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  • Michael Tomlin

    Tim, man, this is absolutely fantastic….without question one of the best presentations of this information I’ve yet come across. None of the info here is new to me, but your manner of presentation and explanation is concise, easy to comprehend and practical. As if the gem that is the leanfuser wasn’t enough, you toss out yet another outstanding and remarkably generous contribution from your deep well of knowledge on the topic of acoustics. Thank you!

    • http://Arqen.com/ Tim Perry

      Michael, thanks for reading! I’m glad you appreciate it, even though you already know about this stuff. There’s lots of great info out there but I wanted to create a practical guide that people can reference as they treat their room.

      I hope this helps people out. It was going to be short but I found it hard to address bass treatment without addressing mid-high frequencies (since most bass absorbers have broadband effects).

      Thanks for your awesome feedback! :-)

      • Michael Tomlin

        You’re very welcome, Tim. From my perspective I’d say you certainly succeeded in creating a useful and practical reference for the uninitiated (and initiated, alike) and I’ve already started sharing it with others. The info, visual aids, suggested treatment scenarios…..just great all around. Very nicely done!

        • http://Arqen.com/ Tim Perry

          Awesome. Thanks again for your kind words and for spreading the word. I truly appreciate it!

          • Smart US

            Hi Tim, great presentation and very educational. I have got a question. would you be able to assess my music room based on pics and draft. its not a typical room and there are some areas I really need to get understanding of acoustics. I tried to google but not much info. I dont have flat ceiling – it is cottage style roof 😉 have fixed the corners with bass traps but need to get understanding how to do the ceiling. thanks. m

  • Peter Buis

    Hi Tim,

    This info comes just in time for I am currently at the stage of finishing the new Elektrophonik studio in Haren, the Netherlands. Pictures of the development can be found at the website elektrophonik.org. Since this studio is mainly built using ecological friendly materials like sandpanels (which I make myself) and natural sheep wool insulation it has become a bit of a time consuming activity. But within two weeks I hope to be up and running and rehearsing with the Elektrophonik Orkestra. Thanks a million Tim, for me this is very useful information indeed!

    • http://Arqen.com/ Tim Perry

      Hi Peter,

      Fantastic that you’re using natural materials like sheep wool insulation and sand panels! I love builds like this.

      Congrats on nearly finishing your build and I wish you the best with the Elektrophonik Orkestra! As a student I took some computer music / electroacoustic courses with some quirky profs like Andrew Schloss http://en.wikipedia.org/wiki/Andrew_Schloss, so I gained appreciation for vintage synths like the Buchla, and unique, custom made instruments like the Radiodrum. Your Elektrophonik Orkestra project sounds very cool!

  • Harm Brands

    Hi Tim, Great Guide.
    I recently moved to an new home. One reason why i selected this house is because i now have the oppurtunity to build an decent home studio.
    The Room has an angled insulated roof covering to whole lenght of it. I consider this as an advantage. Disadvantage of the room is, i have a door in the corner behind me and an window in a corner in front of me.
    So i can’t cover as many coners as i would like to.
    As you guide says, the are still an lot of options. I want to get my bass trapping as effective as possible, i already do have some 2″ Primacoustics panels to fight high/mid reflextion. ( i love them ) And i made 2 3″ glasswool corner traps and reso panels tuned at ~80 hz. I know this is never enough trapping and i am not convident this homemade corner traps are effective enough.
    I love the design of the Pimacoustics full and corner traps, but these are way to expensive for me, to buy these as an gamble.
    So here are my Questions : How effective are these Primacoustic traps for real ? If yes, do you know where to find drawings to build them meself. Or : if i build porous traps what would be better material, Rockwool or GlasWool. Is it posible to damp out the low frequencies from ~50 HZ and up effective with these options?
    Sorry for all these questions, but i want to do this right. P.S. if bass trapping is done i will build those Difuser panels from the website to.
    Thanx for sharing your Knowledge !

    • http://Arqen.com/ Tim Perry

      Hi Harm,

      Here are the specs on the MaxTrap and FullTrap:
      http://www.primacoustic.com/pdf/EDS/primacoustic-eds-maxtrap.pdf
      http://www.primacoustic.com/pdf/EDS/primacoustic-eds-fulltrap.pdf

      When corner mounted (I.e., the MaxTrap), peak effectiveness is at 80Hz, but they do provide some absorption around 50 Hz (thanks to the mass loaded vinyl membrane). Here’s a DIY limp mass bass absorber design that’s similar.
      https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/743040-tims-limp-mass-bass-absorbers.html

      It’s easy to make, and can be built to work at 50 Hz. A good approach is to build several with different center frequencies, say, 30 Hz, 50 Hz and 80 Hz, and place them where bass buildup is strongest for each particular frequency.

      To test bass buildup at specific frequencies you can use a sine wave at that particular frequency, instead of pink noise. You would walk around the perimeter of the room with an SPL meter about 12″ away from the wall, and take measurements every 3 feet or so (make sure to include each corner). If you notice a particular location has high sound pressure at 50 Hz, that would be a great place to put an absorber with a resonant frequency of ~50 Hz.

      Hope this helps!

