JP6336613B2 - Headset porting - Google Patents

Description

  The present invention relates generally to headset porting, and more particularly to a headset having a linearized pressure equalization port characterized by an acoustic impedance having an ultra-low resistance component.

  By way of background, reference is made to US Pat. Nos. 4,644,581, 5,181,252, and 6,831,984, which are incorporated herein by reference, including the review process.

In general, in one aspect, the headset includes at least one earcup having a front cavity and a rear cavity separated by a driver. The cup includes a pressure equalization port that couples the front cavity to the space outside the cup, and the pressure equalization port has a cross-sectional area greater than 2 mm ² and is significantly elongated, mainly with reactive acoustic impedance. Thus, the pressure response of the front cavity including the port can be substantially linear over a wide range of pressure levels within the front cavity.

Implementations can include one or more of the following in any combination. The range of pressure levels in the front cavity can include sound pressure levels between about 120 dB SPL and 150 dB SPL. The pressure equalization port can include a tube having a length greater than about 15 mm. The pressure equalization port can include a tube having a cross-sectional area greater than about 1.75 mm ² . The pressure equalization port can include a tube having a length to inner diameter aspect ratio of between about 10: 1 to 25: 1. The pressure equalizing port tube may be made of metal. The metal can include stainless steel. The pressure equalization port tube can include a metal tube secured inside the wall of the front cavity. The cup can be made of plastic and the pressure equalization port tube can be heat staked to the plastic. An active noise reduction circuit can be coupled to the driver.

In general, in one aspect, the headset has a height between a front cavity and a rear cavity having front cavity compliance and rear cavity compliance, respectively, and a front cavity and a rear cavity having a driver compliance greater than the rear cavity compliance. At least one earcup having a compliance driver. The ear cup includes a mass port and a resistance port connected in parallel to the rear cavity, and a pressure equalization port connected to the front cavity, the pressure equalization port having a cross-sectional area greater than 1.75 mm ² ; Prominently long and primarily provides reactive acoustic impedance, so the pressure response of the front cavity, including the port to the signal input through the driver, is substantially over a wide range of pressure levels in the front cavity. It can be linear. An active noise reduction system is coupled to the driver.

In general, in one aspect, an apparatus is disposed between a first ear cup shell of a headphone, a second ear cup shell of a headphone, and a first ear cup shell and a second ear cup shell. An electroacoustic driver, wherein the first earcup shell and the first surface of the driver define a front cavity, and the second earcup shell and the second surface of the driver define a rear cavity. An electroacoustic driver and a metal tube having a lumen at least 15 mm in length and having a cross-sectional area of at least 1.75 mm ² , fixed in the first earcup shell and around the device A metal tube coupling the front cavity to the space.

  Other features, objects, and advantages will become apparent when the following description is read in conjunction with the accompanying drawings.

It is a perspective view of the headphone cup which has a linearization port. FIG. 2 is a partially exploded view of the headphone cup of FIG. 1 showing a relationship between a port and a headphone cup. It is a top view of the headphone cup of FIG. It is sectional drawing of the headphone cup of FIG. 1 of the cross section AA of FIG. FIG. 4 is a side view of the headphone cup of FIG. 3. 1 is a block diagram showing a logical arrangement of an active noise reduction system embodying the present invention. Fig. 6 is a graph of headphone cup response to various power level inputs. Fig. 6 is a graph of headphone cup response to various power level inputs. 1 is a schematic cross-sectional view of a headphone cup having a linear pressure equalization port. 1 is a schematic cross-sectional view of a headphone cup having a linear pressure equalization port. Fig. 6 is a graph of headphone cup response with different equalization port designs. Fig. 6 is a graph of headphone cup response with different equalization port designs. Fig. 6 is a graph of headphone cup response to various power level inputs. Fig. 6 is a graph of headphone cup response to various power level inputs.

