Frequency and Wavelength

Frequency sets pitch, wavelength sets how sound meets rooms, obstacles and absorbers.

Related

Room ModeAbsorptionCello

The problem

Bass passes through walls and bends around corners; treble dulls when you turn your head. The cause is wavelength, not power.

Physics or room

Wavelength is sound speed divided by frequency. At 20 °C, 20 Hz spans 17 m, 100 Hz 3.4 m, 1 kHz 34 cm and 10 kHz 3.4 cm. Sound bends around objects near its wavelength and reflects from much larger ones; rooms interact with bass on the same scale.

Practice and judgement

Work out the longest room dimension, listening distance and target band. Absorber thickness is judged against a quarter wavelength, so thin foam does little at 100 Hz. Avoid predicted cancellations when placing speakers, then measure.

What to listen for

Sweep 20 Hz to 20 kHz and note which bass notes swell or vanish. Repeat at different positions; treble changes as you move, bass less so. On snare and cymbals, hear whether the top arrives directly or is lost to air.

Common misunderstandings

Wavelength is the spacing between points of the same phase, not successive peaks. Treble fades faster through air, not farther. Bass is omnidirectional only when the source is small against the wavelength.

Sources

• Everest, F. Alton，Master Handbook of Acoustics（McGraw-Hill）— 波长、绕射与吸声章节核对，未引用
• Toole, Floyd，Sound Reproduction（Focal Press）— 房间与听觉章节核对，未引用

Used for fact-checking only; all prose is original.