Placement of Bass Traps when no neat Corners
Old 3rd December 2012
  #1
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Thread Starter
Placement of Bass Traps when no neat Corners

Hi,

I've recently purchased some acoustic tiles and bass traps to treat a very small room (W210cm, L210cm, H250cm).

The ceiling corners of the room are rather awkward and the bass traps i have purchased (60cms in length) are too big to position without any space being left behind them or, in the case of one corner, imposing on the doorway!

I've taken some pictures which are below to help give you an idea of the situation.

Picture 2 seems like the least troublesome one to deal with. I expect I should just trim down the bass trap to to not encroach on the air conditioning unit...?

I'm quite new to this and i'm unsure if I should be aiming for some kind of symmetry in the placement and size of my bass traps in the corners of this room. Given how these corners all present different issues, I'm unsure achieving any kind of symmetry will be possible.

Really hope someone can give me a bit of guidance here :-)

Corner 1 - Distance from ceiling to 1st edge is 37cm. Sticking out from main side wall by 16cm.



Corner 2 - Air conditioner housing 51cms down from the ceiling



Corner 3 - Above the Door (which would be behind my right shoulder, when facing my monitors). The door frame is about 18cms down from the ceiling and it sticks out a couple of cms. The sticking out bit at the top of the adjacent wall is 37cm in length from ceiling to edge.

Old 3rd December 2012
  #2
Gear addict
 

Oh dear "Unclebob", I am afraid whatever you do to this room it is not going to be great, two main reasons:- it is really too small and the geometry is too square, in fact it's almost a cube, which is about as bad as you get! Just take a look at the Room modes on one of the many "theoretical calculators" out there, you will see what I mean!!

Do you have means to measure the room with Room EQ Wizard (...it's free) to verify the problems??

That being said the best you can probably do is aim for a "dead" room. Go for max quantity "pressure based" (ideally tuned) trapping over a good proportion of the flat walls available, to help with the axial modes and deep porous treatment where there are gaps! You will end up with a dead sounding room but you can't really do much
serious design stuff with such a small room, sorry to be the bearer of bad news.

What you do have is good ceiling height (2.5m?). Typically from those dimensions you will have a vertical axial mode at 69Hz (+/- a few Hz, don't hold me to this there are other variables!). I noticed a strange detail over the door where the door frame seems much higher than the door opening? What I would do first is drop the whole ceiling about 300 mm. With a wooden support frame (also continued into the door frame, above the opening! Then, lay 100mm of fibreglass or light mineral wool (somewhere between "pink fluffy" and OC701). Finally finish the underside with 3mm ply, typically about 2kg/m2. [So you get, ply membrane, 100mm porous, 200mm air-gap]

The wall with the "bulkhead" I would be tempted to use the natural recess to create another bass trap (similar to the ceiling) with only 100mm air-gap.

The bass traps you have already purchased can be spread around remaining corners and surfaces. Fill in gaps as necessary with the tiles spread out evenly around the room. As, I say all you can really do with this room is address the LF modes as best you can with pressure absorbers and use as much deep porous as you can, wherever you can.(preferably with air-gap if you can afford the space)

Hope some of that makes sense.
Old 3rd December 2012
  #3
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seen-da-sizer's Avatar
 

Quote:
Originally Posted by UncleBob View Post
I did have a similar corner problem, although not as drastic as yours. In my case I simply built my corner traps over the ceiling beam. Not perfect, but still it did the job:



Here is my corner problem with the door I had to cover:



In your case, I suggest to build the corner trap around the AC, leaving a gap for it. You will not have perfect symmetry, but perfect in a home environment is usually hard to achieve anyway. Build more ceiling-wall corner traps, to get better bass absorption.
Old 6th December 2012
  #4
Gear interested
 

Thread Starter
Hi..thanks for the replies; sorry it's taken me a while to respond.

Unfortunately I'm not in a position to make any amendments to the room shape, as I'm in rented accommodation (and my landlady is a right old battle axe!).

Also, I'm more of a hobbyist musician and I have to draw a line at how much time I should spend treating this room...though the feedback provided is tempting!

To give you some extra context, I've never felt the need to treat a room in the past, but the room i'm currently using (i moved into a new apartment a month ago) has a fairly noticeable echo, especially on low frequencies. If I can reduce that significantly, then i'll be happy.

Some good news since my original post - i discovered i'd initially measured my room incorrectly! Rather than 210w x 210L, it's actually about 210 x 230. Apologies for that. As a result i've moved my room around so the monitors are facing down the long(ish) part of the room.

So now the two most problematic corners (photos 1 & 3) are behind my right and left shoulders respectively. The other two corners (the ones I can see in my seated position, behind the monitors) should be quite easy to apply my bass traps to. I'm sure I read that these corners are the first one's i should apply my traps to..? Is that correct?

In my difficult corners, couldn't i just put a bass trap vertically at the top, then another horizontally, tucked into corner created by the cut into the wall underneath?

The bass traps i have purchased look a bit like these:

Old 6th December 2012
  #5
Gear addict
 

Quote:
Originally Posted by UncleBob View Post
In my difficult corners, couldn't i just put a bass trap vertically at the top, then another horizontally, tucked into corner created by the cut into the wall underneath?
The quick answer, yes you can!


