A new loudspeaker design

Abstract

The authors have been members of a design and development team that has created a new loudspeaker that attempts to resolve several of the primary problems presented by the loudspeaker/room/listener interface, as described in one of the authors’ previous paper. This paper will describe that new loudspeaker, its various new approaches to the interactions between the loudspeaker, the room and the listeners, and a brief review of the research, findings and assumptions underlying its design. The authors hope to have examples of the loudspeaker available for demonstration.

Development of the BeoLab 5 Loudspeaker

The BeoLab 5 is a loudspeaker whose configuration arises out of several disparate research and development threads that are integrated into a functional design topology, a topology that departs significantly from traditional designs. A goal for the loudspeaker that was first articulated in the early development phases and later formally mandated for the design is that the loudspeaker should work to solve as many of the problems facing a domestic consumer loudspeaker as possible.

This led to two concerns throughout the project. The first was that the loudspeaker should exhibit very “musical” behavior, so that it provided as profoundly enjoyable a musical listening experience as possible for its owners, with as few technical intrusions as possible. The second was a concern that one of the authors has called the “Overloaded Bus” problem – the metaphor is a bus that keeps loading more and more payload aboard as the bus progresses, until the bus fails. Considerable care was therefore exercised as development proceeded to prevent this from happening, in spite of the broad array of technologies incorporated in the design.

The following performance areas were addressed:

• High frequency power dispersion and amplitude response
• Low frequency adaptation to the playback room
• Adequate power to provide appropriate acoustic sound pressure levels for listeners
• Robust, reliable and repeatable performance in application
• Operational simplicity and fail-safe protections in application
• Appropriate and functional appearance and build quality for a high quality “musical instrument.”

High frequency power dispersion and amplitude response

Research findings from the Archimedes Project [1,2,3,4] and one of the authors (Moulton) [5,6] has led to the development of a set of criteria for high frequency loudspeaker performance and to a device suitable for obtaining such performance.[7] These criteria were first formally articulated by another of the authors (Pedersen), as

1. "The power response should be as flat and smooth as possible relative to the free field frequency response
2. "Strong floor and ceiling reflections should be avoided
3. "Strong reflection off the wall directly behind the loudspeaker should be avoided"[8]

The device that is used to accomplish this is called an “Acoustic Lens.” It is a scalable reflecting device that fits over a conventional treble dome tweeter or mid-range driver, which is facing upwards. It was invented by Manny LaCarrubba of Sausalito Audio Works, and is licensed to Bang & Olufsen.

	Photo of acoustic lens in prototype form

Post a Comment