US2582130A

US2582130A - Acoustic diaphragm

Info

Publication number: US2582130A
Application number: US55592A
Authority: US
Inventors: Arthur H Johnson
Original assignee: Hawley Products Co
Current assignee: Hawley Products Co
Priority date: 1948-10-20
Filing date: 1948-10-20
Publication date: 1952-01-08
Anticipated expiration: 1969-01-08

Description

Jan. 8, 1952 Filed Oct. 20, 1948 A. H. JOHNSON 2, 30

- ACOUSTIC DIAPHRAGM 3 Sheets-Sheet 1 IN VEN TOR.

Jan. 8, 1952 A. H. JOHNSON 2,582,130

ACOUSTIC DIAPHRAGM Filed 001;. 20, 1948 3 Sheets-Sheet 2 o O 0 g 3 m 0 CYCLE-5 PER MINUTE- IN V EN TOR.

Jan. 8, 1952 Filed OGt. 20, 1948 A. H. JOHNSON ACOUSTIC DIAPHRAGM 3 Sheets-Sheet 5 2% WWW Patented Jan. 8, 1952 ACOUSTIC DIAPHRAGM Arthur H. Johnson, St. Charles, 11]., assignor to Hawley Products Company, St. Charles, 111., a

corporation of Delaware Application October 20, 1948, Serial N 0. 55,592

1 Claim. 1 This invention relates in general to acoustical devices and more particularly to an improved type of sound reproducing diaphragm.

An unfortunate general characteristic of acoustic diaphragms is the drop in the intensity of sound which occurs at around 1000 to 1200 cycles. The intensity of sound increases beyond that point so that the frequency curve of a loud speaker diaphragm will show a valley or icicle at between 1000 and 2000 cycles. Since the above described drop in sound intensity occurs well within the practical audible range, faithful sound reproduction is seriously hampered. Many attempts have been made to remedy this undesirable inherent characteristic of acoustic diaphragms, but up to this time none has been entirely successful.

It is an object of this invention to provide a sound producer or reproducer which will have a substantially even response curve where all sounds of the practical audible range will be produced or reproduced with substantially equal efficiency.

Another object of this invention is to provide a diaphragm capable of reproducing both high and low frequency sounds corresponding in intensity, timbre mellowness, and other qualities with the originally produced sound waves.

Another object of this invention is to provide a diaphragm in which the intensity of sound is maintained uniformly high over the greater part of the practical audible range.

A still further object of this invention is to provide a diaphragm in which the peaks and valleys of sound intensity are smoothed out into a more even response curve.

These and other objects of the invention will become more apparent from the following description of the drawings in which:

Fig. 1 represents a rear plan view of the new conical diaphragm, which is the subject of this invention;

Fig. 2 is a sectional view along the lines 2-2 in Fig. 1 of the new conical diaphragm;

Fig. 3 is a detailed sectional view corresponding to Fig. 2 and showing the individual components of the new diaphragm;

Fig. 4 shows the frequency response curves for a standard diaphragm and for the new diaphragm. The curve for the standard diaphragm is represented by the heavy line while the curve for the new diaphragm is represented by the light line, and

5 is a detailed drawing of the supplemental vibratile part showing the exact curvature and design of the part. The dimensions in this drawing are actual dimensions in inches and the scale of the drawing is eight inches equals one inch.

By the practice of this invention it is now possible to make a sound reproducing diaphragm in which the characteristic drop in sound intensity of standard diaphragms between 1000 and 2000 cycles is eliminated. The new diaphragm, which is the subject of this invention, minimizes the rises and dips in the frequency response curve. The new diaphragm equalizes vibrations in the diaphragm at frequencies Where the standard type of diaphragm suffers severe changes in vibration. Hence, by the employment of the new diaphragm, it now becomes possible to reproduce a substantially even response curve throughout the practical audible range.

Considering the drawings now in more detail, Fig. 1 represents a rear plan view of a diaphragm prepared according to the present invention. The body of the diaphragm corresponds to the standard type of diaphragm in which I represents a border portion which is adapted to be secured within a loud speaker assembly. The vibratile portion 3 is in the shape usually employed in standard diaphragms. The thin corrugated section 2 represents the .undulated portion which is employed in standard speaker diaphragms to allow maximum freedom of vibration of the vibratile portion without interference from the support. Part 4, as is best represented in Fig. 2, shows the type of construction employed in standard speaker diaphragms for the retention of the voice coil 5. The portion 4 is in the form of an inverted cone or reentrant having a flange represented at 6 into which the voice coil 5 is inserted. Up to this point the diaphragm construction corresponds to the ordinary practice within the industry. The diaphragm may be conical in form, or it may be elliptical or pyramidal as desired.

