CN1688179A - Feedback Active Noise Canceling Headphones - Google Patents

Abstract

The present invention relates to a feedback type active noise canceling headphone which is mainly composed of a microphone, a phase shift filter, an amplifier and a speaker, wherein the noise and music received by the microphone minus the music signal output by the audio amplifier is used to obtain pure noise, which is then superimposed on the music signal, and the high and low frequencies are filtered out by the phase shift filter, and then the audio amplifier is used to amplify and reverse the phase to drive the speaker, thereby canceling the external noise. The present invention adopts the feedback type active closed-loop noise cancellation principle to design filtering, phase shifting, amplification and compensation circuits, and has made modifications in the physical structure of the headphone, the arrangement of the feedback loop, the selection of components and headphone materials, so that the performance of the headphone is more stable and the noise cancellation effect is better. The average noise attenuation of the headphone within the range of 100-400Hz is 20db, and the maximum noise attenuation is 35db.

Description

Feedback Active Noise Canceling Headphones

technical field

The invention relates to electronics, communication, and instrument technology, in particular to a feedback type active noise canceling earphone.

Background technique

The noise canceling effect of commercially available noise canceling headphones is not ideal, and the average noise canceling is generally around 10db and the price is expensive. In the European and American markets, the price of a brand-name noise-cancelling headset is more than US$150. For example, the price of Bose brand noise-canceling headset is US$300, or RMB 3,600.

Contents of the invention

The purpose of the present invention is to provide a kind of feedback type active noise canceling earphone according to the defect existing in the prior art, adopt the feedback type active closed-loop noise canceling principle to design filtering, phase shifting, amplification and compensation circuit, in the physical structure of the earphone, the feedback loop The arrangement, the selection of components and earphone materials have been improved to make the performance of the earphone more stable and the noise cancellation effect better. The average noise attenuation of the earphone is 20db in the range of 100-400HZ, and the maximum noise attenuation is 35db.

As shown in Figure 1, the feedback type active noise canceling earphone of the present invention is mainly made up of microphone, phase-shift filter, amplifier, loudspeaker, wherein the noise and music received by the microphone subtract the music signal output by the audio amplifier, The pure noise is obtained, and the pure noise is superimposed with the music signal, and the high and low frequencies are filtered out through the phase shift filter, and then amplified by the audio amplifier and reversely connected to the speaker, so that the noise signal is reversed to drive the speaker, thereby Cancel the outside noise.

The circuit schematic diagram of the feedback type active noise canceling earphone of the present invention is shown in Figure 2, wherein U1, C3, C6, C9, R14, C11, D1 form a power supply module, supply power to TPA711, microphone head, at first, music signal from P5 Come in, through the all-pass filter composed of R2 and C2, the noise received by the microphone and the music signal fed back from the speaker are subtracted by U1, and the pure noise is superimposed with the music signal, and then enters the core chip TPA711 from C8 Amplify and filter, among them, the filter composed of R17, C14, C13, R16, R12, R13, C17, C5, the signal is output from pin 5 and pin 8 of TPA711, and the speaker is connected to pin 5 and pin 8 by reverse connection , so that the noise is output from the speaker in reverse, thereby eliminating the noise. The circuits and structures of the left and right ears are the same.

The TPA711 chip is commercially available. The present invention can be used for single-ear earphones and binaural earphones.

The working principle of the feedback type active noise canceling earphone of the present invention is as follows:

Fig. 3 is the block diagram of the active noise cancellation transmission of the feedback type active noise cancellation earphone of the present invention. When the sound signal is not added, the noise heard by the human ear is reduced to the minimum, that is, the sound pressure of the eardrum is the minimum. After adding the sound signal, the normal listening is not affected. The sound pressure received by the ear is composed of two parts: the first part is the noise P _s (s) from the outside, where the independent variable s=jω; the second part is the sound _PL (s) of the speaker, and the sound pressure that the eardrum bears is P _e (s), then:

P _e (s) = P _s (s) + P _L (s) (1)

P _e (s) generates output P _L (s) after passing through three transmission modules H _f (s), H _m (s), and H _s (s), where H _f (s) is the filter module output by the microphone, and H _m (s) is the amplification module, H _s (s) is the phase shifting module, that is: P _L (s) = P _e (s) · H _f (s) · H _m (s) · H _s (s) into (1) Formula:

