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Old 30th March 2012, 09:11 AM   #1
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Default Makeshift Anechoic Chamber

Currently I am living in a fairly noisy residence on a main road. With what seems like constant noise day and night. While I can mentally block a lot of it out it does present a significant issue in testing the new speakers that I am building and setting up the digital crossover proerly.

Doesn't help that the living area is open with a tiled floor throughout. I was just wondering how large an Anechoic Chamber would need to be in order to be semi useful.

I have a few design idea that might just work. Today I went down to the local hardware store and checked out the prices on some 6mm MDF sheets. $20 for a 2440mm x 1220mm sheet.

Figiring that I could stand the sheets up length ways... that would make it 2.44 meters tall.

For accoustic deadening I could paste these on the walls, top and floor http://www.dealsdirect.com.au/p/the-big-sleep-foam-underlay-queen/
A queen bed measure roughly 2 meter long by 1.5 meters wide. Would it be worth spending a few hundred dollars to try it out?
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Old 30th March 2012, 09:22 AM   #2
SY is offline SY  United States
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Are you trying to make an anechoic chamber or just soundproof the room to block out external noises?
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Old 30th March 2012, 09:28 AM   #3
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At this point in time it would be as an anechoic chamber, but post speaker build the panels would probably be repurposed into accoustic room dampening.
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Old 30th March 2012, 09:39 AM   #4
SY is offline SY  United States
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You'll need a lot better absorption than those thin sheets will get you. In anechoic chambers, the wall treatments are typically 12-20" deep pyramids or wedges of acoustic foam. In a really sophisticated one, there will be several layers with different densities. The lower the frequency you want to go, the thicker the treatment needs to be.

There's a reason that people do quasi-anechoic measurement by gating impulse response, then merging with near-field. An anechoic chamber is a major construction project! It also makes the room totally unsuitable for any other use, including listening.
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Old 30th March 2012, 09:41 AM   #5
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ok perhaps a full blown version might be overkill... but would it be worth constructing a quiet box for the want of a better word to test speakers?
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Old 30th March 2012, 09:50 AM   #6
PChi is offline PChi  United Kingdom
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Based on my limited experience of testing Mobile Phones and accessories if you want to exclude external sounds the chamber needs to have few leaks. The chamber door seal is going to be important. Otherwise the external noise just gets in. The walls need to be reasonably stiff to exclude bass frequencies.
I have only tested handsets in small semi anechoic chambers which were lined with foam designed (at least sold) for anechoic performance and the handset position in the chamber still made quite a difference to the frequency response so I would not expect great performance from the foam underlay.

I have been in an '3 meter' RF anechoic chamber that used carbon loaded foam wedges about 1 m deep for absorption and it seemed pretty good at audio frequencies.
I suspect that much less will not give very accurate frequency response measurements.
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Old 30th March 2012, 10:06 AM   #7
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Ok based on what I'm hearing, perhaps the dollars might be better spent on improving the accoustics in the room.
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Old 31st March 2012, 01:21 AM   #8
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Being in a professional Anechoic Chamber is not a fun experience. Some people get physically ill in the chambers.
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Old 31st March 2012, 08:13 AM   #9
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Hi Speedskater

" physically ill " ...interesting , what do those who get ill put this experience down to ? / or what is the understood reason .

Last edited by epicyclic; 31st March 2012 at 08:16 AM.
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Old 31st March 2012, 11:31 AM   #10
tvrgeek is offline tvrgeek  United States
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Having been down this route, basically we are screwed as the low frequencies will get through almost anything. I used to test outside at 2 AM, but the highway 5 miles away overpowers any LF measurements I wanted to make.

If you have a basement, you can do a little better, but what you need to do is move to MLS and pulse testing. Learn about the noise and live with it. A chamber needs about 40 x 40 x 40 feet and the walls are about 20 feet thick. Not a DIY project.

I find I do pretty well with near-field measurements and then voice by ear in my listening room. Remember, you don't listen in a quiet box. The room is part of the speaker, as is the amp. Test together. Unless you are designing raw drivers, a chamber is not much use. You do not want a speaker that is perfectly flat in a chamber. You want it in a real room.
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