  • Ultrafonic

    Good article but you should remember to point out that resonant devices like membrane absorbers and Helmholz absorbers inherently have a phase shift and a time delay so you may introduce artifacts that are very hard to identify by listening but are also very annoying.

    • http://Arqen.com/ Tim Perry

      Thanks for bringing this up! I agree that people need to know how resonant absorbers are slow to respond and don’t deal with transients properly.

      To avoid bloating this article I’ve been planning to do a future one comparing different types of bass absorbers, in which I’d discuss the inertia issues with resonators.

      But, I think you’re right that I should mention it in this article, as it’s important.

      I’ve just add a note about it.

      Thanks for your valuable feedback!

  • Onur T. Yildirim

    Hey Tim, this is a great article, thank you so much for sharing it. I just wonder why the bass traps should be made of low density material. I was planning to build thick corner traps out of 70-80 kg/m3 acoustic foams. (I tend to stay away from materials like fiberglass etc.) But you are suggesting that it should be lower than 36kg/m3, and I have noticed most of the foam bass traps made by the companies such as auralex, are about 25-30 kg/m3 of density. I am totally puzzled…Isn`t higher density means more absorption?

    • http://Arqen.com/ Tim Perry

      Hey Onur,

      It depends on the thickness.

      I was referring specifically to thick “superchunk” bass traps (e.g. 2 feet thick). They require low density absorption.

      But thinner porous absorbers (e.g. 4″ thick panels straddling your corners) perform better with higher density absorption.

      Higher density porous materials (more specifically, materials with higher gas flow resistivity) tend to offer better low frequency absorption in less space. But if you make them too thick they start reflecting low frequencies instead of absorbing them.

      For example if you’re just using 3″ to 6″ of fiberglass or rockwool straddling a corner, the higher density Owens Corning 705 (6 lb / cubic foot) performs better at low frequencies than 701 and 703. But the thicker you make it, the less of a performance benefit you get over 703 and 701. And if you make it very thick (e.g., the thickness required for a superchunk), 705 will actually perform worse because it starts to reflect low frequencies.

      We see a similar trend with Bonded Logic Ultratouch, where it’s very efficient in thinner slabs (e.g. 3 1/2 inches), but it stops providing any LF absorption gains in slabs over 5 1/2 inches. And once you get over a certain thickness it actually starts to reflect low frequencies because it has a high gas flow resistivity.

      People will call anything a “bass trap” these days, but don’t be fooled. Those foam “bass traps” that you shove in the corners are useless at very low frequencies (the reason discussed in the Quarter Wavelength Rule section of this article, here: http://arqen.com/bass-traps-101/placement-guide/#quarter-wavelength-rule). Technically they should be called low-mid absorbers or something like that.

      • Onur T. Yildirim

        Oh yes… now it makes sense, thanks a lot Tim! I am not going to get one of those foam traps, instead I am planning to build 6inch panels by layering high density acoustic foams on top of each other, and straddle them on the corners.

        Yesterday, I experimented with a thick cushion from my couch while measuring the signal with a mic, placed at the listening position. The cushion definitely sucks up the energy and makes a difference, so I am convinced that the panels I am gonna build are going to smooth out the most problematic peaks in my room. (around 140hz) There is a nasty null around 95 hertz, and I am hoping it will be solved to some extent as well.

        Luckily, below 95hz, I do not have any noticable problem (until 45hz, which is the lowest frequency my speakers are capable of) But I am planning to add a sub next month, and all I do is hoping for the best :)

        Thanks again Tim, this website has been a great resource for me.

        • http://Arqen.com/ Tim Perry

          Awesome. Glad you find this stuff useful!

          The null at 95 Hz is probably due to speaker boundary interference. In this case bass traps will provide some help, but the most effective way to tame this null is to tweak your speaker placement using one of the three recommendations I give here: http://arqen.com/acoustics-101/speaker-placement-boundary-interference/.

          Hope this helps.

  • petfol

    Hi Tim,

    Thank you for this TOP NOTCH/EXCELLENT 101 guide !! However is it possible to elaborate a bit more (or even create a new article) about DIY and placement on limp mass bass absorbers in the room?
    I think it’s really worth a dedicated chapter as they seem often to be overlooked by broadband absorbers.

    Many thanks !

    Peter.

    • http://Arqen.com/ Tim Perry

      I Peter,

      Thanks for your feedback! I’m glad you like the guide.

      Tim Farrant has a nice guide on DIY limp mass bass absorbers here: https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/743040-tims-limp-mass-bass-absorbers.html

      It includes info on how to build them and examples on where to place them.

      I’m not sure I have anything to add that he did not already cover. Either way, he has more experience with limp mass bass absorbers than I do.

      The future articles I’m planning are more focused on how to treat your room and not so much focused on how to build specific acoustic treatments. This is because with my diffuser designs I saw a lot of people jump into the details of building treatments, often with limited understanding of why they are building them, what they should be building, and where they should be placing them.

      In other words, I want to encourage people to think about their room as a whole before they start thinking about the construction details (or before they splurge on treatments). That way people can avoid making costly mistakes.

      Thanks again, and I hope you find Tim’s DIY resources on limp mass bass absorbers to be helpful!

