The equation used to calculate standing waves is as follows:
Hz = speed of sound (340.29 meters per second)
length of room x 2
So to simplify this equation; to find out the fundamental frequency multiply each dimension by 2, then with this number divide it by the speed of sound. So for example using the dimensions in the diagram above these are the results we got using the measurement 7.848 meters:
7.848 x 2 = 15.696
340.29 (speed of sound in meters)
15.696 = 21.6 Hz (this is the fundamental frequency)
Once we worked out the fundamental we then multiply this by 1,2,3,4,5 and so on until we reach 300Hz. The reason for doing this is to create multiples of the fundamental frequencies that may cause standing waves within the room, we only calculate up too 300Hz because frequencies below 300Hz have enough energy to cause standing waves although frequencies above 300Hz can be dealt with using absorption panels and diffusers. This equation helped us work out the axial modes of room 11.
With our results using the above equation we then played a sine wave at the resulting frequencies, what we noticed was that not all frequencies calculated created standing waves. Although in our group we were working with the measurement 7.848 meters, at certain frequencies we could hear at certain parts of the room resonant frequencies i.e. the window at the corner of the room resonating.
Standing waves create problems for performers, sound engineers and the audience within a venue! Untreated standing waves will cause certain frequencies to either be increased in amplitude or cancelled due to phase cancellation. For example the accumulation of in-phase reflections result in a near-doubling of the amplitude, and if the waveform reflects out of phase, the result would cause the reflected frequency to cancel itself (this is known as phase cancellation). All these factors would cause an undesirable sound within a venue for performers and the audience, although we can treat standing waves by either treating the room with absorption panels and diffusers. But in the case of having a venue that cannot be treated with absorption panels and diffusers the best solution is to use a graphic EQ, this will allow the sound engineer to cut the frequencies that are causing the standing waves giving more control over quality sound within a venue.
