Study of low frequency absorption by listeners for Live Sound applications
Firstly, it's all about
rock'n'roll. For a big concert it's extremely important to create an even sound
pressure level (SPL) distribution all over the listening area with the same frequency
response at every listening position. This is the main task of a concert sound
reinforcement system, which gets quite challenging when it comes to lowest
frequencies (20-120Hz). In this case room modes and interference between sound
waves from different loudspeakers create big peaks and dips all over the room.
For large out door events so called distributed subwoofer arrays have lately
become a common solution. Instead of conventional left and right setup,
subwoofers are located in a row in front of the stage.
Introducing signal delays one can control the directivity of array and create even SPL distribution. On the other hand, the sound wave from the array has to travel all the way through the crowd to reach the mixing console and then the back rows, when mid and high frequency waves travel through the air. How much bass will the sound engineer receive in his booth and how much will come to the listeners in front of the stage and in the last row?
How many subwoofers are needed to provide enough low-end for all the listeners and not blow away the first rows? For correct design and operating a sound system it's essential to be able to predict the sound wave propagation through the listeners.
Despite all the rock'n'roll background, the crowd is a layer of moving inhomogeneous medium, located between two other different layers, and its characteristics depend on temperature and density. The main goal of the project is to find a proper matghematical model of the medium and predict the propagation of sound through it at least for the simpliest cases, which involves a lot of live measurements, simulations and theoretical work.