Tired of Moving Furniture? Try Flexible Speakers

[DudeAsInCool]

How It Works: A Speaker That Adjusts for Furniture That's in the Way

February 19, 2004

By HENRY FOUNTAIN

In the universe of hi-fi loudspeakers, where bigger is

often equated with better, the Bang & Olufsen Beolab 5 more

than holds its own. It's just over three feet tall, weighs

134 pounds and, with amplifiers inside it capable of

producing 2,500 watts of power, can make enough noise at a

party to ensure a visit from the police.

Yet for all its brutish qualities, the Beolab 5 has a warm

and fuzzy side as well. With the press of a button, it gets

in touch with its inner self.

The speaker, Bang & Olufsen's top-of-the-line model (with a

top-of-the-line price tag, $16,000 a pair), is equipped to

overcome a common audio problem. Design engineers may be

able to control most of the elements that make for great

sound from a pair of speakers, but they have no control

over perhaps the most important one: the person who buys

them. That consumer may have a living room with poor

acoustics or may otherwise harm the sound by hiding the

speakers behind furniture or shoving them against the

walls.

"Especially in the low-frequency region, placement of the

speaker has a big influence on sound," said Poul

Praestgaard, senior technology manager of Bang & Olufsen,

which is based in Struer, Denmark.

Audiophiles who want to optimize their speaker setup often

use a microphone placed in the listening area and a

computer to analyze the sound and then adjust the response

over ranges of frequencies, a process called equalization,

to compensate for the room's deficiencies.

The Beolab 5 does a similar job on its own. As its

downward-facing deep bass driver, or woofer, emits several

test tones, an onboard microphone at the bottom of the

speaker picks them up. Then a servomotor moves the

microphone several inches so that it protrudes from the

bottom and can pick up reflections from the room, and the

tones are emitted again. A signal-processing chip within

the speaker analyzes the difference between the two tests

and digital equalization circuitry, also on board, adjusts

the sound.

"They're really very tiny differences," Mr. Praestgaard

said. "But they are big enough to calculate the impact of

the room."

The calibration is done only with sounds below 300 hertz

(middle C is about 262 hertz), because these

long-wavelength tones are much more affected by room

acoustics and speaker placement than high-frequency,

shorter-wavelength ones. At any rate, the speaker uses

other tricks, two acoustic lenses, to ensure faithful

reproduction at the higher frequencies.

Acoustic lenses have been used with loudspeakers since the

1940's, said Edgar Villchur, a home-audio pioneer who with

Henry Kloss was responsible for introducing the acoustic

suspension driver, which is now the standard in loudspeaker

design. Early lenses consisted of a series of multicellular

horns that were intended to spread the high-frequency sound

around so that it reflected off room surfaces.

"When you listen to a loudspeaker in a normally reverberant

room, a major part of what you hear is the sound reflected

from the walls, floor and ceiling," Mr. Villchur said. If a

speaker sends most of its high frequencies directly in

front of the speaker with little reflection, he added, "the

sound you hear will be dull."

The Bang & Olufsen speaker uses a different kind of

acoustic lens that sits atop an upward-facing

high-frequency driver, or tweeter. The elliptical walls of

the lens's casting help radiate the sound evenly in a

horizontal semicircle.

The lens is the work of David Moulton and Manny LaCarrubba,

partners in Sausalito Audio Works, a California company

that licenses the technology to Bang & Olufsen. Designing

it has been a long-term project: Mr. Moulton started

developing the concept in 1981, and, he said, "had a big

cognitive breakthrough about the validity of what we were

doing in 1985."

Mr. LaCarrubba invented the lens in its current form in

1990. He and Mr. Moulton installed it on some speakers and

demonstrated it at audio engineering shows. "We realized we

had a winner here," Mr. Moulton said. Bang & Olufsen was

interested in the concept and cooperated with Mr. Moulton,

who works out of his own audio studio in Groton, Mass., and

Mr. LaCarrubba to adjust the design.

Mr. Villchur said that an acoustic lens could improve a

speaker's performance by dispersing sound. But even more

important is ensuring that the reflected sounds have

adequate tonal response, he said, and for that, a lot of

power is needed. "If they start out with a speaker that has

adequate high-frequency energy, then a dispersing lens

might help it," he said.

Bang & Olufsen takes care of the power issue by including

four amplifiers in each speaker - 1,000 watts each for each

speaker's deep- and midbass woofers and 250 watts apiece

for the midrange and high-frequency tweeters.

That's enough to provide window-rattling volume, but Mr.

Praestgaard said that wasn't exactly the point. "You only

need that much power for a fraction of a second," he said.

"You don't need it all the time."

http://www.nytimes.com/2004/02/19/technolo...571912202fb4b12

[Umma]

Those are serious speakers !

[MikeHunt]

1000 watts for each bass speaker and 250 watts for the mid-range and treble....damn.

Thats about as much as Hendrix had at Woodstock.

Apartment lease breakers ..for sure