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The Best (And Only) Insulation Material You Need For DIY Acoustic Absorbers

The Best (And Only) Insulation Material You Need For DIY Acoustic Absorbers

By 169 Comments

It’s a bit ridiculous.

There are about a million different kinds of insulation material available. Some made of mineral wool, some of fiberglass, and even hemp or recycled materials. And then there’s foam! Basotec, pyramid foam, etc.

Choosing the right kind for your DIY absorber can feel like Russian roulette.

What if you spend all that money and end up with something that doesn’t actually work? And when you finally pick one, it turns out it’s not available in your country, or costs WAY more than you can afford.

How do you even tell if it worked!?

The only 2 numbers we need to know

Depending on how densely the fibers are packed the air particle movement is affected more or less[1]. And the denser it is packed, the heavier the material is.

So a) the weight of the material determines how good it is at absorbing sound.

Of course b) its depth will also affect how air particle motion is affected. If the sound travels through enough of a very lightly packed material it will also eventually be stopped completely.

But we don’t necessarily want to waist tons of physical space with a light material if we can achieve the same result with a denser material that is thinner.

Although we don’t want to take that to extremes either. Eventually the material will be so dense that it starts reflecting sound. That would kind of defeat the purpose.

The thing is: Theory says that the deeper an absorber is, the lower a frequency it will absorb. It’s called the quarter wavelength effect and it definitely holds true. We do want to absorb as much bass as possible.

So where is the sweet spot?

What is the ideal ratio of density to depth that will give us the best absorption for the least amount of material?

I’ve spent a lot of time testing this. Some designs were shallow, some ended up being huge! Some were more successful, others not so much.

Here are two designs I tried:

The one on the left was my version of a modular “super chunk”. It worked, but man was it tedious to build. And cumbersome to move! That thing was HEAVY!

The one on the right didn’t work so well. It was simply too thin. It never achieved any useful bass absorption.

Finally I ended up with a simple, straight forward solution.

It’s kind of beautiful actually.

The best bang for the buck absorption is achieved with material 16cm (6″) deep, using insulation material of 40kg/m3 (2.5lb/cft).

06.04.2017 – After consulting with John Brandt I made the following change:

And it doesn’t matter what that material is made of! Mineral wool, fibre glass, hemp, recycled jeans. They all work as long as they’re the right weight.

And as long as you use a mineral wool or fibre glass product in the right weight class this works!

This is the case both for corner traps (bass traps) AND first reflection traps (panels). We can use the same design for everything!

The sheets of insulation material should be around 60cm wide. Especially for the corner traps where straddling the corner will allow absorption down into the low bass frequencies.

Looking at the data

This is the bass response in a room that I treated using only 16cm deep, 60cm wide absorbers:

The standing waves are pretty much eliminated down to 35Hz. Also note the scaling of the y-axis. The frequency response has no more ripple than about +-2.5dB. And that with a smoothing of 1/48th Oct.

This proves that you do not need complicated traps to get controlled bass.

Now, using THE SAME panels at the early reflection points, here is the effect on the impulse response of the left speaker:

Each peak in this graph represents a reflection arriving back at the microphone following the direct sound from the speaker (represented by the peak at 0 seconds).

As a very general rule of thumb, we want to suppress any strong peaks within the first 50 milliseconds.

These early reflections are largely responsible for messing with the stereo image and timbre of what we are hearing. Suppressing them hugely improves the clarity and detail of the stereo sound stage and the body of the instruments.

As a side note: The peak circled in blue arrives just 2ms after the direct sound in both measurements. This is the reflection off of the table. It’s the main reason even a great sounding room will still have a messed up frequency response. It’s also the main reason that you see some mastering engineers work with no table at all!

All this was done using a single absorber design based on 16cm (6″) deep material with a weight of 40kg/m3 (2.5lb/cft).

The beauty is that the reverb time ends up being even all the way down to the bass. A slight bump remains because the room is still uncontrolled below 35Hz. And yes, the overall reverb time is short, but the room does not feel dark or over damped. This only happens when the reverb time is cut down in the high frequencies, but left unchecked in the lows.

That’s another reason to avoid thin absorber panels. They only reduce reverb time in the high and mid frequencies, making the room sound unbalanced and very difficult to work with.

So you see, it can be done. It does not need to be complicated. It’s just a matter of getting the fundamentals right.

To get you started

Here’s list of suitable insulation materials I’ve found in various countries.

If your country doesn’t appear in the list have a look at Knauf which operates in most countries across the globe.

A few things to note:

If you are concerned about your health, you can relax, most insulation material nowadays does not seem to pose a serious health threat. But to be safe I recommend you give it a few days to vent before processing and that you wrap it in a thin plastic foil to avoid fibre flight. Wear protection when handling as the fibers do physically irritate the skin and it’s still probably better not to inhale them.

If you are wondering where foam fits into all of this: It does what it’s supposed to do, just at a much higher price. It’s also sold in panels that are way too thin and so only effective in the high frequencies. As I mentioned earlier, this is something you really want to avoid.



[1]Cox, T.J. and D’Antonio, P., 2017. Acoustic absorbers and diffusers: theory, design and application. CRC Press.

  • you using faced insulation? Also how do I get rid of all the bass loading along my walls long walls should I add some bass traps perpendicular to the wall

  • really great summary & helpful info, thanks!

    I have a question regarding expanding the sweet spot (a bit at least?) even on a budget, using just these broadband absorbers, in a rectangular room.
    as a rule of thumb, would the first step be to add a couple more absorbers on the ceiling, above the listening position?
    or could this cause more problems?

  • Jesco, how do I calculate the optimal material with regards to flow resistivity for a 35cm thick basstrap, to absorb the lowest frequencies (<100hz)?

  • Thanks for creating this great resource! I was curious, however, why you edited out your hemp and cotton recommendation? ATS Acoustics lists absorption specs for cotton batting that are similar to those of O-C 703 and Roxul Safe & Sound.

