High-fidelity crossover circuit

Abstract

The high-quality frequency division circuit provided by the utility model realizes the limiting of low-frequency signals and the accurate frequency division, thereby effectively avoiding the clipping distortion and power amplifier overload problems caused by the overload of low-frequency signals; meanwhile, the special post-stage bass band-pass filter and mid-high sound band-pass filter can accurately separate the audio signals according to the frequency characteristics, and the low-frequency power amplification circuit and the mid-high sound power amplification circuit are used for optimizing amplification, thereby significantly improving the precision of signal processing and the power amplification efficiency, and ensuring that the sound output by the loudspeaker has higher definition, fidelity and dynamic response capability.

Description

Technical Field

[0001] This utility model relates to the field of loudspeaker technology, and in particular to a high-quality crossover circuit. Background Technology

[0002] In modern audio systems, to improve the sound quality of loudspeakers, the input audio signal is typically crossover processed, allowing signals in different frequency ranges to drive corresponding loudspeaker units, such as high-frequency, mid-frequency, and low-frequency units. Traditional crossover circuits are prone to signal clipping and sound quality degradation when processing high dynamic range signals, thus limiting the performance of the audio system.

[0003] In summary, the problems existing in the current technology urgently need to be solved. Utility Model Content

[0004] This invention provides a high-quality crossover circuit to overcome the shortcomings of existing technologies and improve sound quality.

[0005] This utility model provides a high-quality frequency crossover circuit, including: Signal input terminal, bass limiter, power stage bass bandpass filter, bass power amplifier circuit, power stage mid-high frequency bandpass filter, mid-high frequency power amplifier circuit and speaker; The signal input terminal is used to receive external audio signals; The bass limiter is used to limit the maximum signal frequency of the external audio signal; The bass power amplifier circuit is used to amplify the power of external audio signals at bass frequencies to drive the speaker; The mid-high frequency power amplifier circuit is used to amplify the power of external audio signals with mid-high frequencies in order to drive the speaker; The speaker module outputs the amplified external audio signal; The first output terminal of the signal input terminal is connected to the input terminal of the bass limiter, the output terminal of the bass limiter is connected to the input terminal of the post-stage bass bandpass filter, the output terminal of the post-stage bass bandpass filter is connected to the input terminal of the bass power amplifier circuit, and the output terminal of the bass power amplifier circuit is connected to the first input terminal of the speaker. The second output terminal of the signal input terminal is connected to the input terminal of the mid-high frequency bandpass filter of the subsequent stage, the output terminal of the mid-high frequency bandpass filter of the subsequent stage is connected to the input terminal of the mid-high frequency power amplifier circuit, and the output terminal of the mid-high frequency power amplifier circuit is connected to the second input terminal of the speaker.

[0006] The high-quality crossover circuit provided by this utility model further includes a pre-stage bass bandpass filter; The pre-amplifier bass bandpass filter is used to filter out the bass frequency of the external audio signal based on the frequency characteristics of the external audio signal. The post-stage bass bandpass filter is used to filter out harmonics generated by the bass limiter; The first output terminal of the signal input terminal is connected to the input terminal of the bass limiter through the pre-amplifier bass bandpass filter.

[0007] The high-quality frequency crossover circuit provided by this utility model further includes a pre-stage mid-high frequency bandpass filter and a mid-high frequency limiter; The pre-amplifier mid-high frequency bandpass filter is used to filter out external audio signals with mid-high frequencies based on the frequency characteristics of the external audio signal. The mid-high frequency limiter is used to limit the maximum signal frequency of the external audio signal; The post-stage mid-high frequency bandpass filter is used to filter out the harmonics generated by the mid-high frequency limiter; The second output terminal of the signal input terminal is connected to the input terminal of the pre-amplifier mid-high frequency bandpass filter, the output terminal of the pre-amplifier mid-high frequency bandpass filter is connected to the input terminal of the mid-high frequency limiter, and the output terminal of the mid-high frequency limiter is connected to the input terminal of the post-amplifier mid-high frequency bandpass filter.

