Login / Register
 
Positioning of Bass Traps
New Reply
Subscribe
edvedder
Thread Starter
#1
25th March 2013
Old 25th March 2013
  #1
Gear maniac
 
Joined: Aug 2011
Posts: 180

Thread Starter
edvedder is offline
Positioning of Bass Traps

I have two extra bass traps that I'm trying to figure out where to place. I currently have the two main corners taken care of already, as illustrated by the green markings.

Is there any point in placing the bass traps against the wall directly in front of the listening position (behind the speakers), or would it be more useful having it in the far back corner of the room (to the left of the couch)?
Attached Thumbnails
Positioning of Bass Traps-bass-traps.jpg  

Last edited by edvedder; 25th March 2013 at 06:28 PM.. Reason: added pic
#2
25th March 2013
Old 25th March 2013
  #2
Gear Guru
 
Ethan Winer's Avatar
 
Joined: Oct 2002
Location: New Milford, CT, USA
Posts: 13,667

Ethan Winer is offline
Lightbulb

Quote:
Originally Posted by edvedder View Post
Is there any point in placing the bass traps against the wall directly in front of the listening position (behind the speakers)
Not usually:

Front Wall Absorption

Quote:
would it be more useful having it in the far back corner of the room (to the left of the couch)?
As with sub placement (your other thread), the only way to know for sure is to measure as you experiment.

--Ethan

The Acoustic Treatment Experts
__________________
Ethan's Audio Expert book
edvedder
Thread Starter
#3
25th March 2013
Old 25th March 2013
  #3
Gear maniac
 
Joined: Aug 2011
Posts: 180

Thread Starter
edvedder is offline
Thanks. You're a tremendous help!

One other question - my wall left of the listening position is all windows, so I am obviously unable to place an absorber panel there. How does this affect the sound? Is there any way to compensate for this?
#4
26th March 2013
Old 26th March 2013
  #4
Gear Guru
 
Glenn Kuras's Avatar
 
Joined: Jul 2005
Location: Atlanta, GA
Posts: 16,623

Glenn Kuras is offline
Quote:
Originally Posted by edvedder View Post
Thanks. You're a tremendous help!

One other question - my wall left of the listening position is all windows, so I am obviously unable to place an absorber panel there. How does this affect the sound? Is there any way to compensate for this?
If in the early reflection point then it does need to be treated. Watch here.
Video Early or First Reflection Points - GIK Acoustics

As far as the front wall you would only need bass trapping if controlling SBIR.
Speaker Boundary Interference Response SBIR GIK Acoustics
__________________
Glenn Kuras
GIK Acoustics USA
GIK Acoustics Europe
http://www.gikacoustics.de (German Translation)
404 492 8364 (USA)
+44 (0) 20 7558 8976 (Europe)

Built in Slat design (Scattering/Diffusion) on all Bass Traps click here
#5
26th March 2013
Old 26th March 2013
  #5
Gear Guru
 
Ethan Winer's Avatar
 
Joined: Oct 2002
Location: New Milford, CT, USA
Posts: 13,667

Ethan Winer is offline
Lightbulb

Quote:
Originally Posted by edvedder View Post
my wall left of the listening position is all windows, so I am obviously unable to place an absorber panel there.
You do need absorption at that side's reflection point. Even a thick curtain would help, but a panel on a stand would be better, as shown in the photo below.

--Ethan

#6
26th March 2013
Old 26th March 2013
  #6
Gear interested
 
MediaRooms's Avatar
 
Joined: Jun 2011
Location: Outer L.A. area
Posts: 20

Send a message via Yahoo to MediaRooms
MediaRooms is offline
If you aren't experiencing any LF issues, consider not using them at all. They might deteriorate your room sound. No need to use something just because you have it.

That being said, LF transmits as pressure, whereas frequencies above that transmit as particle motion. That means any type of LF absorption should be at the point of highest pressure, which is at the room surfaces. Particle motion is greatest away from the room surfaces, so putting an LF absorber in the middle of the room will diminish it's effectiveness.

So the most effective and convenient location would be built into a wall.
#7
26th March 2013
Old 26th March 2013
  #7
Gear Guru
 
DanDan's Avatar
 
Joined: Aug 2003
Location: Cork Ireland
Posts: 10,966

DanDan is online now
Testing

Measurement will ultimately answer all questions.
+1 to Ethan and Glenn's comments, treat the side reflection points and make a cloud. If your traps are really bass only traps and if your front corners have only two small traps, I would guess that adding them to the front corners or placing both in the available back corner would be useful.

