Vibrating diaphragm type audible device with acoustically improved grille and method

An audible device of the vibrating diaphragm type which has improved acoustical performance by reducing the open area of the acoustical wave egress port. Through use of a masked grille having a small percentage of open grille space it is possible to improve the performance of a vibrating diaphragm type audible device such as a vibratory horn by increasing its energy transfer or acoustical output.

BRIEF SUMMARY OF THE INVENTION 
The present invention relates to a vibrating diaphragm audible device such 
as a vibratory horn, and in particular to a novel masked grille for use 
with such a device for the purpose of improving energy transfer and 
increasing audible output. 
It has heretofore been believed that any blockage of the grille or 
acoustical wave egress port of an audible device such as a vibratory horn 
will necessarily reduce the audible output of such a horn. However, the 
present invention is based upon the discovery that within certain limits 
it is possible to increase the audible output of a vibrating diaphragm 
audible device such as a vibratory horn by blocking off or masking a 
substantial percentage of the open horn grille area to reduce the normal 
acoustical wave egress port provided by the grille. While such masking 
reduces the egress port through which the sound energy must pass, it has 
nevertheless been found that such masking can increase audible output. 
It is therefore a general object of the present invention to provide a 
vibrating diaphragm type audible device including an egress grille having 
substantial portions thereof masked by an acoustically opaque member 
leaving substantially less open grille space than afforded by conventional 
horn grilles and the like. 
The foregoing and other objects and advantages of the invention will be 
apparent from the following description of certain preferred embodiments, 
taken in conjuction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, FIGS. 1-3 show a vibratory horn grille 10 
having a front 12, top 14, bottom 16, and side walls 18 and 20. The horn 
grille 10 is provided with four screw openings 22, one in each corner of 
the grille, to permit the grille to be mounted on the front of a vibratory 
horn or other vibrating diaphragm type audible device. By way of example, 
vibratory horns are commonly mounted on interior walls of buildings to 
function as emergency warning devices such as fire alarm warning horns. 
If the shading in FIG. 1 is disregarded, there is shown a conventional horn 
grille where the front wall 12 is provided with substantial open space to 
permit sound energy to be emitted therethrough. In a conventional horn 
grille, such open space is at least 35% of the total grille area and 
commonly over 60% of the total grille area is open to permit the sound 
energy created by a vibrating diaphragm audible device to pass out through 
the open grille. 
While the specific design of the grille structure per se is not a part of 
the present invention, it will be seen by way of example that the grille 
12 in FIG. 1 is comprised of five square frame members F1 through F5 
arranged in concentric fashion one inside the other and interconnected by 
a plurality of vertical ribs R1 and horizontal ribs R2 spaced apart to 
provide open spaces S between the various vertical and horizontal ribs 
which interconnect the square frames. As indicated above, the open spaces 
S conventionally comprise at least 35% of the area of the total area of 
grille front 12, and commonly comprise 60% or more of that area. 
Furthermore, it has generally been believed that any significant reduction 
of such open grille area will impair the sound output of a horn or other 
vibrating diaphragm type audible device. 
The shaded area of FIG. 1 represents a modification of the grille in 
accordance with the present invention where an acoustically opaque masking 
member is utilized to close many of the openings S and thereby 
substantially reduce the total open area of the grille 12. In the 
embodiment of FIG. 1, the masked area is in the form of a cross comprised 
of a vertical masked strip and an intersecting horizontal masked strip. As 
a result, those openings S which remain are located in four generally 
rectangular corner areas of the grille 12. 
In the embodiment of FIG. 1, the open area is approximately only 13.5% of 
the total grille area. Moreover, efficiency, which is a measure of 
acoustical watts produced divided by electrical watts input, has been 
found to be 4.03%, an improvement of 40.9% over the same grille without 
masking. The particular manner of masking is optional as long as an 
acoustically opaque member is utilized to substantially close a 
significant portion of the normally open grille area. The vibratory horn 
grille shown in FIGS. 1-3 comprises a die cast zinc grille which is cast 
with masking over the entire face of the grille, and a blanking die is 
utilized to punch out the desired openings S which in the FIG. 1 
embodiment are located in four rectangular corner areas outside of the 
masked area which forms a cross design. However, one could utilize a 
standard grille and apply masking tape in the form of a cross pattern, and 
in that alternative manner produce a masked horn grille of the type shown 
in FIG. 1. 
FIGS. 4-6 show the same basic grille 10, and these embodiments differ from 
one another only in the pattern of the masked area on the grille face 12. 
In FIG. 4, the masking is generally in the form of a horizontal H-pattern 
which leaves a strip of openings S across the top and bottom of the grille 
face, and two rectangular open areas at the sides of the grille face 
intermediate the top and bottom strips of openings. Experiments have 
indicated that the percentage of open area is important to achieving 
enhanced energy transfer and maximum sound output, rather than the precise 
arrangement of the masked area on the face of the grille. In the 
embodiment of FIG. 4, the open area is approximately 11% of the total 
grille area. The efficiency, or acoustical watts produced divided by 
electrical watts input, for the FIG. 4 embodiment has been found to be 
4.3%, an improvement of 50.3% over the same grille without masking. 
FIG. 5 illustrates the grille 10 with a further alternative masking 
pattern. In FIG. 5, the masking is in the form of a square masked area 
which leaves a peripheral border of openings S completely surrounding the 
masked area, and which leaves two additional openings S at each side of 
the grille intermediate the top and bottom thereof. In the embodiment of 
FIG. 5, the open area is approximately 13.7% of the total grille area. The 
efficiency, or acoustical watts produced divided by electrical watts 
input, for the FIG. 5 embodiment has been found to be 4.3%, an improvement 
of 50.3% over the same grille without masking, the foregoing improvement 
being the same as for the FIG. 4 embodiment. 
