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Jet Object

Description

Simulates a wind jet created by a flue in a fipple. It can be used with the 'labium connection to create an oscillating air vortex that excites an air column in a tube to produce a recorder/flute model.

(make-object 'jet ... )

Syntax and Default Values

A 'jet object can be created using the following Lisp syntax (the default values are shown for each of the physical parameters): 

(make-object 'jet
             (pressure 1.0)
             (air-density 1.2)
             (air-speed 340)
             (length 0.03)
             (width .02)
             (height .001)
             (flue-labium-distance .004)
             (labium-position 2e-4)
             (mouth-surface 8e-5))

Parameters

The parameters for this object are a little different from regular objects:

  • pressure: pressure controller for the jet.
  • air-density: medium density of sound radiation in the propagating medium (kg/m3).
  • air-speed / celerity: swiftness/speed of the sound in the propagating medium (m/s).
  • length: length of the flue for the jet formation
  • width: width of the flue
  • height: height of the flue
  • flue-labium-distance: distance from the end of the flue to the labium
  • labium-position: position of the labium with respect to the flue
  • mouth-surface: this is set to 8e-5 by default and does not need to be changed

To simulate propagation in air (room temperature at sea level), you should use an air density value of 1.2 kg/m3 (this parameter is sometimes called rho), and the speed of sound in air, 340 m/s, for air-speed (celerity can be used instead of air-speed for this parameter). The final mouth-surface controller has been documented for completeness but does not need to be provided.

Discussion

The jet object is a special object in Modalys because it implements a nonlinear waveguide model, researched and created by Marc Pierre Verge for his doctoral thesis, instead of the usual modal description model. Consequently it is used is a slightly special way in the Modalys environment.

The fipple is the the mouthpiece of a whistle, recorder or other simple flute that generates a jet for sound production. The flue, sometimes also called a duct or “windway,” focuses a jet of air onto the sharp labium - also known as a blade or “windcutter.” The labium itself causes this jet to break into a vortex or whirlpool of air which oscillates back and forth across the labium. The image, above, shows the anatomy of a fipple, with several of its components that relate to this model clearly labeled.

Accesses

The jet is a special object in that it is generally used directly by the 'labium connection, without an access.

In theory you can create accesses at three places on the jet object:

  • 'foot
  • 'flue-exit
  • 'labium

However, for the moment we suggest just using the jet with the 'labium connection, as shown in the simple example script, below:

(setq breath-env (make-controller 'envelope 1 '((0 0) (0.1 100) (1 100) (1.1 0))))
(setq jet (make-object 'jet (pressure breath-env)))
(setq tube (make-object 'closed-open-tube))
(setq tube-acc (make-access tube (const 0) 'long))
(make-connection 'labium tube-acc jet (const 0) (const 4.99 .1 1) (const 0.005))
(setq tube-out (make-access tube (const .9) 'long))
(make-point-output tube-out)


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