JP2003532881A - Gas flow sensor, speaker system, and microphone utilizing measurement of absolute pressure over time - Google Patents

Abstract

Summary The present invention addresses the basic weaknesses of current general microphones and their application in feedback for audio speaker systems. This limitation is due to the fundamental problems of typical membrane microphones in the frequency range 1-100 Hz. The self-noise of membrane microphones increases by about 1 / f in this range, and membrane microphones are sensitive to parasitic inertial vibration, which is usually very important in this frequency range. Removing these limitations allows such sensors (APV sensors) to be used for effective feedback in audio speakers, and dramatically improves performance in the low frequency range of 10-100 Hz. Is done. Without feedback, typical audio speakers suffer from severe attenuation and / or distortion in this range.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to sensors for measuring the temporal variation of the absolute pressure of gas at a point in space, as well as voice reproduction and recording systems based on these sensors. Uses are Motional Feedback (MFB) to improve audio speakers
Including the use of these sensors in systems, and in hybrid microphones. The present invention is particularly useful for audio speaker systems in order to improve the performance of microphones in this frequency range and to enable effective motional feedback in this range, not only at the low frequency end of the audio spectrum, It is also related to part of the very low frequency range.

[0002]

BACKGROUND OF THE INVENTION

The field of acoustic microphones is a mature field that has existed for decades, with hundreds of k
An extremely wide variety of models are commercially available, covering the frequency range from Hz (ultrasonic wave) to 1 Hz or a fraction of a few Hz (ultra low frequency). Particularly for audio applications, the range from 20 Hz to 20 kHz is defined as the range containing signal components related to human hearing.

Membrane microphones typically have limited sensitivity at low frequencies and increased noise (generally having a 1 / f dependence). In addition to this, they are basically prone to parasitic inertial vibrations in the same frequency range as the low frequency sound (pressure) signal concerned.

Low-frequency microphones based on flow rate are based on Robert F.
ehr) "Infrasonic Thermistor Micr
"phone" Audio Technology Society Journal April 1970 Issue 18 Volume 2 Issue 128-
Known from page 132. The microphone device consists of a thermistor arrangement which is arranged in the tube of a Helmholtz resonator which connects the gas volume chamber to the surroundings and which becomes a thermoneemometer type flow sensor. The flow sensor measures the flow rate into and out of the chamber through the tube as a result of the temporal variation in ambient pressure at the tube inlet. This device operates at frequencies as low as 0.1 Hz and is not as sensitive to vibration as a membrane microphone. The described device, on the other hand, has certain limitations that prevent its use in practical low frequency audio applications. First, the described device uses discrete elements (thermistors) as temperature sensing elements of the thermone anemometer, which prevents the achievement of arbitrarily low thermal inertia, resulting in transient frequencies on the order of 1.5 Hz. Occurs, above which the signal is progressively attenuated, which in turn limits the available frequency range of the microphone. Second, the placement of these discrete elements in the flow path (described in the paper as 330 μm in diameter) makes it difficult to use arbitrarily narrow flow paths, thus limiting the available range of flow impedance.

Therefore, if the goal is to detect sounds in the low frequency range of 1 Hz or less, the gas volume chamber must have a considerable volume, for example several hundred milliliters. For applications such as audio microphones, or sensors for motional feedback (MFB-see below), such high capacity is not practical. Thirdly, the sound pressure sensitivity (resolution) of the device described in the fail paper is 1 to
While estimated at 10 Pa, audio applications require sensitivity in the mPa range or higher.

[0006] MFB technology lowers the frequency response of the audio speaker in the low frequency range by about 2
It is well known as an effective way to improve the low frequency fidelity of audio speakers by extending to 0 Hz and reducing low frequency signal distortion. Generally, the MFB method is the sound pressure (or its correlate) generated by the speaker membrane.
And a negative feedback of the detected signal to the power amplifier. The comparison of the external electrical input signal with the measured sound pressure or speaker membrane movement or other correlates allows for automatic adjustment of the delivered power and distortion caused by certain complex non-linear electromechanical properties of the speaker system. Can be compensated.

Mass market digital sound reproduction devices and compact discs (CDs) in the early 1980s
Before the advent of), audiophile-grade sound reproduction was a costly challenge and unfamiliar to most consumers. Today, any inexpensive CD player reproduces audiophile-quality signals of source recordings. This signal is liable to be distorted by the speaker system for low frequency components, for example below 100 Hz and near, especially when the amplitude of the low frequency components is large. Signal clipping may be clearly audible and the listener may generally reduce the volume to reduce the effects of distortion. Audiophiles are still striving to achieve high quality sound reproduction by using high performance speaker systems where reproduction in the lower frequency range is more faithful. Effective MFB
Would enable conventional mass market consumer quality level sound reproduction devices, ie, stereo amplifiers and speakers, to provide audiophile-grade (high quality) reproduction. This means that relatively cheap home stereo devices can approach those that are substantially comparable to more expensive audio systems, as long as the MFB can be successfully implemented.

[0008] Today, a major limitation preventing successful and widespread implementation of MFB is the lack of a suitable (as assessed by a combination of price, size, and performance characteristics) low frequency microphone. The second limitation is that the speaker requires an independent power source to implement MFB. A further limitation is that speakers using MFB require special adjustment.

Motional feedback is generally done in two ways: (1) using accelerometers to measure the acceleration of the speaker membrane (eg US Pat. No. 4,57).
No. 3,189), and (2) a method of measuring sound pressure using a microphone (eg, US Pat. No. 4,592,088).