DD
#8
26th March 2013
Old 26th March 2013
  #8
Lives for gear
 
Joined: Nov 2008
Posts: 597

dodittydada is offline
Quote:
Originally Posted by MediaRooms View Post
If you aren't experiencing any LF issues, consider not using them at all. They might deteriorate your room sound. No need to use something just because you have it.

That being said, LF transmits as pressure, whereas frequencies above that transmit as particle motion. That means any type of LF absorption should be at the point of highest pressure, which is at the room surfaces. Particle motion is greatest away from the room surfaces, so putting an LF absorber in the middle of the room will diminish it's effectiveness.

So the most effective and convenient location would be built into a wall.
Any type? Or just pressure type traps? I ask because I thought the point of getting porous traps a few inchs from the wall surface was so that it can act on the LF wave while it still has some velocity. I.E before it hits the surface of the wall and becomes pressure.
#9
27th March 2013
Old 27th March 2013
  #9
Gear interested
 
MediaRooms's Avatar
 
Joined: Jun 2011
Location: Outer L.A. area
Posts: 20

Send a message via Yahoo to MediaRooms
MediaRooms is offline
The pressure doesn't jump up at the surface of the wall, it rises as you get closer to it. So as you approach a surface, velocity ramps down, and pressure ramps up.

The main reason for spacing a resistive absorber away from a wall is to lower its LF limit. The general rule of thumb is the thickness of the absorber, including the air gap, is a quarter wavelength of LF limit. Just a rough rule of thumb...

Since low frequency is propagated by pressure than rather velocity, the best place to influence it is at a room surface. I find it handy to think of frequencies below 300 Hz. as being pressure and above being particle velocity. But our physical world is analog, so everything ramps from one state to another.

But if you use an air gap, it needs to be sealed, like enclosing the absorber and air gap in an airtight frame.
#10
27th March 2013
Old 27th March 2013
  #10
Lives for gear
 
Joined: May 2009
Posts: 3,365

Syncamorea is offline
Quote:
Originally Posted by MediaRooms View Post
But our physical world is analog, so everything ramps from one state to another.
That's an interesting way to put it. Obviously light is a quantum phenomenon but our experience with it in normal life is very thermodynamic / analog. I had a really awesome prof that taught a grad statistical thermodynamics class that put it all in perspective very well. Your description of LF pressure crossing over to higher frequencies and velocity is very similar to what I was taught. Well done, take a bow!
#11
27th March 2013
Old 27th March 2013
  #11
Gear Guru
 
DanDan's Avatar
 
Joined: Aug 2003
Location: Cork Ireland
Posts: 10,966

DanDan is online now
Interesting

You make several interesting points media, bow away....

I too am delighted with your sliding scale ramping analogies.

But....

The propagation by pressure is cute too, but I always thought waves were propagated by the see sawing between two complimentary out of phase energies. e.g. ElectroMagnetic.
I have a big problem at the moment trying to imagine exactly where the pressure highs are for tangential modes. The usual bounce diagrams suggest the bounce point (HP ZeroV) is mid wall, but the pressure graphs show HP in the corners and elsewhere.

More interestingly (for me).
Quote:
But if you use an air gap, it needs to be sealed, like enclosing the absorber and air gap in an airtight frame.
Intuitively this strikes me as correct, but that would mean RealTraps, GIK and all of use who recommend using airgaps with individual panels are wasting everyones time and effort. If that indeed is the case, I would love to see some test evidence. Perhaps that 'needs' is a tad overstatement.

I think it much more likely that your ramping analogy applies here to.
e.g. One panel on it's own, is not going to benefit much from an airgap without sealing (which would also have that old drum head side effect).
While many panels with only small gaps between, tends towards being a contiguous boundary.

But aren't we forgetting angles of incidence. And what happens to sound that hits the thin sides and the surface facing the boundary. All of this would be blocked by the frame.
But then the frame has a diffractive benefit....
Swings, roundabouts, and ramps, methinks. But if you do have some data, links, tests, I really would love to see them.

DD
#12
27th March 2013
Old 27th March 2013
  #12
Lives for gear
 
Joined: May 2009
Posts: 3,365

Syncamorea is offline
Quote:
Originally Posted by DanDan View Post
The propagation by pressure is cute too, but I always thought waves were propagated by the see sawing between two complimentary out of phase energies. e.g. ElectroMagnetic.
In a listening room, my mental process regarding pressure ignores the electrical side of the system and starts at the drivers of the monitors. The physics from there on is pretty thermodynamic, kind of entropy in action via vibrational transitions.

