Audio

Digital Hearing Assistance System for Classroom Use—Hearing Aid for Hearing Enhancement System

Posted by Product Specialist

On May 13, 2025

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Digital Hearing Assistance System Overview

The proposed digital hearing assistance system is intended to enhance accessibility for students with hearing impairments. The system captures the instructor’s voice through a lavalier microphone and transmits it directly to telecoil-equipped hearing aids or cochlear implants, bypassing ambient noise to deliver clear, intelligible audio.

Technical Requirements for Digital Hearing Assistance System:

1. Digital Transceiver Unit

ListenTALK Transceiver

Frequency Band: Operates in the 1.9 GHz DECT band using Frequency-Hopping Spread Spectrum (FHSS) for interference-resistant performance.
Communication Mode: Full-duplex communication with simultaneous talk and listen functionality.
Security Protocol:
- 40-bit PIN-free group subscription
- 32-bit authentication
- 64-bit AES-level encryption for secure audio transmission
User Group Management:
Supports up to 20 simultaneous groups.
Group pairing via NFC, docking station, or software interface.
Automatic leader designation when inserted with the leader clip.
The leader can configure group mode: Listen Only, Leader Only, or Group Talk.
Audio Interface:
3.5 mm TRRS CTIA-compliant headset port compatible with standard electret microphones and earphones.
Built-in microphone with auto-detection for personal earbud use.
Display & Controls:
High-contrast 64 x 128 OLED screen with auto-dimming.
Status display: group name, volume, mute, battery level, time, signal strength, unit ID, operation mode.
Buttons: Power, Push-to-Talk, Volume Up/Down.
Power Supply:
Removable lithium-ion rechargeable battery (non-proprietary).
Optional AAA battery module (3 x AAA).
Charging via Micro-USB or dedicated charging contacts on the docking station.
Performance: Signal-to-noise ratio: ≥ 70 dB.

Frequency response: 40 Hz – 15 kHz (±3 dB).

Specifications:

Radio
Operating Frequency	1880 to 1900 MHz
Typical Range	Indoor 150 m, Outdoor 300 m depending upon conditions
Modulation	GFSK – FHSSTDD / TDMA / DCA
Security	Subscription – 40 bit ( Pin Free )Authentication – 32 bit Encryption – 64 bit
NFC FrequencyNear Field Communications	13.56 MHz
Physical
Indicators	Display – 64 x 128 OLED, Variable brightnessLED – RED / White multifunction ( Mute, Charge Status )
User Controls	Volume up, Volume Down, Talk, Power/Status, Talk Modes, Pairing
Programming	Via software and USB port on unit or via software and USB port on Docking Station
Connections	Headset- 3.5mm TRRS, CTIA complaintUSB- Micro USB, Control and Charging Charger- 4 Contact, Control and Charging
Audio
Headphone Output	Speaker Load- 16 – 32 ohm loadMax Output Power- 67 mW, 16 ohm load, Threshold of Clipping Side Tone- Adjustable
Microphone Input	Compatibility- Electret, external biasBias- 3 volt, 2 mA Current Maximum Sensitivity Requirement -28 to – 50 dBV/Pa
Internal Microphone	Switching- Auto detect on jack insertion or ManualMaximum Input Level- 109 DBSPL Gain- Adjustable, 30 dB range
System	Frequency Response- 40 Hz to 15 kHz +/- 3dB, 22kHz low pass filterSNR- 70 dB, A- weighted, Threshold of Clipping THD- 0.5% @ 1kHz, 22kHz low pass enabled
Power & Battery Management
Battery Type	Lithium – ion, rechargeable non-proprietary removable, 1200 mAhOptional- 3 AAA Battery Compartment
Typical Operating Time	Li-ion- Participant- 12 HoursAAA – Participant Mode – 7 Hours Li-ion – Leader Mode – 7 hours AAA – Leader Mode – 4 hours
Typical Charge Time	4 Hours
Power Save Modes	Power down on loss of signalPower down on disconnection of headset (1 min) Power down on charging
Compliance
Standards	FCC part 15, ICS-03, CE, RCM, RoHS, WEEEIMDA Registered

2. Digital Receiver Unit

Frequency Band: Operates on 1.9 GHz using FHSS for stable, interference-free reception.
Communication Mode: One-way communication for listening only.
Security Protocol:
40-bit group subscription
32-bit authentication
64-bit encryption for secure transmission
User Group Management:
Supports up to 10 active groups in the same area.
Group pairing via docking station or software suite.
Audio Interface:
3.5 mm TRRS CTIA-compliant port compatible with standard headphones.
Indicators & Controls:
Multifunction Green/White LED for Power, Charging, and Battery Status.
Simple operation with power and volume up/down buttons.
Power Supply:
Removable lithium-ion rechargeable battery (non-proprietary).
Optional 3 x AAA battery compartment.
Charging via Micro-USB or a docking station.
Performance:
Signal-to-noise ratio: ≥ 70 dB.
Frequency response: 40 Hz–15 kHz (±3 dB).

