The Helmholtz resonator is a prototype of a single acoustic resonance, which can be modeled with a digital resonator. This paper extends this concept by coupling several Helmholtz resonators. The resulting structure is called a Helmholtz resonator tree. The height of the tree is defined by the number of resonator layers, which are interconnected. The overall number of resonance frequencies of a Helmholtz resonator tree is the same as its height. A Helmholtz resonator tree can be modeled using Wave Digital Filters (WDF), when electro-acoustic analogies are applied. A WDF tool for implementing Helmholtz resonator trees has been developed in C++. A VST plugin and an Android mobile application were created, which can run short Helmholtz resonator trees in real time. Helmholtz resonator trees can be used for the real-time synthesis of percussive sounds and for realizing novel filtering, which can be tuned using intuitive physical parameters.

Submitted to Proc. of the 15th Int. Conference on Digital Audio Effects (DAFx-12) , York, UK , September 17-21, 2012 .

• Examples for evaluation of tree structure effect
• Helmholtz resonator tree height effect
• Type 0, 2 x 3 Resonator tree generated using VST plugin.
• Type 0, 3 x 3 Resonator tree generated using VST plugin.
• Type 0, 4 x 3 Resonator tree generated using VST plugin.
• Type 0, 5 x 3 Resonator tree generated using VST plugin.


• Helmholtz resonator tree number of branches effect
• Type 0, 4 x 2 Resonator tree generated using VST plugin.
• Type 0, 4 x 3 Resonator tree generated using VST plugin.
• Type 0, 4 x 4 Resonator tree generated using VST plugin.
• Type 0, 4 x 5 Resonator tree generated using VST plugin.


• Helmholtz resonator tree structure effect
• Type 0, 2 x 3 Resonator tree generated using VST plugin.
• Type 1, 2 x 3 Resonator tree generated using VST plugin.


• Examples using Android Mobile application
• Excitation at H00 generated using mobile application, and 3 x 2 resonator tree.
• Excitation at H00 generated using mobile application, and 3 x 2 resonator tree.
• Excitation at H10 generated using mobile application, and 3 x 2 resonator tree.
• Excitation at H11 generated using mobile application, and 3 x 2 resonator tree.
• Excitation at H20 generated using mobile application, and 3 x 2 resonator tree.
• Excitation at H21 generated using mobile application, and 3 x 2 resonator tree.
• Excitation at H22 generated using mobile application, and 3 x 2 resonator tree.
• Excitation at H23 generated using mobile application, and 3 x 2 resonator tree.
• Sequence of excitations generated using mobile application, and 3 x 2 resonator tree.
• Video 1 and Video 2 with sequence of excitations for showing mobile application on real time.
• Sequence of excitations with constant noise at the root generated using mobile application, and 3 x 2 resonator tree.
• Video 1 and Video 2 with noise excitation and sequence of excitations for showing mobile application on real time.
• Variation of H00 generated using mobile application, and 3 x 2 resonator tree.
• Variation of H10 generated using mobile application, and 3 x 2 resonator tree.

• Examples for evaluation of tree structure effect
• Impedance variation for a Type 0, 3 x 2 resonator tree
• Volume variation at H00 resonator.
• Volume variation at H10 resonator.
• Volume variation at H20 resonator.