Method for automatically adjusting the cockpit sound field and sound effects according to the position of the external Bluetooth speaker

Abstract

The present invention discloses a method for automatically adjusting the cockpit sound field and sound effects according to the position of an external Bluetooth speaker, and relates to the technical field of speaker adjustment. The method includes: connecting an external Bluetooth speaker wirelessly; receiving the sound wave information of the external Bluetooth speaker through a vehicle-mounted microphone, determining the position coordinates of the external Bluetooth speaker according to the received sound wave information, establishing a cockpit sound field sound effect model, configuring the playback parameters of the external Bluetooth speaker, using acoustic simulation software to simulate and test the cockpit sound field sound effect model, comparing the simulation result indicators with the actual sound field sound effects, and adjusting the external Bluetooth speaker playback strategy of the cockpit sound field sound effect model. The present invention can flexibly increase the number and quality of speakers without disassembling vehicle components, effectively making up for the defect of poor sound quality performance of the original vehicle-mounted speakers, improving the playback effect of the external Bluetooth speaker in the vehicle cockpit, and enhancing the low-cost and high-demand interactive experience of the driver and passengers for the vehicle cockpit sound.

Description

Technical Field

[0001] The present invention relates to the technical field of speaker adjustment, and a specifically proposed technical solution is a method for automatically adjusting a cockpit sound field and sound effects according to a position of an external Bluetooth speaker. Background Art

[0002] As drivers and passengers improve their driving and travel quality, they are also putting forward higher requirements for the sound effects of the cockpit speakers. The car speakers are the direct hardware for carrying and displaying the sound transmission of the smart cockpit, and their performance directly affects the cockpit sound enjoyment of the drivers and passengers.

[0003] However, due to the limitation of vehicle cost and selling price, many vehicles are equipped with low-quality on-board speakers, few in number and fixed in position. In the actual interactive experience, it is difficult for users to meet their needs for vehicle cabin sound effects by relying on their own on-board speakers. If users are not satisfied with the performance of the on-board speakers, it will be costly to disassemble and replace them, and it is also easy to cause damage to the vehicle cabin, which does not meet the user's demand for low-cost interactive experience.

[0004] To this end, we have designed a method to automatically adjust the cabin sound field and sound effects according to the position of the external Bluetooth speaker to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings in the prior art that the original car-mounted speakers are difficult to meet the requirements of the driver and passengers on the cabin sound propagation effect, and the cost of disassembly and replacement is too high, which affects the user's low-cost interactive experience demand for car use. A method for automatically adjusting the cabin sound field and sound effects according to the position of an external Bluetooth speaker is proposed for the vehicle cabin. The method aims to not destroy the original car-mounted speaker structure, and by connecting a Bluetooth speaker inside and outside the vehicle cabin, the cabin sound field and sound effects are adjusted, the vehicle cabin sound playback effect is improved, and the vehicle interactive experience demand of the driver and passengers is met.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for automatically adjusting the cockpit sound field and sound effects according to the position of an external Bluetooth speaker, comprising the following steps:

[0008] Step S101, connecting the Bluetooth speakers inside and outside the vehicle: wirelessly connecting the Bluetooth speakers and placing the Bluetooth speakers in a fixed position in the vehicle cabin;

[0009] Step S102, determining the position of the external Bluetooth speaker: receiving sound wave information of the external Bluetooth speaker through the vehicle microphone, and determining the position coordinates of the external Bluetooth speaker according to the received sound wave information;

[0010] Step S103, configuring the playback parameters of the external Bluetooth audio system: establishing a cockpit sound field sound effect model based on the location information of the external Bluetooth audio system and the location information of the driver and passengers in the vehicle, and configuring the playback parameters of the external Bluetooth audio system based on the cockpit sound field sound effect model;

[0011] Step S104, strategy matching: using acoustic simulation software to simulate and test the cockpit sound field sound effect model, comparing the simulation result index with the actual sound field sound effect of the cockpit in the car, and adjusting the external Bluetooth audio playback strategy of the cockpit sound field sound effect model according to the comparison result index;

[0012] The process of using acoustic simulation software to simulate the cockpit sound field sound effect model is as follows:

[0013] A geometric model of the vehicle cockpit is established in the simulation software, and the sound absorption coefficient and reflection coefficient are set for each surface of the vehicle cockpit. According to the actual layout of the external Bluetooth speaker, the external Bluetooth speaker is placed in the geometric model, and the position of the driver and passengers is set to simulate the auditory experience of the driver and passengers;

[0014] Run the simulation software to calculate the sound field distribution in the vehicle cabin and view the simulation results including sound pressure level distribution, spectrum response, and reverberation time;

[0015] According to the external Bluetooth audio playback parameters configured by the cockpit sound field sound effect model in step S103, turn on the external Bluetooth audio.

[0016] A recording device is placed at the driver and passenger's position to record the actual sound played by the external Bluetooth speaker, record audio data, import the audio data into the audio analysis software to measure the sound pressure level distribution, spectrum response, and reverberation time at the driver and passenger's position, and compare them with the simulation results of the simulation software. If there are differences in the comparison results, the external Bluetooth speaker playback strategy of the cockpit sound field sound effect model is adjusted until there is no difference in the comparison results or the difference in the comparison results meets the sound effect requirements of the external Bluetooth speaker, and the adjusted external Bluetooth speaker playback strategy of the cockpit sound field sound effect model is output.

[0017] Further preferably, in step S101, the method of wirelessly connecting the Bluetooth speakers inside and outside the vehicle is as follows:

[0018] Turn on the Bluetooth function: Make sure the external Bluetooth speaker is turned on and find the setting option on the car system interface;

[0019] Pairing devices: Select pairing a new device in the car system settings, activate pairing mode on the external Bluetooth audio device, the external Bluetooth audio enters the pairing state, the car system displays the audio logo, click the audio logo, and enter the pairing code to complete the pairing.

[0020] Further preferably, in step S101, the external Bluetooth speaker is arranged at a fixed position in the vehicle cabin, and is fixedly installed at the fixed position in the vehicle cabin by clamping with a clamp or sticking with Velcro.

[0021] Further preferably, in step S102, the vehicle microphone receives the broadcast information of the external Bluetooth speaker, and the vehicle microphone receives the sound waves emitted by the Bluetooth speakers inside and outside the cabin, and determines the position coordinates of the external Bluetooth speaker according to the time of the received sound wave signal, and the process is as follows:

[0022] The midpoint of the line connecting the backs of the front seats in the cockpit is taken as the coordinate origin, the x-axis direction points to the right side of the cockpit, the y-axis direction points to the front of the car, and the z-axis direction points to the top of the cockpit;

[0023] The location coordinates of the external Bluetooth speaker at the sender are , the position coordinates of the receiving end vehicle microphone are , select three reference points with known coordinates in the cockpit , and , the distance from each reference point to the external Bluetooth speaker at the transmitter minus the distance from the reference point to the vehicle microphone at the receiver equals the corresponding time difference multiplied by the speed of light, and the following equation is established:

[0024] ;

[0025] ;

[0026] ;

[0027] In the above formula, is the speed of sound propagation, Indicates The time difference measured from the reference point;

[0028] The location coordinates of the external Bluetooth speaker at the sender are , the calculation process using Newton iteration method is as follows:

[0029] ;

[0030] ;

[0031] ;

[0032] For functions Corresponding variables , , The partial derivatives of :

[0033] ;

[0034] The Newton iteration method is used for iterative update, and the formula for each iteration is as follows:

[0035] ;

[0036] In the formula, represents the number of iterations, is the inverse matrix of the Jacobian matrix, is the function value vector of the current iteration step, and its expression is as follows:

[0037] ;

[0038] Set the convergence condition, when the change between two iterations is less than the threshold Stop the iteration when:

[0039] ;

[0040] When the convergence condition is met, the final The coordinates are used as the location of the external Bluetooth speaker on the sender.