Quote:
Originally Posted by DanDan View Post
Intuitively this strikes me as correct, but that would mean RealTraps, GIK and all of use who recommend using airgaps with individual panels are wasting everyones time and effort.
But the two domains are progressively shared. So a pressure transducer will still couple to some degree in the velocity zone and vice-versa.
#13
27th March 2013
Old 27th March 2013
  #13
Lives for gear
 
Joined: May 2012
Posts: 2,320

OpusOfTrolls is offline
Pressure and Velocity exist everywhere the soundwave exists. The fact that there ARE pressure increases at the boundary is related to reflection. There is no destructive interference at the boundary.
#14
27th March 2013
Old 27th March 2013
  #14
Gear Guru
 
Glenn Kuras's Avatar
 
Joined: Jul 2005
Location: Atlanta, GA
Posts: 16,623

Glenn Kuras is offline
#15
27th March 2013
Old 27th March 2013
  #15
Gear Guru
 
DanDan's Avatar
 
Joined: Aug 2003
Location: Cork Ireland
Posts: 10,966

DanDan is online now
No Pressure

#16
27th March 2013
Old 27th March 2013
  #16
Gear Guru
 
Glenn Kuras's Avatar
 
Joined: Jul 2005
Location: Atlanta, GA
Posts: 16,623

Glenn Kuras is offline
Quote:
Glenn, the sealed plus airgap fibre trap sounds intriguing.
Have you ever tested GIK traps with sealed skirts vs open?
We have done it with "A" mound and "J", but hard to compare as the J mount was spread around the lab with a gap. The point was when something is broad band sealing the sides to the wall won't help. With that said I have seen people use something tuned and put broad band in front of it to absorb a reflection. Mostly, but not all the time, done on the back wall. Seen it done with diffusion also.
#17
27th March 2013
Old 27th March 2013
  #17
Gear Guru
 
DanDan's Avatar
 
Joined: Aug 2003
Location: Cork Ireland
Posts: 10,966

DanDan is online now
J Mount

Thanks Jeff, if you would oblige me I want to tease this out a little more.
If I remember correctly the J Mount seems intended to measure fibre used in suspended ceilings. Afaik the spec is a contiguous sample of say 10 Sq Metres or so, but WITH a sealing skirt.
If this is broadly speaking correct, then I have to say I have seen no tests of individualised panel traps with airgaps with and without skirts. PHwooarrr.
Of course I would love to.

Elsewhere I have seen that acoustically solid or porous framing shows little to no difference in absorption. i.e. The absorbtion of the edge areas is replaced by diffractive absorption of the hard edge.

So it seems to me possible that media may well be right, in that skirted panel traps may perform better.
Again, if anyone has a test please.....

DD
#18
27th March 2013
Old 27th March 2013
  #18
Lives for gear
 
Joined: May 2012
Posts: 2,320

OpusOfTrolls is offline
The calculators used to predict the performance of porous absorbers assume an infinite baffle. This means the soundwave would never reach the edge of the panel.
#19
28th March 2013
Old 28th March 2013
  #19
Gear Guru
 
Glenn Kuras's Avatar
 
Joined: Jul 2005
Location: Atlanta, GA
Posts: 16,623

Glenn Kuras is offline
Quote:
If I remember correctly the J Mount seems intended to measure fibre used in suspended ceilings. Afaik the spec is a contiguous sample of say 10 Sq Metres or so, but WITH a sealing skirt.
That would be "E" test. I believe it has a 16" gap if I remember correctly and yes it is for drop ceiling tiles.
#20
28th March 2013
Old 28th March 2013
  #20
Gear Guru
 
DanDan's Avatar
 
Joined: Aug 2003
Location: Cork Ireland
Posts: 10,966

DanDan is online now
A and E

Sorry Glenn, it's been a while and we have a different set of standards over here.

The silence is gettin kinda loud to my ear.

Does anyone have tests showing Skirts vs Open panels with the airgap?

