Acoustical Measurement Technology of Loudspeakers and Microphones
IRT determines the directivity patterns of loudspeakers and microphones by means of specialised, computer-aided measurement equipment: a rack (quadrant) with 19 measurement microphones, a changeover switch, and a rotary table. The rotary table turns a loudspeaker in five-degree increments in the horizontal plane and the transfer function is measured at the 19 microphone capsules, respectively.
Individual transfer-function measurements are first collected by means of the MLS (Maximum Length Sequence) measuring method and in the form of absolute values and phase values before being stored in a database. 2,049 transfer functions and 2,049 frequency control points (i.e. 4.2 million amplitude values and 4.2 million phase values) are stored for each loudspeaker. Several hours are required to measure one loudspeaker. The automatic measuring system thus generates a data record totalling approximately 33 MB per loudspeaker. And the technique can be slightly modified for microphones, e.g. artificial heads.
Forther information on IRT service measuring the directivity patterns of loudspeakers and microphones
Assessment of Measurement Data
Thanks to extensive data records, our specialists can combine and balance transfer functions to obtain certain sensitivity levels, various directivity indices, or polar curves for given frequency resolutions.
Visualisation of 3-D Directivity Patterns
Measurement data can be depicted especially well via a three-dimensional portrayal of directivity patterns: a single image is provided for a certain frequency band or a video sequence for several frequency bands. The measurement data can be used to calculate angular-dependent level values, which are then portrayed as a spatial grid. The relative level differences can be illustrated by gradations of colour. This coloured grid can, for example, then be visually studied from various spatial perspectives.
For a certain spatial perspective, it is possible to successively portray – as in a film – the spatial envelopes for ascending third-octave centre frequencies (e.g. from 100 Hz to 20 Hz). And the images are accompanied by the corresponding third-octave noise.
In order to play these files (approx. 1.2 MB each), you must have Macromedia Flash Player, which can be downloaded free of charge at www.macromedia.com.
