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At what freq range does corrugated cardboard start to substantially reflect? Effects Pedals, Units & Accessories
Old 10th September 2011
  #1
Gear Nut
 

At what freq range does corrugated cardboard start to substantially reflect?

I'm making some bass traps out of single-wall corrugated cardboard boxes filled with Roxul Safe-N-Sound batts.

A few of these traps will be placed at 1st reflection points (or will themselves create some due to corner straddling, etc.) and so there I will be gluing some supplemental 2" Auralex foam squares to the surface of the box for the 1st reflections. What I'm debating is, should I cut a slightly smaller sized hole in the box directly behind the foam squares or not? If I can avoid doing so, the Safe-N-Sound will stay in the box better, but I haven't been able to find any data about what frequency single-wall corrugated cardboard might start to substantially reflect. If it's a high enough frequency, the foam supplement will do what's needed, but if it's low enough, I'd need the hole behind the foam to let the frequencies pass through to their Safe-N-Sound death.

Anyone know or have an educated guess on what freq range typical single layer corrugated cardboard might start to reflect?
Old 10th September 2011
  #2
Lives for gear
 
Starlight's Avatar
That sounds like something no one has done before. I will be interested to see your measurements afterwards to see whether the foam manages to absorb high frequencies down to the same frequency that the cardboard reflects them, kind of like a crossover.
Old 12th September 2011
  #3
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by dcrhythm View Post
Anyone know or have an educated guess on what freq range typical single layer corrugated cardboard might start to reflect?
Cardboard varies a lot, so you need to measure the particular type you have. It's very easy. Put a large (maybe 4 by 4 feet) piece of cardboard between a microphone and loudspeaker, then play pink noise through the speaker and record the mic. Then use an FFT type program to see what got through and what didn't. Most 2-track editor type programs have an FFT view. Or if you have real room measuring software, that's even better.

--Ethan

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Old 13th September 2011
  #4
Gear Maniac
 

ethan, so here, how would we determine that the sound that didn't get through is reflected rather than absorbed?
Old 14th September 2011
  #5
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

All material absorbs, passes, and reflects in varying amounts. We know that thin cardboard won't absorb much bass, so my suggestion will help you find the transition frequency from reflecting to passing.

--Ethan
Old 19th September 2011
  #6
Lives for gear
 
jhbrandt's Avatar
Quote:
Originally Posted by Ethan Winer View Post
All material absorbs, passes, and reflects in varying amounts. We know that thin cardboard won't absorb much bass, so my suggestion will help you find the transition frequency from reflecting to passing.

--Ethan
+1
-- John
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