneman3]

How about multi-layers of damping from light to heavy? Low bass will go through most things, only mass absorbs it. Less heavy layers absorb higher frequencies

[@paulhirst3548]

Thank you John for this. One thing that I would have liked to have seen done was to get the best results possible with the material you had, and not worry about the material being physically equal. So what is the best that you could get using various amounts of Rockwool vs various amounts of fiberglass. I understand that this would have taken much longer and it is way beyond my patience but it may be worth a try.

[@IBuildIt]

These tests can be used to decide how to get the best results without actually doing that. But then the definition of "best" isn't an objective standard in audio. What's best for you might be less so for someone else - no, definitely would be less so for someone else, given how picky and contentious audiophiles are :)

[@EdwardT9]

@@IBuildIt ...re the last sentence... with some (many?) audiophiles it’s almost more important to find materials that can marketed well rather then work the best. An example is that FG has been criticized in the diy forums for many years, which are full of comments saying don’t use it or get rid of it.

[@gordondyer6310]

Hi, I always enjoy your videos. Can you tell us which accelerometer you use and where you buy it? Thanks

[@ryansemplexyz]

Speaker fill has two purposes: to increase the relative internal volume "seen" by low bass frequencies, and to absorb mid to high frequencies. That being said, there's not a situation where speaker fill will dampen the side panel resonance, unless you use an enormous amount of fill. If making a 3 way design, the mix woofer should be sealed in a separate enclosure, and densely stuffed. The reason to densely stuff the mid woofers compartment is to eliminate internal reflection, which would otherwise interact with the woofer and cause resonance in the frequency response. For the bass section, if ported, then an "ideal" amount of fill should be used based off the internal volume. Since the crossover will limit mid and high frequencies, the main purpose of this fill is to increase the relative volume, and therefore the bass output. In a two way speaker design, ported, a hybrid approach can be taken. Dense fill behind the driver, loose fill everywhere else. There's plenty of online documentation demonstrating the best method to fill your speaker based off the speaker design.

[@gregornolzen570]

Nice video! 👏👏👏 One suggestion for the same video.... May it could be interesst to show the same test with the same speaker in different types of gabinets. Ones that TLs are in theory non ressonant...

[@Steve_Just_Steve]

Hi John, what are your thoughts on both of the "Worlds best speakers" videos by Tech Ingredients? Thanks

[@denisskorski3471]

Hi John, thank you for the video! The following is my uneducated opinion. What if instead of using a bid of silicon gluing plywood and mdf, try to sandwich a whole rubber mat between them? Plywood layer actually seals the box, so anything outside do not need to be sealed. Also instead of rubber mat, the polyurethane mat can be used. The only parts that can transfer the vibration between layers are screws, but they are located, I believe, in the places with the least vibration energy. So, vibration has no choice but go through the mid part of the sandwich.

[@djambush360]

Rubber is a good idea but i would put it as a final layer on the inside of the enclosure. This is more stable. You will get the best results if you mix materials with different resonance-frequencies. A ceramic tile on 60-70% of the side and backwalls (inside) will quieten your box too (may some rubber or bitumen on top of the tiles).

[@scanspeak00]

There are 2 problems to solve. 1 is to absorb the sound in the box so that it doesnt radiate back through the cone (using filling), the 2nd is to suppress panel vibrations being transmitted mechanically by the driver to the cabinet by constructing a rigid/well-damped box. My methodology over many years is to use shelf bracing, often several horizontal and vertical in larger speakers (think B&W matrix) to raise the resonant frequency of the panels where they can be more easily controlled, then glue 1/2" felt to the walls and finally fill with lambs wool.

[@charleshultquist9233]

I'm surprised that the panel transmits so much energy in the higher frequencies according to your graph. I would have thought it would only affect the lowest frequencies.

[@gregsz1ful]

Stuffing for reducing panel resonance is iffy. Best if it lightly touches or is attached. Stuffing has three basic functions. Absorption, ability to make box appear larger, and delay. Open foam rivals fiberglass for all three, and rock wool functions similarly except density varies. Polyfill is just not as effective at all things except it usually spreads out well. Cotton is another stuffing and wool.

