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vpr experiments in very small room
Old 9th June 2019
  #1
Here for the gear
 
datal4b's Avatar
 

vpr experiments in very small room

what's up guys, i'm nixon.. i tried building 2 vpr panels and here was my process. the steel is cold rolled 1m x 1.5m x 1.6mm & powder coated. i'm using a 4" mattress topper for the foam

i used np1 polyurethane sealant spread thin. i know that it is flexible because we use it at work and it has to retain its elasticity for many years so that it doesn't crack.

in my room the bass is very amplified in the back of the room in the corner and back wall, super loud, and pretty quiet near my listening position. the room is completely untreated other than these 2 vprs i have just built. it's 9' x 10.7' x 8' with the wall behind the speakers brick & concrete floor, everything else drywall.

my rew testing seems odd, i'm sure i've done something incorrectly. i've got the mic pointing upwards with the 90deg cal file per instructions in the manual for measuring lf. i'm using the umik-1. my waterfalls seem to indicate that the panels are making my room worse? i'm positive i labeled them correctly.
Attached Thumbnails
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Attached Files
File Type: mdat vpr tests.mdat (9.93 MB, 32 views)
Old 17th August 2019
  #2
Gear Head
 
Mark Alpine's Avatar
What kind of rigid back plate do you use? The metal sheet is the spring, the foam the damper. Thus, the other side of the foam need to be attached to some thing sturdy that doesn't move/resonate.
Old 18th August 2019
  #3
Gear Addict
 

Just a speculation but anyway: In the empty room the walls are more lossy at lower bass but up at upper bass roughly 180 and 210 Hz you have 2 tails. Probably from modes so drywalls are reflective in that range and upwards (probably a bit below as well). At around 70 Hz in the empty room there are no long tails in the waterfall. Drywall on wooden studs often work quite well as membrane absorbers around 70 Hz or so. This may be a reason for no tails in the waterfall there, besides lower bass just passing through. If one sees the drywalls as lossy = low bass is passing through them but getting reflected back from another surface / wall outside your room, one could say the room is acoustically larger than the inner measurements between the drywalls. Placing the VPRs inside the room can then be an incorrect place for the VPRs and you end up with the other waterfalls with very long tails in the lower bass.

I would as a test with measurements put the VPRs at the most rigid and stiff wall inside your room, then perhaps outside the room close to a rigid and stiff wall there.
Old 4 weeks ago
  #4
Quote:
Originally Posted by Mark Alpine View Post
What kind of rigid back plate do you use? The metal sheet is the spring, the foam the damper. Thus, the other side of the foam need to be attached to some thing sturdy that doesn't move/resonate.
That‘s wrong...the metal plate is the mass and the foam is the spring....and there is additional absorption due to the metal plate resonating in its eigenmodes
Old 4 weeks ago
  #5
Here for the gear
 
datal4b's Avatar
 

i've been f'd up for the last 6 wks, fell asleep with my arm cocked all weird under my head on a train from prague to vienna after barely sleeping for 3 days (let it roll weekend) and i damaged the nerve in my arm, have not been able to use my dominant hand barely at all "radial nerve palsy" **** is awful, got a little taste of what having a disability can be like...anyways i've been really wanting to finish these vprs at least to some satisfaction. before i left i built frames for them and i was thinking of suspending them from the frames with thin gauge wire thru the holes that the powdercoating company punched thru them to suspend them during their process, the holes are like 1mm. this is the only idea i have right now to try and get the foam to lay flat against the wall because just laying them against the wall there is always a gap that tapers wider from the top down. once they are slightly suspended from the bottom of the frame i figure i will secure the frames against the wall with a small notch in the frame where the molding is on the floor. criticisms? pointless?
Old 4 weeks ago
  #6
Gear Head
 
Mark Alpine's Avatar
Quote:
Originally Posted by housegezeichnet View Post
That‘s wrong...the metal plate is the mass and the foam is the spring....and there is additional absorption due to the metal plate resonating in its eigenmodes
Thanks for pointing that out. Haven't read the Fraunhofer VPR patent. The back should be mounted on something rigid though, right?
Cheers, Mark
Old 4 weeks ago
  #7
Yes....and very close to the wall for high pressure and to avoid acoustic short cut
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