Acoustics 101: with Professor Arthur Maxx

 

CLASS IS IN SESSION

I often receive questions from VU Members about home studios. The following information will answer your questions about how Acoustics affect your current or future studio.

 

 

There are 2 main factors in "Sound Proofing"...


 

NRC (Noise Reduction Coefficient) & STC (Sound Transmission Class). 


 

NRC - The NRC is a single-number index determined in a lab test and used for rating how absorptive a particular material is. This industry standard ranges from zero (perfectly reflective) to 1* (perfectly absorptive). It is simply the average of the mid-frequency sound absorption coefficients (250, 500, 1000 and 2000 Hertz) rounded to the nearest 5%.


*(Based on the testing methodology, and depending upon the material's shape or surface area, some products can test at an NRC above 1.) 

the materials ability to Attenuate or Absorb noise at a certain frequency range. ie: Ultra touch Insulation, carpet, acoustical foam panels, Non-Square rooms, angled walls, rounded surfaces....the list goes on...


 

STC - Sound Transmission Class (STC) is a single-number rating of a material's or an assembly's ability to resist airborne sound transfer at the frequencies 125-4000 Hz. In general, a higher STC rating blocks more noise from transmitting through a partition.


 

Poor: fabric, wood (what's a piano made from?)


Good: MDF board


 

Better: Drywall ( add layers for better results )


Best: CONCRETE.


Below are 6 examples of Wall Construction to achieve graduated levels of STC

1. Insulation will noticeably improve the STC rating of an assembly. 
Description
Estimated STC Rating
Wall Assembly
3 5/8" metal studs, 5/8" gyp (2 layers total), No insulation
38 - 40
3 5/8" metal studs, 5/8" gyp (2 layers total), Batt insulation
43 - 44



2. Staggered or double stud walls are higher rated than single stud walls.
Description
Estimated STC Rating
Wall Assembly
2x4 stud, 5/8" gyp (2 layers total),
Batt insulation
34 - 39
Staggered studs, 5/8" gyp (2 layers total),
Batt insulation
46 - 47
2x4 studs, 5/8" gyp (2 layers total),
Batt insulation
56 - 59
 


3. Metal stud walls perform better than wood stud walls.
(NOTE: This only applies to single stud assemblies. For double stud assemblies, there is virtually no difference.)

Description
Estimated STC Rating
Wall Assembly
2x4 stud, 5/8" gyp (2 layers total), Batt insulation
34 - 39
3 5/8" metal studs, 5/8" gyp (2 layers total), Batt insulation
43 - 44
 


4. Resilient channel can improve the STC rating of an assembly.
(NOTE: These ratings are based on laboratory tests. Because of the special care required when installing resilient channels, actual results could be substantially lower.) 

Description
Estimated STC Rating
Wall Assembly
2x4 stud, 5/8" gyp (2 layers total), Batt insulation
34 - 39
2x4 stud, 5/8" gyp (2 layers total), Resilient Channel, Batt insulation
45 - 52



5. Adding additional layers of drywall can improve the STC rating of an assembly.
Description
Estimated STC Rating
Wall Assembly
2x4 stud, 5/8" gyp (2 layers total), Batt insulation
34 - 39
2x4 stud, 5/8" gyp (3 layers total), Batt insulation
39 - 40
2x4 stud, 5/8" gyp (4 layers total), Batt insulation
43 - 45



6. Drywall between double studs can dramatically reduce the STC rating of an assembly.
Description
Estimated STC Rating
Wall Assembly
2x4 studs, 5/8" gyp (4 layers total), Batt insulation
44 - 45
2x4 studs, 5/8" gyp (2 layers total), Batt insulation
56 - 59
2x4 studs,5/8" gyp (3 layers total), Batt insulation
59 - 60
2x4 studs, 5/8" gyp (4 layers total), Batt insulation
58 - 63


It really depends on your Budget.

 

NOTE: Fiberglass insulation should only be used "inside" of your partition and should not be left exposed.

 

SO...you don't need to build and you have a room or a closet or...