  • Ja’Maul Redmond

    In corner 1 A/E I have this additional pocket where the door opens into. In other words,,Take the rectangle diagram above and add an additional 3’x3′ box outside the rectangle at corner 1, resulting in an additional corner. The door opens in one of the corners and I have no idea what to do with it but I have a feeling it’s causing some serious problems. Also does a carpeted room help in not having to put panels on the ceiling?

    • http://Arqen.com/ Tim Perry

      Hi Ja’Maul,

      Left-right symmetry is important, especially at the front of your room. Your best bet is to reorient your listening position to achieve symmetry. If you can’t do that, I suggest you make the front left and right walls of your room as dead as you can, so they disappear acoustically.

      I suggest you add bass traps wherever possible in the alcove you described at corner 1. Also, tame the first reflections in the front portion your room using broadband absorption. I’ll soon post an article on early reflection control, but in the meantime Google “reflection free zone” to help you with this. The alcove may allow sound to be reflected in undesirable ways (e.g., flutter echo), so I suggest you treat at least two walls of the 3’x3′ alcove.

      Carpet is not a replacement for acoustic panels. Carpet absorbs high frequencies, but does little to tame mids and lows. This means it can have a cheapening effect on the timbre of your instruments and make your room sound dull.

      To balance this out, focus on applying heavy absorption at low frequencies (using bass traps) and moderate absorption at mid frequencies, without absorbing too much energy at high frequencies.

      To achieve this you can use a combination of absorption and diffusion. Hybrid surfaces are a good option as they let you absorb mids while scattering / diffusing high frequencies. Vicoustic Wavewood panels are an example of this: http://arqen.com/store/vicoustic-wavewood/. An example of a bass trap that scatters high frequencies but absorbs lows is the Super Bass Extreme: http://arqen.com/store/vicoustic-super-bass-extreme/.

      If you’re building DIY bass traps, you can build your own scatter plates for them. But in your 3’x3′ alcove (and on the sidewall opposing it) I suggest you use pure absorption.

      Hope this helps!

      • Ja’Maul Redmond

        Thanks so much for the reply. This will help me out quite a bit. I have a limited amount of funds, so I’m going to have to make some hard decisions. I don’t think I can treat the back wall/ceiling and that corner pocket as well. For now will it be ok to leave the back wall and corners blank and take care of my front and side walls. I have enough to do that.

        • http://Arqen.com/ Tim Perry

          It depends on the distance between your back wall and listening position. If you’re less than about 10 feet from your back wall first reflection points, they should definitely be treated.

          In this case, treating your rear wall first reflection points is higher priority than treating your rear wall corners.

          If you’re close to the rear wall (e.g., 5 feet) I recommend broadband absorption there. At further distances you can use absorption or diffusion (depending on the minimum listening distance for the diffusers).

          Examples of economical rear wall absorption are acoustic panels made of Owens Corning 703 or rockwool. The most economical rear wall diffusers I know of are these DIY diffusers: http://arqen.com/sound-diffusers/.

          • Ja’Maul Redmond

            thanks a lot for this resource. I played the pink noise mp3 and the bass was gathering a lot in that pocket and oddly enough corner 3 of my room. Absolutely none in corner 4. This resource has helped me alot!

          • http://Arqen.com/ Tim Perry

            Great to hear that you tried the pink poise test! That pocket would be a good place for heavy duty bass trapping. It doesn’t surprise me that corner 3 also has a lot of bass buildup, as it’s opposite from the pocket.

            Based on your pink noise test it sounds like some strong room modes are being supported by that diagonal of your room (from the pocket to corner 3). Those are prime corners for bass traps, but ideally you’d also add bass traps to corners 2 and 4 to maintain a level of symmetry.

  • Abbas Reza

    Hi Tim, First of all – Excellent article that saves me from browsing a million pages for the same information. Comprehensive yet concise!

    Secondly, my problem is a bit different – My home theatre room is 5m long by 4m wide (approx).. and 2.7m high.. however its unique in the sense that it actually has 1 full corner at the back left, the other corner has a built-in bookshelf/cabinet and the front 2 corners are almost non-existent as there are 2 sliding doors at those 2 corners. The projection screen falls over the doors and we face that way.

    Because of the 2 doors at front 2 corners, the best place i found for the sub-woofer was in the rear left corner – first of all, is that a good place? (the bass response is amazing, not boomy and i only need half the gain to achieve it) .. however, if i think of adding bass traps, i only have 1 rear left corner, and possibly part of the rear right corner where i could put foam traps .. but what do i do with the front corners (non-existent) .. and does the subwoofer being at the rear have an effect on where the bass traps should be setup?

    Alternatively, i could try moving the subwoofer to the front wall (between the two doors), but it will be center-ish and not quite in a corner.

    I’ve added a curtain to the right wall, and am going to put some foam traps on the left wall at reflection points, but really its the low frequencies that linger on (say after an explosion) that i want to trap ..

    Any advice is appreciated. Thanks!

    • http://Arqen.com/ Tim Perry

      Hi Abbas,

      Glad you find this guide useful!

      Since you’re so close to the rear wall the first thing I recommend is mounting bass traps directly behind you. Your first reflection points are top priority, and treating them will make a big difference to your sound stage, improving clarity and imaging.

