Loudspeakers In Rooms Research Articles

Determining the accuracy of sound field synthesis systems in reproducing subjective source locations

Sound field synthesis systems developed and applied to study human hearing perception differ in terms of the number and arrangement of loudspeakers in rooms of different sizes, and methods used to generate virtual sound environments. Research has evaluated how well such systems physically reproduce room acoustic conditions, but limited subjective data are available. This paper seeks to develop a method for determining the accuracy of the perceived localization of a virtual sound source generated using a multichannel sound synthesis system. A test method is applied to the sound field synthesis facility at Boys Town National Research Hospital, a room (5.8 m x 5.2 m x 2.7 m) with reverberation time of 0.16 s at 125 Hz and below 0.024 s at 250 Hz and above. Short bursts of broadband speech-shaped noise are presented at a number of virtual source locations under free-field and modeled reverberant-room conditions, and listeners are asked to point to the subjective source location. Subjective localization results are compared as functions of virtual sound location, and parameters of early reflections and reverberation in the modeled sound environment. Results are intended to guide future research on subjective room acoustics relevant to children's’ communication needs. [Work supported by NIH GM109023.]

Sound reproduction: Science in the service of art

The vast majority of music we enjoy is generated by loudspeakers of differing pedigree and propagated to our ears through spaces that can mostly be described as acoustically arbitrary. In spite of the obvious huge variations, humans have managed to not only enjoy reproduced music, but sometimes even to exhibit enthusiasm for it. Common acoustical measurements confirm the variations. Are they wrong? In double-blind subjective evaluations of loudspeakers in rooms, listeners exhibit strong and remarkably consistent opinions about the sound quality from loudspeakers. The challenge has been to identify those technical measurements that correlate with the subjective ratings. What is it that these listeners are responding to? A clue: it is not in the specification sheets of most loudspeakers, nor in a secret formula for room design. This tutorial will examine the acoustical properties of loudspeakers (the sound source), rooms (the acoustical conveyance), and listeners (the powerfully perceptive, and adaptable receptor). In some respects, our problems began when we started to make certain kinds of simplistic measurements. Two ears and a brain do not respond to complex sound fields the way an omnidirectional microphone and analyzer do. What our eyes see in these measurements is not always well-matched to what our ears hear.

Sound-field reproduction systems using fixed-directivity loudspeakers

Sound reproduction systems using open arrays of loudspeakers in rooms suffer from degradations due to room reflections. These reflections can be reduced using pre-compensation of the loudspeaker signals, but this requires calibration of the array in the room, and is processor-intensive. This paper examines 3D sound reproduction systems using spherical arrays of fixed-directivity loudspeakers which reduce the sound field radiated outside the array. A generalized form of the simple source formulation and a mode-matching solution are derived for the required loudspeaker weights. The exterior field is derived and expressions for the exterior power and direct to reverberant ratio are derived. The theoretical results and simulations confirm that minimum interference occurs for loudspeakers which have hyper-cardioid polar responses.

Controlling loudspeakers in rooms

How to control the perceived timbre of a loudspeaker in different listening positions, using different loudspeaker positions in different listening rooms is a central problem, when designing and using loudspeakers is discussed. Loudspeaker directivity has been found to be one of the critical parameters in the solution to this problem. This paper presents three hypotheses for the optimal loudspeaker directivity and a novel realization of that directivity, i.e., the Acoustic Lense (ALT). The dominant problem at low frequencies has been found to relate to the fact, that the acoustic power output of loudspeakers is highly dependent on the loudspeaker position and on the acoustic properties of the listening room. This paper also presents a novel system for adapting a loudspeaker to its position and to the acoustic properties of the listening room, i.e., Adaptive Bass Control (ABC).