The first way to achieve MFB is based on the use of an accelerating clock mounted on the membrane of the speaker and detecting its acceleration as a substitute for the actual sound pressure. In order to realize an MFB based on an acceleration clock, complicated technical problems must be solved.
Acceleration watches require very high technical performance for two reasons. The acceleration of the speaker membrane is equal to a = (2πf) ² x. Here, f is frequency and x is amplitude of membrane vibration. At the high end of the frequency range, eg 120 Hz and a maximum motional amplitude of 2 mm of the loudspeaker membrane, an upper acceleration limit a _max ≈100 g can be estimated. Both values are common for audio speakers. Due to the physiological nature of humans and the range of human hearing, MFB also provides effective feedback at frequencies above 20-25 Hz, at low frequencies down to a few Hz and loudness 4 orders of magnitude below the maximum. Must be valid). In this way, the minimum detectable acceleration can be estimated at a level of millig or less. Therefore, there is a need for a high performance accelerometer with a linear dynamic range of at least 5 orders of magnitude and capable of measuring high accelerations up to 100g.

In addition, the acceleration clock attached to the membrane of the audio speaker sometimes has a low frequency (
Respond to unwanted parasitic signals due to, for example, several Hz) vibrations and high frequency (several hundred Hz) instabilities. (U.S. Pat. No. 4,727,584) These effects are caused by variations in air pressure inside the enclosure of the speaker and acoustic resonance of sound waves that interact with the accelerating clock. These factors, which are difficult to control during manufacturing, result in (1) the use of speaker membranes having a "trumpet" shaped appearance, (
2) Inverting the dust cup; (3) Placing a weight on the loudspeaker coil at a position selected circumferentially with respect to the accelerating clock to minimize the effects of instability; It creates a significant design constraint for the driver.

As a result, the use of MFB based acceleration watches requires not only excellent high performance acceleration watches, but also custom designed speaker drivers. Attempts to attach motion-sensing elements to ordinary off-the-shelf speaker drivers tend to give poor results.

The second method of obtaining MFB is based on the direct measurement of sound pressure currently achieved by a microphone placed in close proximity to the membrane of the speaker. Due to the polar and out-of-phase dynamics of the feedback arrangement, the microphone needs to operate at frequencies from a few Hz to a few hundreds of Hz if improvements in the bass in the 20-150 Hz range are required. Two
Effective motional feedback capable of suppressing frequency distortion in the range 0-25 Hz requires reliable operation of microphones with high signal-to-noise ratio (SNR) down to 1-3 Hz. Existing microphones have an inherent increase in noise at low frequencies and a substantial decrease in sensitivity at low frequencies. That is why even the best available microphones have a low cutoff frequency at about 20 Hz.

In general, microphones can measure acoustic pressure inside and outside the speaker enclosure. Inside the enclosure, the measurable pressure is 18
0-200 dB SPL (sound pressure level) can be reached, which is much higher than the typical upper limit of the microphone operating range (120-130 dB SPL).

In addition, there is a serious problem of parasitic vibration-inducing signals (besides the desired signal directly caused by sound pressure). When the microphone is located outside the speaker enclosure, these parasitic signals are generated due to the need to mount the microphone on the angle arm near the speaker membrane. Vibration of the arm can contribute significantly to the output of the microphone, thus degrading the fidelity of the speaker system.

Another general trend in the field of subwoofer design is also relevant to the present invention.
The principle of using a speaker driver with a resonance frequency lower than the cut-off frequency of the sound reproduction system (to prevent sound distortion) is used both in systems with and without MFB. A typical rule in the field is that the speaker driver mounted in the speaker enclosure must have a resonant frequency below 20 Hz. In practice, this requirement results in an increase in speaker driver size, complex (often custom) designs, and sometimes the need to use high starting powers of 1 kW or more.

In recent years, gas mass flow sensors based on thermo-anemometer type sensing elements (such as Honeywell's AWM series) have been developed and widely used in the industry. A sensor enclosed in a flow path package measures the direct gas flow rate through the flow path, which depends on the pressure drop between the two terminals of the sensor. Therefore, these sensors
It can be used to measure the differential pressure between two non-coincident spatial locations, rather than the time-varying absolute pressure at a particular location.

Another thermo-anemometer-type sensor that is open to the surroundings and has a sensing element capable of measuring acoustic streaming and sound intensity is described in HE. de Bree. Le
ussink, T.S. Korthorst, H .; Jansen, TS J.
Lammerink, M .; "The μ-fl by Elwenspoek
own: A novel device for measuring ac
“Sousors and Actuators A”
(1996), v. 54, n. 1, pp. 552-557 and US Pat. No. 5,959,217. The sensor does not directly measure the temporal variation of absolute pressure, but rather the local gas particle velocity, which is proportional to the spatial gradient of acoustic pressure.

It will be appreciated that there is a need for a low frequency microphone capable of recording audible frequencies starting at about 1 Hz and up to tens or hundreds of hertz.

[0020]

[Outline of the Invention]

One of the objects of the present invention is an integrated thermometer anemometer for measuring the temporal variation of absolute pressure, abbreviated as absolute pressure variation (APV) to distinguish typical membrane microphones from flow-based microphones. Utilizing mass flow sensing elements to improve the resolution and accuracy of such measurements, especially at low frequencies, and improve the immunity of the measurements to other inertial mechanical vibrations. The invention's APV sensor (s) is further proposed for use in the MFB of speaker systems and in the fabrication of hybrid microphones with excellent low frequency performance.