  • Density is weight/space, but acoustic absorption properties of any material have to do with its resistance to airflow, usually given in Pa*s/m². Hemp has very low airflow resistance, anywhere between 30% to 1% that of rockwool of similar density. Digging into flow resistivity puts you in the gnarly world of fluid dynamics, and there are several models developed by different physicists on how these materials behave. For practical purposes, know that while 3000 Pa*s/m² hemp wool is almost useless in a 5-10cm acoustic panel, it would actually be a better fill for a 40+ cm bass trap than more airflow resistant materials.

  • Panels using 703 that are 2″ thick with a 2″ air gap have almost the same effectiveness as 4″ at half the cost. That 2″ air gap is magic. If you want the absolute best performance out of a 4″ panel, try to find Rockwool Rockboard 40 with density around 4 lb/ft3. It’s hard to find and often requires a special order from a distributor, but you’ll get effective treatment down to about 100Hz.

  • I’m assuming your calculator uses airflow resistivity as a variable. The best density of rockwool for 8″ panels would be around 30 kg/m3 (1.9 lbs/ft3) with flow resistivity of about 8000 Pa*s/m2. I’m not sure they make that. RWA45 has a flow resistivity of around 10000 Pa*s/m2 which is as close as it’s going to get.

  • This is too dense. When looking for materials, see if you can find “flow resistivity” in the specs. It’s related to density, but not always. For example, glass fiber tends to be more flow resistant at lower density than rock wool. Density of 150kg/m3 will likely have flow resistance between 50000 and 100000 Pa*s/m2, but anything over 30000 is generally not good. To get the best bang for each thickness of panel I’d use materials with flow resistance around 25000 Pa*s/m2 for 5 cm panels (70 kg/m3 rockwool), 15000 for 10 cm panels (50 kg/m3 rockwool), 8000 for 20cm (30 kg/m3 rockwool or 18 kg/m3 glass fibre), and all the way down to 5000 Pa*s/m2 and lower for any panel thicker than 30cm (13 kg/m3 or 0.8 lbs/ft3 glass fiber insulation is the lightest stuff I can find where I live). But, to be honest, a 30 cm panel with low density fiberglass is only marginally better than a 15 cm panel with 40kg/m3 rockwool that has a 15 cm air gap behind it. This article nails it in that 6″ panels with rockwool really are the sweet spot between performance, thickness and cost.

  • Your post is older, but I’ll answer anyway. Lower density material in thick panels can actually be more effective than high density fill material in thick panels at absorbing low mid frequencies, but the denser material will be better at absorbing bass. Doing some modeling math while knowing only that you’re using 25kg material and comparing it to 40kg material (while also making a bunch of assumptions), your panels would be ~100% effective down to 400Hz, while the thicker panels would be ~85% effective at 400Hz. But, your panels will start tapering below 400Hz and are only ~40% effective at 100Hz, while the denser panels would be about 60% effective at this frequency. The math assumes sound hitting your panel at 90 degrees. In reality, all panels absorb better than the math suggests, because sound tends to hit them from all angles, and you can further improve their effectiveness at low frequencies by placing them in corners and creating an air gap behind them. For example, your 200mm panel placed with a 200mm air gap behind it becomes 80% effective at absorbing 100Hz and is still 40% effective at 40Hz. Of course, there are so many ifs in what I wrote that you should only use it as a rough guide. Any engineers reading this and cringing at me using terms like “80% effective” can look up the word “pedantic” in the dictionary.

  • This guide talks about first reflection points. That means if you were to draw a floor plan for your speaker placement and listening position, then draw 2 parallel lines, one through your speakers, and another one through your ears at your listening position, your panels are most effective on walls and ceiling between these lines. At the very least, you should have ceiling panels opposite your ears, and above your head. Later, if you add panels on the wall behind your speakers, especially in between your speakers, your stereo image and clarity will improve further. Make your panels so you don’t have to cut the mineral wool insulation that goes inside. My panels have always been 16×48, 24×48, 32×48, or 48×48 inches, because I can get Safe N’ Sound in 15.25″ and 23.25 “wide.

  • Great guide !! Now to know how which size the panels should be and how to distance them on walls and roof if needed.

  • Hi Jesco and community
    Very interesting topic. I like to build absorbers by myself.
    Here in Switzerland we can’t get the Tamarock from Rockwool. Sonorock is all around.
    But Jesco, you write aboout the *raw density=40kg/m3*?

    Someone have a product I can buy here in Switzerland?
    Thanks a lot for your help.

  • If you want to add Mexico to your list of insulation materials, here is the URL of a mineral wool manufacturer:

    https://www.rolan.com/

    Their FF 40 product is 40kg/m3 and can be ordered 16cm (6″) deep.

  • Hi Jesco,

    Thank you so much for your clear explanations for so many things!

    I have two questions:

    1) I just put fabric on top of one of my new panels and when I go close to it with my ear it seems like it’s clearly reflecting more sound than the ones without the fabric on top of them. Maybe it’s just higher frequencies that I shouldn’t worry too much about?
    The cloth is moderately dense. Blowing through it totally works but there is moderate resistance.

    2) Does leaving an airgap between panel and wall only work if it’s open at the back? Now mine have thin hardboard nailed to the back.

    Thanks!

  • Hi Jesco,

    I’m currently watching all your videos on YouTube 🙂
    Thanks for the knowledge you’re sharing !
    I’m going to build new panels very soon and was thinking about cotton wool. I found some in 25kg/m3 is that too low of a density ?
    (panels’ depth will be 200mm)

  • Hi there! I found a rock woll that has 150 kg/m3
    Thickness 5cm. Do you think this will be a good bass trap material? Or going to be reflective due to density?

  • Hi Jesco,
    Great article, you’ve been really useful with me setting up my home studio! I have a question about density. I’m going to use 8inches of rockwool Rwa45 45kg/m3 with an 8inch airgap behind. This seemed to be the best readings I could get with the pours absorber calculator (and I have lots of space). With 8inches of rwa45 am I going to have any issues with the density being TOO thick and becoming reflective? Should I be looking at a less dense material? Many Thanks! Matt

  • how come you removed organic fibers after that consultation? Would denin ultratocuh not work for some reason? Many say it is ideal for bass traps…

  • Hi , quick question … i was told i need to leave a 2 inch space between the cornings 703 and my wall … i have a small space , ideally my sound panels would only be 4″ deep but that means only 2″ thick cornings . Can i make 4″ thick panels and only space 1 ” off the wall? Or is that useless?

