The Complete Handbook of Motor Vehicle Speakerphones

Chapter 1: Understanding Motor Vehicle Speakerphones

A motor vehicle speakerphone is a self-contained device that provides hands-free telephony and audio communications inside a vehicle cabin. It is distinct from a car's built-in infotainment system, and it is distinct from a simple Bluetooth headset. A vehicle speakerphone is a unit with its own microphone, speaker, amplifier, power management, and a wireless or wired communication interface. It is designed to capture the driver's voice, transmit it to a remote party, and play the remote party's voice back at a level and clarity that is intelligible despite the high ambient noise of a moving vehicle.

To understand why these devices exist as a separate product category, you have to start with the environment. A vehicle cabin is one of the most acoustically hostile places you can put a microphone. At highway speeds, tire noise, wind noise over the A-pillars, the HVAC blower, and the engine and drivetrain all contribute to a noise floor that can easily reach 70 to 80 dB SPL, sometimes peaking higher in commercial vehicles or convertibles. For comparison, a typical quiet office is around 40 dB SPL. A normal conversation happens at roughly 60 dB SPL. The fundamental problem of the motor vehicle speakerphone is to reliably transmit a voice signal that is already close to, or sometimes below, the level of the background noise it is competing against.

A basic hands-free kit from the early 2000s often failed at this task because it used a single omnidirectional microphone