Portable sound emission device

Abstract

Provided is a portable sound emission device that reduces an unpleasant sensation caused by a sound quality change associated with a change in the orientation of a housing. A portable sound emission device 1 comprises a plurality of speakers 21, 22 and an attitude sensor 3 that detects an attitude change of a housing. In accordance with the attitude change (ψ, θ) detected by the attitude sensor 3, an acoustic processing unit 6 applies, to an acoustic signal of two or more channels, a transfer function H-1 (ψ, θ) for maintaining the acoustic characteristics of a sound wave signal that arrives at a fixed point in the real space.

Description

Portable sound emitting device

[0001] The present invention relates to a portable sound emitting device that can be carried around freely and whose installation direction can be freely changed.

[0002] In the past, enjoying music required appropriately placing large speakers and staying at an appropriate listening spot. However, in recent years, it has become possible to listen to music using mobile devices such as smartphones, and there are no longer any restrictions on where you can listen to music. However, the speakers built into mobile devices are small, which limits the enjoyment of high-quality music, high volume, or listening in groups.

[0003] Therefore, portable sound emitting devices have been known that are small, lightweight, and easy to carry, unlike conventional stationary speakers, and are equipped with speakers that are larger than those installed in smartphones, etc. Portable sound emitting devices with built-in batteries can provide a listening environment both indoors and outdoors.

[0004] Portable sound-emitting devices are increasingly being used in daily life while engaging in other activities, for example, by being brought into the kitchen or even in front of the listener in the living room. As a result, for example, a person may want to transition from being immersed in music in front of the portable sound-emitting device to listening to music as background music while moving around, or vice versa. Furthermore, a situation where a person is immersed in music alone may change to a situation where multiple people are listening to music while surrounding the portable sound-emitting device, or vice versa.

[0005] Here, a sound emitting device called a zone player has been proposed that can switch from stereo mode to monaural mode or vice versa by changing the orientation of the device (see, for example, Patent Documents 1 and 2). By applying this concept to a portable sound emitting device, for example, it is possible to switch from stereo mode by pointing the speakers horizontally, allowing the user to be immersed in music, to monaural mode by pointing the speakers upward, allowing the user to listen to music as background music or enjoy music with multiple people around.

[0006] JP 2005-136457 A JP 2019-80342 A

[0007] When the portable sound emitting device is rotated while emitting sound in a mode of two or more channels, such as stereo mode, the volume may change depending on the frequency band during the rotation and before switching to mono mode. Figure 12 shows polar plots for each frequency band when emitting sound in stereo mode.

[0008] As shown in Figure 12, for example, when a listener is relatively located within a range of 10 degrees to the left and right of the axis of symmetry between the left and right speakers, the volumes of 1000 Hz, 2000 Hz, and 8000 Hz are consistent. On the other hand, when the portable sound emitting device is rotated by more than 20 degrees, the volumes of 2000 Hz and 8000 Hz differ by nearly 5 dB. This spectral change may cause the listener rotating the portable sound emitting device to experience a temporary, unpleasant change in sound quality during the transition to monaural mode.

[0009] The present invention has been made to solve the problems of the conventional technology as described above, and its purpose is to provide a portable sound emitting device that reduces the discomfort caused by changes in sound quality that occur when the orientation of the housing is changed.

[0010] In order to achieve the above object, the portable sound emission device of the present invention comprises a plurality of speakers, a posture sensor that detects posture changes of the housing, and an acoustic processing unit that applies a transfer function that maintains the acoustic characteristics of a sound wave signal that reaches a fixed point in real space to two or more channels of acoustic signals in accordance with the posture changes detected by the posture sensor.

[0011] The transfer function may include an inverse filter of a head-related transfer function from the speaker to the fixed point after the posture change.

[0012] The apparatus may further include a storage unit that stores the inverse filter for each degree of posture change.

[0013] The acoustic processing unit may process the acoustic signal in mono mode when at least one of the speakers is positioned on the top surface, process the acoustic signal in two or more channel mode when the housing is rotated 90 degrees around the vertical axis from the mono mode state in which the speaker is facing to the side, and process the acoustic signal in mono mode when the housing is rotated 90 degrees around the vertical axis from the two or more channel mode state in which the speaker is facing to the side.

