US2036980A - Sound-box construction - Google Patents

Description

Aprifi 1936. BE D v 2,036,98Q

SOUND BOX CONSTRUCTION inal Filed Aug.,8, 1931 [N VE/VTOR 725000195 /7 BEA PD ATTORNEY Patented Apr. 7, 1936 UNITED STATES PATENT OFFICE SOUND-BOX CONSTRUCTION Theodore H. Beard, Bridgeport, Conn, assignor to Dictaphone Corporation,New York, N. Y., a corporation of New York 7 Claims. (Cl. 27427) This invention relates to sound-boxes and more particularly sound-boxes such as are employed for recording sounds upon a cylindrical Wax record blank.

One of the defects inherent in such soundboxes as have been heretofore used for the recording of compound sound waves such as are produced by the human voice, or by musical instruments, is the tendency to respond strongly to sound waves of relatively low frequency and weakly or inefficiently to sound waves of relatively high frequency. When a record made under these conditions is reproduced, the sounds produced seem to be lower in tone than the sounds recorded, and have lost many of their quality or personality characteristics. A well-known example of this defect is the reproduction of a wax cylinder record of the human voice. Through the loss of many of the higher wave frequencies and apparent exaggeration of the sound waves of low frequency, the record when reproduced sounds unnatural and the voice is often unrecognizable. Also the general audible effeet is poor, and the reproduction unsatisfactory, often being so dull and muffled as to be almost unintelligible. This is easily understood when it is remember what a large part the high frequency overtones have to play in determining the characteristic qualities of the voice.

It is believed that the cause of the loss of the higher wave frequencies in recording is due to the fact that the energy of speech resides principally in the frequencies below 1000 cycles per second and that articulation and intelligibility reside mostly in the higher frequency sounds, those above 1000 cycles per second. Consequently the diaphragm of the sound box, responding with greater amplitude to the low frequency sounds, produces a record in which these sounds predominate.

Another objectionable feature of the usual type of sound-box is the tendency of the diaphragm to blast when a strong or loud voice is recorded. This seems to be due to the fact that the force of the loud voice or musical note, as the case may be, is greater than the responsive capacity of the diaphragm. A fluttering of the diaphragm results which in a recorder produces breaks in what should be a smoothly continuous hill-and-dale track formed upon the record-cylinder surface. When the reproducing stylus, in reproducing the record, travels over this portion thereof, it produces a harsh and foreign noise, in addition to a distorted reproduction of the original sound. Not only is the sound or note more or less imperfectly reproduced, but the sound occasioned by the concussion of the sapphire against the abrupt edges of the breaks in the record track, is concurrent therewith.

It is usually desirable to get considerable vol-' ume, and this may best be attained by the use of comparatively thin diaphragms, which, unfortunately, are more susceptible to blast than those of greater substance.

It is an object of the present invention to provide a sound-box capable of producing a record substantially free from the evils of blasting, even when sound waves of relatively great amplitude are impressed upon the diaghram. Another object is to provide means adapted to prevent blasting even when diaphragms of exceptional thinness are mounted in the sound-box.

Another object is to provide a device of the nature described capable of recording and reproducing in a highly natural manner. Another object is to increase the voice or tonal range of a sound-box adapted either to record or reproduce.

Another object is to provide an instrument of the character described adapted to attain sharp and clear reproduction of sounds throughout a wide range of wave frequencies.

Another object is to produce a simple and rugged device of the above nature. Another object is to provide a device of the nature described easily adjustable-to adapt it for efficiently re- 30 cording or reproducing sounds of varying loudness and tonal range.

Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangementsof parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the various possible embodiments of my invention:

Fig. 1 is a side elevation of a sound-box of a well known type, showing a portion of the tonearm and disclosing a feature of my invention;

Fig. 2 is a plan View thereof; and

Fig. 3 is a cross section taken on line 33 of Fig. 2.

Similar reference characters refer to similar parts throughout the various views of the drawmg.

The sound-box shown in the present embodiment of my invention involves the use of a sound wave baflle and leak-off. Referring to the drawing the sound-box structure comprises a tonearm or tube I closed at its end, as by the wall 2 and which is provided with a downwardly turned flange 3 surrounding a circular opening 4. The pan or sound-box head comprises a shallow inverted dishlike member 5 having circumferential walls 6. The circular edge 1 of an opening formed in the center of the pan is seated in and secured to the tone-tube by turning the flange 3 over said edge, as at 8, as shown in my present construction, although it will be understood that the tone-arm and pan may be formed integrally. Such an integral construction is shown in the patent'to .Bodine .et 'al., No.

1,606,744, to which reference is made for a de-' scription of the manner in which a combined recorder and reproducer maybe mounted, and

an explanation of its mode of operation as applied to a commercial dictating machine.

The pan is further supported by a boss 9 formed on the tone-arm I to which the pan is attached by means of a screw H). A diaphragm II is suitably mounted in the sound head, as by means of gaskets 12-1-3, which in the present construction are held in place by means of a fillet Hi of plastic material such as beeswax. The diaphragm is preferably made of mica, perforated at its cen ter for the passage of a small screw 15, which is threaded into and makes fast to the diaphragm a stylus or point holder 16. Holder I6 is further supported upon the diaphragm by means of an arm ll having an offset portion 18, which, in assembling, is passed through a perforation in the diaphragm, as at 1'9. The stylus holder is of familiar form and provides a seat for a recording stylus 2'0 and a reproducing stylus 2|, either of which may be brought into operative engagement with a record-cylinder, by means shown and described in the Bodine patent referred to above.

No novelty is claimed for the features thus far described.