[0008] The high-quality frequency crossover circuit provided by this utility model further includes a pre-stage high-frequency bandpass filter, a high-frequency limiter, and a high-frequency bandpass filter; The pre-stage high-frequency bandpass filter is used to filter out high-frequency external audio signals based on the frequency characteristics of the external audio signals. The treble limiter is used to limit the maximum signal frequency of the external audio signal; The high-frequency bandpass filter is used to filter out the harmonics generated by the mid-high frequency limiter. The second output terminal of the signal input terminal is connected to the input terminal of the pre-stage high-frequency bandpass filter. The output terminal of the pre-stage high-frequency bandpass filter is connected to the input terminal of the high-frequency limiter. The output terminal of the high-frequency limiter is connected to the input terminal of the post-stage high-frequency bandpass filter. The output terminal of the post-stage high-frequency bandpass filter is connected to the input terminal of the high-frequency power amplifier circuit. The output terminal of the high-frequency power amplifier circuit is connected to the third input terminal of the loudspeaker.

[0009] The high-quality crossover circuit provided by this invention achieves amplitude limiting and precise frequency division of the low-frequency signal by independently processing the input audio signal into two channels: bass and mid-high frequencies. This effectively avoids clipping distortion and power amplifier overload caused by low-frequency signal overload. At the same time, by using dedicated low-frequency bandpass filters and mid-high frequency bandpass filters, the audio signal can be precisely separated according to its frequency characteristics and optimized and amplified by the low-frequency power amplifier circuit and the mid-high frequency power amplifier circuit, respectively. This significantly improves the accuracy of signal processing and power amplification efficiency, ensuring that the sound output from the speaker has higher clarity, fidelity, and dynamic response. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0011] Figure 1 This is one of the schematic diagrams of the high-quality frequency crossover circuit provided by this utility model; Figure 2 This is the second schematic diagram of the high-quality frequency crossover circuit provided by this utility model; Figure 3 This is the third schematic diagram of the high-quality frequency crossover circuit provided by this utility model; Figure 4 This is the fourth schematic diagram of the high-quality frequency crossover circuit provided by this utility model. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0013] To address the problems in the existing technology, this utility model proposes a high-quality crossover circuit to improve sound quality. The high-quality crossover circuit is described below, as follows: Figure 1 As shown, including but not limited to the following modules: A high-fidelity frequency crossover circuit, characterized in that it comprises: Signal input terminal, bass limiter, power stage bass bandpass filter, bass power amplifier circuit, power stage mid-high frequency bandpass filter, mid-high frequency power amplifier circuit and speaker; The signal input terminal is used to receive external audio signals; The bass limiter is used to limit the maximum signal frequency of the external audio signal; The bass power amplifier circuit is used to amplify the power of external audio signals at bass frequencies to drive the speaker; The mid-high frequency power amplifier circuit is used to amplify the power of external audio signals with mid-high frequencies in order to drive the speaker; The speaker module outputs the amplified external audio signal; The first output terminal of the signal input terminal is connected to the input terminal of the bass limiter, the output terminal of the bass limiter is connected to the input terminal of the post-stage bass bandpass filter, the output terminal of the post-stage bass bandpass filter is connected to the input terminal of the bass power amplifier circuit, and the output terminal of the bass power amplifier circuit is connected to the first input terminal of the speaker. The second output terminal of the signal input terminal is connected to the input terminal of the mid-high frequency bandpass filter of the subsequent stage, the output terminal of the mid-high frequency bandpass filter of the subsequent stage is connected to the input terminal of the mid-high frequency power amplifier circuit, and the output terminal of the mid-high frequency power amplifier circuit is connected to the second input terminal of the speaker.

[0014] First, the signal input terminal receives external audio signals and splits them into two outputs. The first output terminal is connected to the bass limiter, and the second output terminal is connected to the mid-high frequency bandpass filter in the power stage.

[0015] A bass limiter is used to limit the maximum frequency of external audio signals to ensure that the bass signal does not exceed a preset range, thereby avoiding unnecessary impact on the subsequent bass power amplifier circuit. The output of the bass limiter is connected to the subsequent bass bandpass filter.

