Development of the Wide‐Band Noise Siren

The wide‐band noise siren principle [J. Acoust. Soc. Am. 31, 116 (1959)] has been further evaluated in two different, experimental siren designs with various loading arrangements. Acoustic power output, efficiency, power spectrum, and amplitude distribution of the noise generated by the various models will be discussed as a function of the flow conditions. Although the over‐all efficiency of the small models discussed here (power output approximately 5 kw) is still slightly below 10%, experimental separation of the losses involved suggests that for a siren without air leakage and otherwise similar parameters efficiencies of approximately 30% should be attainable. It appears that the efficiency of the wide‐band noise siren could be close to the efficiency of a pure‐tone siren and in the same range as the efficiency of a siren producing sinusoidal waveform with amplitude modulation. Wideband noise sirens with 20‐kw output have been built at other places and a 50‐kw siren is presently under development. The ...