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6' x 6' Bookcase as Absorption -- What to fill with?
Old 14th July 2019
  #1
Gear Maniac
6' x 6' Bookcase as Absorption -- What to fill with?

I am nearing completion of my studio project (mix & tracking room w/drums, baby grand piano, guitars, vocals, and e-piano in a 19' x 12' x tapered ceiling 7' to 10') and the plan was to utilize an existing large 6' x 6' bookshelf as part of the front wall absorption.

Originally I was going to fill the bookshelf with homemade "mini-traps" (12 inch cubes stuffed with f-glass insulation and wrapped with Guilford of Maine fabric).

My question is:

Due to time constraints, what would be the approximate effect if I instead used pre-fabricated foam cubes?
Attached Thumbnails
6' x 6' Bookcase as Absorption -- What to fill with?-20190625_182147.jpg   6' x 6' Bookcase as Absorption -- What to fill with?-20190713_165309.jpg   6' x 6' Bookcase as Absorption -- What to fill with?-20190713_165343.jpg   6' x 6' Bookcase as Absorption -- What to fill with?-20190713_165350.jpg   6' x 6' Bookcase as Absorption -- What to fill with?-bassbroad6.png  

Old 14th July 2019
  #2
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akebrake's Avatar
 

Generic answer

Quote:
Originally Posted by formula428 View Post
...My question is:

Due to time constraints, what would be the approximate effect if I instead used pre-fabricated foam cubes?
The approximate (acoustical) effect would not differ IF the foam and f-glass insulation used have similar Gas Flow Resistivity (GFR) optimized for that 12 inch thickness.

Best

PS What kind of acoustical improvement are you after? Just curious...
Old 14th July 2019
  #3
Gear Maniac
It would be SBIR for the monitors and absorption for the subwoofer.
Old 14th July 2019
  #4
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bowzin's Avatar
I'd consider just placing the fiberglass or mineral wool in the cubes, and covering the outside of the bookshelf with fabric, front and back. That would be really simple, just staple fabric to the entire front and back once. Instead of trying to do something or make something for each of the cubes individually. Not really aware of foam that works well enough compared to fiberglass or mineral wool, and if it did, it would likely be more expensive anyway.

Also, perhaps more importantly, the sides and top of the bookshelf are solid flat reflective surfaces, and are going to reflect. Also all of the flat surfaces in the middle cubes are going to reflect also. That's a lot of random wood reflecting right next to your speakers and listening position. Maybe just build something similar but with 2x4's or 2x3's and WITHOUT all those flat reflective surfaces on the sides, top, and interior shelf spaces. Would be really easy to build, and doesn't have to look good since it will covered in fabric. Leave it all open and exposed, fill it with insulation material, and staple fabric to the outside.
Old 14th July 2019
  #5
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Quote:
Originally Posted by bowzin View Post

Also, perhaps more importantly, the sides and top of the bookshelf are solid flat reflective surfaces, and are going to reflect. Also all of the flat surfaces in the middle cubes are going to reflect also. That's a lot of random wood reflecting right next to your speakers and listening position.
it's the least important.
The most important are :
the good porosity value for the low target frequency.
the maximizing the surface to be treated.
Old 14th July 2019
  #6
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Quote:
Originally Posted by dinococcus View Post
it's the least important.
The most important are :
the good porosity value for the low target frequency.
the maximizing the surface to be treated.
Fair, I assumed they were solid wood, but that wasn't specified in the original post.

Still, they are right next to his full-range speakers, and the sides are solid, so even MDF is going to reflect, no?
Old 14th July 2019
  #7
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Quote:
Originally Posted by bowzin View Post
Not really aware of foam that works well enough compared to fiberglass or mineral wool, and if it did, it would likely be more expensive anyway.
At Gas flow resistivity and thickness equal is the case like the Caruso Isobond or the Melamine.
The wool or the fiber are the most economic solution but i'm nore sure that the performance of the wool or fiber stay stable in the time.
Old 14th July 2019
  #8
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Quote:
Originally Posted by bowzin View Post
Fair, I assumed they were solid wood, but that wasn't specified in the original post.

