## 3 Technologies Supporting Intelligent Acoustic Monitoring
### IoT in Acoustic Systems  
The IoT is a networked system that unites everyday devices with specialised systems and sensors to perform automated processes through device communication. IoT technology operates in various sectors, including residential smart spaces and urban areas, industrial operations, healthcare facilities, and military command systems. The technology depends on sensors to detect environmental data, which they transmit to analytical or control systems. The detection of sounds and acoustic waves in various environmental conditions makes acoustic sensors essential for IoT systems. Acoustic sensors serve multiple functions, including speech recognition, structural analysis, water sound wave study, and security system enhancement for monitoring purposes [13; 14; 15; 16]. MEMS (microelectromechanical system) microphones represent a significant advancement in IoT acoustic sensor technology. The combination of semiconductor technology allows manufacturers to create small devices that maintain their sound quality and sensitivity levels. MEMS microphones operate at low power levels, making them suitable for mobile devices, smart speakers, speech recognition systems, and wearable technology applications. The thin silicon membranes inside their structure convert acoustic pressure fluctuations into electrical signals. MEMS microphones have been widely adopted in IoT systems because they combine CMOS technology with other electronic systems [17; 18; 19; 20]. Acoustic analysis requires hydrophones and ultrasonic sensors as fundamental components for water environments and industrial applications. Hydrophones' underwater sound recording ability makes them specialised underwater microphones that serve oceanographic and biological monitoring, as well as sonar navigation systems. Industrial sensorsemploy hydrophones to detect pipeline leaks and monitor the condition of underwater installations. Industrial systems employ ultrasonic sensors for three main applications: quality control inspections, object detection, and medical imaging diagnostics. The IoT implements ultrasound technology for contactless distance measurements in car parking systems and logistics process automation applications [21; 22; 23; 24]. Directional microphones and microphone arrays are solutions that allow for a significant improvement in sound recording quality. Directional microphones can focus on the sound source, eliminating background noise, which is critical in conference systems, voice recording, and security applications. Microphone arrays, consisting of multiple microphones working together, enable even more precise filtering of unwanted sounds and localisation of the sound source in space. Due to beam-forming algorithms, microphones can adjust their sensitivity according to their surroundings. This makes them useful in robotics, smart voice assistants, and acoustic monitoring systems [25; 26; 27; 28]. Modern technology relies on IoT sensors and devices, including microphones, hydrophones, and ultrasonic devices. The technology extends beyond sound recording because these devices are used for environmental monitoring, detecting acoustic anomalies, and analysing building structures for critical infrastructure. The sensors in IoT systems are linked to communication modules, which enable both remote control operations and immediate data analysis. Artificial intelligence algorithms combined with these sensors enable them to record sounds and interpret their meaning. This ability opens up new possibilities for security systems, monitoring technologies, and how people interact with devices [26; 29; 30; 31]. Figure 2 illustrates a conceptual four-layer architecture for intelligent acoustic IoT systems. It encompasses sensor hardware, wireless communication protocols, edge intelligence (for example, TinyML), and cloud-based analytics and integration.