Author Topic: Building a sound proof box to block very low frequencies  (Read 4338 times)

ivanny04

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Building a sound proof box to block very low frequencies
« on: April 25, 2015, 07:09:53 PM »
I am working on a project and have questions about sound proofing.  I want to build a rectangular box, with inside dimensions of about 27 x 24 inches  x 5 ft, and make it sound proof.  My main goal would be to make it block out "sound" that is around 8 - 200 Hz.  I understand the lower end of that is below the range of human hearing.   I'd also be somewhat concerned about frequencies above 20 KHz.

It had been suggested to me that I do something like first build a box out of 1/2 inch plywood - with the desired outside dimensions.  The bottom would be covered with about 1 to 2 inches of sand, at an angle.  On top of that would be a piece of plywood leaving a gap of about 3 inches on all 4 sides. Then another 1 to 2 inches of sand, at an opposite angle.

I'd then build a shell with the desired inside dimensions, with sides that are parallel to the sides of the outer box, to rest on top of that layer of sand, with a gap of 3 inches on all 4 sides.   I'd then place sheets of plywood in between the internal shell and outer box, at angles, filling the gaps all the way around with more sand.

So, I'd end up with an inner shell, a layer of sand, sheets of plywood at  slightly different angles to the walls of the shell, another layer of sand, and then the outer box.

The theory as it was explained to me was that sound will travel through two walls that have parallel surfaces more easily than two walls that have surfaces that are at slight angles to each other.   The sand further attenuates the sound because the sound waves hit each sand particle, which then transfers that energy to a neighboring sand particles, but slightly attenuated. 

It was suggested to me that sand would be better suited to block out the very low frequencies that I wish to block.

Assuming this makes sense ... would it be best to use very fine grain sand, or larger grain of sand ?  Would there be a better type of material to use besides plywood ?

Randy S

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Re: Building a sound proof box to block very low frequencies
« Reply #1 on: April 27, 2015, 03:21:27 PM »
I would go with larger grain sand and use cement board and lead sheet. You must cover the entire inside of the box with an absorption material as well.
If you gain quality reductions at the lower frequencies then 20 KHz shouldn't be an issue if you use lead sheet 1/32 " 

I would be interested in seeing the results of this box after built, providing you detail the intensity and frequency your testing at and what the DB reduction is.


Feel free to contact me direct to further discuss this project.

Randy S.
760-752-3030 ext 3095

Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

ivanny04

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Re: Building a sound proof box to block very low frequencies
« Reply #2 on: May 02, 2015, 05:12:13 PM »
Hello,

Thanks for replying to my post.   You said  "cover the entire inside of the box with an absorption material as well".
What would you suggest ?

Also, why the large grain sand over smaller grain which would provide for a denser mass ?




Randy S

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Re: Building a sound proof box to block very low frequencies
« Reply #3 on: May 02, 2015, 05:35:39 PM »
I would use cotton fiber panel because they are cheap and have a high NRC.

I am not a fan of using sand in the first place due to the potential of mold and other issues like humidity and keeping it dry.
But by using fine sand it will couple the system together, the finer the sand the more packed down it will be and there for you fall back to mass law..
The best performing systems are based on isolation first then followed by mass.

Randy S.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

ivanny04

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Re: Building a sound proof box to block very low frequencies
« Reply #4 on: May 02, 2015, 07:08:48 PM »
OK ... I know a likely difficult question to answer.   

First, assume that the noise is entering a room through the outside walls.  In the open space in the room, it is very evident (again, I've never measured it).   Assuming I build a "coffin" like box, with an opening of ~ 24" by 24"  at one end,  any idea how much of this low frequency "noise" would be able to enter that small of an opening ?

In other words, If I'm in the middle of the room, the "noise" is bouncing all over the place, and thus easy to feel.  If I reduce some of that impact via an enclosure, but with one end opened, is the enclosure in effect useless ?

Ooops - had trouble with that stupid question down below.   The sky is blue except when seen from space, then its ?
blue, no, black, no, clear, no, white, no, blue, no idiot you said that before, blue, no, blue, no, blue, no, blue.   

Does anyone know - and yes, it is a stupid question.  Blue.


ivanny04

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Re: Building a sound proof box to block very low frequencies
« Reply #5 on: May 03, 2015, 04:29:30 AM »
Are multiple layers of some sort of solid wall, at varying angles to each other, an effective way to block noise transfer from outside an area into a chamber ?   What I'm asking is do I gain anything by have a wall scheme such as

          |\|/|

where something like sand is between each wall, or would multiple parallel walls, with a air gap in between be better ?
Or just solid wall of something like plywood - lead sheeting - plywood - lead sheeting - plywood be better ?

Excellent, I don't have to know what color the sky is !!!

Randy S

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Re: Building a sound proof box to block very low frequencies
« Reply #6 on: May 06, 2015, 04:38:08 PM »
to answer your question about the 24" x 24" opening, yes it would be useless.
Here is a way to design.

Noise source side / exposed absorption/ mass/ isolation/ absorption / mass / receiving side.

the lower the frequency and higher the intensity the greater the value is needed for each principle.

Feel free to call me direct

Randy S.
760-752-3030 ext 3095
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

ivanny04

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Re: Building a sound proof box to block very low frequencies
« Reply #7 on: September 13, 2015, 05:08:31 PM »

My idea was to build this box using a frame 2x4's to then add the layers of soundproofing to.  I'm now wondering what other material would transfer less vibration from outside to inside, yet be able to support multiple layers of material that weighs several pounds per sq. foot ?

Would appreciate any suggestions.

Randy S

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Re: Building a sound proof box to block very low frequencies
« Reply #8 on: September 14, 2015, 03:25:34 PM »
2x4's are fine...to support more weight you can go with 12" OC instead of 16" OC .

Randy S.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

 

anything