[0014] The acoustic processing unit may generate a monaural mode acoustic signal when the change in posture detected by the posture sensor reaches a threshold value.

[0015] The threshold may be set for each frequency band, and the acoustic processing unit may change the mode to monaural mode for a frequency band that has reached the threshold.

[0016] The audio processing unit may downmix the audio signal in the frequency band that has reached the threshold to one channel.

[0017] The threshold may be set for each combination of volume and frequency band, and the acoustic processing unit may change to monaural mode from a frequency band that reaches the threshold selected according to the volume.

[0018] The transfer function may further include a crosstalk cancellation filter.

[0019] According to the present invention, the discomfort caused by changes in sound quality that occur when the orientation of a portable sound emitting device is changed is reduced.

[0020] 1 is a schematic diagram showing the appearance of a portable sound emitting device. FIG. 1 is a schematic diagram showing an installation mode of a portable sound emitting device. FIG. 2 is a block diagram showing the configuration of a portable sound emitting device of a first embodiment. FIG. 3 is a schematic diagram showing the relationship between a portable sound emitting device and a listener. FIG. 4 is a flowchart showing an operation example of the portable sound emitting device of the first embodiment. FIG. 5 is a schematic diagram showing a transfer function table. FIG. 6 is a block diagram showing the configuration of a portable sound emitting device of a second embodiment. FIG. 7 is a flowchart showing an operation example of the portable sound emitting device of the second embodiment. FIG. 8 is a flowchart showing an operation example of the portable sound emitting device of the second embodiment. FIG. 9 is a block diagram showing the configuration of a portable sound emitting device of a third embodiment. FIG. 10 is a flowchart showing an operation example of the portable sound emitting device of the third embodiment. FIG. 11 is a diagram showing a polar plot in stereo mode of the portable sound emitting device.

[0021] Hereinafter, the portable sound emitting device according to each embodiment will be described in detail with reference to the drawings.

[0022] (First embodiment) Fig. 1 is a schematic diagram showing the appearance of a portable sound emitting device 1. The portable sound emitting device 1 is a device that processes an acoustic signal received from the outside, converts it into a sound wave signal, and emits sound. This portable sound emitting device 1 has a portable size that allows a listener to freely change the installation position and installation orientation. The installation orientation is 360 degrees on a horizontal plane with the up-down axis as the axis, and 360 degrees on a vertical plane with the left-right or front-back axis along the horizontal plane as the center.

[0023] The portable sound emitting device 1 has, for example, a cubic shape. Speakers 21 and 22 are distributed on two opposing sides of the six sides of the portable sound emitting device 1. The speakers 21 and 22 are, for example, dynamic, cone, or dome types, and have diaphragms that convert acoustic signals input as electrical signals into sound wave signals through physical vibrations. The speakers 21 and 22 face in opposite directions and emit sound in 180-degree opposite directions.

[0024] 2 is a schematic diagram showing an installation state of the portable sound emitting device 1. As shown in Fig. 2(a), the portable sound emitting device 1 is installed so that the speaker 21 and the speaker 22 are separated into left and right sides as seen from the listener. In this case, the portable sound emitting device 1 operates in stereo mode. The speaker 21 located on the left side as seen from the listener mainly emits the left acoustic signal SL, and the speaker 22 located on the right side as seen from the listener mainly emits the right acoustic signal SR.

[0025] As shown in Fig. 2(b), the portable sound emitting device 1 is installed so that one of the speakers 21 and 22 faces upward when viewed from the listener. Alternatively, as shown in Fig. 2(c), the portable sound emitting device 1 is installed so that one of the speakers 21 and 22 faces directly toward the listener. In this case, the portable sound emitting device 1 operates in monaural mode. That is, the speakers 21 and 22 emit a composite signal (SL+SR) of the left acoustic signal SL and the right acoustic signal SR. The output of the acoustic signal to the other of the speakers 21 and 22 that is blocked by the installation surface and the other of the speakers 21 and 22 that faces away from the listener may be stopped.

