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Question on Sizing Corner Bass Traps

Discussion in 'Room Acoustics / Isolation / Treatment' started by tga$ound, Jun 15, 2015.

  1. tga$ound

    tga$ound Active Member

    Hello guys, I used to come to this forum like 3 years ago(don't remember my other account) but the thing is I learnt a lot of important stuff and for that I thank you guys.

    Now I have a question about corner bass traps in small spaces with 90 degrees angles. Since bass waves are really big, obviously there's a minimum for bass trap sizing. What is the smallest size for rockwool-stacked DIY corner bass trap in a small mixing room situation?

    I've already did a search and didn't find this particular information.

    Thanks in advance,

    Marcelo Targa
     
  2. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    There's no hard answer for that. The smaller the corner trap, the less effective it will be at lower frequencies. The only answer that is almost always true for rooms of this type, make them as big as you can.
     
  3. tga$ound

    tga$ound Active Member

    Thanks for your answer, kmetal. Of course I thought it: the smaller it is, the less effective it will be.

    because of aesthetical issues I was thinking 41cm front face, so the sides are ~ 29cm. I'm gonna have 6 of those in the front corners, and also I'll build traps on the four ceiling corners, as a way to save some room space. Are those dimensions too small for a trap? What if you build it with denser rockwool?

    I could maybe make the front face 'round', as a slice of pizza would (you know, triangle with an arch, which would mean more rockwool and less need for side spacing...sorry for my poor english).
     
  4. pcrecord

    pcrecord Don't you want the best recording like I do ? Well-Known Member

    2 things to consider :
    • Making a triangle shape corner bass trap allow for thicker material and less footprint in the room
    • If placed on a wall, an air space behind it will add to the effectiveness
     
    kmetal likes this.
  5. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Quote" Thanks for your answer, kmetal. Of course I thought it: the smaller it is, the less effective it will be.

    because of aesthetical issues I was thinking 41cm front face, so the sides are ~ 29cm. I'm gonna have 6 of those in the front corners, and also I'll build traps on the four ceiling corners, as a way to save some room space. Are those dimensions too small for a trap? What if you build it with denser rockwool?""



    Its tough to say if it's too small, when I don't know how big the problem is we're all looking at. The depth of the cavity and the thickness/density of the absorbabtive material determine how much trapping the trapping does, and at what frequencies.

    your on the right idea of putting traps in all those corners. Corners are where bass builds up.

    image.jpg

    That's a 'superchunk' style trap. That's from Google. That's what you want your traps (internals) to look like in your case TGA. All the corners can be treated the same.

    How much improvemt you see can be quantified by comprehensive calculations and anylzations, this is beyond my abilities as they stand. And that would also require you to detail your rooms construction methods. It's almost certainly 'gonna help' and probably a decent amount, relative to your untreated area. But that's just in general, true for small rooms.

    Make them as big as you can, and put as many as you can. Then see what your problems, if any are from there. Your treating a broad range of low frequencies, which is where your start. Then you take care of the remaining problems as they are narrowed down, and money/area allows.

    This is just my general thoughts on a general question, acoustics is a facinating area, and I encourage you to poke around and educate yourself further on some of the basics, before your drop a penny, or whatever your currency :).

    RO has had some excellent threads, with real world questions and answers, and there are a few excellent books on the topic, from varying points of veiw, and targeted to anyone from novice, to Phd.

    -kyle
     
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  6. tga$ound

    tga$ound Active Member

    kmetal, I'm about to build it with rockwool.

    My problem here is both acoustical and aesthetical.

    I made an horrible sketch but I think I can illustrate the situation...Check out the file I uploaded!

    The whole thing is about the mix room is precisely the fact that there is a communication window and its frame is set 29cm apart from the front right corner. So, in order not to cover the communication window in a weird ugly way, I go for a "superchunk" exactly like the picture you posted, measuring 29cm sides and ~41cm front.

    So I'd cover the two front corners. The two back corners can't be covered because of doors, so I'll fill the 4 ceiling corners with the same kind of bass trap. It would be 3 90cm units in each front corner + 8 units covering the entire ceiling corners, all measuring 41cm front.

    Is it chunky enough? At least as a starting point? Should I even try with this 41cm front measure? I could definitely make the ceiling ones chunkier, but would it help? Could I have flat rockwool wall absortion pads go along with the 41cm traps to tame the low end without making my mix room a dead room?
     

