Liquid microphones are not, and never were, the best option for projecting sounds. In this day and age we know they are not the most functional devices for the production of music. Regardless, the history of their creation is worth telling. And it is not only because the physics it involves. It is also because liquid microphones were the key for the later creation of the condenser microphone. Let’s take a look at how they work!
Liquid Microphones: The Physics
Liquid microphones, also known as a water transmitters, are based on Ohm’s law. Let’s put it otherwise. They follow the principle that establishes that current in a wire varies in reverse to the resistance of the circuit. When the sound waves of a human voice generate a vibration in a diaphragm, the needle or rod also vibrates. Afterwards, when this vibration is set in water with a little bit of acid, the resistance of the liquid is altered. So is the current within the circuit. To complete this process, the resistance of the liquid must fluctuate over the distance that lies between the vibration of the needle or rod.
This all sounds as if liquid microphones were useful for projecting voices, does it not? Well, here’s the reason why it’s not the case.
Water + Some Acids = Not Great
The combination of water with a little bit of acid tends to be perfect. The reason is it generates enough altering current to transmit audio signals through a long distance. However, it’s worth mentioning that one millimetre of acidulated water has a resistance of 100 ohms. Then, two millimeters have 200 ohms, and so on. As a result, some substances don’t really work out accurately. One example of this is mercury. The resistance of one millimeter of mercury is much lower than a tenth of an ohm.
A Bit of History
Elisha Gray believed that a metal rod with up-and-down vibrations would be able to both lengthen and shorten the distance between the bottom of the rod and the metal plate located at the bottom end of a water-filled glass container. In other words, she described the way a vibrating rod can vary the resistance when inserted in water. Alexander Graham Bell came into the picture. Years later, he and Thomas Watson created a popular water transmitter that worked out perfectly. With a simple needle inserted in water, Bell achieved to lessen the inertial mass of the diaphragm. Over the decades, several alterations were made to liquid microphones. This inspired Thomas Edison to test the resistance variable with dry carbon.