Headphones are available with a wide range of feature sets to make your listening more convenient, useful and pleasurable for your particular listening style.
Noise Cancelling: Noise cancelling headphones are designed to prevent you from hearing ambient noise. They use tiny microphones within the earpieces to sense the ambient noise around you via an active [battery powered] electronic circuit that amplifies, inverts and then adds the signal back to the music signal to "cancel" the acoustic ambient noise. Some of the best noise cancelling headphones use digital signal processing (DSP) to create better isolation performance.
Closed Headphones can block upper treble frequencies nearly as well as noise cancelling headphones, but do not effectively remove low rumble frequencies like those heard in an airplane or train cabin, so they are not as good for travel purposes. Noise cancelling headphones are almost always closed-back earcup designs.
In Ear Headphones provide far more noise blocking ability than any other type of headphone, including noise-cancelling designs. However, some listeners may not like inserting in-ear headphones into their ears like earplugs as required.
Wireless: There are generally two categories of wireless headphones: those designed for use at home (often used for watching TV) and those with Bluetooth wireless (more info below) typically used with portable devices, tablets and smartphones.
A wireless signal can be transmitted a number of ways. Infra-red systems employ an invisible red lightwave like a TV remote control; they are limited to one room and to line-of-site reception and can suffer from poor signal quality. Wireless systems that use radio frequency (RF) are usually 900 MHz FM analog transmission schemes and can usually reach throughout an entire home. However, as you get farther away from the base station transmitter you'll hear more hiss in the audio. Other wireless systems use 900 mHz FM digital transmission. When you're in range, the audio will be crystal clear, but when you begin to slip out of range the wireless signal will waver or drop out entirely.
Bluetooth: Smartphone, tablet, laptop computer and portable device wireless systems can employ a number of different wire-free transmission methods. Bluetooth wireless is most common in smartphone and laptop headset headphones. It offers fair to decent sound quality and is largely noiseless. Recent Bluetooth 3.0 employs an updated, better-performing digital wireless transmission scheme than previous Bluetooth iterations.
Microphone: Headphones with a built-in mic allow you to listen to music and answer your phone calls. There are many different types of headset headphones including in ear headsets, Bluetooth headsets and others.
In the next Headphone 101 series, we'll be walking our way through the various applications of different headphones. We sure hope to see you there!