Does Polyfill make a Box BIGGER? Tested and Revealed

[@johnshore3095]

My listening room was a little small acoustically, I filled it with polyfill foam and it now a perfect size... if a little bit difficult to move around.

[@ohmythatsweird]

But...why do you need to move around?

[@kohnfutner9637]

Cool! You're whole room is a bed/chair/speaker.

[@kalidesu]

cool

[@dunnbizzy79]

Exactly my concensus how does adding mass which takes - space in turn actually add air volume but yet steels the space the air volume needs to exist? I guess if someone who doesn't pay taxes can get monthly tax credit payments, anything is possible.

[@johnshore3095]

@@kohnfutner9637 It is a padded cell.. the fabric is acoustically transparent and it means I can't hurt myself, if I get out of my straitjacket.

[@uncledoug9999]

You were right! My wife rejected my massive dual 18' subwoofer project as designed. However, I told her about the virtues of fiber-fill. Then, when I assured her that a 9.5% reduction in net internal box volume would make the monstrous subwoofer "look" much smaller, she was overjoyed and promptly gave me the cash to move forward with the project. Thank God for fiber-fill.

[@Bassotronics]

Uncledoug Thank God I’m not married!

[@sigitbudhiprasetya5475]

@@Bassotronics 🤣🤣🤣

[@Trouble22some]

@rocknroller1999 😂

[@davidjames1684]

This story sounds made up to me. "Hey hun, I want to build a giant speaker box". Wife: NO EFFIN WAY!". Husband counteroffer: well what about if I make that giant box about 10% smaller. Wife: Oh hell yeah that is a totally different scenario. So bogus. For a 3 dimensional object (such as a speaker box), decreasing the internal volume by about 9.5% only requires about a 3% decrease in each dimension. So for example if the box was originally 34" high and "shot down", you want us to believe that a 33" tall speaker would be accepted? That is ridiculous. Visually, there is very little difference.

[@mindtraveller100]

David James "This story sounds made up to me." Of course it´s made up. Don´t you get sarcasm?

[@sjgoff]

I always assumed it made a difference simply because OEs use it in their boxes and we all know how much they skimp on materials to squeeze as much profit as they can. Great video!!

[@quickclips510]

It makes your bass deeper ar lower levels

[@DanRu13]

Stuff that box and make your wife happy!

[@user-se8nh3yu1e]

Daniel Ruiz .

[@Lowkey_nxthxn]

😂😂😂😂

[@robertrentel1061]

Ya, with cotton candy glass what a joy.

[@duckpk10]

She loves anything that makes it hit deeper!

[@AALavdas]

It's beyond me how anyone can build a speaker without polyfill and/or other absorbent material. I always stuff my boxes full - you get more low-end extension and a flatter curve (ie less booming), as described in the video. You don't really need testing gear to know this, if you've played around enough with speakers there is no question about it.But of course it's nice that a video like this has been posted for people to see and...be convinced! And it does not have to be a small box. My main speakers are huge, and they are still stuffed full.

[@supercleaner]

I agree 100%. In 1994, I put two JL Audio 10W1 speakers in 1.5 cf boxes stuffed with fiberfill and powered by a 75 watt Hifonics Odin amp in 4 ohm stereo. The low end extension was scary. I'm still using the amp today and the speakers are undamaged. If you're not power-hungry, the concept works well.

[@transpermeance1535]

What the polyfill or any fine filament material does is change the compression of the gas inside the box from an adiabatic compression to a isothermal compression so the volume of the gas acts as a softer spring. For Isothermal compression the gas has time to exchange energy with it's environment (polyfill) so the minute increase in momentary temperature when the gas is compressed without the polyfill is changed to a constant temperature environment. There is a diminishing return because the polyfil is actually also replacing the air in the box; so stuffing it with too much polyfil will reduce the volume of the box more than the gain in softer spring constant for that air.

[@JilesMcCoy]

This.

[@2008synack]

Probably a bit late to the party, but BassBox Pro has for years taken into consideration and can plot out the effects of box "damping." You can choose no, light, med, or heavy damping. It's been a long time since I've used it, but it appears to assign a percentage increase of apparent volume to the box based on the amount of material.

[@markfischer3626]

That's not how it works. Woofer/enclosure systems are best modeled using Newtons Second law of motion applied to forced oscillation. Three factors control the frequency response, the moving mass, the damping factor, and the spring constant. In all but one design the damping factor and spring constant are frequency variable. For example in a ported design at some frequencies the speaker pushes air through the port easily, at others it meets strong resistance. In the acoustic suspension design the springiness force depends on the difference in air pressure between the inside and outside of the box. The relationship is linear and independent of frequency. An added bonus is the restoring force is applied uniformly over the surface of the cone. Where does the polyfill come in. The speaker is forced to push and pull air between the fibers. Properly designed the aggregate surface area of the fibers is enormous. This creates an aerodynamic drag proportional to the velocity of air. It is also independent of frequency. Therefore this design can have any desired frequency response just by adjusting these 3 variables mass, spring constant and damping. In the solution as you fill the box with polyfill you are displacing air so as you increase drag you are also increasing springiness. A suitable woofer for an acoustic suspension design will have a low Fs 20 hz or lower, a low Qms around 2 or 3 and a low Vas of around 3 o4 cubic feet. A rule of thumb is optimal enclosure size is about 1/2 Vas and about 1 pound of polyfill per cubic foot. Parts express technical department will help you optimize your design using their computer modeling program and the Theil Small parameters for your woofer.

