PALA '99 - AES Seminar
"Breakthroughs in Loudspeaker Technology"
Thursday, 8 July 1999

reported by: Mr. Jibby Jacob Chairman (Term 1998/99)

The Audio Engineering Society (AES) Singapore Section organised a seminar titled "Breakthroughs in loudspeaker Technology" on Thursday 8th July 1999 at the Seminar Rm. 306 of the Singapore International Convention & Exhibition Centre, Suntec City. The seminar was held in conjunction with the 11th annual presentation of the Pro Audio & Light Asia (PALA '99). It was attended by 13 AES members and 44 non-members from as far away as Australia, USA, India besides Singapore just to name a few. The participants included R& D engineers, scientists, staff of tertiary institutions, sound reinforcement audio consultants, audio professionals both from the government and the private sector. 

This annual trade show held from 8th to 10th July 99 had over 7,023 visitors of which 3,029 were from about 41 countries the rest were from Singapore. The exhibition spanning a gross area of 12,000 sq. metres had displays of 303 exhibitors from 22 countries. 

The AES Singapore Section also held a 3 day exhibition during the show to conduct AES membership drive and to promote the AES publications. The committee was pleased to meet both local and regional AES members who attended the exhibitions. There were many inquiries regarding the AES membership and it's activities and about 400 application for membership forms were distributed to the visitors. Quite a few signed up to apply for the membership at the AES booth. 

AES Seminar registration began at 1.00 pm sharp. The attendees were given a 55 page handout with illustrated notes from the speakers as well as door gifts from the local sponsor Electronic and Engineering Pte. Ltd. 

Jibby Jacob, Chairman of the Singapore Section & the organising committee was the moderator of the seminar. He got the ball rolling for the seminar with a 5 minute introduction. Jacob highlighted the objective of the seminar which was to promote audio education in Singapore. This being the 3rd consecutive year that an AES seminar with 4 international speakers was organised during a PALA presentation. Jacob credited the committee for the excellent organisation of the seminar and he felt that indirectly this was a factor responsible for the popularity & growth of the Singapore Section.

This was followed by the keynote address by Ms Laurel Cash-Jones, AES Vice-President/International Region. In her inimitable way she provided a humorous but thought provoking preface for the seminar. She began by listing the endless terms commonly used in the jargon related to the speakers, but are never quite understood. "SPL, dB, tweeter, electrostatic, horns, frequency response, dynamic range, etc.." were terms everyone used but never quite agreed upon as to the technical reference or the meaning. Further she mentioned that speaker technology advancements never grabbed attention unlike other areas of audio. Industry watchers often perceived that because fundamental acoustic principles that govern the ear still remain and any advancements are received skeptically. She credited the Singapore Section for organising the seminar and that she was honoured to be able to attend it as this being her last year (1999) in the role of Vice-President/International region. 

This was followed by a presentation called "Loudspeaker Primer" by Stephen Low a lecturer at the Ngee Ann Polytechnic, Singapore and an AES member. This was an interesting presentation because after discoursing on the fundamentals of loudspeaker and the historical development of speakers, Low asked the audience to consider the various difficulties in constructing an ideal high efficiency and low cost speakers. Mr Low then spoke about the reproduction criteria which included covering the entire audible frequency range, exhibiting linear phase, offer no distortion and wide dynamic range. Of course modern material technologies would alleviate some of these problems. He challenged the panelists who will follow on to provide answers from alternative technologies that will fulfill the criteria he felt important in the ideal system. Low then offered a demonstration of DVD reproduction of a music selection digitally recorded at 96 kHz. The clarity of the music was remarkable and this he felt also highlights the importance of a high resolution audio source for high quality speaker reproduction.

