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Treating 45Hz in a fully bass trapped room Modular Synthesizers
Old 4 weeks ago
  #61
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Quote:
Originally Posted by johnnyc View Post
Ideally you want the membrane absorber to be physically large and not too stiff.
On the other hand, rigid panel traps do actually work rather well, when constructed correctly, and it can be effective to have a few smaller ones, rather then one large one.... inertia can be an issue with large, massive panels tuned to low frequencies. As Andre said; stiffness or rigidity isn't an issue here. Maybe you are confusing the concept of limp membranes with MSM walls?
Old 4 weeks ago
  #62
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Quote:
Originally Posted by johnnyc View Post
You are thinking like a fellow RF engineer Or were you mixed signal IC?

You are correct in the wave transfer thinking, but perhaps you are overlooking the 3rd component, being transmission in addition to absorption and reflection. For a typical drywall wall, the MSM resonance is also the point where the isolation is lowest, transmission is greatest. So at resonance the wave would see a good impedance match, which in turn would minimize the room mode. But you don't necessarily have a very large amount of absorption, you get some but the drywall does not act like a true limp membrane.
Ha! Mixed signal IC. But, familiar with transmission line theory from my test days.

But yes, transmission. My thinking was that whatever is transmitted beyond the drywall is essentially absorbed as far as the room is concerned. But then I guess we have a moving wall and a cavity and then another wall in this case, which complicates things.

The mass of the wall definitely plays into it, beyond its role in forming a resonator. The transient response will be highly dependent on the wall mass. If the wall is a resonator, the magnitude of the oscillations will build at a rate inversely proportional to the wall mass, reducing its reflective properties and increasing it's transmission properties, until the amount of damping in the wall equals the amount of power transferred to the wall via it's load on the air.
Old 4 weeks ago
  #63
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Quote:
Originally Posted by Soundman2020 View Post
Seem to be a common ailment here on GS... lots of old timers apparent suffer from it....
q.e.d.
Old 4 weeks ago
  #64
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Quote:
Originally Posted by u87allen View Post
Ha! Mixed signal IC. But, familiar with transmission line theory from my test days.
Then maybe the electrical and mechanical analogies may be of use for you: Electrical Mechanical Analogs - Erik Cheever
there is an example of what we are discussing here (but with an additional wall). A mass-spring-mass system ca be descripted as a series inductance (the spring i.e. the air) and two parallel capacitors (the masses). Damping can be introduced with resistors. So this wall forms a third order low pass filter.
Old 4 weeks ago
  #65
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Quote:
Originally Posted by fabelle View Post
Then maybe the electrical and mechanical analogies may be of use for you: Electrical Mechanical Analogs - Erik Cheever
there is an example of what we are discussing here (but with an additional wall). A mass-spring-mass system ca be descripted as a series inductance (the spring i.e. the air) and two parallel capacitors (the masses). Damping can be introduced with resistors. So this wall forms a third order low pass filter.
Thanks.

I've done some speaker modeling in the past and I think this is kind of like the reverse of that, air driving a diaphragm instead of a diaphragm driving air. I'm going to take that approach this weekend and take a crack at this problem.

But basically, SPL converted to Pascals times the area of the wall is the driving force. Any phase shift between the wall vibration and the sound pressure at the wall's surface represents a partial reflection and transmission.
Old 4 weeks ago
  #66
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Quote:
Originally Posted by u87allen View Post
I'm going to take that approach this weekend and take a crack at this problem.
It is not clear what problem you are refering to. With regards to TL the holy grail is Ben Sharp's Wyle WR 73-5. I am having typing problems so search for it and there is a post where I linked the file.

Enjoy!
Attached Files
File Type: pdf Wyle WR 73-5R.pdf (11.69 MB, 39 views)
Old 4 weeks ago
  #67
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Quote:
Originally Posted by avare View Post
It is not clear what problem you are refering to. With regards to TL the holy grail is Ben Sharp's Wyle WR 73-5. I am having typing problems so search for it and there is a post where I linked the file.

Enjoy!
Dang, looks like a good read! Thank you
Old 4 weeks ago
  #68
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Quote:
Originally Posted by Jason Foi View Post
Dang, looks like a good read! Thank you
Yup. It's excellent. Nearly 50 years old, but still one of the best and most complete papers on isolation that you'll find anywhere. Andre put me onto that many many years ago, and I'm REALLY glad he did.

- Stuart -
Old 4 weeks ago
  #69
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Quote:
Originally Posted by u87allen View Post
Thanks.
I've done some speaker modeling in the past and I think this is kind of like the reverse of that, air driving a diaphragm instead of a diaphragm driving air. I'm going to take that approach this weekend and take a crack at this problem.
yes, thats where this approach is very useful, in electroacustical devices. Microphones and speakers can be modeled from electrical input to acoustical output and vice versa.
Old 4 weeks ago
  #70
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Quote:
Originally Posted by akebrake View Post
I'm not Stuart but

Your Soundcard Freq Response was a new one to me.

