We're going to talk tonight about the musical tone burst and its
transients, and about small rooms and their corners. We'll blend
these topics together into the problem area of low frequency room
articulation and then show how bass traps help the situation. Finally,
we'll discuss the new generation of bass traps we've developed over
the last two years.
Traditional testing of rooms utilizes both pink noise and slow
sine sweeps to evaluate the suitability of the room for listening.
Music is neither noise nor steady state tone. The ability of the
room to articulate music is closely related to its ability to track
the details of each discrete tone burst.
The typical listening room is frequently without proper low frequency
decay constants. Instead of actively tracking the tone burst, the
room distorts both of the burst transient: attack and decay.
Let's start by looking at the tone burst decay. In a furnished
room without bass traps the low end tone burst decay will vary between
two extreme characteristics, first there can be the prolonged decay
-- that boomy sound -- because the frequency of the tone burst matches
one of the room's resonant mode frequencies.
The second decay extreme occurs when the room is driven at a non-resonant
frequency. This so-called anti-resonant frequency decay is characterized
by an initial very rapid decay rate, followed by a resurgence of
sound to within 10 dB of the original level. Detailed observation
shows that the resurgent sound has changed frequency of a nearby
resonant mode -- that is some components of a musical chord actually
change frequency during the decay, resulting in 'room coloration'
of the music.
The location of bass traps in a room needs to facilitate the damping
of all resonant modes. There are eight places in each rectangular
room where high sound levels exist for all from resonance modes.
There are the tri corners-for example, the intersection of 2 walls
and the floor. Each tri corner is part of each of the three sets
of parallel walls that determine the room's resonance mode. Properly
designed bass traps can be installed in the tri corners to dampen