EP0935236A1 - Anti-noise device with threshold detection - Google Patents

Abstract

The system is based on standard ear defenders comprising a cavity with a noise absorbing lining that is intended to cover the ear. An additional active noise suppression circuit is incorporated consisting of a microphone, amplifier and speaker to produce active negative audio feedback. A second microphone detects the level of these signals and only enables the amplifier when the noise exceeds a predetermined threshold.

Description

The invention relates to an anti-noise device designed to limit the annoyance caused by noise to a user operating in a noisy environment, that this user whether or not in communication with a third party no one.

We know anti-noise devices made in the form of helmets with two earpieces connected to each other by a support member allowing hold each earpiece on the user's ear. Each earpiece has a wall defining a cavity. The wall is upholstered on the internal side of the cavity, soundproofing material. The wall as well provided provides passive attenuation by absorbing medium and high frequency sound waves but remains permeable to low frequency sound waves. For for this reason, the helmet is preferably fitted with a active noise attenuation circuit eliminating waves low frequency sound. The attenuation circuit active generates, from an incident sound wave received in each cavity, a sound attenuation wave, of identical amplitude but in phase opposition with the incident sound wave. The wave propagating in the user's ear canal is the wave resulting from the sum of the incident wave and the wave generated by the active attenuation circuit.

The active attenuation circuit includes a electronic processing unit connected in each cavity to active attenuation devices including a microphone picking up a sound wave in the cavity and a loudspeaker emitting the attenuation sound wave produced by the unit treatment. Such a circuit must be connected to a source power supply. Many attenuation circuits active are continuously powered so it this results in a significant electrical consumption particularly prejudicial to the duration of use of stand-alone headsets in which the power source consists of accumulators providing only one limited amount of electricity.

To remedy this drawback, we thought of provide the active attenuation circuit with an organ manually operated switch, user-dependent to activate this organ in order to put into operation the active attenuation circuit when it evolves in a noisy environment and stop it working when the surrounding noise decreases. However, a user regularly subjected to noise undergoes addiction. Despite the presence of this noise, the user then delays the activation of the attenuation circuit active so it tolerates noise so increasing even if the power of it is sufficient to cause significant fatigue.

An object of the invention is to obviate the drawbacks cited above.

According to the invention, an anti-noise device is proposed. having at least one earpiece having a cavity delimited by passive attenuation means, a circuit active mitigation having a spatial domain of efficiency and comprising at least one electronic processing unit connected to active attenuation organs including at minus a microphone picking up sound waves in the cavity and a speaker arranged in the cavity for emit sophisticated active attenuation sound waves by the processing unit, at least one switch member selectively operable between a service state of the active attenuation circuit and an idle state of the circuit active attenuation, threshold detection microphone picking up noises outside the space domain of efficiency active attenuation circuit, means of filtering associated with the threshold detection microphone for eliminate noises corresponding to the noises absorbed by the passive attenuation means, and a detector exceeding a noise threshold to control the organ switch in the service or rest state of the circuit active attenuation according to a power level noises detected downstream of the filtering means.

Thus, the triggering of the attenuation circuit active is a function of the noise power level filtered, i.e. noises that match exactly to those to be eliminated by the attenuation circuit active. Optimal protection is thus ensured for a reduced consumption.

According to a preferred embodiment, the microphone threshold detection is carried by a wall of the headset cavity to pick up noise outside the cavity, the filtering means comprising a filtering mounted between the threshold detection microphone and the threshold overshoot detector.

Furthermore, in anti-noise devices comprising two earpieces to form a helmet, the passive mitigation means are commonly constituted a soundproofing material fixed inside the Headsets. Unless the helmet is removed, the user therefore cannot hear the words of people who surround it even when the surrounding noise is low. This results in permanent isolation of the user, even when it is not necessary.

According to a variant of the preferred embodiment of the invention, the device comprises a microphone listening carried by a wall of the cavity of the second earpiece to pick up noises outside the cavity, switching means connected to the detection microphone threshold and at the listening microphone and selectively actuated by an additional overshoot detector threshold as a function of a noise power level picked up by the threshold detection microphone between a first state in which the detection microphone threshold and the listening microphone are connected to speakers respective and a second state in which the threshold detection microphone is connected to the body of filtering and the listening microphone is muted. So, the user can listen to outside noises when these noises have a power level below the threshold of noise from the additional threshold overshoot detector.

