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Old 31st March 2012, 12:35 PM   #11
tvrgeek is offline tvrgeek  United States
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Quote:
Originally Posted by epicyclic View Post
Hi Speedskater

" physically ill " ...interesting , what do those who get ill put this experience down to ? / or what is the understood reason .
Our brain gets upset when our senses are confused. When we see the size of a room, we expect to hear reflections from a room that size. Same problem with sea sickness. What we see and what our inner ear senses conflicts. I find a chamber an interesting experience. Same with cave black.
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Old 31st March 2012, 02:18 PM   #12
PChi is offline PChi  United Kingdom
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I have only been in an RF anechoic chamber which was quite effective at audio frequencies. The low background noise and lack of reverberation is weird. The RF one I was in had a small area of wooden floor above the wedges, OK for RF but not great for audio. I guess that in the audio chambers you are walking on a grid, unnerving. Also there is going to be zero natural light and if the door is closed very little air circulation or ventilation. I believe that the RF chambers do have an RF screened ventilation system but that's not going to be good enough for audio measurements.
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Old 2nd April 2012, 03:29 PM   #13
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Thanks for the feedback on the effects of being inside an anechoic chamber.
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Old 3rd April 2012, 02:08 PM   #14
macboy is offline macboy  Canada
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That 'egg crate' style foam will do much less good than you think. I would suggest something a lot thicker and more dense, like Roxul (aka Rock Wool) "Safe N Sound" insulation. It is similar to fiberglass batting insulation, but is made from stone fibers (no, not asbestos). It will cost you roughly 50 cents per sq foot, and is about 3.5 inch thick. I recently finished my basement into a home theatre/listening room and used this stuff in the all the walls and ceiling as part of my soundproofing. Before the drywall went up, it was similar to an anechoic chamber in there, very dead sounding.
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Old 3rd April 2012, 03:00 PM   #15
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I use a purpose-designed anechoic chamber at work which is a 3.5 x 3.5 x 3.5 metre cube internally, with 350mm deep foam wedges on the walls and ceiling and 180mm foam on the floor. This is only anechoic down to around 300Hz. For anything lower you have to increase the dimensions. In my days with DECT handset testing I used an old British Telecom "Blue Box" (a small 1.5 metre cube foam-damped box), but these were getting inaccurate for measurements below 500Hz. I think trying to do anything DIY is not going to give usable results.
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Old 3rd April 2012, 04:36 PM   #16
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Any idea how loud it is outside? Could you get away with testing at very high volume? Perhaps at high SPL the signal would swamp out any noise. At least good enough. The lower frequencies are usually the biggest issue. So depends what you're trying to get. You could also take your equipment to a large parking lot someplace at night. Cops might wonder what you're up to though.
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Old 3rd April 2012, 09:02 PM   #17
DrBoar is offline DrBoar  Sweden
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An anechoic chamber is a reflectionless room, ie sounds generated inside the is not bounced around in the room. A sound proofed room is a very different animal made to stop sounds coming outod the room/ in to the room.

The simplest solution is to play loud enough while you measure. Sounds/vibrations coming through the walls and floor is something you can do nothing about unless you build a new room floating inside the current room.

Sounds coming hrough an outer wall or window only can be greatly reduced by building a wall spaced away from the offending wall. Double layer of plasterboard well sealed is important. Having some fiber glass or rockwool in between is OK. This material will lower the Q of the resonanses of the plasterboard but not stop any tranmission of sound across the space. There is a lot of information regarding soundproofing. What you really need are as many sealed walls as possible with "resonable masses" A double wall with staggered joists with one row for the inner wall and an other not connected to the first row for the outer wall with double layer plasterboard, will be quite good. This 2+2 plasterboard is way better than say a 8 layers of board on a single wall
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Old 4th April 2012, 01:00 AM   #18
tvrgeek is offline tvrgeek  United States
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If you are not designing traducers, you don't need a chamber. Have you read D'Apollito's book yet? Unless of course you are building a speaker to use inside a chamber in which case you would already have one. The ROOM IS PART OF THE SPEAKER.

You need about 9 or 10 dB margin for testing. I start at 1 watt, so that is between 85 and 90 dB. You can do that outside usually, but it may cause some visits. Test a sub for breakup? Don't even think about that at night.
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