Room acoustic computer modelling has become an important tool in the acoustical design of rooms, and also the range of applications has increased in recent years. Also the room acoustic measurement technique has developed significantly in recent years, e.g. by new methods in ISO 18233. Considering computer modelling as a simulated measurement means that there is a close connection to the measurement methods, particularly as laid down in the ISO 3382 series that covers performance spaces, open plan offices and ordinary rooms. With these new standards the number of room acoustic parameters has grown, so in addition to the traditional reverberation time there is today a rather long list of more specialised parameters. The parameters are used for the design specifications, for the simulations during the design, and finally for the verification measurements. In some projects with special acoustical demands the use of auralisation in the design phase has become a useful supplement to the calculated parameters. In this paper the advantages and weaknesses of room acoustic measurements compared to simulations are discussed, and the state-of the-art methods as implemented in the ODEON room acoustics software are briefly presented with some examples.

The measured impulse response is often used as a true reference of a real room impulse response and geometrical acoustic simulations are considered to be only a crude representation of it. However, both approaches have their own challenges and limitations. Geometrical acoustic models do not include wave phenomena, such as interferences and diffraction, as they simplify sound propagation by rays. The advantages of acoustic simulations with such models include a perfectly omnidirectional and impulsive sound source, no distortion problems, full control of the background noise, and a well-defined onset time of the impulse response. On the other hand, impulse response measurements include wave phenomena, but they do have their own weaknesses, which may cause significant errors in the derivation of the ISO-3382 room acoustic parameters. Due to the presence of background noise in the measured impulse response it is difficult to evaluate which part of the impulse response is valid. In addition, the directivity of the sound source used for measurements often has strong lobes at high frequencies and distortion artefacts may cause errors in the derived results.

In this paper simulated and measured parameters are compared in a number of well documented cases and the various sources of errors are discussed. It is concluded that doing room acoustic measurements correctly may be more difficult than it appears at first glance, and both measurements and simulations require high level acoustical qualifications by the operator.