TR50 Omnidirectional Lavalier Microphone with Shure TA4F The Tram TR50 is a professional omni-directional electret condenser lavalier microphone with a low-profile design resulting in low visibility. The TR50 features a frequency response that enhances the character and frequencies associated with speech. The omni-directional polar pattern provides a generous pick up response at the direct and off-axis sections of the microphone capsule. The result enhances sensitivity and minimizes noise associated with movement, wind and clothing contact. The TR50 features minimum sound coloration and is available in a variety of connectors for direct integration with wireless transmitters. The TR79 power supply (not included - for power supply order XL models) allows direct connection to XLR microphone inputs. Bias is basically which way power flows to the microphone. Think of any piece of electronic equipment that requires a battery to work. When you install the battery, you need to insert it the correct way. The positive(+) side and the negative(-) side of the battery needs to be inserted the proper way. If you insert the battery the wrong way it won't work. If you are using a wireless microphone system or a lavalier power supply, that unit's bias and the bias of the lavalier must match for the microphone to work. Some wireless system only offer negative bias, some only offer positive bias and some offer both bias options. The same goes for lavalier microphones, some can only be used with negative bias, some only with positive bias and some can be wired to be used either way. The ones that offer both options are of course the most versatile, but also the most confusing. Lectrosonics Wireless Systems and Tram Microphones are two examples that offer both bias options. So whether your Tram is wired for positive or negative bias, it will work either way with a Lectrosonics. The problem comes into play when you are using a "detachable lavalier power supply". If the power supply is positive bias, the microphone must be positive bias as well. If you attempt to connect a negative bias microphone into a positive bias power supply, it will not work.