Community's test and measurement system consists of an automated rotator mechanism that rolls out on a track from the third floor of our manufacturing plant. Above this track, a long, horizontal mast measuring 44.3 feet also projects from the side of the building which is used to hold the microphone and its boom.
This arrangement positions the loudspeaker being tested at a distance of 16.4 feet from the nearest reflective surface, and positions the microphone at a distance of just about 40 feet from the loudspeaker, thus satisfying both free field and far field needs.

Because of the great quantity of data collection necessary to produce spherical coverage information, we elected to automate the rotator mechanism and control it with our TEF 20 analyzer. The rotator consists of a horizontal axis section and vertical axis section, each of which is driven by a gear motor and stopped by an air-operated brake. Position sensing is done optically on each section.

The test sequence is as follows: The loudspeaker begins at 0 degrees (pointing directly at the microphone). A response curve measurement is taken, and then the loudspeaker is rotated five degrees clockwise in the horizontal plane.

A second response curve measurement is taken, followed by another five-degree rotation, and so forth until the speaker reaches 180 degrees (pointing directly away from the mic). After the 180 degree measurement is taken, the speaker is returned to the 0 degree position.

On its return trip, it is rotated five degrees clockwise in the vertical plane. Measurements are then taken in five-degree increments from 0 to 180 degrees with the vertical section in the five-degree position. On the way back to 0 the next time, the vertical section is rotated 10 degrees, and the process continues until the vertical section has gone through 90 degrees in five-degree increments and the horizontal axis of the loudspeaker has become vertical.

The resulting response curves are recorded at each five-degree increment on a quarter of a sphere. Even with automation, the angular dispersion portion of a test sequence takes over two hours to complete, and 703 response curves are recorded in the process.

For loudspeakers that are physically asymmetrical in one axis, such as a typical multi-way system, we rotate the vertical section through 180 degrees in response curves recorded at each five-degree increment on one-half of a sphere. This doubles the amount of time and number of response curves recorded, and is the only way to obtain an accurate portrait of the dispersion pattern of these types of loudspeakers in polar graphs, EASE data, and as represented by Q and beamwidth data.

In total, thousands of hours of effort have gone into the testing that produces the specifications for our products. It is our hope that when properly applied, these results will be truly useful tools for all who need them.