Devices and methods for active noise cancellation

Abstract

The present invention provides an active noise cancellation system 1, which can be independent of the earphone 2 of the system 1, wherein the circuit 14 within the system 1 applies the active noise cancellation distribution 24 to the signal of the speaker in the earphone 1 to provide active noise cancellation to the user of the earphone 2, the system 1 is arranged to receive power from both an external power source and the system's battery 6, and automatically modifies the applied active noise cancellation according to whether the system 1 is connected to an external power source.

Description

Technical Field

[0001] The present invention relates to an active noise cancellation system for headphones and a method for active noise cancellation for headphones, particularly, but not limited to, a system and method suitable for use by a user in and after being removed from a vehicle. Background Technology

[0002] Acoustic noise within a vehicle is a combination of sounds from various sources, such as engine noise, wind noise, noise from wheel / rail contact with surfaces, and mechanical vibrations. Especially in the case of tracked vehicles, the acoustic noise level inside the vehicle can be quite high, requiring the use of hearing protection devices to prevent noise-induced hearing loss (NIHL).

[0003] These hearing protection devices typically include in-ear or over-ear headphones that provide passive noise attenuation in the form of a pad forming a seal between the headphones and the ear / head, enhanced by an active noise reduction (ANR) mechanism. For an ANR mechanism, a signal from a noise detection microphone is injected into the headphones and electronically subtracted from the signal fed to the speakers in the headphones, either analog or digitally. This cancels out background noise received at the wearer's ears, thereby reducing the wearer's noise exposure.

[0004] Noise within the vehicle range is at the low end of the audible spectrum, typically below 400Hz. Therefore, in-vehicle ANR headphones are optimized for performance at these frequencies, with the reduction in background noise received at the wearer's ears in this frequency range typically exceeding 10dB compared to equivalent headphones with only passive attenuation.

[0005] When headphones are worn inside a vehicle, they are typically not used solely as hearing protection; they can also be connected to the vehicle's intercom system for communication. In this configuration, power is supplied from the vehicle to the active noise-canceling circuitry within the headphones via a connecting cable. This is known as vehicle line power.

[0006] The noise outside a vehicle is usually less than the noise encountered inside the vehicle or in a moving vehicle, so when leaving the vehicle or getting out of the vehicle, users usually remove the headphones first, or alternatively, remove the communication cable from the headphones, in which case they can continue to benefit from the passive noise cancellation provided by the headphones. Summary of the Invention

[0007] According to a first aspect of the invention, an active noise cancellation system is provided, arranged for wear and / or carry by a user, the system comprising: headphones arranged to provide passive noise cancellation; at least one noise detection microphone arranged to detect noise outside the headphones; at least one speaker for generating sound in the headphones; a battery; and active noise cancellation circuitry arranged to receive a signal from the at least one noise detection microphone and apply an active noise cancellation profile to the signal to generate active noise cancellation at the at least one speaker, wherein the system is arranged to: receive electrical energy from both a power source external to the system and the battery of the system; detect when the system is connected to an external power source; and automatically modify the active noise cancellation based on whether the system is connected to an external power source.

[0008] The active noise cancellation system according to the invention can be arranged to provide active noise cancellation at a first level when connected to an external power source and at a second level when not connected to an external power source. This can be advantageous because, although the noise level outside the vehicle is generally lower than that inside the vehicle (especially when the vehicle is in motion), there may still be significantly higher ambient noise levels outside the vehicle, such as from engines of adjacent vehicles, aircraft, mechanical loading and unloading equipment, etc. The invention thus enables (typically when leaving the vehicle) automatic triggering of the second level of active noise cancellation by disconnecting the external (vehicle) power source from the system, thereby triggering a modification to the applied active noise cancellation. This modification can result in a lower level of active noise cancellation compared to the noise available when connected to an external (vehicle) power source. However, this lower level of active noise cancellation may be acceptable when no longer in the vehicle, which will significantly save power consumed by the system. This is particularly beneficial because in these cases, the active noise cancellation will be powered by the system's battery, significantly extending battery life.

