U.S. patent number 3,571,813 [Application Number 04/826,319] was granted by the patent office on 1971-03-23 for acoustical ear muff with cone-type cushions.
This patent grant is currently assigned to Bolt Beranek and Newman Inc.. Invention is credited to Clayton H. Allen.
United States Patent |
3,571,813 |
Allen |
March 23, 1971 |
ACOUSTICAL EAR MUFF WITH CONE-TYPE CUSHIONS
Abstract
This disclosure deals with a novel acoustical ear muff and the
like employing a novel cushion that provides a soft and compliant
seal, conforming readily to the irregular contour of the head even
when that contour varies with time, as when the wearer is talking
or chewing; but, when firmly sealed to the head around the entire
periphery of the cushion, the cushion then presents a high
stiffness against alternating forces induced by an incident sound
field, thus minimizing any resulting change in enclosed volume of
the ear muff and consequently minimizing the sound pressure
developed at the ear.
Inventors: |
Allen; Clayton H. (Wellesley,
MA) |
Assignee: |
Bolt Beranek and Newman Inc.
(Cambridge, MA)
|
Family
ID: |
25246231 |
Appl.
No.: |
04/826,319 |
Filed: |
May 21, 1969 |
Current U.S.
Class: |
2/209 |
Current CPC
Class: |
A61F
11/14 (20130101) |
Current International
Class: |
A61F
11/00 (20060101); A61F 11/14 (20060101); A41d
021/00 () |
Field of
Search: |
;2/209,174,3 ;128/152
;181/23 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Franklin; Jordan
Assistant Examiner: Krizmanich; George H.
Claims
I claim:
1. An acoustical ear muff having, in combination, a hard shell, a
frustoconical cushion member the larger end of which is intimately
connected with and restrained by said hard shell, the cushion
member being free to deflect at its smaller end in a direction
normal to the surface of the cone thereof to accommodate to the
shape of the head around the ear of the wearer and having elastic
restoring means tending to maintain such frustoconical shape, said
restoring means comprising a viscoelastic material of time constant
that enables rapid accommodation of changes in shape of the surface
of the head of the wearer, as during talking, chewing and the like
at frequencies under approximately 5 Hz. but said time constant
being short compared with the period of vibratory forces impressed
on the cushion member by sound waves of audible frequencies above
approximately 50 Hz. incident upon the muff.
2. An acoustical ear muff as claimed in claim 1 and in which said
hard shell is generally ellipsoidal and has high vibration loss
factor at acoustic frequencies.
Description
The present invention relates to acoustical ear muffs or muffler
devices and, more particularly, to ear protectors that are employed
to protect the hearing of the wearer against the damage of external
noise.
While the art is replete with ear muffs and earphones of various
types (all hereinafter generally referred to as ear muffs), there
has previously not been a satisfactory solution to the problem of
providing a sound-protecting ear muff or the like that has
sufficient softness to permit ready and comfortable compliance with
the head but that obviates the necessity for sizable pressure of
the muff against the head, while adequately muffling both the low
and high audible frequency sounds. While ear muffs have been
provided with soft compliant cushions, the very softness of the
cushion against the head inherently produces a yielding in response
to low frequency sounds that, in turn, vibrates the hard shell
associated with the muff and creates sound pressure therewithin.
This renders the wearer subject to the effects of low frequency
sounds. Attempts to overcome this problem have involved increasing
the volume contained within the ear muff; but this forbids the use
of such devices under helmets, or in other restricted applications.
Other attempts to solve this problem have been to increase the
pressure of he muff against the head; but this prevents the
continual comfortable use of the muff over long periods of time. In
addition, prior art muffs have employed relatively thick cushions
which require a large central opening in order to admit the pinna
of the ear. This construction, however, is difficult to seal
against the irregular contour of the head in the region surrounding
the ear, and, in addition, leaves a relatively large unsupported
central area that tends to allow pumping of air within the shell of
the muff.
In my copending application, Ser. No. 664,154, now U.S. Pat. No.
3,479,669 filed Aug. 29, 1967 for Acoustical Ear Muff and the Like,
a satisfactory solution for many aspects of this problem is
proposed involving two sets of rigid members frictionally engaged
to slide laterally with respect to one another but otherwise
rigidly resistent to deformation, and with the resilient cushion
formed by such members being yieldingly perimetrically conformable
in response to forces in excess of the friction of said slide, but
rigid against deformation produced by low frequency external sounds
and the like. In such a device, sound pressures which do not exceed
the friction and do not cause sliding between such members leave
the cushion substantially rigid and nondeformable. The cushion
motion then is restricted to the motion permitted by the resilience
of the flesh underneath the cushion between the cushion and the
bone of the head.
There are applications, however, where, for purposes of simplicity,
economy and for other reasons, it is not desirable to employ two
sets of frictionally slidable devices in the cushion. It is to the
problem of providing the desired results in a unitary structure
void of the necessity of such sets of frictionally slidable members
that the present invention is, accordingly, primarily directed.
