G.R.A.S. Sound & Vibration aps, Vedbaek, Denmark
The accuracy of acoustic measurements will play an increasing role, if legislation, prediction, and noise control are to be taken seriously. If the traffic intensity is doubled by year 2000, one should expect a 3 dB higher noise level, unless the emitted sound power from each vehicle is reduced by 3 dB. It is unlikely that emitted power will be cut in half, unless a number of sources the sum of which is half are attacked. This calls for better and more accurate measurements. Better monitoring equipment and better source location and source ranking equipment is needed. Outdoor monitoring has undergone a development to more rugged, stable, and accurately calibrated systems. Intensity measurements are getting out of the crib. Standards have evolved and calibration procedures are starting to be evolved. Instrumentation has been improved. It is important that intensity probes can now be produced to narrow specifications to fulfill the demand for precise and reproducible measurements; they are no longer selected from large populations, but manufactured to exact specifications. It is important to make proper calibrations, not just assume that certain parts of a probe are working properly. If intensity measurements shall gain in popularity it is important to develop the instrumentation from magic machines into practical tools for the practitioner. Practical systems, calibration, and applications will be discussed.