Sound Chamber Fundamentals; Reflections And Interference - TDT Medusa4Z User Manual

Sound Chamber Fundamentals

Reflections and interference inside of a sound chamber can distort the stimulus frequency or
have an undesirable effect on the stimulus level. This section provides supplemental
information on these issues and correctly setting-up your sound chamber.

Reflections and Interference

Sound waves are a mechanical force in which pressure is used to transmit energy through a
physical medium. Sound waves can be reflected off surfaces. The reflected signal strength is
based on the angle of incidence and damping factor of the reflecting surface.
Constructive & Destructive Interference
The signal strength at a specific point of interest (e.g subject's ear, calibration microphone
location) can increase or decrease depending on the phase delay, frequency, distance of travel
and damping factor of the material.
For this reason, the measured dB SPL of a specific frequency may vary greatly depending on
the combination of the primary signal and its reflections at the recording site, which may
appear as drop outs or spikes in the calibrated frequency response for your speaker.
Figure 1 - Sound wave reflection vectors inside a sound chamber
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