RU2494570C1 - Method for highly directional reception of sound waves - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method in which during lateral arrival of sound waves at an angle of ±α to the zero position of the axis of a disclosed microphone receiver, directed towards the sound source, a time delay is formed between two acoustic inputs, equal to: $${\text{Δt}}_{\text{d}}=\frac{\text{L}\cdot \text{sinα}}{{\text{C}}_{\text{s}}},$$

where C_s is the speed of sound, L is the distance between acoustic inputs.

EFFECT: smaller linear dimensions of the receiver while improving high directivity of receiving sound.

3 cl, 5 dwg

Description

A method for sharply directed reception of sound waves is proposed, which can be used as reporter sound receivers, as well as in a number of acoustic specific applications of a scientific and research nature.

A known method of directional sound reception in a design performance by tubular type microphones [1] and traveling-wave interference microphones, which is performed by one sound channel — a tube with holes evenly spaced on it [2].

In the known method in the embodiment of [1], the acoustic receiving part is assembled from a bundle of sound channels — tubes with a linearly varying length of tubes, the opposite ends of the tubes are assembled into a single end plane and placed in a precapsular volume of a single microphone. The microphone can be of electrodynamic or condenser type and perceives sound pressure coming into the volume from sound tubes only.

In another design [2], the known method is implemented by one sound channel — a tube with acoustic sound receivers in the form of holes in the tube, which, as in the case of [1], are linearly located along the length, including the entrance to the tube at its end. The opposite end of the tube is also placed in the precapsular volume of said microphone.

The known method assumes that sound waves from the source of interest, arriving along the axial direction of the tubes in [1] or the tube in [2], i.e. when the axis of the sound channels is normal to the front of the sound wave, they arrive at the receiving surface of the microphone with the same phase and their amplitudes are added arithmetically.

Sound waves that arrive at an angle ± α to the axis of the tubes act on the receiving surface of the microphone phase-shifted, i.e. delayed by time.

In extreme cases, when α = 90 °, the value of the time delay is maximum and is equal to Δt _ass = d / _Csv , where d is either the difference in length in the nearest tubes, or the distance between the holes, _Csv is the speed of sound.

Thus, changing the angle α from one extreme position at α = 0 to another at α = 90 ° in the known method, there are changes in the delay Δt _ass from zero (at α = 0) to the maximum.

When α ≠ 0, the delay value can be written in the form (see Fig. 1):

$${\text{Δt}}_{\text{ass}}=\frac{\text{d}}{{\text{C}}_{\text{star}}}-\frac{\text{d}\cdot \text{cosα}}{{\text{C}}_{\text{star}}}\text{where from}{\text{Δt}}_{\text{ass}}\cdot {\text{C}}_{\text{star}}=\text{d (1}-\text{cos}\text{α)}\text{(one)}$$

The product Δt _ass · C _sv has a dimension of length and, therefore, as applied to the sound, it is comparable with the wavelength of sound vibrations (λ _sv = S _sv / f _sv , where f _sv is the frequency of sound vibrations), i.e. 180 ° phase delay corresponds to a delay of 0.5λ _sv . In particular, two sound vibrations of the same frequency and the same amplitude, delayed by 0.5λ _sound relative to each other, completely compensate each other and the sound pressure at this point is zero.

Thus, the expression (1) represents the known method and allows for given values of α d and calculate what frequency f of sound _ulcers should expect full compensation sound pressure in the microphone at its receiving surface. So, at the lower frequency of the sound signal f _low = 340 Hz 0.5λ _sv340 = 0.5 m and the length of the sound channel (tube) at α = 20 ° will be:

$$\text{d}=\frac{\text{0}\text{,5}\cdot {\text{λ}}_{\text{zv340}}}{\text{one}-\text{cos}\text{α}}=\frac{\text{0}\text{,5}}{\text{one}-\text{0}\text{9397}}\cong \frac{\text{0}\text{,5}}{\text{0}\text{06}}\cong \text{8}\text{,3m}$$

and at α = 45 ° and d ~ 1.7 m.

With increasing f _{sv, the} total length of the sound channels, of course, decreases, however, for reporter tasks and receiving speech signals, microphones based on the known method turn out to be either very long or lose their sharp focus when receiving sound. This contradiction, which follows from the expression (1), is the main disadvantage of the known method.

According to its technical characteristics, the known method for the formation of sharply directed sound reception according to [1, 2] can be considered as a prototype (analogue) of the proposed method, the technical solution of which is to reduce the linear dimensions of the receiver while improving the directivity of the sound reception.

