434. SECTIONAL TRANSACTIONS.—G. 
listener’s home. In most cases, however, the reverberation time of a living-room is 
almost negligible, but unfortunately there are exceptions. Apart from the acoustical 
properties of the room, the loud-speaker and associated apparatus are by no means 
standardised. This fact in itself prevents a precise treatment of the problem. Again, 
normally music is reproduced at a much lower strength than the original, but in the 
case of speech the opposite is very frequently the case, a fact which often accounts for 
unnatural speech. ‘ 
Considering studio conditions, microphone design is not finalised, particularly in 
connection with the maximum volume of sound which can be handled. Again, 
account has to be taken of the fact that the number of persons present in the studio 
cannot always be fixed definitely, such variations appreciably affecting the acoustical 
conditions in the case of the larger studios. 
From the economic point of view it is difficult to arrange that a studio is always 
of the correct size in relation to the number of performers taking part. Moreover, 
for the same reason it is not always possible to design a studio with the correct 
relationship between height, width and length. 
The third section describes the principles on which studio design is based in the 
B.B.C. Curves are given showing the number of players which should normally be 
allowed in relation to studio volume, also the correct reverberation period in relation 
to studio volume. Curves are also given showing the reverberation period plotted 
against frequency for two or three existing studios. Comments are made on the aural 
effect of a non-linear reverberation time-frequency curve and the question of the 
design of studios for special purposes such as the production of dramatic effects is 
briefly considered. Reference is also made to Continental practice. 
Col. The Master or Semprtu.—WMotorless Flight. 
Mr. E. F. Retr.—The Compressed Avr Wind Tunnel at the National 
Physical Laboratory. 
After a brief outline of the history of the development of this type of wind tunnel, 
a detailed exposition is given of the theoretical reasoning which leads to the con- 
clusion that a wind tunnel using a compressed gas as the working fluid is the only 
feasible way of conducting model experiments in the laboratory under conditions 
corresponding with those of full-scale flight. A description of the construction of 
the compressed air tunnel at the Laboratory is next given, together with an account 
of the auxiliary plant provided to charge it with compressed air and to circulate the 
air current in the tunnel itself. 
The maximum working pressure is twenty-five atmospheres, at which pressure an 
expenditure of 500 H.P. in the tunnel motor will produce a wind speed of some 
90 ft. sec. in the 6 ft. jet of the tunnel. The Reynolds number obtained on a model of 
an average aeroplane corresponds with full-scale flight at 150 to 200 miles per hour. 
There follows a brief reference to the nature of the various classes of test that 
will be made in the tunnel, leading to a more detailed description of the special balance 
and other measuring equipment that has been designed to meet the requirements 
of these tests. The main feature that differentiates the compressed air tunnel 
from all other types is that the observer cannot operate the measuring apparatus 
directly, so that all balances and other apparatus must be designed for indirect opera- 
tion from outside the tunnel shell. In the present design the aerodynamic forces 
are measured by balancing them against the electro-magnetic attraction between 
coils of wire and observing the current necessary to eflect such balance. Finally, 
the methods adopted to measure wind speed and Reynolds number, involving the 
determination of pressure, temperature, and the value of Qv? in the air jet are 
described. 
Mr. R. McKinnon Woov.—The New Wind Tunnels of the Royal Aircraft 
Establishment. 
The paper opens with a brief discussion of the validity and scope of small-scale 
experiments in aerodynamics and of the principles upon which the use of a wind tunnel 
rests. Small-scale experiments in the wind tunnel have been valuable in guiding the 
designers of aircraft; but the method is sufficiently defective in some respects to 
ee 
ee ee ee ee ee 
ed 
aT, 
| 
| 