[0026] Fig. 3 is a block diagram showing the configuration of the portable sound emitting device 1. As shown in Fig. 3, the portable sound emitting device 1 is equipped with an attitude sensor 3. By analyzing the detection signal of the attitude sensor 3, the portable sound emitting device 1 senses its installation orientation and operates in stereo mode or monaural mode depending on the installation orientation. The attitude sensor 3 is, for example, an acceleration sensor that detects the direction of gravity and acceleration on the X, Y, and Z axes, a gyro sensor that detects rotation on the X, Y, and Z axes, or a six-axis sensor that detects both, and senses rotation along a horizontal plane with the up and down axes as its axis and rotation along a vertical plane with the axis along the horizontal plane as its center.

[0027] Furthermore, as shown in FIG. 3, the portable sound emitting device 1 includes, in addition to the speaker 21, the speaker 22 and the attitude sensor 3, an attitude analysis unit 4, a receiving unit 5, an acoustic processing unit 6, a transfer function table 7, a DAC 8 and an amplifier 9.

[0028] The attitude analysis unit 4 is a computer, microcomputer, or SOC (System On a Chip) having a processor, ROM, and RAM, and acquires orientation information 42 of the portable sound emission device 1 by calculation from the sensor signal of the attitude sensor 3. The attitude analysis unit 4 also has mode switching threshold information 41. The mode switching threshold information 41 is orientation information that serves as a threshold for switching from stereo mode to mono mode, or from mono mode to stereo mode. The attitude analysis unit 4 compares the orientation information 42 with the mode switching threshold information 41 to obtain a determination result 43 as to whether the orientation of the portable sound emission device 1 has reached the orientation for switching modes.

[0029] The audio processing unit 6 is a computer, microcomputer, or SOC having a processor, ROM, and RAM, or a digital filter circuit. The audio processing unit 6 includes a decoder 61 and a mode change unit 62. The decoder 61 decodes the audio signal So output by the receiving unit 5 to restore a left audio signal SL and a right audio signal SR. If the audio signal So input from the receiving unit 5 is surround data such as 5.1 channels, the decoder 61 downmixes it to a left audio signal SL and a right audio signal SR.

[0030] The mode change unit 62 switches the mode of the portable sound emission device 1 in accordance with the determination result 43 of the posture analysis unit 4. The mode change unit 62 maintains the current mode if the mode does not need to be switched. That is, in the monaural mode, the mode change unit 62 generates a composite signal (SL+SR) of the left acoustic signal SL and the right acoustic signal SR.

[0031] When the mode change unit 62 is in stereo mode and the current mode is maintained without switching the mode, the mode change unit 62 performs acoustic processing to maintain the acoustic characteristics of a sound wave signal that reaches a fixed point in real space, regardless of the installation orientation of the portable sound emission device 1. More specifically, the mode change unit 62 performs acoustic processing to simulate an installation orientation in which the speakers 21 and 22 are symmetrical to the listener, i.e., a stereo front, even if the installation orientation of the portable sound emission device 1 is changed. In other words, the mode change unit 62 performs different acoustic processing depending on the installation orientation of the portable sound emission device 1 so that the acoustic characteristics of a sound wave signal that reaches a fixed point in real space are maintained. The fixed point in real space is a point on the stereo front when sound emission is started in stereo mode and the installation orientation of the portable sound emission device 1 is not changed.

[0032] 4 is a schematic diagram showing the relationship between the portable sound emitting device 1 and a listener. As shown in FIG. 4, the portable sound emitting device 1 is tilted from the front of the stereo system by a yaw angle ψ in the horizontal direction and a pitch angle θ in the vertical direction. In this case, the head-related transfer function (HRTF) from the speaker 21 on the left side of the listener to the cavity of the concha of the listener's left ear is expressed as H ＬＬ（ψ，θ） The head-related transfer function from the speaker 21 to the cavity of the concha of the listener's right ear is defined as H ＬＲ（ψ，θ） The head-related transfer function from the speaker 22 on the right side of the listener to the cavity of the concha of the listener's right ear is defined as H ＲＲ（ψ，θ） The head-related transfer function from the speaker 22 to the cavity of the concha of the listener's left ear is defined as H ＲＬ（ψ，θ） Let's say.

[0033] When an unprocessed left acoustic signal SL is emitted from the speaker 21 and an unprocessed right acoustic signal SR is emitted from the speaker 22, the left ear acoustic signal PL that reaches the cavity of the concha of the listener's left ear and the right ear acoustic signal PR that reaches the cavity of the concha of the listener's right ear are expressed by the lower determinant (1). Note that the system from the speakers 21 and 22 to the listener's ears is regarded as a causally stable linear time-invariant system.