A method for sharply directed reception of sound waves is proposed, in which sound is received either by the inputs of sound channels in the form of tubes with a linearly varying length, and the opposite ends of the tubes are combined in the precapsular volume of a microphone of an electrodynamic or condenser type, into which sound waves come only from sound channels, or reception is carried out through the entrance of one channel with the presence of linearly located holes along its length, into which sound waves enter both the tubes mentioned above, and opolozhny end of the channel included in said volume predkapsyulny the same microphone. In accordance with the proposal, two sound channels are used — tubes of equal length, which are combined in the microphone’s precapsule volume so that the axes of the channel ends are set either normal to the microphone’s receiving plane, and the channels themselves are bred by 180 ° bending when they exit the precapsule volume the opposite sides and at a length of these bends of at least 10 cm from the bend point form a conditional single channel axis parallel to the microphone receiving plane, or sound channels are introduced into the precapsular volume of the mic the microphone so that the channel axes immediately form a conditional single channel axis parallel to the microphone receiving plane, and outside the microphone, this axis is kept uniform at least 10 cm long on both sides of the microphone, while the direction of the channels to the sound source is zero when the conditional single the axis of the channels is parallel to the front of the sound waves of the source, and with lateral influences of the fronts of the sound waves at an angle ± α relative to the zero position of the single axis of the channels, the sound waves arrive at the receiving surface Background with a time delay Δt _ass, which is determined from the expression:

$${\text{Δt}}_{\text{ass}}=\frac{\text{ΔL}}{{\text{C}}_{\text{star}}}=\frac{\text{L}\cdot \text{sinα}}{{\text{C}}_{\text{star}}}\text{(2)}$$

where ΔL = L · sin α, a L = L ₁ + L ₂ is the distance between the inputs at the ends of the sound channels, and L ₁ and L ₂ are the lengths of the tubes counted from the microphone, ΔL is the distance between the inputs of the channels, measured along the normal to the front of the sound wave.

In another embodiment, a method is proposed in which the distance L is changed from the value L _max , in which the conditional single axis of the channels is maintained along the entire length of the tubes to the value L <L _max , which is obtained by bending the sound channels from a size of at least 10 cm symmetrically towards the alleged sound source or in the form of a direct bend, or bending is performed as part of a circle or an ellipse, while the axis of the bent channels form a plane that can be either parallel to the receiving plane of the microphone, or at right angles to this plane.

In yet another embodiment, a method is provided in which, in the walls of sound channels, holes are additionally arranged symmetrically with respect to the microphone on the side of the tubes that are directed to the sound source.

The essence of the proposed method is illustrated by the following schemes and figures:

Fig 1 is a sharply directed tube-type sound receiver, where 1 is the sound wave, 2 is the front of the sound wave, 3 are the acoustic inputs into the tubes, 4 are the receiving sound channels (tubes), 5 is the precapsular volume, 6 is the microphone, 7 is the receiving plane a microphone;

Fig 2 - sharply directed sound receiver of the type "traveling wave", where 8 are the holes in the sound channel;

Fig 3 is a first embodiment of a device for implementing the proposed method of directional sound reception, where 9 is a conventional single axis of sound channels;

Fig 4 is a second embodiment of the proposed method, where 10 is an element that excludes direct communication between channels;

Fig 5 - options for the design of the limb of the sound channels with sharply directed sound reception and the location of the receiving plane of the microphone relative to the plane of the axes of the channels.

The proposed method of directional sound reception can be implemented by the circuits shown in figure 3 and figure 4. In Fig. 3, a sound wave 1 with a front 2 acts on the acoustic inputs 3 of the sound channels 4. In this case, the channels 4 are introduced into the pre-capsule volume of the microphone 6 so that the channel axes are normal to the receiving plane 7 of the microphone 6. When exiting the pre-capsule volume 5, the channels are separated by bending them 180 ° in opposite directions. Using these bends form a conditional single axis 9 of the channels, which is parallel to the receiving plane 5 of the microphone 6. This axis is kept uniform at a channel length of at least 10 cm on both sides of the microphone.

In figure 4, the sound channels 4 are introduced into the pre-capsule volume so that the axes of the sound channels 4 immediately form a single axis 9 parallel to the receiving plane 5 of the microphone 6. Outside the microphone 6, this single axis is stored for a length of at least 10 cm on both sides of the microphone axis.

Figure 3 also shows two cases of exposure to sound wave 1 with a front 2 on the acoustic inputs 3 of sound channels 4:

- in the first case, in which the conventional single axis 9 is parallel to the front 2, the zero position of the sound channels is shown, in which α = 0 is the angle between the wave front and the conventional single axis of the channels;

- in the second case, the action of sound wave 1 with front 2 forms an angle α between the front of wave 2 and the single axis of the channels 9.

If in the first case, when the length of the channels is equal and α = 0, the sound waves entering the acoustic channels affect the receiving surface of the microphone in phase (the amplitudes add up), then in the second case, the common mode is broken. This is due to the fact that the sound wave with its front hits first in one channel, and after some time - in another.