An object of the invention, therefore, is to provide a new and
improved acoustical ear muff and the like that, in a unitary,
nonsliding part structure enables soft compliance with the head
while providing each of minimal volume, minimal unsupported area
and minimal force against the head, while simultaneously overcoming
the problem of muffling the low frequency sounds (as well as the
high frequency sounds) and, additionally, brings the pressure point
of the muff very close to the ear and in intimate engagement with
the head close to the base of the pinna of the ear.
A further object is to provide a novel ear muffler device.
Other and further objects will be explained hereinafter and are
more particularly set forth in the appended claims. In summary,
however, the invention provides a frustoconical cushion member
constrained at its larger end by a hard shell and free to deflect
at its smaller end to accommodate to the head around the ear of a
wearer, and with certain critical elastic properties. Preferred
details are hereinafter set forth.
The invention shall now be described with reference to the
accompanying drawing:
FIG. 1 of which is an oblique section of an ear muff constructed in
accordance with the invention; and
FIG. 2 is a similar view of a preferred embodiment.
Referring to FIG. 1, the muff is shown comprising what is shown as
a lower relatively rigid, frustoconical annular member 1, as of
resin-bonded fiberglass cloth or similar material having the
property that, while flexible enough normal to its surface to
permit adaptation to the contour of the head around the base of the
ear, is substantially inextensible and will not stretch or
substantially give in the radial or circumferential directions. The
frustoconical member 1 is shown embedded in a rubberlike or
elastomeric covering 3 that provides a resilient spring force
urging the frustoconical member 1 to tend to maintain its desired
frustoconical shape even when applied to the base of the ear.
Secured to the outer periphery or larger end of the member 1--3
(shown above), as by cement or otherwise, is a hard shell somewhat
ellipsoidal member 2, as of rigid plastic or the like having the
property of high vibration loss factor at acoustic frequencies,
such as rigid polycarbonate plastic and the like.
This form of the conical cushion provides dual stiffness by the use
of the frustoconical member 1--3 which is free to deform in a
direction perpendicular to its surface but which is substantially
inextensible in any direction along its surface. The small end of
the conical member 1--3 (shown at the bottom) fits around the ear
and presses against the head, close to the base of the pinna of the
ear; and a slight pressure causes the normally oval-shaped
perimeter of the opening to alter its shape so as to fit against
the head by changing only the angle of the elements of the conical
member 1--3 relative to the plane that is fixed by the rim of the
hard shell member 2 against which the outer or larger end is firmly
held in airtight, unitary contact, as before explained. When the
shape of the frustoconical member 1--3 has been distorted so as to
fit against the head along the entire perimeter of the conical
opening, no further distortion can readily take place since the
conical surface itself is, as previously described, substantially
inextensible. The cushion then becomes extremely rigid toward any
alternating forces caused by incident sound waves and the enclosed
volume is held substantially constant.
In the embodiment of FIG. 2, the frustoconical cushion 4 provides
the same type of dual stiffness as the cushion 1--3 by use of a
viscoelastic material which has a time constant such that it is
free to deform elastically at low frequencies, below approximately
5 Hz. and thus can accommodate easily and rapidly to the irregular
head contour even though that contour may continually change with
the wearer's movements. The viscoelastic material 4 is designed,
however, to have time constant short compared to the period of
vibration, so as to be substantially rigid against rapidly
alternating forces, such as those induced by incident sounds at
frequencies of 50 Hz. and higher. The same rigid member 2 is
securely bonded to the larger end of the cushion 4, as in the
embodiment of FIG. 1. Suitable viscoelastic materials that possess
these necessary properties include, for normal ambient
temperatures, a high damping viscoelastic core (such as the Lord
Manufacturing Company "HD" Elastomer) covered by silicone rubber;
whereas, for a wide temperature range of operation, a solid
frustoconical cushion of, for example, the Lord Manufacturing
Company BTR damping elastomer has the necessary properties.
Improvement of at least the order of 10 d. in greater muffling of
the low audio frequency sounds has been produced with such
structures with substantially the same high frequency sound
attenuation of the best present day mufflers.
The frustoconical members 1--3 (FIG. 1) are substantially
inextensible in all directions along their surfaces, but may bend
freely in the curved direction of the cone while being constrained
always to remain substantially rigid in the direction along the
elements of the cone. Such elements at the larger end of the
frustoconical member are held firmly restrained against the
peripheral surface of the hard shell 2 while the same elements at
the small end of said conical member are free to deflect in a
direction perpendicular to the surface of said cone so as to
accommodate to the shape of the head around the ear of the wearer,
but with such deflection being accompanied by a change in the angle
of the elements relative to the axial direction of said cone. The
elastic portion of the cushion, either as part of said
frustoconical member 1 or as a separate member 3 intimately
connected with said frustoconical member 1, provides a restoring
force tending to maintain the frustoconical member in its initial
shape, such restoring force being sufficient in magnitude to
prevent buckling or collapse of the cushion under the normal
biasing force used to hold the ear enclosure against the head of
the wearer. The elastic member also provides a smooth pressure pad
around the rim of the small end of said frustoconical member for
the purpose of comfortably sealing and supporting such cushion on
the head of the wearer.
Further modifications will also occur to those skilled in this art
and all such are considered to fall within the spirit and scope of
the invention as defined in the appended claims.
* * * * *