P _e (s) = P _s (s) + P _e (s) · H _f (s) · H _m (s) · H _s (s) (2)

From formula (2), we get:

P _e (s) = P _s (s)/[1-H _f (s) H _m (s) H _s (s)] (3)

When the absolute value of the denominator |1-H _f (s) · H _m (s) · H _s (s) | is very large, P _e (s) = ε (s) tends to zero, so by increasing the amplifier Gain of H _m (s) to use ear sound pressure reduction. When the denominator of equation (3) is zero, the system will become unstable, that is, the Nyquist plot of the transfer function H(s)=H _f (s) H _m (s) H _s (s) surrounds When the point (1, 0j) is reached, the system produces undesirable low-frequency or high-frequency vibrations in certain frequency bands. In addition, when the phase shift of a certain frequency is equal to -360 degrees, the overall loop gain is greater than 1, and positive feedback will also cause howling. For this reason, a low-pass filter is introduced behind the output of the microphone to make the high frequency that is easy to cause howling If the frequency gain is less than 1, it is a negative decibel.

When the voice signal S(s) is added, its transmission block diagram becomes Figure 4. At this time, the sound pressure P _e (s) of the human ear is still sounded by the speaker P _L (S) and the noise P _s (s) invading the earmuffs Synthesis, after the microphone is converted into an electrical signal and then synthesized with the voice signal, and sent to the low-pass filter H _f (s) and then amplified, so there is still:

P _e (s) = P _s (s) + P _L (s)

Among them: P _L (s) = [P _e (s) + S (s)] · H _f (s) · H _m (s) · H _s (s) into formula (1) to solve:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

When the magnification is very large, the formula (4) becomes: P _e (s) = ε (s) + S (s) (5)

ε(s) is the sound pressure generated by noise, that is, the speech signal is not affected by filtering and amplification. When the amplification factor is large, ε(s) is small, the signal-to-noise ratio is large, and clear speech signals can be heard.

Compared with the prior art, the present invention has the following advantages:

1. Adopt active electronic noise cancellation, built-in microphone as sensor, closed-loop negative feedback, and second-order all-pass phase-shift filter to eliminate noise to the greatest extent without causing howling or oscillation, ensuring the stability of the circuit.

2. The communication signal compensation module is designed to reduce the influence of the noise elimination link on the communication signal and keep the signal from being distorted.

3. Designed low-frequency and high-frequency oscillation suppression circuits and a reasonable earphone structure to make the system stable and suitable for long-term wearing in noisy environments.

4. The system design meets the technological requirements of mass production, and the cost of mass production is within 50 yuan each, which is cost-effective.

5. Compared with conventional physical sound-proof earphones, this earphone can effectively eliminate the noise entering the human ear, protect the human auditory system, and enable people to work normally in heavy noise environments (aircraft takeoff and landing, artillery or heavy machinery operations, etc.) , Communication, not disturbed by external noise; the average noise attenuation of the earphone is 20db in the range of 100 ~ 400HZ, and the maximum noise attenuation is 35db.

Description of drawings

Fig. 1 is the structural representation of earphone of the present invention;

Fig. 2 is the schematic circuit diagram of Fig. 1;

Fig. 3 is the transmission block diagram of the earphone feedback type denoising of the present invention;

Fig. 4 is the transmission block diagram after earphone of the present invention adds voice signal;

Fig. 5 is a structural schematic diagram of a closed-loop noise canceling ear;

Fig. 6 is a structural schematic diagram of a second-order low-pass filter;

Fig. 7 is the frequency characteristic of the second-order low-pass filter among Fig. 6;

Fig. 8 is a schematic structural diagram of an amplifier module;

Fig. 9 is the frequency characteristic of the amplifier in Fig. 8;

Figure 10 is the transfer characteristic from the speaker to the microphone;

Fig. 11 is a noise reduction effect diagram of the earphone of the present invention;

Figure 12 Frequency characteristics of horn and microphone.

Detailed ways

The headphone of the present invention is made of polymer material with good sound insulation effect, which can isolate most of the high-frequency noise above 500 Hz, and eliminates the low-frequency noise below 500 Hz by using a closed-loop denoising circuit.