  Referring now to the drawings, and more particularly to FIGS. 1 and 2, there is shown a perspective view of a headset cup embodying the present invention. In order to avoid obscuring the principles of the present invention, most conventional components of the headset including the cup portion will not be described in detail. Headset cup 11 includes a front cavity 12 partially encapsulated by shell 12A and a rear cavity 13 partially encapsulated by second shell 13A. The two cavities are separated by an electroacoustic transducer or driver 17. The front cavity couples the sound output by the driver to the user's ear. The air encapsulated by the rear cavity provides a controlled acoustic impedance to the driver movement and controls driver response and headset acoustic performance. The rear cavity 13 is coupled to the air around it by a resistance port 14 having a resistance port shield 15 and a mass port tube 16.

  Both ports provide impedance to the air flow having a resistive component and a reactive component. Resistive port 14 is negligible in length, so the port impedance is dominated by the resistance of the port shield. The mass port 16 is significantly taller, so its impedance is dominated by its reactance, which depends on the acoustic mass of the volume of air inside the tube. The impedance of the mass port 16 varies with the frequency of the sound pressure in the rear cavity 13, and the sound pressure in the rear cavity 13 causes an air flow through them. Specifically, as the frequency decreases, the contribution to the total impedance from the reactive component of the mass port decreases, allowing it to be dominated by the resistive component of the mass port impedance at lower frequencies, which is It is relatively constant with respect to frequency. However, the resistance component varies with the sound pressure level inside the cavity, and this variable impedance results in a response that is non-linear with pressure at the frequency dominated by the resistance component.

  Non-linearity in the response of the acoustic system, ie the impedance that increases with the sound pressure level, limits the power level at which the ANR circuit can operate, the higher impedance requires more force to move the air Requires more current to flow through the motor of the converter, possibly exceeding the capacity of the converter or amplifier. FIG. 7 shows the normalized response of an earcup using a conventional port for various input power levels, but the resistance port (corresponding to 14 in FIG. 1) is blocked, so only the mass port operates. ing. The first dotted line 100 shows the response when 1 mW of power is applied. It can be seen that when the power is increased to 10 mW on the solid line 102 and to 100 mW on the broken line 104, the response between about 30 Hz and 150 Hz decreases with increasing power. In certain headphones tested with the front cavity sealed against a flat plate (not the human ear), these power levels provided a power level of 122-137 dB SPL at 60 Hz. Since these tests were done without using any compression to avoid overloading the driver (as described below), the actual power provided by the complete product is significantly lower. It should be. Achieving higher SPL levels in this frequency range should require significantly more power. However, to avoid overloading the converter, the maximum output power of the ANR circuit is limited, for example, by compression or clipping, limiting the level of sound that the ANR circuit can cancel. In conventional ANR headsets, non-linearity is not important at the pressure level experienced in normal operation, and thus limiting the output power is not noticed by most users. However, military headsets may experience significantly higher sound pressure levels, at which point port response nonlinearity becomes a problem. Traditional military ANR headsets have been limited to erasing sound pressure levels of about 120 dB SPL to avoid compressing the signal.

To address this issue, the mass port is modified to reduce the resistive component of its impedance relative to the traditional design, the reactive part dominates, and the total impedance as a function of frequency is essentially Expand the linear frequency range. The resistance is reduced by increasing the diameter of the mass port 16. Increasing only the diameter reduces the effective acoustic mass of the port, thus maintaining the original reactance and increasing the length of the mass port. Increasing the length has a greater impact on the acoustic mass than resistance, so this does not detract from the benefits of increasing the diameter. In one example, the cross-sectional area of the port tube is increased from 2.25 mm ² in a conventional headset to 9.1 mm ² . To maintain the reactance, the length is increased from 10 mm to 37 mm (the termination effect results in a slightly longer effective length resulting in an effect that increases with diameter). That is, a 4-fold increase in area corresponds to a 4-fold increase in length. FIG. 8 shows the response when the mass port is expanded in the same test as FIG. The dotted line 110 shows the response to 1 mW of power, the solid line 112 shows the response to 10 mW, and the dashed line 114 shows the response to 100 mW. As shown in the figure, the response is much more linear over the frequency range, with less variation due to power level, and only decreasing with power by a small amount in the narrower range of 50-90 Hz. These normalization curves correspond to an SPL range of 125 dB to 143 dB at the 70 Hz peak. In practical applications (opening the resistance port and sealing the front cavity against the human head), the headset's ANR circuit has a sound pressure level as high as 135 dB SPL at frequencies between approximately 60-100 Hz. Can work effectively. In contrast, the prior art design embodied in the Bose® TriPort® Tactical headset is a sound pressure well below 120 dB SPL in the same frequency range to avoid overloading the circuit. Should clip the ANR output by level. Increasing the port size also improves the consistency of the acoustic response over the audible frequency range.

