THE REDUCTION OF NOISE 253 
electric motor horns and other devices for giving the audible warning of 
approach specified in the Act, to prepare a paper examining the character- 
istics which render such a signal effective as well as those which cause it 
to be offensive. 
This paper will be read by Mr. E. O. Turner, and a demonstration of 
various sound signals will be given. 
Wing-Commander Cave suggested that in order to produce a general 
decrease in exhaust noise it was necessary not only to determine the principles 
on which better silencers should be based, but to outline an organisation 
whereby these principles could be given general practical effect. He pro- 
posed that the Committee should work towards the objective of enabling 
an authority to be set up to which manufacturers could submit new types of 
motor vehicle to be tested for a certificate of approved silence. 
For this purpose it would be necessary to determine a satisfactory instru- 
ment for measuring the noise produced by the vehicle and to specify the 
conditions under which tests should be made. 
It would also be necessary to indicate to this authority what should be 
accepted as a reasonable standard to which vehicles must conform. For 
this latter purpose he proposed to undertake some preliminary tests upon 
the silencers of motor bicycle engines. 
He was able to obtain the advice of the Motor Cycle Manufacturers and 
Traders Union as to the requirements which a silencer must meet. He 
then made some preliminary experiments’ to determine which general 
principles of noise reduction were the most effective. The results of these 
preliminary tests were encouraging, but the subsequent experimental work, 
carried out at the University College, Southampton, was only rendered 
possible by a donation of £50 made by Lord Wakefield to him for that 
purpose. 
A number of designers visited Southampton, and considered the pre- 
liminary results so far satisfactory that they selected and sent to Southampton 
a 2-stroke and 4-stroke bicycle, each of normal type, as sold to the public. 
Wing-Commander Cave’s work and the conclusions which he has reached 
will be described in his own paper and demonstrated in trials on the road. 
They indicate that it is now quite possible to effect a great reduction of 
exhaust noise by the use of a silencer which results in a small increase of 
horse-power rather than a decrease when compared with that attained with 
the silencers as now commercially sold. 
The Committee wishes to express its great appreciation of the assistance 
rendered by the Motor Cycle Manufacturers and Traders Union in discussing 
the problem and then supplying Wing-Commander Cave-Browne-Cave 
with the two bicycles and every incidental detail he required. 
Dr. Davis, of the National Physical Laboratory, agreed to undertake a 
critical review of various instruments and methods available for measuring 
noise, with particular reference to the question of testing noises of a given 
type, e.g. exhaust noises. His conclusions will be given in his paper and 
suggest that, if agreement can be reached as to the conditions under which 
a test could be made, it is within the scope of suitable noise meters, which 
do not depend upon personal judgment, to determine satisfactorily whether 
the noise of a unit submitted for test does or does not exceed that of a 
standard noise of the same kind agreed to be the maximum acceptable 
under a regulation. 
The whole of the money allotted to the Committee has been spent, and 
if the full cost taken by University College, Southampton, were included, 
there would be considerable over-expenditure, even with Lord Wakefield’s 
generous donation. 
