Research areas Electroacoustics

For the measurement of room acoustical parameters (ISO 3382)sound sources with omnidirectional sound radiation are required. To achieve this, dodecahedron type cabinets comprising 12 identical loudspeaker systems are commonly used. For a single dodecahedron of typically 50 cm diameter (as is used in building acoustics) the frequency range is limited up to 1 kHz with respect to the above mentioned directivity aim. To maintain omni-directinality for a frequency range from 50 Hz to 8 kHz different loudspeakers of different size must be used.

The measuring loudspeaker developed in the ITA consistes of three cabinets (low: 40 Hz - 232 Hz, mid: 232 Hz - 1414 Hz, and high: 1414 Hz - 15 kHz). The low frequency cabinet can be used as a support for either the mid or the high frequency unit providing identical center position for both systems. Alternatively the high frequency unit can be placed above the mid frequency unit thus providing a full range three-way loudspeaker system.

The following picture shows the system in the three-way set-up.

The subwoofer uses a 6th order band-pass design with two chambers and one radiating opening. The diameter of the radiating bore is 10 cm and oriented upwards, thus providing perfect radiation in all directions.

The midrange dodecahedron is build up with 12 low-frequency drivers of 8 cm diameter which allows a cabinet diameter of only 26 cm. The radiation is perfectly spherical up to 2.5 kHz.

For higher frequencies the construction becomes more complicated and special loudspeaker systems with neodymium centre magnet are used to maintain a sphere of only 9 cm diameter bearing 12 dome tweeter with silk-membranes.

A 3-dimensional, animated plot of the directivity is shown in the next picture