[@alcaponemafia]

Have you tried using compressed chip foam or carpet underfelt / underlay. zig zag it in the box. Try high density foam.

[@jamesmay1322]

Very interesting testing. However, the point of internal stuffing has nothing to do with damping the speaker cabinet resonances. It's purpose is two fold a) to change (slow) the speed of sound within the box, thus altering tuning, effectively makes the box bigger from the perspective of the drive unit, and more importantly b) to absorb and damp internal acoustic resonances which will impact the drive units frequency response. To see the real impact of internal speaker stuffing, you need to measure the drive units response with each (and with nothing as a reference point). It would have been intersting if you'd had a 5mm (or so) matt of low compliance rubber to place between the two panels when doing the constrained damping test. I think that would work better at actually isolating the outer panel from being driven by the inner panel than silicone would, as it's more compliant.

[@stevefisher8323]

Great effort here, but have to say the shape of the cabinet is close to a cube, which can have significant standing wave problems and is less typical of the taller / thinner shape of many of todays speakers. A good experiment would be to buy actual speakers (whatever you can afford) and test these with their damping and remove it, then test other damping alternatives. The cabinet bracing would be held constant of course as you'd have a pre-manufactured product.

[@caletzm]

I always had look at speaker as a form of a piano- box with a mechanical equipment generating unique sound, why stuff the speaker box if the idea is to resonate the natural material with sound production of the speaker and finding that unique sound. Or am I over looking the process of sound-vibration?

[@jcugnoni]

To me the stuffing also helps preventing internal acoustic resonnance or reflected waves propagating back to the speaker cone. Thus it would make more sense to compare the sound capture than the vibration.

[@isaeagle4031]

Bracing has the largest effect by raising the resonant frequency of the panel beyond the point that the driver, when crossed over will excite the panel. And by varying the location of the bracing so that no more than 2 panels share the same dimensions helps further.

[@IBuildIt]

My tests show that it's harder to do that than it seems. The panels need to be very small to drive the resonance up high enough, which means a ton of bracing. And in a fullrange speaker there's always a driver that can excite it,

[@socksumi]

Measuring it's R factor should determine how much acoustic insulation you need and it's effectiveness. And also how dense you can make it and how easy to adhere the enclosure walls. I used to use lambs wool and also a material called Tufflex. Lambs wool was especially effective as it had a very high R factor but it was also difficult to work with and had a tendency to settle. Tufflex had a decently high R factor was easy to cut, came in rolls and (similar to foam) was rigid enough to stay in place.

[@karlsonkab51]

Was Tufflex something like Kimberly-Clark's "Kimsul" ?

[@wingnutbert9685]

Hi John. Do you think something like 3M's VHB tape would work better then the silicone? Kinda pricey to cover the side with it. But it's a 1/16" thick and kinda like a neoprene foam so would/may act different then the silicone. Also, do you think there'd be a difference made with how you've got the panel attached? Gluing it to the box vs the screws as used? Thanks!

[@rewind9536]

This is what every KZbin video about audio should look like.

[@mikemcconnell2794]

Very interesting test. However, the stuffing in a speaker isn't for deadening the cabinet panel resonance. That's done with using the right cabinet materials and bracing. The fill has two functions. One is to deaden the reflected sound that would come back through the cone. Which is usually thin paper or plastic. Sometimes metal etc. The second is to slow the sound waves to make the cabinet seem larger than it is which means that you're lowering the cabinet resonance. A good quality MDF board is good for home stereo. That should keep your cabinet resonance down.

[@IBuildIt]

Damping is damping. It will damp everything inside the box - the airspace and the panels. This is the way that I chose to measure how effective the damping is, by measuring the panel. Could be you are getting confused by the other testing I did at the end with direct panel damping to put the results into perspective. I should have been a bit more explicit in explaining my procedure, but it's very difficult to anticipate what needs to be emphasized.