[0016] The function of the post-amplifier bass bandpass filter is to bandpass filter the input bass signal, making it conform to the preset low-frequency range so that it can be transmitted to the bass power amplifier circuit. The filtered signal is then input to the bass power amplifier circuit.

[0017] The bass power amplifier circuit amplifies the bass signal to drive the bass unit in the speaker. The amplified signal is then input to the first input of the speaker through the output of the bass power amplifier circuit.

[0018] Meanwhile, the second output terminal of the signal input terminal is connected to the mid-high frequency bandpass filter of the subsequent stage. This filter is used to perform bandpass filtering on the mid-high frequency signal, so that only signals that conform to the preset mid-high frequency range are transmitted to the mid-high frequency power amplifier circuit.

[0019] The mid-high frequency power amplifier circuit amplifies the filtered mid-high frequency signal, and the amplified signal is input to the second input terminal of the speaker to drive the mid-high frequency unit in the speaker.

[0020] Finally, the speaker module outputs the amplified external audio signal, achieving crossover processing for bass and mid-high frequencies, and ensuring high-fidelity audio signal output.

[0021] In another embodiment, the bass limiter employs a diode clamping circuit to effectively limit the low-frequency signal. The diode clamping circuit limits the signal amplitude within a preset range through voltage clamping, thereby further optimizing the stability of the bass signal.

[0022] In addition, the post-amplifier bass bandpass filter can be an active filter, such as a Sallen-Key low-pass filter, to provide a steeper filter slope, thereby effectively separating low-frequency signals.

[0023] In the mid-high frequency signal path, the post-amplitude mid-high frequency bandpass filter can be a combination of multiple active filters to improve the accuracy of the bandpass filter and ensure the quality of the output signal.

[0024] This invention's high-quality crossover circuit, through its rational circuit design, effectively distinguishes between bass and mid-high frequency signals, amplifies them separately, and ultimately drives the speaker to output a high-quality audio signal. This invention features simple structure, accurate signal crossover, and excellent power amplification, making it suitable for high-fidelity audio systems, home theater systems, and other audio equipment.

[0025] As a further optional embodiment, a preamp bass bandpass filter is also included; The pre-amplifier bass bandpass filter is used to filter out the bass frequency of the external audio signal based on the frequency characteristics of the external audio signal. The post-stage bass bandpass filter is used to filter out harmonics generated by the bass limiter; The first output terminal of the signal input terminal is connected to the input terminal of the bass limiter through the pre-amplifier bass bandpass filter.

[0026] refer to Figure 2The high-quality crossover circuit also includes: a signal input terminal, a pre-amplifier bass bandpass filter, a bass limiter, a power amplifier bass bandpass filter, a power amplifier bass amplifier circuit, a power amplifier mid-high frequency bandpass filter, a power amplifier mid-high frequency amplifier circuit, and a speaker module.

[0027] First, the signal input terminal receives the external audio signal and splits it into two outputs. The first output terminal is connected to the input terminal of the bass limiter via a pre-stage bass bandpass filter. This pre-stage bass bandpass filter filters out the bass frequency signal based on the frequency characteristics of the external audio signal, ensuring that only the bass portion of the signal is transmitted to the bass limiter.

[0028] A bass limiter is used to limit the maximum frequency of an external audio signal to prevent the bass signal from exceeding a preset range and to avoid unnecessary interference with the subsequent bass power amplifier circuit. The output of the bass limiter is connected to the subsequent bass bandpass filter.

[0029] The post-amplifier bass bandpass filter receives the output signal from the bass limiter and filters out any harmonics that the bass limiter may generate. It also bandpass-filters the bass signal to ensure it meets the preset low-frequency requirements. The filtered bass signal is then transmitted to the bass power amplifier circuit, which amplifies the signal to drive the bass unit in the speaker module.

