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?
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?
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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
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.
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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