78
ARCHITECTURAL ACOUSTICS
VARIATION IN REVERBERATION WITH
VARIATION IN PITCH
Six years ago there was published in the Engineering Record and
the American Architect a series of papers on architectural acoustics
intended as a beginning in the general subject. The particular phase
of the subject under consideration was reverberation,—the continua¬
tion of sound in a room after the source has ceased. It was there
shown to depend on two things,—the volume of the room, and the
absorbing character of the walls and of the material with which the
room is filled. It was also mentioned that the reverberation depends
in special cases on the shape of the room, but these special cases w^ere
not considered. The present paper also will not take up these special
cases, but postpone their consideration, although a good deal of
material along this line has now been collected. It is the object
here to continue the earlier work rather narrowly along the original
lines. The subject was then investigated solely with reference to
sounds of one pitch, C4 512 vibrations per second. It is the inten¬
tion here to extend this over nearly the whole range of the musical
scale, from Ci 64 to C7 4096.
It can be shown readily that the various materials of which the
walls of a room are constructed and the materials with which it is
filled do not have the same absorbing power for all sounds regard¬
less of pitch. Under such circumstances the previously published
work with C4 512 must be regarded as an illustration, as a part of a
much larger problem, — the most interesting part, it is true, be¬
cause near the middle of the scale, but after all only a part. Thus a
room may have great reverberation for sounds of low pitch and very
little for sounds of high pitch, or exactly the reverse; or a room may
have comparatively great reverberation for sounds both of high and
of low pitch and very little for sounds near the middle of the scale.
In other words, it is not putting it too strongly to say that a room
may have very different quality in different registers, as different
as does a musical instrument; or, if the room is to be used for
speaking purposes, it may have different degrees of excellence or
defect for a whisper and for the full rounded tones of the voice,
different for a woman’s voice and for a man’s — facts more or less