.As shown in figure 3, the wavefront (t. A and B) in the acoustic input 4 of the left channel of t. A will reach the microphone after a time L ₁ / C _sound . The wave front in the acoustic input 4 of the right channel in t.S will reach the microphone after a while $$\frac{\mathrm{AT}\mathrm{FROM}}{{\mathrm{FROM}}_{s\mathrm{at}}}+\frac{{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="00000013.png,00000014.png"\; state="\{\{state\}\}">L</figure-callout>}}_2}{{\mathrm{FROM}}_{s\mathrm{at}}}$$

.

The total delay time is equal to:

$${\text{Δt}}_{\text{ass}}=\frac{\text{Sun}}{{\text{FROM}}_{\text{star}}}+\frac{{\text{<figure-callout id="2" label="L" filenames="00000013.png,00000014.png" state="{{state}}">L</figure-callout>}}_{\text{2}}}{{\text{FROM}}_{\text{star}}}-\frac{{\text{L}}_{\text{one}}}{{\text{FROM}}_{\text{star}}}=\frac{\text{Sun}}{{\text{FROM}}_{\text{star}}}\text{(3)}$$

since by hypothesis L ₁ = L ₂ .

From the triangle ABC in figure 3, the side BC = (L ₁ + L ₂ ) · sin α, whence

$${\text{Δt}}_{\text{ass}}=\frac{\text{ΔL}}{{\text{FROM}}_{\text{star}}}=\frac{{\text{(L}}_{\text{one}}+{\text{L}}_{\text{2}}\text{)}\cdot \text{sinα}}{{\text{FROM}}_{\text{star}}}=\frac{\text{L}\cdot \text{sinα}}{{\text{FROM}}_{\text{star}}}\text{(four)}$$

where L is the distance between the entrances to the sound channels, ΔL = L · sin α is the distance between the entrances to the channels, measured along the normal to the front of the sound wave.

From (4) Δt _ass · _Csv is the metric size of the time delay, which can be measured with the sound wavelength equal to _λsv . As already noted in the delay between channels is equal 0,5λ _ulcers (phase shift of 180 °) in the microphone sound waves cancel each other.

Using expression (4) and setting the delay value Δt _ass · C _sv = 0.5 · λ _sv for a given angle α, we determine the length of sound channels (L ₁ + L ₂ ) for three values of sound frequency - 350 Hz, 500 Hz, 2000 Hz, at which the sound pressure in the microphone is compensated.

Table 1 shows the calculated values of the length of the sound channels (L ₁ + L ₂ ) from the angles a for the proposed method of sharply directed sound reception, and table 2 for comparison shows the calculated data for the prototype using expression (1), where

или $$\text{d}=\frac{\text{0}\text{,5}\cdot {\text{λ}}_{\text{зв}}}{\text{1}-\text{cosα}}$$

$$\text{d}=\frac{{\text{Δt}}_{\text{ass}}\cdot {\text{FROM}}_{\text{star}}}{\text{one}-\text{cosα}}$$

or $$\text{d}=\frac{\text{0}\text{,5}\cdot {\text{λ}}_{\text{star}}}{\text{one}-\text{cosα}}$$

Table 1 α, ° 10 twenty thirty 40 sin α 0.174 0.342 0.50 0,0643 f _sv = 340 Hz 0.5λ _sound = 0.5 m (L ₁ + L ₂ ), m 2.9 1.46 1,0 ~ 0.75 f _sv = 500 Hz 0.5λ _sound = 0.34 m (L ₁ + L ₂ ), m ~ 2.0 1,0 ~ 0.7 0.5 f _sv = 2000 Hz 0,5λ _eV = 0.085 m (L ₁ + L ₂ ), m ~ 0.5 ~ 0.25 ~ 0.19 ~ 0.13

table 2 α, ° 10 twenty thirty 40 cos α 0.985 0.940 0.866 0.766 1 - cos α 0.015 0.06 0.134 0.234 f _sv = 340 Hz 0.5λ _sound = 0.5 m d, m 33 ~ 8.3 ~ 3.65 ~ 2.1 f _sv = 500 Hz 0.5λ _sound = 0.34 m d, m 23 5.7 ~ 2.5 1.4 f _sv = 2000 Hz 0,5λ _eV = 0.085 m d, m ~ 5.7 ~ 1.41 0.62 0.36

From tables 1 and 2 it follows that at the indicated frequencies in the region of acute directivity a (from 10 ° to 20 °), the proposed method has obvious advantages over the prototype in the linear dimensions of sound channels.

It should be noted that the circuit in figure 4 requires placement in the pre-capsule volume 5 between the inputs of the channels 3 of the element 10, which exclude direct communication between the audio channels. Such an element is installed with gaps between the ends of the channels to eliminate distortion of the acting sound waves. The design of such an element is most appropriate to choose in the process of experimental testing.

