Airflow noise in telephone handsets and methods for its reduction

Area of Science:

• Acoustics
• Telecommunications Engineering
• Fluid Dynamics

Background:

• Plosive sounds in speech can generate disruptive airflow noise in telephone handsets.
• This noise originates from air bursts interacting with the microphone and mouthpiece design.
• Existing handset designs may not adequately mitigate this specific type of acoustic interference.

Purpose of the Study:

• To investigate the sources and characteristics of airflow noise in telephone handsets.
• To evaluate the effectiveness of different mouthpiece port and tube configurations in reducing this noise.
• To identify optimal design parameters for minimizing airflow-induced noise in telephone microphones.

Main Methods:

• Experimental investigation of modified telephone handsets with varied port and tube arrangements.
• Utilized a narrow air stream to probe the mouthpiece and recorded microphone signals.
• Systematically analyzed the impact of single, dual, and multiple exterior hole configurations.

Main Results:

• Single microphone holes can lead to static pressure buildup and noise generation.
• Dual-hole configurations can reduce noise but may increase it for specific airflow directions due to stream interaction.
• A large number of small exterior holes (under 0.5 mm) reduced airflow noise by over 30 dB across all incident directions.
• Positioning exterior holes away from the direct line of the sound tube to the microphone is beneficial.

Conclusions:

• Telephone handset mouthpiece design significantly impacts airflow noise levels.
• Optimizing the number, size, and placement of exterior holes is crucial for noise reduction.
• A multi-hole design with numerous small apertures offers substantial broadband noise attenuation, enhancing call clarity.