  • HI Jesco, Great article! Just wondering. You mention that they should be around 40kg/m3 density. All I can find is this spec. Would this work ok? RWA45 insulation slabs achieve Lambda 0.035 W/mK and are available in seven standard thicknesses from 25-100mm, with a density of 45 kg/m3. Thank you in advance.Kindest regards, Ali

  • Hello Jesco,
    One quick question,
    Why Hemp material at 40kg/m3 is not as good as rockwhool ?
    Merci
    Jp

  • Hallo Jesco
    Thank you so much for puting together your articles and videos. 16cm is quite thick! Other sources emphasize the importance of having a gap between the wall and the panel. What is your opinion on that? Could that be used to cut thickness of material?

  • Hi Jesco,

    Did you use 1×8 or 1×6 boards for the frames?

    I ask because 1×6 are actually 3/4 by 5 1/2 and am curious if you were okay with a little compression, or maybe went up to the 1×8 which are 7 1/4 wide.

  • Hey Jesco,
    first off all, thanks for this superb knowledge you are sharing with us!
    Do I understand you right, that you built one absorber module 60 x 100 x 16+ cm (mineral wool 16 cm + frame on the front) and then just stack them diagonal in front of a corner for using it as a bass trapp? Do you then measure the air gab from the inner centre side of the frame into the corner (so the longest distance)? Do you use a simple light plastic bag for the mineral wool? There isn’t any construction manual of yours, or is it? 🙂

    liebe grüße

  • Mimi thank you very much for that info…
    I am from Greece and we also have the Ultracoustic P but I didn’t know the flow resistivity of that product( they just say that is >5 kPa.s/m2). I wanted to use it because of the improved air quality and the ecose thing (formaldehyde free) but I didn’t know if it was good for jesco’s absorber. Know I can tell you that it is pretty good for that (Knauf KR SK which is 40kg/m3 density also has around 10000pa*s/m2). I am not 100% sure but I will waiting for Jesco’s opinion on that as he is the expert.

  • Thanks so much for the article, I built 21 of these boxes and put them up in my rectangular drywall basement room, very big improvement… I still plan on adding some diffusers as well and maybe some foam in the corners and something covering the windows and doors etc etc but just having the boxes in there is fantastic, I uses Rock wool safe n sound, 2 foot by 4 foot, two 3 inch batts in each box in a 20 by 22 foot room with 8 foot ceilings. here are some pictures if anyone is interested. I probably spent 30 hours or so on teh project, but it was well worth it. https://photos.app.goo.gl/4py3gowA3Dmqtd3L9

  • Hi, I was going to use the 4 inch of Knauf board 3.0 pcf you suggested with 4′ airspace behind it for early reflections. Some people say “NO”. Use something like 6 or 9 inch Safe N Sound. What do you think?

  • Hello J . Thank you for the information it is very helpful. My situation is a bit tricky and if anybody could take a few minutes to jump in , i would greatly appreciate it.
    NOTE : i have NO intention to make a full guns out pro recording studio . I am a musician singer songwriter and i go to professional studios in my city to record a full production.
    But , i like to do a lot of acoustic covers now and then , or demos for my songs to send to the musicians who will play the parts.
    That being said , i have a small corner in my apartment , which is arround 2×2 m . Its like a separate room but there is no door ( could block it with a broadband panel ) .
    Could i make anything decent out of the space or would it be a waste of time and money ? I repeat , i have no intention to mix master in it a full production with drums and what not , only vocals , piano , and maybe a guitar. I could fit the panels you mentioned in the article in corners and on the walls. I dont mind if it gets very small . I have a desk in it with lap , speakers and my keyboard . And a question that i think many have but don’t know yet : would it be of any use to put diffusion foam on the the front of the broadband panels for the mids and highs or is the panel doing the job already ?

    If you made it this far , thank you for your time . I appreciate every bit of help/ info.
    Demetrius

  • Hi Jesco, in my country the rockwool comes in 50mm thick boards, for convenience, I’m planning to combine 3 boards into a bass trap that is 15cm think. Will this be a huge difference from your prescribed 16 cm? Thanks for all you do.

  • Hi from Spain!
    Sorry if i don’t get it, as this confused me a little bit. I have foam and i’m reselling it right now as it was not good at all, not only that one you know of 2.5, but also the one of 4.5cms is not good and if you use too much you end up with dry empty sound.

    As i see you put a layer of 1.6cms of mineral wool? and then it goes in a kind of cage? what’s inside the cage? empty cage of 16cms deep?

    And then it says 60cms wide when in the picture the rectangle seems to bee pretty big, like of 1 meter long? or is the perspective of the picture?

    thanks for your content, and advice!

    Lucho

  • For 50mm panels, there probably isn’t much difference between those two densities.

    But I would recommend you make your panels 16cm deep. Not much use for 5cm, or even 10cm panels in a music studio. And for that material depth you’ll want a less dense material.

    J.

  • Hey Jesco, great article, very informative and useful… It helped me loads! I did speak to the team at GIK Acoustics and they said the 242 panels use Knauf RS 60 (60Kg M3) but these are typically 2 inches thick panels with I think 50 mm (or can be doubled up to make thicker panels with 100mm of the same material) with the Knauf inside this. Their stuff is very good and lots of professionals rate them highly, would that work on this type of panel, or are their 242 panels too dense? I have a small room and don’t want to have too dense a material or else it’s counter-productive. Thank you, Mark.

  • I just checked the other comments and got my questions covered! Sorry for not looking in advance!!

  • Thank you so much for the comprehensive explanation and profound facts! Very helpful within this forest of confusing and partly contradicting territory.. No mumbo jumbo!

    I was just wondering about some things. Besides the wooden frame, I guess the back part is open to prevent further reflections, right? And the other thing is about the plastic foil around the insulant material. I’ve seen it on some pictures and you wrote, that it’s good to wrap it around because of health issues. But when putting everything together with the fabric around it, I would guess it should be without the foil, right? And I really like the optic with this Cara fabric, that you use! But do you put some other fabric on the back as well? I was thinking to put some simple fleece to cover the back.

