US3298455A

US3298455A - Noise masking installation

Info

Publication number: US3298455A
Application number: US351128A
Authority: US
Inventors: Michael J Kodaras; John F Duda
Original assignee: ELOF HANSSON Inc
Current assignee: ELOF HANSSON Inc
Priority date: 1964-03-11
Filing date: 1964-03-11
Publication date: 1967-01-17
Anticipated expiration: 1984-01-17

Description

Jan. 17, 1967 M.J. KODARAS ETAL 3,298,455

NOISE MASKING INSTALLATI ON Filed March 11, 1964 2 Sheets-Sheet 1 FIG J z;

M" V V Ff/I if: v I

'W/ n LV77777l H// i United States Patent 3,298,455 Patented Jan. 17, 1567 ice - 3,298,455 NOISE MASKING INSTALLATION Michael J. Kodaras, Scarsdale, N.Y., and John F. Duda, Dumont, N.J., assignors to Elof Hansson, Inc, New York, N.Y., a corporation of New York Filed Mar. 11, 1964, Ser. No. 351,128 3 Claims. (Cl. 181-.5)

This invention relates to the art of sound masking and more particularly to an installation for masking undesirable sounds of noises in a given area.

As conducive to an understanding of the invention, it is noted that in many environments such as in private offices, hospital rooms, homes, theatres and the like, the ambient noise level, i.e., the noise level created by many indeterminate sounds, is too low to prevent objectionable or undesired sounds from being heard. More particularly for purposes of illustration, in the situation where a waiting room is adjacent a private office, and the door between the two rooms is open, if the ambient noise level in the waiting room is too low, conversations held in a normal tone in such private office can readily be heard in the waiting room.

To mask the undesired sounds in a given area, air conditioning or ventilating devices present in the area may have their orifices or outlets designed to provide noise, or noise generating devices may be installed in the ducts leading to such outlets, Where there are no air conditioning or ventilating devices, sound generating devices having loud speakers associated therewith may be installed in the walls or ceiling of such area to project sound directly into the'area.

All of these devices are inadequate for their intended purpose, for their sound is directional and can readily be located by the occupants of the area in which the masking sound is generated so that it is distracting to such occupants; the sounds generated frequently have objectionable frequency spectrum characteristics; or the devices requiring air flow suffer from lack of control to provide the proper sound level required to mask the undesired noise or sound.

It is accordingly among the objects of the invention to provide a relatively low cost installation which utilizes substantially conventional components and which for a given area will provide a sound that is non-directional in character; that is non-irritating to the occupants of the area and which will mask undesired sounds.

More particularly, it is an object of the invention to provide an installation of the above type for use in areas such as waiting rooms or the like in which it is desired to mask or render unintelligible conversations being held in adjacent rooms without need for closing of communicating doors between such rooms or of soundproofing the room in which the conversation is being held.

According to the invention, the area in which the sound is to be masked to provided with a hollow wall or plenum chamber defined between one of the walls of the area, such as the ceiling of the building and an acoustical ceiling suspended therefrom, the latter being of partially sound transparent material.

Positioned in the plenum chamber is a sound projecting device oriented to project the sound emitted therefrom away from the acoustical wall of the plenum chamber so that it will strike the building ceiling and diffuse through the entire plenum chamber, thereby affording substantially uniform distribution of the sound against the inner surface of said acoustical ceiling which will permit partial transmission therethrough of such sound.

More particularly, the frequencies of the sound emitted by the sound projecting device and the volume of such sound may be set depending upon the characteristics of the acoustical ceiling, the acoustical characteristics of the room and the nature of the sound to be masked.

In the accompanying drawings in which is shown one of various possible embodiments of the several features of the invention,

FIG. 1 is a top plan view of a typical installation according to the invention,

FIG. 2 is a sectional view showing the building ceiling with the acoustical ceiling suspended therefrom and the sound projecting device,

FIG. 3 is a circuit diagram of a typical electrical sound generating device, and

FiG. 4 is a chart illustrating frequency range and intensity level of various sounds.

Referring now to the drawings, as shown in FIGS. 1 and 2, the sound masking installation illustratively is incorporated in the waiting room 11 of an office 12, for example, which have an intercommunicating door 13 which is normally to be left open.

