|
|
     |
TOBY Corp has a long history of making open baffle speakers for public address use. They have been used in clubs, schools, churches, and concert halls. The latest TOBY dipole is named Molly, after my daughter, who sings through one, hoping for an Ella Fitzgerald tone.
Bass Performance Hall bought five Molly Dipoles, because they could not understand speech through their million dollar sound system. The Fort Worth Dallas Ballet Company bought their own set of Toby speakers.
Superstar classical guitarists, Christopher Parkening and Pepe Romero have played concerts through TOBY dipoles.
Van Cliburn Piano Competition audition tapes have been played for the jurors though Toby dipoles.
From our list of users, you can see, it's about accurate, uncolored tone.
The latest TOBY dipole speaker measures 18 by 24 inches and is 3 1/2 inches deep. It weighs a scant 25 pounds. Like all dipole speaker systems, it must be used on a speaker stand in open space-not against a wall. In a permanent installation, it may be suspended from the ceiling.
Hundreds of professional musicians have chosen Toby dipoles. It's easy to see why... They get uncolored sound and reduced feedback. The front speaker and the monitor speaker are in one package in one place. The musicians "monitor" the same sound the audience hears. As a bonus, it takes only one amplifier to do the job, not two. Dipole means two poles, like an FM antenna. The sound goes through the plane of the baffle. It is not trapped in a box. This feature drops the level of sound at the sides, as well as the top and bottom, and it accounts for the resistance to feedback. The dipole dispersion pattern is often referred to a "peanut shaped." ..equally loud on the front and the back, and equally diminished on the sides.
In pressure speakers, which means speakers in boxes, the highs and most of the mids go one direction, and the lows go in six directions. This obviously makes for an unbalanced sound in the room, lacking in clarity. In the dipole, the frequency spectrum is balanced all over the listening room. It's an amazing thing to hear.
An example: If a drummer is playing in a club, you hear all frequencies no matter where you walk. With the dipole you hear all frequencies no matter where you walk, except all frequencies are softer at the sides. You can aim the dipole, but you can't aim the drummer. …and you can only aim the higher frequencies of the pressure speaker.
By just looking at it, the TOBY dipole has some normal-looking speakers on a board, with a tweeter in the back. This much is true. It looks that way, but it's much more complicated. You can put a tweeter on the back of any pressure speaker, but it won't be a dipole. To get a smooth frequency curve from a dipole, the baffle board must be the right size and shape, and the positions of the speakers must be carefully selected. A tweeter IS used on the back of the Molly, but the trick is to use the rest of the frequency spectrum from the backs of the other speakers. Finally the sound of the rear of the dipole must be blended to, as nearly as possible, match the sound of the front.
Of course, going beyond the looks, the drivers must be carefully selected for dipole use. They must have high efficiency and low coloration and low distortion. And, without saying, they must be reliable.
Fortunately, 30 years of experience and sophisticated sound measuring equipment enable us to make a variety of dipoles. The bigger they are, the lower in frequency they play. One design was for a corrugated box--making factory larger than a football field. Although the ambient noise was 92 dB, the noisy plant was covered by two dipoles suspended in the center. The circular baffles were 8 feet in diameter. The drivers were four twelves and two big horns. Efficiency was 105 dB/watt (on both sides).
The resonance of a dipole is a wavelength that is two times the diagonal of the baffle. In the Molly Dipole this point is right below 200 Hz, but the response is down only 6 dB at 100 Hz, owing to the first order roll-off of a dipole. If you want to go half an octave lower, the baffle must be half again larger. So, if you want bass, use a subwoofer. It's a very practical thing to do.
The frequency curve of each Molly Dipole is attached. Four drivers are used, a ten, a 6 1/2, and two horn tweeters. The sensitivity of the two cones is 97 dB/watt/m, and the tweeter is 105 dB/watt/m. All together, with the proper crossover network, the system efficiency is 95 dB/ watt/m on the front and 95 dB/ watt/m on the back. Impedance is 8 Ohms. Power handling above 100 Hz is 100 watts. Price is around $500 each, depending on the finish, and number purchased.
There is much more to be said about dipoles in general, and Toby dipoles in particular.
But you really have to HEAR a Public Address Dipole for the first time in your life.
-- Toby Guynn