[@MomirPeh]

Great explanation! Love it.

[@HighVybeTribe]

Very well said , thank you

[@HighVybeTribe]

Yer building my next box lol

[@avergison]

"Properly designed the aggregate surface area of the fibers is enormous." That is exactly the point. But NOT to create drag, but rather to cool the air during compression (and heat it on decompression). Without such stuff the woofer will do adiabatic (=isolated from the environment) compression and decompression which heats and cools the air. Let's just continue with compression only, for understanding. Due to the gas law (P * V = constant * T), the decreasing volume (compression by woofer) will be balanced by a raising pressure, assuming the temperature is constant. However, adiabatic compression will raise the temperature. It follows that the pressure will raise more, because now both V and T changed. The Polyfill will just try to keep the air temperature constant, so to avoid the extra increase in pressure by temperature. Heating/cooling occurs in milliseconds or even faster. So it looks as the box become larger.

[@markfischer3626]

@@avergison The overwhelming majority of heat in an acoustic suspension woofer and all of it in other designs comes from i squared r heating of the voice coil. If anything filling the enclosure with fibers restricts the dissipation of heat.

[@LTVX2]

The first enclosure I built was back in '84, when most drivers were in the 8 ohm variety and the only crossovers out there were passive 100-150 Mh coils with caps. Finding a driver with the T/S parameters were almost non-existent. SpeakerLab was a good choice. Any-who... Enclosure stuffing was one of two ways of killing off the unwanted 100Hz and up resonances that would pile inside of the enclosure and it would always yield better low end. I even used fill in mid applications for the same reasoning.

[@yvesboutin5604]

I use fiber-fill or foam to absorb reflections and standing waves in 2 way or 3 way speakers and also because it dampen some of the midrange nasty peaks.

[@soundsnvisions]

Read "The Loudspeaker Cookbook". It tells you that polyfill simulates a 20% increase in box volume - not 50%. Also, it depends on the material used for the fill. 100% wool offers the best response. It's a tough (ie dry) read, but has LOADS of information regarding box building.

[@Toid]

That's Scott, I have read it. I did an extreme example to show you couldn't reach 50%.

[@nomon95]

the thermodynamic applies here, the stuff with polifill, wool or other absorption sound waves, acts as a heat sink. and the internal compression of the air has an adiabatic compression , and the air rise a bit less his temparature, and tha air dont rise his volume with the rise temperature. the fill is approx 1 lib/cubic foot

[@IliyaOsnovikov]

@@Toid Step from the twice smaller box to the large one in not 50 but rather 100%.

[@Karizma231]

I thought fibreglass was best

[@nunyabiznatch243]

Professional audio engineer here. Love your stuff. Two things on this video; 1) the frequency response of microphones when placed close to a sound source are impacted by proximity effect which causes a significant bump in the low end response of the mic. All things being equal that doesn't invalidate your comparison as long as the mic placement is exactly the same between both measurements, but it is worth noting that the low end output of the source as measured at the microphone is inaccurate compared to the actual acoustic low end output measured at 1m. 2) When doing these kinds of measurements it is much more accurate to use sine sweeps and/or pure sinewave test tones at various specific frequencies to give precise comparisons of output level at various frequencies.

[@jgharding2]

Also an audio engineer, with a correction to point one: the Dayton mic is omnidirectional, and omnidirectional microphones do not exhibit proximity effect.

[@phillipbartlett1819]

We were doing this in the late 80's early 90's. I went with the rule of thumb 1lb per cf. I only would reduce the box by 1/3 but I'm sure 1/2 would have been fine. I had 8 kicker 8" comps in my t-bird in a 3 cf box and it went low for 8". Awesome to see you demonstrate it on here because we just played it by ear. Awesome video

[@ericbachmann8037]

PolyFill slows down the air inside the box resulting in the sub thinking (performing) like it's in a bigger box. A good rule to start, 1lb of PolyFill per .75cf.

[@kohnfutner9637]

1 pound per 75 cubic feet? 🤔 You mean the room? Oh, I just saw the dot. Per .75cf. got it. Per .75 cf the box is too small, I assume.

[@Blue_3is]

1lb????

[@ericbachmann8037]

@@Blue_3is yes 1 pound

[@Bassotronics]

I always add polyfill to my sub enclosures. But for SPL competitions, I think it’s not recommended. I think it’s because even though it drops the frequency response, it also reduces the SPL slightly. I could be wrong though since I’m not into SPL competitions.

[@Gtrjerry73]

It would yes. A speaker produces sound waves in both directions of travel. So you can think of it like it is two speakers. One firing sound forwards and one backwards. The sound travelling into the box gets absorbed by the damping material and doesn't have a chance to reflect back out the front of the cone. The fill slows the sound waves down though lowering the frequency so for sound quality you will want damping material especially when ported

[@mariusloubeeka5810]

A software to calculate the polyfill amount does exist! AJHorn can calculate boxes with a roughly given amount of polyfill. You can enter a value in it for a parameter called beta (β) at different places, where zero means no polyfill and 1000 means fully stuffed. Just try out the demo version where the horn lenght parameter is limited to the values of zero and 50 centimetres. With it you can at least calculate closed boxes if you set the horn legth to zero and the areas at beginning and end of the horn to the size of piston area of the driver. You can verify the amount of polyfill by comparing the measured impedance response to the simulated one. I personally think it's totally worth the 120 euros if you use it frequently because its calculations are very accurate and it's capable of calculating closed boxes, bass reflex, transmission lines, frontloaded horns, backloaded horns and band pass boxes including the influences of a crossover network. Just above ~200 Hz its accuracy decreases because it doesn't take baffle step and measured frequency responses into account. But there are other programs for that.

