Multiple Position Room Response Equalization

Abstract

This chapter is concerned with the equalization of acoustical responses, simultaneously, at multiple locations in a room. The importance of equalization is well known, in that it allows (i) delivery of high-quality audio delivered to listeners in a room, and (ii) improved rendering of spatial audio effects for a sense of audio immersion. Typical applications include home theater, movie theaters, automobiles, and any loudspeaker based playback environment (headphones, cell phones, etc.). Because experiencing movies and music is now primarily a group experience (such as in home theaters, automobiles, and movie theaters), and headphone/earbud acoustics vary due to ear coupling effects, it is important to include acoustic variations in the design of an equalization filter. Thus, an equalization filter designed to compensate for the room effects (viz., multipath reflections) at a single location performs poorly at other locations in a room. This is because room impulse responses vary significantly with differing source receiver (viz., listener) positions. Agood equalization filter should compensate the effects of multipath reflections simultaneously over multiple locations in a room. This chapter briefly introduces some traditional room equalization techniques, and presents in detail a new multiple listener (or multiple position) equalization filter using pattern recognition techniques. Because the filter lengths can be large, a popular psychoacoustic scheme described in this chapter allows design of low filter orders, using the pattern recognition technique, for real-time implementation. Additionally, a room response and equalization visualization technique, the Sammon map, is presented to interpret the results. Furthermore, one of the major factors that affects equalization performance is the reverberation of the room. In this chapter, the equalization performance of the pattern recognition method [60] is compared with the well-known root mean square averaging-based equalization, using the image method [61] for synthesizing responses with varying reverberation times T60.