| Acoustics Research & Loudspeaker Development A description of my background and professional experience By Peter Chapman |
| College & University Education A-levels in pure mathematics, applied mathematics and physics (three A grades, 1992), Grimsby College of Technology and Arts, Grimsby, England. Batchelor of Engineering in Electroacoustics (first class with Honours, 1996), Department of Applied Acoustics, University of Salford, Salford, England. |
| Above, the Beolab 1 loudspeaker which was the first commercially available product for which I was responsible for the complete acoustical design. The Beolab 1 is constructed around a 184cm tall extruded aluminium cabinet. Below, the Beolab 5 loudspeaker, quite a revolution in the audio industry. It is a fully digital loudspeaker with a patented room correction system, two acoustic lenses and 2500W of amplifier power. The Beolab 5 was released in 2002. It stands only 107cm high but weighs 62kg. |
| Professional Career My professional experience began with a 10 month industrial placement in the Acoustics Research and Development Department at Bang & Olufsen in Denmark. During this intense year, my work was dedicated to researching modern programme material on CD and looking at thermal issues when loudspeaker drive units reproduce sound. The work culminated in the publication of two papers for the Audio Engineering Society (preprints 4277 Copenhagen in 1996 and 4667 Amsterdam in 1998) and one for the British Institute of Acoustics (Windermere in 1998). During the 10 months, I also designed and built a pair of 4-way active loudspeakers from scratch (though with Quad amplification). The system consisted of stereo loudspeakers each with a 12 inch woofer in a 170 litre bass-reflex box tuned to 19 Hz and a top system comprising two 6 inch mid bass units, two 3 inch midrange units and a 19mm tweeter. Following my final year at university, I continued working in the acoustics faculty for six months, writing course material for a new postgraduate certificate in reproduced sound. I wrote modules on mathematics and vibration. For the next 11 years I was employed as a loudspeaker engineer back at Bang & Olufsen in Denmark. During this time my work was divided between acoustics research in the field of audio and sound reproduction, and the development of consumer and professional loudspeakers at the forefront of sound performance. Bang & Olufsen has been the worlds third largest loudspeaker manufacturer seen in terms of annual turnover from loudspeaker sales. |
| Professional Experience - Research Areas of research have included the Medusa project in cooperation with Nokia, Genelec and the University of Surrey. This project looked into, amongst other things, the accuracy of subjective level adjustment and headphone versus free-field listening tests. Furthermore, I continued work on the thermal properties of drive units including the development of a lumped thermal model (which has been adopted by Klippel) and intelligent thermal protection for active loudspeakers. This work resulted in the publication of another AES paper (preprint 5112 Paris in 2000). For several years I was involved with evaluation and further development of an acoustic lens developed originally by Sausalito Audio Works (Manny LaCarrubba and David Moulton - www.sawonline.com) who are based in the US. The lens offers controlled vertical and wide horizontal directivity without diffraction giving a wide listening area and superb imaging. I have worked extensively on bass management in multi-loudspeaker setups. It is rare that consumers have identical loudspeakers in all channels, and therefore it is necessary to look at optimal bass management. It is important that customers can choose their system from all loudspeakers in a portfolio rather than being limited to 'surround sound sets'. Relevant for the future, I have looked at bass management algorithms for fully automatic digital systems. Based upon my earlier work on programme material analysis, I have furthered knowledge by introducing more advanced power testing - power testing that represents more worst case use of loudspeaker systems, such as 'party music'. This type of material contains 3 dB more energy in the critical 50-100 Hz region than the old IEC simulated programme signal. I have researched the effects of temperature, humidity and atmospheric pressure changes on acoustic measurements. This work has culminated in the newer Bang & Olufsen loudspeakers being produced with strict tolerances as calibration includes online measurement and correction for temperature and atmospheric pressure. For your interest, normal variations in atmospheric pressure alone lead to variations in measured SPL of +/-0.7 dB. More recently I have worked on an idea and system for correcting the timbre of a loudspeaker system based on the measured reverberation time or decay time in the listening space. Read the white paper here. I have also authored the patent WO/2008/111023 which can be seen in brief on the World Intellectual Property Organisation website. |
