Introduction

In the ever-advancing landscape of professional audio applications, sound reinforcement remains one of the most widely utilized acoustic technologies. The primary goal of sound reinforcement is to ensure that the speaker's voice is clearly audible in every corner of the room. A significant challenge of the Voice Lift feature is to evenly distribute sound throughout the entire space.

The CM50 ceiling microphone, employing beamforming technology and equipped with Yealink's dynamic feedback suppression algorithm, excels in sound reinforcement scenarios such as classrooms, training rooms, and large conference halls. The Yealink Dante audio solution, centered around the CM50, combined with Yealink's intelligent deployment technology, facilitates the swift and easy setup of sound reinforcement systems.

This document will primarily introduce two sound reinforcement technologies based on meeting scenarios: Sound Reinforcement and Voice Lift. It will discuss the challenges in implementing these technologies and present the Yealink professional audio solution centered around the CM50, offering a more intelligent and robust audio deployment experience to the market.

Sound Reinforcement Technology

Sound reinforcement technology is a type of audio system amplification technology that can enhance the speaker's voice within a space, ensuring that the speaker's voice can be clearly heard from any position in the room. In general, when the distance between the speaker and the audience exceeds 8 meters (26 feet), sound attenuation can cause voice clarity issues. For most listeners, introducing sound reinforcement becomes essential to ensure efficient information transmission in the space. The commonly used sound reinforcement technologies in the market can be categorized into Voice Lift and Sound Reinforcement.

Differences Between Voice Lift and Sound Reinforcement

The implementation of sound reinforcement functionality is the result of a coordinated effort between both software and hardware within an entire audio system. Audio engineers need to ensure that feedback is prevented throughout the entire audio chain while guaranteeing that each speaker achieves the appropriate gain. Compared to Sound Reinforcement systems, Voice Lift represents a more complex collaborative mechanism (generally, Sound Reinforcement merely requires feedback avoidance; a simple audio configuration can satisfy the sound reinforcement needs of the scene, whereas Voice Lift necessitates consideration of the location and size of sound sources). The following are practical issues to be considered when implementing sound reinforcement functionality.

Attenuation and Compensation of Sound

According to the principles of sound propagation, sound signals gradually attenuate as the distance between the sound source and the receiver increases. The change in sound pressure level (SPL) can be calculated using the inverse square law in physics, indicating that the SPL decreases by 6 dB each time the distance from a point source is doubled.

Here is an example of sound attenuation and compensation. We consider the speaker as a point sound source with a sound pressure level of 70 dB at a distance of 1 meter. According to the inverse square law, the relationship between sound pressure level and distance during natural attenuation is as follows. The data represents the signal attenuation at distances of 1m, 2m, 4m, 8m, and 16m from the sound source:

The table above illustrates that due to sound attenuation, speakers need to be deployed beyond 8 meters to compensate for sound (in actual deployments, sound attenuation may not be as severe due to room reflections and other factors).

Functional Scenarios

• The application of sound reinforcement in conference spaces is more focused on larger areas such as training rooms and classrooms. When the speakers in the space will only be speaking in specific areas, we recommend using sound reinforcement to meet the functional requirements. The lectern in a classroom is a typical example. Using the Yealink CM50 for sound reinforcement can effectively replace handheld microphones and create a more convenient and effortless sound amplification experience.

• Voice lift is more suitable for conference scenarios where multiple people speak from different positions due to its unique usage. When a parliamentary hall with an area of 200 square meters is equipped with a voice lift system, it is necessary to ensure that the sound is evenly distributed and consistent throughout the room when people speak from different positions. Compared to the traditional gooseneck microphone solution commonly used in such scenarios, deploying the Yealink CM50 for voice lift offers greater convenience and a more aesthetically pleasing design.

Feedback Suppression

Feedback is one of the most common and significant challenges in sound reinforcement scenarios. Essentially, it occurs when the sound from a speaker is picked up by a microphone again and replayed through the sound reinforcement system. Without suppressors or specialized handling, this process can cause the accumulation of certain high-intensity signals, resulting in howling.

Common factors causing feedback include:

1. Distance between the microphone and the speaker.

2. Directionality (polar pattern) of the microphone.

3. Acoustical characteristics of the environment, such as room reverberation.

Common feedback mitigation methods include frequency shifting and notch filtering. The Yealink CM50 microphone adopts an embedded dynamic feedback suppression algorithm, using the speaker's playback sound as a reference signal to dynamically eliminate feedback risk, coupled with an in-built frequency shifter for feedback suppression.

PAG & NAG

PAG & NAG stand for Potential Acoustic Gain Value and Needed Acoustic Gain Value, respectively. Generally, when the potential gain exceeds the needed gain, the sound reinforcement system is considered stable and unlikely to produce howling. Conversely, if the potential gain is less than the needed gain, the system's stability is lower, with a higher likelihood of resulting in howling.

Yealink provides an online PAG/NAG calculator to assist users in deployment decisions, ensuring that the deployment positions of microphones and speakers meet the needs of the reinforcement scenario, significantly reducing the calculation and design workload for audio engineers during project deployment.

Yealink's Professional Sound Reinforcement Solution Based on CM50

The Yealink CM50 beamforming microphone has built-in feedback suppression capabilities and beamforming focus capabilities, effectively addressing feedback issues. Coupled with noise cancellation and acoustic fence functions, the CM50 microphone can significantly reduce noise and interference, enhancing sound purity while greatly minimizing the likelihood of howling. Based on the CM50 microphone, Yealink has introduced an efficient automated sound reinforcement solution, reducing construction difficulty and improving deployment efficiency.

Customized Pickup Areas & Acoustic Fence Technology

Each Yealink CM50 has 8 independently operable pickup areas. Users can configure the location, size, and attributes of these pickup areas via the Yealink Room Designer, precisely defining the pickup range. With priority settings for pickup areas, users can adjust the priority of each area in the mix, further filtering out ambient noise, highlighting the speaker's voice, decreasing noise sensitivity, and reducing the risk of howling.

With Yealink Acoustic Fence technology, these customized pickup areas can actively suppress and filter out noise outside the pickup areas. In conference scenarios, noise from air conditioning vents, projectors, and water dispensers could affect sound quality; such fixed-frequency noises can easily cause feedback through frequency overlap. Acoustic Fence can significantly reduce the risk of feedback formation through filtering.

Feedback Suppression Technology

Feedback suppression technology effectively raises the system's Potential Acoustic Gain (PAG) value, reducing the likelihood of feedback in the room's audio system. The Yealink CM50 has an in-built feedback suppression module, utilizing an automatic feedback suppression algorithm coupled with a frequency shifter to suppress feedback, thereby enhancing the potential acoustic gain and controlling potential howling scenarios in conference rooms. You can customize the amplification area for use and configure additional reference signals for the feedback suppression module.

Automatic Gain Limit Adaptation and Detection

In the sound reinforcement chain, adjusting signal gain or controlling tone and frequency response through filters is challenging due to the uncertainty of feedback thresholds. The Yealink CM50, through Yealink's audio system's automatic solution, can actively detect gain limits across various frequency bands in the audio signal, assisting users in making adjustments.

Case Studies

Case Study 1: Training Room

In a training room measuring 15x10 meters, the voice from the podium area is amplified and transmitted to remote locations. In this instance, a Sound Reinforcement solution should be employed. Simply configure the CM50 as shown in the image, set the podium area as the pickup area and amplifier area.