To spend an evening listening to Itzhak Perlman in concert is to leave the hall marveling at his violin virtuosity.
For Gabriel Weinreich, evenings in the concert hall also raised an intriguing question: How can such a small instrument generate sound that fills the hall and seems to come from everywhere at once?
The University of Michigan physicist's quest to solve that riddle not only has led to an answer, it also led him to design a unique hi-fi speaker that mimics the violin's ability to radiate sound in ways that bring concert-hall expansiveness to the rec room.
"This could change the whole face of audio," says Carleen Hutchins, a New Jersey-based violinmaker and prizewinning acoustician.
Others are a bit less effusive, but still see potential. After listening to a before-and-after demonstration of Dr. Weinreich's speaker at a recent meeting of the Acoustical Society of America, speaker designer Alex Butler of Image Acoustics in Cohasset, Mass., said, "It definitely sounded better" than a standard speaker, adding, "I've never seen anything like that design."
Weinreich didn't set out to become a speaker designer. Instead, he says, he was interested in unlocking the secrets to the violin's all-embracing sound. "In some way, when you hear a violin live, it has a mysterious way of seeming to come from a larger source than the physical violin," he says.
Violin holds the key
The key, he reasoned, lay in the way sound radiates from a violin's hollow shell. So he ran tests to measure sound-radiation patterns from four violins. He found that each note comes off a violin with its own unique complex pattern - stronger in some directions (lobes), weaker in others (nulls). These highly directional lobes and nulls, as well as the angles at which they come off the instrument, change dramatically with pitch. A change as small as a semitone makes a big difference, he says.
In the concert hall, each note's different lobes bounce off the walls and ceiling and arrive at the listener's ear from different directions and at different times.
"This gives the illusion that every note is coming from a different direction," he says. The results left him wondering if hi-fi speakers could "mimic that special sense of spaciousness."
That question runs counter to conventional speaker design, according to Daniel Queen, who heads an acoustics consulting firm in New York.
"You're trying to simulate a live performance, fooling the mind into thinking that it's in a large hall," with sound that is uniform and coming from one direction: in front of you, he says. "Or you're trying to create a sound field that a producer feels should be created; that's the idea behind films and surround sound. Either way, you want the sound to be highly uniform and controlled for a predictable outcome." Weinreich, he says, is trying to reproduce the unpredictable sound pattern of a real instrument.
As a first cut at the challenge, Weinreich placed an off-the-shelf hi-fi speaker in a special box. Sound left the enclosure through plastic plumbing pipes of various lengths poking out at different angles. It worked, he recalls, "but it was big and clumsy and hard to experiment with."
His latest version uses one woofer, a speaker that reproduces lower pitches, and four tweeters, speakers that cover higher pitches, in a standard enclosure less than 2 feet high. Each tweeter has its own signal processor, which alters timing and other characteristics of the programming material, based on its pitch. Each tweeter also radiates its own lobe pattern at each frequency.
So far the speaker has been tested only as a stand alone unit, and not as one of a pair of stereo speakers. Still, some who have heard it say it yields high-quality sound throughout a room. This suggests, they say, that if used with a stereo, "directional tone color" speakers could free listeners from having to sit in a "sweet spot" between a pair of speakers.
Mr. Queen notes that because different instruments vary in how they radiate sound, designing a speaker around one could limit its application. Weinreich concedes that for instruments with simple, direct sound-radiation patterns - particularly the human voice - his "directional tone color" speaker is less effective. Designers probably would use a hybrid unit that uses standard and DTC approaches, he says.
His design is drawing interest from some manufacturers. John Roberts, a biophysicist-turned-tech-transfer specialist at the University of Michigan, says a representative from Yamaha came to hear the speaker recently. It seems that the company isn't entirely happy with the sound quality of its electric pianos. According to Dr. Roberts, the representative came, listened, and opined: "Ahh. Very spacious."