Basically, the resonator is a tube, closed at one end and open at the other end (what acousticians call a quarter-wave resonator) with a place for the stack and heat exchangers somewhere inside. In practice, there are a couple of modifications we'll make to this basic idea.
First off, the tube can't be open to the outside air (unless we restrict the working gas to air at one atmosphere, which isn't the best choice). But we have to keep the open end open, or the resonator won't resonate. So what we do is attach a large volume to the open end.
Here's an example of a complete thermoacoustic engine. This one is
driven by a loudspeaker at the top, rather than the driving stack that
we've been talking about, but everything else is pretty much the same.
Notice that the device is oriented so that the closed end of the resonator is at the top, and the open end (with its spherical volume) is at the bottom. Why? Because heat rises, and the closed end is the hot end. For efficiency, the hot end is usually placed above the cold end.
Also notice that the stack and heat exchangers are placed close to the
closed end (at the top). This placement helps to reduce viscous
losses (viscous effects are proportional to velocity, so we put the
stack close to the velocity minimum).
This page maintained by Wil Howitt