There are two ways to approach this:

1. The right way ie measure the room with an analysis package like Room EQ Wizard (free from hometheatreshack). Then treat the space accordingly by identifying the problem walls and, importantly, the correct areas of walls/ceiling to treat.

OR

2. The "sling it up in the corner and hope" approach.


I fully accept both that you are in rented accomodation and are a musician, so you just want a good sounding room without a Masters in acoustics right? But, use this as an opportunity to learn

Take a look at this hunecke.de | Room Eigenmodes Calculator it is very good for visualising the issues. Insert your room dimensions. The dark areas are pressure maxima (white areas by inference minima) of standing waves (room modes, eigenmodes) in your room. Modal issues are, I believe, why you are experiencing a boomy bottom end!?. Normally one would expect to treat these modes with pressure based absorbers, these are tuned, panel type absorbers. If you look at the first three modes on the above mode calculator these are the fundamental axial modes, arguably the strongest modes and in your case 69, 75, and 82Hz, right in the crucial bass drum/ bass guitar part of the spectrum. You are going to get ringing (longer decay time) around that area. Importantly notice that the pressure maxima of those primary modes are across the whole area of their associated wall, not just at the corners!

The "bass" traps you have bought are really glorified "velocity" based absorbers, ie they are porous foam (of some sort). You will notice from the above mode calculator that all modes to a greater or lesser extent have pressure maxima in the tri-corners. This is the reason that they are sold/marketed on the basis of corner placement for max effect, despite the fact that technically they are not pressure absorbers. By tri-corner placement you are "bracketing" the number of modal pressure maxima the treatment is in contact with, all be it with velocity based absorbers. They will have some effect of course (not at very low frequency) however in a room such as yours if you are just going to have corner placement then be aware that you are going to need a lot of them and they will have minimal effect on the axial modes.

When you have put up all the treatment you can afford/justify (in a rented room) experiment with listener/loudspeaker relative placement. You are not going to have much of a tolerance for moving about but you should be able to find an optimum seating position with respect to loudspeakers to minimise modal issues. If I were you I would start with seating in the centre of the room and experiment with small adjustments from there. When you are as happy as you can be with relative listener/loudspeaker location, think about some free standing absorbers (DIY on legs?) to cover first reflection points on the side walls? Good luck
Quote
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Old 7th December 2012
  #6
Gear interested
 

Thread Starter
Thanks Icecube. You're right, this is an opportunity to get my head round a few things. This weekend I'll go over some of the stuff you mentioned and report back.

:-)
Old 7th December 2012
  #7
Lives for gear
 
Jens Eklund's Avatar
 

Quote:
Originally Posted by Icecube1 View Post
The quick answer, yes you can!


There are two ways to approach this:

1. The right way ie measure the room with an analysis package like Room EQ Wizard (free from hometheatreshack). Then treat the space accordingly by identifying the problem walls and, importantly, the correct areas of walls/ceiling to treat.

OR

2. The "sling it up in the corner and hope" approach.


I fully accept both that you are in rented accomodation and are a musician, so you just want a good sounding room without a Masters in acoustics right? But, use this as an opportunity to learn

Take a look at this hunecke.de | Room Eigenmodes Calculator it is very good for visualising the issues. Insert your room dimensions. The dark areas are pressure maxima (white areas by inference minima) of standing waves (room modes, eigenmodes) in your room. Modal issues are, I believe, why you are experiencing a boomy bottom end!?. Normally one would expect to treat these modes with pressure based absorbers, these are tuned, panel type absorbers. If you look at the first three modes on the above mode calculator these are the fundamental axial modes, arguably the strongest modes and in your case 69, 75, and 82Hz, right in the crucial bass drum/ bass guitar part of the spectrum. You are going to get ringing (longer decay time) around that area. Importantly notice that the pressure maxima of those primary modes are across the whole area of their associated wall, not just at the corners!

The "bass" traps you have bought are really glorified "velocity" based absorbers, ie they are porous foam (of some sort). You will notice from the above mode calculator that all modes to a greater or lesser extent have pressure maxima in the tri-corners. This is the reason that they are sold/marketed on the basis of corner placement for max effect, despite the fact that technically they are not pressure absorbers. By tri-corner placement you are "bracketing" the number of modal pressure maxima the treatment is in contact with, all be it with velocity based absorbers. They will have some effect of course (not at very low frequency) however in a room such as yours if you are just going to have corner placement then be aware that you are going to need a lot of them and they will have minimal effect on the axial modes.

When you have put up all the treatment you can afford/justify (in a rented room) experiment with listener/loudspeaker relative placement. You are not going to have much of a tolerance for moving about but you should be able to find an optimum seating position with respect to loudspeakers to minimise modal issues. If I were you I would start with seating in the centre of the room and experiment with small adjustments from there. When you are as happy as you can be with relative listener/loudspeaker location, think about some free standing absorbers (DIY on legs?) to cover first reflection points on the side walls? Good luck
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