Filter
Top Products
38
Loudspeaker Measurements
Returning to loudspeakers, a similar situation has developed. Although nobody listens to
music in an anechoic chamber, loudspeaker measurements are commonly performed in
them.
3
Although various proposals have been made for performing low frequency
measurements in a more realistic setting, there has been no agreement as to what that setting
should be. Loudspeakers continue to be measured in a test chamber that is equivalent to the
absence of any room at all.
There is a developing appreciation that this traditionally performed measurement is not an
accurate predictor of the performance actually attained in the listener's room. Certainly,
in-room frequency response is more important than anechoic response in determining a
speaker's tonal accuracy. Placement of the speaker within a room will cause changes in the
frequency response compared to the anechoic condition.
4
At lower frequencies, the speaker's
output is modified by the acoustic loading presented by the walls and floor. However, when
making measurements, it is difficult to separate the effects of a room's bass reinforcement
from standing waves and other resonances associated with that room.
3
Since an anechoic chamber which performs accurately to low frequencies is extremely large and
expensive, other measurement methods are also commonly used. These include near-field
measurements, when the microphone is extremely close to the driver, and half-space
measurements, when the speaker under test is buried with its front baffle flush with the ground,
facing upwards. Both of these methods are equivalent to anechoic measurements below the
frequency at which the speaker baffle appreciably changes the acoustic load to the woofer,
typically between 100 and 200 Hz. Note that these conditions are also non-representative of an
actual listening situation.
4
Since this discussion is concerned with the reproduction of low frequencies, we will not delve
deeply into the high-frequency variations between the anechoic response and the in-room response
of a loudspeaker. Briefly, the interaction of the dispersion pattern of the speaker with the reflective
surfaces in the room (and the variation of both with frequency) creates an in-room frequency
response that may vary markedly from the anechoic response.