      Since there are obstructions in your wall-wall corners, what about soffit bass traps around the edges of the ceiling? Is that a possibility for you?

      Another option is pressure activated bass traps (like the RPG Modex) that mount flat on the wall, so you can mount them beside the corner instead of right in the corner.

      Finding the best subwoofer placement requires testing (both by listening and measuring the frequency response in high resolution). Multiple subwoofers is often beneficial in home theaters as I’ve discussed here: http://arqen.com/acoustics-101/surround-sound-speaker-placement/#multiple-subwoofer-placement).

      If you’re using only one subwoofer a good starting position is close to the front wall of your home theater, slightly to the left or right of the center line. This is a common placement in professional studios, except they flush-mount it in the front wall, which is even better.

      Corner placement is the loudest. It excites all your room modes rather than emphasizing just some, but it won’t have the flattest low frequency response unless your room has extensive bass trapping.

      You should of course experiment to find the best placement.

      Also, if you place your subwoofer right up against the wall (which I recommend) or in a corner you need to apply EQ to correct for bass boost caused by SBIR: http://arqen.com/acoustics-101/speaker-placement-boundary-interference/. Your subwoofer may have built in boundary gain compensation (BGC) control to make this easy.

      Hope this helps!

      -Tim

  • Romina Jones

    This is great! I am just putting on the finishing touches after spending the last few weeks acoustically treating my studio (building bass traps, new bamboo floor to replace carpet, opening part of a wall). This affirms everything I’ve been studying but it is the best laid out and most clear I have seen; wish I’d seen it a month ago, wouldn’t have had to use Google so much. Hope you get your SEO a bit higher as I only encountered the link via your newsletter, and it would be great for other search happy acoustic heads to find it easier.

    • http://Arqen.com/ Tim Perry

      Hey Romina,

      Glad this helps validate everything you’ve learned so far!

      This is a new article and while I’ve not been actively promoting it outside of email, it’s been climbing in the ranks thanks to people sharing it over the last few months. It’s now the first result for bass trap placement and getting lots of organic visitors (more than my sound diffuser resources), so obviously this is an important topic for people.

      My goal was to create the most comprehensive guide out there for setting up bass traps, so it should steadily rise in Google over the long term as people share it. Hopefully more audio heads who are installing bass traps will find it it in the future.

      I wish you the best with the finishing touches on your studio. That bamboo floor sounds sexy! Carpet being replaced by bamboo is music to my ears. Sounds like you have an acoustical victory in the making. :-)

  • Lester Dragstedt

    Tim,

    Thanks so much for all this info!

    I have a home rehearsal/recording room that is 33X21x8. I have made all the usual mistakes in trying to improve it’s acoustics. I have applied some of the info I’ve gotten form the web, but it is hard to make the financial and work commitment when you aren’t confident you are doing the right thing. I realize you normally get paid for this sort of thing, so I will try to hone down my thousands of questions.

    1. Due to architectural and lifestyle demands, I can’t do anything close to a symmetrical bass trap placement. Is symmetry as critical or desirable in a recording situation? Should I just fit them in where I can get them in?

    2. The drum set sits about 6 feet from the back wall. I assume that this would be a good spot for a diffuser. any recommendations?

    3. I would like to make some removable plywood fronts for my existing bass traps. I figure through trial and error I can get some liveliness back into the room. Does this seem like a reasonable Idea? If so, what thickness?

    Thanks again!

    Les

    • http://Arqen.com/ Tim Perry

      Lester, you’re in luck, because symmetry is generally not desired in recording rooms. Put the bass traps wherever you can fit them (with corners the first priority, of course).

      Since it’s rather close to the wall you’ll want to use diffusers that don’t diffuse low frequencies. My Leanfractal or Leanfuser design (a modulated array of 5 or 7 panels) would work. The RPG Flutterfree, mounted over top of absorption would be well suited as it only diffuses higher frequencies. 2D “Skyline” style diffusers would also work, like the Vicoustic Multifuser series or a DIY primitive root diffuser (lots of free resources online for building these). Without doing measurements I’m not sure what the best solution is, but any of these would work.

      Yes, it’s a good idea to add plywood in front of your bass traps to preserve liveliness in your room. Anything from 1/8″ to 5/8″ will work, so long as it’s practical to work with. The thicker and denser the material, the lower the absorption-reflection transition frequency will be (it’s not a black and white transition, of course, but reflectivity increases as thickness increases).

      It’s often beneficial to use wooden slats with gaps or cut a pattern of openings in the surface as it helps scatter sound (similar to an MLS diffuser). Also, this ensures that you’re still getting good absorption at upper bass / low mid frequencies, which could otherwise reflect (depending on the thickness and density of the material).

      I wish you the best with your room!

  • https://www.youtube.com/channel/UCT49zuhYVs6F7ZD8_F_SvgA/videos Warren_Budget

    this article rules man. thanks so much.

    • http://Arqen.com/ Tim Perry

      Warren, man, I’m glad you like it and were able to fit it into your strict regimen of hallucinogens and Zen Buddhism. :-)
      Thanks for your feedback!

