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The secrets of bass trap placement

by Nyal Mellor February 09, 2011

One of the things I get asked quite often is 'where is the best place to put bass traps and why?'. This short article will explain a little about what bass traps do and how they work before going on to discuss the three different places where bass traps can be placed.   Bass Traps and room modes The most effective place to add bass traps is in the corners of the room since all room modes have a pressure high or node in the corner. The three key points about room modes are summarized below, but if you want to know more be sure to read the detailed article Room Modes and Room Mode Calculators on our main website.
  • ALL rooms have naturally occurring resonance frequencies - variously called room modes, standing waves, eigentone, eigenmodes or modal resonances.
  • Room modes are the main cause of acoustic distortion below 300Hz or so, causing peaks and dips in the frequency response of 20dB or more.
  • Modal resonances store energy and decay slowly compared to nearby frequencies causing audible problems such as 'one note bass' and 'boominess'.
  How Bass Traps work Bass traps are acoustic absorbers designed specifically to be effective down into the frequency range where room modes cause problems. Typical 3" thick fiberglass absorber panels start to lose effectiveness at around 250Hz whereas most of our modal resonance problems occur below 150Hz in the so called 'sparsely populated modal region'. Bass traps typically incorporate elements such as membranes, airspaces and additional thicknesses of fiberglass (up to 6" or more) to extend absorption down into the double digit range.   The three places where Bass Traps can be installed There are three main places where bass traps can be installed: [caption id=" align="alignright" width="100"]Tri-corner bass traps Tri-corner bass trap[/caption] 1. Tri-corner, where the two walls meet the ceiling or the floor. There are 8 tri-corners in a square or rectangular room, although placing bass traps at the four on the floor may not be practical. Placing a bass trap in this location affects all room modes. There are specific triangular bass traps designed for installation in the tri-corners, such as the Primacoustic Cumulus. [caption id=" align="alignleft" width="257"]Corner mount bass traps Corner mount bass trap[/caption] 2. A wall / wall corner, such as the interface of the side and back wall. There are 4 corners in a square or rectangular room. Placing a bass trap in a wall / wall corner will affect the main length and width modes and some of the height modes. Stacking two 4' tall corner mount bass traps such as the Primacoustic MaxTrap, one above the other, in the corner can affect all room modes, since the tri-corner location will also be covered in a standard 8ft ceilinged house. Wall mount bass traps Wall mount bass trap[/caption] 3. A wall or ceiling. There is plenty of wall and ceiling area available in most rooms for installing bass traps such as the Primacoustic FullTrap or the amazing RPG Modex Plate. Generally a wall mount bass trap will most strongly impact the room modes caused by the two parallel surfaces. Placing a bass trap on the side wall, for example, will mainly affect the width mode. Are there any other things you want to know about bass trap placement or bass traps in general?  width=

Nyal Mellor
Nyal Mellor


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Nyal Mellor, Founder, Acoustic Frontiers

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