[0041] Further preferably, in step S103, an automatically adjusted cabin sound field sound effect model is established according to the position of the external Bluetooth speaker and the position of the driver and passengers in the cabin, and its expression is as follows:

[0042] ;

[0043] In the formula, is the location coordinates of the external Bluetooth speaker, is the position coordinate of the driver and passenger seats in the vehicle cabin, Indicates the distance from each external Bluetooth speaker to the driver and passengers in the vehicle cabin. Represents the unit vector from each external Bluetooth speaker to the driver and passengers in the vehicle cabin; Indicates distance Adjust the output volume of each external Bluetooth speaker. Indicates the base volume of the external Bluetooth speaker; Indicates the time delay for the sound from the external Bluetooth speaker to be transmitted to the driver and passengers in the vehicle cabin. is the speed of sound propagation, Indicates the frequency of the audio signal of the external Bluetooth speaker. Indicates the phase of each external Bluetooth speaker;

[0044] Configure the output volume of the external Bluetooth speaker in the cockpit sound field model based on the position coordinates of the external Bluetooth speaker and the position of the driver and passenger seats in the vehicle cockpit ,frequency and Phase , complete the configuration of the external Bluetooth speaker playback parameters.

[0045] Further preferably, adjusting the external Bluetooth audio playback strategy of the cockpit sound field sound effect model includes adjusting the sound source parameters of the output volume, frequency and phase of the external Bluetooth audio.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows: by wirelessly connecting Bluetooth speakers in the vehicle cockpit, the present invention can flexibly increase the number and quality of speakers without disassembling vehicle components, effectively making up for the poor sound quality of the original vehicle's onboard speakers. According to the position of the Bluetooth speakers inside and outside the cockpit, a cockpit sound field sound effect model is established, and the cockpit sound field sound effect model is simulated and tested using acoustic simulation software, and the simulation result indicators are compared with the actual sound field sound effect in the vehicle cockpit. According to the comparison result indicators, the external Bluetooth speaker playback strategy in the cockpit sound field sound effect model is adjusted to improve the playback effect of the external Bluetooth speakers in the vehicle cockpit, and enhance the low-cost and high-demand interactive experience of the driver and passengers with the vehicle cockpit sound. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The present invention provides a flow chart of a method for automatically adjusting the cockpit sound field and sound effects according to the position of an external Bluetooth speaker. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0049] Reference Figure 1 In this embodiment, a method for automatically adjusting the cockpit sound field and sound effects according to the position of an external Bluetooth speaker is proposed, and the method includes the following steps:

[0050] Step S101, connecting the Bluetooth speakers inside and outside the car: Purchase a Bluetooth speaker with good sound quality, connect the purchased Bluetooth speaker wirelessly, and place the Bluetooth speaker in a fixed position in the car cabin.

[0051] This embodiment introduces Bluetooth connection. It should be understood that the actual operation should not be limited to Bluetooth connection. Wi-Fi connection can also be used. The specific selection of wireless connection method does not affect the implementation of the technical solution. The method of wirelessly connecting the Bluetooth speakers inside and outside the car is as follows:

[0052] Turn on the Bluetooth function: Turn on the external Bluetooth speaker and make sure it is turned on, then find the setting option on the car system interface;

[0053] Pairing devices: Select pairing a new device in the car system settings, activate pairing mode on the external Bluetooth audio device, the external Bluetooth audio enters the pairing state, the car system displays the audio logo, click the audio logo, and enter the pairing code to complete the pairing.

[0054] In order to avoid disassembling the vehicle cabin finish and to be able to conveniently fix the external Bluetooth speaker, the external Bluetooth speaker in this implementation is arranged in a fixed position in the vehicle cabin. According to user needs, the external Bluetooth speaker can be fixedly installed in a fixed position in the vehicle cabin by clamping or Velcro.

[0055] In step S102, the position of the external Bluetooth speaker is determined: sound wave information of the external Bluetooth speaker is received through the vehicle microphone, and the position coordinates of the external Bluetooth speaker are determined according to the received sound wave information.

[0056] The principle is: the car microphone receives the broadcast information of the external Bluetooth speaker. After the car microphone receives the sound waves emitted by the Bluetooth speakers inside and outside the vehicle cabin, the position coordinates of the external Bluetooth speaker are determined according to the time of the received sound wave signal. The specific process is as follows:

[0057] First, determine the reference point coordinate system, with the midpoint of the line connecting the backs of the front seats in the cockpit as the coordinate origin, the x-axis pointing to the right side of the cockpit, the y-axis pointing to the front of the car, and the z-axis pointing to the top of the cockpit.

