Automatic Equalization for Live Venue Sound Systems Damien Dooley, Final Year ECE Initial Presentation, Tuesday 2 nd October 2007

Contents Background Project Description Initial Work (Room Acoustic Modeling)

Background In live venues it can be quite challenging to get a balanced sound Several factors can influence a significant deviation between the desired output and the actual output of the system. Factors include, room dimensions, room structure, number of people in the room, furniture, sound source and listener location.

The Project This project aims to create a tool that will help automate the process of achieving a balanced sound. This will be achieved by developing a DSP system which will acoustically model the environment in which the PA system is setup. This system will compensate for the specific properties of the room to ensure that the perfect sound is achieved in each venue.

The system will consist of a microphone which will record the sound at a particular location in the room. A pre-determined sound sequence will be played through the PA and the DSP system will record the audio signal received. The system will then estimate the impulse response of the system which will be a combination of the input signal and the room acoustics.

The Project Capture audio signals using MATLAB Develop and implement filters on the audio Create a simple acoustic model in SIMULINK, (more on this…) Develop an adaptive filter that can adapt to the acoustic properties of the room, again thru SIMULINK Create an active DSP system which will adjust the discrepancies in the audio in real time (adaptive filtering)

Initial Work

Room Acoustic Modeling In order to properly understand how to implement this design, one must understand how sound behaves in various rooms. This is known as room acoustic modeling. When a sound is generated in a room the listener will first hear the sound via the direct path to the source. The listener will then hear the reflections in the sound and the magnitude will decrease exponentially after each echo.

Room Acoustic Modeling Sabine’s equation for reverberation time RT = 0.161V/A This equation yields the time it takes (in seconds) for the sound of the room to decay by 60dB. V = Volume of the room A = Absorption Window (A is calculated by taking the total surface area of the room and multiplying it by it’s absorption coefficient.)

Room Acoustic Modeling Some absorption coefficients are laid out as follows

Example Taking a concrete room painted, with no furniture, pip at 500Hz. V = 2 X 5 X 10 = 100m 3 A = (Surface Area) x (Absorption Coefficient) A = {2(50) + 2(20) + 2(10)} X {0.06} A = 9.6 RT = 0.161V/A RT = 0.161(100)/9.6 = 1.677s Hence, it takes seconds for the pip at 500Hz to drop by 60dB.

Summary The project will require a deeper understanding about how sound behaves in different environments. It will greatly increase my knowledge of MATLAB and SIMULINK, and the general area of DSP.

Questions?