[0009] Preferably, the system is configured to apply a first active noise cancellation distribution when connected to an external power source, and to apply a second active noise cancellation distribution different from the first active noise cancellation distribution when not connected to an external power source.

[0010] The aforementioned features are advantageous because the noise levels encountered when removed from the vehicle may differ significantly from those encountered while inside the vehicle. Therefore, when operating on battery power, it is advantageous to use a second active noise cancellation distribution tailored to the various noise levels that may be encountered at frequencies during removal from the vehicle. This second active noise cancellation distribution can then differ from the first active noise cancellation distribution that the wearer might use in the vehicle when connected to an external (vehicle) power source. Here, the first active noise cancellation distribution is preferably subsequently tailored to the various noise levels that may be encountered inside the vehicle.

[0011] The first active noise cancellation distribution can be more biased towards reducing low-frequency noise (encountered inside the vehicle) than the second active noise cancellation distribution. This can be particularly advantageous for noise cancellation distributions that target low-frequency noise. When connected to an external power source, it will typically tend to consume power at a higher rate than the noise cancellation distribution, rather than being specifically designed to reduce low-frequency noise.

[0012] Active noise cancellation circuitry may include active noise cancellation filter elements that allow the unfiltered portion of the spectrum to pass through unmodified, and wherein the applied filter settings differ depending on whether an external power source is connected. In this way, the connection to an external power source can automatically alter the filter characteristics of the active noise cancellation system. For example, when disconnected from an external power source, the filter characteristics can be selected to avoid active noise cancellation at frequencies associated with human speech, but when connected to an external power source, active noise cancellation at those same frequencies is permitted. This is because, when connected to an external power source, the headset may be connected to an in-vehicle intercom system, where noise cancellation at frequencies associated with human speech will not be an issue, as speech will not be received from outside the headset but only via the in-vehicle intercom system. In this scenario, the external power source may be vehicle line power with a single connecting cable that then extends between the headset and the vehicle, providing access to both the in-vehicle intercom system and the vehicle line power.

[0013] The active noise cancellation system of the present invention may include at least one audio amplifier associated with headphones for amplifying an active noise cancellation signal received from an active noise cancellation circuit. The system includes means for switching the voltage supplied to the at least one amplifier depending on whether the system is connected to an external power source. Therefore, when the system is connected to an external power source, the at least one amplifier may be powered at a higher voltage compared to when the system is disconnected from the external power source (and thus the active noise cancellation signal can then be amplified to a greater extent).

[0014] Therefore, in addition to modifying the active noise cancellation distribution and possible filter settings, or alternatively, in addition to changing the active noise cancellation distribution and possible filter settings, the power supply voltage to one or more amplifiers in the headphones can be controlled by detecting the connection and disconnection of an external power source, providing a lower voltage when disconnected from the external power source.

[0015] Powering the amplifier with a lower voltage will degrade the performance of the headphones' active noise cancellation features, but this may not have a significant impact on the performance perceived by the user. This is because the system may be exposed to lower levels of external noise when disconnected from the external power supply, which can still be adequately reduced even when the amplifier is connected to a lower voltage supply. However, lowering the supply voltage will automatically and significantly reduce the power consumed by the amplifier.

[0016] In one embodiment, the active noise cancellation system may further include a first power supply circuit arranged to be connected to an external power source and powered by both a first voltage and a second voltage lower than the first voltage; a second power supply circuit connected to or arranged to be connected to a battery and powered by both, or approximately, the second voltage and a third voltage higher than the second voltage but not higher than the first voltage; one or more switching components arranged to supply the active noise cancellation circuit with the second voltage from the first power source when connected to an external power source, and to supply the active noise cancellation circuit with the second voltage from the second power source when disconnected from the external power source; and one or more switching components arranged to supply at least one amplifier with the first voltage from the first power supply circuit when connected to an external power source, and to supply at least one amplifier with the third voltage from the second power supply circuit when disconnected from the external power source.