[@vincentrobinette1507]

It seems to me, that that program would be most useful for ported bass reflex boxes, because of the need to precisely control resonance, rather than trying to eliminate it all together.

[@mariusloubeeka5810]

@@vincentrobinette1507 : You can enter beta in five different places: At the beginning of the horn/transmission line, at the end, inside the front chamber, inside the rear chamber and inside the absorber chamber. It is capable of calculating bass reflex, transmission lines, horns, band-pass (also 6th order band-pass) and everything in between. Just have a look and try the demo version: www.aj-systems.de/indexe.htm Which resonance in bass reflex enclosures do you want to control with polyfill? In a three-way design you don't need polyfill at all in vented boxes, if the crossover frequency is lower than about 250 Hz. In two-way designs it's best to use only a little amount at the top and bottom end if it's a long floor standing speaker and high density material (1-2 cm thick felt or e.g. _Bondum 800)_ on the walls in the middle to absorb the mid-frequencies. The standing wave between top and bottom should better be treated with an absorber chamber instead of stuffing in the middle of the enclosure. If none of the inner dimensions is bigger than 50 cm standing waves aren't even a problem. Source of all my knowledge: German DIY loudspeaker magazine _Hobby HiFi_

[@Grommet2007]

Hronresp can simulate the impact of stuffing.

[@MrAtrandom]

You should have ran some impedance plots to see where the Fsc was before stuffing and after stuffing. That would allow you to see how much the Q of the system changed. Another thing worth noting that was not in the video is the mechanical power handling difference between the two enclosures.

[@akassasin5768]

It makes sense that it works. When the air in a sealed box gets compressed it also gets hotter giving it evwn more pressure and the same thing happens in the exact opposite way when it gets depresurized. The polyfill absorbs that heat making the preassure in the box decrease during compression and increase during expansion. This would also simulate a slightly bigger box that would have less preassure overall in both circumstances due to the fact that there is more air compress and decompress.

[@LoudLabsAudio]

I've used insulation inside of speakers and subwoofers to "color" the sound. The larger the box, the more the insulation, or lack of, effects the sound, but it also does effect the sound of small speakers. Very interesting, I'll have to do a similar test and measure it myself.

[@ianaintsaying1625]

PF doesn't make the box "bigger". PF slows down the sound pressure waves inside the enclosure making them act as if they were in a larger enclosure.

[@attainableaudio7130]

"it's bigger on the inside" lol plus it's not 50% difference it more around 15%, not to mention if you put too much in it kind of "kills" the sound.

[@MomirPeh]

I believe that it will not slow the waves down at all as that would mean that it would change their frequency, but, instead, it just scatters the wave propagation inside the box, so it effectively minimizes the standing waves and harmonic resonances caused by the shape of the box and natural resonances of the box and the speaker. I hope this is comprehensive enough.

[@Toid]

Thanks for the clarification. I thought I said that fairly well from around 40 to 60 seconds. I hope no one thinks I'm implying the box itself actually gets bigger. Although, that would be a pretty cool trick.

[@Toid]

@@attainableaudio7130 I agree it definitely isn't 50%. I think the test showed that. All this test is designed to do is to see if polyfill actually makes the speaker react as if it would in a larger box. But even with a completely filled enclosure, we couldn't reach that number. The cool part, is that this does work. Which means you can make the box smaller if you need to and try to make up some of the difference with polyfill. As far as it it "kills sound quality," that wasn't tested.

[@crystalstanborough4053]

i made yer moms box bigger

[@bradt4229]

It changes the relation of the front sine wave to the rear wave, but it will also have a direct correlation on other aspects as well (like power handling/requirements, excursion, phase, etc.)

[@vincentrobinette1507]

You forgot to mention how Polyfill also dampens standing wave resonance. Given the choice, I think you'll get a flatter response curve, by using the option that works well with Polyfill. A flat frequency response, with no ringing is going to give the best sound. You want to listen through the speaker, not to the speaker.

[@florinwizz]

this box I have has this "ringing" output do you think polyfill might do the trick? the sub in free air seems to sound clean.

[@RCElectricFlyer]

Thought experiment. The additional stuffing increases viscous damping. Viscous damping implies velocity damping. Velocity damping lengthens rise time. Lengthening rise time limits transient response. So does the addition of a large amount of stuffing end up degrading the transient response?

[@Openeyesopenheart42]

RCElectricFlyer spot on, hence it raise’s box q or alignment and sounds slower looser because it IS slower and looser.

[@robertrentel1061]

@@carlosoliveira-rc2xt I'm with you on this. The greater the damping the quicker the rebound. Quick = transient

[@skyblockjake]

When you say hertz are you meaning to say decibels?