    Attached Files:

  7. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Lmao, that sounds pretty chunky. Definately a good starting point, and should do quite a bit towards balancing the low end. Although with a room sporting those dimensions the bass response will never be amazing, there's certainly opportunity for improvement.

    The flat absorbsion panels are henerally for mids/highs and usually aren't very effective below 200hz (if at all). So use those to grab what do well. If you want to make some sort of a helmholtz or slat resonator (or other tuned trap) for the rear wall you creatainly could.

    If you stacked them flat so they were .5 meters thick, then your talking bass absorbsion, but that also makes the room smaller. So it's a compromise.

    If it were me, I'd have a tuned trap broadband resonator on the back wall about .75-1m high, and the mid/high panels about that. I would use the bass traps top as a shelf, for whatever things are laying around.

    This is a helpful link Kurt posted a little while back.

    http://www.mh-audio.nl/AcousticCalculations.asp

    I ran some of your basic numbers to get you started.

    Here's a calc that illustrates how your modal energy will distribute
    http://www.hunecke.de/en/calculators/room-eigenmodes.html

    You want your traps you have enough depth/ density to trap your particular problem frequencies, and place them in areas of high concentration. As you already are doing, corners are a good place to start.

    The floor-wall-wall, and ceiling- wall -wall (trihedral) corners are where the most bass will build. But any corner that is available, is a place where bass will build up.
     

    Attached Files:

  8. Brien Holcombe

    Brien Holcombe Well-Known Member

    In respect to super chunk type trapping, Eric Desart says that being as close to the hard boundary as possible is more effective.

    To quote " Just make stuff and shift it as close as logically can be into the corner."
    http://forum.studiotips.com/viewtopic.php?f=1&t=3753
     
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  9. DonnyThompson

    DonnyThompson Distinguished Member

    @Brien Holcombe

    Brien..

    Is this because of the type of material used in the super-chunk bass traps? The density, the shape? Or is it because of its intended purpose, and that any low-frequency treatment is best used with no air gap between it and the boundary?

    Eric Desart said:
    " Don't make a gap for chunks worse than it is. It doesn't have to be airtight. Just shift that thing close to the corner. If it leaves a gap so be it. I think for chunks it matters less than for SCAs, but still even then it's no disaster. Just make stuff and shift it as close as logically can be into the corner. Don't sleep a minute less if some gap remains. It's much more important that you have enough of them than finding THE perfect design." ©2010 Eric Desart

    (Source:
    http://forum.studiotips.com/viewtopic.php?f=1&t=3753)

    So in this case, from what I understand, Mr. Desart is saying that having an air gap between the super-chunk treatment and the boundary is not really a problem, but, is he also saying that nor is it beneficial, either; as perhaps it is with some other types of treatment, such as Clouds, or BB Absorbers, made with OC Rigid or Roxul Safe & Sound ? Can you please explain the differences as to why? And could you also please explain what the "SCA" that he referred to is?

    -d.
     
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  10. avare

    avare Active Member

    Eric was writing specifically about SSCs. As the topic of SSCs evolved, Safe N Sound was recommended as a cheaper, better acoustically material.

    SSC is Studiotips Super Chunks. A fancy name for stack 703 triangles in a corner.
    SCA is Studiotips Corner Absorber. A fancy name for place panels of 703 across a corner making a triangle.

    Enjoy!

    Andre
     
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  11. tga$ound

    tga$ound Active Member

    Hello dudes, I'm gonna build a round corner bass trap. As a triangle, its front is about 41cm, which means, with sides 29 each, I've got a 42 cm²...BUT If I make the front round one fourth of a circle, we're talking about a ~66cm² area bass trap, with same sides but 45,5cm front.

    It adds 57% more area to the original triangle shaped one.

    I uploaded a file taken from https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/238192-ceiling-mounted-bass-traps-pictures.html that illustrates what I'm gonna do.

    Now that I sorted out the shape and side of the bass trap, I need some detail on the little itchy guys, the rockwoollies.

    What's the recommended density for rock wool? As I see in tutorial pictures, it seems denser then the ones I used for the interior of my speech room's dry wall(which i don't remember)...They are usually stacked so tight in those images. I believe there's a concern not to compact them too much, right? What density should I aim for?
     

    Attached Files:

  12. avare

    avare Active Member

    The corner acts a horn. There is no advantage to what you are proposing.

