A balanced armature is a sound transducer design primarily intended to increase the electrical efficiency of the element by eliminating the stress on the diaphragm characteristic of many other magnetic transducer systems. As shown schematically in the first diagram, it consists of a moving magnetic armature that is pivoted so it can move in the field of the permanent magnet. When precisely centered in the magnetic field there is no net force on the armature, hence the term 'balanced.' As illustrated in the second diagram, when there is electric current through the coil, it magnetizes the armature one way or the other, causing it to rotate slightly one way or the other about the pivot thus moving the diaphragm to make sound.
Sports headphones are among the most popular types of headphones and the best ones are now wireless. Sweat-resistant or even totally waterproof, they can be used at the gym or for running or biking. Some are have an open or semi-open design to let some sound in for safety reasons (so you can hear traffic noise). However, other models have a sealed, noise-isolating design.
The QuietComfort 20 headphones have been around for years and years; and they’re essentailly an in-ear alterative to Bose’s QuietComfort 25. They offer the same great active noise-cancellation that the company is known for, just in a traditional wired and in-ear form factor. The QuietComfort 20 can also be switched to an “Aware” (aka ambient) mode, so you can better hear the world around you.
The Soundsport Free, released in the fall of 2017, are Bose’s first truly wireless earbuds. They utilize the same StayHear+ Sport tips as the company’s other in-ear headphones, making them naturally more sweat-resistant and more secure than AirPods. They work with the Bose Connect app, which is pretty basic but does have a “Find My Buds” feature that, when enabled, can help you find your earbuds should you misplace them.
Passive noise isolation is essentially using the body of the earphone, either over or in the ear, as a passive earplug that simply blocks out sound. The headphone types that provide most attenuation are in-ear canal headphones and closed-back headphones, both circumaural and supra aural. Open-back and earbud headphones provide some passive noise isolation, but much less than the others. Typical closed-back headphones block 8 to 12 dB, and in-ears anywhere from 10 to 15 dB. Some models have been specifically designed for drummers to facilitate the drummer monitoring the recorded sound while reducing sound directly from the drums as much as possible. Such headphones claim to reduce ambient noise by around 25 dB.
Earbuds have small speakers that rest on the ear canal of the wearer. These are usually much less expensive than on-ear and over-ear headphones and reproduce the sound well. However, outside sounds, such as traffic or power tools, can get past the earbuds and interfere with your enjoyment. Earbuds also don't stay in place very well if the wearer is moving much, such as exercising. These also are lower fidelity than on-ear and over-ear headphones.