Anechoic or Semi-Anechoic chamber build

[jordanb885]

Hi Guys, I am new to this forum but was looking for some help.
I'm looking to do some sound testing on a boiler project of mine but require a space that is 30db or lower ambient sound, The boiler itself is required to run at 40-42db so I was told a chamber with a ambiant sound of 30db would be ideal,

Would anyone have any links to Anechoic chamber self builds or all in one units that might fit my purpose? the boiler that needs to be tested takes up a space of 500mm x 550mm x 2000mm,

I've seen some booths online that say they have "Sound-absorbing walls, floor and ceiling for an attenuation of 30 dB (measured according to ASTM E595, NIC value calculated according to ASTM E413)" Would this be what I need?

Any help you can give would be much appreciated,
Thanks in advance
Jordan

 

[alex-z]

Practical approach, what is the largest room you can use for this project, and what is the current background noise of it?

What frequency range do you need to analysis?

With that data you can predict how much absorption material will be required.

 

[617]

What frequency range do you need to measure?

 

[jordanb885]

What frequency range do you need to measure?

The testing is to be conducted on heat pumps, boilers and air conditioning units so the frequency range would be the low range possibly 300 DB and below

 

[jordanb885]

Practical approach, what is the largest room you can use for this project, and what is the current background noise of it?

What frequency range do you need to analysis?

With that data you can predict how much absorption material will be required.

current background noise is approximately 50-55db and planning to analyse 20db-300db,
How would I go about predicting how much absorption material i may need?

 

[Wes]

I bet the engineering society that deals with these items has the info you want. I forget the name of it tho. Are you in the US?

also, testing can be done outdoors which can approach an anechoic chamber except for the ground plane effects (which you'll have anyway)

 

[alex-z]

current background noise is approximately 50-55db and planning to analyse 20db-300db,
How would I go about predicting how much absorption material i may need?

I assume you mean 20-300Hz, because 300dB is literally impossible within Earths atmosphere AFAIK.

So you need 25dB of attenuation, focused on low frequencies. Given the wavelengths involved, such a chamber will be relatively large and expensive. Absorbing low frequencies is best handled with mass, so I would start with a poured concrete or brick wall as thick as is practical.

If you intend to use absorption material such as mineral wool, the most effective location is 1/4 wavelength from the boundary, which for 20Hz would mean approximately 14ft. Such absorption would need to be relatively thick. A half metre absorber built with mineral wool has only a .35 coefficient at 20Hz.

http://www.acousticmodelling.com/porous.php

The entryway will be a source of significant noise leakage, as will any ducting needed for boiler testing. Making those damped and airtight is outside my realm of knowledge. I would consult someone who has built a full sized chamber before, their thoughts on air exchange would be valuable.