  • Kenny MacKay

    Fantastic presentation thank you thank you

    • http://Arqen.com/ Tim Perry

      Kenny, thanks for your feedback! I’m glad you like it and I hope it helps you improve your sound. May you tame many bass ways during the coming bass trapping season.

  • BudMac

    Hi Tim,
    Great article! I am hoping you can comment on the last diagram in your article which shows a professional control room with bass traps front and rear. The material in the traps is at an angle. I have seen this in books on recording studio design but I have not been able to get specific information on the construction of these traps and why the (I assume 705) is at an angle. Could you please comment on the construction technique and the materials used. Thank you!!

    • http://Arqen.com/ Tim Perry

      Hi BudMac,

      Those are sometimes called “waveguide” panels or Hidley panels, after studio designer Tom Hidley who popularized them.

      They haven’t been extensively studied so the complete mechanism of how they work is not fully know. Some engineers and designers avoid them because of this, but in practice we see that many tight sounding, world class control room rely on Hidley panels extensively for bass “trapping”.

      They attenuate low-to-mid frequencies by providing flow resistance and damping. The angles are there to create long channels with lots of surface area.

      Hidley’s idea was that sound waves will loose energy when they are forced through the absorbent-lined channels created by the hanging “waveguides”. As the waves try to squeeze through, the forces on the panels cause them to vibrate, converting sound energy into heat. The panels are also covered in a fibrous material that absorbs mid-high frequencies.

      There are many ways to build them but the basic elements are a core of
      chipboard or plywood with a layer of absorption (such as recycled cotton felt)
      on either side.

      Common core materials are 5/8” or 3/4” chipboard or plywood. For budget builds I’ve also heard of people using 1/8″ pegboard.

      Any medium density (3-6 pcf) broadband absorption should work for the outer layers. Options include:
      – 1-2″ Bonded Logic acoustical panels or Ultraliner sound blanket
      – 1-2″ Rockwool (E.g. Roxul Rockboard) or Fiberglass (E.g. Owens Corning 703)
      – 2 cm thick A1 (a cotton waste felt product available in the UK)

      If you search online for “Hidley panels” or “studio waveguide panels” you should find some example construction photos. I believe there are some photos in the diary for Branko’s studio build in Portugal: https://www.gearslutz.com/board/photo-diaries-recording-studio-construction-projects/519158-new-rooms-portugal.html

      • BudMac

        Thank you Tim for the very informative response!

        • http://Arqen.com/ Tim Perry

          You’re very welcome!

          • Paul Keenan

            what are the best traps in UK? I need help with this.

          • http://Arqen.com/ Tim Perry

            I don’t know the extend of what’s available but in the lower price range I think Blue Frog Audio and GIK make decent bass traps and have UK presence.

            In the medium price range you start getting into more sophisticated devices like the Vicoustic Super Bass Extreme (made in Portugal but available in UK), which I like for its extended low frequency performance, high frequency scattering and aesthetics. They make it in both a fabric front (called the Suber Bass Extreme Premium), and a Wavewood front like this: http://arqen.com/store/vicoustic-super-bass-extreme-trap/

            At a higher price point you have high performance, low profile devices like the RPG Modex Broadband and Modex Plate (made in USA but available in UK). I’m guessing these are technically the best bass traps in the UK, but best depends on your needs and budget.

          • Paul Keenan

            I am treating my room, home theater. Trying to get an accurate stereo image for front and rear speakers. Normally right side is dominant. The wall on that side is thinner.

  • DasLicht

    How does those panel absorbers compare to corners fully filled?

    • http://Arqen.com/ Tim Perry

      I’m assuming you mean the angled panels? These are often called hanging Hidley panels (see my response to BudMac’s comment for more details on them).

      That’s a good question, and the answer is that no one I know of has done a direct performance comparison. I like them for applications that take up high volume (like giant rear wall bass traps), because you can get away with less absorptive material.

      Hidley panels have been used for broadband bass control in many world class studios, but they have not been extensively studied. Some people don’t use them because of this, which is understandable.

      But I encourage people who want to experiment (or don’t want to buy truckloads of absorption) to try hanging Hidley panels as an alternative to the boring ol’ superchunk “bass trap”. It would be great to see someone try both broadband bass control approaches in a room and compare them using acoustic measurements. :-)

  • Richard Johnson

    As Michael Tomlin stated, This is the best article I’ve come across. I’ve read so much but something are hard to understand, you’ve made this crystal clear and now it’s really on!! Thanks.

    • http://Arqen.com/ Tim Perry

      Glad you like it Richard! Low frequency absorption is a huge topic but I’ve tried to cover the key practical points. Thanks for your feedback. :-)

  • http://ledgernote.com Ledger Note

    That very last image with the 5.1… I’ve never considered just covering an entire wall with paneling, although I guess that’s what university auditoriums do to some degree. If you covered every inner surface of your room, could you over do it? Is that possible?

    • http://Arqen.com/ Tim Perry

      In a small room you’d be hard pressed to add too much bass absorption, but you can certainly overdo it at higher frequencies!