[@mikemcconnell2794]

@@IBuildIt well I think you may not quite understand why companies put dampening materials in their speakers. There are 2 reasons why companies use MDF. Its low in resonance and also fairly stiff. Pro speaker companies usually use Baltic birch because of their stiffness and because of the multiple layers do the same as your last test with 2 boards sandwiched together. You can feel the side of the cabinet and a good cabinet won't vibrate much. After that it's the specific placement and material that decides the internal damping that they want. Most high quality speakers will have a thin, maybe inch or 2 of sound deadening layer attached to the cabinet sides. If you are going to "fill" the cabinet, it's to stop reflections and mechanically make the cab larger. Your test for sound dampening testing doesn't really give you a good idea on what to use as sound dampening other than it will help stop a poor cabinet material from resonating. As an example, 2 sandwiched boards gave you better results. Now ask yourself how much it stopped that from coming back out that piece of paper called a cone speaker. The speaker cone isn't made of 1/2 inch wood.

[@mikemcconnell2794]

@@IBuildIt I'm sorry but I should have mentioned horn speakers and transmission line speakers. On horns, you shouldn't use any fill. In transmission lines you will need a lot of fill. It depends on the type of speaker you're building.

[@IBuildIt]

Well I think you don't know enough about me to determine how much I know. Read through the other comments on here and my replies, and watch my other recent videos rather than going with assumptions.

[@mikemcconnell2794]

@@IBuildIt I'm sorry if I came off that way. I've been a sound engineer for 40 plus years and was trying to impart some of my knowledge. No offense meant. Sorry again.

[@GavinParsons-qd3oz]

I am rebuilding a set of Berkley cabinets for my 12" Gold Monitors. When I originally built them in 1972 and used Rockwool for sound deadening. I have worked in multlex theatres installing sound panels. I have a few left. They are one inch thick of compressed of what looks like insulation. What are your thoughts on putting this on the cabinets walls instead? Thanks

[@yvesboutin5604]

I like your videos a lot because I don't have the software to take some measurements, but I have to agree with some of the comments posted that stated damping is used mostly to avoid sound from the bass driver to bounce back in the cabinet and coming back with a delay and smearing the response. The fact that some materials are damping the cabinet walls is just an added bonus, so that material should be placed in the area around the mid-bass driver to absorb or slow down those pesky resonnances. My preference goes to acoustical foam because it is a very efficient sound absorbant and its elastic properties damp slightly the cabinet walls and stay where you put it. Beside what I have said before, I still appreciate the efforts you put on those videos, they make our knowledge about acoustic advance by leap and bounds. Thanks!

[@murphymmc]

Interesting. I've had to deal with sound attenuation on a couple of building projects that needed some serious noise reduction. Your fill test with different media was conducted by weight rather than volume, I think that it skews the results. The mineral wool at about 3lb/cu.ft. vs fiberglass at .6lb/cu.ft. doesn't utilize the density advantage by volume filled. That's still a marginal advantage anyway. Your conclusion with vibration inhibiting barriers that create isolation is the best process. You may even try a sound attenuation drywall that incorporates an isolation barrier built in. Pricey stuff, probably close to $100.00/4x8 sheet. Another product that works very well is a caulking called Green Glue, specifically designed for soundproofing and attenuation. Fasteners that bridge the isolation barrier( like screws) will negate the full effects of isolation. It take a bit of thought to bypass that sound transference issue. Good stuff John, by the time you are done you may blow all my suggestion out of the water, or I may have contributed. ;-)

[@trell2k]

Just wondering if you have tried cncing a diverse surface inside the box? Similar to room treatment. Might be fun.

[@jonesaleroy]

John I also found fiberglass is much better. Poly just don't have the density and mass to absorb much energy.

[@1974UTuber]

I would have thought some deadening strips between the box endes and rear panel would have given a better result. Stopping any chance of wood chattering against wood seems like it would have more of an effect

[@derekleclair8787]

Great experiment. Gives great examples as to why to brace and double baffling with cld!

[@collinbpeep]

John, very interesting video. My thoughts on dampening materials had always been centered on the driver output difference, or lack thereof, but seeing how they changed panel vibration was intriguing. However being you have this setup ready could you please do a quick comparison of the effects on driver output? Too many times I've read differing opinions on the subject and I believe it would be beneficial for more than just "Toids DIY Audio" ( iirc) having tested the subject on video. Thanks either way though as now I know I could use less bracing and more stuffing if necessary.

[@johnwehunt4305]

I purchased safe and sound intended for 2x4 framing. Haven't used it yet.