Therefore, the objects of the present invention are as follows. (1) Utilizes an integrated thermometer anemometer type mass flow sensing element to measure absolute pressure over time. Absolute pressure variation (APV) sensors are invented to provide high sensitivity down to a few hertz or below and up to at least 100 Hz. It is also invented to have a small size and to be insensitive to inertial (non-sound pressure) vibrations. (2) Utilizing APV sensor based motional feedback (MFB) to improve the frequency response and reduce sound distortion of sound reproduction and recording systems at low frequencies. (3) Utilizing MFB based on a specially designed and vibration insensitive APV sensor to improve frequency response at low frequencies, reduce sound distortion and provide stable operation under external vibration / acceleration To do. (4) Utilize the above sensor-based MFB in a sound reproduction system where a relatively small speaker driver and speaker enclosure are desired. (5) Utilizing the MFB based on the above sensor in a sound reproduction system using a speaker driver having a resonance frequency higher than the minimum reproduction frequency. (6) Using the APV sensor, create a hybrid microphone with excellent low frequency performance. (7) Used by an APV sensor (or accelerating clock) that does not require feedback to the input of the amplifier and allows the speaker and feedback system to remain powered only from the (single cable) audio signal from the amplifier. One aspect of possible motional feedback is provided. (8) Utilize the APV sensor in such a system of motional feedback without connecting back to the input of the amplifier.

According to the present invention, there is provided a conversion device for temporal fluctuation of pressure, which comprises a chamber and a restriction flow path for communicating gas from the surroundings to the chamber via a hot gas flow rate sensor, the sensor being on a substrate. A converter device having a thermo-anemometer type sensing element integrated into a substrate and having a low thermal inertia. The low thermal inertia is about 50H
z, preferably having an upper cut-off frequency higher than about 150 Hz. The flow path can be coupled with a sensor such that the gas flow rate at the sensing element is the same or higher than in the flow path to improve sensitivity. The sensor is preferably provided inside the chamber and the flow path can also be provided inside the chamber.
Preferably, the thermo-anemometer type sensing element is provided inside the channel and the rest of the sensor is provided outside the channel.

The device preferably has at least two sensors, the sensor and the flow path being geometrically arranged to provide a signal that can be coupled to cancel out inertial vibration related components. .

The invention also relates to a membrane microphone sensitive to acoustic signals in the normal range, a thermo-anemometer microphone equipped with the converter according to the invention for detecting low-frequency audio signals, and a membrane microphone. There is also provided a hybrid microphone having a combiner circuit for combining an output and a thermo-anemometer type microphone to provide a composite output signal having excellent response from a low audio frequency to at least a normal audio frequency.

The present invention also provides a speaker, circuitry for varying the input audio signal to compensate for low frequency attenuation and distortion introduced by the speaker in response to the feedback signal, and for producing the feedback signal. The present invention also provides a motional feedback (MFB) speaker apparatus including the microphone according to the present invention, wherein the microphone includes the conversion apparatus according to the present invention or the microphone including the hybrid microphone. The flow path is preferably perpendicular to the sound wave propagation axis of the speaker.

The invention further includes a speaker, circuitry for varying the input audio signal to compensate for low frequency attenuation and distortion introduced by the speaker in response to the feedback signal, and for generating the feedback signal. A MFB speaker device with a microphone, the circuit applying variable attenuation to an audio signal between an amplification source and a speaker, the variable attenuation being modulated to provide compensation. A speaker device having a level is also provided.

The circuit applies variable attenuation to the audio signal between the amplification source and the speaker, the variable attenuation preferably having a base level that is modulated to provide compensation. The circuit can be powered by an audio signal. The circuit is preferably housed in a housing adapted to be placed next to the speaker, the housing preferably comprising a mount for holding the microphone in front of the speaker. The enclosure can also provide a base or stand for the speaker.

The variable attenuation is preferably provided by a pulse width modulation (PWM) circuit operating at high frequencies that does not cause audible interference to the speaker. The circuit also separates the low frequency components of the audio signal from the medium / high frequency components, changes only the low frequency components for compensation, demodulates the compensated low frequency components, and outputs the compensated and demodulated low frequencies. It is also possible to mix frequency components with medium / high frequency components.

The invention will be better understood by the following detailed description of preferred and other embodiments in connection with the accompanying drawings.

[0030]

Detailed Description of the Preferred or Other Embodiments

In order to utilize an integrated mass flow sensor based on a thermo-anemometer type sensing element for measuring absolute pressure fluctuations, a special pneumatic housing of the sensor is used. In general, the sensor according to the preferred embodiment comprises at least one thermo-anemometer-type sensing element 1 arranged in a container containing the flow channel 2. Flow path is connected to the sealed chamber 3 having rigid walls and a capacitor V _o as shown in FIG. The other end of the flow path is open to the surroundings. The operating principle of the sensor will be described below.

The absolute pressure of the ambient gas is represented by P _o + P _a (t). Where P _a (t) (| P _a (t)
The | << P _o ) term represents the pressure fluctuation for a constant P _o . These fluctuations P _a (t)
Is the signal of interest, namely the absolute pressure variation (APV).

The pressure inside the closed chamber 3 fluctuates as P _o + P _c (t). Here, P _c (t) is generally different from P _a (t). Under these conditions, the differential pressure applied to the channel 2 produces a gas flow rate F (t) in the channel 2, which can be determined from the following equation.

[Equation 1]

At low frequencies, the contribution of the flow path inductance can be neglected:
The flow rate caused by the absolute pressure fluctuation can be obtained from the following equation.

[Equation 2]

For sinusoidal pressure fluctuations, P _a (t) = ΔP sin (2πft), where ΔP and f are the pressure amplitude and frequency, respectively, and the gas flow rate through the flow path is .

