User manual SENNHEISER HMEC 25-KA

[. . . ] The Problem of Noise The negative effects of noise pollution have been proven by studies, and everybody will have experienced them at some time or another: Nervousness Lack of concentration Irritability And these are only the most obvious effects on the human body. Noise also affects the autonomic nervous system and can lead to permanent hearing damage. [. . . ] A noise reduction of 10 dB is generally perceived as a halving of the loudness, another 10 dB decrease halves the loudness yet again whitch corresponds to a loudness reduction of 75 %, and so on. As per ARINC it receives its operating voltage via a connector from the aircraft´s internal power supply. This is a dynamic headphone system which, in addition to reproducing the original audio signal, electronically cancels the low frequencies of the ambient noise. This active noise compensation operates on the principle that sound and "anti-sound" (in phase opposition) cancel each other out. The NoiseGardTM compensation circuitry in the headphone requires an extra power supply, so a battery compartment has been integrated into the headset cable (see illustration on the right). Clearly intelligible communication is ensured, and the pilot no longer has to turn the volume up to overcome ambient noise. Inserting the batteries into the battery box The NoiseGardTM compensation circuitry is powered via a battery pack integrated into the headset cable. Insert two AA size batteries into the box as shown in the digram below. Switching the power supply on/off The on/off switch for the power supply of the compensation circuitry is at the front of the battery box. Pilot light An LED on the battery box indicates the battery status: When the LED lights up green, the power supply for the compensation circuitry is sufficient. When the LED is red, the batteries are almost flat and should be changed immediately. If the LED does not light up at all when the power supply is switched on, the batteries are completely flat. [. . . ] Sound pressure level Output voltage Terminating impedance Operating voltage Noise-cancelling back-electret condenser microphone capsule Contact pressure Weight without cable Cable Connectors HMEC 25-KA KG declare that this device is in compliance with the applicable CE standards and regulations. Up to date information on Sennheiser products can also be found on the Internet at "http://www. [. . . ]