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.
In early powered radios, the headphone was part of the vacuum tube's plate circuit and carried dangerous voltages. It was normally connected directly to the positive high voltage battery terminal, and the other battery terminal was securely grounded. The use of bare electrical connections meant that users could be shocked if they touched the bare headphone connections while adjusting an uncomfortable headset.
Noise cancellation: Noise-cancelling headphones play specific tones, much like white noise, to cancel out all of the sound around you and allow you to enjoy your music uninterrupted. Noise-cancellation is an active process, so headphones with this feature require batteries. If you’re a frequent flyer, or if you’ve got a noisy commute to work each day, you’ll love noise-cancelling headphones: they’re fantastic at keeping the cacophony of the outside world at bay.
If you’re buying wireless headphones, keep a spare pair of wired headphones around in case the others run out of battery. Wireless headphones are definitely the future, and the convenience is a huge benefit, but they rely on battery power to work their magic, and batteries run out. If you’re going to be in a place where you won’t be able to recharge your wireless headphones, consider keeping a backup wired pair with you so the music never has to stop.
Released in 2015, the SoundLink Around-Ear II are Bose’s wireless over-ear headphones that don’t have active noise cancellation. They’re lighter and slightly more travel-friendly than a lot of the company’s other offerings, and they could sound quality at the forefront. At the time, the big selling point for the SoundLink Around-Ear II was their sound quality — Bose claimed that they sounded as good as wired headphones, which admittedly doesn’t hold up in 2019 (streaming and Bluetooth have gotten too good).
LDAC is a strange family of codecs, not merely because they’re the only codecs that really attempt the hi-res thing, but because they have perplexing issues with common phones. For example, the bitrate defaults are wildly different from phone to phone. The Samsung Galaxy Note 8 and LG V30 both default to 660kbps, and the Google Pixel 3 defaults to the lesser 330kbps. However, the noise present with every LDAC connection is far greater than it is with a regular old 3.5mm headphone jack.

At the heart of the WH-1000xM3 is outstanding wireless sound. Sony’s LDAC technology delivers a wireless signal at what the company claims is three times the quality of standard Bluetooth streaming, and the headphones also support the latest aptX HD codec (with supported devices). The 1000xM3 even “upscale” wireless music from high-resolution audio devices using a special chip, helping to make music sound dynamic and beautiful, with authoritative bass and clear treble response held together by a well-rounded midrange.
Be sure to assess the build quality of your prospective headphones. Some earbuds and portable devices are relatively fragile, for instance. If the headphones fold up for easy storage, are the hinges robust, or will they fall apart in a month or two? Don't forget to consider that the earpads and earbuds will get extensive wear and tear over the life of the headphones.

I think it’s fair to compare the Grados and HD598, but the M50 is very different and seems not to fit in that comparison. The DT770 is a better comparison to the M50, although the 770 is a better more expensive item. A long time ago I had a Grado 325 and a Sennheiser HD565 – very similar, very enjoyable. Today for that type of sound I might choose the Soundmagic HP100.
Today they are typically used only in in-ear headphones and hearing aids, where their high efficiency and diminutive size is a major advantage.[20] They generally are limited at the extremes of the hearing spectrum (e.g. below 20 Hz and above 16 kHz) and require a better seal than other types of drivers to deliver their full potential. Higher-end models may employ multiple armature drivers, dividing the frequency ranges between them using a passive crossover network. A few combine an armature driver with a small moving-coil driver for increased bass output.
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.