B&W electronics 70 User Instruction Handbook - page 21
-21-
meaningless without reference to the polar distribution,, the
frequency response of the system at points considerably off
axis, tone burst oscillograms, pulse oscillograms and a very
complete set of distortion measurements.
At an early stage in the development of the electrostatic
unit it became obvious that the axial plot became less smooth
as the dispersion was increased. Two factors contributed to
apparent increase in the irregularities of the response plot.
Firstly, our test chamber which was not truly anechoic. As
dispersion of the unit was increased so minor reflections
within the chamber were shown. These reflections were not
even excited with the more limited distribution pattern of
conventional units. The second factor which became obvious
was the size of the diaphragm on the calibration microphone.
Where this approached half-wavelength at the frequency under
measurement standing waves were built up and the response plot
degraded.
In co-operation with Messrs. B & K Laboratories these
problems were thoroughly investigated and resolved. We
subsequently purchased the complete range of B & K microphone
equipment including no less than five calibration microphones
allowing pressure and grazing incidence measurements,to be
taken both with and without free field correction.
The foregoing somewhat lengthy exposition only sets out
to point the way to new and more complete thinking in terms
of measurement associated with loudspeaker units and it is not
the writer's intention within this article to do more than touch
on the subject.
PRESENTATION
Conflicting requirements must always be reconciled with a
loudspeaker design which is primarily required for domestic use.
This is especially true of the larger systems where there is a
frequent interchange of requirements as between the stylist and
the acoustics engineer. There is no escaping the fact that
however good an acoustical design may be it must also be
accepted in the home furnishing scheme before it is a success.