I just finish building superchunk bass traps and first reflection point absorbers and I have bass traps in the back corners.
I plan on making diffusers as door on my LP book case on the back wall.
I was going to put a 4x8 sheet of OC703 on the ceiling as a cloud absorber but as is the room is perfect for absorption. So I will build diffuser the ceiling.
The question:
1. should the lines of the QRD (for example) go for me to the speakers or from side wall to side wall?
2. What is the best diffuser design for a ceiling?
I plan on making diffusers as door on my LP book case on the back wall.
I was going to put a 4x8 sheet of OC703 on the ceiling as a cloud absorber but as is the room is perfect for absorption. So I will build diffuser the ceiling.
The question:
1. should the lines of the QRD (for example) go for me to the speakers or from side wall to side wall?
2. What is the best diffuser design for a ceiling?
Normally such a QRD is oriented side to side, mainly to spread the first ceiling reflection. For secondary or later reflections orientation isn't that important imho. If you're in doubt: there are QRD diffusors that act in two directions, mostly called QRD 2D. But these are more laborious and more difficult to suspend. Alternatively normal QRD modules 3'x3' or 4'x4' with different orientation can be used.
As to design: the diffusor ideally has to act from several hundred Hz. Think of some 6 to 8 inches high. Designs are all over the WWW.
As to design: the diffusor ideally has to act from several hundred Hz. Think of some 6 to 8 inches high. Designs are all over the WWW.
If you have a rectangular room and speakers are positioned at the short wall:
Placing the "lines of the QRD" parallell to the long walls will spread the sound like a plume towards the long walls (across the room width)
Placing "lines of the QRD" parallell to the short walls will spread the sound like a plume towards the short walls (along the room length).
A 1D diffuser = a QRD, can lower the strength of the reflection about 7 dB.
A 2D diffuser, a "skyline", can lower the strength of the reflection about 20 dB as it spreads more like a half sphere.
If you are sitting close to the diffuser, the 2D one could be preferred on the sidewall + ceiling, as it "dampens" the reflection strength more than a 1D one.
If you have the diffuser at the wall behind you at a "respectable distance", say > 1,5-2,5 m / 5-8,2 feet a 1D version with "the lines" vertical could be better than a 2D-one. -You want some strong good and wanted lateral reflections reaching LP somewhere in the range 15-30 ms, not sooner. As vertical 1D diffusses sideways towards the sidewalls => LP, you get good stronger lateral reflections with these than with 2D. Often recommended is a 20 ms delay for these reflections together with a minumum distance of 3 x wavelength versus calculated cut off frequency for the diffuser. A 15 cm / 6" deep 1D will reflect 180 degrees out phase for 30 cm / 12" => frequency about 1100 Hz.
A 2D may look more cool but might be a worse choice depending on distance from it to LP. Common recommendations for "bad early reflections", say shorter than about 15 ms, are at -20 dB or lower compared to the direct sound. The "good later reflections" from 15 ms and upwards are wanted stronger than the early ones. Very low early reflections and fairly strong late ones will fool the brain into thinking that you are sitting in a room larger than its physical dimensions, = usually preferred.
So, -what is the distance from diffuser to LP and do you want a strong reflection from it or a weak one? Perhaps an absorber is the better choice for early specular reflections.
Placing the "lines of the QRD" parallell to the long walls will spread the sound like a plume towards the long walls (across the room width)
Placing "lines of the QRD" parallell to the short walls will spread the sound like a plume towards the short walls (along the room length).
A 1D diffuser = a QRD, can lower the strength of the reflection about 7 dB.
A 2D diffuser, a "skyline", can lower the strength of the reflection about 20 dB as it spreads more like a half sphere.
If you are sitting close to the diffuser, the 2D one could be preferred on the sidewall + ceiling, as it "dampens" the reflection strength more than a 1D one.
If you have the diffuser at the wall behind you at a "respectable distance", say > 1,5-2,5 m / 5-8,2 feet a 1D version with "the lines" vertical could be better than a 2D-one. -You want some strong good and wanted lateral reflections reaching LP somewhere in the range 15-30 ms, not sooner. As vertical 1D diffusses sideways towards the sidewalls => LP, you get good stronger lateral reflections with these than with 2D. Often recommended is a 20 ms delay for these reflections together with a minumum distance of 3 x wavelength versus calculated cut off frequency for the diffuser. A 15 cm / 6" deep 1D will reflect 180 degrees out phase for 30 cm / 12" => frequency about 1100 Hz.
A 2D may look more cool but might be a worse choice depending on distance from it to LP. Common recommendations for "bad early reflections", say shorter than about 15 ms, are at -20 dB or lower compared to the direct sound. The "good later reflections" from 15 ms and upwards are wanted stronger than the early ones. Very low early reflections and fairly strong late ones will fool the brain into thinking that you are sitting in a room larger than its physical dimensions, = usually preferred.
So, -what is the distance from diffuser to LP and do you want a strong reflection from it or a weak one? Perhaps an absorber is the better choice for early specular reflections.
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