Noise Levels in Computer Room at Metropolitan Life Insurance Company

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Technical Note (National Research Council of Canada. Division of Building Research), 1963-12-01

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Noise Levels in Computer Room at Metropolitan Life Insurance Company

Northwood, T. D.; Rowe, E. C.

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J

r!'-" NATIONAL RESEARCH COUNCIL OF CANADA

DIVISION OF BUILDING RESEARCH

'f

EClHIN ][CAlL

NOTlE

RESTRICTED CIRCULATION

No.

409

PREPARED BY T.D. Northwood

and E.C. Rowe

CHECKED BY _{APPROVED BY} N.B.R. DATE December

1963

PREPARED FOR

SUBJECT

Mr. S.D. Meredith, Metropolitan Life Insurance Company, Ottawa

NOISE LEVELS IN COMPUTER ROOM AT METROPOLITAN LIFE INSURANCE COMPANY

The object of this study was to determine whether it would be feasible to reduce noise in the work areas of the computer room to a more comfortable level. Noise analyses were made in the work area and also near the principal noise sources, to determine whether the noise was sufficiently localized that a significant improvement could readily be achieved. After the initial survey, two additional sets of measurements were made following the installation of temporary curtains intended to act as partitions between the principal noises and the work area.

Procedure

Complete spectrum measurements were made at Position 1, the operating console in the work area (Figure 1). Additional A-weighted sound level measurements were taken at many points in the work area and in the vicinity of the computing racks. It was observed that the principal noise was fan noise, issuing . from the ventilator openings at the bottom rear of the oomputer cabinets.

There were additional intermittent noises, associated with tape unit operations, the console typewriter, etc., but

these tended to be SUbmerged in the general level of fan noise and made little difference to A-weighted sound levels.

I'

-2-The'noise spectrum observed at this time (17 April 1963) at the instrument console is indicated by Curve A of Figure 2.

For comparison, the broken curve labelled NC-55 represents a noise spectrum that would be satisfactory for easy communication at about 3 feet; this is taken to be an acceptable noise spectrum.

Since the noise originated largely from the rear of the computer cabinets, it appeared feasible to reduce the amount reaching the work area by erecting a partition from the front edge of the cabinet rows to the ceiling, and similarly closing the ends of the cabinet rows o This was partially done on a temporary basis early in June, but with inadequate resultso A more complete curtain installation was done in September1 with

the results shown also on,Figure 2. A substantial improvement in steady noise was accomplished (Curve C), though operation of the nearest tape unit still gives a high level (Curve B). With the curtain in place the spectrum at the desk near the south wall approached the design requiremento

Both experimental partition arrangements consisted of

double layers of moderately heavy but porous curtains. Observations on a particular curtain showed that it was ineffective at the

lowest frequencies and provided only about 10 db improvement at the highest frequencies. It is expected that a proper partition of solid panels, or a heavier and more impervious curtain material, could achieve a reduction of another 10 db, at middle and high frequencies. At this point it would also be desirable to stuff

or tape the cracks between instrument cabinets. The design

objective,would then be easily met at the south desk and also at the console except possibly when the nearest tape units are active. The portion of tape-drive noise emitted from the front of the

cabinets cannot readily be reduced, but because of its intermittent character it may be acceptable.

A suitable design of solid partition would consist of a 2- by 2-in. wood frame, with i-in. plywood on the work-area face, glass fibre batts in the space between framing membersl ' and

a perforated hardboard on the other face. Partition panels might be hung from the ceiling or they might be free-standing on top

of the instrument rows with a suitable padded base to prevent vibration. A small crack (up to ｾ in.) could be tolerated at

the ceiling, but no cracks should be left at the instrument level. Where curtains are used they should be in the form of two free-hanging layers; each layer should incorporate a heavy impervious materia,l (.e.g. vinyl, or latex-coated fabric). Even in these circumstances the curtain will not equal the performance of the panel unless the surface density per layer is about

i

Ib per sq ft, but a somewhat lighter construction might be tolerated at the points of access to the rear of the computers.

-

-3-An alternative solution may also be ｳｵｧｧ･ｳｴ･､ｾ Since the ventilation exhaust openings are located in the floor

immediately behind each computer cabinet, it would probably be a feasible procedure to close in from each cabinet opening to floor opening with a movable box or a hood hung over the cabinet opening0 If this procedure appears attractive its effectiveness

might be tested by a measurement on a single unit, at some period when the rest of the computer system is not operatingo

Printer Noise

Measurements were also made in the printer room, adjacent to the computer roomo It was found that levels with

the printer operating were of the same order as in the computer room (Figure 3)0 Unfortunately, the design of the machine is such that it would be difficult to reduce the noise level in the immediate vicinity without seriously impeding the operator. Therefore no recommendations are offered regarding the printer0

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