Still, they are right next to his full-range speakers, and the sides are solid, so even MDF is going to reflect, no?
wood or mdf : no difference.
Old 14th July 2019
  #9
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Quote:
Originally Posted by bowzin View Post
Fair, I assumed they were solid wood, but that wasn't specified in the original post.

Still, they are right next to his full-range speakers, and the sides are solid, so even MDF is going to reflect, no?
it's possible to make hole in the wall's box with a bell saw.

Last edited by dinococcus; 14th July 2019 at 04:15 PM..
Old 14th July 2019
  #10
Quote:
Originally Posted by formula428 View Post
Due to time constraints, what would be the approximate effect if I instead used pre-fabricated foam cubes?
If you know the GFR numbers, you can find that out here: http://www.acousticmodelling.com/
Old 14th July 2019
  #11
Gear Maniac
I do not know the GFR, only that they are about 1 pcf density.
Old 14th July 2019
  #12
Quote:
Originally Posted by formula428 View Post
I do not know the GFR, only that they are about 1 pcf density.
If your bookshelf is 12 inches deep and you stuff it with Basotect (12400 Pa.s/m2 as far as I remember), the absorption coefficient is 0.6 at around 50 Hz. From playing with acousticmodelling.com and Basotect's values, I think basotect is good up to 30-40 cm with almost no benefit beyond that.
Old 14th July 2019
  #13
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Quote:
Originally Posted by formula428 View Post
I do not know the GFR, only that they are about 1 pcf density.
1 pcf = 16 Kg /m3 and a GFR between 6.4 and 5.3. this value of GFR require a great thickness. You can check it in acousticmodelling
Old 14th July 2019
  #14
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Quote:
Originally Posted by johannburkard View Post
If your bookshelf is 12 inches deep and you stuff it with Basotect (12400 Pa.s/m2 as far as I remember), the absorption coefficient is 0.6 at around 50 Hz. From playing with acousticmodelling.com and Basotect's values, I think basotect is good up to 30-40 cm with almost no benefit beyond that.
the performance of the basoctect do not change beyond 400 mm. Between 200 mm and 400 mm, the change is light.
this is the same thing for all foam, wool and fiber with the same GFR.
Old 15th July 2019
  #15
Gear Maniac
So the consensus is either Basotech or rigid fiberglass, correct?

I don't typically see panels being 12" depth (aside from diy), so how much Basotech would equal 4" of OC703? 6" of OC703? Would it just be using the gfr of 703 and plugging it into the calculator?
Old 15th July 2019
  #16
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avare's Avatar
 

Rockwool Rockboard 40 is acoustically superior and cheaper than OC 703.
Old 15th July 2019
  #17
Quote:
Originally Posted by formula428 View Post
So the consensus is either Basotech or rigid fiberglass, correct?
That depends on what frequency you need absorption down to.

Also, keep in mind that Basotect is very expensive.
Old 15th July 2019
  #18
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Measurements?

Quote:
Originally Posted by formula428 View Post
It would be SBIR for the monitors and absorption for the subwoofer.
GS people love to watch some REW measurements.
Did your measurement show problems with SBIR or subwoofer absorption?

Best
Old 11th August 2019
  #19
Gear Maniac
Sorry for the delay in getting these - I have the measurements and this is without any bookcase absorption. As part of the correction, I tried to get everything as flat as possible with the sub/monitor adjustments available to me (KH805 and KH120a). So the notes on each measurement are referring to the dip switches and adjustments available on the sub and tops.

I used REW version 5.1.

With that being said, it looks like the room has a major issue at 45 hz and 122hz, and then some dips in the low mids @ 255, 341, 427, 664.

What would be some suggestions to tame the 45 and 122 dips? Any other suggestions (I've attached the PDF layout of the room).