[0017] The above arrangement allows the same voltage source to be supplied to the active noise cancellation circuitry, regardless of whether the system is connected to or disconnected from an external power source. At the same time, when the system is disconnected from an external power source, the power supply voltage of one or more amplifiers is automatically reduced.

[0018] Preferably, the entire active noise cancellation system, including the battery, is contained within the headset, allowing the user to disconnect only the vehicle's connection cable when leaving the vehicle, disconnecting the headset from the vehicle's wiring and potentially also from the in-vehicle intercom system, thus allowing the user to subsequently leave the vehicle. However, they will then continue to benefit from active noise cancellation using the battery within the headset, which is typically a standard "AA" battery. These batteries are relatively small, lightweight, and generally easy to replace, but can provide a sufficient level of active noise cancellation when the user is away from the vehicle.

[0019] According to a second embodiment of the present invention, an active noise cancellation method is provided for headphones having an internal battery and an external power supply connected to both. The method includes detecting noise outside the headphones, applying an active noise cancellation distribution to the external noise signal, and using the active noise distribution within the headphones to provide active noise cancellation for the wearer of the headphones. The method also includes detecting when the headphones are connected to an external power supply and automatically modifying the active noise cancellation based on whether the system is connected to an external power supply.

[0020] It should be understood that the above-described method provides advantages similar to those discussed with reference to the first aspect of the present invention. Attached Figure Description

[0021] An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

[0022] Figure 1This is a schematic diagram illustrating the components of the active noise cancellation system according to the present invention;

[0023] Figure 2 It is a graphical representation of the noise levels typically experienced inside a vehicle, and shows the first active noise cancellation distribution that the system of claim 1 can use when the system is connected to an external power source; and

[0024] Figure 3 Is with Figure 2 The graphical representation corresponds to the graphical representation, but shows the noise level that the outside of the vehicle may typically experience when the system is disconnected from the external power source, as well as the distribution of active noise reduction that the system of claim 1 can apply. Detailed Implementation

[0025] Now for reference Figure 1 , Figure 1 The components of an active noise cancellation system according to the invention are schematically shown, and the system is generally indicated as 1. System 1 includes an earphone 2 having a left ear shell 3 and a right ear shell 4, each ear shell having a pad forming a seal between the ear shell and the user's head, the pad providing passive noise attenuation. Each ear shell will also contain a speaker (not shown), and one or each ear shell 3, 4 may accommodate a noise detection microphone 5 behind a protective foam insert within the ear pad.

[0026] To illustrate the components of the system, the noise detection microphone 5, independent of the earphone 2, and other components of system 1, such as... Figure 1 As shown. However, apart from the connecting cable 6, these cables are housed inside the headset 2, and therefore all cables are arranged to be carried by the user whenever the user wears the headset.

[0027] Figure 1 System 1 receives power from an internal battery 7 or via a connecting cable 6 connected to an external power source. The connecting cable 6 can, for example, be connected to a socket inside the vehicle to provide power to the vehicle's wiring. The same connecting cable 6 can also be used to connect System 1 and the headset 2 to an in-vehicle intercom system, so that the headset 2 can also be used as a communication device.

[0028] Battery 7 can be a 1.5V AA battery, small enough to be contained within the headphones 2, and generally quite readily available, allowing the headphone wearer to carry a spare battery or purchase a replacement locally if necessary. However, this limits the total usable power of such a small battery.

[0029] like Figure 1As shown, the 1.5V power supplied by the battery 7 is supplied to both the first DC to DC converter 8 and the second DC to DC converter 10. The first DC to DC converter 8 provides a 1.8V output to the first input terminal of the power switch 9, and the second DC to DC converter 10 provides a 3.3V output to the audio amplifier power switch 11.