  The resistance port 14 in parallel with the mass port 16 also provides a resistive impedance, and it is desirable that the two impedances, both resistive and reactive, remain in parallel rather than in series. A pure resistance port improves performance at one frequency (in which case a back cavity with only a pure resistance port should have port resonance and should significantly reduce output power), but performance at other frequencies. To lose. While the reactive port has the lowest possible resistance, this resistance should be placed in a controlled pure resistance port to address the compromise and realize that benefit is most beneficial to the entire system. Is possible.

Therefore, the performance of the headset for high noise environments is improved by expanding the operating frequency range where the acoustic impedance of the mass port from the back cavity to the surrounding environment as a function of frequency is pure resistance, and thus the total back surface The cavity response remains substantially linear with sound pressure level. This is achieved by increasing both the diameter and length of the port, but in practice it is more difficult to manufacture such a port. As noted, the port in the example is 37 mm long for an aspect ratio of approximately 10 times the length to diameter, and has a cross-sectional area of 9.1 mm ² or a diameter of 3.4 mm. Another way to consider the size of the mass port is to set the volume of air inside the tube to 337 mm ³ , while the volume of the rear cavity (not including the volume occupied by the tube itself) is 11,100 mm ³ and about The ratio of the volume of the 33: 1 rear cavity to the volume of the mass port is given. A conventional mass port should have a significantly smaller volume and thus have a significantly larger rear cavity volume to mass port volume ratio. For example, for the conventional mass port described above with an area of 2.25 mm ² and a length of 10 mm, the volume is 22.5 mm ³ and in the same size rear cavity, the ratio is 493: 1. Adding 10 percent tolerance to the port volume and cavity volume, the ratio of the current design can vary from approximately 27: 1 to 40: 1, while the ratio using the conventional port size is approximately 400 1 to 600: 1. In applications, it has also been found that the ports are preferably of uniform cross-section in order to obtain a consistent response between units. It is also preferred that the port be smooth on the inside to avoid creating turbulence that can reintroduce the resistive component into the response. Providing long tubules with uniform cross-section and no internal protrusions can be extremely difficult with ABS plastics conventionally used to form headset shells 12A and 13A. Forming a tube with such long stretches cannot be finished to a uniform cross-section, and assembling the port from multiple parts should result in rough edges and possibly assembly variations.

  To solve this, in the embodiment shown in FIGS. 1-5, the mass port 16 is made of metal, such as stainless steel, has a uniform cross-sectional lumen over its entire length, Maintain reactivity. In addition, the metal port provides a smooth inner surface without protrusions that cause turbulence, thus keeping the resistance component of the port response low. In addition to providing the desired port response, the metal mass port provides further advantages. The high mass of the port tube itself prevents ringing of the tube structure (as opposed to the acoustic volume within the tube). For assembly, one end of the tube is formed with a rough surface, such as knurling (FIGS. 2 and 4), allowing the metal tube to be heat staked into the ABS plastic of the outer shell 13A. Thus, a reliable and reliable connection can be obtained between the parts. The portion of the tube that extends into the rear cavity can be kept smooth to facilitate insertion and avoid creating turbulence inside the rear cavity. As shown in some of the figures, the tube 16 extends outside the cavity 13 enclosed by the rear shell 13A. This reduces the amount that the tube structure itself occupies the volume of the rear cavity and removes the volume available for air. Specifically, the portion of the tube that is textured on the surface and secured to the plastic extends outside the rear cavity.

  The exploded view of FIG. 2 shows the mass port tube 16 removed from the opening 16A, which accommodates the mass port tube 16 in the rear shell 13A. The rear cavity shell 13A is also removed from the front shell 12A to show the driver 17.

