The ICOSSA Project - An improved omnidirectional sound source for room acoustic testing

One type of loudspeaker that is commonly used for acoustic testing of rooms is the “dodec” which is a twelve-sided enclosure each containing typically a 125 mm driver. This arrangement is intended to produce true omnidirectional radiation for measurement of room acoustic parameters such as strength, clarity and lateral energy. Although this arrangement of drivers works well at low frequencies, it produces significant lobes in the radiation pattern at frequencies above 1.5 kHz. As international standards allow up to 8 dB of variation in polar frequency response, the responses of premium “dodecs” comply with those standards. However, these lobes will produce errors in the 3D impulse responses and the associated acoustic metrics. This paper details the development of an improved transducer topology and an associated signal processing algorithm to produce a significantly more consistent polar frequency response.