[0030] The connecting cable 6 can typically be connected at one end to an external power supply with a voltage between 5V and 35V. At the other end, the connecting cable 6 is connected to the input of a third DC-to-DC converter 12 that provides a 5V output. When the third DC-to-DC converter (and therefore system 1) is connected to an external power supply, the third DC-to-DC converter 12 also provides a signal schematically represented by line 13 to the active noise cancellation circuit 14, indicating a connection to the active noise cancellation circuit 14. However, this indication of connection to an external power supply can also be indicated by other means, such as the availability of a 3.3V power supply from the first low-drop regulator 15 to the active noise cancellation circuit 14.

[0031] like Figure 1 As shown, the 5V output of the third DC-to-DC converter 12 is connected to: a first low-dropout regulator 15, which in turn provides 3.3V power to the active noise cancellation circuit 14; a second low-dropout regulator 16, which in turn provides 1.8V power to the power switch 9; and to the audio amplifier power switch 11.

[0032] The active noise cancellation circuit 14 includes a microcontroller and digital signal processing functions for controlling the active noise cancellation system and for providing digital signal processing in a conventional manner. The active noise cancellation circuit 14 is also schematically shown as including an active noise cancellation processing circuit 18, but in practice, the active noise cancellation processing circuit 18 is typically included within the overall noise cancellation circuit 14. In addition to inputs from two other sources, the active noise cancellation processing circuit 18 also receives input from a noise detection microphone. Arrow 19 indicates an audio input, which can be provided, for example, when connected to a vehicle via a connection cable 6, wherein the audio input can be an audio signal from an in-vehicle intercom system.

[0033] The active noise cancellation processing circuit 18 receives a second audio input, indicated by arrow 20, which is an audio input derived from a Universal Serial Bus (USB) connection. The USB-derived audio input 20 is only available when System 1 is connected to an external power source via connection cable 6, because the active noise cancellation circuit 14 requires a 3.3V power supply to process the USB-derived audio input. When System 1 is connected to an external power source, the 3.3V power supply is only available from the first low-dropout regulator 15.

[0034] The active noise cancellation processing circuit 18 provides an output signal to the audio amplifier 17 on line 21, wherein the signal is amplified by the amplifier 17 before being fed to the speakers in the ear shells 3 and 4 of the headphones 2.

[0035] First, consider the case where system 1 is connected to an external power source (e.g., vehicle wiring power) via connecting cable 6. Here, the 5V power supply is received by each of the first and second low-dropout regulators 15 and 16, as well as by the audio amplifier power switch 11. Furthermore, the active noise cancellation circuit 14 is aware of the availability of the external power source through a signal provided to it (schematically represented by line 13).

[0036] When the connecting cable 6 is connected to an external power source, the active noise cancellation circuit 14 automatically receives 1.8V power via the third DC-to-DC converter 12, the second low-dropout regulator 16, and the power switch 9. In the presence of 1.8V power from the second low-dropout regulator 16, the regulator 16 is connected to the active noise cancellation circuit 14. This is preferable to connecting the battery 7 to the active noise cancellation circuit 14 via the first DC-to-DC converter 8, thereby conserving battery power when the system is connected to an external power source.

[0037] When powered on, the active noise cancellation circuit 14, including the active noise cancellation processing circuit 18, receives a signal from the noise detection microphone 5. This signal is processed to provide an electronically subtracted signal from the signal fed to the speaker in the headphones via the signal and amplifier 17 on line 21, in order to eliminate noise that would otherwise be received by the user.

[0038] When system 1 is connected to an external power source via connection cable 6, the audio amplifier power switch 11 defaults to connecting amplifier 17 to a 5V power source from the third DC-to-DC converter 12. This voltage source is higher than the voltage received on battery power (see further discussion below) and is able to provide a higher noise cancellation signal, and therefore has more active noise reduction compared to when the amplifier is powered by a lower voltage source.