    Andre
     
  13. tga$ound

    tga$ound Active Member

    kmetal, the room calculator is awesome, thanks.
    --
    Andre:

    Sorry, it may be my low english level but... what do you mean by 'the corner acts a horn'?

    Do you mean the idea is of no advantage at all? Well I'm adding more absorbing material to it, how couldn't it be?

    I guess you're telling me that trapping is actually about how big the sides straddling the corner are...?
     
  14. Brien Holcombe

    Brien Holcombe Well-Known Member

    Donny, the SCA was the beginning in the evolution to the SSC. http://forum.studiotips.com/viewtopic.php?t=535 as Andre has pointed out.
     
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  15. Brien Holcombe

    Brien Holcombe Well-Known Member

    Corners are the hard boundaries where all frequencies enter and exit, in the case of low frequency this is the area that has to be deliberate in your intentions, namely reducing low frequency energy. It is common knowledge that sound placed in a corner will increase the level by 6 dB...there's your horn.

    Low frequency trapping it should be designed to reduce the low frequency energy that is in the room.

    So saying that it is of no advantage speaks directly to the intention of reducing low frequency energy. In the case of shaping like a pizza slice, while it will look good in the room, it will not improve the low energy reduction (simply by adding this rounded face) since you have added very little in respect to depth of the trap because the traps are rounded and will not have any added reduction at the target frequency.
     
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  16. tga$ound

    tga$ound Active Member

    I think I understood what you guys are saying...the depth is the 29cm side(that goes along with each wall) so the depth is what matters, not the 'radius' from the corner of the walls to the frontal point...

    So I thought it was the golden idea of the century, the acoustics nobel prize winner...Not this time...I was wrong. It DOES look good, thou... hehe

    Well, I'm around studying the subject of room acoustics in rooms that weren't designed for it. Got some stuff downloaded, trying to figure out some stuff while I build the traps...a lot of them.

    My idea is build all of those traps, and THEN use my Shure KSM44 + room EQ wizard (is this particular mic good for it? For me it is pretty accurate and crystal clear).

    you fellas are really helpful, thanks a lot. Surely I'm coming around to make some stuff clear. Already reading some acoustics books. Thinking about creating a QRD Diffuser on the wall behind the listening position, but I think it would be better to analyse the already trapped room...
     
  17. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Link removed

    This is the one I got. It's probably the most common spl meter if there is such a thing.

    There's calibration file for it available from REW.

    I'm not exactly sure why ldc s and other mics aren't used but it comes down to frequency response. You want the measurement mic to be flat one way or the other.

    On diffusion, like the curved bass trap design it would look cool but be acoustically not very effective.

    Keep it simple. Build your traps, your cloud, and your wall panels. Fire up the REW move the speakers till it can't get better whatever better is to you, and then see where your problems are.

    Willy nilly acoustic treatments can make problems worse, and harder to fix. Read : more expensive.

    Expect realistic results from your realistic circumstances with regard to room and budget. And keep learning, so when your ready you can make the next one that much better.
     
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  18. DonnyThompson

    DonnyThompson Distinguished Member

    @Brien Holcombe @avare @kmetal

    Guys, check me on this...

    I've never heard of an LD condenser being used for testing purposes. I understand that the 44 does have an omni pattern select, but the more common mics used for this are Omni SD's and in particular, Earthworks.

    http://www.earthworksaudio.com/measurement/

    Having a mic that is, as you say, "crystal clear" may be great for recording vocals and instruments, but you're not only looking for "clear"... you're looking for flat. There's a difference. The KSM44 has several pronounced "bumps" in the upper frequency ranges, which could end up skewing your measurements.

    http://cdn.shure.com/specification_sheet/upload/104/us_pro_ksm44a_specsheet.pdf

    But, I could very well be wrong about this. Kyle, Andre or Brien would be the guys to listen to.

    FWIW

    d.
     
  19. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    We used an earthworks at triad-Normandy. I like them a lot better for that than anything else, classical recordings not included in that hate

    Does the diaphragm size probably relates better to measurements purposes because of a faster trainsient response?, I'm guessing there. Either way the test mics with drive racks, are sd, and the earthworks is like tiny diaphram, which may be a new category? I'm just rambling 9am is early for me.
     
  20. tga$ound

    tga$ound Active Member

    Would someone recommend a cheap mic that can be used for acoustic testing purposes?
     

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