Cohousing-L Mailing List: RE: Noise in Common House

[Jimwheeler (Jimwheeler]

Rob

To answer your questions:

Q1  What about acoustic tiles?

A1  There is a wide variety of acoustical tiles--including Tectum.  I would 
not consider any that have an NRC below about 0.8 at 500 Hz (see Tutorial 
below).


Q2  Do narrower tables really help?

A2  Depends on whether or not the ceiling surface is parallel to the table 
surface.

Jim Wheeler
Tierra Nueva
jimwheeler [at] aol.com


                        BRIEF TUTORIAL ABOUT DINING ROOM ACOUSTICS
                                                     Jim Wheeler

I am an engineer who has spent a lot of time solving acoustical problems but 
I am not a professional acoustical engineer.  I wrote the noise ordinance for 
the town I lived in, I built an acoustical walk-in chamber, and I was 
instrumental in developing the unique noise control regulation for San 
Francisco 
airport.  I am an active member of the Audio Engineering Society but we do not 
do 
acoustics.  Acoustical standards are produced by the Acoustical Society of 
America.  Their websites are:  http://asa.aip.org and www.acoustics.org

I live in Tierra Nueva and am gathering data for various acoustical materials 
for our Common House dining room.  I am trying to connect with a Tectum 
representative to obtain samples of Tectum materials as well as the NRC 
specification.  I understand that Tectum panels are being used in some 
CoHousing dining 
rooms.

The basics are:
  Parallel, smooth, flat surfaces are the worst offenders.
  Any material that is thick and textured is desired.  Alpaca or wool 
blankets from Peru--for example.  (see note 1)
  Thick draperies are good
  Carpet on the floor is good
  Windows and doors are bad because the glass or flat wood reflect about 100 
percent of the sound.  It looks like the curved mini blinds used at Jackson 
Place is a solution.
  Ceilings that are not parallel to the floor are probably not a problem.
  Corners are a problem because certain soundwave frequencies will be 
reinforced and reflected (focused) at a larger magnitude.  (see note 2)

Notes:  
1.  For best effect, blankets should be hung at least 4 inches and preferably 
6 inches from the wall.  This will nearly double the sound absorption because 
most of the soundwaves that pass through the blanket and reflect off the wall 
will be absorbed on this second pass.
2.  Corner problems can be eliminated by making triangular shaped cushions 
about 8 inches per side and glued into the corners of the room.  These can be 
made by using a burlap-like fabric or white canvas to cover a triangular piece 
of foam or fiberglass.

I go to Peru every couple of years to do archaeology.  I have a Peruvian 
friend who can get blankets made to whatever design I give him.  The prices 
vary 
but my guess is something like $400-$500 US for a four foot by five foot 
blanket.  I suspect that the four foot width is the maximum a loom can handle 
but I 
have not asked him.  I have some photos of blankets with various patterns.

How the acoustical material LOOKS is not an issue because it can be covered 
or draped with very thin cloth that has a pleasing pattern.

There is no way to scientifically quantify the acoustics of a complex room.  
The human ear is very sensitive and we get phase additions/cancellations 
merely by turning our head slightly.  The only way that we will know how well a 
particular solution will work is by trying it.

Manufacturers of acoustical material can measure the absorbing quality of 
their materials.  This is called the Noise Reduction Coefficient (NRC) or the 
sound absorbing rating.  The old 5/8 inch acoustical ceiling tiles have an NRC 
of 
about 0.50.   Acoustical Solutions makes a nice looking "Designer" tile with 
an NRC of 0.61 at 500 Hz.  That means that 61 percent of the soundwaves 
between about 300 and 700 Hz, will be absorbed.  300-700 Hz is the range of the 
sound that we want to suppress.  Normally, NRC is expressed as an average over 
the 
entire audio spectrum but it is only the 300-700 Hz range that we are 
interested in.  An average NRC figure is not adequate.

What we want is a material with an NRC of 1.0 at 500 Hz.  3 inch thick 
pyramidal foam has an NRC of 1.0 at 500 Hz. but it costs $4-$8 per square foot.

Tutorials and a lot of acoustical info can be obtained on the Internet:
www.acousticalsolutions.com
www.soundproofing.org
www.armstrong.com  (go to ceilings)
www.tectum.com
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