[Equation 3]

The flow sensor thus has a low cutoff frequency f _L = 1 / (2πτ) = P _o / (2πV _o R).

At higher frequencies, the sensitivity of the sensor is limited by the inductance of channel 2 and the high cutoff frequency is defined as f _H = R / (2πL) = (192η) / (ρD ² ).
In the case of a sensor having a flow passage 2 with an inner diameter of D = 2 mm, f _H = 660 Hz (D =
F _H = 295 Hz at 3 mm).

Moreover, the sensitivity of the sensor is further limited due to the inertia of the thermo-anemometer type sensing element 1 at higher frequencies. Generally, the frequency response of recent thermometers has reached a maximum of 150 to 200 Hz, but it can be improved to a maximum of several hundred Hz. This sound pressure sensitivity mainly depends on the careful design of the flow sensing element in the flow path. In particular, it is desirable to accumulate the entire flow in close proximity to the heated element. Although the mass flow rate in the channel is constant, for higher sensitivity it may be desirable to increase the velocity of the flow near the sensing element, for example by using constriction.

Referring to FIG. 2, the sound reproduction system includes a speaker driver 5 attached to a speaker enclosure 6. The input audio signal is applied to a power amplifier 7 which drives a speaker driver 5. The absolute pressure fluctuation (APV) sensor 4 with the flow rate sensing element 1 is arranged outside the speaker enclosure 6 and near the speaker driver 5, and detects the generated sound pressure. The output signal is amplified by electronic processing circuitry and filtered (if necessary). The processed signal is sent to the negative phase input of the power amplifier 7. This negative feedback ensures that the generated sound pressure faithfully tracks the audio signal.

In FIG. 2, the MFB mechanism shows that the output from the APV sensor 4 is fed back to the input of the amplifier 7. In practice, this imposes certain constraints / conditions on the amplifier / speaker system. If the amplifier 7 is not integrated inside the speaker enclosure 6, an additional cable from the speaker to the amplifier is required. Also, the amplifier 7 must provide access to its input, but not necessarily in this case.

In response to these inconveniences, the present invention can be used in an independent speaker and can operate from a single output line from the amplifier only, without the need to feed back the signal to the input of the amplifier. Provide a feedback mechanism. There are several possible embodiments of this mechanism.

One embodiment is shown in FIGS. 15a and 15b. Here, the audio signal is separated by the crossover filter 24 into low frequency components and medium / high frequency components. During/
The high component is appropriately attenuated by filter 24 or other circuitry and sent directly to the medium / high speaker driver (not shown), and perhaps speaker driver 5 in the embodiment of Figure 15a. The low frequency components are sent to the speaker driver 5 via an electronic module 20 which provides pulse width modulation of the audio signal. The signal from the APV sensor 4 corresponding to the measured sound pressure is amplified by the module 23 and compared with the input low frequency electrical signal. Depending on the result of this comparison, the electronic module 20 modifies the parameters of the pulse width modulation to compensate for the distortion. It is important that the normal level of pulse width modulation is not maximal and that either the supplied power can be increased or decreased if necessary to compensate for the distortion.

Generally, such circuit elements require a power level on the order of tens of mW,
The power supplied from the amplifier 7 to the speaker driver can reach hundreds of watts, which adds an AC-DC converter 21 to power the electronic circuit without significantly degrading the input signal. Makes it possible to power the entire electronics from the audio signal line. If the input power is low or zero,
Distortion is unlikely to occur and the compensation circuit does not need to work.

The present invention is also used as a retrofit unit in a normal loudspeaker that accepts the input from the amplifier 7, senses the sound pressure in front of the loudspeaker, realizes the compensation and applies an accurate signal to the loudspeaker input. It also includes the possibility of forming a stand-alone enclosure 22 as shown in Figure 15b. In order to provide a stand-alone unit that can be used with a standard loudspeaker having its own crossover filter 25, the unit 22 is provided with PWM prior to recombining the low and medium / high components to the loudspeaker. There is a demodulator unit 26 that can remove high frequency components from the low frequency component signal.

The embodiments of Figures 15a and 15b are merely some examples. In general, it is highly desirable, but not necessary, to use audio signals to power circuitry. Similarly, the use of PWM as a variable attenuator is desirable, but
Not necessarily required. This embodiment makes it possible to provide audiophile-grade results with an essentially stand-alone add-on device to conventional low-priced speakers. All loudspeakers should be equipped with a device 22 as the power from the amplifier 7 needs to be increased during normal listening for attenuation. Bypass or off switches, as well as the ability to adjust base level attenuation, are useful accessories. An indicator for indicating when the MFB is valid is desirable, as is an indicator for indicating when the MFB is unable to provide full compensation.

FIGS. 3 a and b show the most important functional part of the APV sensor according to the preferred embodiment, namely where the thermone anemometer is attached to the flow path. In this embodiment, the capillary 12 has an incision groove into which the silicon substrate 1 is fitted. The capillary 12 is mounted so that it covers the integrated heating and sensing element in a general and symmetrical manner. In this particular embodiment, a micromachined central heater 8 and a micromachined temperature sensitive thermal resistor 9 are appropriately shaped silicon substrate 1 to provide high sensitivity and low thermal inertia for the device. Suspended above the cavity 10. The size of the thermal resistor can be as low as 100 μm, so that the inner diameter of the channel 2 can have almost the same size (100-200 μm), which allows the total gas flow rate to accumulate in a small cross section. Which gives a high gas velocity and a high sensitivity of the sensor. The use of small inner diameter capillaries 12 makes it possible to significantly increase the flow impedance and to reduce the required volume of the chamber in which it is mounted, which is of great importance for the overall miniaturization of the sensor. FIG. 3b schematically shows a cross section of the sensor in which the tube 12 is attached and sealed to the silicon substrate 1 using epoxy 13 or other suitable adhesive. The tube 12 need only cover the integrated thermone anemometer sensing elements 8,9. For example, the wire bonding pad 11 for electrical connection need not be in the flow path 12.

