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:
- 10 seconds
- 30 seconds
- 60 seconds
Each variety uses the thresholds as described in ISO 1996-2:2017 Annex K, which are as follows:
- 15 dB for low-frequency bands (25–125 Hz)
- 8 dB for mid-frequency bands (160–400 Hz)
- 5 dB for high-frequency bands (500–10000 Hz)
No tonality will be determined below 25 Hz and above 10000 Hz.
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 Annex K 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 the sound is tonal:
(Ltone − Llower > ΔLcrit & Ltone − Lupper > ΔLcrit = tonality)
- For ΔLcrit, use the following thresholds:
15 dB for low-frequency bands (25–125 Hz)
8 dB for mid-frequency bands (160–400 Hz)
5 dB for high-frequency bands (500–10000 Hz)- The portal does not automatically apply a correction and merely indicates whether tonality is present using the described method.
0 Comments