[@thethoughtmaster]

Surely poly fill dampens sound when sound hits it it changes how it bounces and deflects it and makes it bounce in multiple paths. It does not make it bigger, it dampens the higher frequencies and makes the lower frequencies resonate more efficiently.

[@bigbirdwpg]

My thinking on this is, just as you don't want a listening room full of hard reflective surfaces, and to that end we put carpets on the floor, and some other sound absorbing material in the room, so one would want to eliminate that in a speaker box. For me it's not about "making the box seem bigger", but eliminating the hollow booming sound of an empty box with an opening in it.

[@jimgardiner1558]

Interesting video. I have always thought that polyfill tends to slow down the speed of the sound wave but have heard other opinions saying that it does not significantly change the speed of sound. I think most would agree that it does dampen the wave motion (particularly the higher frequencies) which can help reduce diffraction effects in the enclosure. I designed and built a transmission line speaker and experimented with polyfil to try and tune the transmission line to optimize the base response and it seemed to work for me. They do caution that too much fill can reduce the base response. As well as improving the base extension of the speaker it helped reduce the harmonic distortion inherent in transmission line speakers.

[@jeremymoreside1444]

Poly fill delays the response back to the woofer cone in a sealed box. It tricks the woofer into thinking the box is larger.

[@Fretslapper97]

I always hear that scenerio and think: if I'm not allowed to have large equipment in the house this isn't going to work out. But luckily I don't have that problem. Cool to see that stuffing will do more than just kill resonances anyway, cause I'm trying to fit a 15" on a bicycle just for fun

[@vlad1889]

If you stuff your sub box it will be less peaky and be able to play lower notes better, however, it will be quieter than the same box empty. While a properly sized large box will be louder and play lower. Basically, if you want SQ lower tones and have no space stuff but if you want loud SPL and low end, you need the right space for proper box.

[@dtwistrewind7361]

Standard fiberglass insulation works great in large cabs 15 and upwards but don't use in a ported enclosure unless you like breathing glass dust, but the Eco wool loft insulation is made of recycled plastic bottles and is much cheaper staple gun it to all internal walls sorted, to tell the truth what I notice most is a tighter thump and a less hollow flimsy output in the low-end.

[@ridered7262]

That's why I pack polyfill in my underwear.

[@ogairbender808]

LMFAO 😂

[@saleemhoosen2236]

How's the sound difference bro?

[@Karizma231]

😂

[@jawnjw]

Dont you guys remember when kicker created the first solo barics...I had the 15 inch sub and the box was small I didn't think it would hit being the sub looked bigger then little cube box,hooked a punch 100 with the low end chip in it and that's the deepest bass I've ever had,..poly fill was in the box and it was a sealed..

[@hadbl12]

James Westerfield kicker and the punch 100.... classic combination.

[@troubleship6064]

Kicker had us wondering. Back then it was the box had to be big, solos came out and were in tiny boxes. Lots of wth moments

[@pureonyx5090]

I still have my set of 12L5 still mint condition. They want die lol.

[@jawnjw]

the 90's were the good old days of car audio I'm running a 1995 crossfire 600 and two 12"db okur at 2ohms and already blew one of the subs voice coil..and they say 1200 they can handle..thinking about a skar 10 inch woofer heard there good and hit low

[@Moto_Aaron]

If a box is already perfect size for the sub/speaker and you fill it up, would that cause it to have a worse sound or would it still improve it ?

[@GamePro-gd7rm]

Do it . Put stuff in and remove echo

[@kharnakcrux2650]

i just love the sound of a heavy stuffed box. always. just love what it does.

[@michaelkowalski2931]

Polyfill works great for under seat truck boxes that are shallow mount.

[@WTFisjuice1]

This is exactly the research I was doing thankyou

[@joppepeelen]

you can increase the liters with about 10% by adding poly. or any other non branded cheapers stuf like rockwool or whatever

[@Toid]

Thanks Joppe! I appreciate the amount you can actually do that would have been a lot of testing. :D

[@jonathansturm4163]

The problem with many cheaper substitutes is they tend to compact whereas teased-out polyfill remains teased out.

[@HifiVega]

Excellent video! I appreciate the effort that goes into this kind of testing and love seeing the results.

[@Toid]

Thanks man! Love the channel! Keep up the awesome work over there!

[@HifiVega]

123Toid Thanks man! You too

[@KimLetkeman]

A very interesting test, this could have been a really great video. But... The lack of clear explanation of the results, the difficulty and actually seeing what the curves were meaning, all this conspired to make the video very unsatisfying. Just an extra minute or two of the theory and the exact results and you had a winner.

[@Toid]

I really appreciate the constructive criticism. I'll keep that in mind for my future videos. Thank you

[@kenso.1]

okay. reading through the comments, i thought i was the only one left hanging. video seemed to contradict itself throughout.

[@russellborrego1689]

I saw this video within a few minutes of you releasing it. And loved it! But forgot to comment. I worked in car audio for many years and always 'knew' the benefits of poly fil... and 'heard' the benefits of it. But never really knew 100% if either was true. This, without a doubt eliminated that 1% of my thinking that it was more of a placebo effect than actual results. There's very little evidence-backed stuff on KZbin regarding this topic... You've done everyone a great service. If you ever decide to revisit this topic? the comparison/difference in possible materials to use would be great. As an example? Vance Dickason said the pink fiberglass insulation was the best material to use for sealed boxes in one of his editions of the loudspeaker design cookbook. It would great to know how it stacks up to polyfil. Again, thank you so much for this!