    Thank you so much for your time and the great help through your work here, podcasts and Youtube!

    Greetings from Mainz
    Alexej

  • love this explanation. Very helpful. Would like to see your build plans for the frames! The pine and burlap look excellent together. Cheers!

  • Thanks Harsh, much appreciated.

    I understand your dilemma. The problem is that you’re solution won’t improve the situation unfortunately. Acoustic treamtment doesn’t help with sound isolation. It’s not made to keep sound in or out of a room, it’s made to improve the sound in the room.

    Different thing entirely.

    You need to look at isolation techniques, not acoustic treatment techniques.

    J.

  • The problem is its pre constructed and I can’t make any permanent changes my idea was covering 60 percent of the room with Rockwool panels and cover the windows and doors with rockwool panels.

    The rockwool i am using is 50 mm deep i.e 2 inches with 65 kgmcu density.

    Am I going wrong somewhere.

    Btw you are the best reviewer and I have watched all your videos. Truly an asset to the community!

  • Hey Harsh,

    what you need is isolation, not acoustic treatment.

    So it’s not about how much absorption/treatment you add, but how you build the room’s walls, floor and ceiling. Totally different thing. You need mass (heavy walls) to stop bothering the neighbours.

    J.

  • I live in a apartment block, my flat is on 2nd floor, sandwiched between 3 flats. Neighbours are there. I don’t have the budget to cover the whole room. What should be the percentage of absorbtion/treatment area I would need to cover so neighbours don’t get disturbed.

    I am using Focal 80 speakers in Stereo setup.

    My room size is 15 feet * 11 feet * 11 feet. One of the walls is non parallel to other wall.

    Construction of wall is red brick plastered and painted with 6 inch depth.

    Please help!

  • Found this site through watching the wonderful YouTube video content you’ve shared. This site is incredible!! I am sure by now you’ve heard that phrase a million time. 🙂
    May I ask about the Plastic Film you’d mentioned on this article? Are they the same as cling wrap, those plastic wrap use on sandwiches and such? How would you recommend the insulation material be wrapped, by per sheet or when combined?
    Thank you so very much for sharing your wealth.

  • Hey Joris,

    you could do that, but I doubt that’s going to make things cheaper, easier or more effective than just building only standard 16cm panels, because you’ll need a whole bund more to cover the same surface area in your room.

    Fabric: Camira Cara looks great but there are loads of good options. The more expensive it is, the better it will look and the easier it will be to work with. But even cheap fabrics can work great. Good way to save some money as the fabric contributes a large chunk to the material costs. Just make sure you can breath through it and it’s non-stretch.

    J.

  • Hey JP,

    looking at it on the site, it’s even 55kg/m3. That’s a little high in my opinion. It will work, just not as well and might start reflecting high end. Have a look to see if you can find something under 40kg/m3 instead. Better compromise.

    J.

  • Hello from France !
    Your site is incredible, a real game changer for me after years of feeling like all this accoustic stuff was beyond my comprehension !! Thank you so very much !
    I have just one question, if you have a minute can you have a look at this link, basically rockwool Mbrock, width is 145mm and density is 50kg…
    https://www.leroymerlin.fr/v3/p/produits/4-panneaux-en-laine-de-roche-mbrock-rockwool-1-35×0-57m-ep-145mm-r-4-2-e1400217080
    Can’t seem to find anything at 40kg density in France so far…
    Would this be ok as is, like only using one panel and maybe leaving 1 cm of the wall ? or is 50kg density to much ?
    Thank you lots !

  • Hi there,

    Thanks for making this site and sharing all your nollege.

    I have a question for you. IKEA is selling little boxes easy to install. The size is 35x25x35.
    If I fill this with 20cm or 24 cm of Rockwool and buy more of them, will it work ?

    This is the link:

    https://www.ikea.com/nl/nl/p/eket-kast-wit-70332124/

    Or is 16cm the maximum you will advice ?
    And I will olso make the bigger boxes with size 120x 60x 16

    And with fabric can you advice ?

    Thanks a lot and with kind regards,
    Joris (Holland Amsterdam)

  • Hey Trevor,

    1: Any thin plastic will do. Whatever your hardware store has. And no, it’s not necessary. But I still recommend it to be safe.

    2: Yes, if the unit weight is the same, it’s probably fine.

    Best,

    Jesco

  • Hi Jesco,

    Thanks for the amazing website! I have two questions:

    1. What type of “foil” do you use to wrap the insulation (like you said in the comment above)? And is it really necessary with mineral wool? I’ve been told it’s not as important as with regular fiberglass.

    2. Would Rockwool AFB be equivalent to RW Safe n’ Sound? They both have 2.5lbs/cubic foot density and the NRC ratings look exactly the same on their website. I just can’t locate the SnS in my area.

    Thanks!
    Trevor

  • Hey Jesco, great article! question: would 9″ deep Roxul (now called Rockwool in Canada), effect even lower frequencies at 40kg/m3?

  • Hey Jesco,
    Thank you for the article. I’ve been searching for reliable information on mineral wool densities for bass traps for some time now.
    I have older corner traps made with Roxul Comfortbatt 80 as this was the highest density available (128kg/m^3).
    I thought that the more dense the material, the better it will perform at 125 Hz and so it should also be the best material for under 125.
    I was planning to rebuild the traps larger anyways so I’m glad I came across this article.

  • Hey Samual,

    the problem with published absorption coefficients is that they always stop at 125Hz. What about bass frequencies though?

    So a slightly denser material might be a little better at higher frequencies, but what ultimately matters for low frequency absorption isn’t the density, it’s the depth of the material core.

    And at the necessary depths, you need less dense material for sound to properly penetrate it.

    Unfortunately that’s something that is never properly measured (actually close to impossible to do reliably in real life down to 63Hz or less).

    So in general published numbers aren’t really relevant for our purposes.

    J.

  • Hi,

    thanks for this article. Still one question though: How much did you experiment with different densities or is 40 kg/m3 based on calculations? Sorry if I missed something.

