The speaking trumpet was the only voice amplification system for centuries

Evidence

The inventors were not bickering over a scientific curiosity, but rather an effect with significant military and public benefit: the only voice amplification system known at that time, and for hundreds of years to come. Morland stated very clearly the benefits this instrument might have at sea. (The speaking trumpet was once an essential instrument for amplification and direction of the voice used by the British Royal Navy for communication between ships.) — Eric J. Heller, Why You Hear What You Hear- An…, 567

Categorization

• XREF: Connects to the reader’s earlier passing on horn loading and directionality; also to naval command-and-control history.