Phase
What is Phase?
Phase is a measure of the position of a point in time on a waveform cycle. It describes the relationship between two or more waves of the same frequency, indicating how aligned or misaligned they are in time. Phase is typically measured in degrees, with a full cycle represented by 360°
Measuring Phase:
Phase is measured in degrees (°) or radians, with 360° or 2π radians representing one complete cycle. For sound waves, we can also express phase differences in terms of time delays or distances:
Time delay (t): t = (θ / 360°) * (1 / f) - where θ is the phase angle in degrees and f is the frequency in Hz.
Distance (d): d = (θ / 360°) * λ - where λ (lambda) is the wavelength.
For example:
A 1 kHz tone (f = 1000 Hz) with a 90° phase shift has a time delay of: t = (90° / 360°) * (1 / 1000 Hz) = 0.00025 seconds or 0.25 milliseconds
At room temperature (approx. 20°C or 68°F), where the speed of sound is about 343 m/s (1125 ft/s), this corresponds to a distance of: d = 0.00025 s * 343 m/s ≈ 0.086 meters or 3.38 inches
Figure illustrating the key concepts of phase
In Phase (0°): Blue and red waves align perfectly. The purple wave shows their combined amplitude is doubled.
180° Out of Phase: The red wave is inverted compared to the blue wave which when combined, cancel out (purple line).
90° Out of Phase: The red wave is shifted by a quarter cycle. Their combination (purple) results in a wave with the same frequency but different amplitude and timing.
Phase Diagram: A circular representation of a wave cycle, showing key phase angles.