[0039] When connected to an external power source, the wearer of headset 2 may be in a vehicle. In the case of operating a tracked vehicle, the noise detection microphone 5 receives the typical noise distribution, such as... Figure 2 As shown by line 23 in the diagram. Here, as indicated by the left vertical axis, the peak noise level can reach 130 dB. The expected noise level is... Figure 2 The amplitude represented by line 23 is already processed by the active noise reduction circuit within its software. Figure 2 The gain setting, indicated by the vertical bar 24, is set at the corresponding frequency indicated along the X-axis. Furthermore, filtering is applied at frequencies above 800Hz; above this frequency, the noise level is expected to be at an acceptable level and without active noise reduction.

[0040] If the user disconnects the connection cable 6 while the system is in use (e.g., when it is removed from the vehicle), or if the system 1 is turned on without being connected to an external power source, power from the battery 7 will be received by the active noise cancellation circuit 14 via the first DC-to-DC converter 8 and the power switch 9. If no power is received from the second low-dropout regulator 16, the first DC-to-DC converter 8 will be connected to the active noise cancellation circuit 14 by default. The active noise cancellation circuit 14 will then determine that there is no signal on line 13 and therefore knows that the system is operating using battery power.

[0041] When a signal is subsequently supplied to the speakers in the earcups 3 and 4 via amplifier 17, the active noise cancellation circuit 14 recognizes that the system is powered by battery 7 and supplies a signal on line 22 to "enable" the second DC-DC converter 10 and the audio amplifier power switch 11, connecting the 3.3V power from the second DC-DC converter 10 to amplifier 17. In this way, the second DC-DC converter 10 and the audio amplifier power switch 11 are powered only when the headphones are producing audio, thus saving power at all other times and extending the life of battery 7.

[0042] In addition to the above, supplying the amplifier with 3.3V instead of 5V will approximately halve the power consumption of amplifier 17. Since this is roughly half the power consumed by system 1, (compared to supplying amplifier 17 with 5V from battery 7) this will increase battery life by approximately 25%. While this power saving will limit amplifier 17's ability to generate such a high cancellation signal compared to when the system draws power from battery 7, it will generally be acceptable. This is because, when the user is away from the vehicle, a typical noise distribution might be as follows: Figure 3 As shown in line 25, (and) Figure 2Compared to 130dB in the previous case, the noise peak is only about 100dB. For this low noise level, amplifier 17 can achieve sufficient active noise cancellation even when powered from a 3.3V supply.

[0043] As described above, when system 1 is not connected to an external power source, the noise level is expected to be... Figure 3 The amplitude is shown by line 25 in the diagram. Therefore, the second active noise reduction distribution is stored in the active noise reduction circuit 14, and in response to the failure to detect a signal on line 13 (indicating connection to an external power supply), the active noise reduction circuit 14 modifies the active noise reduction distribution applied by the active noise reduction processing circuit 18 to have the current... Figure 3 The distribution is shown in section 26. Furthermore, the filter function is applied again at frequencies above a certain level, but here, the filter function is now applied to frequencies above 250Hz, where the noise level is expected to be acceptable and therefore not subject to active noise reduction. Therefore, the reduced frequency range is subject to active noise reduction, thereby further reducing battery consumption and extending the life of battery 7.

[0044] An embodiment of the invention has been described by way of example only with reference to the accompanying drawings; however, it should be understood that many modifications can be made to this embodiment and the method employed that fall within the scope of the appended claims. In particular, it will be noted that when powered from battery 7, the described system saves power by modifying the active noise cancellation distribution applied by the active noise cancellation processing circuit 18 relative to the active noise cancellation distribution applied when system 1 is connected to an external power source, and additionally by reducing the power supply voltage supplied to amplifier 17. Both of these features reduce battery consumption; therefore, while it is advantageous to use both of these features in the system, a system using only either of these features will also extend battery life and is therefore also beneficial. Thus, it is foreseeable that system 1, described above and shown with reference to the drawings, can be modified to provide only one of the two features mentioned above.