    I’m just wondering since I found a producer of stonewool pannels that published it’s soundabsorptioncoefficient, measured after the EN ISO 11654 (if that says anything to you) and it seems that their pannel with 60 kg/m3 is in the lower frequency slightly more efficient than the one with 38 kg/m3 which is closer to your number. (https://www.flumroc.ch/anwendungen/akustik/flumroc-daemmplatten-unverkleidet-1 it is in german but I’m sure you understand the relevant numbers here).

    The numbers look otherwhise quite evenly spread to me or what do you think?

    Thanks again!
    Sam

  • Hi Jesco.
    The various densities of rockwool are confusing me.
    I see that mostly 35-50kg/m3 is recommended for superchunks, but for 10cm broadband absorbers some opt for a greater density (60-80kg/m3). I was taught that using Knauf DP8 (now Naturboard Ventacusto) was the best for broadband. DP8 had 80kg/m3 and Ventacusto now has 70. We mostly have only Knauf available here, thus I refer to their stuff.
    Since my room is small I wouldn’t use broadband absorbers thicker than 10cm. Would it be better to go with density of about 70kg or with 45 despite only 10cm thickness?
    Thank you very much!
    Rok

  • Hey Daz,

    I only really deal with home and project music studios on Acoustics Insider.

    There are just too many differences in goals, techniques and strategies when treating other types of rooms for me to cover it all.

    So I can’t help you with that unfortunately.

    J.

  • Thanks for the article much appreciated. Am looking to build a home cinema room, if starting from scratch would it be worth building all the walls full of insulation covered in fabric? Have also read about activated carbon, have you any experience if this although seems a lot more complicated?
    Thanks

  • It is a nice article on your work. Thanks for the info.
    It would have been nice to see a waterfall of before you install your 6in panel to see the difference between before and after.

  • If you make the material too dense for a given depth, it will not only start reflecting low frequencies, but mainly also high frequencies.

    As a thought experiment, just think about what happens when sound hits concrete, which is super dense.

    J.

  • Hey Leon.

    Thermal conductivity doesn’t tell us anything about sound absorption properties. So unless you can find the unit weight or the gas flow resistance of this materials, it’s going to be difficult to make any recommendations.

    J.

  • Hi,

    you said and I qoute you:

    “The best bang for the buck absorption is achieved with material 16cm (6″) deep, using insulation material of 40kg/m3 (2.5lb/cft).”

    What is the most effective because if I increase the density of the rockwool material I heard somewhere that at some point if the material gets to dense (mine is 85kg/m³) low frequencies get reflected and you get a narrow band absorber.

    Please give me more intel on this.

    Thanks!

  • I build 8 Absorbers with this rockwool https://www.amazon.de/gp/product/B07CHKJSCJ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

    They are 120mm thick and are in the
    thermal conductivity group 034. I don’t know yet how dense the material is.

    I asked the seller what density they have. Waiting for an answer there. If it is really dense (cause it feels and looks denser than your recommended Rockwool 40 (40kg/m³) how should I continue? Should I stack up with Rockwool 40 or build completely new? I wouldn’t want to through out so much money now that I spent it.

    Greetings from Hamburg,
    Germany

  • Fabric: Camira Cara
    Instructions: By the time you read this I should have a course available dedicated to designing and building your own combined Bass Trap – Difffusor.

  • Hey Mark,

    mixing densities makes things a whole lot more complicated, so I can’t recommend it unless you really know what you’re doing. But yes, it’s possible, and specialist will combine different densities for various purposes.

    On GIK: Their 6inch absorbers work great in my opinion.

    J.

  • What happens if you remove some of the less dense material from the back of current GIK 4 inch bass traps and replace it with a layer of Denser Material .. better towards the front or in the rear ..they have scatter plates and are used at first reflection points and in 6 inch corner bass traps also with scatter plates

  • great article! thank you very much! 2 questions:
    – what fabric did you take for the wrapping? it looks great!
    – is the instructions you took for this absorber online anywhere? if so can you please provide a link?

    greetings
    meek

  • Hi Jesco,

    First off, awesome article!
    Love the insights you’re sharing, gives a whole fresh perspective on acoustics.
    I’m living in Holland and thinking about getting RockFit mono 433 as you suggested.
    My question is: can i just stack 2/3 rockfit mono’s on top off each other to get to the 16cm thickness? Or does stacking it up make no sense? I’m asking this because i can only find Rockwool panels at a thickness of 5/6cm on the internet.

    Would love to hear from you!

    Thanks ! 🙂

  • Hey Thilo,
    for now, just build the new ones as in this article. But ultimately, if you want that low end control, you’re not going to get around doing what it takes. 😉
    J.

  • Hi Jesco,

    Thanks for this great article.

    I have a question concerning my already built absorbers.

    The situation:
    I built 8 absorbers 1000x600x120 mm with termarock 50 (55 kg/m3) and placed them on the first reflection points. Now the High and Mid Frequencies are under 300 ms reverb time but in the bass and low mids (from 400 Hz downwards) my room still needs absorption. I wondered to build some of the 160 mm thick absorbers exactly as you described them in this article and place them from in the corners of my room (from ground to ceiling).

    Now my question: Can I continue with what i have already built and try to tame the lower frequencies with your absorber type in the corners or would you recommend to build all the absorbers new in the style of this article?

    Thanks!
    Cheers

  • Jesco, I learned this EXACT thing years ago and was shocked you didn’t mention it until I saw this comment! Bravo man! You are really educating people. GREAT article! I’m actually looking into coming up with an unorthodox, hypoallergenic, safe to handle alternative to these insulation materials and I would like to speak with you about it, maybe at some point send you a sample to test in your studio when all the kinks are worked out. Send me an email when you can.

  • Thank you for this article… but what is the difference between the second try you did (white panel) and the third panel you say is so effective on the low end?
    they look the same size to me… am I missing something?

  • Hello,
    first of all thank you very much for this article. I want to make few panels to my home office and your info helped me a lot. Is it ok to use diferent material than fiberglass? I found natural material panels from Jute fibers whith density around 40kg/m3 – Thermo Jute 100.
    https://www.ecologicalbuildingsystems.com/UK/Products/Product-Detail/Thermo-Jute-100
    And will it be so much worse to make thinner panels (100mm)? I dont need to achieve perfect studio enviroment, I only want better acoustic for music listening when I am working and the concrete walls made terrible echo. But I dont want to reduce space with thick panels.
    Thanks for help.