According to another aspect of the invention in conjunction with an anti-noise device according to the aforementioned variant and comprising a communication circuit, said loudspeakers are associated with the communication circuit and the device includes means for interrupting any link between the microphones and said speakers respective when receiving a communication. So when receiving a communication signal, user is not bothered by noise regardless of the power level of these.

• la figure 1 est une vue en perspective d'un dispositif anti-bruit selon l'invention ;
• la figure 2 est une vue schématique, en coupe par un plan vertical II de la figure 1, d'une oreillette du dispositif anti-bruit selon un premier mode de réalisation de l'invention ;
• la figure 3 est une vue schématique d'un deuxième mode de réalisation ;
• la figure 4 est une vue schématique d'une variante du deuxième mode de réalisation.

Other characteristics and advantages of the invention will emerge on reading the following description of particular non-limiting embodiments of the invention in relation to the appended figures among which:

• Figure 1 is a perspective view of an anti-noise device according to the invention;
• Figure 2 is a schematic view, in section through a vertical plane II of Figure 1, of a headset of the noise-canceling device according to a first embodiment of the invention;
• Figure 3 is a schematic view of a second embodiment;
• Figure 4 is a schematic view of a variant of the second embodiment.

With reference to the figures, the anti-noise device according to the invention is here produced in the form of a helmet and has two earphones 13 connected one to the other by a hoop 14 constituting a support member for headsets 13.

A headset 13 includes a wall 1, here represented in the form of a spherical cap, defining a cavity 2. A soundproofing material 3 constituting a means of passive attenuation of noises having a frequency within a specified range of frequencies is arranged, in a manner known per se, in the cavity 2. A bead 11 is fixed along the edge of the wall 1.

The noise canceling headset also includes known per se, an active noise attenuation circuit generally designated in 4 and connected to a food source tion in electrical energy not shown.

The active attenuation circuit 4 includes, for each atrium 13, an electronic processing unit 6 connected to a microphone 5 and a speaker 7. The processing unit 6 is also connected to the source supply by a supply line 15.

In conventional operation, the microphone 5 picks up a sound wave in the cavity and transmits a signal electric incident representative of the sound wave at the processing unit 6. The processing unit 6 develops then a representative electrical attenuation signal of a sound wave of identical amplitude but in opposition phase with the sound wave picked up by the microphone 5. The electrical attenuation signal is transmitted to the speaker 7 which emits the corresponding attenuation sound wave in a portion of the cavity constituting the domain of the active attenuation circuit.

According to the invention, a switch member 8 is disposed in each earpiece 13 on the supply line 15 between the power source and the processing 6. The switch member 8 is either in a state passer-by in which the switch member allows the supply of the processing unit 6, either in a state blocker (shown in Figures 2, 3 and 4) in which the switch member 8 interrupts the supply of the processing unit 6.

According to the first embodiment of the invention and with reference to FIG. 2, a detector of threshold 9 exceeded, placed in one of the two ear cups 13, is connected to the switch members 8 for the order. The threshold crossing detector 9 is connected to a threshold detection microphone 10 housed in the cavity of this headset to pick up the noises in the portion of this cavity outside the space domain of the active attenuation circuit. These noises have been filtered by the sound insulation material and have frequencies in the frequency range of noise processed by the active attenuation circuit so that the threshold overshoot detector 9 analyzes the sounds that are mostly likely to be processed by the active attenuation circuit.

In operation, the noise captured in the cavity 2 by threshold detection microphone 10 is transmitted to the threshold overrun detector 9.

When this noise is of a power level greater than a predetermined threshold of the overshoot detector of threshold 9, this commands the setting to the on state switch members 8, thereby activating the active attenuation circuit.

When the filtered noise is of a power level below the predetermined threshold, the threshold 9 being exceeded commands blocking of each switch member 8. The processing unit 6 no longer supplied with power, then emits no electrical signal mitigation. The active attenuation circuit is then in a state of rest and the processing unit does not consumes no energy.

