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panel trap physic
Old 28th May 2009
  #1
Gear Head
 

panel trap physic

Hello,

i´ve got a question about panel traps with a plywood front. How do they work correctly? I´ve read a lot of different things about them. Some people told that they start to resonate with 90° out of phase and produce an own sound wave wich is out of phase. Others told, the membrane grab some energy and absorbs it beacause of the damped vibration.

The other question i have is..how long should a panel trap resonate? I think this is dependant on which of the above function ist correct.

Assumed a room has a mode at 140HZ with a time of 0,7 seconds. Should a panel trap now have the same amount of resonating time 0,7 seconds? Or should it be much shorter, so it can better damp it? If it resonates longer than the mode i think it will be audible as an own sound source.

It would be nice if someone can tell a little of the physics behind it.))

thank you
Old 28th May 2009
  #2
Lives for gear
 
HookedOnHardware's Avatar
 

Perhaps Ethan Winer, Jason Jones or Glenn Kuras could chime in.

Old 28th May 2009
  #3
Lives for gear
 

A panel resonator is basically a drum in reverse. It's going to operate over about a 2 octave range depending on exact construction. Most of the energy is reflected. What is absorbed is that which matches the resonant frequency of the structure defined by the depth of the sealed cavity and the mass of the front panel.

You're not going to tune the decay on it.

Bryan
Old 28th May 2009
  #4
Gear Guru
 
Glenn Kuras's Avatar
Quote:
Originally Posted by HookedOnHardware View Post
Perhaps Ethan Winer, Jason Jones or Glenn Kuras could chime in.

Actually Bryan just nailed it.
Old 28th May 2009
  #5
JWL
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JWL's Avatar
 

Also, in most panel bass traps there is absorbent material inside the sealed cavity, which is what dampens the vibration. For more, see Ethan's article.

Broadband bass traps are generally more effective, especially in small rooms. You definitely want to start with those; resonant traps can be useful to tame any problem frequencies that might remain after adding broadband trapping.
Old 28th May 2009
  #6
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

All good answers so far and I'll just add two points:

A panel trap is good for about an octave bandwidth.

The way I like to think of panel traps working is that they're basically a shock absorber for sound waves. The offer a controlled resistance to the waves that strike the front of the panel.

--Ethan
Old 28th May 2009
  #7
Gear Head
 

okay thank you so far.....!!! Based on your descriptions i would say both points are a little bit true from my question?

I think decay time of panel traps can be really important to tune? If a short bass impulse (a short kick) for example excites the room and the trap....
and the panel trap resonates longer than the room itself it can easily be heard as an reverb, if i´m standing in the near of the trap or if panel traps were placed near the listening point. I had equal impressions by tuning some helmholtzabsorber.
Old 29th May 2009
  #8
Lives for gear
 

I think you'd have less chance with a panel absorber with regard to ringing than a Helmholz. This is especially true when you try to tune very very low.

Bryan
Old 29th May 2009
  #9
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by Okatvius View Post
I think decay time of panel traps can be really important to tune?
There's nothing to tune. The whole point of the rigid fiberglass inside the trap is to damp the resonance. So if the panel rings, just add more fiberglass.

--Ethan
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