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Is it all "Ovoids" ?
Is it all "Ovoids"?

 

photo of Denis

"16mm total depression, oversquare, non-axially bored valve section giving unit throughput of 12mm (that's 0.4724" for oldies)."

It may sound all "ovoids" to you, but to me, it is music in my ears - and to lots of other people too.

I suppose the idea surfaced light years ago during the second hour of Wagner's "Das Rheingold" in the orchestra pit of the Royal Opera House, Covent Garden. You know the bit - one of the exciting climaxes where Wotan transfers his spear from his right hand to his left, and when the brass section are beginning to regret that earlier pint of beer.

Sitting contemplating the genius of Sir Georg, and wondering what he'll do when he finds I've knotted his towel to the pit rail outside, I oiled one of my trumpet valves and whispered to Mr Dilly, the principal trumpet:

"Harry, I'm going to redesign these valves without bumps in the ports - they muck up the airflow."

"Shut up Denis, I was asleep - I don't play for another twenty minutes."

Which I suppose is when it all started.

Bumps impede airflow

One might at this stage imagine that a "bump" in the port of a trumpet valve is trivial (possibly: take a look if you haven't noticed one before). Perhaps though, this is not so: closer inspection will reveal that there are in fact two bumps in each valve and that each bump is a small mound about 2mm high.

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If we add the height of these little mounds together we've got a 4mm mound. And, as most of us use three valve trumpets, we now have an impedance to the airflow through the valve section of our trumpet of 2mm x 2mm x 3 (valves): this equals 12 whole millimetres.

This blockage in the valve section is then larger than the bore of the instrument. Have you ever wondered why the G# above the staff is a bit unsafe?

Valve depression length

The reason why piston valve ports are distorted (that's bumps to you and me, mate) is very simple. The distance of valve depression is directly related to how closely one squeezes together the three port holes in each valve.

Reduce the length of valve depression and we get bigger bumps in the ports where they overlap. Increase the length of valve depression and we get a smaller overlap (but still bumps) in the ports.

The answer then would appear obvious. Increase the valve length of depression until there is no overlap.

Eureka! did I hear someone say?

Well, er, actually no: if we did make the valve depression long enough to ensure clear ports, then by the time we'd have got the valves up and down a few times to play the Rheinmaiden's motif that evening, all the girls would have drowned, and Sir Georg's towel would have been realigned around my neck.

Pre-Wedgwood then, the answer has always been to compromise.

Vincent Bach designed an acceptable length of valve depression with an acceptable valve port distortion.

Mr Benge designed a slightly longer length of valve depression with lesser distortion in the ports.

Reynold Schilke, whose engineering is superb, went further by offsetting the valve casing ports.

Wedgwood, as usual, went further still and completed the process by

i) offsetting the valve casings,

ii) offsetting (non-axially boring) the valves themselves,

iii) increasing the valve diameter to "oversquare".

Phew!

This equation resulted in a shorter distance of valve length depression and no impedance (that's still bumps, mate) to the airflow through the instrument, giving a continuous uninterrupted bore of 12mm.

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Now that's worth a Eureka!

Explanation

It works like this: take a can of beer, as brass players do, or any cylindrical object. Imagine this to be your valve. Bore, or imagine boring, a hole through the axis of the beer can and out the other side. It is of course a round hole, and it obviously looks round.

Now, bore, or imagine boring, a round hole not through the axis of the can, but to one side of the axis (i.e. non-axially bored). It's still a round hole, but it doesn't look round. It looks egg-shaped. This is the trick. You have created an ovoid. Now drink the beer.

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By moving some of the valve ports on the Wedgwood instruments to "non axial positions" this means that we've created a little more room for the other ports to fit in without overlapping (which causes the bumps) and without increasing the length of valve depression. This formula gives us a clear bore throughout the casings.

Thickness of six human hairs

Life really starts of course when ovoids meet axials and more beer is needed to demonstrate this.

Initial comments when players test a Wedgwood trumpet are significant in themselves.

The two main ones are:

"Isn't it easy to play?" and

"Oh, the bore of the instrument is very large."

To the first question: "Yes, it is easy to play."

The second is more fun to answer.

"Yes, a Wedgwood is slightly larger bored than a Vincent Bach. They are slightly larger by about the thickness of six human hairs". Being as I am somewhat in short supply of the latter, this is better proved by plucking out and measuring the follicles of the nearest student.

Does this thickness of six hairs make the trumpet easier to play?

"I don't think so. What does make it easier to play, and makes people feel as though 'notes are in slots' is the uninterrupted bore throughout the instrument."

**Two footnotes for the technically minded:

1. "Total depression"

When the valve is depressed, the holes in the valve align perfectly with the holes in the casing of the instrument. This is possible because all my instruments have removable bells. Therefore it is possible to look through the valve casing with the bell removed, and perfectly regulate each valve in turn by the use of very thin washers under the valve stems. Hence, "total depression".

2. "Oversquare"

On practically all piston valves up to now, the diameter of the valve itself is slightly less than the distance between the "up and down" position of the valve (depression).

For example, a Vincent Bach trumpet valve is approximately 16.84mm (0.663") in diameter. The distance the valve is depressed is approximately 16.12mm (0.635").

The Wedgwood valve is 20.06mm (0.790") in diameter. The depression is 16mm (0.629") hence the expression "oversquare" and a reduced distance to push the valve down. So, in our 12mm bore instruments, we have a lesser distance valve depression than Mr. Bach.

 
Is it all "Ovoids"?

(c) 1999 Medici