CN1688179A - Feed back type active noise eliminating earpiece - Google Patents

Abstract

This invention relates to a feed-back active noise-elimination earphone composed of head, a phase shift filter, an amplifier and a loudspeaker, among which, noise and music received by the head subtract the music signals output by the audio amplifier to get pure noises to be laminated with music signals, then the high and low frequencies are filtered out by a phase shift filter and the rest is amplified by the audio amplifier and inverted to drive the loud speaker so as to cancel outside noises. This invention applies a feed-back active closed-loop noise-elimination theory to design filter, phase shift, amplification and compensation circuits and reforms the physical structure, arrangement of feed-back loop, and selection of the device and earphone materials.

Description

Feed back type active noise eliminating earpiece

Technical field

The present invention relates to electronics and communication, technology of instrument and meter, specifically is feed back type active noise eliminating earpiece.

Background technology

Commercially available de-noising earphone de-noising effect is desirable not to the utmost, and average de-noising is generally about 10db and cost an arm and a leg.In a famous brand de-noising earphone price on the American-European market all more than 150 dollars, as 300 dollars of Bose board de-noising earphone prices, 3600 yuan of RMB.

Summary of the invention

The objective of the invention is to defective according to the prior art existence, a kind of feed back type active noise eliminating earpiece is provided, adopt the reaction type initiatively filtering of closed loop de-noising principle design, phase shift, amplification and compensating circuit, in the physical structure of earphone, the arrangement of feedback loop is transformed in the selection of components and parts and earphone material, make the performance of earphone more stable, de-noising effect is better, and the decay of earphone average noise is at 20db in the 100-400HZ scope, and maximum noise is decayed at 35db.

As shown in Figure 1, feed back type active noise eliminating earpiece of the present invention mainly is made up of 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, passes through all-pass filter, low-and high-frequency is filtered, the process audio frequency amplifier amplifies and passes through the loudspeaker reversal connection again, thereby makes the anti-phase loudspeaker that drive of noise signal, thereby the noise cancellation of outside is fallen.

The circuit theory diagrams of feed back type active noise eliminating earpiece of the present invention as shown in Figure 2, U1 wherein, 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, entering acp chip TPA711 from C8 amplifies 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, and loudspeaker are by connecing instead to 5 pin and 8 pin, thereby make noise from the anti-phase output of loudspeaker, thereby eliminate noise.Circuit, the structure of left side ear and auris dextra are identical.

The TPA711 chip can bought on the market.The present invention both can be used for the monaural earphone, also can be used for split headphone.

The operation principle of feed back type active noise eliminating earpiece of the present invention is as follows:

Fig. 3 is the active de-noising transmission block diagram of feed back type active noise eliminating earpiece of the present invention, and when not adding voice signal, the noise that people's ear is heard is reduced to minimum, and promptly the acoustic pressure minimum of bearing of ear-drum behind the adding voice signal, is listened to unaffected normally.The acoustic pressure that ear receives is made up of two parts: first is the noise P from the outside _s(s), independent variable s=j ω wherein; Second portion is the sounding P of loudspeaker _L(s), establishing the acoustic pressure that ear-drum bears is P _e(s), then:

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

P _e(s) through three transport module H _f(s), H _m(s), H _s(s) back produces output P _L(s), H wherein _f(s) filtration module of exporting for microphone, H _m(s) be amplification module, H _s(s) be phase shift block, that is: P _L(s)=P _e(s) H _f(s) H _m(s) H _s(s) substitution (1) formula gets:

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

Solve from (2) formula:

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

When the denominator absolute value | 1-H _f(s) H _m(s) H _s(s) | when very big, P _e(s)=and ε (s) levels off to zero, and therefore can be by increasing amplifier H _m(s) gain uses the otoacoustic emission pressure to reduce.When the denominator of formula (3) was zero, it is unstable that system will become, i.e. transfer function H (s)=H _f(s) H _m(s) H _s(s) Nyquist diagram has surrounded point, and (1, in the time of 0j), system produces undesirable low frequency or dither in some frequency range.In addition, when the phase shift of a certain frequency equals-360 degree, overall loop gain greater than 1, produces positive feedback and also will cause and utter long and high-pitched sounds, and introduces a low pass filter in the output back of microphone for this reason, makes easily to cause the high-frequency gain of uttering long and high-pitched sounds less than 1, is negative decibel.

