Traditional aircraft used an audio panel in the avionics stack to handle multiple radios, audio sources, and intercom between the occupant headsets. This was logical when there were so many audio sources which needed to be monitored for different segments of flight – two radios, identifying VORs and NDBs, listening for the outer marker signal, etc.
With the growing availability of GPS for all segments of flight including precision landing, some aircraft have done away with an ADF and even NAV radios. My plane is one of these. There are pros/cons to this configuration but for a lot of domestic flying, it’s safe and complete.
Many newer radios incorporate the intercom and even have alert and auxiliary audio inputs. With all of he capabilities of these modern radios, most of the audio panel capabilities are redundant. The exception is supporting two radios.
Two radios are handy since one radio should always be setup to talk to the airport or to air traffic control. The second radio can handle things like checking weather at the departure or arrival airport. It can also be helpful when you know you will be changing frequencies multiple times in a short period – eg: weather, clearance, ground, tower, then departure control.
Having two radios doesn’t dictate an audio panel. Switching frequencies has become much easier with database integrated radios and EFIS/GPS connected radios. With these systems, a frequency change is often a press of a button.
This leaves the listening to weather and the “convenience cases” when you want to load up clearance and ground to a second radio. The “listen” to the second radio can be handled through an auxiliary input on the primary radio. Now we have only one case to solve – temporarily switching to the second radio.
In a side-by-side airplane, both occupants have access to the panel but in a tandem (or solo) only the pilot can reach the panel. Only the pilot really needs access to both radios. My airplane is a tandem and I fly 99% solo.
A pilot headset has a MIC, a push-to-transmit, mono or L/R headphones, and the ground wire. That’s 5 connections. A switch can handle toggling all 5 wires at once between two radios.
The sixth switch lets us listen to the second radio while connected to the first.
Below a video of the switch. The switch has both solder lugs and PCB pins. The pins can be cut off when using the solder lugs. The push button switch “latches” when pressed and releases when pressed again. It has a mechanical colored indicator that is visible when pressed to the “latched” position.