DD
#21
28th March 2013
Old 28th March 2013
  #21
Gear Guru
 
Glenn Kuras's Avatar
 
Joined: Jul 2005
Location: Atlanta, GA
Posts: 16,623

Glenn Kuras is offline
Quote:
The silence is gettin kinda loud to my ear.
????????
#22
28th March 2013
Old 28th March 2013
  #22
Gear Guru
 
DanDan's Avatar
 
Joined: Aug 2003
Location: Cork Ireland
Posts: 10,966

DanDan is online now
SShhh

LOL, sorry Glenn, you should know me better. I am referring to the fact that I have asked the same question a couple of time now with no answer. i.e. if there were tests showing better behaviour with skirts a couple of times in a couple of threads. In both cases it was because of mediaroom's intriguing statement. I neither doubt the statement nor blindly accept it. I am genuinely curious. Skirted panel traps could be a quite viable and practical design IMO. IF there is a benefit.
I have made the same point as your self about the extra surface area of absorbent which is lost by skirting, vs potential 'drum head' effects and whatever other benefit the sealing may bestow.
So to be clear.
Mediarooms, with respect, I would appreciate any answer. A reason why in your opinion
Quote:
if you use an air gap, it needs to be sealed, like enclosing the absorber and air gap in an airtight frame
If this is true, then we should be doing it and encouraging it I reckon.

DD
#23
28th March 2013
Old 28th March 2013
  #23
Lives for gear
 
avare's Avatar
 
Joined: May 2004
Location: Hamilton, On Canada
Posts: 4,829

avare is offline
Quote:
Originally Posted by DanDan View Post
LOL, sorry Glenn, you should know me better. I am referring to the fact that I have asked the same question a couple of time now with no answer. i.e. if there were tests showing better behaviour with skirts a couple of times in a couple of threads. In both cases it was because of mediaroom's intriguing statement. I neither doubt the statement nor blindly accept it. I am genuinely curious. Skirted panel traps could be a quite viable and practical design IMO. IF there is a benefit.
I have made the same point as your self about the extra surface area of absorbent which is lost by skirting, vs potential 'drum head' effects and whatever other benefit the sealing may bestow.
So to be clear.
Mediarooms, with respect, I would appreciate any answer. A reason why in your opinion
If this is true, then we should be doing it and encouraging it I reckon.
It was difficult to parse the post for quoting purposes so I quoted all of it.

1. I am not Mediarooms.
2. Do the lines 1 and 2 on graph on page 5 of the attachment help any?
3. Thank you Eric. You are missed!

Andre
Attached Files
File Type: pdf Playing-with-baffles.pdf (572.7 KB, 47 views)
__________________
Good studio building is 90% design and 10% construction.
#24
28th March 2013
Old 28th March 2013
  #24
Gear Guru
 
Glenn Kuras's Avatar
 
Joined: Jul 2005
Location: Atlanta, GA
Posts: 16,623

Glenn Kuras is offline
Got yea Dan Dan,
Not sure if this is much help but our panels are built with air gap in the back so in a way it is "sealed" per say when mounted flush. I really don't think it being sealed adds to it, but the gap does. I always recommend spacing off the wall even further if they can.
#25
28th March 2013
Old 28th March 2013
  #25
Gear Guru
 
DanDan's Avatar
 
Joined: Aug 2003
Location: Cork Ireland
Posts: 10,966

DanDan is online now
Ta

Asked and answered. Thank you Andre, and Eric.
That document is a treasure trove.
I mixed a few concerts in Leuven over the last few years.
Perhaps I could have met Eric.....
DD
edvedder
Thread Starter
#26
1st April 2013
Old 1st April 2013
  #26
Gear maniac
 
Joined: Aug 2011
Posts: 180

Thread Starter
edvedder is offline
My two additional bass traps have a thin wood backing on one side, and the other side is open. I have a blanket wrapped around to keep the mineral wool inside.

My question is this: Which way should I have the traps facing the wall? With the open side facing the wall or the side with the wood backing facing the wall?
#27
1st April 2013
Old 1st April 2013
  #27
Gear Guru
 
Glenn Kuras's Avatar
 
Joined: Jul 2005
Location: Atlanta, GA
Posts: 16,623

Glenn Kuras is offline
The wood would go against the wall. A proper bass trap for straddling the corner or spacing off the wall should not have a wood back.
New Reply Submit Thread to Facebook Facebook  Submit Thread to Twitter Twitter  Submit Thread to LinkedIn LinkedIn  Submit Thread to Google+ Google+ 
 
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Similar Threads
Thread
Thread Starter / Forum
Replies
Cojo / Bass traps, acoustic panels, foam etc
1260
Watersound / So much gear, so little time!
21
Ydope / Low End Theory
34
mad_hatter / Low End Theory
3
fatgaz / Low End Theory
64

Forum Jump

SEO by vBSEO ©2011, Crawlability, Inc.