[0030] Meanwhile, the second output of the signal input is directly connected to the subsequent mid-high frequency bandpass filter. This filter is used to bandpass filter the mid-high frequency portion of the external audio signal, selecting signals that conform to the preset mid-high frequency range. The filtered mid-high frequency signal is then sent to the mid-high frequency power amplifier circuit, and after power amplification, it is finally transmitted to the mid-high frequency unit in the speaker module to drive the mid-high frequencies.

[0031] Finally, the speaker module outputs the amplified bass and mid-high frequency signals to achieve high-fidelity audio signal crossover and output.

[0032] In this embodiment, a pre-stage bass bandpass filter removes small-amplitude mid-to-high frequency signals from the signal source. This pre-stage bass bandpass filter ensures the bass limiter only processes large-amplitude bass signals, avoiding noise caused by clipping of mid-to-high frequency signals, thus significantly improving the purity of the audio signal. The post-stage bass bandpass filter effectively filters out harmonics generated by the bass limiter, ensuring the purity of the bass signal, reducing distortion caused by harmonic interference, and further improving the quality and stability of the bass signal.

[0033] As a further optional embodiment, it also includes a preamplifier mid-high frequency bandpass filter and a mid-high frequency limiter; The pre-amplifier mid-high frequency bandpass filter is used to filter out external audio signals with mid-high frequencies based on the frequency characteristics of the external audio signal. The mid-high frequency limiter is used to limit the maximum signal frequency of the external audio signal; The post-stage mid-high frequency bandpass filter is used to filter out the harmonics generated by the mid-high frequency limiter; The second output terminal of the signal input terminal is connected to the input terminal of the pre-amplifier mid-high frequency bandpass filter, the output terminal of the pre-amplifier mid-high frequency bandpass filter is connected to the input terminal of the mid-high frequency limiter, and the output terminal of the mid-high frequency limiter is connected to the input terminal of the post-amplifier mid-high frequency bandpass filter.

[0034] In this embodiment, reference Figure 3 Furthermore, a pre-amplifier mid-high frequency bandpass filter and a mid-high frequency limiter have been added to specifically process the mid-high frequency components of the external audio signal, thereby improving the accuracy of signal processing and sound quality. The specific structure and connection method are as follows: Signal splitting The signal input terminal receives external audio signals and splits them into two outputs. The first output terminal passes through the pre-amplifier bass bandpass filter and enters the bass processing path; while the second output terminal is connected to the input terminal of the pre-amplifier mid-high frequency bandpass filter to form the mid-high frequency signal processing path.

[0035] Preamp mid-high frequency bandpass filter The preamplifier mid-high frequency bandpass filter filters out mid-high frequency signals based on the frequency characteristics of the external audio signal. By allowing only mid-high frequency signals to pass through, this filter effectively isolates the low-frequency range, ensuring that the subsequent mid-high frequency limiter only processes mid-high frequency signals, thereby avoiding unnecessary interference caused by signal mixing.

[0036] Mid-high frequency limiter The output of the preamplifier's mid-high frequency bandpass filter is connected to the input of the mid-high frequency limiter. The mid-high frequency limiter is used to limit the maximum amplitude of the input signal, preventing clipping of the mid-high frequency signal during subsequent processing, while controlling the signal amplitude within a preset range to ensure signal stability and dynamic characteristics.

[0037] mid-high frequency bandpass filter for power amplifier The output of the mid-high frequency limiter is connected to the mid-high frequency bandpass filter of the subsequent stage. The main function of this filter is to filter out the harmonics and other interference signals that may be generated by the mid-high frequency limiter during the clipping process, so as to ensure that the signal finally transmitted to the mid-high frequency power amplifier circuit is pure and accurate.

[0038] Subsequent power amplification and output The filtered mid-high frequency signal then enters the mid-high frequency power amplifier circuit, and after power amplification, it is transmitted to the corresponding mid-high frequency unit in the speaker module to achieve accurate output of the mid-high frequency signal.