  Referring to FIG. 3, a top view of the headset cup of FIG. 1 is shown.

  Referring to FIG. 4, a cross-sectional view of section AA of FIG. 3 is shown, showing the relationship between the mass port tube 16 and the rear cavity 13.

  Referring to FIG. 5, a side view of the headset cup of FIG. 1 is shown.

  The headset of FIG. 1 typically comprises an active noise reduction headset incorporating circuitry of the type described in the aforementioned US Pat. No. 6,831,984 and other patents described therein. .

  Referring to FIG. 6, there is shown a block diagram showing the logical arrangement of a system incorporating the present invention substantially corresponding to FIG. 1 of the aforementioned '581 patent and FIG. 4 of the aforementioned' 252 patent. . A signal combiner 30 algebraically combines the signal desired to be reproduced by the headphones, if any, on the input terminal 24 with the feedback signal provided by the microphone preamplifier 35. The signal combiner 30 provides the combined signal to the compressor 31, which limits the level of the high level signal. The output of the compressor 31 is applied to the compensator 31A. The compensator 31A includes a compensation circuit to ensure that the open loop gain meets the Nyquist stability criterion, so the system will not oscillate when the loop is closed. The illustrated system is replicated once for each of the left and right ears.

  The power amplifier 32 amplifies the signal from the compensator 31 </ b> A and supplies power to the headphone driver 17 to provide an acoustic signal in the cavity 12. The acoustic signal is transmitted from the region represented by the acoustic input terminal 25 into the cavity 12. Combined with the incoming external noise signal, a combined acoustic pressure signal is created in the cavity 12 represented by the circle 36, thereby providing a combined acoustic pressure signal that is applied to the microphone 18 and converted by the microphone 18. The microphone amplifier 35 amplifies the converted signal and supplies it to the signal combiner 30.

  A port featuring a port with a high acoustic level and linear acoustic impedance to enable improved noise reduction in a very noisy environment where the acoustic level may be greater than 120 dB SPL between 60-100 Hz A headset with is described. It will be apparent to those skilled in the art that numerous uses and modifications of the specific devices and techniques described herein may be made and departing from the devices and techniques without departing from the inventive concepts. Accordingly, the present invention is presented in the apparatus and techniques described herein, owned by them, and limited only by the active scope of the appended claims, including any and all novel features and combinations of novel features. It shall be interpreted as including.

  As shown in FIGS. 9-14, another port in the noise reduction headset that benefits from linearization is the pressure equalization (PEQ) port. Unlike the above ports, which primarily serve to control the acoustic response of the headset, the pressure equalization (PEQ) port is primarily responsible for the pressure inside the ear cup's front cavity (eg, caused by an external force pressing the ear cup) It is intended to allow equalization with the pressure outside the earcup. Since the goal is not to transmit the sound pressure outside the earcup into the earcup, providing a hole through the earcup has the potential to impair the noise cancellation characteristics of the headset. This is usually balanced by making the pressure equalization (PEQ) port as small as possible, so the pressure equalization (PEQ) port equalizes only the pressure at low frequencies, ie the pressure equalization (PEQ) port is Equalize the steady pressure difference, not the SPL difference within the audible range.

  Nevertheless, conventional pressure equalization (PEQ) port designs still produce some reduction in noise reduction performance. Furthermore, small pressure equalization (PEQ) ports may behave as if they were closed at high pressures even at low frequencies. This can be improved by increasing the port area and allowing more air flow at higher pressures, but such larger holes further impair passive noise reduction. By making the pressure equalization (PEQ) port more reactive in the same manner described above with respect to the mass port, the lost passive damping is recovered by increasing the port area. By making the pressure equalization (PEQ) port longer, its resistance as well as its reactance increase. This increased resistance is offset, at least in part, by the drop in resistance caused by the larger port area, so the net resistance increase is sufficient to detract from the improved linearity of the larger port. Not big.