[@Toid]

Thanks. I might revisit this in the future. I really appreciate comments like this. It helps me know that people enjoy them. My only concern with pink polyfill, which I don't believe Vance talked about, was that it breaks down over time a little more than other materials. I;m not sure how I would go about testing the longevity. But I might at least test the results.

[@jeffreyallen3796]

@@Toid I have had 2 10" MB Quart RLP254 in .6cuft. HEAVY POLY-FIL! For 6yrs I have played them poly-fil is still in good shape and going into .4cuft. sealed enclosures per sub and the Poly-fil is going into these enclosures next vs buying new fil. 350wRMS per sub.

[@theburnhams2925]

@@Toid Hi Toid! Enjoyed your video. As a "straw-bachelor" (DWM) I can have enormous cabs. My latest fave insul is "rock wool" batts. It's heavy and not "itchy" but expensive (compared to f.g.) Since it has no backing, securing in cabs requires mech. support of some kind. Encapsulating it w/spkr grill cloth works, but f.g. window screening is cheaper, can be stapled in place and is also acoustically transparent. I believe the rock wool is more flexible (compliant) which should mean it's not as brittle and therefore less subject to mech. fatigue-failure over time. It's also "softer" feeling which might not be as destructive of v.c. gaps should it "get loose" in there... I've read (somewhere) that the old long-fiber wool is still the best, f.g. second and fiber-fill (pillow stuffing) third performance-wise. The weight (mass) of f.g. makes it better than poly-fill (greater inertia) and it has almost infinite interstices. Hopefully the rock wool will be even better than either of the others for these reasons. I sure hope so---it's several multiples in cost of f.g. (the pink or yellow stuff) and can be hard to find. bob

[@davidjames1684]

Better idea, add a 2nd woofer in clamshell isobaric arrangement. Then the box acts as if it was twice the physical size (6 cu ft. vs. 3 cu. ft for example). Adding polyfill AND doing the double isobaric woofer as described will make it behave more like a 7 cu ft. box (being 3 cu ft actual and assuming the 3 cu ft box was not stuffed with polyfill).

[@annonomis9299]

You got a diagram of this? I think I see what you’re saying but visual aids always help lol

[@davidjames1684]

There are tons of videos on isobaric alignment/arrangement of woofers. Just search KZbin. Here is a good one... kzbin.info/www/bejne/eJWpaKGKisSEhbM Pay particular attention starting at 0:53 elapsed.

[@Grommet2007]

Yeah, but that requires another woofer be bought. Polyfill is cheap. Buying another woofer? Probably not so cheap :-)

[@davidjames1684]

Some bad assumptions going on. First, adding a 2nd woofer (in an isobaric arrangement) will make it play WAY DEEPER than just adding polyfill to a single woofer. Secondly, maybe someone (like me) has an identical 2nd woofer lying around doing nothing so in that case it would actually be CHEAPER (relatively speaking) than buying even a little polyfill.

[@steveo5174]

There's a reason car audio guys have been doing this for years!

[@raymond1672]

What happens if you keep increasing the box size. Will the low end keep rising ?

[@florinwizz]

The low end keeps rising you mean by that you will get more low end output, the tuning freq will decrease. At the same time you lose from upper bass output. Once you get pass the recommended enclosure specs, at least with a ported one you'd also lose from tightneass linearity bass sounding boomy

[@endall39]

Good video. I encounter this challenge when I want to build a speaker inside of an existing object (e.g., vintage radio case). Sometimes the ideal space just isn't there. I'd love for you to address the question of whether or not you get same impact from poly-fill in a ported enclosure. Also, the "weight" of speaker poly-fill you get from places like Parts Express is much heavier and or denser than the typical pillow stuffing. What about the different impact of type of fill? what about fiberglass wall insulation? I see people using that stuff as well. You can do more on this subject that would be of great interest. Thx!

[@pitbullturtle]

I would definitely want to see more videos like this where you test bigger drivers/enclosures and ported enclosures as well. I actually thought this was a myth until I saw this.

[@Toid]

I really enjoy these videos as well. If you have any thoughts on other videos like this you'd like to see tested, let me know.

[@pitbullturtle]

Absolutely m8

[@kaedeschulz5422]

In my experience for subs only it's better to have none in a ported box as it's dampening the port function wich can't be avoided in some enclosures and in a sealed box it can be helpful. In a fullrange 3way (or any other fullrange speaker) it should always be used as the frequencies are so high that polyfill is needed to reduce reflections in the enclosure. TBH every audio person should have a mic. Even if it's only for getting the placement of the speakers or listening spot dailed in.

[@AmmoDude]

I use about 12 oz. of polyfill (after removing the factory installed foam) in my vintage Klipsch KG-4s. They have a passive 12 inch radiator instead of a port. They sound amazing! I have found filling (poly, fiberglass or wool) does not effect air "flow", it effects the air "pressure" inside the enclosure. Increase the fill and you increase the pressure. However, there is a saturation point where too much fill will decrease bass response. I add/subtract to get the right sound.