[0034] The above determinant (1) is replaced with the following equation (2).

[0035] In order to deliver the left acoustic signal SL to the cavity of the concha of the left ear of the listener and the right acoustic signal SR to the cavity of the concha of the right ear of the listener regardless of the orientation of the portable sound emitting device 1, the mode change unit 62 uses the inverse filter H －１ （ψ，θ） is convoluted with the left acoustic signal SL and the right acoustic signal SR. In the following equation (3), E is a unit matrix.

[0036]

[0037] Inverse filter H －１ （ψ，θ） is the matrix H （ψ，θ） Since it is the inverse matrix of

[0038] Inverse filter H －１ （ψ，θ） are stored in the transfer function table 7. The transfer function table 7 is a memory, and stores the inverse filter H －１ （ψ，θ） Each inverse filter H －１ （ψ，θ） is obtained by measuring the impulse response from the speaker 21 and the speaker 22 of the portable sound emitting device 1 to a dummy head microphone which is made by placing a microphone at the ear part of a human head model. ＬＬ（ψ，θ） , head-related transfer function H ＬＲ（ψ，θ） , head-related transfer function H ＲＲ（ψ，θ） , and the head-related transfer function H ＲＬ（ψ，θ） It is generated by obtaining

[0039] If the determination result 43 of the posture analysis unit 4 does not result in mode switching, the mode change unit 62 selects an inverse filter H from the transfer function table 7 using the orientation information of the posture analysis unit 4. －１ （ψ，θ） is called, and convolved with the left acoustic signal SL and the right acoustic signal SR as shown in the following equation (5), to obtain a new left acoustic signal SL Ｎ and right acoustic signal SR Ｎ Generate.

[0040]

[0041] This inverse filter H －１ （ψ，θ） is the head-related transfer function H ＬＲ（ψ，θ） and the head-related transfer function from the speaker 22 to the concha cavity of the listener's left ear is H ＲＬ（ψ，θ） The crosstalk is also eliminated, and the mode change unit 62 also cancels the crosstalk.

[0042] The mode change unit 62 performs a Fourier transform on the left acoustic signal SL and the right acoustic signal SR, and then applies the Fourier transform to an inverse filter H －１ （ψ，θ） Alternatively, the mode change unit 62 may process the left acoustic signal SL and the right acoustic signal SR in the time domain and apply an inverse Fourier transform to the left acoustic signal SL and the right acoustic signal SR. －１ （ψ，θ） may be convoluted.

[0043] The DAC 8 outputs the left acoustic signal SL processed by the acoustic processing unit 6. Ｎ and right acoustic signal SR Ｎ The amplifier 9 is a digital-to-analog converter that converts the analog left acoustic signal SL Ｎ and right acoustic signal SR Ｎ The left acoustic signal SL is amplified and output to the speaker 21 and the speaker 22. Ｎ The speaker 22 converts the right acoustic signal SR Ｎ is converted into a sound wave signal and emitted.

[0044] The left acoustic signal SL and the right acoustic signal SR may be stored in a memory included in the portable sound emitting device 1, or may be received externally by the receiving unit 5. The receiving unit 5 has an antenna or an infrared receiving unit, and receives an acoustic signal in the form of a radio wave signal via a wireless communication standard such as Bluetooth (registered trademark), Wi-Fi, ZigBee, wireless LAN, or infrared, demodulates the acoustic signal So in the form of digital data, and outputs the digital data to the acoustic processing unit 6.

[0045] 5 is a flowchart showing an example of the operation of the portable sound emitting device 1. In the portable sound emitting device 1, the attitude sensor 3 detects a change in the orientation of the portable sound emitting device 1 (step S01). The attitude sensor 3 inputs acceleration information corresponding to the change in orientation of the portable sound emitting device 1 as a detection signal to the attitude analysis unit 4. The attitude analysis unit 4 analyzes the acceleration indicated by the detection signal by integration or the like to generate orientation information 42 of the portable sound emitting device 1 (step S02).

