Re: Re: electronic valve action tuba.


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Posted by Rick Denney on June 23, 2000 at 09:49:08:

In Reply to: Re: electronic valve action tuba. posted by Joe S. on June 22, 2000 at 23:10:32:

Joe, there are several options for actuating valves eltromechanically, I'm sure including several I don't know about. If properly designed, none of them make noise while actuated. The hum you talk about is usually caused by a transformer or coil that is carrying alternative current. The devices below would use DC current and would not hum. Here are a few I know a little about:

Solenoids: They have to be well-damped to avoid mechanical noise. They are fast, require high power, and apply high power depending on how big they are. They are also binary, meaning that they have only two positions, which is appropriate for the application. Professional tape equipment in audio setups is (or used to be) controlled by solenoid actuators.

Voice-coils: Not a lot different than solenoids, but are much easier to control (the amount of excursion is controllable). The damping can be done electronically, but the more electronic damping you use, the higher the power required. Now used to move pickups on computer hard disks.

Stepper motors: Many stepper motors are quiet when they are pulsed faster than the step rate. The advantage is that they are very easy to control with a simple digital system. They also can be self-damping. The power required is fairly high. These weren't fast enough for computer hard disks, which is why they are no longer used. These are often used for autofocus systems on cameras, but the cheaper implementations are noisy.

Servo motors: I'm on thin ice here, but I haven't seen many that I think are fast or quiet enough. They are analog devices and may require a separate monitoring circuit.

The constant in all these is that you need the power not only to start the movement and to move fast enough, but also to stop the movement. And if you want fine control on starting and stopping, that is if you want to control the acceleration and deceleration to provide damping, the you need more power still. And the heavier the valve, the more power required.

I would think the operation is more suited to rotaries, for tuba-sized valves, just because they can be designed to be light and nearly friction-free. If you built hollow rotors (instead of machining them from solid brass), and made them from, say, thermoplastic (e.g. nylon) or fiber-reinforced composites, you could mount them in a needle bearing on each side instead of the common tapered bushing. Adjustment would be critical, but nothing beyond what's found in a typical consumer-grade camera. With ultra-light valves and strict control of friction, movement could be fast and require relatively little power. And the less power needed, the smaller the contraption and the smaller the batteries. Doing it right would probably add $1000 or more to a production tuba.

If the valve is light enough, the two positions of the valve could be controlled electronically (and adjustible on the tuba). That way, you could remove the mechanical stops. If you wanted to spend more money, you could put alignment devices on the rotor, and have the start and stop controlled by a feedback controller that would turn the valve until the alignment indicator is reached. That would ensure perfect alignment for as long as the batteries last.

Personally, I think it's a great idea for experimentation. One of the problems I have with technique (just one) is that I don't press the valve buttons as fast as I really need to. My hands just don't have enough of those fast-twitch muscle fibers, I suppose.

I have this nagging thought, however. For decades, the best organs were electromechnical, because they were so much easier to construct than tracker-action organs. But the newest and best organs have all-manual tracker actions, and organists consider these to be superior. Why?

Rick "Is it always musically desirable to move the valves fast?" Denney


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