Specifications:

Radio
Operating Frequency	1880 to 1900 MHz
Typical Range	Indoor 150 m, Outdoor 300 m depending upon conditions
Modulation	GFSK – FHSSTDD / TDMA / DCA
Security	Subscription – 40 bit ( Pin Free )Authentication – 32 bit Encryption – 64 bit
NFC FrequencyNear Field Communications	13.56 MHz
Physical
Indicators	Variable brightness LED – Green/White multifunction ( On, Charge Status, Battery Status )
User Controls	Volume up, Volume Down, Power/Status
Programming	Via software and USB port on unit or via software and USB port on Docking Station
Connections	Headset- 3.5mm TRRS, CTIA complaintUSB- Micro USB, Control and Charging Charger- 4 Contact, Control and Charging
Audio
Headphone Output	Speaker Load- 16 – 32 ohm loadMax Output Power- 67 mW, 16 ohm load, Threshold of Clipping
System	Frequency Response- 40 Hz to 15 kHz +/- 3dB, 22kHz low pass filterSNR- 70 dB, A- weighted, Threshold of Clipping THD- 0.5% @ 1kHz, 22kHz low pass enabled
Power & Battery Management
Battery Type	Lithium – ion, rechargeable non-proprietary removable, 1200 mAhOptional- 3 AAA Battery Compartment
Typical Operating Time	Li-ion- Participant- 12 HoursAAA – Participant Mode – 7 Hours
Typical Charge Time	4 Hours
Power Save Modes	Power down on loss of signalPower down on disconnection of headset (1 min) Power down on charging
Compliance
Standards	FCC part 15, ICS-03, CE, RCM, RoHS, WEEEIMDA Registered

3. Docking Station

Capacity: Supports simultaneous charging and programming of up to four (4) digital transceivers or receivers.
Power Input: 100–240 VAC, 50/60 Hz.
Power Output: 12 VDC, 5 A (60 watts).
Connectivity: USB Type-B interface for PC-based programming using the manufacturer’s Software Suite or Management Tool.
Controls:
The pairing button is for quick group creation and device pairing.
Status button to check device information without removing it from the docking slot.
Compliance: Must meet or exceed the following certifications: UL, CE, RCM, RoHS, WEEE

Specifications:

Physical
Unit Capacity	4 units
User Control	Pairing Button – For pairing all the transceivers and receivers at onceInformation Button – Activate all the transceivers display
Interconnections
Connection/s	USB Type BPower
Compliance
Standards	FCC part 15, ICS-03, CE, RCM, RoHS, WEEE

4. Neck Loop Interface

Compatibility: Works with all standard telecoil-equipped hearing aids and cochlear implants.
Design: Comfortable, hands-free design worn around the neck.

Function: Inductively transmits received audio signals to telecoil devices for clear speech reproduction.

Physical
Connectors	3.5 mm Stereo (TRS)
Loop Cable Length	81.3 cm
Cable Lead Length	55.9 cm
Audio
Frequency Response	20 Hz – 15 KHz (+/- 3 dB ref 1 kHz)
Impedance	3 – 6 ohms @ 1 kHz
Input Sensitivity / Magnetic Field Strength	380 mVrms @ 1 kHz produces 400 mA/m
Max Power Input	1 W

Specifications:

5. Lavalier Microphone (TRRS)

Microphone Type: Omnidirectional (non-directional).
Mounting: Clip-on design for placement near the speaker’s mouth.
Connection: 3.5 mm TRRS plug compatible with the digital transceiver unit.

Application: Captures voice with minimal background interference for accurate wireless transmission.

Specifications:

Physical
Connectors	Male 3.5 mm (TRRS)
Loop Cable Length	94 cm
Weight	17.6 g
Audio
Frequency Response	65 Hz – 18 KHz
Impedance	Less than 1k Ohms
Sensitivity	-30 dB +/-3 dB (0dB = 1V / PA 1kHz)
Phantom Power	3 VDC Required

Additional Requirements for Digital Hearing Assistance System:

User Training

The contractor shall provide comprehensive user training upon delivery and installation of the system.
Training must cover operational procedures, pairing setup, battery charging, audio optimization, and troubleshooting.

Regulatory Compliance

The entire wireless communication system must fully comply with Singapore’s Infocomm Media Development Authority (IMDA) licensing and radio frequency regulations.

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