[@kgtaillon27]

I remember doing this! You can also do a similar trick with a vented box. Build the box a little smaller and run a longer vent. The longer vent length should be able to get to the correct tuned frequency.

[@westelaudio943]

It's not a "trick", it's very basic box design.

[@RMatner]

But don't forget, if you make a port longer you also need to make the enclosure larger as the port deducts away from the internal volume and you'll have an untuned box.

[@thenotoriousrvh6091]

You can also add polyfill to a porter enclosure by using screen material or chicken wire to keep it from blowing out the port. I didn't do that once and after cranking it for a bit, it looked like a stuffed animal exploded in my hatch area 😂😂

[@benjamin5909]

What happens if you stuff the right size box?

[@65amps-i1y]

Great video. Quick question. Is it possible to use the usb microphones that come with your high-end AVRs for room correction (i.e. Marantz, Yamaha, etc...) as a replacement mic instead? In addition, where do you get the software? Is the software free? Or do you have to buy it?

[@ostelo84]

When you keep saying Hertz are you referring to where the smaller box starts dropping in db / deviating from the proper size enclosure?

[@jeanpierresnyman652]

Yes, he's confused about a very basic concept.

[@kyekillian]

great video! thank you. I've had a question about polyfil for a while if anyone can shine some light! I always get nervous stuffing the enclosure completely because I have a nightmare of things overheating and igniting after prolonged use if its stuffed completely and the polyfil is covering the amp board or any other electronics. Has this ever been an issue? should the components be separated from the polyfil via enclosure design, or am I overthinking things? Thanks in advance!

[@Toid]

So that is a good question. You really don't want to over stuff a box. There are quite a few reasons for this. Some would include the fact that some subwoofers have a vented pole, so you will want to keep that obstruction free. Then there is the chance of it getting behind the subwoofer cone, also not a good thing. So when, I say full, I don't mean overstuffed. You want room for everything to still breathe.

[@kyekillian]

@@Toid Appreciate your response!

[@xtv007]

How do the results compare in ported enclosures? Will poly fill make a small ported enclosure act like a larger one as it does for sealed enclosures?

[@jasonneal]

I’ve always had sealed box’s in my car. Built a ported box and is much louder but the kick drums sound too boomy. I listen to speed metal. Have you done a experiment on ported box with the poly mat?

[@baronvonlimbourgh1716]

For metal closed boxes are much better in my opinion. If you want it to be louder just put in 2 and build an isobaric setup with 2 woofers if you don't have the room for 2 traditional boxes.

[@ernestdeitz1670]

Not only dos it change the inside dimensions of the box but it also works off of hot cold cycle’s from the air being compressed and uncompressed rapidly threw the movement of the speaker moving the air back and forth

[@benjamin5909]

So what happens when you stuff the full size box?

[@CoreyDon-l1p]

I have a question. I have some 30inch deep canadian scoop but I'm not getting the chest pounding bass that im expecting. Can you help me out with how far the baffle board should be from the woofer and what length the actual baffle board should be. Or can you provide me with the correct specs please, I'd appreciate some help

[@mikehartigan2703]

I've heard that it makes a big difference in a ported box, and even more of a difference in T-lines and horns. This is because the sound waves (air) have to work their way through the polyfill (compared to traveling in a straight line when they're unobstructed) which means they have to travel a longer distance before they exit the port... In other words, simulating a larger box.

[@modernbassheads5051]

Yeah that’s not true whatsoever, it works the best in sealed applications because the pressure is larger inside the box and has nowhere to go except the fibers. In a ported application it takes the path of least resistance which is the port, still makes its way through the fibers but it’s not as effective I would definetly not use much in a ported box only lining the walls

[@aubreyholman1951]

Thanks for the vid. This is the best answer I've found so far on the poly-fil issue.

[@peteropezio6106]

I wish you had done this with a ported box instead, but this is really nice work

[@oldguyBMX]

I've heard the polly fill can make subs run hot, especially in sealed enclosures, where the sub tends to run hot already....

[@VINNY5674]

Heat stays in the box running subs hard will heat and shorten the life of the coils

[@Reolzomic]

Is a box on 44 liter good to two 8 inch speakers? Or is too small so I have to add poly-fil

[@criven3128]

That would depend on the T/S parameters of your specific drivers

[@ygwaltgmb]

I was told to put a empty jug in there but tape it so it doesn't move. Normal speaker box not subs. Its supposed to make the norm box sound like it has subs

[@stevemiller5355]

Can this be done on a vented box?

[@VEC7ORlt]

Yes, but take care not to block the port - you don't want fill anywhere near the port. Polyfill slows down sound speed and in turn increases apparent volume.

[@stevemiller5355]

@@VEC7ORlt thank you

[@kevinAuman1]

This polyfill thing has been tested and proven before but my question to you is, will it work equally as well in a ported enclosure as it does in sealed???

[@jamesbannister7512]

I've use poly filled in my ported sub and it made a noticeable difference in sound quality

[@Drgluee]

@@jamesbannister7512 I am curious how. Better lows? Better response? Did you have to sacrifice a db or 2?

[@jamesbannister7512]

Yea dropped atleast 2 db but my sub sounds alot cleaner. No more boomieness and I can hear the audio alot easier. Kick drums sound better and bass sounds alot smoother. I also noticed that because I tested it both ways. Sub placement is alot harder to find with the ear now. Before I could spot it easily as soon as I walked in the room. Now for my sub it blends in alot more then it did before and half the time I forget where I have it at

[@jeffreyallen3796]

Heavy fill!! And if you cannot put a big sealed enclosure then POLY-FIL a smaller box.

