Mr. Hardesty Lightened the Load
The late Richard Hardesty was a respected
audio engineer, consultant, writer, audio reviewer, and I read
he was a respectable pianist. He was also a pioneer of
high-end audiophile retailing in Southern California.
acknowledged that in his early retail days, he drove to his
customers' homes with a heavy load of audio test gear to deal
with room acoustics.
As time passed, the amount of heavy gear decreased as
succeeding visits became a near acoustical replay of the
previous visits. Although test gear must have certainly
looked cool in the customer's eyes, much of it became
unnecessary. It had become apparent that many of their
rooms were just another enclosed box with predictable issues
and routine acoustical solutions.
The goal of this chapter
is to skip the heavy-gear phase And solve acoustical
issues with a practical mix of advice from Mr. Hardesty, the
Master Handbook of Acoustics, Aruatex Acoustics,
long-forgotten sources, plus many of my colleagues.
The Acoustical Small Room .....
it's your room.
As outlined in Handbook Chapter 2,
wavelength, amplitude, and frequency are used to describe
sound waves. Sound wavelengths range from 56.5 feet to
about 3/4 of an inch. Any room with dimensions
comparable to acoustical wavelengths is acoustically a small
room. Therefore, rooms with a dimension of 56.5 feet, or
less, is an acoustically small room.
Small Rooms Distort
Acoustical small rooms can erupt into
resonating cavities of agitated-low-frequency energy.
The small-room is also an acoustic reflecting mirror of
high-frequency sound that competes with the direct sound from
the speaker system. It may even have a noisy neighbor.
The acoustical-small room is your room with a predisposition
to generate acoustical distortion.
Audio distortion is the corruption of
reproduced sound. Acoustical-distortion is an audio
distortion created by the room. Three types of sound
perception are affected by acoustical-distortion: timber,
imaging, and spatial impression. Each influenced by the
acoustical-elements of room modes, specular reflections, comb
filtering, absorption, diffusion, and noise. However,
the management of room modes, specular reflections, and noise
is the principle-concern in the acoustical-small room.
Each boundary of the acoustical-small room
causes low-frequency sound waves to resonate, much as waves in
the ocean. They are acoustical-described as standing waves or
room modes. The primary axial room modes of opposite
boundaries (length, width, height) are the most
significant. The wavelengths of the three primary
axial-modes are equal to dividing half the speed of sound by
its room dimension -- length, width, height.
Handbook Note: Speed of sound = 1130 ft /second
Their resonating energy
can produce an uneven distribution of low-frequency sound that
causes deviations from flat frequency response. That is
a principle definition of distortion.
Specular reflections are room boundary
reflections of a short-acoustical wavelength that compete with
the direct sound from a speaker. Their physics is
identical to a ray of light reflecting off a mirror.
Formally defined as the angle of incidence equals the angle of
reflection, specular reflections distort imaging, and spatial
Noise is a random unwanted competing
sound. Noise generated within a room or adjoining areas
distorts imaging, timber, spatial impression, and compresses
the dynamic range of sound. Noise is the most corruptive