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Mineral fibre ceiling tiles with absorbent behind
Old 23rd December 2010
  #1
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Mineral fibre ceiling tiles with absorbent behind

On their own, 16mm (5/8") thick mineral fibre ceiling tiles have quite modest sound absorption. NRC approximately 0.55. Often are installed over 400mm airspace which give say 0.4 absorption at low frequencies. I am curious as I couldn't readily find any data about what happens to the absorption if the tiles are backed with OC 703 or even thick thermally rated batts.

Anyone have any ideas?

(edit: I expect it will go up but by how much? This is for a dance studio that is refurbishing and didn't want to throw out the whole of the existing ceiling but wanted better reverberation control of the room).
Old 23rd December 2010
  #2
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Glenn Kuras's Avatar
If you stack the fiberglass then you can use the numbers of that thickness. Needless to say the numbers matter, but testing the room before and after is really what matters.
Old 23rd December 2010
  #3
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Ethan Winer's Avatar
 

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Quote:
Originally Posted by Sebg View Post
I couldn't readily find any data about what happens to the absorption if the tiles are backed with OC 703 or even thick thermally rated batts.
The absorption of ceiling tiles at mid and high frequencies is determined by the reflectivity of their front surface. So no matter how much fiberglass you put above the tiles, they still will not absorb mids and highs enough to be useful for reflection points and other critical places. But adding fiberglass above does increase absorption at low frequencies.

--Ethan

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Old 23rd December 2010
  #4
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Glenn Kuras's Avatar
Quote:
Originally Posted by Ethan Winer View Post
The absorption of ceiling tiles at mid and high frequencies is determined by the reflectivity of the front surface. So no matter how much fiberglass you put above the tiles, they still will not absorb mids and highs enough to be useful for refection points and other critical places.

--Ethan

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Good point!! You want to remove any kind of plastic on the front of them if using in early reflection points.
Old 24th December 2010
  #5
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Quote:
Originally Posted by Ethan Winer View Post
The absorption of ceiling tiles at mid and high frequencies is determined by the reflectivity of their front surface. So no matter how much fiberglass you put above the tiles, they still will not absorb mids and highs enough to be useful for reflection points and other critical places. But adding fiberglass above does increase absorption at low frequencies.

--Ethan
This is what I think as well. From a text book:

Frequency bands .. 125Hz .. 250 ... 500 ... 1kHz ... 2k ..... 4kHz
Tiles on solid back . 0.05 ... 0.15 ... 0.50 .. 0.75 ... 0.65 ... 0.50
Tiles, 400mm space 0.30 ... 0.40 ... 0.55 .. 0.80 ... 0.70 ... 0.55

So I presume that by putting batts behind the tiles over 400mm airspace, frequencies up to and including 250Hz would increase but not 1k, 2k, 4k. I am not so sure about whether 500Hz would go up as well.
Old 24th December 2010
  #6
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If you use 1 inch 705 cut to fit the grid (and ditch the regular ceiling tiles altogether) you will get a resonator effect as well. This is one of studio designer Chris Pelonis' secrets. But don't tell him I told you. heh
Old 24th December 2010
  #7
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Quote:
Originally Posted by Magickman View Post
If you use 1 inch 705 cut to fit the grid (and ditch the regular ceiling tiles altogether) you will get a resonator effect as well. This is one of studio designer Chris Pelonis' secrets. But don't ell him I told you. heh
Oh, and use an FRK backing and turn it away from the room for even more low frequency absorption.

Shhh! Mum's the word!
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