9 and 10 schematically illustrate a prior art pressure equalization (PEQ) port and an improved pressure equalization (PEQ) port. In FIG. 9, the ear cup 202 includes a short, small diameter pressure equalization (PEQ) port 204 that is essentially merely a hole through the plastic shell of the ear cup. In FIG. 10, the ear cup 206 has a longer, wider pressure equalization (PEQ) port 208 in the form of a tube that extends into the ear cup front volume. In one particular example, the front volume of both ear cups is 100 cm ³ and the original pressure equalization (PEQ) port 204 is 1 mm in diameter × 1.5 mm in length. The improved pressure equalization (PEQ) port 208 is 1.7 mm in diameter and 20 mm in length. This corresponds to an increase of the effective area of about 3 times (2.27 mm ² from 0.78 mm ^2), it corresponds to an increase of 13.3 times the length. At a minimum, the port preferably has an effective area of at least 1.75 mm ² and a length of at least 15 mm. The length to diameter ratio should be in the range of 10: 1 to 25: 1. The actual area can vary along the length of the tube, such as when flaring is provided at one or both ends. The effective area corresponds to the average area or the area that can be determined by measuring the acoustic effect of the tube and assuming that it is uniform.

  Similar to the mass port above, increasing the diameter of the pressure equalization (PEQ) port while maintaining a longer pressure equalization (PEQ) port maintains the resistance component of its acoustic impedance, but its length Is increased, the reactive component is maintained, in which case the reactive component is increased. As shown in FIG. 11, which shows the modeled behavior, the effect of this increase is to increase the passive transmission loss (PTL) between 100 Hz and 700 Hz, ie, the ear cup passive attenuation by about 2 dB. Curve 302 shows the original design passive transmission loss (PTL), and curve 304 shows the new design improved passive transmission loss (PTL). As shown in FIG. 12, which shows measurements for an actual headphone prototype, passive transmission loss (PTL) is significantly improved from about 200 Hz to about 800 Hz. Curve 306 shows the actual performance of the conventional pressure equalization (PEQ) port used in the prototype earcup, and curve 308 shows the actual performance of the new pressure equalization (PEQ) port in the same prototype earcup. Show.

  Although not directly audible, low frequency pressure fluctuations below 20 Hz, which can be caused by physical movement of the earcups, can produce an audible effect referred to as buffeting in active noise reduction systems. Increasing the diameter of the pressure equalization (PEQ) port reduces the audible buffeting in the ANR headset by allowing the port to remain linear at higher pressure levels.

  FIGS. 13 and 14 compare the pressure in the front ear cup in response to different input signal levels in the prior art design and the improved design, respectively. Different input signal levels correspond to different absolute pressure levels inside the ear cup, as higher signal levels cause the driver to generate higher pressure. Since the response is shown as dB SPL per volt, the curve compares the shape of the response, not the absolute level of response. In FIG. 13, there is a noticeable variation in the shape of the response at various input signal levels, particularly at low frequencies, highlighted by the dotted ellipse 322. Dashed line 310 shows the expected response at low input signal levels. For medium and higher signal levels, curves 312 and 314, the curves indicate that there is a higher pressure that occurs inside the earcup. This higher pressure can cause problems for ANR systems, as described above. In FIG. 14 with a longer and wider port, especially at the low frequencies of interest highlighted by the dotted ellipse 324, there is little variation in the shape of the response between the different input signal levels, curves 316, 318, and 320. There is no. This indicates that the pressure in the ear cup is consistent regardless of the input signal, and the disturbance to the ANR system has been removed.

11 Headset Cup 12 Front Cavity 12A Shell 13 Rear Cavity 13A Second Shell, Rear Shell, Rear Cavity Shell 14 Resistance Port 15 Resistance Port Shield 16 Mass Port Tube 16A Opening 17 Driver, Headphone Driver 18 Microphone 24 Input Terminal 25 Acoustic input terminal 30 Signal combiner 31 Compressor 31A Compensator 32 Power amplifier 35 Microphone preamplifier 36 Circular 100 First dotted line 102 Solid line 104 Broken line 110 Dotted line 112 Solid line 114 Broken line 202 Ear cup 204 PEQ port 206 Ear cup 208 PEQ port 302 Curve 304 curve 306 curve 308 curve 310 broken line 312 curve 314 curve 316 curve 318 curve 320 curve 322 dotted ellipse 324 dotted ellipse

