Frequency Spectrum

Returning to our piano example above, where only a few adjacent notes around middle-C were played, if we measure the sound level with the filters successively switched from low to high, we would get a strong meter reading only with the filter for the frequency band centered around 250 Hz; all the other readings would be much lower (corresponding to the ambient room noise).

This would tell us that, if we wish to attenuate this noise, we should use a Tuned Resonant Absorber.

Figure 8. The SLM readings are plotted at the standard octave-band frequencies, in order to exhibit the narrow spectrum from four adjacent piano notes, as in Fig. 5.