In the initial experiment, increasing the magnification of the circuit can indeed reduce the noise in the earmuffs and improve the signal-to-noise ratio, but it also causes low-frequency or high-frequency oscillations, making the circuit unstable. The equation (4) will Oscillation occurs at the frequency where the denominator is zero (satisfying the phase and amplitude conditions at the same time), so the low-pass filter and phase shifter must be carefully designed to make the system reach the best balance point in terms of stability and noise elimination.

Closed-loop noise reduction uses a large magnification to reduce noise, and uses sealed earmuffs to attenuate high-frequency noise. The heat accumulated in the sealed earmuffs and the pressure formed to eliminate noise disturbances bring great discomfort to the earphone wearer. For this reason, a semi-enclosed structure is designed, and the earmuffs are divided into two separate spaces by a partition for installing the speaker, as shown in Figure 6. These two spaces have small holes communicating with the outside, which reduces the load on the ears during work. Pressure, noise cancellation effect will also be reduced. In Figure 5, spaces 1 and 2 must be strictly separated, otherwise the sound wave from cavity 1 will be introduced into cavity 2 to form positive feedback, causing oscillation and destabilizing the system.

When designing, choose sesame resistors and capacitors, small speakers, microphones, and small-package audio amplifiers. The printed circuit board should be designed so that the entire system must be installed in the earmuffs.

The filter uses sallen_keg second-order low-pass filter, as shown in Figure 6:

its transfer function; $h\left(S\right)=\frac{\frac{A_f}{R_1{R}_2{C}_1{C}_2}}{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="A20051003363800105.png,A20051003363800111.png"\; state="\{\{state\}\}">S</figure-callout>}}^2+S(\frac{1}{R_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20051003363800105.png,A20051003363800112.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}+\frac{1}{R_2{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="A20051003363800105.png,A20051003363800111.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}+\frac{1-A_f}{R_2{C}_2})+\frac{1}{R_1{C}_1{R}_2{C}_2}}---\left(6\right)$

in: $A_f=1+\frac{R_3}{{\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="A20051003363800106.png"\; state="\{\{state\}\}">R</figure-callout>}}_4}$

The amplitude-frequency and phase-frequency characteristics of the filter are shown in Figure 7:

where the eigenfrequencies are: ${\mathrm{\&omega;}}_0^2=\frac{1}{R_1{C}_1{R}_2{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="A20051003363800105.png,A20051003363800111.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}$

ω Amplitude at ₀ frequency: $h_0=1+\frac{R_f}{R_r}$

The Q value is calculated by the following formula: $\frac{1}{Q}=\sqrt{\frac{R_2{C}_2}{R_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20051003363800105.png,A20051003363800112.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}}+\sqrt{\frac{R_1{C}_2}{R_2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20051003363800105.png,A20051003363800112.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}}+(1-A_f)\sqrt{\frac{R_1{C}_1}{R_2{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="A20051003363800105.png,A20051003363800111.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}}$

Order: R1·C1=R2·C2 then: $\frac{1}{Q}=3-A_f,Q=\frac{1}{3-A_f}$

When A _f →3, the Q value has a peak point. The unit of the calculation result of the above ω ₀ is radian, and it needs to be divided by 2π when converting to Hz.

The amplifier is selected as a high-precision audio amplifier with necessary external circuits as shown in Figure 8.

The transfer function of the amplifier:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\frac{{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="S"\; filenames="A20051003363800105.png,A20051003363800111.png"\; state="\{\{state\}\}">S</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C"\; filenames="A20051003363800105.png,A20051003363800112.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="A20051003363800105.png,A20051003363800111.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ]</span>$

The amplitude-frequency characteristics and phase-frequency characteristics of this amplifier are shown in Figure 9.

The phase shifter adopts an all-pass filter with a gain of 1, and adjusts the phase appropriately in the range of 100-500Hz. In the frequency range of 100 ~ 500HZ, the amplifier has a large gain, but the phase should not change greatly. When the circuit parameters are not selected properly, the circuit gain is large. The phase shift already has 360 degrees, which will cause oscillation or howling, making the circuit unstable. The adjustment of the circuit parameters must be carried out very finely in order to eliminate the noise to the greatest extent without causing howling or oscillation to ensure the stability of the circuit.

