porous insulation is velocity-based (converts kinetic energy via particle velocity into heat). as such, it needs to be placed at areas of high particle velocity to be effective.
particle velocity and pressure are inversely proportional. hence, directly at the boundary where pressure builds, velocity goes to zero (as the waveform is about to reflect and reverse direction). much like a billiards ball on a pool table. maximum velocity occurs at 1/4wavelength for a particular frequency.
since we are discussing LF absorption, the wavelengths become very long ... and reaching this 1/4wavelength distance is simply not feasible in small spaces. absorption is still efficient well before that, but it is wise to have an understanding of what is going on before proceeding.
as such, the further the material spaced from the boundary, the more effective it will be (as you are placing the insulation further towards areas of high particle velocity).
placing porous insulation directly against the boundary is very ineffective for LF modal issues - as that is an area where pressure is maximum and velocity is approaching zero.
bear in mind too that adding an air-gap between the insulation and the boundary
there is no data that i am aware of that insists that using multiple types of insulation (gas-flow-resistivity) is any more effective.
the StudioTips SuperChunks (corner chunks/triangles) - are surely effective at mid/high LF absorption (addressing freq response via modal issues as well as LF decay times) - but are not very effective for the lower octaves.
what is important regarding porous insulation is the gas-flow-resistivity
values. if you are limited by how much real estate (corner space in your room), then you will have thinner corner traps and will function better with a material with higher gas-flow-resisitivity. (OC703, OC705, equivilant mineral wool, etc). but, as learned above, the thicker the panel (either with thick absorption or absorption with a large air-gap), will perform better for LF absorption.
the ideal way to do this is to make very thick traps of cheap, pink fluffy insulation (which has a low gas-flow-resistivity), and one could loosely fill large plastic bags of this insulation and stack into the corners.
it entirely depends on the design constraints of the individual. but, the thicker the traps, the lower the GFR value material you will want to use.
a simply idea i have is to take your typical 48"x24" batts (OC703, etc) and instead of making 6" thick panels that straddle the corner .... turn these panels on their sides such that they are 48" wide and 24" tall, and then stack those from floor to ceiling. it will provide you with a "thicker" trap (material + air gap spacing from boundary) than a 34" faced corner triangle trap and will also not require any cutting
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choice of fabric isn't terribly important for the LF corner porous traps for modal issues. although many will quickly over-deaden their rooms due to the fact that the corner trap is broadband not just for LF but for the specular range as well. as such, many apply reflective surfaces to the outer face of the corner trap to reflect some mid/HF specular content back into the room.
for broadband panels to combat specular reflections (that function as 'rays'), you will need to use thick enough insulation such that the entire specular reflection is attenuated to the required gain (eg., -20dB, or whatever your design requirements are).
for these, the fabric most certainly needs to be 'breathable'.
porous insulation is velocity-based (converts kinetic energy via particle velocity into heat). as such, it needs to be placed at areas of high particle velocity to be effective.
particle velocity and pressure are inversely proportional. hence, directly at the boundary where pressure builds, velocity goes to zero (as the waveform is about to reflect and reverse direction). much like a billiards ball on a pool table. maximum velocity occurs at 1/4wavelength for a particular frequency.
since we are discussing LF absorption, the wavelengths become very long ... and reaching this 1/4wavelength distance is simply not feasible in small spaces. absorption is still efficient well before that, but it is wise to have an understanding of what is going on before proceeding.
as such, the further the material spaced from the boundary, the more effective it will be (as you are placing the insulation further towards areas of high particle velocity).
placing porous insulation directly against the boundary is very ineffective for LF modal issues - as that is an area where pressure is maximum and velocity is approaching zero.
bear in mind too that adding an air-gap between the insulation and the boundary
there is no data that i am aware of that insists that using multiple types of insulation (gas-flow-resistivity) is any more effective.
the StudioTips SuperChunks (corner chunks/triangles) - are surely effective at mid/high LF absorption (addressing freq response via modal issues as well as LF decay times) - but are not very effective for the lower octaves.
what is important regarding porous insulation is the gas-flow-resistivity
values. if you are limited by how much real estate (corner space in your room), then you will have thinner corner traps and will function better with a material with higher gas-flow-resisitivity. (OC703, OC705, equivilant mineral wool, etc). but, as learned above, the thicker the panel (either with thick absorption or absorption with a large air-gap), will perform better for LF absorption.
the ideal way to do this is to make very thick traps of cheap, pink fluffy insulation (which has a low gas-flow-resistivity), and one could loosely fill large plastic bags of this insulation and stack into the corners.
it entirely depends on the design constraints of the individual. but, the thicker the traps, the lower the GFR value material you will want to use.
a simply idea i have is to take your typical 48"x24" batts (OC703, etc) and instead of making 6" thick panels that straddle the corner .... turn these panels on their sides such that they are 48" wide and 24" tall, and then stack those from floor to ceiling. it will provide you with a "thicker" trap (material + air gap spacing from boundary) than a 34" faced corner triangle trap and will also not require any cutting
choice of fabric isn't terribly important for the LF corner porous traps for modal issues. although many will quickly over-deaden their rooms due to the fact that the corner trap is broadband not just for LF but for the specular range as well. as such, many apply reflective surfaces to the outer face of the corner trap to reflect some mid/HF specular content back into the room.
for broadband panels to combat specular reflections (that function as 'rays'), you will need to use thick enough insulation such that the entire specular reflection is attenuated to the required gain (eg., -20dB, or whatever your design requirements are).
for these, the fabric most certainly needs to be 'breathable'.
