This post explains multi-path, diversity receivers, and a new antenna for eliminating the problem.
When a microphone transmitter sends out a radio wave signal, it spreads through a room, like ripples on a pond. As the wave encounters flat surfaces, like walls and ceilings, it reflects and continues forward at different angles. Since there are multiple surfaces in every room, there are multiple reflections and hence multiple paths--some longer and some shorter--that a wave takes before reaching the wireless receiver.
Usually, the receiver is able to process two or more signals arriving at slightly different times without difficulty. But if the signals overlap in such a way that they cancel each other out (creating a “null”) you get a drop in volume or complete drop-out. Sometimes, the shape of the room can cause a multi-path null to perpetually hover over a receiver. Other times, when the speaker walks past a certain spot on the platform, a dead spot will develop and you’ll hear a quick drop-out.
Diversity receivers filter out multi-path interference by using two antennas instead of one. Most wireless receivers that have two antennas are diversity receivers. Since a multi-path null occurs only in specific and relatively small locations, it is less likely that a null will exist over both antennas. This is called “spatial diversity.” But spatial diversity does not work 100% of the time.
Some of the possibilities are that the null can cover both antennas, that two nulls can be over each antenna, or that the dead spot can move around as the microphone moves across the stage or platform.
Recently, RF Venue has developed an antenna based on polarization diversity that is able to eliminate 100% of multi-path interference when used with diversity wireless receivers.
Radio waves have a unique property called “polarization,” which is the type of shape of movement that the wave takes as it travels. The basic explanation is that polarization changes when the wave encounters reflective surfaces.
The RF Venue Diversity Fin uses a cross-polarized design that discriminates between waves of different polarizations, instead of waves that are in different locations. The result is zero multi-path interference in a single antenna device. You can watch a video about the Diversity Fin on our product page.
There are other wireless problems that cause drop-outs and interference, like competing signals and low signal. But getting rid of multi-path is often enough to significantly improve wireless performance in your auditorium.