FIG. 1 schematically shows an absolute pressure fluctuation sensor consisting of a flow path 2 and a thermometer anemometer type sensing element 1 connected to a closed chamber. Proper design of the pneumatic part of the sensor (flow path 2 and chamber 3) makes it possible to establish the level of frequency f _L required for a particular application. For example, the flow impedance R of the flow path 2 is 1000.
A sensor with Pa · s / ml has f _L = 15 Hz when it is connected to chamber 3 with a volume V _o = 1 ml. In order to reduce the cut-off frequency to, for example, 0.3 Hz, a chamber 3 with a larger volume of 50 ml must be used.

Adjustment of the cutoff frequency f _L can also be achieved by a suitable design of the flow path 2. For example, connecting an additional capillary with a length of 1 cm and an inner diameter of 0.2 mm in series with the sensor channel 2 increases the total flow impedance by approximately 14000 Pa · s / ml and lowers the cutoff frequency of the sensor. In this case, only 0.3 ml is needed instead of 100 ml to achieve 3 Hz.

The immunity to vibration of the APV sensor according to the preferred embodiment is explained by the following physical phenomenon. The sensor schematically shown in FIG. 1 has sensitivity to vibration acting in a direction parallel to the Y axis. The vibration sensitivity is caused by the vibration-induced movement of the heating capacity of the gas near the heater of the thermometer type sensing element 1. An important feature of the thermometer is that it has vibration sensitivity in the same direction as flow sensitivity. The sensor has negligible sensitivity to vibrations acting in a direction parallel to the XZ plane, since in this case there is no temperature difference across the sensing element. Thus, the inventive sensor can be used to measure absolute pressure fluctuations under vibration acting in one preferred direction or in one preferred plane. Immunity to vibrations in this case is achieved by orienting the sensor so that the vibrations are perpendicular to the flow path 2 in the vicinity of the thermo-anemometer type sensing element 1.

In order to provide immunity to vibrations acting in all directions, a sensor, which is schematically shown in FIG. 4, is provided. It comprises two thermo-anemometer-type sensing elements 1 arranged along one flow path 2 connected to a closed chamber 3. Immunity to vibrations acting in a direction parallel to the XZ plane is explained for the same reason as for the one element sensor. The immunity to vibrations acting in the Y direction is explained by the following reasons. The gas flowing in the flow path 2 passes through the thermometer 1 in the opposite direction. Therefore, the heating capacity of the gas near the heaters of both thermone anemometers will also move in the opposite direction, producing a negative phase output signal. When acceleration is applied in a direction parallel to the gas flow (and axis Y), the heating capacity of the gas moves in the same direction on both thermonemmometers, producing the same output signal increment on both sensors. Then two flow sensing elements 1
The output signal of is processed by electronics and one signal is subtracted from the other signal. Sensor output 1 = (flow rate) + (acceleration) Sensor output 2 =-(flow rate) + (acceleration) Sensor output 1-sensor output 2 = 2 ^* (flow rate)

If the two thermo-anemometers 1 are identical, the sensitivity of the entire APV sensor to acceleration can theoretically be reduced to zero. In practice, immunity to acceleration is limited by the mismatch of the two thermometer anemometers and their sensitivity calibrations. 2001 for more details on flow sensor configuration and design.
Please refer to Applicant's co-pending PCT publication WO 01/18496, published March 15, 2014.

FIG. 5 shows an APV sensor including a thermone anemometer type sensing element 1 arranged inside the chamber 3. The present design provides better mechanical protection of the sensing element due to its additional enclosure 14. The disclosed configuration is preferred when designing the chamber 3 with a volume V _o of a few ml or more. The walls of the chamber can also be used to enclose the relevant sensor signal processing circuitry.

It is necessary to note the following. (A) Other than those shown in FIGS. 1 and 3-5, the APV sensor can be proposed as a combination of chambers of different flow rate assembly and volume. For example, in FIG.
A two-element sensing element (shown in FIG. 3) can be placed inside the chamber 3 as shown in FIG. The particular design should be selected to best fit the requirements of the application. (B) The particular configuration of the thermometer anemometer-type sensing element 1 is not important to the disclosed invention, except that it must have the following features. It must be bidirectionally sensitive to the gas flow passing through the flow path 2 and can include an electric heater arranged between the two temperature sensing elements and the thermone anemometer element. It can also include only two self-heating temperature sensing elements. Sensors and Actuators A (1996)
v. 54, n. 1, pp. HE at 552-557. de Bree
See the above papers, et al. The specific design of its functional element, which can be a thermal resistor, thermopile, or other means of converting temperature into an electrical signal, is also
It is not important to the disclosed invention.

Experimental prototypes were manufactured and tested to demonstrate the APV sensor (see Figures 3a and 3b). The prototype is based on a micromachined thermone anemometer 1 according to FIGS. 3a and 3b mounted in a channel 2 having a flow impedance of about 500 Pa · s / ml. The sensing element of the thermometer 1 includes three polysilicon resistors that are thermally isolated from the silicon substrate and package. The central resistor 8 acts as a heater, while the other two symmetrically arranged 9 on both sides detect the temperature difference caused by the gas flowing in the flow path 2. The channel 2 is connected to a replaceable chamber with rigid walls.