      A key goal in small room acoustics is to tighten up the bass without rending the room completely dead at mid-high frequencies… because no one with an ounce of sanity wants to spend all day listening in an anechoic chamber. :-)

  • Saleem Merkt

    Tim, excellent article the delves a bit into the physics of bass traps! What are your thoughts on a curved corner bass trap? Based on the pressure simulation above it seems that a convex shape would provide more even absorption, but a concave shape (with a large radius) would eliminate the corners all together. Maybe even a concave shape between the side walls blending into the ceiling such that the bass trap is tangent to the side walls and the ceiling?

    I’m an aerodynamics/cfd engineer and would really like to delve into the acoustic side of it, but right now the thoughts of corners makes me cringe!

    • http://Arqen.com/ Tim Perry

      Saleem, good observation. Convex shapes are great. For a porous absorber type bass trap, which has maximum performance a quarter wavelength from the wall, convex shapes it increases the absorption at lower frequencies. Another big benefit is that if you add a reflective convex surface to the front of the bass trap, it’s a great surface for scattering sound.

      People generally call these polycylindrical diffusers, poly cylinders, or just polys. The downside is that when you make them large they take up a lot of space.

      Reflective concave shapes are generally avoided in acoustics as they focus the sound. Large concave shapes (like domes) are particularly terrible, causing extreme resonance. I was having a conversation a couple weeks ago with a world class acoustical engineer, and we happened to be sitting right at the focal point under a convex ceiling. Even with our prior experience, were amazed at just how distracting it was to simply talk.

      The worst shape for a room, acoustically, is a sphere.

      For a porous corner bass trap the approaches that make sense are to have it straddle the corner (triangle cross section), have a rectangular block that sits in the corner (square cross section), or have a convex surface or even a full cylinder that sits in the corner. A concave surface doesn’t make sense for a velocity activated (i.e. porous) absorber.

      You could make a concave resonant absorber (pressure-activated bass trap), but if the surface of it is reflective it would focus higher frequency energy. Concave curves are naturally problematic in acoustics unless they are part of a larger shape, like the RPG Waveform Spline diffuser, which is an optimized curved surface.

      BTW there are huge opportunities for computational modelling in acoustics. We’re years behind the aeronautical / cfd / electromagnets world. My original background was electrical engineering (signal processing / control systems), and I went far off the standard path to get involved with computational acoustics. Most acoustical engineers don’t have experience with numerical methods, so there’s an opportunity there.

      • Saleem Merkt

        Thanks for the response Tim! Now that you mention it, there is definitely focusing with concave shapes. I need to see if I have enough room for a convex/poly bass absorber while still making it aesthetically pleasing.

        It’s good to hear that there is opportunity in the realm of aeronautical/CFD/numerical methods in the audio world. I got the sense that it may be missing to a certain degree from the lack of citing/depth in regard to CFD. The more I get into audio on the side the more I keep hearing about either very rigid “rules” or purely experimentation, but I wasn’t sure if that’s just because I’m looking from outside the industry. Accurate/efficient CFD is a complex subject for aeronautical engineers, so I imagine it must seem even more like black magic to acoustical engineers.

        It definitely sounds like you went off the beaten path! There is plenty of signal processing work in audio but most of what I’ve seen has not been with computational acoustics.

  • jmagesy

    Hi Tim, I hope it’s not asked before. Thank you for this really valuable article for me. I have a question, is a Bass Trap need to be sealed/closed to trap the bass? Thank you

    • http://Arqen.com/ Tim Perry

      It depends what type it is. Diaphragmatic/panel/membrane bass traps need to sealed. When the membrane vibrates it forces the air in the cavity to move through the fibrous/porous fill material, which absorbs energy due to friction, damping the membrane.

      If it wasn’t airtight, the air would be able to escape instead of being forced through the absorptive fill. Instead of being damped the membrane would vibrate until it stopped on it’s own, sending energy back into the room instead of absorbing it.

  • Wade

    Hi Guys,I built a room with in a room so that bands can play and I can drum so hardly any noise can escape to annoy my neighbours or advertise my equipment.The room used to be my garage so behind the drywall and sound absorbtion is concrete walls,ceilings and the flooring being concrete.
    My question now is how to acoustically treat my room so that on the one side of the room I have it as a mixing room and the other side is wher i play my drums aswell as guitarists jam so they got a live feel

    • http://Arqen.com/ Tim Perry

      Hi Wade,

      Have a look at some of the multi-use one-room studio ideas in this thread: https://www.gearslutz.com/board/high-end/361471-one-room-studio-setups-not-bedrooms.html

      The most basic approach would be a LEDE (live-end dead-end) setup, which has simple rules to follow. But there are more interesting ways to do it, depending on the size and shape of your room, if you design with attention to the Hhaas effect, initial signal delay gap and RFZ (reflection free zone) criteria. I’ve explained all these here: http://arqen.com/acoustics-101/reflection-free-zone/#haas-effect.

      If you want a fairly lively room overall and you have the resources and will to experiment with large quantities of diffusers, have a look at some of the less standardized room design approaches like ESS (Early Sound Scattering), FDRZ (Fully Diffused Reflection Zone) or Ambechoic rooms. Blackbird Studio C is an example of an Ambecoic room.

  • run13

    Like others have said, this is a really good article and help. Really clearly written and full of information. Thank you

    • http://Arqen.com/ Tim Perry

      Glad you found it helpful and thanks for your kind words!