[@anaxa4883]

Would it actually reduce the bass output if you stuffed a box that uses a passive radiator?

[@soupflood]

An almost 10% internal volume reduction with fiber stuffing would only make sense on a industrial production level, not on a home diy level.

[@heavyset0223]

There is a big negative effect for using polyfill. The drivers get hotter than normal due to less air movement and cooling and I have had them burn out on me. No longer will I use smaller boxes with polyfill.

[@chuckymystic]

How do i fix the opposite problem, i made a big ported box for my 13w7 tuned down to like 18 or 19 hz. After hearing this, it rsttles the damn walls but plays so low that I now want to tune it higher to maybe 26hz. Any ideas?

[@timcasiglia2064]

Change the dimensions of the port. There are calculators all over the internet.

[@joseduranjr3152]

I have a BOSE acoustic wave cd unit. Why is there poly fill in the small speakers and some by the inner speaker used in the waveguide?

[@mikeortiz2139]

So if I just bought the 15" HO driver from Parts Express and the Denovo sealed enclosure, to get the best performance, I should use polyfil and a lot of it right?

[@TimpBizkit]

I don't believe it will have the same efficiency as the larger box. You can't cheat physics. Just like adding weight to the cone will bring down the resonant hump on a small box, but the efficiency of the upper bass will suffer, and a more lossy suspension (Low Mechanical Q) will also damp a resonance down. The polyfill probably works like an Aperiodic membrane which works to damp a resonance.

[@davidjames1684]

A good compromise starting with a single woofer non polyfill stuffed ideal size box (let's say 9 cu ft) as a reference would be to build a 2/3rds size (6 cu. ft) box and stuff it about 50% with polyfill. Taking it a step further, you could use an isobaric pair of those woofers in a clamshell arrangement (woofers face to face) with one woofer inside the box and the other outside the box, and that would only require about a 3 cu. ft box. So we went from 9 cu. ft down to 3 cu. ft withOUT losing any low bass extension. Happy wife = happy life.

[@johnq6123]

Isn't overheating going to be a concern? Or the fill getting into the speaker itself? I love the idea but worry about the potential issues

[@lukasHenchman]

it aint getting inside the speaker, unless it is literally touching the coil and clings on to something sharp.

[@letterphase]

Does pollyfill tighten up the bass? Does it muffle the bass?

[@kencohagen4967]

I have a pair of old speakers I'm refurbishing. I couldn't find a woofer in a 10" that would work correctly with the small cabinet, so I installed a pair of varivents in the boxes. One for each box. Will that help? I'm still waiting on crossover parts so I can put these back together, but I don't have an A/B speaker to test it for myself. I'm also putting some dpstuffing in it along the walls, but not impeding the flow of air in and out of the vent.

[@600zxr]

Can you do same test but use the polyfill that's for quilts attached to each side of the box?

[@scottlowell493]

Polyfill, a powerful driver, a powerful amp, and bass eq,

[@Steve211Ucdhihifvshi]

Isnt dacron (or pillow stuffing) exactly the same?

[@Vincent-lw2sp]

How would using a material with a higher density work? Like if you filled the speaker box with insulation?

[@Toid]

I think that's a great question and I think it's worth exploring. For example is there a material that works better than polyfill. Maybe we will do a video on that in the future

[@attainableaudio7130]

@@Toid I would guess something fibrous that would convert movement to heat better, I actually sometimes use denim base insulation.

[@Toid]

@@attainableaudio7130 I think it would make a great video. Especially testing various stuffings to see which performs the best

[@davidcameron7628]

I think this video is begging for a" part 2 experimenting with different fill materials to if the smaller box could out perform the large box"

[@RoaroftheTiger]

@@Toid Believe It or Not - Back in the '80's, in Britain's 'HiFi News & Record Review' was a DIY speaker article, in which the author suggested a low cost alternative to Long Haired Lamb's Wool. Then considered to be the Ideal material, for these applications. The suggestion was Newspaper put through a Paper Shredder ! The reasoning was that Newspaper actually has a high cotton rag content. Mind you, The DIY enclosure in the article was a Aperiodic box. Which like a Transmission Line, would require vast sums of the stuff to line it properly. So the suggestion was truly a cost savings measure.

[@timschutte8310]

, try gluing or staple some foam or sound deadening material on the "sides" of the box instead of just stuffing the box. this makes more of a difference than just stuffing a box.

[@vincentrobinette1507]

Are you recommending acoustic foam INSTEAD OF, or in ADDITION TO the polyfill? To me, getting rid of standing waves is critical, there is no such thing as over-damping a sealed box. for bass reflex ported boxes, you don't want to over-damp, because some resonance is required for the port to do its job.

[@timschutte8310]

Vincent Robinette , I suppose just testing different methods. I've actually done both

[@attainableaudio7130]

Another option to look into would be an Aperiodic Speaker Enclosure.

