The results have come back from the
lab at UNSW for my first Equal Tempered Bugle (valveless trumpet). Tested on their world class, super long impedance tube.
My design uses an existing bell and
mpc but adjusts the bore in between to create the intonation, desired. In this case the design goal was a bugle that would play the
equal tempered pitches of the A harmonic series. Tuning control is possible because every step it the bore can be modeled as a conical section, each with its own
input impedance. If we decrease the
diameter at a high pressure area, the pitch rises, we decrease the diameter at a low pressure area, the pitch falls. (This is call
perturbation theory in acoustics). Using a computer and several days of computer time, the cumulative effect of such changes can eventually be calculated to give an instrument of any desired tuning. The original design simulation was run till the design was tune to with in 1/1000 of a semitone so that a real instrument, with its inevitable construction flaws, would still be dam good. In a real instrument, the tube is never perfectly round, the ends never perfectly flush and so on. However the prototype instrument returned values with in 3c which is less that the error in the
FFT used. In real trumpets tuning errors of 20-40c are standard! A trumpet with tuning to less than 10c is called "
superb". So for my first effort, I'm totally stoked. What does it play like you ask? Firstly the notes just start with out any resistance, the tuning locks in and stays there through any crescendo or decrescendo. Its just a bugle but mate, its one hell of a bugle! It is proof the a bore does not have to be smooth to play smooth. A bore in fact needs to have changes in it, but you have make those steps work for you instead of just being random.
THE MARK II. So currently I am running simulations on various trumpet BELL FLARES. Depending on the bell flare chosen the bell itself may return a harmonic series or not and may be close to Equal
temperament or not, it may radiate a lot of sound or trap it. Hence bell choice is critical to the
finished instrument. Concurrently I am examining the acoustic effect of the design and location of a valve section as this is the most disturbed part of the bore. The MARK 2 will be a one valve bugle will have one of my own bells on it and a single valve to drop the pitch a tone.
After that I should be ready to prototype a 3 valve trumpet. EXCITING TIMES - stay tuned.
Regards
Peter Miles
Kartu http://www.tresmambo.com/