| Professional Experience - Product Development Before the development phase of any loudspeaker product there is a period of concept development. This period includes close cooperation with the designer and a concept team, tailoring the concept until the right product is born. The roll of the acoustic engineer is to verify and evaluate potential solutions and often, as in the case with Bang & Olufsen, develop new technologies and ideas in order to solve a particular problem, such as very limited space. I have enjoyed cooperation with concept teams and Bang & Olufsens' chief designer David Lewis on many varied projects. This process teaches you to keep a very open mind and I have never had the simple task, as many have, of simply choosing rectangular box dimensions for a loudspeaker. The first commercially available loudspeaker for which I was responsible for the complete acoustic design and performance was the Beolab 1 loudspeaker. Released in 1999, it has sold in over 15000 pairs and received very good reviews in the Hi-Fi press. Since then, I have worked on numerous concepts and the development of some fantastic loudspeakers, including a professional studio monitor for near-field monitoring. This monitor was built around a concept and has a rather unusual but very practical design. The loudspeaker is a 2 or 3-way modular active loudspeaker with an acoustic lens and provides unrivalled imaging and sound performance. The system was tested over a lengthy period by artists such as Erann DD and Jean Michel Jarre and at the Plant Studios in California. George Massenburg also had a set on loan - he was quite sad to give the speakers back. Weislaw Woszczyk at McGill University in Canada was also involved in testing. Later I developed the Beolab 7-1 loudspeaker which has been available since December 2004. It is a stereo 3-way active loudspeaker for the latest Beovision LCD and plasma displays from Bang & Olufsen. It offers, without doubt, the best television sound on the market (for more information, see Bang & Olufsens' website - www.bang-olufsen.com, and Grammophone magazine from May 2005 for a short review). Development of commercial products involves many aspects, including drive unit design and close cooperation with specialist drive unit manufacturers such as Peerless, Vifa and Scanspeak in Denmark, Foster in Japan and Philips Speaker Systems in Belgium. A very important roll of the loudspeaker engineer is the ability to move the product from prototype assembly to large scale production. For me, this work has included the design and specification of state of the art test equipment including test boxes for level adjustment (for drive unit sensitivity differences, including compensation for atmospheric temperature and pressure variations), frequency range measurements and rub and buzz and air leak measurement and failure registration. This area also includes detailed tolerance chain analysis and general quality control of drive units. Furthermore, I have been responsible for technical documentation regarding the products I have been responsible for, such as technical input for user manuals and service documentation. I have also taken part in training seminars for service personnel, technical assistants and dealers, both in Denmark and in the US, where I was involved with teaching a basic understanding of sound and acoustics to staff as part of a larger training programme. On a day to day basis, I used the following tools for loudspeaker development: measuring equipment including the Bruel & Kjær 2012 and 2144 analysers, assorted B&K microphones and pre-amplifiers including the Nexus range, the Klippel measuring system, the Audiocore software and the DP200/226 digital equalisers, Yamaha digital mixing consoles, Cooledit, pcRTA room measuring equipment, MLSSA, custom measuring equipment combined with a 12x12x13m measuring chamber, also near-field, 2pi, free-field and anechoic measuring techniques, various personal MathCad programs, and the usual PC programs. A large area of loudspeaker development is understanding listening room acoustics and how loudspeakers interact with the room. I have experience of designing listening rooms to IEC standards and correction of existing rooms. On the more practical side, I am not afraid to get a soldering iron going and I have taken care of the complete control room installation for one of the IEC listening rooms at Bang & Olufsen. Finally, my favourite music includes material by Mark Knofler, The Doky Brothers, Kari Bremnes, Schumann and Mahler. |
| Left, at The Plant Studios in Sausalito with David Moulton. Below, the Beolab 7-1 loudspeaker on a floor stand with the Beovision 7 32" LCD television. The loudspeaker is a stereo 3-way active design and is 100cm long with the bass units facing downwards. The cabinet is moulded aluminium and the grill is perforated adonised aluminium. Bottom: The Beovision 40" with the Beolab 7-4 centre loudspeaker. This is probably the best performing dedicated center loudspeaker on the market. It is an active 2-way loudspeaker with 2 x 250W of power driving a 5" woofer in a closed aluminium cabinet and 3/4" tweeter in an acoustic lens. I have done the acoustic design on all of these products. |
| Below, the Beolab 9, my latest acoustical contribution to the Bang & Olufsen loudspeaker portfolio released in January 2007. This is a compact floorstanding 3-way active loudspeaker with 640 W of amplifer power driving a 10" woofer, 5" midrange and 19mm tweeter. |