[0058] Next, select three reference points with known coordinates in the cockpit. , and These reference points can be fixed devices in the vehicle cabin that are easy to measure, and the distances from the reference points to the coordinate origin and other points can be measured manually.

[0059] Select an external Bluetooth speaker as the sound wave signal transmitter. It will periodically send a synchronous sound wave signal. Other external Bluetooth speakers and the above reference points will receive this synchronous sound wave signal and record the timestamp of the received signal. For each receiving end, calculate the difference between the time it receives the signal and the time the transmitter sends the signal.

[0060] Set the location coordinates of the external Bluetooth speaker on the sender to , the position coordinates of the receiving end vehicle microphone are .

[0061] The distance from each reference point to the external Bluetooth speaker at the transmitter minus the distance from the reference point to the in-vehicle microphone at the receiver equals the corresponding time difference multiplied by the speed of light, establishing the following equation:

[0062] ;

[0063] ;

[0064] ;

[0065] In the above formula, is the speed of sound propagation, Indicates The time difference measured from a reference point.

[0066] The location coordinates of the external Bluetooth speaker at the sender are , the calculation process using Newton iteration method is as follows:

[0067] ;

[0068] ;

[0069] ;

[0070] For functions Corresponding variables , , The partial derivatives of :

[0071] ;

[0072] Each partial derivative can be calculated using the chain rule. For example, In terms of

[0073] ;

[0074] Similarly, other partial derivatives can be calculated.

[0075] The Newton iteration method is used for iterative update, and the formula for each iteration is as follows:

[0076]

[0077] In the formula, represents the number of iterations, is the inverse matrix of the Jacobian matrix, is the function value vector of the current iteration step, and its expression is as follows:

[0078]

[0079] Set the convergence condition, when the change between two iterations is less than the threshold Stop the iteration when:

[0080]

[0081] When the convergence condition is met, the final The coordinates are used as the location of the external Bluetooth speaker on the sender.

[0082] Considering that floating-point representation and calculation in computers will have certain rounding errors, the threshold cannot be too small, otherwise it may cause numerical instability or failure to converge. Combined with engineering practice, the threshold The value range is arrive , for the dimensions of a conventional passenger vehicle cabin, the threshold in this embodiment is The best choice , in order to achieve sufficient accuracy while avoiding over-computation.

[0083] Step S103, configuring the playback parameters of the external Bluetooth speaker: based on the location information of the external Bluetooth speaker and the location information of the driver and passengers in the vehicle, a cockpit sound field sound effect model is established, and the playback parameters of the external Bluetooth speaker based on the cockpit sound field sound effect model are configured.

[0084] According to the position of the external Bluetooth speaker and the position of the driver and passengers in the cockpit, an automatically adjusted cockpit sound field sound effect model is established, and its expression is as follows:

[0085]

[0086] In the formula, is the location coordinates of the external Bluetooth speaker, The position coordinates of the driver and passenger seats in the vehicle cabin can be input by manual measurement. Indicates the distance from each external Bluetooth speaker to the driver and passengers in the vehicle cabin. Represents the unit vector from each external Bluetooth speaker to the driver and passengers in the vehicle cabin; Indicates distance Adjust the output volume of each external Bluetooth speaker. Indicates the base volume of the external Bluetooth speaker; Indicates the time delay for the sound from the external Bluetooth speaker to be transmitted to the driver and passengers in the vehicle cabin. is the speed of sound propagation, Indicates the frequency of the audio signal of the external Bluetooth speaker. Indicates the phase of each external Bluetooth speaker.

[0087] Generally, the farther the distance, the louder the volume needs to be to compensate for the attenuation of sound waves during propagation. In order to ensure that the sounds from different speakers arrive at the listener synchronously, the phase of each speaker needs to be adjusted. Phase adjustment can be achieved by calculating the time delay of sound wave signal transmission and converting this time delay into phase delay.