The frequency response curve for a standard daphragm is represented by the heavy line on the chart in Fig. i. It will be seen from Fig. 4 that a response curve for a standard type diaphragm reaches a peak of about 110 decibels of sound intensity at about 1000 cycles and then rapidly drops off to about 90 decibels at about 1500 cycles. Such a severe and sharp drop in the intensity of the sound being reproduced by this diaphragm results in very unsatisfactory listening qualities. In the past it has been the practice to attempt to regulate the sound intensity in the above-mentioned range by artificial means, but results have not been satisfactory.

According to the present invention, a second vibratile portion of very special design is attached to the vibratile portion 3 of the standard diaphragm at the point I where the diaphragm is inverted to form a receptacle for the voice coil 5. In Fig. 3 the supplemental portion 8 is seen as composed of a flared or curved outer section 9 which connects the overlapping support section In and the flat centerpiece l l. The design of the curved portion 9 must be very carefully controlled as shown in Fig. 5. The supplemental vibratile piece 8 is attached to the standard cone at the point i by any suitable method such as, for instance, by gluing the parts together.

The function of the supplemental vibratile part 8, which may be referred to generally as a reentrant member, is that of preventing rises and dips in the frequency response curve of the standard diaphragm. Hence, the reentrant may be called an antiresonant since its purpose is to be antiresonant when the rest of the system is resonant, and to be resonant when the rest of the system is antiresonant. The particular design of the reentrant 8 is such that its natural resonant period occurs at the frequency (1000-2000 cycles) where the response curve of the standard diaphragm shows a gap or icicle. The light curve in Fig. 4 represents the frequency response curve of a diaphragm modified according to the present invention. It will be seen that the response curve is relatively flat between 100 and 1500 cycles. Then, instead of dropping from 110 decibels to 90 decibels as the standard diaphragm does, the new diaphragm reproduces sounds smoothly and with steady intensity up to about 2000 cycles, rising gently to a maximum of about 113 decibels at about 2200 cycles. Then there is a gradual falling off in intensity to about 108 decibels at about 3500 cycles, after which the frequency curve of the new diaphragm assumes approximately the same characteristics as that of the standard diaphragm. Hence, it will be apparent that the intensity of sound reproduced by my new diaphragm does not undergo the usual changes at the center of-the audible range to which ordinary diaphragms are subject. On the contrary, uniformly high intensity of sound is produced which carries from the lower limit of the audible range up to 3500 cycles on the upper limit of the practical audible range.

The shape of the reentrant diaphragm 8 must be carefully controlled according to the design shown in Fig. 5. The reentrant member 8 is shown therein as consisting of a neck or centerpiece I l, a curved portion 9 and a border Ill. The exact curvature of the portion 9 is indicated by the reference dimensions under the curve. The

shape is particularly important because the reentrant must vibrate in such manner as to fill in the frequency response curve at the point (between 1000-2000 cycles) where a standard diaphragm undergoes a loss in intensity. At the same time the supplemental reentrant should be antiresonant duuring the periods when the standard diaphragm is resonant. It has been found that the reentrant 8 must correspond closely to the design of Fig. 5 in order that the above described results may be obtained. Other shapes and designs of vibratiles have been tried in place of the design of Fig. 5 but none gives the supplementing vibrations which are required to fill in and extend the frequency response curve of the standard diaphragm. For example, fiat pieces and other designs of diaphragms and caps have been employed without satisfactory results.

The standard diaphragm and the reentrant 8 are preferably made of molded fibrous material. Any of the commonly known fiber molding methods may be employed, such as, for instance, the method outlined in U. S. Patent 1,984,019, issued to Jesse B. Hawley, December 11, 1934:. By such a method the parts are made in one single piece and without any seam. They are thin and light in weight to reduce to a minimum the mass inertia or momentum thereof. In the process of molding the fibers are preferably deposited on a porous former until a blank is made. The blank of sub stantially uniform thickness throughout is ordinarily compressed while still wet or moist to compact the fibers. The blank may then be dried according to any of the ordinary methods, and it may be further treated with a bonding or waterproofing agent as desired.

It will be apparent from the foregoing disclosure and descriptions that the practice of this invention now makes possible the reproduction of all sounds within the practical audible range without a damaging gain or loss in intensity at a point within said audible range. As a result, a remarkable faithfulness of sound reproduction is accomplished which has heretofore been impossible to achieve.

The invention is hereby claimed as follows:

An acoustic diaphragm comprising a primary vibratile sound producing member of general conical diaphragmatic type having a reentrant apical portion and an auxiliary vibratile reentrant member enclosing the top of said apical portion of said primary member, said auxiliary member comprising a flat centerpiece and a flared outer section, the curvature of said outer section corresponding to the curve shown in Fig. 5 of the drawings.

' ARTHUR H. JOHNSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,512,323 Gersch June 20, 1950 FOREIGN PATENTS Number Country Date 435,670 Great Britain Sept. 25, 1935