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DIY Acoustics and Soundproofing Thread
mikep:
We're seeing some good points here. Direk's suggestion is very good. You can try that approach to see what LF resonates the room. Skunkyfunks suggestion is good as well. The important thing is that you should know the different frequencies of the various keys or note, i. e., open E string is 40 hz., etc.
To soundproof a room, a 6 inch CHB will give you an STC of about 43. You paint the pores, it become 45. If you sound is about 100 dB, you still have to contend with something like 55 dB, which is still a lot of sound. If you are talking of a practice room for drums, it may not affect your neighbors anymore as long as you do not practice during late evenings. For recording, noises from the outside can still affect your recording especially during soft passages. You have to remember that you have to control sound coming out and coming in to the studio or room.
How do you treat your roof? Put glass fiber insulation under the GI sheets, about 50 mm, held by GI wire. Then, allow an air gap. Then install at least 2 pieces of 12mm gypsum board on ceiling sleepers. Put about 100 mm of glass fiber batt, the one that is rolled, 16 or 38 kgm, whatever you can afford, on top (inside) of the gypsum ceiling. Caulk all joints and possible areas where sound can seep through with silicon caulk or better yet, any non-hardening caulking material. After which you deal with the acoustics of the room. Put heavt drapes on 2 sides of the room from top of wall to floor. Put them so that the drapes are about 3 to 4 inches away from the wall. For the ceiling, install acoustical tile. For the floor, ordinary wood or T & G wood flooring.
So, there. A less expensive way of soundproofing and taming your room acoustics. As to the modes, that's another story. You have to go through room ratios and if there are still problems, specific traps using resonators like Helmholtz ones to tame resonating frequencies.
Where to put traps? At the back where the waves develop into their full potential. Also, the areas where the side walls meet the back wall. Bass tends to deveop in those areas. In the ceiling? Normally you put mid frequency absorbers there.
How big must the trap be? Definitely if you talking about low frequencies, you need more space to trap it. The trap should have at least a depth of 12 inches (.30 mtrs.).
Direk is right. You just do not put bass traps if there are not offending frequencies in the room. You might be over doing it and destroy the sound of your room.
FWIW
Direk:
--- Quote from: mikep on November 27, 2006, 06:35:33 PM --- As to the modes, that's another story. You have to go through room ratios
--- End quote ---
Let's consider first what happens along the length of a room when the air inside is excited by sound from the loudspeakers. A room's resonant frequencies are determined by the distance between the room's wall. The farthest apart the walls are, the lower the resonant frequency. Specifically, the lowest resonant frequency called the fundamental resonance, occurs within the room's length equals the half wavelength of sound. Put another way, a resonant mode will occur when the sound's wavelength is twice the length of the room. Other resonant modes occur at twice this frequency, three times this frequency, and so on. Whenever the length of the room is a multiple of half of the sound wavelength, a resonant mode will occur.
Here's an example and how to determine your room resonant modes based on your room's length, width, and height. The formula is F1 = 1130/2L. F1 is the first resonant mode, 1130 is the speed of sound in air (in feet per second), and 2L is two times the room's length (in feet). If the room is 21' long, its first resonant mode (F1) will be 27Hz (1130/2 x 21).
We know that the next mode will occur when the wavelength equals the room's length, at 54Hz (2 x F1), then again at the next multiple of half a wavelength ( 1- 1/2 wavelengths) at 81Hz (3 x F1), again at 108Hz (4 x F1), and so forth. Again, it is only necessary to consider room modes up to 300Hz.
The room's height and width will also create their own resonant modes. If we have an 8' ceiling, the resonant modes will occur at 71Hz (1130/2x8), 141Hz , 212Hz, and so on. If the width is 13', the resonant modes modes will be at 43Hz (1130/ 2 x 13), 87Hz, 130Hz, 174Hz, 217Hz, 261Hz, etc. We end up with a chart that look like this:
Mode Length Width Height
21' 8' 13'
F1 27Hz 71Hz 43Hz
F2 54Hz 141Hz 87Hz
F3 81Hz 212Hz 130Hz
F4 108Hz 282Hz 174Hz
F5 135Hz 353Hz 217Hz
F6 162Hz 260Hz
F7 189Hz 304Hz
F8 216Hz
F9 243Hz
F10 270Hz
F11 297Hz
F12 324Hz
Interpreting the resonance modes; Let's say for room distance, L24', W16', H8'; Length mode (F3) at 72Hz, coincides with the second mode width (F2) 70Hz and the first height mode (F1) 71Hz, these combine modes, will pile-up creating a huge peak in the response at this frequency. This undesirable situation occurs because the room's length, width, and height are multiples of each other. Expect a thick, peaky, and very colored bass reproduction.
We can minimize the frequency-response peaks and dips caused by room resonance modes by choosing a room ( this isn't always possible unless you build a room from scratch, or convert a garage or basement into a listening/monitoring/studio room) with dimensional ratios that more evenly spread the resonant modes over the low-frequency band. This gives you a head start in getting great sound from your system.
Goodluck!
mikep:
Korek, Direk (it rhymes, too). The terms are axial, tangential and oblique modes.
FWIW
toink:
--- Quote from: mikep on November 27, 2006, 06:35:33 PM ---How do you treat your roof? Put glass fiber insulation under the GI sheets, about 50 mm, held by GI wire. Then, allow an air gap. Then install at least 2 pieces of 12mm gypsum board on ceiling sleepers. Put about 100 mm of glass fiber batt, the one that is rolled, 16 or 38 kgm, whatever you can afford, on top (inside) of the gypsum ceiling. Caulk all joints and possible areas where sound can seep through with silicon caulk or better yet, any non-hardening caulking material. After which you deal with the acoustics of the room. Put heavt drapes on 2 sides of the room from top of wall to floor. Put them so that the drapes are about 3 to 4 inches away from the wall. For the ceiling, install acoustical tile. For the floor, ordinary wood or T & G wood flooring.
--- End quote ---
sori po sir medyo hindi ko naintindihan hehe. saan po b ako makakabili ng mga ganyang gamit? my room is 9 1/2 x 16 1/2 feet. mga magkano kaya gagastusin sa soundproofing nung roof
Direk:
--- Quote from: mikep on November 28, 2006, 07:28:27 PM ---Korek, Direk (it rhymes, too). The terms are axial, tangential and oblique modes.
FWIW
--- End quote ---
By the way, this explanation of room resonance modes and the examples given are greatly simplified. I've just covered what are called axial mode--those that exist between one pair of surfaces. Other modes resulting from the two surfaces pairs (tangential modes) and three surfaces pairs (oblique modes, from all six walls of a room) aren't discussed.
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