[0088] Configure the output volume of the external Bluetooth speaker in the cockpit sound field model based on the position coordinates of the external Bluetooth speaker and the position of the driver and passenger seats in the vehicle cockpit ,frequency and Phase , complete the configuration of the external Bluetooth speaker playback parameters.

[0089] Step S104, strategy matching: Use acoustic simulation software to simulate and test the cockpit sound field sound effect model, compare the simulation result indicators with the actual sound field sound effects in the vehicle cockpit, and adjust the external Bluetooth audio playback strategy of the cockpit sound field sound effect model based on the comparison result indicators.

[0090] The first step is simulation testing. Use acoustic simulation software (such as EASE (Enhanced Acoustic Simulator for Engineers), Odeon, CATT-Acoustic, etc.) to simulate the cockpit sound field sound effect model as follows:

[0091] A geometric model of the vehicle cockpit is established in the simulation software (including the roof, front windshield, windows, door interior, seats, cockpit instrument panel, etc. of the vehicle cockpit), the sound absorption and reflection parameters of different materials are queried, and the sound absorption coefficient and reflection coefficient are set for each surface of the vehicle cockpit in the geometric model. According to the actual layout of the external Bluetooth speaker, the external Bluetooth speaker is placed in the geometric model, and the position of the driver and passengers is set to simulate the auditory experience of the driver and passengers.

[0092] Run the simulation software to calculate the sound field distribution in the vehicle cabin and view the simulation results including sound pressure level distribution, spectrum response, and reverberation time;

[0093] The second step is the actual environment test. According to the external Bluetooth audio playback parameters configured by the cockpit sound field sound effect model in step S103, turn on the external Bluetooth audio.

[0094] A recording device is placed at the position of the driver and passenger to record the actual sound played by the external Bluetooth speaker, record the audio data, import the audio data into the audio analysis software (such as Audacity, MATLAB) to measure the sound pressure level distribution, spectrum response, and reverberation time at the position of the driver and passenger, and compare them with the simulation results of the simulation software. If there is a difference in the comparison results, the external Bluetooth speaker playback strategy of the cockpit sound field sound effect model is adjusted. The strategy includes adjusting the sound source parameters of the output volume, frequency, and phase of the external Bluetooth speaker until there is no difference in the comparison results or the difference in the comparison results meets the sound effect requirements of the external Bluetooth speaker, and the adjusted external Bluetooth speaker playback strategy of the cockpit sound field sound effect model is output.

