Purpose and basic principle of looper control

Active Control of Sound

Sound control is an important science and technology in order to obtain an acoustic environment with good listening quality. Conservative sound control measures mainly focus on the use of soundproof materials, including the installation of soundproof panels or walling around the noise source, or the installation of acoustic absorbers to decrease sound reflection. For cases where the noise source cannot be easily removed or replaced, such as factories or industrial facilities, so-called active sound control methods might be needed to alleviate the sound problem.

Active sound control is an active control method applied to reduce undesired sound. It focuses on the acoustic control of sound, rather than on the soundproofing of buildings as in passive sound control. Instead, it is an active system that actively controls sound, generating anti-noise (sound pressure with antiphase) or specific acoustic radiation to absorb noise energy to suppress and counteract undesired sound. The goal is to reduce sound levels and to suppress the transmission of sound.

The principle of active sound control is that when two sound waves with the same frequency and amplitudes, but with opposite phase, are simultaneously emitted in the same place, they will combine and synchronize to form a new wave, which has neither intensity nor sound pressure, but only a phase change at the point of intersection. Thus, a fully or partially consistent antinoise wave may be generated, and if it is correctly superimposed on the noise wave in an air medium, the two waves will be canceled out and the noise level will be reduced to a great extent.

To achieve good sound control results, the system must be adjusted to achieve the desired cancelling out effect. Sound control system is generally composed of the following four subsystems: acoustic feedback control system, antenna system, acoustic wave generator, and error microphone.

The acoustic feedback control system is a part of the overall feedback control system. Its main function is to control and adjust the entire system based on the acoustic wave sound field. The main structure of the feedback control system includes the error micro phone and two branches of the feedback control loop. The first branch is the acoustic wave generator, which generates multi-frequency wave signals with different waveforms and amplitudes; the second branch is the antenna system, which effectively radiates the generated wave sounds into air.

The acoustic wave generator is essential for the sound control system as it can generate an antinoise wave or an acoustic radiation field so that it can superimpose the initial sound wave field. It also can be applied to generate other waveforms, such as frequency modulation sound wave, and balance the wave depth continuously.

The antenna system, consisting of transducers and acoustic lenses, is responsible for converting and distributing the generated waveforms into the air in order to create the desired sound wave field. It must have high performance and good directional radiation characteristics so that the generated waveforms can propagate in the shortest time.

The error microphone is used for monitoring and correction of the sound pressure field: it can accurately detect the sound pressure field changes in the air, such as frequency modulation and acoustic intensity, and then send the information to the controller to adjust the parameters of the entire sound control system.

Active sound control systems may have sound suppression capability up to 50dB with adaptive control, suitable for long-term and dynamic noise control. In addition, its system structure is relative simple, low cost, and easy to maintain. Therefore, active sound control is becoming more and more popular in many places, especially in aircraft and engine noise suppression and industrial noise control.

Lets first talk about the purpose of the active control system. Active control system is a process in which an active device, either a component or a system, is connected in the electronics’ feedback loop to achieve the desired response. A basic example of active control is using an audio system with a microphone, wherein the sound is corrected automatically by an amplifier connected in the loop. The purpose of active control is to control uncertainty by manipulating the signal’s waveforms.

Active control systems are designed to provide a faster response to external disturbances than static control systems. When implemented properly, active control systems reduce sensitivity to noise and can adjust to changing external conditions. This makes active control systems more reliable for use in harsh or unfamiliar environments.

The basic principles of active control system can be divided into three layers: feedback control, signal transmission, and transfer functions. Feedback control is the primary source of control and is achieved by sensing the environment and sending appropriate signals back to the controller. Signal transmission is used to transmit the sensed data to a control processor, which operates using transfer functions. Transfer functions cover the transformation of the signal from an input form to the output form.

The basic principle of active control system is that it allows for real-time optimization of the environment. This is made possible by providing immediate feedback and adjusting the control system based on the current conditions. By using the controller, the system can be calibrated to respond more accurately to the existing environment, while avoiding unnecessary or incorrect responses.