These methods take their name from techniques for the analysis of electrical networks having two pairs of wires - or ports - which can be connected to external sources, loads, etc.. The acoustical equivalent is a system having two locations at which acoustic variables (pressure & velocity, or equivalents) are specified.

The resulting frequency domain descriptors are incredibly useful in forming models of a wide range of "low ka" acoustic systems.

I picked up the basics from David P Egolf when working at the Department of E.E. at the University of Wyoming.

Modelling Acoustic Waveguides

	For example, a uniform lossless acoustic waveguide 
	of cross section S, extending from x=0 to x=L,  
	has the acoustic variables at each end related by a matrix equation:

	In which k is the wavenumber.
	So the square "chain" matrix is a fixed descriptor of the waveguide
	which completely describes how the waveguide will behave in  any  application !

	Show me some code !
	Show me some applications !

I soon realised that the same two port method can be applied to electroacoustic transducers, and to the acoustic systems in which they are operated. I don't claim that this is novel - but I have taken the methods a long way and developed a range of modelling techniques (and associated computer code) which I have proven in a number of real engineering applications.

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	For example, the two port model of a 
	direct radiating electrodynamic loudspeaker is....

	in which 	V and i are the input electrical variables, 
			p and u are the cone pressure and velocity, respectively, 
			and all other symbols have their usual meaning. 

	So the square "chain" matrix is a fixed descriptor of the loudspeaker
	which completely describes how it will behave in  any  application !

	Show me some code !
	Show me some applications !

I presented a paper describing some applications of two port loudspeaker driver models at the AES conference "The Ins and Outs of Audio" and I based much of the Postgraduate Certificate in Reproduced Sound at the University of Salford on the two port method.

I can offer professional support for applications of two port methods in electroacoustics and MATLAB code to make low frequency models of loudspeakers, microphones, lumped acoustic elements, waveguide segments, generalized impedances AND perform the neccessary matrix manipulations on the resulting frequency domain chain matrices - contact me.

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