The time response τ of a sensor connected to a chamber with a volume of 10 ml was measured by subjecting the sensor input to stepwise overpressure. A few milliseconds after the signal reaches its maximum, a few milliseconds after the beginning of the phase, it drops exponentially due to the pressure balancing inside the chamber and at the input of the sensor. The time constant of this equilibration was measured to be τ = 0.05s. The cut-off frequency f _L = 3 Hz is calculated therefrom.

The same experiment was repeated with a chamber volume of 60 ml. The measured time constant is τ = 0
． 3 s, which corresponds to f _L = 0.5 Hz. The data obtained, the cutoff frequency is coincident with the theoretical estimates predict that decreases with increasing volume V _o.

The frequency response of the APV sensor is shown in FIG. The pressure fluctuation (sound pressure) was generated by an audio speaker driver and controlled by an instrumentation microphone (AUDIX TR-40) with a flat (± 1 dB) frequency response from 20 Hz to 20 kHz. The measured frequency response has been demonstrated to be flat (within 3 dB) up to about 220 Hz. This same high cutoff frequency of f _H = 220 Hz was obtained for both 10 ml and 60 ml chamber volumes.

[Speaker System with Motional Feedback Utilizing APV Sensor] FIG. 7 schematically shows an APV sensor 4 in which a thermo-anemometer type sensing element 1 (such as a flow rate sensing element) is attached to a speaker enclosure with a support arm 15. Shown in. The sensor includes a flow sensing element assembled in a package with a flow path.
The flow path allows the flow of air between the surroundings and the enclosed chamber (sensor enclosure internal volume V _o ). The sound pressure generated by the membrane of the speaker causes a pressure drop across the flow path (from its input to its output) and thus a gas flow. Near the flow sensing element, the gas flows parallel to the X axis.

The sensor shown in FIG. 7 has negligibly small sensitivity to vibrations acting in the direction parallel to the XZ plane as described above. With better immunity to vibration,
The sensor shown in FIG. 8 can also be used for MFB.

FIG. 9 shows another preferred embodiment of the speaker system in which the APV sensor 4 is located in the speaker enclosure 6. It is well known that at low frequencies the acoustic pressure inside a closed enclosure is proportional to the displacement of the speaker cone, while the acoustic pressure outside the enclosure is proportional to the acceleration of the cone. Achieving MFB is A
Note that it is possible to place the PV sensor 4 either inside or outside the enclosure 6. If the APV sensor 4 is placed inside the enclosure 6, both signal processing (frequency filtering) must be modified and the sensor itself must be adjusted to accommodate much higher acoustic pressures up to 180-200 dB SPL. I won't. The structure of the invented APV sensor 4 allows easy adjustment to this range. An additional capillary with a small inner diameter connected in series with the sensor limits the gas flow rate in the thermometer 1 and switches the operating range of the device to higher pressures.

The following prototype speaker system and test procedure were used to demonstrate the effectiveness of the disclosed concept of MFB with an APV sensor.

The Optimus ^™ bi-directional bookshelf size speaker STS65 was selected and adapted for experimentation. The speaker, which has a capacity of 16 liters, includes a 6.5 inch speaker driver and tweeter. A crossover filter of its own and a tweeter isolation, an 8th order lowpass filter with a cutoff frequency of 120 Hz was installed to limit the reproducible frequency range to that typical of subwoofers.

As shown in FIG. 7, the APV sensor 4 was attached to the speaker enclosure 6 by the three support arms 15 at a distance of 1 cm from the speaker membrane. The thermometer anemometer type sensing element 1 was mounted in a hollow spherical enclosure with a diameter of 3.5 cm (internal volume of about 8 ml). The flow path 2 of the thermone anemometer, which has a pneumatic impedance of about 500 Pa · s / ml, allows the flow of air between the surroundings and the enclosed volume of air inside the spherical enclosure. The gas flow rate caused by the sound pressure at the input of the flow path is detected by the thermone anemometer 1 and the amplified signal is sent to the negative phase input of the 100 watt power amplifier 7. The frequency response of the sensor is 10-220Hz
Is flat (within 3 dB).

A test microphone AUDIX TR-40 having a flat (± 1 dB) frequency response from 20 Hz to 20 kHz was placed 1 cm from the speaker membrane,
The generated sound pressure was measured (neighborhood measurement). The amplified signal was digitized on a 12-bit acquisition board, then visualized by a computer, processed and stored.

FIG. 10 shows the frequency response of the subwoofer with and without feedback. The use of the MFB of the invention based on absolute pressure fluctuation sensors allows the extension of the operating frequency range and the reduction of the cut-off frequency (3 dB level) from 65 Hz to 25 Hz.

The MFB also provides effective suppression of subwoofer harmonic distortion. FIG. 11 shows the frequency spectrum of the sound generated by the subwoofer at the same sound pressure level when there is no MFB (a, b) and when there is MFB (c, d). The harmonic distortion of the prototype speaker system was tested in the frequency range from 20 Hz to 110 Hz. Figures 11a and b show the data without MFB on two different vertical scales, and Figures 11c and d show the data with MFB on the same two vertical scales. The apparent effective suppression of higher harmonics provided by the MFB according to the invention was experimentally confirmed over the operating frequency range. About 50Hz (20H
No undesired additional distortion due to the natural resonance of the loudspeaker system, which is present above the low operating frequency of z) was found.