A method is also proposed in which the distance L is changed from the maximum value L _max = L ₁ + L ₂ on a single axis of the channels along their entire length to the value L <L _max , which is obtained by bending the sound channels from a distance of at least 10 cm from the microphone symmetrically towards the intended sound source. Figure 5 shows two options for bending sound channels - after bending the channel remains linear or bending is performed as part of a circle (figure 5) or an ellipse. Bent channels are always located on the same plane. Figure 5 also shows 2 options for placing a microphone with a receiving surface, and in the first embodiment, the plane of the bent channels is parallel to the receiving surface of the microphone, and in the second embodiment, these planes are mutually perpendicular.

A change in L even during the practical operation of a microphone manufactured by the proposed method can be attributed to its advantage, since it allows you to take into account the change in the frequency range of acoustic signals (frequency shift upwards). Bends are performed from a distance of at least 10 cm on both sides of the microphone on a single conventional axis. According to the authors, keeping the conventional axis unified at a length of 20 cm provides comfortable conditions for pointing the microphone at the sound source.

The proposed method also assumes that on the sound channels facing in the direction of the sound source, additional openings are located, which, like the acoustic inputs at the ends of the channels, act as acoustic inputs. Such channels, as noted in [2], make sharply directed sound reception in a certain frequency range of sound frequencies. Additional holes are located on the walls of the channels symmetrically with respect to the microphone on a single axis, and the holes themselves are directed, like the bends of the channels, towards the sound source, and their number is determined by the frequency range of the recorded sound signals. According to the authors, an additional image of the said openings on the channels is not required, since their presence does not affect the essence of the proposed method.

Thus, a method for sharply directed sound reception is proposed, which significantly reduces the overall dimensions and improves the directivity characteristics of microphones.

Literature

1. Textbook for universities. I.A. Aldoshin, E.I. Volodin, A.P. Efimov et al. “Electroacoustics and sound broadcasting”. - M .: Hot line - Telecom. Radio and communications, 2007 - 872 p.

2. Textbook for universities. Sh.Ya. Vakhitov, Yu.A. Kovalgin, A.A. Fadeev, Yu.P. Shcheviev. "Acoustics". - M .: Hot line - Telecom, 2009 - 660 s.

Claims (3)

1. A method of sharply directed reception of sound waves, in which sound is received either by the inputs of sound channels in the form of tubes with a linearly varying length, and the opposite ends of the tubes are combined in a precapsular volume of an electrodynamic or condenser type microphone, into which sound waves come only from sound tubes, or reception is carried out through the inputs in one sound channel — the tube, which are made in the form of holes linearly spaced along the length of the tube, into which sound waves enter, as mentioned e tubes, and the opposite end of the tube is placed in the said precapsular volume, characterized in that two sound channels are used - tubes of equal length, which are combined in the precapsular volume of the microphone so that the axes of the ends of the tubes are set either normal to the microphone receiving surface, and the tubes themselves when leaving the precapsular volume, they are bred by 180 ° bending in opposite directions and a single conditional axis parallel to the microphone receiving plane is formed on the length of these bends at least 10 cm from the bending point, either the tubes are inserted into the pre-capsule volume so that the channel axes form a single conditional tube axis parallel to the microphone receiving plane, and outside the microphone this axis is kept uniform at least 10 cm on both sides of the microphone, and the tubes are directed to the sound source zero, for which the conditional single axis of the tubes is parallel to the front of the sound waves of the source, and with lateral action of the fronts of the sound waves at an angle ± α with respect to the zero position of the single axis of the tubes, the sound waves arrive at microphone receiving surface with a time delay Δt _back , which is determined from the expression:
$${\text{Δt}}_{\text{ass}}=\frac{\text{ΔL}}{{\text{C}}_{\text{star}}}=\frac{\text{L}\cdot \text{sinα}}{{\text{C}}_{\text{star}}}\text{(2)}$$

,
where L = L ₁ + L ₂ is the distance between the inputs at the ends of the sound channels, and L ₁ = L ₂ is the length of the tubes counted from the microphone, ΔL is the distance between the same inputs in the tubes, measured normal to the front of the sound waves. 2. The method according to claim 1, characterized in that the distance L is changed from the value L _max , at which the conditional single axis of the channels is maintained along the entire length of the tubes, and the values L <L _max are obtained by bending the tubes symmetrically in the direction to the intended sound source or in the form of a direct bend, or in the form of a part of a circle or an ellipse, while the axes of the bent tubes are placed in one plane or parallel to the receiving plane of the microphone, or at right angles to it. 3. The method according to claim 1, characterized in that the additional inputs of the sound waves in the form of holes in the tubes are arranged symmetrically with respect to the microphone on the side of the tubes, which are directed to the sound source.

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