In theaters, auditoriums, conference halls, and other public venues, audience members seated toward the rear frequently complain that they "cannot hear clearly." Even when a sound reinforcement system provides sufficient volume, reverberation, background noise, and phase interactions among multiple loudspeakers can significantly degrade speech intelligibility.Field measurements have shown that speech recognition rates in the rear seating areas of some theaters can be as low as 65%, causing substantial portions of spoken dialogue to be lost.
Why Are Traditional Sound Reinforcement Systems Challenging for Hearing Aid Users?
Telecoils, also known as hearing loops or induction loop systems, provide a well-established solution to this problem.
Using electromagnetic induction, a hearing loop system transmits audio signals directly to the T-coil inside a hearing aid, bypassing many of the acoustic challenges associated with sound traveling through the air.
As a result, the signal-to-noise ratio (SNR) can improve by more than 15 dB, enabling people with hearing loss to hear speech much more clearly.
How Do Telecoils Work?
A hearing loop system consists of three primary components:
- Copper Loop Cable
A loop conductor is installed around the listening area, typically beneath the floor, above the ceiling, or within surrounding walls.
- Audio Amplifier
The amplifier drives the loop and generates an alternating magnetic field carrying the audio signal.
- Hearing Aid T-Coil
The telecoil inside the user's hearing aid receives the magnetic field and converts it back into sound.
- Core Advantage
Unlike airborne sound waves, magnetic fields are largely unaffected by room reverberation and ambient noise.
As a result, hearing aid users receive a much cleaner audio signal directly through their devices without relying on microphone pickup.
Field tests have demonstrated that speech recognition rates can increase from approximately 65% to over 92%.
EN 60118-4: Four Critical Parameters That Determine System Performance
| Parameter |
Compliance Requirement |
Engineering Significance |
| Magnetic Field Strength | ≥100 mA/m, edge attenuation <3 dB | Ensures uniform coverage throughout the listening area, including rear seating positions |
| Frequency Response | 100 Hz–5 kHz, ±3 dB | Covers the full speech frequency range and preserves natural voice reproduction |
| TDMA Noise | Distortion ≤1.5% | Suppresses pulsed interference generated by mobile devices and wireless communication systems |
| Harmonic Distortion | @ 1 kHz≤3% | Prevents muffled audio and unnatural "robotic" sound characteristics |
Technology Outlook for 2025: AI Noise Cancellation and Bone-Conduction Hybrid Solutions
- AI-Powered Real-Time Noise Suppression
Next-generation telecoil systems are beginning to incorporate AI algorithms capable of identifying and suppressing transient noises such as coughing, paper rustling, and other environmental distractions.
Demonstration systems have achieved speech isolation performance approaching 95%.
- Bone-Conduction Hybrid Systems
In environments with strong magnetic fields-such as MRI facilities-bone-conduction technologies may serve as an alternative audio transmission channel through vibration sensors positioned along the jawbone.
- New European Standard: ETSI TS 103 224 (2025 Edition)
The updated standard introduces stricter accessibility requirements, including a mandatory Speech Intelligibility Index (SII) of ≥0.78.
AI-enhanced telecoil systems are expected to offer significant advantages in meeting future compliance requirements.
Design Support for EN 60118-4-Compliant Hearing Loop Systems
Shinhom provides high-quality copper loop conductors and engineering support for telecoil-based hearing loop installations.
Our audio engineering team can assist with:
- Loop magnetic field simulation based on venue dimensions
- Guidance for EN 60118-4 compliance testing
- Customized loop conductor sizing
- Amplifier matching recommendations
- System optimization for speech intelligibility and coverage uniformity
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