Claims (24)

At least one ear cup having a front cavity and a rear cavity separated by a driver,
The earcup includes a pressure equalization port that couples the front cavity to a space outside the earcup;
The pressure equalization port has an effective cross-sectional area greater than 1.75 mm ^{2 and} comprises a longitudinal tube , mainly providing reactive acoustic impedance;
Thus, a headset comprising an ear cup, wherein the pressure response of the front cavity including the pressure equalization port is substantially linear over a wide range of pressure levels within the front cavity. The range of pressure levels in the front cavity comprises a sound pressure level of between 150 dB SPL from 120 dB SPL, the headset according to claim 1. The pressure equalization port, comprises a long tube than 15mm length, the headset according to claim 1. The pressure equalization ports 10: 1 to 25: comprising a tube having a length to internal diameter aspect ratio of between 1, headset according to claim 1.   The headset of claim 1, wherein the pressure equalization port tube is made of metal. The headset of claim 5 , wherein the metal comprises stainless steel. The headset of claim 5 , wherein the pressure equalization port tube comprises a metal tube secured to the inside of the front cavity wall. 6. The headset of claim 5 , wherein the ear cup is made of plastic and the pressure equalization port tube is heat staked to the plastic.   The headset of claim 1, further comprising an active noise reduction circuit coupled to the driver. At least one ear cup having a front cavity and a rear cavity having front cavity compliance and rear cavity compliance, respectively;
A high compliance driver between the front and rear cavities having a driver compliance greater than the rear cavity compliance,
The earcup comprises a mass port and a resistance port connected in parallel to the rear cavity and a pressure equalization port connected to the front cavity;
The pressure equalization port has an effective cross-sectional area greater than 1.75 mm ² , comprises a longitudinal tube and mainly provides reactive acoustic impedance;
Accordingly, a high compliance driver, wherein the pressure response of the front cavity including the port to a signal input via the high compliance driver is substantially linear over a wide range of pressure levels in the front cavity;
An active noise reduction system coupled to the high compliance driver. The pressure equalization ports 10: 1 to 25: comprising a tube having a length to internal diameter aspect ratio of between 1 headset of claim 10. The range of pressure levels in the front cavity comprises a sound pressure level of between 150 dB SPL from 120 dB SPL, the headset of claim 10. The pressure equalization port, comprises a long tube than 15mm length, the headset of claim 10. The headset of claim 10 , wherein the pressure equalization port tube is made of metal. The headset of claim 14 , wherein the metal comprises stainless steel. The headset of claim 14 , wherein the pressure equalization port tube comprises a metal tube secured to the inside of the front cavity wall. 15. The headset of claim 14 , wherein the ear cup is made of plastic and the pressure equalization port tube is heat staked to the plastic. A first ear cup shell of headphones;
A second ear cup shell of the headphones;
An electroacoustic driver disposed between the first earcup shell and the second earcup shell, wherein the first earcup shell and the first surface of the electroacoustic driver are front portions. An electroacoustic driver defining a cavity, wherein the second earcup shell and the second surface of the electroacoustic driver define a rear cavity;
A metal tube having a lumen of at least 15 mm in length and having an effective cross-sectional area of at least 1.75 mm ² fixed in the first earcup shell and in front of the device in a space around the device A metal tube that joins the cavities;
An apparatus comprising: The first earcup shell includes plastic, and the metal tube includes a rough outer surface at one end, and the rough outer surface is secured within the plastic of the first earcup shell. Item 19. The apparatus according to Item 18 . The apparatus of claim 18 , wherein the lumen of the metal tube is generally uniform in cross section. The apparatus of claim 18 , wherein the lumen of the metal tube is generally smooth. The apparatus of claim 18 , wherein the metal tube is made of stainless steel. Pressure equalization port, 10: 1 to 25: comprising a tube having a length to internal diameter aspect ratio of between 1, apparatus according to claim 18. The apparatus of claim 18 , further comprising an active noise reduction circuit coupled to the electroacoustic driver.