2020/01/20

THE POLARITY OF WIRELESS BELT PACK SYSTEMS

Polarity-cover.jpg
When using wireless microphone systems, the polarity of the signal chain from input to output of the reciever should be preserved: A positive-going pressure in front of the microphone membrane should provide a positive-going voltage at pin 2 of the output (XLR) connector.
A normal wired (balanced) microphone works in this way.

However, the problem is that some manufacturers of (unbalanced) miniature microphones make units with reversed polarity due to some technicalities. To overcome this problem, some wireless systems (belt pack transmitter plus receiver) have built-in polarity reversal (reverse + reverse = not reversed).

DPA miniature and instrument microphones are all in-phase. Thus, the user should be aware of this when using a transmitter system with reversed polarity.

Polarity-of-wireless-belt-pack-systems-illustration-(1).jpg

Below is a list of wireless belt-pack based manufactures. The list indicates the polarity of the transmission system from the (electrical) input of the belt-pack to the output of the receiver.

Please note that within each brand there might be custom-designed systems, where specs do not follow these general rules. Additionally, as mentioned, some of the more sophisticated digital transmitters have an option for switching polarity. 
 
 Brand Polarity
 AKG N
 Audio Limited N
 Audio-Technica P
 Beyerdynamic P
 LD Systems N
 Lectrosonics P
 Line 6 P
 Micron P
 Sennheiser N
 Shure P
Some models (ULX) are switchable
 Sony Depends on the model
 TOA N
 Trantec P
 Wisycom Switchable
 X2 Digital Wireless N
 Zaxcom P
N = Negative: reversed polarity
P = Positive: correct polarity

 

If using a DPA miniature microphone with a signal-reversing transmitter, you can correct the polarity at the input of your mixer or recorder in two ways:

  1. Insert a passive phase inverter between the output of the receiver and the input of the mixer/recorder. An example of a phase inverter is an XLR adapter where pin 2 and 3 are reversed.

Example of XLR adapter for phase reversal: Neutrik NA3FMX

 
  1. If the input channel has the phase-reversal function, activate the phase switch (a button with a sign like: φ or: Ø).

Example of phase reversal button.
 

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