  • mmercedo

    Hi Tim.
    Loving the website.
    Do you have a “how to make” or a blue brint for a bass trap?
    I’m from Brazil and I’d like to make myself a couple of bass traps for my home studio.
    Thanks.

  • Bobby Rubon

    First of all, awesome article! I’ve been taking a crash-course in room acoustics, and this has cleared up so many issues for me…

    I’m building a dedicated 2-channel listening room. It is 17x14x9, and currently has a 4 foot walk-through on left wat wall close to front, and 4 foot walk-through on back wall, close to right wall. It also has 2 windows on right wall, spaced evenly…

    Listenting position will be around at 38% from back wall, and in unilateral triangle with the speakers. I’m planning on doing corner floor-to-ceiling bass traps.

    Onto my question… Not sure what to do about the openings and windows! I’m open to going as drastic as closing off the left opening fully, but any suggestions would be welcome!

    • http://Arqen.com/ Tim Perry

      Hi Bobby,

      If the windows are not on first reflection points you can generally leave them untreated if natural light is important.

      But if they are on first reflection points you should put treatment over them. You can build a window-plug style insert if you want it removable, or simply use a 4″ slab of broadband absorption. I recently designed a control room like this where they had custom millwork done so the windows are part of an 8″ thick absorptive wall, but the window parts can swing open to let in light. The millwork was expensive but light was important for them as the studio doubles as an interactive classroom for learning about music technology.

      Also, you want left-right symmetry with whatever treatment you use on the sidewalls. If one sidewall has a window, that could effect how you treat the other sidewall.

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  • nikoli

    What about when you have a rectangle room, but the ceiling isn’t flat, but rather peak up in the shape of a pyramid ?

    • http://Arqen.com/ Tim Perry

      Treat the peak as an extra corner that can be put to great use. Straddle it with as many bass traps as you can.

  • lanre

    hi Tim, i’m an architectural student and i was given an assignment to state the major issues in recording studios. have tried to read up on so many write ups but none of it is really giving me what i want….can u please in clear terms state the major issues in recording studio

  • Ridley Bronson

    I have a curved wall in my mixing room. The desk is facing the curved wall and each corner of the desk are almost touching the curve as it moves into the rectangular shape of the room. How would I install bass traps behind my desk on the curved wall?

    • http://Arqen.com/ Tim Perry

      Ridley, concave curves are generally very undesirable in mixing rooms as they focus the sound. In the ideal world you would cut the curve off and turn the whole thing into a giant bass trap (e.g., fill the entire curve with low density fibrous material to create a super chunk trap, or use hanging, angled Hidley panels like in the surround sound mixing room shown at the end of this article).

      I discuss these DIY solutions a bit more here: http://arqen.com/acoustics-101/room-setup-acoustic-treatment/#diy-bass-trapping

      And here’s a 3D rendering of a control room with Hidley panels (in this case they’re along the back and side walls): http://arqen.com/wp-content/gallery/room-setup-acoustic-treatment/control-room-acoustic-treatment-sonic-rocket-studio-1.jpg

      But how you treat it in practice will depend on how deep the curve is. Can you give me an idea of how wide your room is before the curve starts, and how deep the curve is relative to the the flat parts of the wall?

  • JonnyNinja

    Tim, awesome guide! Thanks for posting.

    One question. As of now, I have enough traps to cover any two power corners…or I could cover all 8 trihedral corners.

    Generally speaking, does one get more bang for the buck covering power corners 1 & 2, or covering all 8 trihedrals?

    • http://Arqen.com/ Tim Perry

      Hi Jonny, glad you like it! I answered this on Gearslutz but I’ll answer it here too in case you didn’t see it. The effectiveness of one over the other would be subject to variables like ceiling height, and the depth of the bass traps / how far they are spaced off the wall. I’ve not seen test results comparing the two options so I’m not sure which will be better from a performance perspective.

      But there are other things to consider, like available floor space and aesthetics. For both of these reasons I would usually prefer various combinations of floor-to-ceiling and soffit-mounted bass traps over simply putting large traps in each trihedral corner. The extra surface area coverage can also be beneficial provided you’re not over-absorbing your mids and highs.

      • JonnyNinja

        Thanks, I saw it there on GS. As far as floor space and aesthetics, none of it is a problem as I have a dedicated room, it’s fairly large, and my wife is cool with it.

        I have opted (for now) to cover the two power corners behind the DAW desk floor to ceiling and it seems to be working well. I tested by putting my head in the areas while some low end material was playing, trying it with and without the treatment, the difference is quite noticeable. From the mixing position at the desk, I definitely get more bang for the buck in the two corners you mentioned as being most important in the article, so thanks for the advice!

        I’m finding myself turning up the low end in mixes quicker than usual (before I wasn’t turning it up enough until AFTER hearing it on other playback systems and noticing that it’s too low), and it seems to translate well from the beginning now.

        Thanks again!

        • http://Arqen.com/ Tim Perry

          Glad the floor to ceiling bass traps are working out well for your Jonny. Enjoy your mixing!

  • Captnimmo

    Excellent information.

    • http://Arqen.com/ Tim Perry

      Glad you find it valuable!