[0039] This embodiment effectively filters out mid-to-high frequency signals through a pre-stage mid-to-high frequency bandpass filter, ensuring good isolation between the mid-to-high frequency processing path and the bass path, thereby ensuring that signals in each frequency band receive targeted processing. A mid-to-high frequency limiter limits the amplitude of the mid-to-high frequency signals, preventing clipping caused by excessive signal amplitude. Simultaneously, a post-stage mid-to-high frequency bandpass filter further filters out harmonics that may be generated during the limiting process, ensuring the purity and stability of the mid-to-high frequency signals. By performing dedicated filtering, limiting, and power amplification on the bass and mid-to-high frequency signals respectively, high fidelity is maintained in all frequency bands, ultimately achieving high-fidelity audio signal output and significantly improving the sound quality of the entire audio system and the user's listening experience.

[0040] As a further optional embodiment, it also includes a pre-amplifier high-frequency bandpass filter, a high-frequency limiter, and a high-frequency bandpass filter; The pre-stage high-frequency bandpass filter is used to filter out high-frequency external audio signals based on the frequency characteristics of the external audio signals. The treble limiter is used to limit the maximum signal frequency of the external audio signal; The high-frequency bandpass filter is used to filter out the harmonics generated by the mid-high frequency limiter. The second output terminal of the signal input terminal is connected to the input terminal of the pre-stage high-frequency bandpass filter. The output terminal of the pre-stage high-frequency bandpass filter is connected to the input terminal of the high-frequency limiter. The output terminal of the high-frequency limiter is connected to the input terminal of the post-stage high-frequency bandpass filter. The output terminal of the post-stage high-frequency bandpass filter is connected to the input terminal of the high-frequency power amplifier circuit. The output terminal of the high-frequency power amplifier circuit is connected to the third input terminal of the loudspeaker.

[0041] refer to Figure 4 In this embodiment, in addition to the aforementioned bass and mid-high frequency processing paths, a separate path for high frequency signal processing is further provided. This path includes a pre-stage high-frequency bandpass filter, a high-frequency limiter, a post-stage high-frequency bandpass filter, and a high-frequency power amplifier circuit. Its specific structure and connection method are as follows: Signal splitting After receiving an external audio signal, the signal input terminal splits the signal into two outputs. The second output terminal supplies signals to both the mid-high frequency processing path and the high frequency processing path.

[0042] Preamp tweeter bandpass filter The second output terminal of the signal input is connected to the input terminal of the pre-amplifier high-frequency bandpass filter. This filter selects signals that meet the preset high-frequency range based on the frequency characteristics of the external audio signal, thereby ensuring that only high-frequency signals enter the subsequent processing stages.

[0043] Tweeter limiter The output of the preamplifier bandpass filter is connected to the input of the tweeter limiter. The tweeter limiter is used to limit the maximum amplitude of the input signal, preventing over-amplification or clipping of high-frequency signals during processing, thereby reducing noise and distortion that may be introduced during the limiting process.

[0044] Power amplifier treble bandpass filter The output of the tweeter limiter is connected to the input of the subsequent tweeter bandpass filter. The subsequent tweeter bandpass filter is mainly used to filter out harmonics and other interference signals generated by the clipping of the tweeter limiter, ensuring that the signal sent to the tweeter power amplifier circuit is pure and conforms to the preset high-frequency characteristics.

[0045] High-frequency power amplification and output The output of the high-frequency bandpass filter is connected to the input of the high-frequency power amplifier circuit. The high-frequency power amplifier circuit amplifies the filtered high-frequency signal, and the amplified signal is transmitted from its output to the third input of the speaker module, thereby driving the tweeter unit to work and achieving effective reproduction of the high-frequency signal.

[0046] This embodiment adds an independent high-frequency processing path. The pre-stage high-frequency bandpass filter can accurately filter out the high-frequency components based on the frequency characteristics of the external audio signal, ensuring that the subsequent high-frequency limiter only processes the target signal and effectively avoids interference from low-frequency and mid-frequency components. The high-frequency limiter limits the maximum signal amplitude to prevent over-amplification and clipping. Furthermore, the subsequent high-frequency bandpass filter filters out harmonics and noise generated during the limiting process, ensuring a clean and pure signal sent to the high-frequency power amplifier circuit. By adding an independent high-frequency processing path to the traditional crossover circuit, this invention is more suitable for applications requiring high-precision, high-fidelity audio processing, such as high-end audio systems, home theater systems, and professional recording studio equipment, further expanding the application scope of this invention.

