Calculate air gap for porous absorbers

Porous absorbers also called Frictional or Velocity Absorbers, these are by far the most common when it comes to getting good bass traps. Mostly because they are the cheapest and most “DIY-friendly” bass traps out there. Not just that, they also are effective at minimizing the higher and mid frequencies as well, potentially giving your room a dryer sound in the process.

Do not provide low frequency absorption when you mount porous absorbers flat on your wall. You can, however, lower the minimum frequency absorbed by mounting them with an air gap between the absorptive panel and wall.

For porous absorbers, the bigger the air gap, the lower the minimum frequency absorbed.

Calculate Optimal Gap Size for Given Frequency

Given frequency : Hz

Select frequency range : 20 - 300 Hz   300 - 4500 Hz  

The best gap size for the given frequency = meter feet

Calculate Frequency for Given Gap Size

Metric or Imperial :
Given Gap Size : meter feet

Optimal Gap Size for the given Frequency = Hz

Finding bass buildup hot spots

Bass energy buildup can vary from corner to corner due to factors like your speaker and subwoofer placement, as well as the geometry of your room. You may not be able to treat all your corners, so a great way to prioritize bass trap placement is to determine which corners have the most bass buildup.

The best way to find hot spots is to use a test microphone and room measurement software like Room EQ Wizard (Free for Windows and iOS).

Download this filtered pink noise wav file

Pink noise has energy at all frequencies so it can excite all the modes in your room. High frequencies have been filtered out of this pink noise to make it easy for you to hear or measure the low end.
Start playing the noise in your room.
Walk around the room, sticking your head into all the corners and listening to find where bass energy is accumulating most. Place bass traps in the corners that have the most bass buildup.

If you have one, an SPL meter is a better diagnostic tool than your ears ;-)

Get here a SPL Meter app for your iPhone or iPad


More about different absorber types    Where to Put Bass Traps – Quick & Easy Guide

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