The above embodiments are not the only possible embodiments of the use of APV sensors in acoustic systems with MFB. The ported (ventilated) speaker system
Basically, there are two sound sources (speaker driver and port), so it operates more complicatedly. In principle, a feedback system consisting of one or several APV sensors can be constructed with the sensors located in various positions inside and / or outside the speaker enclosure.

[Hybrid Microphone Utilizing APV Sensor] A typical membrane microphone has specific performance limits. The response at low frequencies is often limited by an intrinsic increase in intrinsic (self) noise, and such microphones generally respond to parasitic mechanical vibrations as well as related signals (sound pressure vibrations). Inventive APV sensor has excellent signal-to-noise ratio (SNR) at low frequencies
And has high immunity to vibration. However, its high cutoff frequency is limited to the range of a few hundred Hz, which is not sufficient to cover the full range of operation of typical microphones. In order to utilize the features of both the APV sensor of the invention and a general inexpensive microphone, they are used in combination to create a hybrid microphone, and the inferior low frequency performance of an inexpensive membrane microphone is superior to that of the APV sensor. Can be replaced with low frequency performance. This combination not only has reduced sensitivity to mechanical vibrations at low frequencies, but also enhanced SNR at low frequencies.
have.

FIG. 12 shows a schematic electrical diagram of how the two components are connected in a hybrid microphone to obtain a flat frequency response over the entire range (including crossover). The experimental prototype schematically shown in FIG. 12 comprises the above-mentioned APV sensor 4 and a commercially available Panasonic WM-54 microphone 16 together with a primary low-pass electric filter 17 and a primary high-pass electric filter 18. The two filtered signals from sensors 4 and 16 are summed using summing amplifier 19.

The performance of the prototype prototype hybrid microphone shown in FIG. 12 was measured using an instrumentation microphone A with a flat frequency response of +/− 1 dB from 20 Hz to 20 kHz.
Experiments were performed comparing with udix TR-40. These two microphones were placed on a common rigid mechanical support. The gains of the two instruments were adjusted so that their output electrical signals were of comparable amplitude for a given 30 Hz acoustic input of 94 dB. The acoustic inputs were then sealed so that the instrument was isolated from acoustic disturbances and exposed to mechanical movement in order to emphasize sensitivity to vibrations at low frequencies (such as roughly 5 Hz). FIG. 13 shows the response of the two instruments, demonstrating that the hybrid was much more immunized to these (common) mechanical disturbances. The acoustic input of the instrument was then reopened and a similar mechanical movement was applied. With the acoustic input open, the instrument is able to measure these low frequency pressure fluctuations induced by motion.

FIG. 14 shows the response of the device. While the hybrid is highly sensitive to these pressure fluctuations (note that the scales in the two figures are different), the response of TR40 is suppressed at frequencies below 20Hz by the high order high pass filter included in the microphone. Because it is much lower. Of course, depending on the desired application, a portion of the low frequency range may be filtered, for example 10-20 Hz for music.

[0071]

【The invention's effect】

Capacitive (electret) membrane sound pressure transducers are often known to be high resistance signal sources. One of the features of modern microphones is that they are high resistance signal sources. From general physics and electronics, it is well known that when dealing with high resistance sources, there is the problem of avoiding electromagnetic interference (EMI), which can be solved by proper grounding, shielding, etc. Fortunately (for the present invention), thermone anemometer sensors have low resistances in the hundreds of ohms to a few kΩ. As a result, they are much less affected by EMI.

[Brief description of drawings]

[Figure 1]   1 is a schematic diagram of an APV sensor having one thermonemometer type sensing element.

FIG. 2 is a schematic diagram of a sound reproduction system including an absolute pressure variation sensor based on a flow sensing element in motional feedback.

FIG. 3a is a perspective view of a channel having an integrated thermometer anemometer type sensing device fitted in a recess cut into the channel tube.

3b is a cross-sectional side view of a flow channel having an integrated thermometer anemometer-type sensing device fitted in a recess cut into the flow channel tube shown in FIG. 3a.

FIG. 4 is a schematic diagram of an APV sensor having two thermo-anemometer-type sensing elements arranged along one flow path.

[Figure 5]   1 is a schematic diagram of an APV sensor located inside a chamber.

FIG. 6 shows the experimentally determined frequency response of an APV sensor in a configuration with replaceable chambers.

FIG. 7 is a schematic diagram of an APV sensor with a thermo-anemometer type sensing element attached to a speaker.

FIG. 8: Vibration-insensitive APV consisting of two thermo-anemometer type flow sensing elements
3 is a schematic diagram of a sensor.

FIG. 9 is a schematic diagram of a speaker system having an APV sensor located inside the speaker enclosure.

FIG. 10 shows an example of experimentally measured frequency response of a speaker system at low frequencies with and without MFB.

FIG. 11a shows experimentally measured frequency spectra of the sound produced by a speaker system excited by a 25 Hz tone with and without MFB, respectively.

11b shows experimental measurements of the frequency spectrum of the sound produced by a speaker system excited by a 25 Hz tone, with and without MFB, respectively.

FIG. 11c shows experimental measurements of the frequency spectrum of the sound produced by a speaker system excited by a 25 Hz tone, with and without MFB, respectively.

11d shows experimental measurements of the frequency spectrum of the sound produced by a speaker system excited by a 25 Hz tone with and without MFB, respectively.

FIG. 12 is a schematic diagram of a simple hybrid microphone with a combination of an APV sensor and a capacitive membrane microphone.

FIG. 13a is a graphical representation of the response of a hybrid microphone versus time to a common inertial disturbance of approximately 5 Hz with the acoustic input sealed.