  • Totally enjoyed this article! I’ve got a bundle of six 4″ batts of 24×48″ Roxul rockwool to make absorbers. How many units did your room need, and where did you place them? Perhaps a subject for another article??

  • Any experience with the recycled blue jean materials that are now available? I’m in the US and did use Rockwool for filling the walls and ceiling of my home theater set up. I have a small audio post room and six inches of depth eats up a lot of room so I’m curious if the fabric type insulation would give enough density so I could do three inches or so. What is the best way to determine how many and how large the panels need to be? I know I have a significant flutter echo in the room, and some nasty reflections from my table top. What is the best way to address those issues?

  • I can not thank you enough for explaining this in such simple terms. I’m gonna go with an overkill 20+cm thick panel and be done with it haha.

  • Hi Jesco, thanks for sharing. I’m about to start building some panels for my home studio using RWA45 rockwool. I like your design which leaves the timber exposed and was wondering how you achieved such a neatly stretched fabric covering. The corners looks so crisp! Cheers.

  • Hi, Jesos.
    Here in Brazil I know your panel with the name of wide band acustic panel. It will be my option for serious, medium and acute treatment. His positioning is the magic key.
    My doubt is in relation to the density of wool. in the minga region only the rock wool with 32kg / m3 or 64kg / m3. Which of these densities do you tell me?
    Also wanted to know if you made your panel with wood or fabric background? thankful.

    https://musicaeadoracao.com.br/38792/absorvedor-de-faixa-ampla/

  • I came across a chart on the net listing all the sound absorption values for a whole lot of different insulation products and the best one was normal foil backed fibreglass. Would this be OK to use in panel with the foil at the rear ?
    Thanks again 🙂

  • Would 30-32kg/m3 at 200mm thick be as effective ?
    Almost impossible to find 40kg/m3 here in Australia 🙁

  • Hey Jesco,

    Will the plastic foil/membrane affect the characteristics of the trap? If we are looking for an acoustic transparent fabric, why it’s ok to use a plastic foil which doesn’t let the air pass? Or does the foil have transparent characteristics?

    Thanks.

  • Hi Jesco,

    Which camira model did you use for your traps. I’ve having breathing issues with GOM FR701. I whant to try a different fabric.

    Thanks,
    Francisco.

  • Hi there,
    Looks amazing!
    What do you say about Knauf 24kg/m3 5mm thick mineral wool for the panels ?

    should I put 3X5 mm boards on top of each other to create 15mm thick of material ?

    for the dimension -60 cm wide on 120 cm long should be fine?
    thanks

  • Hey Daniel,
    with other types of insulation material, you can rely on the flow resitivity corresponding to the density/weight in the same way.
    J.

  • Hi John,

    thanks for the feedback, you’re welcome! I use Camira Cara preferably. As long as you use an acoustically transparent fabric (i.e. you can breath through it), it doesn’t make a difference to the performance of the absorber. So it’s purely an esthetic decision.

    J.

  • Hey Chris,

    in my opinion there is no reaon to use any other panel than a 6″ panel anywhere. Ultimately you want full braodband absorption everywhere anyway, so no point in bothering with thinner panels. It doesn’t make a different if you use a subwoofer or not. Most speakers are more than capable of putting out low bass.

    J.

  • If a 6″ absorber is ideal for low end in most situations, when and where would it practical to use a 4″ or 2″ panel instead? If I’m using a subwoofer, should all my broadband panels be 6″ around the room?

  • Hi Jesco,

    Firstly thanks for putting the info out there, great to read a personal but at the same time in-depth and professional article about this subject.

    I’ve looked doing this before and came to similar conclusions. One thing I don’t think you mentioned in the article was the material that covers the fibreglass.

    What you’re using there looks like a kind of hessian/raw cotton. Is there a fabric type you recommend and would it pay to use a different material for bass traps and higher frequency units?

    Thanks again!

  • Hi Dilby,

    definitely keep on using them. But if you intend to build more, I recommend you go for Termarock.

    J.

  • Hi Jesco,

    I have built some absorber panels last year (unfortunately I hadn’t found your site at that stage). I used Rockwool Sonorock as it was all that was available at the baumarkt near my studio. The panels have 2 sheets of 40mm Sonorock and a 60mm air gap in the frame from the Sonorock to the wall. I read, and it was conformed by a Porous Absorber Calculator, that the air gap was as good as having another layer of Sonorock.

    So, the panels are made with a different material, and are 14cm (inc. a 6cm air gap). Will they still be working to any useful degree or should I start again using Rockwool Termarock and a deeper frame?

    Cheers,

    Dilby

  • I got rockfit mono 15cm, does the 1cm make a important difference?

    Thanks for sharing your knowledge.

  • Hey, Jesco!

    Thanks for your article. Really helpful!

    I’m gonna make something like that for the corners, but using Recycled Pet wool (don’t know the real name in english) instead mineral wool/fiberglass. After a big research I found the Pet Wool a better option because it’s way easier to work with, it came in the same size as mineral wool for example and it’s eco friendly. More expensive, but I had problems with stone wool before.

    The Pet Wool is 30kg/m3 and 5cm deep. (120cm x 60cm x 5cm)

    I’m wondering if I put 3 panels in a row the results are gonna be “the same”
    Total 15cm deep plus 30kg/m3 each panel.

    Maybe I could put one more panel to make a 20cm deep. Bad idea?

    What are your thoughts?

    No pressure, but your answer is important to me, and I would love to have it asap (sorry)! hahaha

    Thank you very much!

  • Hi.

    I got some 145mm rockwool flexibatts insolation for free. It only has a density of 30kg/m3. Will this still work as superchunks or rectangular bass traps, and broadband first reflection absorbers?

    Cheers

  • Hey Marco,

    my recommendation only works for mineral wool or fibreglass. If you want to use foam, you’ll have to dig a little deeper. What’s the specific flow resistance of the foam you are using?

    J.

