Biomedical Engineering Reference
In-Depth Information
Figure 3-15.
the absorption properties of a few common building materials as a
function of frequency. Notice that the low-frequency sounds are absorbed more than
the high-frequency sounds. also, notice the degree of absorption. Even though these
materials absorb more of the low-frequency sounds, they do not absorb much of them.
more low-frequency sounds reverberat-
ing in the listening environment than
high-frequency sounds, the difficulty
trying to understand speech increases; we
know that low-frequency sounds contrib-
ute very little to our ability to understand
speech and the low-frequency sounds
mask the high-frequency speech sounds.
The latter is known as the upward spread
of masking. These difficulties are exacer-
bated by high-frequency hearing loss.
In Figure 3-16, we see a speaker and
a listener with only some indication of the
reverberation, illustrated by the circles
and/or curved lines. In Figure 3-16A,
the listener is within the critical distance
and will have a better chance of under-
standing the speaker than the listener in
Figure 3-16B.
These examples are simplified to
illustrate the role of reflected versus direct
sound energy in listening. A listener can
be beyond the critical distance and remain
within the same room as the speaker. We
can expand this idea to other challenging
listening environments, such as those of
listening while in a stairwell and a hall-
way. Trying to understand speech in a
