John Heisz - Speakers and Audio Projects | Sound Pressure VS Sound Velocity - Room Acoustics Basics @IBuildIt | Uploaded 1 month ago | Updated 12 hours ago
IN THE VIDEO I used an SPL meter to measure the 40Hz tone playing in various parts of my listening room. As shown there was a wide range - nearly 20db - between the nulls and the peaks. This is caused by a room mode at 40Hz because my room has a mode at that frequency.
ROOM MODES ARE resonances at frequencies that correspond to the physical dimensions of the room - length, width and height. If the frequencies are there in the content (music, movies, etc.) you are playing in the room, the modes will be activated. If your room has a mode at 40Hz, then anything you play in that room that has 40Hz in it will resonate at that frequency.
ROOM MODES DOMINATE the bass response in every small room and there's nothing that can be done to stop that completely. Room treatment will help to reduce the impact of the room modes, but cannot fully solve the problem.
IN PARTICULAR, effective acoustic treatment will reduce the reverb time (the length of time the resonance continues to "ring"), but it doesn't prevent the mode from being activated.
EQ CAN REDUCE the level of the output at the mode frequencies, but does not reduce the reverberation time of the resonance. It does not "fix" the pressure (amplitude) variations that modes create.
MY ROOM USES porous absorbers, also known as velocity absorbers that work when the sound passes through the damping material. The damping material converts some of the sound energy to heat, reducing it slightly. The thicker the damping material, the more energy it will absorb.
BUT ALL DAMPING has an effective range where it works best, and porous absorbers are less effective for bass frequencies.
PLACEMENT OF THE absorbers isn't critical since even though there are pressure (amplitude) variations throughout the room (as shown in the video), the sound is still moving at the same speed - velocity. If the sound can pass through the damping material, regardless of where it is, it will be effective.
THAT'S WHY these types of absorbers work best with an air gap behind them. The sound can then pass fully through the damping material while it's moving at a constant velocity. If the absorber is tight to a wall or other reflecting surface, the sound velocity reaches 0 at the point of reflection and the absorber becomes less effective.
THE PRESSURE (amplitude) buildup and nulls demonstrated in the video are areas where the sound is either adding together or cancelling out, but the sound is still moving at the same velocity.
"PRESSURE" TRAPS are different from velocity absorbers in that they react to the amplitude of the sound, so you must place those where that amplitude is greatest.
THEY NEED that extra AMPLITUDE to operate properly because the sound amplitude is what they react to. The sound energy (vibration) causes the membrane in the pressure trap to vibrate, and that vibration absorbs the sound energy.
THAT'S WHY the best overall approach to budget room treatment that actually works is with porous absorbers. You can put them anywhere and they will be effective. They must be THICK enough and you'll have to use a lot of them, but they will improve the sound quality you'll get in your room.
You can help support the work I do in making these videos:
Project plans for sale: ibuildit.ca/plans
Join the ibuildit community on Loacals: ibuildit.locals.com
Support this channel on Patreon:
patreon.com/user?u=865843&ty=h
#diyspeakers
#johnheisz
#audio
My "Scrap bin" channel:
youtube.com/c/IBuildItScrapBin
My main channel:
youtube.com/user/jpheisz
Website: ibuildit.ca
Facebook: facebook.com/I-Build-It-258048014240900
Instagram: instagram.com/i_build_it.ca
IN THE VIDEO I used an SPL meter to measure the 40Hz tone playing in various parts of my listening room. As shown there was a wide range - nearly 20db - between the nulls and the peaks. This is caused by a room mode at 40Hz because my room has a mode at that frequency.
ROOM MODES ARE resonances at frequencies that correspond to the physical dimensions of the room - length, width and height. If the frequencies are there in the content (music, movies, etc.) you are playing in the room, the modes will be activated. If your room has a mode at 40Hz, then anything you play in that room that has 40Hz in it will resonate at that frequency.
ROOM MODES DOMINATE the bass response in every small room and there's nothing that can be done to stop that completely. Room treatment will help to reduce the impact of the room modes, but cannot fully solve the problem.
IN PARTICULAR, effective acoustic treatment will reduce the reverb time (the length of time the resonance continues to "ring"), but it doesn't prevent the mode from being activated.
EQ CAN REDUCE the level of the output at the mode frequencies, but does not reduce the reverberation time of the resonance. It does not "fix" the pressure (amplitude) variations that modes create.
MY ROOM USES porous absorbers, also known as velocity absorbers that work when the sound passes through the damping material. The damping material converts some of the sound energy to heat, reducing it slightly. The thicker the damping material, the more energy it will absorb.
BUT ALL DAMPING has an effective range where it works best, and porous absorbers are less effective for bass frequencies.
PLACEMENT OF THE absorbers isn't critical since even though there are pressure (amplitude) variations throughout the room (as shown in the video), the sound is still moving at the same speed - velocity. If the sound can pass through the damping material, regardless of where it is, it will be effective.
THAT'S WHY these types of absorbers work best with an air gap behind them. The sound can then pass fully through the damping material while it's moving at a constant velocity. If the absorber is tight to a wall or other reflecting surface, the sound velocity reaches 0 at the point of reflection and the absorber becomes less effective.
THE PRESSURE (amplitude) buildup and nulls demonstrated in the video are areas where the sound is either adding together or cancelling out, but the sound is still moving at the same velocity.
"PRESSURE" TRAPS are different from velocity absorbers in that they react to the amplitude of the sound, so you must place those where that amplitude is greatest.
THEY NEED that extra AMPLITUDE to operate properly because the sound amplitude is what they react to. The sound energy (vibration) causes the membrane in the pressure trap to vibrate, and that vibration absorbs the sound energy.
THAT'S WHY the best overall approach to budget room treatment that actually works is with porous absorbers. You can put them anywhere and they will be effective. They must be THICK enough and you'll have to use a lot of them, but they will improve the sound quality you'll get in your room.
You can help support the work I do in making these videos:
Project plans for sale: ibuildit.ca/plans
Join the ibuildit community on Loacals: ibuildit.locals.com
Support this channel on Patreon:
patreon.com/user?u=865843&ty=h
#diyspeakers
#johnheisz
#audio
My "Scrap bin" channel:
youtube.com/c/IBuildItScrapBin
My main channel:
youtube.com/user/jpheisz
Website: ibuildit.ca
Facebook: facebook.com/I-Build-It-258048014240900
Instagram: instagram.com/i_build_it.ca