FIG. 13b is a graph of the response of an instrumentation microphone versus time to a common inertial vibration disturbance of approximately 5 Hz with the acoustic input sealed.

14a is a graph of the response of a hybrid microphone versus time for a common movement similar to that of FIG. 13 with acoustic input open. FIG.

14b is a graph of instrumentation microphone response versus time for a common movement similar to that of FIG. 13 with the acoustic input open. FIG.

FIG. 15a is a schematic diagram of a circuit that provides the MFB with variable attenuation to the speaker signal by pulse width modulation using a PWM frequency above the audio frequency, with the power of the circuit derived from the audio speaker signal itself. .

FIG. 15b is a schematic diagram of the physical setup of the MFB system according to the embodiment of FIG. 15a, where the circuitry is provided on the base, with the speaker seated thereon, the base supporting the microphone mount.

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE, TR), OA (BF , BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, G M, KE, LS, MW, MZ, SD, SL, SZ, TZ , UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, B Z, CA, CH, CN, CO, CR, CU, CZ, DE , DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, I S, JP, KE, KG, KP, KR, KZ, LC, LK , LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, P T, RO, RU, SD, SE, SG, SI, SK, SL , TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW (72) Inventor Gludin, Oleg             Quebec, Canada H3H2N7, Mont             Triol, Du Fort Street               1411, apartment 2404 (72) Inventor Florov, Gennady             Quebec, Canada H3H2N7, Mont             Triol, Du Fort Street               1411, apartment 812 (72) Inventor Landsberger, Leslie, M.             Quebec, Canada H3Z 1Z5, Ue             Stormont, Elm Avenue 310 F-term (reference) 2F035 EA08 GA01                 5D020 AC01 CD02 CD04                 5D021 DD06

Claims (20)

[Claims] 1. A conversion device for temporal fluctuation of pressure, comprising: a chamber; and a restriction channel for communicating gas from the surroundings to the chamber via a hot gas flow rate sensor, wherein the sensor is a substrate. A converter having a thermonemometer-type sensing element integrated thereon and having low thermal inertia. 2. The device of claim 1, wherein the low thermal inertia allows the device to have an upper cutoff frequency greater than about 50 Hz. 3. The device of claim 1, wherein the low thermal inertia allows the device to have an upper cutoff frequency greater than about 100 Hz. 4. The device of claim 1, wherein the low thermal inertia allows the device to have an upper cutoff frequency greater than about 150 Hz. 5. The flow path is connected to the sensor so that the gas flow rate on the sensing element is the same as or greater than in the flow path, and the flow path is connected to the sensor. apparatus. 6. The apparatus according to claim 1, wherein the sensor is provided in the chamber. 7. The apparatus according to claim 6, wherein the flow path is also provided in the chamber. 8. An apparatus according to claim 1, wherein the thermo-anemometer type sensing element is inside the flow channel and the rest of the sensor is outside the flow channel. 9. The device comprises at least two of said sensors, said sensor and said flow path being geometrically arranged to provide a signal that can be coupled to cancel out inertial vibration related components. The device according to any one of claims 1 to 8, which is installed. 10. A membrane microphone that is sensitive to acoustic signals in the normal range, and a thermometer anemometer microphone that includes the conversion device according to claim 1 for detecting low frequency audio signals. And a combiner circuit for combining the output of the membrane microphone and the thermometer anemometer microphone to provide a composite output signal with excellent response from low audio frequencies to at least normal audio frequencies. . 11. A speaker, circuitry for modifying an input audio signal to compensate for low frequency attenuation and distortion introduced by the speaker in response to the feedback signal, and a microphone for generating the feedback signal. And a hybrid microphone according to claim 10, wherein the microphone is one of the conversion device according to any one of claims 1 to 9 and the hybrid microphone according to claim 10. A speaker device comprising a provided microphone. 12. The circuit of claim 11, wherein the circuit adds variable attenuation to the audio signal between an amplification source and the speaker, the variable attenuation having a base level that is modulated to provide compensation. Speaker device. 13. The speaker device according to claim 11, wherein the flow path is perpendicular to a sound propagation axis of the speaker. 14. A speaker, circuitry for varying an input audio signal to compensate for low frequency attenuation and distortion introduced by the speaker in response to the feedback signal, and a microphone for generating the feedback signal. A feedback feedback (MFB) loudspeaker device comprising: a circuit for adding variable attenuation to the audio signal between an amplification source and the speaker, the variable attenuation being modulated to provide compensation. A speaker device having a base level. 15. The speaker device according to claim 11, wherein the circuit is powered by the audio signal. 16. The circuit is housed in a housing adapted for placement next to the speaker, the housing comprising a mount for holding the microphone in front of the speaker. 16. The speaker device according to any one of 11 to 15. 17. The speaker device of claim 16, wherein the housing provides a base or stand for the speaker. 18. The speaker device according to claim 12, wherein the variable attenuation is provided by a pulse width modulation (PWM) circuit operating at a high frequency that does not cause audible interference in the speaker. . 19. The circuit separates low frequency components of the audio signal from medium / high frequency components, changes only the low frequency components for the compensation, demodulates the compensated low frequency components, and The speaker device according to claim 18, wherein the compensated and demodulated low frequency component is mixed with the medium / high frequency component. 20. The circuit separates low frequency components of the audio signal from medium / high frequency components, only the low frequency components are varied for the compensation, and the compensated low frequency components are converted to the medium / high frequency components. Mixing with frequency components, 12 to 1
7. The speaker device according to any one of 7.