Some time ago, we communicated from ENMO Consultancy that we have an acoustic chamber available for you as a customer to make measurements on your products. One of our requirements was « to be able to measure products in accordance with ISO 3744 – sound power measurements ». This means having a relatively low background level (background noise K1) between 100Hz and 10kHz (1/3 octave band) and a reflective surface. In our case, concrete.
To measure sound power, we not only need the background level but also need to be able to say something about the acoustic behaviour of the room. We call this the K2 value. To determine it, we need an acoustic source whose sound power we know in third bands. An ideal source for this is the Brüel & Kjaer 4204. The broadband acoustic level of this source, calibrated at 230V, is known and we can use it to determine the K2 value of the room. By determining this value, we can apply a correction and know exactly what the sound power of the product to be measured is.
Below is an image of the 4204 sound source in the acoustic chamber. A circle with 6 segments and a diameter of 1 metre has been drawn on the ground. The circle is drawn so that it is in the centre of the chamber so that the acoustic field to all directions is as equal as possible. In the ISO 3744, a calculation formula is given what the different microphone positions are (x-y-z) hence the 6 segments.
After measuring the 9 microphone positions, we can determine the K2 value and can say something about the behavior of the acoustic chamber and perform sound power measurements in accordance with ISO 3744. By measuring the chamber on a regular basis like this, we guarantee that the sound power figure we give is always correct.