Claims

1. An active noise cancellation system, configured to be worn and / or carried by a user, the system comprising: The headphones are configured to provide passive noise cancellation; At least one noise detection microphone is arranged to detect noise outside the headphones; At least one speaker for generating sound in the headphones; Battery; as well as An active noise cancellation circuit is arranged to receive a signal from the at least one noise detection microphone and apply active noise cancellation to the signal to generate active noise cancellation at the at least one speaker, wherein the system is arranged to receive power from both an external power source and the system's battery; Detects when the system is connected to an external power source; The applied active noise cancellation is automatically modified based on whether the system is connected to an external power source; and When connected to an external power source, a predetermined first active noise cancellation distribution is applied; and when not connected to an external power source, a predetermined second active noise cancellation distribution, different from the first active noise cancellation distribution, is applied. Wherein, the first active noise cancellation distribution is customized for active noise cancellation inside the vehicle, and the second active noise cancellation distribution is customized for active noise cancellation during unloading from the vehicle; and The first active noise reduction distribution is more biased towards reducing low-frequency noise than the second active noise reduction distribution.

2. The active noise cancellation system according to claim 1, wherein, The active noise cancellation circuit includes an active noise cancellation filter element that allows the unfiltered portion of the spectrum to pass through without modification, and wherein the applied filter settings vary depending on whether an external power supply is connected.

3. The active noise cancellation system according to claim 1 or 2, wherein, The system is configured to receive power from the external power source at a voltage exceeding that of the battery.

4. The active noise cancellation system according to claim 1 or 2, wherein, The external power source is the vehicle's electrical wiring.

5. The active noise reduction system according to claim 4, wherein, The system is configured to connect to the vehicle's in-vehicle intercom system via a connecting cable and to receive power from the vehicle's wiring via the same connecting cable.

6. The active noise cancellation system according to any one of claims 1, 2, and 5, comprising at least one audio amplifier associated with the headphones for amplifying an active noise cancellation signal received from the active noise cancellation circuit, wherein, The system includes means for switching the voltage supplied to the at least one amplifier depending on whether the system is connected to an external power source, such that when the system is connected to an external power source, the at least one amplifier is powered by a higher voltage supply, thereby achieving greater active noise reduction than when the system is disconnected from the external power source.

7. The active noise cancellation system according to claim 6, further comprising: A first power supply circuit is arranged to be connected to an external power source and powered by both a first voltage and a second voltage lower than the first voltage. A second power supply circuit is connected to or arranged to be connected to the battery and is powered by both the second voltage and a third voltage that is higher than the second voltage but not higher than the first voltage. One or more switching components are arranged to supply the active noise cancellation circuit with the second voltage from the first power source when connected to an external power source, and to supply the active noise cancellation circuit with the second voltage from the second power source when disconnected from the external power source; as well as One or more switching components are arranged to supply power from the first power supply circuit to the at least one amplifier at the first voltage when connected to an external power source, and to supply power from the second power supply circuit to the at least one amplifier at the third voltage when disconnected from the external power source.

8. The active noise cancellation system according to any one of claims 1, 2, 5 and 7, wherein, The entire system, including the battery, is contained within the headphones.

9. An active noise cancellation method for headphones having an internal battery and a connection to an external power source, the method comprising detecting noise outside the headphones and applying active noise cancellation to the external noise signal, and using the signal within the headphones to provide active noise cancellation for a wearer of the headphones, the method comprising detecting when the headphones are connected to an external power source, and automatically modifying the active noise cancellation based on whether the headphones are connected to an external power source; In response to detecting that the headphones are connected to an external power source, a predetermined first active noise cancellation distribution is applied; and in response to detecting that the headphones are not connected to an external power source, a predetermined second active noise cancellation distribution, different from the first active noise cancellation distribution, is applied; and The first active noise cancellation distribution is customized to optimize active noise cancellation inside the vehicle. in, The first active noise reduction distribution is more biased towards reducing low-frequency noise than the second active noise reduction distribution.

10. The method of claim 9, further comprising supplying power to an amplifier for a speaker of the headphones at a higher power supply voltage when the headphones are detected to be connected to an external power source, and supplying power to the amplifier for a speaker of the headphones at a lower power supply voltage when the headphones are detected to be not connected to an external power source.

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