Loudspeakers only beam sound once their radiating part exceeds the wavelength.

Evidence

Although a standard loudspeaker looks like it should radiate sound in the direction that its drivers are pointing, in practice it doesn’t. This is because at many frequencies, it is small with respect to the wavelength; for example, a 200 mm (8”) loudspeaker will only start becoming directive at about 1 kHz! Note that the size of the box has very little influence; it is the size of the part that radiates the sound that matters. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2501

Categorization

• CANDY: An 8-inch speaker only beams sound above roughly 1 kHz — a satisfying gotcha for audio conversations.
• XREF: Ties to the book’s earlier wavelength-versus-source-size analysis of directivity.