Hz — Frequency
The hertz (Hz) is the unit of frequency — how many times a sound wave cycles per second. Low frequencies (bass) have low Hz; high frequencies (treble) have high Hz. Human hearing spans roughly 20 Hz to 20 kHz, with speech mostly in the 250–4000 Hz range.
dB — Sound Level
The decibel (dB) is a logarithmic unit of sound level (sound pressure). A 10 dB increase sounds roughly twice as loud to most people. Because it is logarithmic, two equal sources do not double the dB level.
dB(A) — A-weighted Level
dB(A) is sound level weighted to match human hearing sensitivity (which is weaker at low and very high frequencies). It is the common unit for environmental and background noise.
RT60 — Reverberation Time
RT60 is the time (in seconds) for sound to decay by 60 dB after the source stops. It describes how "echoey" a room is.
NRC — Noise Reduction Coefficient
NRC is a single-number rating (0–1) of a material's sound absorption. It is not a percentage and not sound insulation.
Rw and STC — Airborne Sound Insulation
Rw (ISO) and STC (ASTM) are single-number ratings of how well a building element blocks airborne sound. They are related but not identical.
Quick Reference Table
| Symbol | Measures | Unit |
|---|---|---|
| Hz | Frequency | hertz |
| dB | Sound level | decibel |
| dB(A) | A-weighted level | decibel |
| RT60 | Reverberation | seconds |
| NRC | Absorption | unitless (0–1) |
| Rw / STC | Airborne insulation | dB / rating |
Related Yamamah Solutions
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Frequently Asked Questions
Why is dB logarithmic? Because human hearing spans a huge range of intensities; the log scale compresses it into usable numbers.
Is dB(A) the same as dB? No — dB(A) is a frequency-weighted version that approximates how loud humans perceive a sound.
Verified Sources
- ISO 3382 / ISO 354 / ISO 717-1.
- ASTM C423 / E413.