JPH03165694A - High-compliance headphone driving device - Google Patents

Abstract

PURPOSE: To realize high compliance by separating a front part and a rear part cavity by a baffle and limiting the maximum deviation of a diaphragm. CONSTITUTION: A front part, i.e., an internal cavity is separated from a rear part, i.e., an external cavity and the baffle 11 which has a built-in high- compliance driver having a diaphragm is provided. Plastic finger-shaped small pieces 15 are provided around a shaft of the driver at equal angular intervals. Namely, a deviation of the diaphragm 14 is limited to a space from its stop position to a plane sufficiently close to a stop plane, when the diaphragm 14 is positioned in the center so as to enable the diaphragm to move freely to an axis direction without obstacles when headphones performs ordinary sound reproduction while properly fitted to a head of a user. Consequently, a high- compliance and low-mass driver is realized and passive transmission attenuation below an open resonance frequency is greatly improved to increase the efficiency of the system.

Description

Description: TECHNICAL FIELD This invention relates to high compliance drivers for active noise reduction headsets, and more particularly to devices for protecting driver diaphragms.

BACKGROUND OF THE INVENTION In active noise reduction headphones, it is well known to use headphones that have a front (internal) cavity and a rear (external) cavity separated by a nozzle containing a small driver.

SUMMARY OF THE INVENTION The driver of this invention is a high compliance driver. Another feature of the present invention is that it has a structure that limits the firing deviation of the diaphragm. Another feature of the present invention is that the diaphragm is formed with a circular groove or depression having a component transverse to the waveform near the periphery of the diaphragm. Another aspect of the invention includes a raised portion on the surface of the cage below the diaphragm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Other features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings. The attached drawing is a schematic plan view of a high compliance driver with a headphone cup for showing the appearance of the present invention.

An embodiment of the invention is shown in the drawing. The invention includes a bubble 11 that separates the front or inner cavity from the rear or outer cavity and contains a high compliance driver having a diaphragm 14. Plastic fingers 15 are spaced equiangularly around the axis of the driver, extend radially inwardly, and are arranged along the axis of movement of the driver to maintain a temperature of .degree. Ru. This limits the excursion of the diaphragm from its center or rest position to a plane sufficiently close to the rest plane when the diaphragm is centered so that a portion of the voice coil is always within the air gap. , and sufficiently far from the central plane to allow the diaphragm to move freely axially without obstruction during normal sound reproduction with the headphones properly attached to the user's head.

The active noise reduction mounting structure 16 is described in U.S. Pat.
．． A microphone (not shown) is mounted near the diaphragm for use with an electronic circuit consisting of a device generally corresponding to the active noise reduction device disclosed in No. 544.765.

Having described the physical configuration of the embodiment above, it would be appropriate to consider its principle here. It is convenient to refer to the cavity closest to the user and surrounding the user's head when the headphones are properly positioned as the front or inner cavity, and the cavity farther from the user as the rear or outer cavity. It is desirable to make the volume of the anterior cavity as small as practical to minimize the sound pressure generated by the small actuator in the Eustachian tube to eliminate low frequency noise. .

However, it is desirable to increase the volume of the front cavity to increase the passive transmission attenuation of ambient noise around the ear and through the ear cup sealed by the ear.

It has been found that the effective amount of air that determines this transmission damping is a function not only of the front cavity volume, but also of the driver compliance (below the free air resonant frequency) and the rear cavity volume. Where Cf is the front cavity air volume compliance, Cr is the rear cavity air volume compliance, and Cd is the driver compliance, the effective compliance Ceff, which determines the passive transfer damping, is the driver opening. Below the (free air) resonant frequency - the front cavity compliance in series with the parallel combination of the driver compliance and the rear cavity compliance, i.e. Ceff = Cf + CrCd/(Cr + Cd).

Since the air mass compliance of a closed space is proportional to the volume, for a given volume with ear cups separated into front and rear cavities, the effective compliance Ceff is determined by maximizing the driver compliance. can be maximized. In this way, very high compliance (low stiffness) and low mass (
to resonate at as high a frequency as is practical)
The driver having the above-mentioned method greatly improves the passive transfer attenuation below the driver's open resonant frequency without audibly affecting the sound reproduction. Within limits, when the compliance of the driver is much greater than the compliance of the air in the rear cavity, the effective compliance is the sum of the compliances of the rear cavity and the front Mr cavity C
Equal to f+Cr.

High compliance here means that the compliance of the driver is greater than the compliance of the rear cavity.

Another advantage of a high compliance driver is that at very low frequencies (below the rear cavity port resonance when ports are provided in the rear cavity), the higher the compliance of the driver, the more efficient the system will be. This increased efficiency reduces the power required to generate the sound pressure needed to cancel high levels of low frequency noise. This feature is particularly useful in battery powered active noise reduction hectocets and hearing protectors.

When the opening of the headset is sealed by the head or other surface, movement of the ear cup relative to that surface changes the volume of the front cavity. Small changes in volume generate large subsonic sound pressures. If the volume increases, for example when the cushion is placed snugly against the head and then the ear cup is moved away from the head, the resulting lack of pressure will cause the actuator diaphragm to be pulled toward the opening of the ear cup. It will be destroyed. High compliance,
Since the low mass driver moves very freely, this pressure will very easily cause the voice coil to be forced out of the gap beyond its normal maximum excursion range. There is therefore a risk that the voice coil will become stuck in the heel of the driver or in the magnet and will not return to its nominal rest position even after the pressure deficit has been resolved.

