Sidebar 3: Measurements As expected from its use of a horn-loaded tweeter, the Odeon La Traviata is almost 10dB more sensitive than the average for a direct-radiating design, at an estimated 96.4dB(B)/2.83V/m. It will go immensely loud with only a few amplifier watts, though the downside of this high sensitivity is the need for exceptionally quiet amplifiers and source components. (See, for example, RD's review of the Quicksilver Horn Mono amplifier elsewhere in this issue.)
In addition, the Odeon's plot of impedance magnitude and phase (fig.1) reveals it to be an extremely easy…
There was something odd about the clock on Jim Thiel's office wall. I didn't get it at first, other than noting that instead of the minutes being marked off at 12 five-minute intervals, Jim's clock had 24 markings. That was it: as well as the number "12" in its usual place at the top of the face, there was another "12" at the bottom, where the "6" usually is. The clock that Jim built was typical of everything this laconic loudspeaker engineer is involved in: logical, functional, and different from what anyone else in the same field does. In his cigarette-strained drawl, Jim explained that…
Thiel: That's correct. If the drive-units are not the same distance from the listener, you will still hear the sound from the drive-units separately in time. They have to be physically aligned. Coincidentally, at about the same time [that I was thinking about time coherence], other companies were also starting to think about the problems caused by the differences of arrival time. We came up with the approach of mounting the drivers on a sloping baffle, which did not introduce the problems caused by the stepped baffles that were being used in some other designs. We introduced our Model 03…
Atkinson: One of your goals appeared to be reduced woofer distortion. You reinvented the idea of using a copper shorted turn on the magnet pole-piece. Thiel: What that does is stabilize the strength of the magnetic field in the gap. The ferrite permanent magnets that almost everyone uses are not perfectly stable under load. And when you run many amps of current through the driver's voice-coil, the magnetic field it generates pushes against the permanent field of the ferrite magnet and actually demagnetizes it to some degree. So the magnetic reference point that the voice-coil is…
Atkinson: The first drive-units you designed and made in-house were the passive radiators in the CS2 2 and CS3.6. Thiel: Yes. And that was really very simple—not many parts involved and not many variables. The woofer for the CS7 was the first driver that we manufactured completely in-house.
Atkinson: And now the design loop is very much more efficient because you can model the drive-unit on your computer, your CNC machine tool produces the molds or whatever from your computer model, and you can actually go to many more iterations?
Thiel: Very many more. Especially in the…
Atkinson: However, you've more than doubled the moving mass. Thiel: Yes, the sensitivity of the unit would, everything else being equal, be quite low. We've had to compensate for that by utilizing two very large magnets to achieve the sensitivity we need. For obvious reasons, the cost is high—the diaphragm is expensive, and the large magnet system is quite expensive. But you end up with very good results. The styrofoam both damps the resonances [that metal cones can have] and adds a lot of stiffness to the composite system so that the resonances are moved well above the main operating…
Thiel: I view the ear as a measurement tool. And you can use it to evaluate the differences between the sound of loudspeaker designs just as usefully as you can use a computer to evaluate objective differences. Take the different materials that can be used for woofer chassis, for example. We use cast aluminum chassis in all of our woofers. I know of no measurement that can tell you that this driver basket will sound better than that one. But in fact, it's very easily audible. Cast aluminum sounds much better than stamped steel. Now maybe it's because aluminum's nonmagnetic and there's less…
Thiel: Not only have you reduced costs because of the reduction in cabinet and woofer size, you very likely have been able to decrease the speaker from a three-way to a two-way, or a four-way to a three-way, because of the reduced requirements in moving air that you need for deep-bass reproduction. And the fewer number of drivers and the consequent reduction in the complexity of the crossover network all contribute to greatly reducing the costs. Beyond that point, I'm willing to make a product for a lower price that doesn't achieve quite the degree of sonic qualities that the more expensive…
Atkinson: There seems to be a lack of recognition outside of our small audiophile world that very good hi-fi equipment is made here in the United States. Thiel: I think American culture does not do a very good job of appreciating quality. This is one of the advantages high-end audio companies have in the Asian market, where quality has a lot stronger place in the cultural wisdom. In the mainstream American culture, things are treated more as commodities, and our culture is more price-oriented. It's very noticeable that in Eastern cultures, more people have an appreciation of differences…
Atkinson: The contrast is between the public perception of audio manufacturing, which is of large offshore companies producing commodities, and the reality, which is that America is a hotbed of relatively small, high-technology companies, like Thiel, making products with a huge amount of quality designed in. How does that perception get out to the wider America? Thiel: That's a question I think no one has been able to answer, because our industries are not large enough to afford large advertising budgets. And also because the price ranges of the products are such that they are not really…
