Loudspeaker measurements require high-quality facilities and equipment. The large anechoic chamber
in the
Helsinki University of Technology,
at the
Acoustics and Audio Signal Processing laboratory offers the best
laboratory in Finland to do the measures. The recently (Summer 2005) renovated chamber yields anechoic conditions
(less than 1 % of the sound wave is reflected from walls / ceiling / floor) from above ca. 70 Hz.
Free-field loudspeaker measurement in the large anechoic chamber at the
Acoustics and Audio Signal Processing laboratory
Loudspeaker measurement in the large anechoic chamber at the
Acoustics and Audio Signal Processing laboratory.
The standard measurement distance is 2.5 m for the free-field, which reduces the weight of disturbing reflections (at low frequencies) as well as the
distance aberration between different elements. A short measurement distance causes problems in cases of large loudspeakers with multiple elements, whose distances to the microphone
are no longer identical.
The base response is measured in the near-field, at a 0.5 m distance so that room reflections become insignificant.
The (typ. 0.1 octave smoothed) free-field and base response are then level equalized
for a common measurement distance of 1.0 m, and the final response is constituted from the two curves, where the limiting frequency is chosen as the
optimal one in the frequency range of 80 - 130 Hz.
Free-field loudspeaker response, measured in the large anechoic chamber at the
Acoustics and Audio Signal Processing laboratory
References
Since 1996 I have measured all the loudspeakers for the Finnish
HIFI Magazine, the sole
magazine specialized in audio and video.
I have also done loudspeaker measurements for other newspapers and companies, e.g.
