Rotating Woofer-Port and Cabinet

It is straightforward to extend the above computational model to include the rotating woofer port (``baffle'') and wooden cabinet enclosure as follows:

• In [189], it is mentioned that an AM ``throb'' is the main effect of the rotating woofer port. A modulated lowpass-filter cut-off frequency has been used for this purpose by others. Measured data can be used to construct angle-dependent filtering in a manner analogous to that of the rotating horn, and this ``woofer filter'' runs in parallel with the rotating horn model.

• The Leslie cabinet multiply-reflects the sound emanating from the rotating horn. The first few early reflections are simply handled as additional sources in Fig.5.6.

• To qualitatively simulate later, more reverberant reflections in the Leslie cabinet, we may feed a portion of the rotating-horn and speaker-port signals to separate states of an artificial reverberator (see Chapter 3). This reverberator may be configured as a ``very small room'' corresponding to the dimensions and scattering characteristics of the Leslie cabinet, and details of the response may be calibrated using measurements of the impulse response of the Leslie cabinet. Finally, in order to emulate the natural spatial diversity of a radiating Leslie cabinet in a room, ``virtual cabinet vent outputs'' can be extracted from the model and fed into separate states of a room reverberator. An alternative time-varying FIR filtering approach based on cabinet impulse-response measurements over a range of horn angles is described in [191].

In summary, we may use multiple interpolating write-pointers to individually simulate the early cabinet reflections, and a ``Leslie cabinet'' reverberator for handling later reflections more statistically.

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About the Author: Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.