The upper wall of the tone-arm is perforated, as by'punching or otherwise, at a point directly opposite the center-of the opening 4, and the portions 22 of the wall, which are inturned by the punch, are internally threaded to receive a solid threaded plug 23 terminating in an enlarged conical end 24 which extends downwardly through the opening 4 into close proximity to the diaphragm. A slot 25 formed in the upper end of the plug is adapted to receive a screw driver 'by means of which the position of the plug may beadjusted by screwing it in or out of the sound-box. This adjustment permits of varying the clearance between the base of its conical end and the diaphragm, and also permits control of the size of the annular portion of opening 4 surrounding the cone. The object of this plug member is to prevent the impinging of sound waves directly at the center of. the diaphragm and to cause them to strike an annular portion of the diaphragm adjacent the periphery thereof, and has other objects as will presently appear.

The result of this limitation of impact appears to be twofold. In the first place it serves to prevent blasting and thus ensures the tracing -of a smoothly continuous track upon a record-cylinder during recording. This result permits the use of thinner diaphragms, from which it follows that a tone of a certain intensity will produce sound wave tracks upon the record of greater amplitude; and greater volume is attained when the record is reproduced.

And secondly, it has been found that the defiection of the sound waves accomplished by the conical plug tones down the effect produced upon the diaphragm by vibrations of lower frequency and permits it to respond more accurately to vibrations of higher frequency, thus enabling a record to be made of these higher frequency waves and a consequent improvement of the quality of the tone and the attainment of a higher pitch when the record is reproduced.

Many tests of the standard type of recorderreproducer, in which the conical plug is omitted,

establishes the fact that it is naturally responsive to sounds up to '2500 cycles per second and, with increasing weakness, to sounds up to 4000 cycles per second. On the other hand, tests with soundboxes in which :theconical plug was used showed that they were naturally responsive to sounds of 3500 cycles per second and, with increasing weakness, to sounds up to 5000 cycles per second. As would be expected, this resulted in more natural recording and reproducing, in that there were saved many overtones and other characteristics which determine timbre or voice personality. This result .is believed to be in part due to the damping effect of the air cushion established between the end of the solid plug and the center of the diaphragm, which aids in preventing blastin'g and makes the diaphragm more responsive to sound waves of higher frequency.

But a further improvement in the action of the device when used as a recorder has been effected by the provision of a leak-off passage 26 in the'for-m of a perforation extending through the end wall 2 of the tone-arm I. This passage connects with the interior of the sound-box at a point above the annular opening formed between the conical end of the plug and the rim of the opening 4.

The chief benefit derived from the leak-off seems to be that by its use the recorder is able to handle with .substantially equal efficiency vibrations covering a wide range of intensity. The excess energy of a loud voice is drained off to the surrounding atmosphere so that the diaphragm is not put under an overstrain. This prevents rattle and blast of the diaphragm and ensures the production of a good record.-

Waves of low frequency which have a larger share of the energy of speech than those of high frequency, are leaked off to a greater extent than are the latter, and thus the leak-off passage aids the baffling and damping efiects of the plug in effecting the recording of more of the higher overtones or partials of the voice and so enhance the quality of reproduction.

It willbe seen that there is provided a construction of an essentially practical nature in which the several objects of this invention are attained.

As many possible embodiments may be made of the above invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1.. In a dictating machine, in combination, a tone-tube closed at its end by a wall and having an outlet opening disposed in a plane substantially normal to said wall, a sound-box connected with said tone-tube at said opening, a conical plug mounted in the wall of said tube opposite said opening and extending into said opening,

means for shifting said plug to vary the size.

of the unobstructed area of said opening, and a leak-off port provided in the said end wall of said tube.

2. In a dictating machine, in combination, a tone-tube closed at its end by a wall and having an outlet opening disposed in a plane substantially normal to said wall, a sound-box connected with said tone-tube at said opening, a stud threaded into the wall of said tube opposite said opening and having a conical head extending through said opening into said sound-box, and a leak-off port in the said end wall of said tube.

3. In a dictation-recording machine, in combination, a tone-tube having a closed end and an opening adjacent said end, the axes of said tube and opening being substantially normal to each other, a sound-box secured to said tone-tube at said opening, a diaphragm in said sound-box supporting a recording stylus, a solid conical plug mounted in the wall of said tube and extending into said opening, the base of said plug being directed toward said diaphragm, and a leak-01f port provided in a wall of said tube adjacent said opening.

4. In a dictating machine, in combination, a tone-tube closed at its end by a wall and having an outlet opening disposed in a plane substantially normal to said wall, a sound-box connected with said tone-tube at said opening, and a plug mounted in the wall of said tube opposite said opening and extending into said opening, and a leak-off port in the end wall of said tone-tube.

5. In a dictating machine, a sound-box, a tonetube connecting with the interior of said soundbox through a circular opening, a conical plug having a diameter at its base substantially equal to the diameter of said opening mounted concentrically in said opening to provide a gradually expanding annular passage connecting the interior of said sound-box with said tone-tube, means for shifting said plug to vary the size of the unobstructed area of said opening, and a leakoff port in a portion of the wall of said tone-tube in close proximity to said conical plug.

6. In a dictation recording machine, in combination, a sound-box, a stylus actuating diaphragm, a tone-tube connecting with the interior of said sound-box through an opening, a leakoff port in said tone-tube, and a wave-baffle positioned in said opening operatively to coact with said leak-off port in effecting at said diaphragm a controlled balance of the energies of sound wave components of widely difierent frequencies.

7. In a dictating machine, a sound-box, a tonetube connecting with the interior of said soundbox through a circular opening, a conical plug having a diameter at its base substantially equal to the diameter of said opening mounted concentrically in said opening to provide a gradually expanding annular passage connecting the interior of said sound-box with said tone-tube, and means for shifting said plug to vary the size of the unobstructed opening of said area.

THEODORE H. BEARD.

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