Simulation: The simulation of circuit frequency characteristics can be performed on an electronic circuit simulation platform (such as EWB), but it is difficult to simulate the speaker and microphone link (Figure 10) in the closed-loop system. The transmission characteristics between them are related to the respective frequencies of the speaker and microphone. The characteristics and their relative positions are related. The frequency characteristics of the speakers and microphones measured in this system are shown in Figure 12. The transmission characteristics of this link are shown in Table 1. The signal input to the speaker is generated by the signal generator , the effective value of the voltage is 0.5V, the external voltage of the microphone is 1.8V, and the voltage dividing resistor is 4.7K.

Table 1 shows the transmission characteristics from the speaker to the microphone. Design a circuit transmission module that is the same as the transmission characteristics from the speaker to the microphone in Table 1. Then use this module to replace the transmission module from the speaker to the microphone, and perform circuit simulation to align the amplitude and frequency of the system. And phase-frequency characteristics, when the circuit parameters are improperly selected, the circuit will have an output waveform at the output, indicating that the system is unstable and oscillations occur.

Table 1 frequency 100 150 200 300 400 500 600 700 800 900 U _o (mv) 4.8 4.2 2.8 2.7 2.3 1.6 1.0 0.4 0.2 0.2 Phase difference (degrees) 5 10 18 25 32 47 65 80 90 95

The attenuation decibel data and all data are obtained through actual measurement on the B&K electroacoustic comprehensive tester, as shown in Table 2.

Table 2

It can be seen from the above table that, compared with the same kind of earphones at home and abroad, the present invention has a larger number of decibels of noise attenuation. The earphone of the present invention can adopt following element:

Quantity Value Value Serial Number Package

2 1K5 R15 R16 0603

8 1K 1K C15 R5 R6 0603

R7 R10 R13

R19 R20

1 2.2UF C7 1206

1 2.2uF/16V C8 1206

3 3K3 R8 R9 R14 0603

2 3K3 VR1 VR2 VR

2 10uF/16V C3 C6 1206

1 22UF/16V C16 DIP

1 22u/16v C17 DIP

2 33K R17 R18 0603

2 47K R3 R4 0603

2 82K R1 R2 0603

2 103 C4 C5 0603

3 104 C9 C10 C13 0603

2 104 C12 C14 RAD0.2

1 104uF C11 1206

2 202 C1 C2 0603

2 470 R11 R12 0603

1 7150-1 U1 SOT-89

1 LED D2 DIP1

2 MIC MICL MICR P1

2 SPK SPL SPR P1

Among them, the microphone is aimed at the speaker and placed in the middle of the inner panel of the earphone, and some two core chips use TPA711.

Claims (3)

1, a kind of feed back type active noise eliminating earpiece, it is characterized in that mainly forming by miaow head, all-pass filter, amplifier, loudspeaker, wherein received noise and the music of miaow head deducts the music signal of being exported by audio frequency amplifier, obtain pure noise, pure noise is superimposed with music signal again, by all-pass filter, low-and high-frequency is filtered, amplify and the anti-phase loudspeaker that drive through audio frequency amplifier again, thereby the noise cancellation of outside is fallen.

2, feed back type active noise eliminating earpiece according to claim 1 is characterized in that described miaow head aligning loudspeaker, is placed in the middle of the earphone wainscot.

3, feed back type active noise eliminating earpiece according to claim 1 and 2, it is characterized in that in its circuit, U1, C3, C6, C9, R14, C11, D1 forms power module, give TPA711, the power supply of miaow head, at first, music signal is come in from P5, process is by R2, the all-pass filter that C2 formed, noise that the miaow head receives and music are subtracted each other by U1 from the music signal that loudspeaker feed back, obtaining pure noise superposes with music signal again, enter acp chip TPA711 from C8 and amplify and filtering, wherein, by R17, C14, C13, R16, R12, R13, C17, the filter that C5 formed, signal is from 5 pin and the output of 8 pin of TPA711, loudspeaker are by connecing instead to 5 pin and 8 pin, thereby make noise from the anti-phase output of loudspeaker, thereby eliminate noise.

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