FIG. 6 illustrates the grille 10 with still another alternative masking 
pattern. In FIG. 6, the masking is in the form of a rectangular border 
strip which leaves a central square area where the openings S remain open. 
In the embodiment of FIG. 6, the open area is approximately 12.5% of the 
total grille area. The efficiency, or acoustical watts produced divided by 
electrical watts input, for the FIG. 6 embodiment has been found to be 
4.38%, an improvement of 53.1% over the same grille without masking. 
In addition to improving the acoustical output of audible devices of the 
vibrating diaphragm type by utilizing masking of conventional grille 
openings in accordance with the present invention, it will be understood 
that in accordance with the present invention one may mount an 
acoustically opaque sign or other acoustically opaque member on the front 
of a horn grille, and if arranged to block only an appropriate 
predetermined portion of the normally open grille space, the resulting 
blockage will not impair sound output but on the contrary will enhance it. 
Reference is now made to FIG. 7 which shows the same basic horn grille 10 
having a warning sign 30 mounted across the front 12 of the grille. The 
sign 30 includes four corner lugs 32 which fit over the previously 
described screw openings 22 in the grille face 12. The sign 30 may thus be 
mounted by using the existing mounting holes 22, without requiring 
modification of the grille 10. The particular sign 30 shown in FIG. 7 
covers or masks certain areas of the grille 12 to achieve essentially the 
same effect as the masking described in the embodiments of FIGS. 1-6. In 
this instance, the masked area comprises a relatively wide vertical strip 
down the center of the grille, and two narrow strips across the top and 
the bottom of the grille. The resulting open areas comprises a pair of 
rectangular areas, one on each side of the grille, which are longer in 
their vertical dimension as compared to their horizontal dimension. 
The sign 30 of FIG. 7 may be dimensioned to provide a desired predetermined 
percentage of open grille area comparable to the embodiments of FIGS. 1-6. 
If desired, the sign itself may be relied upon to provide the desired 
masking of the grille. Alternatively, the masking may be provided in the 
casting of the grille and subsequent punching of the desired openings in 
the manner previously described to produce a masking pattern which 
corresponds to the outline of the sign. In the latter case the improved 
audible output will be achieved by such masking and will be wholly 
unaffected by mounting of the sign, which is of the same outline as the 
masking and thus does not affect the predetermined open area of the 
grille. In either case, it is important to understand that contrary to 
what has heretofore been believed, it is possible to mount a sign or other 
acoustically opaque member on the front of the egress grille for a 
vibrating diaphragm type audible device and thereby improve rather than 
impair the acoustical output of the device. 
FIG. 8 shows the same basic grille 10 with an additional alternative 
masking pattern. The masking pattern is that which would be produced by 
the sign 30 of FIG. 7, but with an additional wide horizontal masking 
strip. The pattern of FIG. 8 will also be recognized as similar to the 
cross masking pattern of FIG. 1, but with a narrow horizontal masking 
strip added across both the top and bottom of the grille. The remaining 
open areas where the openings S are not masked are in the form of four 
small rectangular areas generally located in the four corners of the 
grille. In the embodiment of FIG. 8, the open area is approximately 9.3% 
of the total grille area. The efficiency, or acoustical watts produced 
divided by the electrical watts input, for the FIG. 8 pattern has been 
found to be 4.13%, an improvement of 44.4% over the same grille without 
masking. 
As shown by the above data, variations in masking patterns have been found 
to result in different degrees in the percentage of improvement in sound 
output which is achieved by such masking as compared to a conventional 
unmasked grille. However, the differences in enhancement of energy 
transfer produced by different masking patterns have been found to be 
relatively small as contrasted with the importance of controlling the 
degree of masking to achieve a preferred percentage of open grille area as 
compared to total grille area. In the several embodiments of FIGS. 1-8, 
the percentage of open grille area as described hereinabove is in the 
range of 9% to 14% open. Based upon such experiments, it is believed the 
preferred range for the masking is to leave 9% to 15% open space compared 
to the total area of the grille, as contrasted with conventional horn 
grilles which are often 60% or more open. However, significant 
improvements in energy transfer for vibrating diaphragm type audible 
devices can be achieved through masking down to a range of 5% to 25% open. 
The cross-shaped masking pattern of FIG. 1 has the advantage that a 
vertical sign as shown in FIG. 7 can be mounted on the front of the 
grille, or a horizontal sign can be mounted thereon, without varying the 
acoustical output of the audible device, as long as the sign merely covers 
portions of the grille which have already been masked. For the foregoing 
reason, there are advantages in using relatively simple masking patterns 
which can be made to correspond to the area of a sign to be mounted on the 
grille face. It will of course be understood that the cross pattern of 
FIG. 1 can be modified by providing only the vertical or the horizontal 
portion thereof. 
It is important to understand that the present invention is based on the 
discovery that masking of a grille as described herein significantly 
increases energy transfer of a vibrating diaphragm type audible device 
such as a vibratory horn. It is believed the masking improves the 
efficiency of the vibrating diaphragm member. On the other hand, the 
present invention is not intended for use with other audible devices such 
as speakers which do not include a vibrating diaphragm. 
It will further be understood that existing vibratory horns such as wall 
mounted emergency warning horns may be modified in accordance with the 
present invention by masking the horn grille through addition of an 
acoustically opaque member, which member can be masking tape, or if 
desired can be an acoustically opaque sign mounted on the horn grille as 
shown in FIG. 7.