[@krishanthadissanayake]

An idea of fillings inside the box is to HIDE some air inside the box(inside the cavities in the fillings)...so speaker cone is free to move, fiberglass whole is the best i find, you get better dynamics ,Bass become more pleasurable

[@deoncruywagen5191]

Oh, and another product to test, and I'd be very interested in the results, is NoRez from GR Research.

[@b1782w]

I've used eggshell foam padding sprayed on glue on all the panels but obviously didn't test with anything... just used it bcuz I had some laying aound and I figured they use that similar setup in recording rooms

[@ellasfella1205]

for dampening speaker cabinets 3/8 carpet padding henry Multi-Purpose Flooring Adhesive and seal & peel are your 3 best friends

[@IBuildIt]

Did you measure it to confirm your conclusions, or are you just going on assumptions or second-hand advice?

[@ellasfella1205]

@@IBuildIt I'm just your average nobody that fell off a baby when i was a high chair. line the inside of the box with the 3/8 padding with the adhesive put seal & peel on the lip of the woofer. all things will be made clear.

[@IBuildIt]

@@ellasfella1205 what's clear in audio (and most other things) is how many people think they know more than they really do. And then they get on forums or other places (like here) acting like they have the answers. I think the technical term is "talking out of one's rear-end".

[@ellasfella1205]

@@IBuildIt i agree but then again not many people have had the privilege to work for a company that worked on Whitney Houston's Phil Collins and Metallica's stage speakers & equipment

[@ellasfella1205]

@@IBuildIt i would like to apologize to you cause before today this was the only video i ever saw of yours. when i was giving you the advice i thought you were trying to be cocky & arrogant with your reply that's why i replied the way i did. but after seeing 2 more of your video's i can see your not that type at all you are genuine and like your delivery so once again i would like to apologize. when i was giving you the advice it was professional advice. back in the early 90s i worked for crest audio we worked on Whitney Houston's stage equipment and we also built special speaker cabinets for Phil Collins & Metallica we did the same thing to their cabinets. so keep doing what do and stay safe

[@getsum8931]

An interesting test. Those materials are not meant to change the resonant frequency of the panels but dampen the driver. There are lots of better alternatives for panel dampen

[@IBuildIt]

Damping is damping. It will damp everything inside the box - the airspace and the panels. This is the way that I chose to measure how effective the damping is, by measuring the panel.

[@getsum8931]

I appreciate the videos. Your tests are valid and prove those materials don't dampen enclosure well however what they do well is change the q factor of the driver simulating increased airspace which is proven and tested with frequency measurements.

[@georgemartinezza]

once I read (I don't remember, maybe in Popular Mechanics Mag) about small speakers, inside with cardboard/aluminum/foamy, to "enhance" the sound and make the box to be shield agains magnetisms). can it be "good option" to add those?

[@vikassm]

Ha! Nice to see the sandwich panel at work! I believe a thinner, more even layer of rubber adhesive damps better than a thick layer of silicone (because the glue is working in shear mode?)

[@typedeaf]

Surprised you didnt test 'acoustic' foam variants. I have some old B&W that are just lined with some 1 or 2 inch thick grey foam. Other boxes ive seen use adhesive foam. There must be all kinds of foam. What about memory foam? :)

[@davidcorzo5515]

By the way, i like the idea to use an accelerometer. How you rigged to the laptop? Is there an interface in between? At this moment im using my cellphone app.

[@tweakerman]

Natural lambs wool, I find is the best, because its a natural & not man-made, like fiberglass & polyester dacron, that colour the sound, nice video👍

[@marcusm5127]

Love your testing, I am afraid cld increases the volume of the sound coming out through the driver but maybe more stuffing will compensate for that and still be the best.

[@bartwalters6694]

I enjoy your videos. I have not built a speaker yet but I am very interested. I restore and tinker with cars as a hobby. When I saw what you were doing with the silicone I couldn’t help but think about the isolators that are used between engine intakes and carburetors, especially on high revving race engines. They do reduce resonant vibrations that cause problems for the fuel and air. What would be the effect of isolating the woofer and tweeter by gaskets or silicone? I understand the purpose of a rigid box, but what happens if gaskets or silicone are sandwiched between all of the joints? Of course using a ported box. I’m sure I’m way off here somehow, but I am curious.

