Tonality is the degree to which a sound contains distinct, audible tones (peaks at specific frequencies), rather than just broadband noise. A tonal sound is perceived by people as much more disruptive than an equally loud, noisy sound. For example:
- A fan with a distinct humming sound
- A humming transformer
- A heat pump with a single-frequency beep
That is why tonality is often penalized in regulations. In the Netherlands, the penalty is 5 dB. It is crucial to establish tonality in a simple and legally sound manner.
How can tonality be determined in the portal
We currently offer tonality determination using 3 different sampling periods, each with a 5 dB limit
- 10 seconds
- 30 seconds
- 60 seconds
In the portal, the properties can be found under the "Spectra" category on the graphics page
Example of a measurement over which the tonality calculation with a sample rate of 60 seconds has been performed. The discovered frequencies can be read from the Hz y-axis, displayed on the right side in this example.
The used method as determined in ISO1996-2:2017 is as follows:
- Compare the level of a 1/3 octave band with the adjacent bands, using an average over, for example, 10-30 seconds (most common), to 1 minute (occasionally). Tonality must be determined over a representative, sufficiently long period during which the tone is audible and stationary. Many environmental services implicitly ask: "Would a resident perceive this as a continuous tone?"
- If the difference between both bands is large enough (In the Netherlands > 5 dB) → sound is tonal. So: (Ltone − Llower ≥ ΔLcrit & Ltone − Lupper ≥ ΔLcrit = tonality)
- The portal does not automatically apply a correction and merely indicates whether tonality is present using the described method and a 5 dB limit.
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