There have been a couple of audio VNA's (AVNA) in QEX. Here is mine:
This is not a commercial product, but rather a construction project with a PCB, etc. It covers 10 Hz to 40 kHz with S11, S21 and a bunch more stuff. There is a pretty good pdf instruction book to see how to use it.
The bad news is that the Teensy 3.6 microcontroller/DSP is no longer available. The good news is that there is a redo planned for the project using the Teensy 4.1, that is available. See the groups.io for more:
/g/AVNA1/topic/new_version_of_avna_with/109504643This is not for everyone as some assembly is required, but the end result is an instrument that is very parallel to RF VNA's.
I believe there is a sound card version of an AVNA around, but I have no personal experience with it.
73, Bob W7PUA