[0095] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for automatically adjusting the cockpit sound field and sound effects according to the position of an external Bluetooth speaker, characterized in that: The following steps are involved: Step S101, connecting the external Bluetooth speakers inside and outside the vehicle: wirelessly connecting the external Bluetooth speakers and placing the external Bluetooth speakers in a fixed position in the vehicle cabin; Step S102, determining the position of the external Bluetooth speaker: receiving the sound wave information of the external Bluetooth speaker through the vehicle microphone, and determining the position coordinates of the external Bluetooth speaker according to the received sound wave information, the process is as follows: The midpoint of the line connecting the backs of the front seats in the cockpit is taken as the coordinate origin, the x-axis direction points to the right side of the cockpit, the y-axis direction points to the front of the car, and the z-axis direction points to the top of the cockpit; The location coordinates of the external Bluetooth speaker at the sender are , the position coordinates of the receiving end vehicle microphone are , select three reference points with known coordinates in the cockpit , and , the distance from each reference point to the external Bluetooth speaker at the transmitter minus the distance from the reference point to the vehicle microphone at the receiver equals the corresponding time difference multiplied by the speed of light, and the following equation is established: ； ； ； In the above formula, is the speed of sound propagation, Indicates The time difference measured from the reference point; The location coordinates of the external Bluetooth speaker at the sender are , the calculation process using Newton iteration method is as follows: ； ； ； For functions Corresponding variables , , The partial derivatives of : ； The Newton iteration method is used for iterative update, and the formula for each iteration is as follows: ； In the formula, represents the number of iterations, is the inverse matrix of the Jacobian matrix, is the function value vector of the current iteration step, and its expression is as follows: ； Set the convergence condition, when the change between two iterations is less than the threshold Stop the iteration when: ； When the convergence condition is met, the final The coordinates are used as the location of the external Bluetooth speaker on the sender; Step S103, configure the playback parameters of the external Bluetooth audio: based on the location information of the external Bluetooth audio and the location information of the driver and passengers in the vehicle, establish a cockpit sound field sound effect model, and configure the playback parameters of the external Bluetooth audio based on the cockpit sound field sound effect model. The cockpit sound field sound effect model expression is as follows: ； In the formula, is the location coordinates of the external Bluetooth speaker, is the position coordinate of the driver and passenger seats in the vehicle cabin, Indicates the distance from each external Bluetooth speaker to the driver and passengers in the vehicle cabin. Represents the unit vector from each external Bluetooth speaker to the driver and passengers in the vehicle cabin; Indicates distance Adjust the output volume of each external Bluetooth speaker. Indicates the base volume of the external Bluetooth speaker; Indicates the time delay for the sound from the external Bluetooth speaker to be transmitted to the driver and passengers in the vehicle cabin. is the speed of sound propagation, Indicates the frequency of the audio signal of the external Bluetooth speaker. Indicates the phase of each external Bluetooth speaker; Configure the output volume of the external Bluetooth speaker in the cockpit sound field model based on the position coordinates of the external Bluetooth speaker and the position of the driver and passenger seats in the vehicle cockpit ,frequency and Phase , complete the configuration of external Bluetooth speaker playback parameters; Step S104, strategy matching: using acoustic simulation software to simulate and test the cockpit sound field sound effect model, comparing the simulation result index with the actual sound field sound effect of the cockpit in the car, and adjusting the external Bluetooth audio playback strategy of the cockpit sound field sound effect model according to the comparison result index; The process of using acoustic simulation software to simulate the cockpit sound field sound effect model is as follows: A geometric model of the vehicle cockpit is established in the simulation software, and the sound absorption coefficient and reflection coefficient are set for each surface of the vehicle cockpit. According to the actual layout of the external Bluetooth speaker, the external Bluetooth speaker is placed in the geometric model, and the position of the driver and passengers is set to simulate the auditory experience of the driver and passengers; Run the simulation software to calculate the sound field distribution in the vehicle cabin and view the simulation results including sound pressure level distribution, spectrum response, and reverberation time; According to the external Bluetooth audio playback parameters configured by the cockpit sound field sound effect model in step S103, turn on the external Bluetooth audio. A recording device is placed at the driver and passenger's position to record the actual sound played by the external Bluetooth speaker, record audio data, import the audio data into the audio analysis software to measure the sound pressure level distribution, spectrum response, and reverberation time at the driver and passenger's position, and compare them with the simulation results of the simulation software. If there are differences in the comparison results, the external Bluetooth speaker playback strategy of the cockpit sound field sound effect model is adjusted until there is no difference in the comparison results or the difference in the comparison results meets the sound effect requirements of the external Bluetooth speaker, and the adjusted external Bluetooth speaker playback strategy of the cockpit sound field sound effect model is output.

2. The method of automatically adjusting the cockpit sound field and sound effects according to the position of the external Bluetooth speaker according to claim 1, characterized in that: In step S101, the method of wirelessly connecting the Bluetooth speakers inside and outside the car is as follows: Turn on the Bluetooth function: Make sure the external Bluetooth speaker is turned on and find the setting option on the car system interface; Pairing devices: Select pairing a new device in the car system settings, activate pairing mode on the external Bluetooth audio device, the external Bluetooth audio enters the pairing state, the car system displays the audio logo, click the audio logo, and enter the pairing code to complete the pairing.

3. The method of automatically adjusting the cockpit sound field and sound effects according to the position of the external Bluetooth speaker according to claim 1, characterized in that: In step S101, the external Bluetooth speaker is arranged at a fixed position in the vehicle cabin, and is fixedly installed at the fixed position in the vehicle cabin by clamping with a clamp or sticking with Velcro.

4. The method of automatically adjusting the cockpit sound field and sound effects according to the position of the external Bluetooth speaker according to claim 1, characterized in that: Adjusting the external Bluetooth speaker playback strategy of the cockpit sound field sound effect model includes adjusting the output volume, frequency and phase parameters of the external Bluetooth speaker.

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