All you want to do is to get the noise and reverberation GONE!

 

There are many things around the house that can "Deaden" your space. Carpet ( of course...right?)

pillows, polyester stuffing is great!

The idea in Noise Reduction (absorbtion/diffusion) is to provide as many surfaces possible to quiet the room...know what I mean?

 

There are some great products you can buy:

Bonded Acoustical Cotton - Black - Echo Eliminator



ECHO ELIMINATOR™

Bonded Acoustical Cotton (B.A.C.) 
The Most Cost Effective Acoustical Absorbing Material On The Market

Echo Eliminator is a high performance acoustical material made from recycled cotton. This product is ideal for noise control applications. Echo Eliminator can be used as an acoustic wall panel or hanging baffle. Common applications are school gyms, classrooms and lunch rooms and any application where a high performance noise control product is needed. Echo Eliminator is LEED eligible, Class A fire retardant and 100% recyclable.

• Recycled cotton (green acoustical material)
• Class A - nonflammable (Per ASTM E-84)
• Lightweight
• Easy to install (adhesively applied)
• Impact resistant
• Durable
• Low cost
• Hi-light reflectance
• Hi-performance acoustical absorption
• Relocatable (with grommets)


 

Auralex Studio Foam

Studiofoam Wedgies - acoustic foam absorption panels - application photo #1Roominators Project 2 - Performance Series Acoustic Sound Control Kits

Class dismissed.

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Comment by David W Stone on April 12, 2011 at 9:03am

V.L. writes...

  I just read your whole post.  You mention that the shape of the room affects the absorbtion of noise, but I can't tell what's good or bad.  Is a rounded room good or square?  Mine looks more like a trapezoid.  Also, what is Resilient Channel?  And is Batt a specific type of insulation?

 

Sometimes, studio builders will purposely build the walls "out of square" ... So, if your room is 20 feet from one corner, along the wall, to the other corner...the opposite wall would be 22 feet (Trapezoidal) This is done to reduce sound wave reflection (reverb) By the way... a round room isn't so great either.

Resilient Channel is a specially-formed, sturdy metal device that, when used to hang drywall (instead of just attaching the drywall directly to the studs or joists or installing double layer drywall), GREATLY improves the sound transmission characteristics of the wall or ceiling system. Most types add 1/2" of airspace between the studs and drywall and can provide as much as 10 dB of isolation if used properly.

"Batt" insulation ie; 2' x 4'  or 16" x 8' as opposed to "blown in" insulation.

Comment by KC Cady on April 7, 2011 at 6:01pm

Very good info!

Thanks for sharing!!!

~KC

Comment by David W Stone on April 6, 2011 at 11:01am

Hey Pablo, My Recommendation... Move!
Just Kidding Bro!...I'd much rather live in PR than Cali!


Seriously, You have a Great low-end noise blocker in Concrete!

If you have the means to do so and/or the ability, I would recommend building your studio or recording booth using the dual framing system depicted in "Example" #6 Using like an R-30 fiberglass insulation or double up with R-19. Now walls are easy compared to the ceiling but for your situation, I would think a double layer of 5/8 gypsum board with insulation above, should block most sound. Make sure that any gaps are filled with an acoustical sealant, (similar to caulking).

OH...almost forgot!...Is any noise transferred through your floor?? If so, There is a way to build a "floating" floor.. or at least construct a built-up floor(Let me know).

Then there is the issue of the interior, but we can save that for later...


Let me know if this helps !

Comment by Pablo Hernandez-Pagan on April 6, 2011 at 9:26am

My house is made of concrete. I live in an anti-VO environment: lots of trees around the neighborhood which means there are many many birds singing, there is a factory one block away from my house, two block away in the same direction there is a highway, at the other side of the highway there is an airport, less than 300 feet away from my house there is a car repair shop and add to that the barks of the dogs that are around the block. What would be your recommendation to improve that "situation'?

 

-Pablo Hernandez-Pagan

Comment by David W Stone on April 6, 2011 at 12:19am
If you have any questions please ask!
Or...
If you have any suggestions...Suggest away!

 

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