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  2. Sound-powered telephone - Wikipedia

    en.wikipedia.org/wiki/Sound-powered_telephone

    Modern emergency telephone powered by sound alone. A sound-powered telephone is a communication device that allows users to talk to each other with the use of a handset, similar to a conventional telephone, but without the use of external power. This technology has been used since at least 1944 [1] for both routine and emergency communication ...

  3. Active noise control - Wikipedia

    en.wikipedia.org/wiki/Active_noise_control

    Noise control is an active or passive means of reducing sound emissions, often for personal comfort, environmental considerations, or legal compliance. Active noise control is sound reduction using a power source. Passive noise control is sound reduction by noise-isolating materials such as insulation, sound-absorbing tiles, or a muffler rather ...

  4. Mobile radio telephone - Wikipedia

    en.wikipedia.org/wiki/Mobile_radio_telephone

    t. e. A mobile radio telephone. Mobile radio telephone systems were mobile telephony systems that preceded modern cellular network technology. Since they were the predecessors of the first generation of cellular telephones, these systems are sometimes retroactively referred to as pre-cellular (or sometimes zero generation, that is, 0G) systems.

  5. Sound reinforcement system - Wikipedia

    en.wikipedia.org/wiki/Sound_reinforcement_system

    On the other hand, a sound reinforcement system can be as simple as a small public address (PA) system, consisting of, for example, a single microphone connected to a 100-watt amplified loudspeaker for a singer-guitarist playing in a small coffeehouse. In both cases, these systems reinforce sound to make it louder or distribute it to a wider ...

  6. Phone etiquette 101: When it’s rude to be on speaker - AOL

    www.aol.com/news/phone-etiquette-101-rude...

    Don’t use speakerphone. Do not use speakerphone for calls you make in public — use headphones. This is especially true for video calls or when watching to something on your device. This ...

  7. What 'secret' loudspeaker codes mean at department stores - AOL

    www.aol.com/news/2010-10-13-what-secret...

    If you've been shopping in a big box retail store you've probably heard an announcement on the loudspeaker such as, "code yellow toys, code yellow toys." This "code" is one of many innocuous ...

  8. Noise-cancelling headphones - Wikipedia

    en.wikipedia.org/wiki/Noise-cancelling_headphones

    Noise -cancelling headphones alongside a carry case. Noise-cancelling headphones are headphones which suppress unwanted ambient sounds using active noise control. This is distinct from passive headphones which, if they reduce ambient sounds at all, use techniques such as soundproofing . Noise cancellation makes it possible to listen to audio ...

  9. Why sudden loud booms sometimes occur when it's very ... - AOL

    www.aol.com/weather/why-sudden-loud-booms...

    During extreme cold events, you may hear a loud boom and feel like you have experienced an earthquake. However, this event was more likely a cryoseism, also known as an ice quake or a frost quake ...