After adding voice signal S (s), its transmission block diagram becomes Fig. 4, at this moment the acoustic pressure P of people's ear _e(s) still by sound horn P _L(S) and the invasion earmuff noise P _s(s) synthetic, synthetic with voice signal again after changing into the signal of telecommunication through microphone, a And sends into low pass filter H _f(s) amplify again, so still have:

P _e(s)＝P _s(s)+P _L(s)

Wherein: P _L(s)=[P _e(s)+and S (s)] H _f(s) H _m(s) H _s(s) substitution (1) formula solves:

$P_e\left(s\right)=\frac{P_s\left(s\right)+S\left(s\right)\·H_f\left(s\right)\·H_m\left(s\right)\·H_s\left(s\right)}{1-H_f\left(s\right){\·H}_m\left(s\right)\·H_s\left(s\right)}---\left(4\right)$

(4) formula becomes when multiplication factor is very big: P _e(s)=ε (s)+S (s) (5)

The acoustic pressure that ε (s) produces for noise, promptly voice signal is not subjected to the influence of filtering and amplification, and when multiplication factor was very big, ε (s) was very little, and signal to noise ratio is very big, can hear voice signal clearly.

The present invention compared with prior art has following advantage:

1, adopt active electronics de-noising, built-in microphone is made transducer, close loop negative feedback, and second order all-pass all-pass filter reaches and eliminates noise to greatest extent, does not cause again to utter long and high-pitched sounds or vibrate, and guarantees the stability of circuit.

2, design of communications signal compensation module has reduced the influence of de-noising link to signal of communication, has kept the undistorted of signal.

3, designed the low frequency and the higher-order of oscillation and suppressed circuit and rational Headphone structure, made system stability, suited to wear in the noise circumstance midium or long term.

4, system design meets the technological requirement of production in enormous quantities, produce in batches cost each in 50 yuan, the cost performance height.

5, this earphone can be eliminated the noise that enters people's ear effectively with conventional physics sound insulation earphone comparison, protection people's auditory system, make people (takeoff and landing, cannon or heavy-duty machinery operation etc.) energy operate as normal, communication in the environment of heavy noise, be not subjected to the interference of external noise; The decay of earphone average noise is at 20db in 100～400HZ scope, and maximum noise is decayed at 35db.

Description of drawings

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

Fig. 2 is the circuit theory diagrams of Fig. 1;

Fig. 3 is the transmission block diagram of earphone reaction type of the present invention de-noising;

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

Fig. 5 is a closed loop de-noising ear structure schematic diagram;

Fig. 6 is the second-order low-pass filter structural representation;

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

Fig. 8 is the amplifier module structural representation;

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

Figure 10 is the transmission characteristics of loudspeaker to microphone;

Figure 11 is the de-noising effect figure of earphone of the present invention;

The frequency characteristic of Figure 12 loudspeaker and microphone.

Embodiment

Headphone of the present invention adopts soundproof effect better polymerization thing material to make, and can exclude the above most of high-frequency noise of 500Hz, then adopts the closed loop de-noising circuit to eliminate to the low-frequency noise below the 500Hz.

In initial test, the multiplication factor of increasing circuit can reduce the noise in the earmuff really, improve signal to noise ratio, but also cause the low frequency or the higher-order of oscillation thus, make circuit become unstable, to formula (4) will be that zero frequency (satisfying phase place and amplitude condition simultaneously) locates to produce vibration making denominator, thus must careful design low pass filter and phase shifter, make system on stable and de-noising effect, reach optimal balance point.