[@amb3cog]

Oops never mind. I was confusing this with Steve Guttenberg's video that I watched right before this. That's actually a really good point. The infamous Dynaco A25 is one, as is the KLH Model 33 (I own a pair of these actually, pretty nice sounding too). It's a great way to make a box seem bigger, and increase the bass extension. This is used in car audio frequently too. Due to the obvious space constraints. Maybe we can get him to do a test on that too. I would be very interested to see the actual results of such a test. I've always been interested in this type of enclosure, especially since I have a small listening room.

[@wishusknight3009]

Aperiotic can artifically inflate box volume by about 25%. And if done right can give the effect similar to infinite baffle.

[@jonathansturm4163]

Varying the amount of polyfill is a great way to fine tune a transmission line cabinet. Much more reliable than the long fibre wool I used in the 1970s. It got eaten by clothes moths!

[@wishusknight3009]

@@jonathansturm4163 indeed. Getting the mathe just right can be a pain, but sometimes a little polyfill can correct them.

[@jeffreyallen3796]

@@amb3cog I use it in car audio after seeing it in my home setup. I have 2 10" subs that use Poly-fil due to small places but the subs are recommended for 0.4-0.6 cu' and Heavy Poly-fil so I used a bag in each enclousure and they hit hard. Now I am using them on my doors of 91 Nis Hardbody in a .4cu' enclosure per door. And going to tune from 50Hz on 12dB slope up to 90Hz so it will play down to 40Hz-100Hz as more of a MidBass vs Sub!

[@vusstoppyv4612]

What would the differences be in a ported/vented enclosure?

[@edwardbustamante8376]

I'm just curious, but have you considered eliminating the potential room reflections by simply using a vocal isolation stand positioned behind the mic? (when getting measurements)

[@davidjames1684]

I started building an acoustic suspension subwoofer enclousure but had to stop due to my claustrophobia, that is, I felt boxed in.

[@Gsauce08]

damn

[@c.n.h4841]

so taking it as seen on the test and what it will do is take up the air space so the speaker has less air to breathe in turn the speaker/sub will not last as long the voice coil needs the air to breathe an cool down the manufacturer specs or speaker box size for Porter or sealed enclosures a quarter can be taken off without damaging the speakers so if it says 1 and 1/2 Pur sealed enclosure you can take it down to 1.25 without damaging it this is all based off of experience and building boxes and enclosures for car audio and home systems now that is based off of quality built speakers that actually cost you a bit of money not a cheap hundred dollar set

[@dougbrook6223]

So if you are completely whipped by your wife....polyfill.

[@95Sn95]

What if the box is a smidge on the large side already? My sub calls for 1.25cf and the box is supposed to be 1.5cf? Plus its a labyrinth "SPL" box because has a extra divider in the slot port at least doubling the length of usual prefab slot ports. (By the way it's a killer $50 prefab)

[@kennethblackmore2146]

Adding insulation is only good to add 10% to cabinet space. It also helps to prevent box resonances.

[@tallmanDavid]

What would the result be if you put polly fill in the larger box

[@Scorpio-tn4vy]

Room reflection would be equal if there sitting side by side would it not? It would still be an even test.

[@oneshot3552]

I'm confused. There's no bass in that audio used to test the sub enclosures. Not sure how much bass you get out of synth sounds

[@Toid]

That's just background music that was added during editing. You use a frequency sweep to test frequency.

[@mr.a5147]

Does it have The same effect in ported enclosures? Or Can it allow shorter port lengths?

[@cboyamg]

Similar results. the only way to reduce port length is raise the tuning frequency or make the port smaller

[@jasoncurtis4404]

Polyfill slows down the "apparant" speed of sound, so the sound wave slows, and stretches, so it makes a lower freq. Hard to type out the explanation in full.

[@mrmikewayne64]

what if its a prefab 7 cub ft ported box that already has it in it came from skar audio. Dont make sense to have poly if its 7 cubs and ported idk.

[@hubertallicock4336]

Might wanna document box size and amount of poly fill stuffed next time for reference but great test

[@Toid]

Thank you. I'll have to keep that in mind for next time. I appreciate hearing the feedback

[@ubacow7109]

Can rockwool do the same & can you put too much fill?

[@aaronrobbins1458]

This may have already been answered. If you have a used subwoofer that does not have much or any polyfill, what kind of results, if any could you expect if you filled it up?

[@lukasHenchman]

bass will be cleaner and less distorted below the tuning frequency, the polly will absorb the funny noise the speaker makes when it can't handle low frequencies, however you do sacrifice a little bit of high frequencies.... for better low frequency response, but nothing major... only a small difference like 5%, no more than 10%, but it is noticeable if you listen to your speaker everyday, you get smoother sound, the bass kicks sound less clunky, but if the box is already big enough, you should only add a minimal ammount of pollyfill, just enough to get rid of the sound waves that are bouncing around inside the box, creating unwated noise

[@tee-jaythestereo-bargainph2120]

I thoight it helped with box vibration and resonance sound from a box sound lol Wouldnt you want the mic at you listing spot ? that's what matters right ? I didn't know their was a saying that it makes it louder but cleaner sound

[@bradenwomac5000]

Does it work with ported boxes as well

[@squirrel6687]

Or go outside in like a parking lot or something on an early Saturday. High school football stadiums at the 50 yard line are cool too. Mic placement idea still sound. Sound...

[@chubbyadler3276]

Gotta make sure the wind doesn't tamper with the measurements though. Otherwise, totally doable.