If the volume is reduced, such as when an ear cup is accidentally pressed against the head, the excess pressure created causes the thin, flexible diaphragm to deform from its normal shape. Drivers with plastic membranes typically have angular grooves or corrugations formed in the outer annulus between the voice coil and the end of the diaphragm. These grooves expand and contract as the voice coil moves, helping to ensure linear piston-like motion. Under overpressures such as those mentioned above, these grooves can become irreversibly deformed and prevent the driver diaphragm from returning to its normal shape and position.

The present invention prevents suction or underpressure problems by providing a voice coil deflection limiting structure above the diaphragm in the earcup. This structure 15 is provided in a position such that when the diaphragm of the driver is in the normal range of excursion, the diaphragm does not contact the structure 15 and its movement is not impeded. Close enough so that the voice coil makes contact with the diaphragm before it is fully pulled out of the gap.

The voice coil is not pulled out of the gap, so when the suction is released, the coil returns to its normal resting position and does not get caught in the cage. Preferably, the structure 15 is sufficiently small so as not to cause diffraction. Otherwise, it will affect the sound pressure detected by the active noise reduction microphone except in the case of high frequencies (above 10 KH, z). In this invention, three plastic fingers (
This is accomplished using the finger) 16.

If you touch the diaphragm with a small dot-like finger in a place other than where it touches the voice coil, there is a risk of puncturing or damaging the diaphragm.

An alternative embodiment of a structure to stop diaphragm movement is a fine wire mesh screen 16 shaped to maximize contact with the surface of the diaphragm at the maximum allowable outward excursion of the diaphragm. By increasing the contact area, the pressure at any point can be made small enough not to damage the driver.

The invention prevents the problem of driver deformation or overpressure by using a driver with a diaphragm that returns to its original shape when deformed. This prevents irreversible deformation by changing the shape of the grooves or corrugations in such a way that if the diaphragm is deformed, the wrinkles return to its original shape.An alternative solution is to There are ways to change the shape of the metal cage, or to manually add structural members to the cage.

The cage surface below the diaphragm is usually flat. This surface is raised at several points to support the diaphragm under overpressure, thereby preventing the diaphragm from deforming to the point where permanent failure or change in shape occurs.

In a preferred embodiment of the present invention, the mounting structure for the driver, the mounting structure for the active noise reduction microphone, and the means for preventing deviation of the driver under pressure are integrally molded as a single plastic member. . This method reduces the effects of machine tolerance build-up, ensures accurate positioning of all parts, and provides stable performance. This structure can also be combined with a bubble separating the front and rear cavities.

Specifically, the device functions as follows. When the headset is removed from the head and there is insufficient pressure, the limiting factor 1
5 limits the excursion of the diaphragm 14 to prevent the voice coil from exiting the gap. With this structure,
This ensures that the diaphragm 14 returns to its nominal position. These limiting elements 15 do not interfere with the normal range of motion of the diaphragm 14.

In conditions of overpressure, such as when a headset is pressed against the head, the grooves 17 on the surface of the diaphragm 140
If the diaphragm is deformed due to increased pressure, it will return to its original shape. In other embodiments, a raised point on the bottom of the diaphragm 14 supports the diaphragm during overpressure conditions to prevent deformation.

In one embodiment of the invention, the volume of the front cavity is approximately 100 cc (cubic centimeters) and the volume of the rear cavity is also 100 cc.

The driver has an open resonance of 250 Hz and an acoustic compliance of lX10-' (meters) S/newtons).

This compliance is equivalent to a volume of 150cc of air. Therefore, the effective compliance is Veff=1
0DXI DO”150/(100+150)=16
It is 0cc. The driver diaphragm is made of 1 mil thick Mylar. The driver is mounted within a plastic bubble with three underpressure excursion preventers placed in contact with a diaphragm that is offset by approximately 30 mils. At maximum operating conditions (high noise and high communication levels) the driver deflection will not exceed 20 mils. Rear cavity port tuning is set to 90Hz. The port tuning is selected due to the need for increased driver output to provide noise cancellation in the 50 Hz to 83 Hz range without reducing passive attenuation. , a much larger rear cavity would eliminate the need for a rear cavity port, but it would be less stylish.

Other embodiments are within the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of a high compliance driver with a headphone cup to show the appearance of the present invention.

Claims (7)

[Claims] 1. at least one ear cup having a front cavity and a rear cavity; a bubble separating the front cavity and the rear cavity; a high compliance driver having a diaphragm coupled to a voice coil typically within a gearup attached to the bubble; A headset consisting of an active noise reduction device. 2. 2. The headset of claim 1, further comprising a limiting structure that limits the maximum excursion of the diaphragm so that the voice coil remains at least partially within the gap. 3. 3. The headset of claim 2, wherein said limiting structure comprises a plurality of plastic elements, said plastic elements being located at a portion where said voice coil is coupled to said diaphragm. 4. 3. The headset of claim 2, wherein the active noise reduction device mounting structure, the driver mounting structure, the bubble and the plastic element are integrally molded plastic. 5. a fine wire mesh shaped so that said limiting structure makes maximum practical contact with the surface of the diaphragm at the maximum allowable outward excursion of the diaphragm, thereby preventing further movement; 3. The headset of claim 2, comprising a screen. 6. 2. The headset according to claim 1, further comprising diaphragm deformation recovery means configured to restore the diaphragm to its original shape when the diaphragm is deformed, such as when the diaphragm is deformed. 7. Claim 1: The lower part of the diaphragm has a raised portion to prevent irreversible deformation of the diaphragm.
Headset as described.