The next presenter was Dr Nick Hill, senior physicist at the NXT company, UK which researches in flat panel loudspeaker technology. In his lecture "Theory of Distributed Mode technology" Hill offered a totally different perspective to speaker construction. Hill then presented 2 working models of the actual "flat panel speakers". One application of which was incorporating it in a notebook computer, the "thin"speakers which literally looked as if it was an extension of the screen. In his explanation Hill felt audiophiles and audio professional would be understandably suspicious of this idea which so comprehensively inverts the status quo. Using animation, Hill demonstrated visually the fundamental principles of the distributed mode loudspeakers (DML). The sound radiation pattern of the flat panel at various frequencies showed an even and larger sound emission compared to conventional speakers. This was because the diaphragm of a DML vibrates in a complex pattern over it's entire surface. Intriguing was the fact that the loudness was smooth and not variable with the distance from the emitting source, this is close to the directivity of a true point source-i.e. approaching omnidirectionality. Though NXT company does not manufacture loudspeakers with the technology, it licenses it to other manufacturers. 

The 3rd speaker for the day was Dr Tony Hooley, who presented the "Fundamentals of Digital Loudspeakers" (DLS) . Hooley who pioneered the technology and founded the 1..limited company, UK, has several patents related to the digital loudspeaker program. 2 reasons were given by Hooley on why he decided to move away from the analogue loudspeaker to the digital loudspeaker. The former being a 75 year old technology with limited scope for further development and it is the weakest link in the audio chain with poor efficiency, high distortion, bulky, heavy and inconvenient. Incorporating true digital theory, Hooley created the picture of the DLS as a electroacoustic digital to analogue convertor. Introducing the concept of the digital pulse transducer he then presented the real world speaker as a vast array of identical pulse transducers that is triggered to respond to binary codes.

Working with the base 1(unary digital loudspeaker) Hooley then described the prototype components necessary to design the DLS. The MK III DLS system was elaborated on. The usual digital techniques for quantisation, oversampling, noise shaping and binary to unary conversion were still in force according to Hooley. The early prototypes of the transducers included helical Piezoelectric bender, linear gas bearing & ceramic types. Some of the benefits Hooley felt the users will enjoy included the absence of a power amplifier &wires and no digital to analogue converters. 

The final speaker of the day was Professor Malcolm Hawksford from the Centre for Audio Research and Engineering, University of Essex, UK. His lecture was titled "Crossover alignments for analogue and digital active loudspeaker". Hawksford with exhaustive and indisputable formulae discussed the problems of both analogue and digital crossover design. He argues that a digital system has greater freedom and repeatability than analogue systems. 1st, 2nd, 3rd & 4th order crossover alignments were then described. Digital equalisation was the next critical issue that Hawksford tackled in relation to analogue crossovers. 

However the solution was using Digital Signal Processing (DSP) and he then went on to describe the response of an equalised and unequaled loudspeaker system. Experience and experimentation with digital equalisation confirms that there is an enhanced tonal accuracy, an apparent reduction in enclosure coloration, sharper and better defined transient response. Among other features a digital system can also have a universal hardware that can be software tailored. It could be a simple system replication with identical filters so there is no thermal drift. Thus Hawksford reviewed the basic elements of both analogue and digital crossover filters and explained their fundamental differences. Hybrid analogue-digital technology was also cited as being particularly attractive and cost effective, though the emphasis here was on active loudspeakers.

A 10 minute Question and Answer session followed with attendees asking about real world products which incorporated the technologies presented. 

Other questions raised in the lively dialogue between the participants and the speakers included the impact of these revolutionary speakers on multi-channel sound reproduction. The speakers offered more updates and answers from the respective companies internet websites and private correspondence.

The Master of Ceremonies, Christopher Yap then thanked the panelists and plaques of appreciation were presented to them by the Chairman of AES Singapore Section for their participation. 

AES Singapore Section would like to thank AES Head office in New York for their continuous support and specially to Ms Laurel Cash-Jones VP International Region for her guidance of the Section. Further acknowledgment of support goes to the co-sponsor of the seminar and organiser of the PALA 99 presentation, IIR Exhibitions.Pte. Ltd. and in particular Mr. Patrick Tan, Managing Director, Ms. Rosalind Ng-Seah, Project Director, and Ms. Darrell Lee, Senior Marketing Manager.

A plaque of appreciaton from Jibby Jacob Chairman AES S,pore Section to Rosalind Ng-Seah, Project Director IIR Exhibitions for co-sponsoring the event - photograph by Robert Soo.