Suspended from the building ceiling 14 of the waiting room, as shown in FIG. 2, are a plurality of panels 15 of acoustical material such as thin plywood, wood fibre, gypsum board, plaster board, erf-orated metal acoustical ceilings or the like which panels 15 are also partially sound transparent. As the acoustical ceiling may be suspended from the building ceiling in any conventional manner,

such as for example, as shown in Patent No. 3,103,868,

the method of suspension will not be described as it is well known in the art and per se forms no part of the invention.

As is clearly shown in FIG. 2, the space between the building ceiling 14 and the acoustical ceiling 15 defines a plenum chamber 16'. In the illustrative embodiment shown, sound projecting devices such as one or more loud s eakers 16 are positioned in the plenum chamber adjacent the acoustical ceiling 15. The mouth 17 of each speaker is directed upwardly as shown, so that the sound emitted therefrom will strike the building ceiling 14 and then be diffused through the entire plenum chamber 16 and against the entire inner surface of the acoustical ceiling.

Even though the masking sounds from the speakers 16 are initially directional, due to the diffusion of the sound through the plenum chamber, the sound will pass uniformly through the partially sound transparent acoustical ceiling and as the latter covers substantially the entire area of the room, the net effect will be non-directional to the occupants of such room.

Although the sound emitted by the speakers 16 may be generated by any suitable equipment, a typical device is shown in FIG. 3.

Thus, a transistor 21 which has an inherent noise level which is amplified, acts as the sound generating element and the noise voltage is developed across the load resistor 22 of said transistor 21. Resistor 23 and capacitor 24 act as a filter circuit for the supply voltage to transistor 21.

Transistor 25 which is a conventional amplifier stage, is coupled to transistor 21 through capacitor 26; the base resistor 27 providing stability, the resistor 28 being the collector load resistor and resistor 29 providing bias to the base of transistor 25.

The transistor 31 forms part of an emitter follower and is directly coupled to transistor 25, the resistor 32 serving as the load resistor for such emitter follower. The output of the emitter follower is coupled through capacitor 33 to transistor 34 of another amplifier stage in which resistor 35 is the emitter resistor and diode 36 and resistor 37 form the collector load.

Transistors 39, 41 form a push-pull output stage in which direct coupling to transistor 41 and between diode 36 and resistor 37 to transistor 39 provides bias stability and signal coupling.

The resistor 42 serves to bias transistor 34 which in turn biases transistors 39, 41 and provides degenerative feedback for stability.

Capacitors

33, 45 control the frequency spectrum by limiting the low frequency response through capacitor 33 and by passing the high frequencies through capacitor 45, thereby providing proper frequency spectrum characteristics.

The values of capacitors may be selected based on the frequency response to suit the particular system.

Capacitor 46 feeds the output signal to the loud speakers 16 through variable resistor 47 which may be set to adjust volume.

In the operation of the system to mask out the sound of normal conversation in an ofiice adjacent a waiting room, referring to FIG. 4, the typical speech signal may have a curve shown at A, i.e., at lower frequencies its sound pressure level in db is low, then such pressure level rises to a maximum at say 300 cycles per second and then falls with increase in frequency.

The ambient noise in the waiting room may have the curve shown at B in FIG. 4, i.e., at low frequencies, the sound pressure level is high and would mask low frequency speech signals. However, at the major portion of the conversation range, i.e., from approximately 220 c.p.s. to 3,800 c.p.s., the sound pressure level of such ambient noises would be insuflicient to mask the speech signal.

Accordingly, the sound emitted by the speaker is adjusted in frequency and volume so that when heard in the waiting room it would follow the curve shown at C in FIG. 4, which curve is a composite of the ambient noises and the sound emitted through the acoustical ceiling.

Thus, the sound represented by curve C has a frequency range and sound pressure level such that it will override or mask the speech signal passing into the waiting room thereby rendering such speech signal unintelligible to the occupants of the waiting room.

With the installation above described, occupants of a private oflice may talk freely without likelihood of their conversations being overheard by occupants of an adjoining waiting room even when direct and unimpeded communication exists therebetween.

