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FAQ

• What does the NoiseGard on/off switch do?

  The NoiseGard on/off switch is the switch that allows you to turn the active noise compensation circuitry on or off. It comes with a two colors LED for-power on and low battery-on headsets using a battery pack.

  NOTE: If you should turn off the NoiseGard system there is no loss of, or reduction of, the received audio and you still retain the passive capabilities of the headset. You may have to increase the receiver volume to compensate for the increase of ambient noise due to the loss of the NoiseGard feature. The LED is located on the control-unit respective to the battery pack of the headsets. The control unit is included in-line on the models HMEC 45/46 series, HMEC 25/26 series, and HMEC 460 series. An optional battery pack is available for the HMEC 350 series.

  
  
  
• What is the maximum SPL of a dynamic microphone?

  It is a common saying that dynamic microphones just have no maximum SPL.
  This saying is not technically exactly correct but for every day use use of dynamic microphones you will not find gain limitations. At SPL levels above 160 dB some mechanical problems might occur (for example the voice coil might crash onto the magnet) but these SPL levels are very hard to find in real world.
  Here at Sennheiser we use dynamic microphones for distortion measurements on loudspeakers at very high sound pressure levels. At Sennheiser we have measured the SPL and THD inside a large 2" driver/horn combination with a MD 421. The max SPL this combination was able to produce was 150 dB and the THD level recorded by a MD 421 was below 1% (produced by the driver not by the mic)
  So as a conclusion we can state the MD 421 has no maximum SPL limitations for practical use. However if using dynamic microphones at high SPL levels a user should be aware that the very high voltage (up to several volts) delivered by the microphone might cause problems when connected to mic preamps.