Here is a shot of a home made ribbon microphone and frame that is built out of six pieces of iron and a couple of flat magnets. You can't see the ribbon which is well in the middle of the magnets which are quite wide and not very long.
This motor unit was made to measure the flux density of the gap with and without back iron. The advantage of back iron is that it increases the magnetic field strength, and the disadvantage is that it represents an acoustic obstacle and therefore limits the high frequency response.
There have been a couple of licensed public spectrum users (what I once referred to as "ham" radio) who I have spoken with who have recently built similar home constructed ribbon mics and put them on the air recently. The public has access to spectrum for this type of on-the-air experimentation in most countries of the world. Generally referred to as "amateur radio", the resource is gradually being accessed by a new generation of experimenters and others who want to have free access to some usable spectrum for personal communications and for scientific, engineering and educational purposes. To access spectrum in your country, you may or may not need a license, depending upon the portion of spectrum you wish to use. Generally if you want to get good distance you must use fairly high power, which requires a simple license indicating you know how to use it safely and without making a lot of interference or noise which would disrupt others.
There are a lot of people doing long-haul Wifi, for example, and getting free internet access as a result.