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March 1995: Volume 3, Number 7


Digital Signal Processing Applied to the Equalization of the Loudspeaker Room Interaction

Dr. Claude Fortier, President, State of the Art Electronik Inc


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The Topic:

The variations in responses due to loudspeaker position, measured and combined over six listener positions in an experimental room, are of the order of ±11 dB. The loudspeaker position was shown to be the dominant effect in the measured response below 400 Hz. It is shown that the CARC/NRC DSP based equalization engine could reduce the variation in the measured response to ±2 dB, independent of the loudspeaker position. The computations required were accomplished without the need for user interaction, thus permitting full automation of the system. Any target desired could easily be matched. The very high performance of this system will allow us to proceed to the next generation of studio monitor loudspeakers.

The Presenter:

Dr. Claude Fortier, President, State of the Art Electronik Inc. received his Ph.D. (Particle Physics), from the University of Ottawa, 1984. The research was performed at Lawrence Berkeley Laboratory, Berkeley, California, and at Fermilab National Accelerator Lab, Batavia, Illinois.

He has also had extensive studies at the graduate level in Electrical Engineering, with courses in analog and digital circuits, computers, microprocessors, systems and digital signal processing.

He has presented and attended various professional and industrial seminars and conferences in acoustics, physics, electronics, communications and computers in Ottawa, Toronto, Montreal, Quebec, Chicago, New York, Los Angeles, San Francisco, London, Paris, etc., including participation at the 12th International Congress on Acoustics, and the presentation at the AES annual meeting in Los Angeles in October, 1988 of a paper outlining the results of his research into loudspeaker design. He also presented on-going research at the 1989 AES Convention in New York which outlines a new technique of physical modeling to be applied to smaller critical listening rooms than had previously been possible. Other more recent research in acoustics has been presented at international and local conferences of the Audio Engineering Society and the Canadian Acoustical Association in 1990.

Dr. Fortier was the founding president of the Canadian Audio Research Consortium, an industry - NRC research consortium inaugurated by the Minister of Science and Technology in 1989. The consortium was formed for the purpose of developing active loudspeakers and interactive audio room environments using digital signal processing. The project is ongoing to develop a new generation of audio equipment for the professional and consumer markets. He has also been elected its technical director.

Dr. Fortier has been awarded a patent for an electronic loudspeaker crossover filter system, and has developed a wide range of professional loudspeaker systems used around the world, notably in New York, Nashville, Dallas, Los Angeles, Minneapolis, Hamburg, Toronto, Montreal, Ottawa, Quebec, Winnipeg, Halifax, Banff, etc.

Dr. Fortier currently teaches a graduate course in acoustic measurement at McGill University, and has been qualified as an expert witness in the field of acoustic measurement by the Supreme Court of Ontario.

His professional memberships include the Acoustical Society of America, Audio Engineering Society, Canadian Acoustical Association, Institution of Noise Control Engineering.


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AES Last Month's Meeting Review

by Konrad Skreta

The CBC Radio Drama department proved to be a great attraction to the members of AES Toronto section. A crowd of more than 50 attended the February section meeting - a count substantially greater than number of chairs available (apologies accepted, Peter). In other words, some of us chose to stand during the opening ceremony.

Denis Tremblay, Toronto Section chairman, opened the meeting with a welcome message to all the guests. Then John McCarthy (Studio Manager for the Radio Performance Production Suite), talked about the 70 years long history of Radio Drama at CBC and how it has evolved with audio technology. First shows were played live to air, with one microphone placed carefully between actors, sound effects people and musicians - just imagine the art and sorcery required to achieve some sort of level balance between them. Not to mention lack of any human error correction mechanism (LIVE TO AIR!).

As technology developed, radio shows were recorded prior to broadcast. First - on acetate disks, then - on magnetic tape. In the latter case, material could be edited (splicing block and razor blade - does it ring any bells?) before being aired.

Introduction of multitrack tape recorders again changed the way radio drama was created. Great control over all the sound components was a blessing for people responsible for mixing. At the same time, due to the nature of multitrack tape, moving anything in time was inconvenient, to say the least.

Conveniently, there are now networked Digital Audio Workstations handy - some 30 years later. And that's what this meeting was all about.

The CBC Toronto Radio Performance Production Suite acquired a formidable fleet of Sonic Solutions workstations and an amazing network connecting them. This arrangement allows to maximize use of manpower and technology by:

A tour of the facility, following the speeches, was a proof of all that had been said. In groups of 12 (±5) guests were led through rooms housing all those wonders:

The tour was almost 2 hours long, and quite exhausting, so everybody gratefully accepted coffee and doughnuts (what else is new?) graciously provided by Adcom Electronics. People formed small circles of discussion groups. The February 1995 Toronto Section meeting came to an end.

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AES Editorial

This is the decade of the information superhighway, and like it or leave it, it will have an impact on our lives that we can only yet dream about.

A little less than half a century ago, television was beginning to make its presence felt in the lives of millions of people, and whole lifestyles were being altered in response to it. But even as it burst into the homes of ordinary people, critics were claiming that its impact would be minimal, and that eventually we would tire of the novelty, and go on with our lives as before.

This time, as a new way of communicating and sharing information develops before our expectant eyes, there are far fewer critics. The Star Trek generation that has long been intrigued by the seductive potential of computer technology is now waiting impatiently for technology to catch up to what we dream possible!