  • Hey Neil,
    705 is extremely dense at around 100kg/m3. I guess you could use it for thinner pannels to put on the wall. But I generally recommend to stay away from those because they only absorb highs and high mids, and that is the opposite of what you want in a small room.
    Sorry.

    I haven’t looked at the data by RPG, so I can’t comment specifically. But in my experience porous absorber panels do tend to perform better than simulated in the standard version of the Porous Absorber Calculator. I prefer to use it as a test environment to test trends. The theory is sound, so overall, the effects you see are accurate.

    Remember: A porous absorber is more like a shotgun than a sniper rifle. It’s pointless to put a scope on it, and aim really accurately. Just make sure it works, get close enough, then pull the trigger. If you want to hit more, simply shoot more. 😉

    J.

  • Hi Jesco,

    This article is just great! 🙂

    I landed on a ton of OC705 which is twice as dense as OC703 but I got it all for free!! How thick would you recommend me making my panels with the 705?

    Also, I used the Porous Absorber calculator that you linked to to generate absorption frequency response differences between 703 and 705 at various thicknesses. The results were quite different from the RPG acoustics acoustic data for their Absorbors, which are just 705 fabric wrapped panels. The RPG data looked much better. Do you have any idea why? Who do I believe?

    Thanks!

    Neil

  • Hi, I can have polyurethane foam, 15 cm deep, density 42 kg/m. Do you think i can have the same results?
    Regards

  • So the 6″ design works better than a superchunk 34″ face?
    If I were using the 6″ rectangle design, would I backfill the corner with absorbent or not ? Did you design this as an open back frame? What is the lowest frequency this design will absorb, if straddled in a corner?

    Thanks,

    Rick

  • Hey Fred,

    that totally makes sense.

    But my short answer is: Yes I have tried both, and it doesn’t make a difference. All the panels in this article had a plastic wrap around the insulation material, and that is how I build them to this day, and I recommend you build them as well.

    The reason is simple: Sound waves simply pass through the plastic, since it is not the air molecules that physically have to enter the material from the outside. A sound wave is an impulse of energy that is passed on from one molecule to the next. The individual molecules actually stay where they are (more or less). And that impulse is easily passed through the plastic sheet.

    As an example, image waves in the ocean. The water actually only moves up and down, while the energy is passed along with the motion of the wave.

    And as a practical test, just put a plastic bag over one of your speakers and play some pink noise. Then take the bag off, and listen for the change.

    Does that make sense?

  • Jesco,

    Great article. I am planning to build some acoustic panels, and in researching different methods I have found two schools of thought regarding fiberglass or mineral wool panels wrapped in plastic.

    One is that very thin plastic will only have a slight affect on high frequencies and won’t affect the low and mid frequency performance. The other is that fiberglass and mineral wool require air to actually enter the insulation, which is why the cloth used to cover the panels needs to be a material you can blow through. This idea also suggests that plastic would reduce the effectiveness of the insulation since it would prevent air from entering the insulation.

    Anyway, does my concern make sense? It seems like these two ideas are conflicting. Have you done any comparisons between panels wrapped in plastic vs without plastic?

    Thanks,
    Fred

  • Hey, Jesco! Great post here. Had a quick question:

    Would stacking three sheets of 2″ Owens Corning 703 be too dense? I know you said the optimal density is 40kg/meters cubed and the Owens Corning sits at 48kg/meters cubed.

    Thanks!

  • How about dimensions? Paroc makes a 38kg/m3 material in 56.5cm x 96.5cm. Would it be ok to just build around these to get the right effect.

  • Hi Jesco.

    How do you build these absorbers. In the picture you have the fabric indside the wood. Is it on a frame you build and put in the outer frame, or how do you get it looking so nice?

  • Thanks for your reply Jesco.
    I find when using Knauf no odor or airbourne particles are produced.
    Owens 703 is a very diffeent situation.
    Loking forward to your posts in 2018.

  • Hey Rob,
    thanks for the kind words!
    In terms of plastic sheets, any thin plastic foil will work. I like to use the stuff that painters use to cover up the furniture before they paint the walls. Some people have also successfully used mattress covers.

    One thing to understand:

    This is not trying to emulate the “membrane” that is often talked about to increase bass absorption. I experimented a lot with that type of design and did not notice any benefit in the low end that warranted the extra cost or effort. All I got back instead was the reflection I was trying to reduce in the first place.

    The plastic foil I talk about is purely to reduce the flight of fibres, and potentially help with the smell.

  • Hi Jesco,
    Great blog!
    I enjoy hearing you talk on podcasts and I like your style of Blog writing. Thank you for what you are doing.
    I have used Owens 703, rock wool, mineral wool, and have settled on Kanuaf as of a few years ago. It’s the easiest to work with, doesn’t cost much and even has slightly better performance results in acoustic testing. To top it off no itchy mess and airborne particles when i am building devices.
    Question: could you recommend some “thin plastic foil ” examples. I have tried a few vinyl membranes but didn’t like them. I have been using craft paper to create a membrane to help maintain some high freq. reflections so as not to deaden my rooms too much but I like the idea of a thin plastic foil to do the same.
    Some folks swear that the Owens fiberglass with foil on one side is great for this reason. Any thoughts on this would be greatly appreciated. keep up the good work!
    Rob Kuhlman
    Root Cellar Music Studio
    (Just moved from Atlanta GA to Ithaca NY)

  • Hello good sir,

    I’m just wondering about the basic design for the trap that worked for you. Looks like 1″x4″ slats, I’m just curious how you’re attaching it all. Did you have some kind of basic guide for your design?

    Thanks!

  • Hi Jesco
    For corner traps is the thickness or eliminating a 90degree corner more important? In other words should my trap be square or triangle?

  • Hey Phil,

    they are in fact, roughly proportional. At least for mineral wool and fiberglass products. I’ll do a post about it at some point. The thing is, the actual density matters far less than the thickness of the material. As long as the density is in the ballpark, they all perform roughly the same for a given depth. Play around with some numbers here: http://www.acousticmodelling.com/porous.php to see what I mean. 14k rayl/m should work fine.

    J.

