Handbook for Sound Engineers

632 Chapter 17

usually on axis. This is the equivalent of assuming

that the on-axis response will be equalized flat,

which is not always a good idea. The caveat: anom-

alous narrowband behavior on axis (i.e., a notch)

that disappears off axis will create features (peaks)

in the normalized curves that are unrepresentative of

what would occur in actual use.

3. On-axis amplitude response, accompanied by polar
   plots at various frequencies. The common usage of
   only vertical and horizontal polar curves is problem-
   atic. The omission of polar curves at angles between
   0° and 90° rotation leaves a lot of a loudspeaker’s
   performance to speculation, Fig. 17-55.


4. On-axis amplitude response, accompanied by
   isobars at various frequencies. This format is useful
   for showing overall coverage behavior of a loud-
   speaker. Lobes, where present, are not generally
   revealed in isobar plots.


5. Directivity data for use with sound system modeling
   software. The format of this data will be dictated by
   the requirements of the predictive program. Some
   standards for the presentation of this are being
   discussed, but there is not at yet an industry-wide
   consensus on a final standard, Figs. 17-56 and
   17-57.

Of course, various combinations of the above can be
provided. The formats available for the presentation of
loudspeaker data continue to evolve. The availability of
inexpensive mass data storage media and ever more
sophisticated acoustic modeling software will continue
to make the presentation of loudspeaker response and
directivity information more effective and intuitive.

17.10 Direct Radiation of Sound

The physics and mathematics of loudspeaker behavior

are diverse and complex. In order to account for the

conversion of an electrical signal to sound, one must

develop both acoustic and electromechanical models.

Several of these models, which are developed and

presented in almost every introductory text on acoustics,

are presented here without proof. The interested reader

is encouraged to study the references.

Figure 17-54. Graph of a loudspeaker’s on-axis amplitude
and phase response, -octave smoothed. Courtesy
Frazier Loudspeakers.

(^1) / 6
Figure 17-55. Vertical and horizontal polars, one octave
averaged. Courtesy Frazier Loudspeakers.
Figure 17-56. Octave band averaged isobar. Courtesy
Frazier Loudspeakers.
3 dB, 6 dB, 9 dB, coverage isobars