The closed loop de-noising adopts big multiplication factor to reduce noise, and use sealed type earmuff attenuate high frequency noise, heat that is gathered in the sealing earmuff and the pressure that forms for the elimination noise disturbance bring very big discomfort to the earphone wearer, designed semi-enclosed structure for this reason, with the dividing plate that loudspeaker are installed earmuff is divided into two spaces that separate, sees Fig. 6, these two spaces have aperture respectively and are interlinked to the outside, the pressure that ear bears when having reduced work like this, de-noising effect also can decrease.1,2 spaces want strictness to separate among Fig. 5, will form positive feedback otherwise the sound wave in 1 chamber is introduced into 2 chambeies, cause that vibration makes system's shakiness.

Select sesame resistance and capacity cell, miniature loudspeaker, microphone, little encapsulation audio frequency amplifier when design for use, the design of printed circuit board (PCB) should make whole system to be installed in the earmuff.

Filter adopts the sallen_keg second-order low-pass filter, as shown in Figure 6:

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

Wherein: $A_f=1+\frac{R_3}{R_4}$

The amplitude-frequency of this filter and phase-frequency characteristic be as shown in Figure 7:

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

ω ₀The amplitude at frequency place: $H_0=1+\frac{R_f}{R_r}$

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

The order: R1C1=R2C2 then: $\frac{1}{Q}=3-A_f,Q=\frac{1}{3-A_f}$

Work as A _f→ 3 o'clock, the Q value had a peak dot.Above ω ₀Result of calculation unit be radian, will be when being converted into Hz divided by 2 π.

Amplifier selects for use the high accuracy audio frequency amplifier to be equipped with necessary external circuit as shown in Figure 8.

The transfer function of amplifier:

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

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

Phase shifter adopts all-pass filter, and gain is 1, in 100～500Hz scope phase place is done suitably to adjust.Amplifier has bigger gain in 100～500HZ frequency range, the very big variation but phase place does not have, when circuit parameter was selected not at that time, circuit gain is bigger, though good de-noising effect is arranged, but some frequency phase shift had 360 the degree, will cause the vibration or utter long and high-pitched sounds, make the circuit instability.The adjustment of circuit parameter must very trickle carrying out, and eliminates noise to greatest extent to reach, and is unlikely to again to cause to utter long and high-pitched sounds or vibrate, and guarantees circuit stability.

Emulation: the channel frequency characteristic Simulation can be carried out on certain electronic circuit emulation platform (for example EWB), but loudspeaker in the closed-loop system and microphone link (Figure 10) are difficult to emulation, transmission characteristic between them is relevant with microphone frequency characteristic and the relative position between them separately with loudspeaker, in native system, record loudspeaker and microphone frequency characteristic separately as shown in figure 12, the transmission characteristic of surveying this link is as shown in table 1, the signal of input loudspeaker is produced by signal generator, voltage effective value is 0.5V, the external voltage of microphone is 1.8V, and divider resistance is 4.7K.

Table 1 is the transmission characteristics of loudspeaker to microphone, it is identical to the transmission characteristic of microphone with table 1 loudspeaker to design a circuit transmission module, replace the transport module of loudspeaker with this module again to microphone, carry out circuit simulation, in order to amplitude-frequency and phase-frequency characteristic than Barebone, to select not at that time when circuit parameter, circuit has output waveform in output place, show system's shakiness, produced vibration.

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 (degree)	??5	??10	??18	??25	??32	??47	??65	??80	??90	??95

By at B﹠amp; The actual measurement of K electroacoustic comprehensive tester obtains decibel data, all data of decay, and is as shown in table 2,

Table 2

As can be seen from the above table, compare with domestic and international similar earphone, the present invention has bigger noise attentuation decibels.Earphone of the present invention can adopt following elements:

The encapsulation of quantity numerical value serial number

2?????????1K5???????????R15?R16????????0603

8?????????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

Wherein the miaow head is aimed at loudspeaker, is placed in the middle of the earphone wainscot two acp chip TPA711 that have.

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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