  • Hi Jesco
    What about the third ‘number’ that might be useful – Flow resistivity?
    From what I’ve read, that is not directly proportional to weight/density?
    The GFR of my product is 14,000 mks rayl/m

  • Hey Jesco,

    you said, any material that you can breath through will work, to cover the material. In your article you said that if someone wants to be sure about no material flying around, one should cover the material with plastic foil. But isn’t the plastic foil a material you can’t breath through, so the the effect of the absorbers is (at least partially) gone?!

    Thanks and cheers

    Chris

  • Great write up, where do you place the final product panel? I have safe n sound and was planning on tall triangles completely but everything is pointing me to this design (partly bc of the air pocket it creates). Do you have multiple panels, are they in your back corners or behind the monitors? Any laying flat against a wall? I believe that design is also an effective broadband treatment when used like that.

  • Sure, you could make the absorber deeper, but you would have to use a different insulation material as it would become reflective at this density. The absorber would also start becoming very bulky and heavy in practice. While you don’t gain much from an acoustics perspective. That’s why this is the best bang for your buck.

  • Hi Steffen,
    yes, it will reflect a tiny amount of high end. But nothing that would cause any problems. As a simple test, hold the plastic over your speaker and have a listen to what happens to the high end. For all intent and purpose you can think of the plastic not affecting the acoustics.
    J.

  • Hi. Great stuff!!!
    What if the depth of material is deeper than 16cm???
    Is that an issue?

  • Hi. The wrapping in plastic?
    Will it NOT make the whole thing reflect the HF more?

  • Hi Dani,
    no, it’s all about the relationship between weight and depth. A higher weight of the same depth would be too dense so sound would start reflecting off it.

    But make it less deep with higher density and you lose bass absorption.

    This really is the sweet spot.

    J.

  • Hi Jesco!

    Great article, but it left me with a question. Would a higher weight – same material panel work even better??

    Thanks for your insight!

  • Hi Chris,
    the approximation of the right density through weight only works with mineral wool or glas fibre. So yes, I would recommend you use rockwool mineral wool and wrap it in plastic instead.
    Best,
    Jesco

  • Danke für den tollen Artikel! Ich wollte das Ganze wegen meinem Asthma bisschen “Öko” machen und Holzfaserdämmplatten benutzen. Ich habe jedoch nur welche mit 50 kg/m3 gefunden. Ist es dann auch noch in Ordnung oder sollte ich dann lieber Steinwolle in Folie packen?

    Vielen lieben Dank und weiter so!

    Cheers

    Chris

  • Hey Robin,

    thanks! Any material that you can breath through will work. So it depends on how the cotton is woven. Can you get a sample? Just hold it up to your mouth and try and blow through it. If you can, you’re good to go.

    J.

  • Hi Jesco,

    Great article! I was wondering: What kind of material do you use for the front panel? Will cotton work as well or is this too dense?

  • When building an early-reflexion absorber, do I need to leave an air gap when mounting it on the wall? Would I gain any absorption in doing so?
    For example: having six inches deep of fiberglass mounted in an 8 inch frame. That would leave roughly 1 and a half inches between the wall and the fiberglass. Interested in your thoughts.

  • Hey Ola,

    thanks! I’m glad you like them.

    I keep the insulation material wrapped in foil inside the absorber to avoid fibre flight and keep the smell at bay. Sometimes the stuff is a bit stinky 😉

    And yes, it does reflect high frequency energy a bit, but not enough to cause any problems. In fact it works in our favor because we tend to absorb too much high frequency energy anyway.

    J.

  • Hi,

    Great looking absorbers!

    I´d like to build absorber panels covered on both sides with thin plastic (and fabric), but I´ve read it will impact the absorption of mf and hf (described as plastic reflects mf and hf). What´s your opinion about that?

    You say that you wrap the insulation in plastic foil. Is it only to store the insulation safely before you mount it in the frames or do keep the plastic foil underneath the fabric?

    /Ola

  • Hey Nicolás,

    if the material those panels use is around the 40kg/m3 mark, then you can stack them, yes.

    A heavier material won’t work unfortunately, since it is so dense that it actually starts reflecting energy if you make it deep enough to absorb bass, i.e. 16cm (6″). You can make a thinner absorber from denser material, but it’s not as effective for the reasons I described above.

    40kg/m3 really is the sweet spot.

    J.

  • Hi Jesco! Lovely articule!

    Here in Perú I’ve found a place where they sell panels that are only 2″ thick, is tehre a problem if I stack them? Also, they sell em in 60kg/m3, 70kg/m3, 100kg/m3 and 175kg/m3, would it be an improvement to get the most dense? or would the 60kg/m3 be fine?.
    Thanks!!

  • True but Chris’ point is a good one and some room dimensions would also be good which are missing and that’s an important factor.

  • Hey Santeri. That sounds like a great place to start. Can you send me a link to the particular product? I’ll add it to the list.

  • Awesome article, thanks! Paroc has panels that are 15cm thick with a density of 38kg/m3. Are these good enough, if I apply them to all corners from floor to ceiling?

  • Just found you through the URM podcast! Love everything I’ve heard and read so far! Thanks for sharing your findings and experiments.

    I’m currently acoustically treating my studio, and trying to find as much info as I can on how to go about properly addressing diffusion, and I’m not quite sure where to start.

    My instincts tell me that I should be using my room dimensions to calculate which frequencies I should be targeting with diffusion, but I don’t really know where to start.

    Perhaps you could point me in the right direction, or possibly make that a topic in any upcoming blog posts!

  • Yes but the rest of the decay time is better than a lot of DIY treated rooms I’ve come across. For free information it’s kinda a take it or leave it thing.

  • The decay time in the low bass is horrible on your waterfall graph. The peaks may have been solved for the most part, but having an even decay across the frequency spectrum is just as important. The pressure is likely taking almost 1 second to dissipate which is “bass reverb” and will not be a true representation of the audio

  • Hey Ray, ah yes, good point. Lost in translation. I use the kind of thin plastic that painters use to cover up furniture before they paint. What would you call that? I’ll make sure to correct it in the article.

  • What do you mean when you write, “wrap it in a thin plastic foil to avoid fibre flight.” I am confused as to what plastic foil is. Is it the same as saran wrap?

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