[0046] After generating the orientation information 42, the posture analysis unit 4 compares the orientation information 42 with pre-stored mode switching threshold information 41 (step S03). In the comparison, it is determined whether the yaw angle ψ and pitch angle θ indicated by the mode switching threshold information 41 reach the yaw angle ψ and pitch angle θ indicated by the orientation information 42.

[0047] If the orientation information 42 reaches the mode switching threshold information 41 (step S03, Yes), the mode change unit 62 of the acoustic processing unit 6 generates a composite signal (SL+SR) by combining the left acoustic signal SL and the right acoustic signal SR generated by the decoder 61 (step S04), and outputs this composite signal (SL+SR) to both the speaker 21 and the speaker 22 (step S05).

[0048] The composite signal (SL+SR) output toward the speaker 21 on the left side as seen from the listener, and the composite signal (SL+SR) output toward the speaker 22 on the right side as seen from the listener, are converted into analog signals by the DAC 8, amplified by the amplifier 9 according to the adjusted volume, and converted into sound wave signals by the speakers 21 and 22 and emitted as sound.

[0049] The mode switching threshold information 41 may be any angle that is a boundary at which the stereo mode cannot be maintained, and may be a value less than 90 degrees, such as 70 degrees. Therefore, when either the speaker 21 or the speaker 22 is positioned on the top surface, the sound signal is already processed in mono mode. Also, when the portable sound emitting device 1 is rotated 90 degrees about the up-down axis from the mono mode state in which the speaker 21 or the speaker 22 faces sideways, the sound signal is already processed in stereo mode. When the portable sound emitting device 1 is rotated 90 degrees about the up-down axis from the stereo mode state in which the speakers 21 and 22 face sideways, the sound signal is already processed in mono mode.

[0050] On the other hand, if the direction information 42 does not reach the mode switching threshold information 41 (No in step S03), the mode change unit 62 of the acoustic processing unit 6 maintains the stereo mode in accordance with steps S06 to S10. －１ is read from the transfer function table 7 (step S06). －１ offsets the head-related transfer function from the portable sound emitting device 1, whose orientation has been changed by the yaw angle ψ and the pitch angle θ, to the listener, and also cancels crosstalk. As a result, the sound wave signal, which has been convoluted with the head-related transfer function by propagating through real space, is delivered to the listener as a left acoustic signal SL and a right acoustic signal SR.

[0051] Therefore, the mode change unit 62 changes the read inverse filter H －１ is applied to the left acoustic signal SL to obtain the left acoustic signal SL Ｎ (step S07), and the inverse filter H －１ is applied to the right acoustic signal SR to obtain the right acoustic signal SR Ｎ (Step S08). －１ The application of may be convolution in the time domain, or may be integration of the left acoustic signal SL and the right acoustic signal SR after Fourier transform.

[0052] The generated left acoustic signal SL Ｎ is outputted to the speaker 21 on the left side as seen from the listener (step S09), and the right acoustic signal SRＮ is output to the speaker 22 on the right side as seen from the listener (step S10). The positional relationship between the speakers 21 and 22 can be determined by cumulatively integrating the detection signals of the attitude sensor 3, and depending on the orientation of the portable sound emitting device 1, the speaker 22 may be on the left side as seen from the listener and the speaker 21 may be on the right side as seen from the listener, and the output destinations may be reversed.

[0053] The left acoustic signal SL is output to the speaker 21 on the left side of the listener. Ｎ and the right acoustic signal SR outputted to the speaker 22 on the right side as seen from the listener. Ｎ is converted into an analog signal by the DAC 8, amplified by the amplifier 9 according to the adjusted volume, and converted into a sound wave signal by the speakers 21 and 22 and emitted as sound.

[0054] As described above, the portable sound emitting device 1 includes a plurality of speakers 21, 22 and an attitude sensor 3 that detects attitude changes of the housing. The acoustic processing unit 6 calculates a transfer function H that maintains the acoustic characteristics of a sound wave signal that arrives at a fixed point in real space in response to the attitude change (ψ, θ) detected by the attitude sensor 3. －１ （ψ，θ） is applied to audio signals with two or more channels.

[0055] The fixed point in the real space is the transfer function H －１ （ψ，θ） corresponds to the position of the dummy head microphone where the impulse response was collected when generating the transfer function H －１ （ψ，θ） is an inverse filter of the head-related transfer function from the speakers 21 and 22 to the fixed point after a posture change.

