I devised custom loudspeakers for my high-quality fully automated HRTF measurement / multi-modal experimentation system. Eleven electrodynamic transducers were measured using a standard baffle (IEC 268-5, 1989) and the chosen 4” midrange element prdoces a usable frequency range of approx. 100 ~ 16000 Hz (±5 dB) without any anomalies or strong directivity pattern impeding the HRTF system compensation.

Design

Spherical shape was considered as the optimal enclosure for the one-way loudspeakers with minimal diffraction (Olson, 1957). The casings for the far-field sources were modified polycarbonate spherical lamp covers (Ø = 190 mm).

Responses of finished KAR-SLP loudspeaker (190 mm spherical plastic enclosure) measured at a 2.0 m distance. Curves show the vertical directivity of the loudspeaker (θ = 0°), Brüel&Kjær 1/2” free-field microphone Type 4133 at δ = 0° (uppermost plot), 5°, 10°, 15° and 20°, 0.1 octave smoothed responses, offset 5 dB.

Also, another smaller loudspeaker enclosure (Ø = 150 mm) was constracted for near-field HRTF measurements. The finished loudspeaker with a 3" midrange element yields a good response within 80 ~ 16000 Hz (±5 dB).

(KAR-961b turntable and) spherical loudspeaker framework of the HRTF measurement system in the large anechoic chamber at HUT / Acoustics and Audio Signal Processing Laboratory.