I guess I was hoping for better results in the freq response, but it's a starting point. However, from what I can tell (and the limited that I know about waterfall graphs), it seems that the decay is actually quite good (except at 30hz). Please correct me if I'm wrong.

** Note: I had to compress the file in order stay under the 16mb limit (was 20mb). It was compressed with WinRAR.


Thanks in advance!
Attached Files
File Type: pdf StudioV8.pdf (85.3 KB, 10 views) File Type: zip SleepyStudios-2019-08-10-GS.zip (12.92 MB, 5 views)
Old 12th August 2019
  #20
Quote:
Originally Posted by formula428 View Post
With that being said, it looks like the room has a major issue at 45 hz and 122hz, and then some dips in the low mids @ 255, 341, 427, 664.
I woud worry about the first two dips but not about the others as they're relatively narrow.

Quote:
Originally Posted by formula428 View Post
What would be some suggestions to tame the 45 and 122 dips? Any other suggestions (I've attached the PDF layout of the room).
Those are probably interferences. There may be paths from speaker to microphone where there is no absorption that's effective at these frequencies.

I'm guessing that would be your 244 panels.

The downside is that even a Monster Bass Trap won't do much at 45 Hz, according to their data.


Quote:
Originally Posted by formula428 View Post
However, from what I can tell (and the limited that I know about waterfall graphs), it seems that the decay is actually quite good (except at 30hz).
The decay times are certainly very good, maybe even a bit too low. Does it feel too dry in there?
Old 13th August 2019
  #21
Gear Maniac
Quote:
Originally Posted by johannburkard View Post
I woud worry about the first two dips but not about the others as they're relatively narrow.



Those are probably interferences. There may be paths from speaker to microphone where there is no absorption that's effective at these frequencies.

I'm guessing that would be your 244 panels.

The downside is that even a Monster Bass Trap won't do much at 45 Hz, according to their data.




The decay times are certainly very good, maybe even a bit too low. Does it feel too dry in there?
So I'm looking for 1/4 wave lengths for 45 and 122, correct? And that distance could be a reflected distance, too, such distance A + B = C = 1/4 wavelength...correct?
Old 13th August 2019
  #22
Gear Maniac
It's a little dry, but not terrible.
Old 13th August 2019
  #23
Couldn't you try to temporarily place a few Monster Bass Traps over the 244 panels on the sides and measure again? If the dip fills up, you'll know you'll need deeper treatment there.

I don't know much about acoustics but I have tested 20+ positions in one day. I just measure, keep notes and then look at the measurements later.
Old 14th August 2019
  #24
Gear Maniac
Quote:
Originally Posted by johannburkard View Post
Couldn't you try to temporarily place a few Monster Bass Traps over the 244 panels on the sides and measure again? If the dip fills up, you'll know you'll need deeper treatment there.

I don't know much about acoustics but I have tested 20+ positions in one day. I just measure, keep notes and then look at the measurements later.
I will try that and return with the results. Thanks!
Old 4 weeks ago
  #25
Gear Maniac
I went back and tried moving the sub into multiple locations. Albeit, I'm still constrained because there isn't much room for movement with the bookcase still at it's original location.

Bottom line - moving the sub does help. I noticed some relief at the lowest null, but only by about 6dB, which also resulted in moving the null up in the frequency band (from 45 to 57.5) Interestingly enough, it seems that my tops and sub are fighting for frequencies at those lower nulls, but helping to even things out in the lower mids (95, 122). Best results so far came by placing the sub nearest the front wall (22.25 inches away) and relatively centered in the room. Unfortunately due to the length of the sub and the table in the way, I had to fire the sub into the front wall (into a cubby of the bookcase). I also couldn't try the 1/4 room dimension away from walls theory since there is other gear in the way.

I will start moving major furniture around today, and then I will double the panels on the side walls (as suggested above) and move the tops around.


QUESTION - should I start off with the tops and getting them perfect, or the sub? Logic tells me tops first, but I could be wrong.


Results attached as well.
Attached Files
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