[0056] As a result, the head-related transfer function from the portable sound emitting device 1 to the listener, which is generated due to a change in orientation, is canceled out in advance, and the sound wave signal convolved with the head-related transfer function by propagating through real space can be delivered to the listener as the left acoustic signal SL and the right acoustic signal SR. Therefore, while the orientation of the portable sound emitting device 1 is changed, the listener does not perceive changes in tone, such as changes in volume for each frequency, and discomfort felt by the listener can be reduced.

[0057] Although this portable sound emission device 1 has been described using an example in which it has two speakers 21 and 22, it may also have a mode in which a center speaker is placed between the two speakers 21 and 22 and three-channel audio signals can be output.

[0058] In addition, the above embodiment has been described in which the mode switching threshold information 41, which is a threshold for a change in posture, is compared with the change in posture detected by the posture sensor 3, but the method for switching between the stereo mode and the monaural mode is not limited to this.

[0059] As shown in FIG. 6, the transfer function table 7 stores the inverse filter H －１ （ψ，θ） For the direction information 42 for performing sound processing in monaural mode, monaural mode information for instructing a change to monaural mode is stored.

[0060] The mode change unit 62 generates a monaural signal by combining the left acoustic signal SL and the right acoustic signal SR when the monaural mode information corresponds to the orientation information 42 received from the posture analysis unit 4. In this case, the transfer function table 7 also serves as the mode switching threshold information 41.

[0061] Second Embodiment Next, a portable sound emitting device 1 according to a second embodiment will be described in detail with reference to the drawings. Note that the same components or functions as those in the first embodiment will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0062] 7 is a block diagram showing the configuration of the portable sound emission device 1 of the second embodiment. As shown in FIG. 7, the posture analysis unit 4 stores a threshold value for switching between stereo and monaural modes for each frequency band. For example, the posture analysis unit 4 stores low-frequency band mode switching threshold information 41L for the low-frequency band and high-frequency band mode switching threshold information 41H for the high-frequency band. The posture analysis unit 4 then compares each of the low-frequency band mode switching threshold information 41L and the high-frequency band mode switching threshold information 41H with the orientation information 42.

[0063] In the low frequency band, the amount of correction required to maintain the acoustic characteristics of a sound wave signal reaching a fixed point in real space may become excessive, exceeding the gain performance of the amplifier 9 and the sound emission performance of the speakers 21 and 22. Therefore, when the low frequency band mode switching threshold information 41L reaches the direction information 42, the mode change unit 62 downmixes the low frequency band to one channel and switches to mono mode, while maintaining the stereo mode for the other frequency bands.

[0064] Specifically, when the low-frequency band mode switching threshold information 41L reaches the direction information 42, the mode changing unit 62 changes the low-frequency signal SL of the left-side acoustic signal SL. ｌｏｗ and the low frequency signal SR of the right acoustic signal SR ｌｏｗ For other frequency bands, if the direction information 42 is not reached, the mode change unit 62 synthesizes the inverse filter H －１ （ψ，θ） is read out and applied to the left acoustic signal SL and the right acoustic signal SR, and the left high frequency signal SL ＮＨｉ and right high frequency signal SR ＮＨｉ Generate.

[0065] Then, the mode change unit 62 changes the left high frequency signal SL ＮＨｉ and a low-frequency monaural signal SM are synthesized and output to the speaker 21 on the left side of the listener, and a right-side high-frequency signal SR ＮＨｉ and the synthesized low frequency signal (SL ｌｏｗ +SR ｌｏｗ ) are synthesized and output to the speaker 22 on the right side of the listener.

[0066] 8 and 9 are flowcharts showing an example of the operation of the portable sound emitting device 1. When the attitude sensor 3 detects a change in the orientation of the portable sound emitting device 1 (step S11) and the attitude analysis unit 4 generates orientation information 42 (step S12), the attitude analysis unit 4 determines whether the orientation information 42 reaches the low-frequency band mode switching threshold information 41L (step S13). The attitude analysis unit 4 also determines whether the orientation information 42 reaches the high-frequency band mode switching threshold information 41H (step S14).

