Like many instruments, accordions have trouble keeping up with louder and amplified instruments and over the years people have tried many ways to amplify their sound.
One of the earliest accordion amplifying techniques is the crystal microphone, which was starting to come into use by the late 40’s. Crystal mics were relatively small and inexpensive so a good system could have 6-7 mics with stereo separation of a sort, with separate tone and volume control for the left and right sides. Simpler crystal mic systems had as few as one mic and no onboard volume control at all.
Crystal mics vary in quality and their response is uneven through the audio frequency range. What’s more, response of these mics can deteriorate over time and in some cases they can die entirely. I will occasionally install crystal mic systems in accordions for people who need a vintage sound and I often have to sort through old sets to match up a new set . They can also have a strange echo at the end of each note, but placement of resistors can help.
Condenser mic systems for accordions are a newer type and have been around since at least the 70’s but they too run into some of the same problems that installers found with crystal systems: there is no such thing as a standard accordion so there can be no standard microphone system. Some systems appear to have been designed in a lab by somebody with little experience with accordions and can suffer for reliability issues and no troubleshooting support.
Quality of installation can vary wildly and have a effect on the long term reliability of a mic system, and the types of plugs used to connect the parts of the mic system is important. (The fun ones to work on have no plugs so you can’t separate the bellows from the accordion for service or sometimes the grill is attached by the mic wires and can’t be removed completely.)
It takes 5-6 hours to install one of these mic systems and then they weren’t always reliable, which added on even more hours of (unpaid!) work because of the warranty I offer Most mic systems were not adaptable to the many variations of accordion construction and many older accordions have no clearance under the grill, and finding a location for the output jack can be a problem.
In response to these problems, I designed a mic system of my own: With modern tech the boards did not need to be large, but I did want the solder points to be accessible to normal soldering tools and wire. Plugs would be industry standard and findable in the future for service. The mics would be on wires so the board could be put in whatever space was available and the mics could be placed for optimum sound.
I use two mics in the bass side so you get an even volume across the bass range to reduce the risk of “hot spots” or uneven output on larger accordions. Three mics seems to be enough to get an even response on the right side. (Some Limex systems I’ve worked on use as many as 12 on the right side!)
I find that internal mics under the grill are best for performing accordions because the closer you can get a microphone to the source of the sound, the less likely feedback will occur. The microphone capsules are directional by design so they are less sensitive to outside noise than sound from the accordion.
A obvious solution would seem to be to place the mics inside close to the reeds like some of the older crystal systems. Condenser mics can’t generally be placed inside the accordion as the changing air pressure will eventually damage them, and will cause distortion. It is also difficult to get separation of the left and right side of the accordion this way. Separation is achieved by placing mics under the grill and inside the bass machine area, a nice side effect is separate volume control that will allow you to do things like use only the piccolo reed on the right and the master register on the left.
This setting would be unusable on most accordions as the piccolo would be drowned out by the bass. With good separation you can turn down the bass to match the output of the keyboard. This will sound unbalanced on the accordion but will sound fine coming out of the amp.
Don’t forget that amplifiers have a big effect on the sound. Standard solid state guitar amps can make almost any accordion sound sharp and metallic. In a pinch a bass amp will give a better sound overall. Keyboard amps are better than guitar amps in most cases but they seem to vary. I have been really happy with the sound of tube or hybrid amps because they seem to warm the tone somewhat and generally sound better with accordions.