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Tuned Bass Trap positioning
Old 4 weeks ago
  #1
Tuned Bass Trap positioning

Quick question: How sensitive are tuned bass traps to positioning?

My <deleted> mode is at 65 Hz but the area around the speakers is already used by other bass traps.

I could place a tuned bass trap left and right in the room at floor level, below the other bass traps. I guess at around 5 m wavelength, it wouldn't make much difference but I'd like to be sure.

Glenn has said

Quote:
Originally Posted by Glenn Kuras View Post
it has to be placed in the area that the problem is coming from
Thanks

Last edited by johannburkard; 4 weeks ago at 07:54 PM.. Reason: It's not the 0-1-0 mode.
Old 4 weeks ago
  #2
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Quote:
Quick question: How sensitive are tuned Bass Traps to positioning?
Very! The trap needs to go where the problem is (just like Glenn says). There's no point putting a tuned device on the ceiling if it is trying to treat the lengthwise axial modes...

In your case, it is the width-wise axial modes, so the devices need to be on the side walls, since that's where the peak velocity is (assuming that you are building velocity-based tuned traps). Best location is in the corners or close to the corners, but anywhere on the wall is still reasonably good for modal issues, and especially down at 65 Hz. One good trick is to use REW to check: set up your mic roughly where you are thinking of placing the trap, and see if there is major activity at 65 Hz: if so, then that's a good spot for the trap.

The device also has to be large enough to do the job: a shoe-box sized device won't have much effect at all on 65 Hz! A closet-sized device will do a much better job in a typical home studio. (Or perhaps two or three smaller devices that together have the area of a closet). Closet-sized devices on both walls will do an even better job.


- Stuart -
Old 4 weeks ago
  #3
Quote:
Originally Posted by Soundman2020 View Post
One good trick is to use REW to check: set up your mic roughly where you are thinking of placing the trap, and see if there is major activity at 65 Hz: if so, then that's a good spot for the trap.
That's a great idea, I'll run a few tests with my microphone in various possible spots.

Quote:
Originally Posted by Soundman2020 View Post
The device also has to be large enough to do the job: a shoe-box sized device won't have much effect at all on 65 Hz!
I hope GIK have done their homework with their 60x60 cm scopus traps.
Old 4 weeks ago
  #4
Thanks @ Soundman2020 for the idea. I've now measured a few spots along the side walls where I could place a tuned bass trap.

To illustrate why, I need to get rid of this guy:

Tuned Bass Trap positioning-ouch.jpg

Now I had incorrectly assumed that this is the 0-1-0 mode (side walls). However, along the side wall, a new mode at 56 Hz appeared.

Tuned Bass Trap positioning-ouch2.jpg

I now realize that this mode is not visible at the desk position because I'm in the middle of the room. The mode I want to get rid of is probably a 1-1-0 and 2-0-0 mode more or less overlapping.

What's interesting is that the 64 Hz mode seems stronger closer to the floor than to the ceiling. It also becomes stronger as you approach the height of the desk. Here is the response at floor level after the speakers:

Tuned Bass Trap positioning-position1.jpg

And here is it at the height of the desk. Decay at 64 Hz is much longer here:

Tuned Bass Trap positioning-position2.jpg

Extrapolating, I would guess that at the height of the desk would be a good position to place tuned traps for this frequency, not close to the front wall/speakers. Also, the rear wall may be good, too.

If you want to take a look, the REW .mdat is at https://johannburkard.de/resources/J...pus-tests.mdat (22 MB).
Attached Thumbnails
Tuned Bass Trap positioning-ouch.jpg   Tuned Bass Trap positioning-ouch2.jpg   Tuned Bass Trap positioning-position2.jpg   Tuned Bass Trap positioning-position1.jpg  
Old 4 weeks ago
  #5
Lives for gear
 

Yup, you sure do have some nasty ringing there!

I'm not sure if you saw this very recent thread about a guy who built his own tuned traps, with great success, tuned to a similar range to what you need (a bit lower, actually):

Helmholtz for the people!

He just needs to lower the Q a little to cover a slightly wider range, which he can do with fabric (pay no attention to the strange comments from the dreamers). Trying different types of fabric, or perhaps even very thin, light insulation (eg, kitchen hood filter material just a couple of mm thick) will do the job.

One thing you could do is to build something like he did, tuned to your problematic frequencies, then slide it around the locations you identified to find the best spot for it. You might need a couple of those on opposite walls to get the full effect.

What other treatment do you have in your room? From the MDAT, there's still more that could be done to improve it. Got any photos of the room?

- Stuart -
Old 4 weeks ago
  #6
Quote:
Originally Posted by Soundman2020 View Post
What other treatment do you have in your room? From the MDAT, there's still more that could be done to improve it. Got any photos of the room?
Lots. Will post photos after everything is installed and all the spots on the walls have been painted over (oops).
Old 4 weeks ago
  #7
Quote:
Originally Posted by Soundman2020 View Post
Yup, you sure do have some nasty ringing there!
...even worse I now think I have three modes around 65 Hz instead of just two. amroc suggests that at least. Due to the window, it's not easy to calculate the "real" dimensions of the room but amroc is close to what I see in REW.

However, I played with REW's room simulator and I might better off moving a bit to the front which would also move me closer to the speakers.

I'm currently 1,75 m away from the speakers and even though the impulse response has nothing anymore above -20 dB for the first couple of ms, I can still tell I'm sitting too far from the speakers. Just not used to that distance.
Old 4 weeks ago
  #8
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akebrake's Avatar
 

Pink Periodic Noise

Quote:
Originally Posted by johannburkard View Post
...even worse I now think I have three modes around 65 Hz instead of just two.
That's correct. The tangential mode at ≈66 Hz is weak in the middle of the room. (if observed in "isolation") See Hunecke. (or amroc) pic 1

1. Check acoustical dimensions that correlate with measured response.

2. A good mic/ spkr position can be found quite conveniently by chosing Generator: Pink Periodic Noise (Pink PN) while simultanously watching the RTA when moving the mic /or speaker. See result in real time!

Pic 2. (That's my built in Mac spkr and mic. Not my room )

Tuned Bass Trap positioning-spkr-pos-rta-tst.jpg
Pic 3. Compare Sweep to Pink PN.

Best
Attached Thumbnails
Tuned Bass Trap positioning-hun-revised-johann.jpg   Tuned Bass Trap positioning-spkr-pos-rta-tst.jpg   Tuned Bass Trap positioning-pink-pn-vs-sweep.jpg  
Old 4 weeks ago
  #9
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Starlight's Avatar
 

Quote:
Originally Posted by johannburkard View Post
Will post photos after everything is installed and all the spots on the walls have been painted over (oops).
Photos of before, during and after are better than just the room after all is finished.
Old 4 weeks ago
  #10
Quote:
Originally Posted by Starlight View Post
Photos of before, during and after are better than just the room after all is finished.
Old 4 weeks ago
  #11
As suggested by REW's Room Sim tool, I've tried moving the desk closer to the front wall and that really helped. The hole between 70 and 85 Hz is gone.

The sound is different, more upper bass and I'm also sitting closer to the speakers which I wanted for a while.
Attached Thumbnails
Tuned Bass Trap positioning-desk.jpg  
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