Studio Acoustics

Radio Record, Volume III, Issue 13, 11 October 1929, Page 7

Studio Acoustics

Waitomo Relay Arouses Much Interest

HH recent relay of a concert from Waitomo Caves created great interest among listeners. Owing to the acoustic qualities of the caves, the concert was looked forward to by .very many as an opportunity for making comparisons between -the’ effect -of broadcasting from a cave and from a specially prepared studio. The result was that the station manager at 1YA received many letters from listeners who expressed their opinion and discussed the relative merits of studio and cave broadcasts. A listener in North Auckland reported on the relay as follows :--"This was looked forward to generally as a promising novelty. I regret that actually the result did not justify the trouble. The acoustic effect on the microphone was curious, and probably attributable to the size and damping effect of the ,walls of the cave. A vocalist singing loudly appeared quite normal, especially a male voice. inging softly, it was almost ingudible, and the soprano appeared very thin and reedy, as if the bulk of the sound were lost. Not a ‘trace of any echo was ‘noticeable. There is little doubt that a military band at full strength would have come over quite satisfactorily. The same effect-loss of body-was observed with the piano solo, as if most of the minor sound wavés were lost, before they could affect the microphone. Actually, the concert might have been set out from a very poor studio acoustically. Some items were omitted from the programme." In connection with this, the chief engineer of the Broadcasting Company, Mr. J. M. Bingham, has prepared a brief memorandum, as follows :- "Phe various remarks received by the station director at 1YA from listeners in respect to thé relay from Waitomo Caves concerning acoustic effects

apply not so much to actual acoustic effeet as to the echo. "Under certain conditions a . slight echo effect is not only desirable, but can be used with good results. At the same time when endeavouring to obtain this particular effect a large number of conditions have to be taken under consideration. , "The governing factor is really what is termed the ‘reverberation time,’ that is, the time that a note will continue to sound till it dies away to. negligible intensity. The permissible time period for good audio quality depends directly upon the cubie content of the studio or auditorium. It will thus be seen that a much higher time period can be permitted, for instance, at Waitomo Caves, than in a relatively small studio as is the case at 1YA. "If an attempt is made to obtain an echo in tHe studio merely by the removal of the drapings, trouble will probably be encountered through the resultant interference caused by undue aecentuation or diminution of certain tones, as well as a tendency to blurr on speech. There are always certain spots in a studio where such effects are more noticeable than in others, and these positions can only be found by experiment; but in practically every case they may be avoided by placing the microphone relatively close to a wall, taking eare that a certain amount of draping is placed behind, below, and overhead. This method of microphone placing is practically standard in the large broadcasting and gramophone studios in thg United States. "In the case of a studio the size of that at 1YA a desirable reverberation time would be approximately one second for best results, and as the studio is built with hard plaster walls a certain quantity of draping will always be necessary."