[0067] If the orientation information 42 reaches both the low-frequency band mode switching threshold information 41L and the high-frequency band mode switching threshold information 41H (step S13, Yes, and step S14, Yes), the mode change unit 62 of the acoustic processing unit 6 generates a composite signal (SL+SR) by combining the left acoustic signal SL and the right acoustic signal SR generated by the decoder 61 (step S15), and outputs this composite signal (SL+SR) to both the speaker 21 and the speaker 22 (step S16).

[0068] If the orientation information 42 does not reach both the low frequency band mode switching threshold information 41L and the high frequency band mode switching threshold information 41H (step S13, No and step S14, No), the mode change unit 62 selects the inverse filter H －１ from the transfer function table 7 (step S17). Then, the mode change unit 62 reads out the inverse filter H －１ is applied to the left acoustic signal SL to obtain the left acoustic signal SL Ｎ (step S18), and the inverse filter H －１ is applied to the right acoustic signal SR to obtain the right acoustic signal SR Ｎ (Step S19). The generated left acoustic signal SL Ｎ is outputted to the speaker 21 on the left side as seen from the listener (step S20), and the right acoustic signal SR Ｎ is outputted to the speaker 22 on the right side as seen from the listener (step S21).

[0069] If the orientation information 42 reaches the mode switching threshold information for the low frequency band 41L but does not reach the mode switching threshold information for the high frequency band 41H (step S13, Yes, and step S14, No), the mode change unit 62 of the acoustic processing unit 6 separates each of the left acoustic signal SL and the right acoustic signal SR into high frequency band and low frequency band signals (step S22).

[0070] The mode change unit 62 outputs the left low-frequency signal SL, which is a low-frequency signal. ｌｏｗ and right low frequency signal SR ｌｏｗ The mode change unit 62 also synthesizes the inverse filter H corresponding to the orientation information 42 to generate a low-frequency monaural signal SM (step S23). －１ from the transfer function table 7 (step S24). Then, the mode change unit 62 reads out the inverse filter H －１ The left high frequency signal SL is a high frequency signal. Ｈｉ Applying to the left high frequency signal SL ＨｉＮ (step S25), and the inverse filter H －１ The right high frequency signal SR Ｈｉ Applying to the right high frequency signal SR ＨｉＮ is generated (step S26).

[0071] Next, the mode change unit 62 outputs the low-frequency monaural signal SM and the left-side high-frequency signal SL. ＨｉＮ are combined to form the left acoustic signal SL Ｎ (Step S27). The mode change unit 62 generates the low-frequency monaural signal SM and the right-side high-frequency signal SR ＨｉＮ are combined to form the right acoustic signal SR Ｎ is generated (step S28).

[0072] The generated left acoustic signal SL Ｎ is outputted to the speaker 21 on the left side as seen from the listener (step S20), and the right acoustic signal SR Ｎ is outputted to the speaker 22 on the right side as seen from the listener (step S21).

[0073] (Effects) As described above, in this portable sound emission device 1, the mode switching threshold information 41 is set for each frequency band. Then, the acoustic processing unit 6 switches to monaural mode from the frequency band that reaches the mode switching threshold information 41. As a result, even if the amount of correction required to maintain the acoustic characteristics of a sound wave signal that reaches a fixed point in real space becomes excessive and exceeds the gain performance of the amplifier 9 and the sound emission performance of the speakers 21 and 22, it is possible to reduce discomfort to the listener.

[0074] Third Embodiment Next, a portable sound emitting device 1 according to a third embodiment will be described in detail with reference to the drawings. Note that the same reference numerals are used to designate the same configurations or functions as those in the first or second embodiment, and detailed descriptions thereof will be omitted.

[0075] 10 is a block diagram showing the configuration of the portable sound emitting device 1 of the third embodiment. As shown in FIG. 10, the threshold information storage unit 4a included in the posture analysis unit 4 stores thresholds for switching between stereo and monaural modes for each combination of volume and frequency band. For example, the posture analysis unit 4 stores low frequency band mode switching threshold information 41L for the low frequency band. Ｖ１ , 41 Ｖ２ , ... for each volume information Vo. The posture analysis unit 4 also stores high frequency band mode switching threshold information 41H for the high frequency band. The posture analysis unit 4 then stores low frequency band mode switching threshold information 41L according to the currently set volume. Ｖ１ , 41 Ｖ２ and compares it with the orientation information 42.