[0047] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0048] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A high-fidelity frequency crossover circuit, characterized in that, include: Signal input terminal, bass limiter, power stage bass bandpass filter, bass power amplifier circuit, power stage mid-high frequency bandpass filter, mid-high frequency power amplifier circuit and speaker; The signal input terminal is used to receive external audio signals; The bass limiter is used to limit the maximum signal frequency of the external audio signal; The bass power amplifier circuit is used to amplify the power of external audio signals at bass frequencies to drive the speaker; The mid-high frequency power amplifier circuit is used to amplify the power of external audio signals with mid-high frequencies in order to drive the speaker; The speaker module outputs the amplified external audio signal; The first output terminal of the signal input terminal is connected to the input terminal of the bass limiter, the output terminal of the bass limiter is connected to the input terminal of the post-stage bass bandpass filter, the output terminal of the post-stage bass bandpass filter is connected to the input terminal of the bass power amplifier circuit, and the output terminal of the bass power amplifier circuit is connected to the first input terminal of the speaker. The second output terminal of the signal input terminal is connected to the input terminal of the mid-high frequency bandpass filter of the subsequent stage, the output terminal of the mid-high frequency bandpass filter of the subsequent stage is connected to the input terminal of the mid-high frequency power amplifier circuit, and the output terminal of the mid-high frequency power amplifier circuit is connected to the second input terminal of the speaker.

2. The high-fidelity crossover circuit according to claim 1, characterized in that, It also includes a preamp bass bandpass filter; The pre-amplifier bass bandpass filter is used to filter out the bass frequency of the external audio signal based on the frequency characteristics of the external audio signal. The post-stage bass bandpass filter is used to filter out harmonics generated by the bass limiter; The first output terminal of the signal input terminal is connected to the input terminal of the bass limiter through the pre-amplifier bass bandpass filter.

3. The high-fidelity crossover circuit according to claim 1, characterized in that, It also includes a preamplifier mid-high frequency bandpass filter and a mid-high frequency limiter; The pre-amplifier mid-high frequency bandpass filter is used to filter out external audio signals with mid-high frequencies based on the frequency characteristics of the external audio signal. The mid-high frequency limiter is used to limit the maximum signal frequency of the external audio signal; The post-stage mid-high frequency bandpass filter is used to filter out harmonics generated by the mid-high frequency limiter; The second output terminal of the signal input terminal is connected to the input terminal of the pre-amplifier mid-high frequency bandpass filter, the output terminal of the pre-amplifier mid-high frequency bandpass filter is connected to the input terminal of the mid-high frequency limiter, and the output terminal of the mid-high frequency limiter is connected to the input terminal of the post-amplifier mid-high frequency bandpass filter.

4. The high-fidelity crossover circuit according to claim 3, characterized in that, It also includes a pre-amplifier high-frequency bandpass filter, a high-frequency limiter, and a power amplifier high-frequency bandpass filter; The pre-stage high-frequency bandpass filter is used to filter out high-frequency external audio signals based on the frequency characteristics of the external audio signals. The treble limiter is used to limit the maximum signal frequency of the external audio signal; The high-frequency bandpass filter is used to filter out the harmonics generated by the mid-high frequency limiter. The second output terminal of the signal input terminal is connected to the input terminal of the pre-stage high-frequency bandpass filter. The output terminal of the pre-stage high-frequency bandpass filter is connected to the input terminal of the high-frequency limiter. The output terminal of the high-frequency limiter is connected to the input terminal of the post-stage high-frequency bandpass filter. The output terminal of the post-stage high-frequency bandpass filter is connected to the input terminal of the high-frequency power amplifier circuit. The output terminal of the high-frequency power amplifier circuit is connected to the third input terminal of the loudspeaker.

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