They usually shows a flat line from ≈2 Hz to 1/2 sample rate)
The mic cal file looks normal.

Possible feedback, ground loop or..? I don't know

Best
Yeah. Hmm. I must have screwed up the soundcard measurement. I have an Apogee Element, so I would expect it to be pretty flat.

All the rest of the measurements and setup in Stuart's instructions was easy to do but for some reason I could not get the soundcard measurement to work.

Do I need to do ALL my measurements again or can I just do the soundcard measurement?
Old 4 weeks ago
  #71
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Quote:
Do I need to do ALL my measurements again or can I just do the soundcard measurement?
Just re-do the sound card measurement. You can apply the new calibration file to all of your existing measurements, no problem. The line should be almost flat, with just a slight "wiggle" towards the extreme ends. Most sound cards give quite flat response these days.

- Stuart -
Old 4 weeks ago
  #72
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Quote:
Originally Posted by Soundman2020 View Post
Just re-do the sound card measurement. You can apply the new calibration file to all of your existing measurements, no problem. The line should be almost flat, with just a slight "wiggle" towards the extreme ends. Most sound cards give quite flat response these days.

- Stuart -
Thanks Stuart. I created a calibration file for my soundcard and I think it worked correctly this time.

https://www.dropbox.com/s/cvsd1yytue...ent46.cal?dl=0

Please let me know if this one works.

Edit: I updated the mdat file to use the new calibration file:

https://www.dropbox.com/s/w3p1w7mdtt...udio.mdat?dl=0

Last edited by metaBit; 4 weeks ago at 10:26 PM..
Old 2 weeks ago
  #73
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akebrake's Avatar
 

Switch Off monitoring

Quote:
Originally Posted by metaBit View Post
Please let me know if this one works.
No. You have to switch off monitoring (= feedback) which creates this comb filter.
Then, start doing valid room measurements.
No loopback needed. Use one sweep (not 2)

Quote:
Edit: I updated the mdat file to use the new calibration file:

https://www.dropbox.com/s/w3p1w7mdtt...udio.mdat?dl=0
E.g. That measurement (R only here) looks like this.
Treating 45Hz in a fully bass trapped room-meta-feedback.jpg
See this link also

https://www.avnirvana.com/threads/ca...-trouble.4546/

Best
Attached Thumbnails
Treating 45Hz in a fully bass trapped room-meta-feedback.jpg  
Old 2 weeks ago
  #74
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Glenn Kuras's Avatar
Quote:
Originally Posted by metaBit View Post
Fair enough. I guess what I meant is that I have bass traps (Auralex Lenrd) floor to ceiling in every corner of the room.

I actually just discovered a company (GIK Acoustics) who are helping me find a solution to treat the 45Hz, perhaps with their Scopus Tuned Membrane Bass Traps.
Yes the Scopus trap is a tuned device that is like what the other guys are talking about in this thread. Just know though you need way more than just 1 to treat a 45hz problem. Not saying you need to cover 100% of the wall (but some people do) but a good portion of the wall should covered to get the results.
Old 2 weeks ago
  #75
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Quote:
Originally Posted by akebrake View Post
No. You have to switch off monitoring (= feedback) which creates this comb filter.
Then, start doing valid room measurements.
No loopback needed. Use one sweep (not 2)
Sigh... I will try again!

Thanks for the feedback, no pun intended. Lol
Old 2 weeks ago
  #76
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Ok. I finally got a good soundcard calibration for my Apogee Element46.

Here it is:

https://www.dropbox.com/s/cvsd1yytue...ent46.cal?dl=0

And here is the other measurements using it:

https://www.dropbox.com/s/w3p1w7mdtt...udio.mdat?dl=0

It is unexpected that the Element46 would have a spike on the low end of its frequency response like my loopback test is showing. I'm talking to Apogee now and they gave me these specs for the Element46:

The A/D converter's frequency response is expected to be 10 Hz -20Khz: > +/-0.2dB (@44.1Khz).
The D/A converter's frequency response 10Hz -20 Khz: > +/- 0.05dB (@44.1Khz).
This means that you are expected to see less than +/- 0.05dB of frequency boost/cut from 10 Hz to 20kHz.

They suggest I try a manual loopback test where I connect the output to the input, send pink noise, and use a frequency analyzer to see if that peak shows up.

I'll give that a try this weekend and report back.

Last edited by metaBit; 1 week ago at 08:15 PM..
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