[0076] In the low frequency band, the amount of correction required to maintain the acoustic characteristics of the sound wave signal reaching a fixed point in the real space becomes excessive, and depending on the volume information Vo that is set, this may exceed the gain performance of the amplifier 9 and the sound emission performance of the speakers 21 and 22. Therefore, the low frequency band mode switching threshold information 41L selected according to the volume information Vo Ｖｘ When the direction information 42 is reached, the mode change unit 62 downmixes the low frequency band to one channel and switches to monaural mode while maintaining the stereo mode for the other frequency bands.

[0077] The volume information Vo may be acquired from any of the sound processing unit 6, the DAC 8, and the amplifier 9, which are involved in volume adjustment. Ｖｘ 10 is a flowchart showing an example of an operation up to determining whether the orientation information 42 reaches the target position.

[0078] 11, the posture sensor 3 detects a change in the orientation of the portable sound emitting device 1 (step S31), and the posture analysis unit 4 generates orientation information 42 (step S32). The posture analysis unit 4 also acquires volume information Vo (step S33), and generates low-frequency band mode switching threshold information 41L corresponding to the volume information Vx. Ｖｘ (Step S34). Then, the orientation information 42 is selected as the low frequency band mode switching threshold information 41L. Ｖｘ (Step S13). Thereafter, the processes from step S13 onward in FIGS. 8 and 9 are executed.

[0079] (Effects) As described above, in this portable sound emission device 1, the mode switching threshold information 41 is set for each combination of volume information Vo and frequency band. The acoustic processing unit 6 then switches to monaural mode from the frequency band that reaches the mode switching threshold information for low frequency bands 41L selected according to the volume information Vo. This makes it possible to reduce discomfort to the listener even if the gain performance of the amplifier 9 and the sound emission performance of the speakers 21 and 22 are exceeded depending on the set volume information Vo.

[0080] (Other Embodiments) As described above, several embodiments of the present invention have been described. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as defined in the claims.

[0081] 1 Portable sound emitting device 21, 22 Speaker 3 Posture sensor 4 Posture analysis unit 41 Mode switching threshold information 41L Low frequency mode switching threshold information 41L ｖ１ , 41L ｖ２ Low frequency mode switching threshold information 41H High frequency mode switching threshold information 5 Receiving unit 6 Acoustic processing unit 61 Decoder 62 Mode change unit 7 Transfer function table 8 DAC 9 Amplifier

Claims

1. A portable sound emitting device comprising: a plurality of speakers; a posture sensor that detects posture changes of a housing; and an acoustic processing unit that applies a transfer function that maintains the acoustic characteristics of a sound wave signal that reaches a fixed point in real space to two or more channels of acoustic signals in response to the posture changes detected by the posture sensor.

2. The portable sound emitting device according to claim 1, wherein the transfer function includes an inverse filter of a head-related transfer function from the speaker to the fixed point after the posture change.

3. The portable sound emitting device according to claim 2, further comprising a storage unit for storing the inverse filter for each degree of the posture change.

4. The portable sound emission device of claim 1, characterized in that the acoustic processing unit processes the acoustic signal in mono mode when at least one of the speakers is located on the upper surface, processes the acoustic signal in two or more channel mode when the housing is rotated 90 degrees about the up-down axis from the mono mode state in which the speakers are facing to the side, and processes the acoustic signal in mono mode when the housing is rotated 90 degrees about the up-down axis from the two or more channel mode state in which the speakers are facing to the side.

5. A portable sound emitting device as claimed in any one of claims 1 to 3, characterized in that the acoustic processing unit generates an acoustic signal in monaural mode when the change in posture detected by the posture sensor reaches a threshold value.

6. The portable sound emitting device according to claim 5, wherein the threshold value is set for each frequency band, and the acoustic processing unit switches to monaural mode from a frequency band in which the threshold value is reached.

7. The portable sound emitting device according to claim 6, wherein the sound processing unit down-mixes the sound signal in the frequency band that has reached the threshold value to one channel.

8. The portable sound emitting device of claim 6, wherein the threshold is set for each combination of volume and frequency band, and the acoustic processing unit changes to mono mode from the frequency band that reaches the threshold selected according to the volume.

9. The portable sound emitting device according to claim 2, wherein the transfer function further includes a crosstalk cancellation filter.

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