  • maz

    Excellent information Tim . Thanks alot.I’d like to ask you a question. I am using the loft of my house as a recording and mixing. it has already mounted some acoustic panels on the walls but I don’t know whether I need to put some bass traps in corners or not . because there is a sloping roof .
    Many thanks
    Maz

    • http://Arqen.com/ Tim Perry

      Hi Maz. Yes, every edge/corner is a candidate for bass traps, even if the angle is not 90 degrees.

      Definitely put broadband bass traps or a thick broadband absorptive cloud straddling the peak of the roof above your head. This will provide both bass absorption and first reflection control.

      I would also add bass traps to the front and back corners, both along the short vertical part of the corners, and along the sloped corners that head to a peak.

      You also need treatment (I’d use broadband absorption) at your sidewall first reflection points. The ideal thing here, if we ignore aesthetics and if you don’t mind making the room feel narrower, would be large broadband panels that go up above ear level, while also straddling the sidewall corners at waste level. These would both absorb first reflections, and add some bass absorption. If you don’t like this sidewall straddle approach (it’s pure function over aesthetics), then simply mount the panels on the sloped part of the sidewalls at your first reflection points, ideally with an air gap.

      As to how to make this look presentable… that’s another story :-).

  • Andrea Lucchi

    Hi Tim, I don’t know if I’m too late for a reply, but I will ask you anyway: Is there any way this kind of soundtraps will work in a plain plasterboard room 6 x 4 meters with only a heavy fire door on a side? I use this room to rehearsing with my band, and I want to handle the sound so it would be more balanced. Should I build corner traps?

    • http://Arqen.com/ Tim Perry

      Hi Andrea. Yes, corner bass traps will help balance the sound in your rehearsal space. They’ll also tighten up the low end for increased clarity. In general, all domestic sized rooms used for music applications benefit from low frequency absorption.

  • Nicolas

    Hi Tim, what a joy to read such clearly laid out info on the total ballgame regarding acoustics! I’m really stoked about this site and will recommend it dearly to friends! Can I trouble you for a bit of your experertise? I couldn’t find info regarding my problem…

    The following sketch is my little studio to be. As you can see quite a weird room. Height is low (2,4m), thin single glass windows on the right, chimney sticking out into the room, another window on the bottom left, and what you cannot see: the bottom wall with the door curves into the ceiling during the last 40cm.

    So I have tried the stupid way: placing my monitors at the corner of the chimney for aesthetics. Result was a huge bass null in mixing position. So I am left with two options placing my monitors:

    Option 1) Monitors as close as possible to the big windowed wall 1-2. When trying this out in the untreated room taking into account the 38% mixing position with one speaker, bass seemed to be there finally, but it seemed as if I had a little less mids. Let’s say, punchy bottom end, with articulate but perhaps a bit scattered highs. Not a lot of sweet spot margin when moving the listening position backwards, the bass null came fairly quickly, perhaps due to the bass bouncing back off the rear wall and nulling itself?

    Advantages and disadvantages:
    + very nice inspirational outdoor view if it’s ok to tilt my monitors slightly upwards :)
    + the 3 Windows are a huge bass trap by themselves?
    + I could treat the hell out of that back wall by maybe bass trapping the whole of it with 4inch thick rock wool. Or make your diffusers and trap the corners instead.
    + same type of sidewalls so good early reflection symmetry.
    + I can bass trap the front corners 1 and 2 equally
    – the three Windows provide a lot of reflections in the highs?
    – bass trapping corner 3 is going to be hard due to the single window.

    Option 2) Monitors as close as possible against wall 3-4. When trying this out at 38% mixing position, I had even more bass with more sweet spot margin, with a bit firmer sound, although perhaps a bit muddier too. (I have a bit of Eq on my monitors though so I could lower the bass and lessen the shelving). So less clarity but more solidity. Perhaps in this situation the bass just shoots through the windows on the back wall so they can’t bounce back and weaken themselves or create a null right behind me?

    Advantages and disadvantages:
    + the rear wall Windows function as a big bass Trap?
    + I can bass trap corners 1 and 2 fairly equally.
    – early reflection side walls aren’t equal so perhaps will sound a bit different.
    – no other rear wall treatment possible due to 3 Windows
    – it’s a darker uninspirational wall

    So there you have it. How would you do it? What does science dictate? I would love a nice view if it would be ok to slightly tilt my monitors upwards instead of high up on their stands to clear the view a bit, but of course sound is the most important thing so I will do what has to be done!

    Cheers! Oh and Canada rocks! :)

  • Patrick Carpenter

    Hi Tim – this is brilliant. Thanks.
    I am thinking of stacking paper back books, spine to the wall, in the corners of my room as a bass trap. If I make it 2′ thick, will it work?
    thanks
    Patrick

  • RACBEATZ

    Hi Tim,

    Very informative website you’ve got.

    I have a issue with some major bumps and dips as you can see in the picture [after measuring with REW]. The biggest bump is in 140Hz section. I have tried to move the speakers in every direction [incl length and width] but nothing seems to help. The room is 2.64 length x 2.48 width x 2.28 height. its almost a cube. I have treated all corner with rockwool [about 10 cm thick, except one corner, 5 cm], incl cloud.

    What can I do to get rid of those bumps and dips?

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