By Bruce Black
Back in our December 2013 issue, I
explained the difference between bass traps
and Helmholtz resonators as ways to control
the bass response of a room. While bass
traps have their strengths, I brought to your
attention the Helmholtz resonator-a bass
control device that's small, easy to design
and build, can be hidden away anywhere in
your room, and can be covered to match
your decor without affecting its performance. Pretty neat!
I ended that article with a promise that "next time" we'd learn how to build one,
and after a bit of a delay on the Editorial side [Guilty-MM], "next time" is finally
here. It's time to learn just how easy it is to build a Helmholtz resonator and get
your low end under control!
The theory
We'll start by looking at the Helmholtz resonator drawing in Figure 1. The
Helmholtz resonator in the drawing is a general-purpose device tuned to 100 Hz,
and designed to not be intrusive in even the smallest room. It should be placed
with its port as close as possible to a corner where two or three room surfaces
meet ("bicorner" or "tricorner"). This allows it to influence the resonances inherent
Fig. 1: A construction diagram for the resonator. The port size shown in the picture
is for a 100 Hz resonator; five other port sizes are listed in the notes at right.
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RECORDING March 2014