As many changes could be made in the above installation, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described our invention what we claim as new and desire to secure by Letters Patent of the United States is:

1. An installation for masking undesired sounds in a chamber having two adjacent areas defined by an intervening wall having an opening, each of said areas having a ceiling, said installation comprising a plenum chamber extending over one of said ceilings, said one ceiling defining the lower wall of said plenum chamber, said plenum chamber having an upper wall spaced from the lower wall, said lower wall having its outer surface exposed to the interior of the area associated with the plenum chamber and its inner surface exposed in said plenum chamber, said lower wall being of partially sound transparent material, a sound generator positioned in said plenum chamber and mechanically isolated from saidlower wall, said sound generator comprising a sound projecting device and means to create a sound to be emitted by said sound generating device, said sound having a frequency spectrum that is between predetermined ranges which is substantially equal to the frequency range of the sounds to be masked, said sound projecting device being oriented to project the sound generated toward the upper wall of said plenum chamber, whereby the sound projected by the sound projecting device will diffuse through the entire plenum chamber affording substantially equal distribution of such sound against the inner surface of the lower wall of the plenum chamber, said lower wall permitting partial transmission therethrough of such sound, thereby masking the objectionable sounds.

2. The combination set forth in claim 1 in which means are provided to suspend said lower wall from said upper wall, to define said plenum chamber.

3. The combination set forth in claim 2 in which said sound projecting device comprises a loud speaker positioned in said plenum chamber with the mouth of said loud speaker directed upwardly toward said upper wall.

References Cited by the Examiner UNITED STATES PATENTS 811,140 1/1906 Garney 18133.03 2,001,812 5/1935 Biasi 1810.5 X 3,104,543 9/1963 Kaminski 181-05 X 3,229,429 1/1966 Conard 181-05 X BENJAMIN A. BORCHELT, Primary Examiner. M, F, HUBLER, Assistant Examiner.

Claims

1. AN INSTALLATION FOR MASKING UNDESIRED SOUNDS IN A CHAMBER HAVING TWO ADJACENT AREAS DEFINED BY AN INTERVENING WALL HAVING AN OPENING, EACH OF SAID AREAS HAVING A CEILING, SAID INSTALLATION COMPRISING A PLENUM CHAMBER EXTENDING OVER ONE OF SAID CEILINGS, SAID ONE CEILING DEFINING THE LOWER WALL OF SAID PLENUM CHAMBER, SAID PLENUM CHAMBER HAVING AN UPPER WALL SPACED FROM THE LOWER WALL, SAID LOWER WALL HAVING ITS OUTER SURFACE EXPOSED TO THE INTERIOR OF THE AREA ASSOCIATED WITH THE PLENUM CHAMBER AND ITS INNER SURFACE EXPOSED IN SAID PLENUM CHAMBER, SAID LOWER WALL BEING OF PARTIALLY SOUND TRANSPARENT MATERIAL, A SOUND GENERATOR POSITIONED IN SAID PLENUM CHAMBER AND MECHANICALLY ISOLATED FROM SAID LOWER WALL, SAID SOUND GENERATOR COMPRISING A SOUND PROJECTING DEVICE AND MEANS TO CREATE A SOUND TO BE EMITTED BY SAID SOUND GENERATING DEVICE, SAID SOUND HAVING A FREQUENCY SPECTRUM THAT IS BETWEEN PREDETERMINED RANGED WHICH IS SUBSTANTIALLY EQUAL TO THE FREQUENCY RANGE OF THE SOUNDS TO BE MASKED, SAID SOUND PROJECTING DEVICE BEING ORIENTED TO PROJECT THE SOUND GENERATED TOWARD THE UPPER WALL OF SAID PLENUM CHAMBER, WHEREBY THE SOUND PROJECTED BY THE SOUND PROJECTING DEVICE WILL DIFFUSE THROUGH THE ENTIRE PLENUM CHAMBER AFFORDING SUBSTANTIALLY EQUAL DISTRIBUTION OF SUCH SOUND AGAINST THE INNER SURFACE OF THE LOWER WALL OF THE PLENUM CHAMBER, SAID LOWER WALL PERMITTING PARTIAL TRANSMISSION THERETHROUGH OF SUCH SOUND, THEREBY MASKING THE OBJECTIONABLE SOUNDS.