To avoid interference between the microphone threshold detection and the attenuation circuit activates it is essential that the threshold detection microphone be outside the spatial domain of circuit efficiency active attenuation. In practice this embodiment could be used in case the attenuation circuit active is mounted in an earplug.

In order to increase the capacity of the microphone 5 to capture strong sound waves, resistance acoustic 12, consisting for example of a mesh fabric tight, is preferably placed on the microphone 5. For example, for a microphone 5 sensitive to noise with a power level ranging from 20dB to 120dB, the provision of an acoustic resistance of 20dB allows increase the operating range from 40dB to 140dB. The threshold of commissioning of the active attenuation circuit being for example of the order of 60dB, we thus obtain a range effective attenuation from 60dB to 140dB or 80dB, instead from a range of 60dB to 120dB or 60dB only with the same microphone without acoustic resistance. Protection brought by the headphones is thus extended to noise higher power without saturation of the microphones of the active attenuation circuit.

Elements identical or analogous to those previously described will relate in the following description the same reference number.

According to the second embodiment, shown in FIG. 3, the noise canceling headset comprises, as above a threshold overshoot detector 9 connected to the switch members 8 for controlling them. Microphone threshold detection 10 is this time carried by the wall a headset to capture all outside noise to it and the threshold overshoot detector 9 is connected to a filtering member 19 adapted to ensure a elimination of noise in the frequency range of means of passive mitigation.

In addition the filtering member 19 and the loudspeaker 7 of the headset supporting the threshold exceeded 9 are connected to the detection microphone threshold 10 through a switching 20.

A listening microphone 22 is fixed to the wall of the other earpiece to pick up noise outside this headset and is connected to the corresponding speaker 7 through the switching member 20.

An additional overshoot detector threshold 21 is connected to the threshold detection microphone 10 and to the switching member 20 for controlling the switching member switching between a first state (represented in the figure 2) in which the threshold detection microphone 10 and the listening microphone 22 are connected to speakers 7 and a second state in which the detection microphone threshold 10 is connected to the filtering member 19 and the listening microphone 22 is muted.

In operation, the noise picked up outside cavities by the threshold detection microphone 10 is transmitted to the additional overshoot detector threshold 21.

When the noise picked up by the microphone from threshold detection 10 is at a lower power level at a predetermined threshold of the additional detector threshold exceeded 21, for example 80 dB, the detector additional threshold overshoot 21 controls setting of the switching member 20 in the first state. The external noises picked up by microphones 10 and 22 are then transmitted to the user by the speakers 7.

When this noise is of a power level higher than the predetermined threshold of the additional detector threshold 21 exceeded, the latter commands the setting of the switching member 20 in the second state. The speakers 7 are therefore cut from the outside. Simultaneously, the noise picked up by the threshold detection microphone 10 filtered by the filtering member 19, is transmitted to the threshold overshoot detector 9. When noise filtered at a power level above a threshold predetermined threshold crossing detector 9, by example 120 dB, the threshold overshoot detector 9 controls the switch-on state of the switching devices 8, thereby activating the attenuation circuit active. When the filtered noise has a power level below the predefined threshold of the overshoot detector threshold 9, the threshold overshoot detector 9 controls the blocking state of the switch members 8 of so that only passive noise attenuation is assured.

With reference to FIG. 4, and according to a variant of the second embodiment, the helmet comprises a outdoor communication circuit including an antenna reception associated with a processing element 30 of the communication signal, and speakers 31 arranged in each cavity and connected to the processing element 30 by tilting members 32. The tilting members 32 are also connected to the switching member 20.

In this variant, provision is made, when this is possible to transmit outside noise to the speakers communication 31. To this end, the communications body switching 20 is selectively operable between a first state in which the detection microphone threshold 10 and the listening microphone 22 are connected to the tilting members 32 and a second state in which the threshold detection microphone 10 is connected to the filtering 19 and the listening microphone 22 is cut off.

The tilting members 32 are selectively actuable between a first state in which the signal communication from processing element 30 is transmitted to speakers 31 and a second state in which the switching member 20 is connected to the speakers 31. The tilting members 32 are brought into their first state when a communication signal sent by the processing element 30 reaches them and switches over to the second state in the absence of such a signal. So in presence of a communication signal, the organs of toggle 32 go into the first state to transmit primarily this signal to the speakers 31, and this, regardless of the power level of external noise or filtered noises.