Today's BBSs and the Internet are primitive examples of what is yet to come, but don't ignore them because of that. Here is an excellent opportunity to watch a new era dawn.

The Toronto AES Section is actively participating in this technology. We are accessable on a BBS, and are working towards linking with the Internet.

Someday, sooner perhaps than you may think, the traditional monthly section meeting will be only one way in which section members are able to interact. Indeed, the concept of the section may be far more loosely defined than it is now.

I encourage you to log in to Horizons, and explore its potential. Return again often, and watch it grow. We hope it will become a gateway for you to an exciting new world.

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AES Special Feature

The following article appeared recently in the Globe and Mail. It has been reprinted with the permission of Mary Gooderham and the Globe and Mail.


Work In Progress

How To Muffle The Music From The Big Chill

By Mary Gooderham - Applied Science Reporter... The Globe and Mail

A weekly series chronicling the ascent of a 30-story office building.

The top floor of a high-rise tower is where you expect to find suites filled with avant-garde furniture and wet bars, reserved for pampered executives who conduct their business in hushed tones against the backdrop of the urban panorama.

Standing on the 30th floor of Simcoe Place, taking in the 25,000 square feet of space with its impressive views of Toronto, you can easily imagine the tinkling of ice in glasses of celebratory scotch consumed at the end of hard-won business deals.

Until you hear a 13 tonne chiller being rolled across the bare concrete on the floor above.

But the squeaks and scrapes drifting through the air this week as four machines take their place in the mechanical penthouse are nothing compared to the cacophony that will soon follow. When the chillers begin cooling the air in the building, they will emit bone-shaking vibrations and 100 decibels of high- pitched sound. The noise- equivalent to a jet plane at takeoff- is so loud that technicians wear heavy-duty ear protection whenever they're in the vicinity.

All this noise and vibration could pose a problem for the tenants directly below, were it not for the intervention of Tom Paige and the crew at Vibron Inc., a firm of acoustical consultants and contractors.

We last saw Vibron toiling at the building's foundation, making sure that below-ground vibrations from Simcoe Place did not trouble the delicate sensibilities at the CBC Broadcast Centre next door. Having accomplished that task to his satisfaction, Mr. Paige, a senior project engineer, has turned to the problems noise and vibration present for Simcoe Place itself.

One of the greatest challenges in an office building is to soften the noise given off by pumps, air-handling units, boilers and other machines that keep the temperature at a comfortable level. This equipment is not just confined to the huge podium level between the building's fourth and fifth floors and the three mechanical penthouses about the 30th floor. Air-handling units are placed on each floor, which makes the ventilation system more efficient but also spreads the noise problem.

In a competitive property market, developers want to rent out as much space as possible - including areas near mechanical and electrical installations. To maximize their profits, though, they first have to spend money on reducing noise, since potential tenants now realize its effect on employees' health and productivity. Municipalities in turn impose their own constraints: codes require developers to consider how noise levels in a new building affect both occupants and the surrounding neighbourhood.

All of this creates work for companies such as Vibron. As awareness grows of the problems associated with noise, so do expectations. "Standards are getting higher and better," says Mr. Paige.

The standard for background noise in typical high-rise buildings, for example, before office equipment and workers move in, is roughly 40 decibels, equivalent to the sound of light traffic. Simcoe Place's prime tenants, the Workers' Compensation Board of Ontario, which wants a workplace that reflects its corporate image, asked for a background level of 35 decibels. (Even more sensitive places, such as the radio drama studios at the CBC, require background levels of 12 to 15 decibels, barely a whisper.)

To meet the WCB's request, Vibron installed buffers around fans in air-handling units and put special silencers in the ducts that run from the units to the rest of the building. Usually fibreglass is sufficient to muffle the sound. But because of concerns about the fibres in the air supply, the silencers at Simcoe Place are made of perforated metal.

More extensive work must be undertaken to silence larger equipment. Under part of the penthouse where chillers, pumps and transformers are stationed, Vibron is installing thick rubber pads, sheets of fibreglass and plywood. A layer of concrete will soon be poured onto this platform, thereby creating a second floor that is isolated from the one directly below.

Known as a floating floor, this feature resembles the sprung floors found in dance studios; but instead of cushioning dancers' joints as they hit a hard surface at full force, the floating floor will prevent noise from being transferred to the building structure and offices below.

Vibration coming from the huge rotating motors chugging away in the fans and pumps also poses a problem. To isolate their shakes and rattles, such machines are mounted on top of large metal springs, some of them 30 centimetres high. These in turn sit on top of concrete pads used to support the heavy weight of the machine.

In his time, Mr. Paige has installed the springs under a wide array of equipment, including washers and driers that sit on floors above offices in health clubs, and huge speakers in bars and night clubs.

When heavy equipment, be it an amplifier or a chiller, sits on the floor, Mr. Paige says, "it turns the whole structure into a loudspeaker." People plagued by midnight music lovers should at least be thankful they don't have a souped-up chiller for a neighbour.

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Logo Copyright 1995, Audio Engineering Society Toronto Section Bulletin

Articles may be used with the Author's Permission. Contact the Bulletin Editor: earlm@hookup.net

Editor: Earl McCluskie Assistant Editor: Anne Reynolds Layout Editor: Lee White

The Bulletin is prepared in print by Lee White, and on Horizons and the Internet by Earl McCluskie.