[@djambush360]

You can use cellular rubber (1 or 2 mm thick) to reduce resonances and to mount the chassis airtight. Also a ported box needs an airtight mounted speaker. Mounting a chassis with some kind of rubber-metal-mix as they use on engines (Vergaserfuß in German [carburetor-foot]), the chassis would beginn to move in any diections. This would take a lot of acoustic energy, especially in the hights and cause many problems more. It would be the best mounting if the speaker is the baffle itself. No airleaks, no noise transmitting. Use the right screws and thighten them equally and it will work fine.

[@mariusbezuidenhout8851]

Thank you for this, I love these type of tests, one thing I've heard of was car sound deadening sheets, have you ever tested those? Thanks

[@stefanweilhartner4415]

900 Hz resonance with the speed in air of about 343,2 m/s results in a wavelength of 0.381m. divided by two is about 19cm. is this the inner distance between your top and bottom panel? because i think you have a standing wave there. to break that up you would need a panel with 4 big holes in between but not exactly in the middle because that would result in two synchronous standing waves at about 1800Hz. you would need to split up the 19cm distance in an odd ratio that the resulting two compartments have a different height. usually the "golden ratio" is a good idea. then the two new standing waves are not feeding a combined resonance. does this "sound" reasonable?

[@djambush360]

2:55 I thought you're talking about damping and not about repress or quieten sound. This is not the same. sound damping means that you will lower the velocity and energy of soundwaves. Repress means that you will improve the enclosure to be quiet and take down all responses or resonances, making it 'acoustic dead'. With this accelerometer you measure how good your enclosure represses the forcees that are treating it. The reduction of enclosure movement in combination with the damping-stuff is a result of the reduced wave velocity and energy that is absorbed by the polyfill etc. 7:14 and 8:16 this is a good way to improve the enclosure. By mixing materials with different resonance-frequencies you will get a better result, Many high-end speaker builders use rubber mats as a final layer inside. Stoneware or ceramic tiles put some weight on larger sidewalls. You only need tiles on 60-70% of the area to have a good result. You can hear the quality of your work by knocking on your box. It will sound dull within a lower frequency. Then you can start damping your boxed in air. To much damping stuff can be contra-productive. Ported boxes don't need much damping, in fact they work less good if you put stuff into the way the air should move. They only need some flat panels on the sidewalls to dampen the mid frequencies. A 6th order bandpass sub dosent need any damping at all but will get better with a solid enclosure. Long things short: Polyfill is pretty good and it's cheap. You get NO advantages if you buy high end super state of the art Polyfill wich is 'extra' designed for high quality sound. That's bullshit. You even could use ikea pillow-filling with the exact same results. The only thing with this stuff is that it mostly comes in little pieces. They are a bit difficult to get them to stay where they should. But if this is no problem you could use them. Greetings from Germany.

[@mkshffr4936]

Very interesting as usual. I wonder if using rubber sheeting between the two panels instead of the silicon would have more or less effect.

[@luminousfractal420]

I found 3m make some very specific rubber sheet. I wouldnt doubt they have something suitable.

[@robbiedw1495]

Would it make a difference if the 1/8 rubber was loose? Maybe just corner staples to hold it?

[@silicon.alchemist]

Isn't part of the function of stuffing to reduce internal reflections around the inside of the box as well? These reflections can be bounced around inside the enclosure, and get redirected out through the driver out of phase (or in phase) and affect the sound. In this case, would it not be better to actually line each panel with stuffing, to absorb these reflections, rather than just randomly putting in a plug of stuffing in half of the enclosure?

[@AuDHDQ]

Don't know if I will ever build a speaker but if I do I will remember this technique!

[@xcvbxcvb2179]

Can a short signal sweep reveal any resonance frequency in the box. Intuitively I'd say it more likely to take a sustained signal in order to start some materials to resonate. I had a pair of speakers that started to resonate at 260 Hz under certain circumstances when played at or above a certain spl. Would it be beneficial to play the signal sweep way slower in order to get slow starting resonance going?