Of course, the invention is not limited to described embodiments and we can bring variant embodiments without departing from the scope of the invention as defined by the claims.

Although the headset support has been illustrated in the form of an arch to which these are connected, the support could consist of a helmet or a headdress with associated ear flaps by passive mitigation means delimiting the cavities.

Although the commissioning or stopping of active mitigation organs has been described in relation with a switch 8 disposed between the processing unit 6 and the power source, we can arrange this switch between processing unit 6 and loudspeaker 7 or even between the processing unit 6 and the microphone 5. In the latter case, the processing unit does not receives no signal from microphone 5 when the organ switch is in its blocking state. The unit of processing then develops an electrical attenuation signal corresponding to an amplitude attenuation sound wave nothing.

The provision described concerning the different organs can be changed. In particular, we can plan a treatment unit common to both earbuds or still associate the microphone 10 and the detector 9 on the headset support.

In the second embodiment, one could provide that when the switching member is in the first state, the threshold detection microphones and listening devices are connected to separate speakers active attenuation circuit speakers.

Although the implementation of the second mode of realization has been described with an overshoot detector threshold 21 set to a lower threshold than the threshold 9 is exceeded, these detectors can be set to any levels relative to each other depending of the desired regulation. Indeed when noises are basically in the frequency range of passive attenuation it may be useful to cut the connection between the external microphone and the speakers without that it is necessary to put the attenuation circuit active in service.

Although in the embodiments described, the anti-noise device according to the invention is produced in the form of headphones, the noise canceling device could for example be integrated into the earpiece of a cellphone. In this case, the detection microphone threshold will preferably be the communication microphone of the telephone associated with a filtering device.

Claims (7)

Anti-noise device comprising at least one atrium (13) having a cavity (2) delimited by passive attenuation means (3), a attenuation circuit active (4) having a spatial domain of efficiency and comprising at least one electronic processing unit (6) connected to active attenuation devices (5, 7) comprising at least one microphone (5) picking up waves sound in the cavity and a loudspeaker (7) arranged in the cavity to emit attenuation sound waves active developed by the processing unit (6), and at least a switch member (8) selectively operable between a state of service of the active attenuation circuit and a quiescent state of the active attenuation circuit, characterized in that the device includes a detection microphone threshold (10) picking up noise outside the domain efficiency of the active attenuation circuit, filtering means (3, 19) associated with the microphone threshold detection to eliminate corresponding noises to the noise absorbed by the passive attenuation means, and a detector (9) for exceeding a noise threshold for control the switch member (8) in the operating state or rest of the active attenuation circuit depending a power level of the noise detected downstream of the filtering means. Anti-noise device according to claim 1, characterized in that the detection microphone threshold (10) is disposed inside the cavity (2) of the atrium (13). Anti-noise device according to claim 1, characterized in that the detection microphone threshold (10) is carried by a wall (1) of the cavity (2) of the atrium (13) for picking up noises outside the cavity, the filtering means comprising a filter (19) mounted between the detection microphone threshold (10) and the threshold overshoot detector (9). Anti-noise device according to claim 3, characterized in that it comprises two earpieces, one listening microphone (22) carried by a wall (1) of the cavity (2) of the second atrium (13) to capture the noises outside the cavity, switching means (20) connected to the threshold detection microphone (10) and to the listening microphone (22) selectively operable by an additional detector (21) for exceeding the threshold in function of a power level of the noises picked up by the threshold detection microphone (10) between a first state wherein the threshold detection microphone (10) and the listening microphone (22) are connected to speakers respective (7) and a second state in which the microphone detection device is connected to the filtering device (19) and the listening microphone is muted. Anti-noise device according to claim 4, characterized in that said respective speakers are the loudspeakers (7) of the active attenuation circuit (4). Anti-noise device according to claim 4, characterized in that it includes a communication circuit, in that said respective speakers are associated with the communication circuit and in that the device comprises means (32) for interrupting any link between microphones and said speakers respective when receiving a communication. Anti-noise device according to one of the claims previous, characterized in that a resistance acoustic (12) is arranged on the microphones (5) of the active attenuation circuit.

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