Ampico Valves in Duo-Art Vorsetzer
By Craig Brougher
|Dan Wilson misquoted my comment about Duo-Art expression levels by pasting two sentences together which didn't make sense. If we "quote" each other, I feel it is required to not take things so completely out of context as to make the other sound foolish!
I would also like to explain that had I wanted to go into detail about Duo-Art coding, I could have said that while Duo-Arts are set up to "trigger" the Theme response waiting on the expression box, it IS possible to "lead" the system and catch a few expressions on the fly. However, that is NOT the basic design of the Duo-Art. That is a _coding technique_ to work around the limitations of the system. Please acknowledge the difference. Dan stated:
> I've never seen any theorizing about the Duo-Art that takes proper
> account of the exponential delays that in fact take place in the
> suction level changes, and are significant once the level change is
> more than say 5 or 6. It takes something like a third of a second
> for a fresh level to be established, against Ampico's 0.1 second.
> So all the fast coding in Duo-Art rolls has to compensate for this
> by dotting in higher or lower levels than are strictly needed, just
> to get a steeper slope.
Beginning at square one: Time is always linear. There is no such term as an "exponential delay," so I don't know what that means. Suction level changes with regard to expression steps in a Duo-Art are always linear, not exponential. (Loudness is exponential when measured against pressure, but that isn't addressed.)
The claim that we can bank on a third of a second per change in a Duo-Art is unclear, since the accordions during quickly changing passages of the music are always in rapid motion, changing the spring tension constantly. Since it's the spring tension primarily which determines how quickly the expressions can set up (assuming valve travel is optimized) the real answer is, "There is no specific fraction of a second which one can trust to be the timing unless you first specify which expression box you are speaking about, and which section of the accordion!" Spring tension increases as more sections get pulled down. A shorter section takes half as much time as the section below it, etc. etc.
I also would like to correct the notion that an Ampico is able to react to a new expression level in a tenth of a second. That is grossly understated and can be proven a number of different ways. However, my article in the MBSI a few years ago entitled, "The Capabilities of the Ampico" should definitely put this misconception to rest! You can see that this is not right when all you have to do is measure on the roll just how close an expression code can be to the note accented.
To figure the necessary lead time of an expression, it's really simple. You just divide the measured expression lead (the shortest you can find, of course) by the number of inches per second the roll is traveling. For example, at a tempo of 80, it is going 1.6"/sec we'll say. That means it takes a lead time of about .03 sec to resolve a .050 inch lead. You'll find that very comfortable tolerance all over the place. If the shortest resolution of an Ampico was, as Dan says, .1 second, then the closest expression hole to an accented note at tempo 80 would be roughly 3/16"! That would not allow an Ampico to be called a reproducer!
Also, in defense of the Ampico valves in a Duo-Art Vorsetzer, I find no real proof that an Ampico valve just couldn't cut the mustard. If the purpose of the letter was to show that these valves are inferior to Duo-Art valves or to imply that the instrument didn't perform well because of the valve used, then I have to object to that. There is really nothing all that spectacular in the performance of either the Aeolian or Ampico valve. Either one is perfectly adequate for the task.
If you want to get into some really spectacular valves, we can do that! For example, one of the finest in all playerdom was the late model Straube hinged swing valve! Another was the (properly rebuilt) Schultz valve. There were plenty of valves on the market that could play rings around Aeolian and Ampico. The fact is, however, the overkill wasn't required, and manufacturing costs were more important! Probably the very best valve of all time (overall) was the Ampico model B valve. But had it been built under the Straube patent with a ball bleed, it would have definitely set the all-time record for speed and sensitivity.
(Message sent Sun 16 Mar 1997, 15:43:11 GMT, from time zone GMT.)