December_1970 — Page 21

80

Spectrum in sending room

Spectrum in receiving room

IT.L.

125 250 500 1000 2000 4000 OCTAVE FREQUENCY, Hz

Fig. 7a. Attenuation through a wall (note the frequency dependence) this makes possible masking without annoyance. No such spectrum shaping takes place when sound travels across landscaped offices. Consequently, if the noise is attenuated sufficiently to bring its high frequency components below the appropriate N.C. curve, to prevent annoyance, its low frequency content will be too quiet to provide masking (see Figs. 7a and 7b).

Obviously, an ideal solution to both these problems would be to pro- duce ceiling and screen designs which would provide adequate attenuation As has already been pointed out, with the correct frequency depen-

Choose

BOLTON

OCTAVE BAND INTENSITY LEVEL

70

60

T.L.

50

Spectrum at source

A.N.

A.N.

40

Received spectrum

20

10

T.L.

125 250 500 1000 2000 4000 OCTAVE FREQUENCY, Hz

Fig. 7b. Attenuation across office, showing need for artificial noise (A.N.) dence. Until this is possible the ex- pedient of artificial noise can be adopted. In this, 'N.C. shaped' noise is supplied to the room, either elec- tronically or by means of noisy ven- tilator grilles, so that masking is pro- vided without annoyance. Such ‘acous- tic perfume' is a rather unsatisfactory measure, but seems to represent the only solution currently available.

The acoustic problem in land- scaped offices is by far the most in- tractable; in fact there must be some doubt as to whether it will ever be capable of fully satisfactory solution.

SOUTIE

Built from TOP QUALITY materials

to withstand many years of continual

...for the

best in Shutter Doors!

Agents:

use. Time-tested, fully reliable and readily adaptable to difficult site. conditions. Corrosion resistant, top hung for smooth operation, and of

elegant appearance. Standard sizes or special sizes

up to 50 ft. (15′2 m) high x 200 ft. (61 m) wide. Manual or power operation. Write for details under

ref FE 820

Guthrie Waugh (Singapore) Pte. Ltd., Singapore, Jesselton, Sandakan, Kuching, Sibu, Brunei Town, Seria. Guthrie Waugh (Malaysia), Sendirian Berhad, Malaysia. Kuala Lumpur, Petaling Jaya, Penang, Malacca, Ipoh,

BOLTON

GATE CO LTD

Far East BUILDER, December 1970

Seremban, Kota Bahru.

Hong Kong and Macao - Deacon & Co. Ltd., Hong Kong Bank Building, Hong Kong. The Bolton Gate Co. Ltd. Bolton BL1 2SP, Lancs., England.

BG. 820

21

F