An electret driver functions along the same electromechanical means as an electrostatic driver. However the electret driver has a permanent charge built into it, whereas electrostatics have the charge applied to the driver by an external generator. Electret and electrostatic headphones are relatively uncommon. Original electrets were also typically cheaper and lower in technical capability and fidelity than electrostatics. Patent applications from 2009-2013 have been approved that show by using different materials, i.e. a "Fluorinated cyclic olefin electret film", Frequency response chart readings can reach 50 kHz at 100db. When these new improved electrets are combined with a traditional dome headphone driver, headphones can be produced that are recognised by the Japan Audio Society as worthy of joining the Hi Res Audio program. US patents 8,559,660 B2. 7,732,547 B2.7,879,446 B2.7,498,699 B2.
The tech-speak description for this type of headphone is "circumaural," which includes any headphones with earcups that fully enclose your ears. Because of their size and their acoustic isolation, full-size headphones are often considered to be better-suited to home use rather than as a portable option, but the recent popularity of full-size, noise-canceling Beats headphones are challenging the rule.
Headphones (or head-phones in the early days of telephony and radio) traditionally refer to a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an audio source privately, in contrast to a loudspeaker, which emits sound into the open air for anyone nearby to hear. Headphones are also known as earspeakers, earphones[1] or, colloquially, cans.[2] Circumaural ('around the ear') and supra-aural ('over the ear') headphones use a band over the top of the head to hold the speakers in place. Another type, known as earbuds or earpieces[1] consist of individual units that plug into the user's ear canal. A third type are bone conduction headphones, which typically wrap around the back of the head and rest in front of the ear canal, leaving the ear canal open. In the context of telecommunication, a headset is a combination of headphone and microphone.
However, we also move up to high-resolution audio files, as well as a wide variety of sources, including plugging in directly to a PC or Mac, using USB DACs (digital-to-analog converters), and employing high-quality, dedicated portable players and amplifiers. Finally, we compare the headphones to some of our go-to models, both in their class and price point, as well as a level or two above to find out if they can punch above their weight.
There are many good articles here on Headfonia. You could click on Buyers’ Guides and read through those, then click on the Headphones topic header for each individual report. The “process” you go through is learning your own sound preferences, then matching that to the products that are available. It is a process, so you have to learn the major differences. Any shortcuts you take might be OK, but when you buy something that you discover you don’t like, make sure you can return that item.
Once you’ve got that all order, to put a cherry on top it would be ideal for the amp to play nice with my laptops (PC at work, Mac at home) *and* my *iPhone* 4S.  I haven’t found a headunit that works with PCs and iDevices.  If one doesn’t exist it would be a big plus for the amp to include inputs so I can get digital sound out of my iPhone (with the Pure i20 or its ilk) and into my headphones.
Over-ear and on-ear headphones effectively block out outside sounds, allowing you to hear your music or whatever else you're listening to crisply and without distraction. Over-ear headphones are sometimes known as full-size headphones because they completely envelop the wearer's ear. This results in what's known as passive noise reduction, which makes these some of the most-preferred headphones available. The only drawback is that your ears and the skin around your ears can get warm and sweaty. These are usually the heaviest type of headphones.