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Rectangular Membrane - Fixed


A rectangular membrane with a thickness of zero, fixed at the edges.

(make-object 'rect-membrane ... )

Syntax and Default Values

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

(make-object 'rect-membrane
             (modes 80)
             (length0 .5)
             (length1 .5)
             (tension 1000)
             (surface-density .1)
             (freq-loss 10) 
             (const-loss 10))


The arguments for the physical parameters can be either numerical values or Modalys controllers (either dynamic or constant). If a given parameter is not supplied when using the Lisp syntax, the default parameter value will be used.

  • modes: number of modes.
  • length0: length along the x-axis in meters.
  • length1: length along the y-axis in meters.
  • tension: in Newtons.
  • surface-density: surface density in kg. NB: was named "mass" in older versions of Modalys.
  • freq-loss, const-loss: loss coefficients. See General object information.

Note that, unlike other objects, the values for freq-loss and const-loss default to 10 for this object.


A rectangular membrane can be accessed in its z-direction ('normal) from any point on its surface.

(make-access my-membrane my-2D-controller 'normal)
This makes an up-and-down access (in the z direction) at a point on the surface of my-membrane. The point is defined by my-2D-controller where the first dimension is x and the second is y (the membrane's corners being the points (0, 0), (0, 1), (1, 0) and (1, 1)). For example, in order to access the center of the plate we can say:

(make-access my-membrane (const 0.5 0.5) 'normal)



A rect-membrane can be tuned to a specific pitch, using the (set-pitch ...) function, by adjusting one of the following physical parameters:

  • 'size
  • 'tension
  • 'mass

Note that for 'size, both the x and y dimensions are scaled together proportionally in order to preserve the harmonic relationships the membrane's mode frequencies.

(setq my-membrane (make-object 'rect-membrane))
(set-pitch my-membrane 'size (const 110))

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