How do it works?
Rezonator (outer piston with mass) moves but inner membrane follows with phase delay,
because gas behaves in the loop (due to the mass of the gas) as if it were a solid displace piston.
Outer membrane is 40mm (pvc tube) wide and inner is 80mm (jam jar cap
Inner membrane is only on 10-15mm wide disc connects the rod.
So far, I have built twice, and immediately worked well.
I don't know how the engine changes when the pressure is higher (not atmospheric).

-iron mop handles about 20-30cm long:
-membranes thin rubber gloves

Why is this a good engine?
Compelling Engine
This engine forces the frequency
so works in a wide frequency range.
No adjusting problem.

It works very simply, easily  and stably.
The resonance frequency of the engine is not the loop resonance frequency. Mass of the resonator gives the frequency of the engine. So engine works variety of resonator mass.
We can use it easily under pressure engine!
It is very simple for model and you can buld easily.
How doec compelling thermoacoustic engine?

1. When the gas (air) is heated then it expands.
When the gas (air) colled then it shrinks.

2.The gas (air) is in the tube as a  spring.

3.The gas (air) is in the tube as a piston (mass).

Small membrane is 4 cm wide.
Big membrane is 8 cm wide.
Membranes are from thin and flexible rubber gloves:

Merkel and her companions must be very punishment!