Cisco 7940 - IP Phone VoIP Phone Manual page 14

In some cases, hum may be reduced or eliminated by using a local power cube or power
Note
injector.
These environmental and hardware inconsistencies in the locations where Cisco Unified IP Phones are
deployed means that there is not a single headset solution that is optimal for all environments.
Cisco recommends that customers test headsets in their intended environment to determine
performance before making a purchasing decision and deploying en masse.
Audio Quality Subjective to the User
Beyond the physical, mechanical and technical performance, the audio portion of a headset must
sound good to you (the user) and to the party on the far end. Sound quality is subjective and Cisco
cannot guarantee the performance of any headsets. However, a variety of headsets from leading
headset manufacturers have been reported to perform well with Cisco Unified IP Phones. See
manufacturer's sites for details.
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