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.
We use a commercially-available Bluetooth high-def interface with an S/PDIF output to test the Bluetooth output of four flagship phones. This way, we’re able to record test signal output and compare the datasets with our in-house analysis software. We kicked the tires on a 96kHz/24-bit test file to see how Bluetooth handled high-bitrate music, as well as normal 44.1kHz/16-bit files to see how each codec treated CD-quality streaming audio. We then measured the recorded sample against the original file. We used both lograrithmic sine sweeps, and complex signals like square waves in order to provide a more realistic set of tests for how people actually use Bluetooth headphones.
The impedance of headphones is of concern because of the output limitations of amplifiers. A modern pair of headphones is driven by an amplifier, with lower impedance headphones presenting a larger load. Amplifiers are not ideal; they also have some output impedance that limits the amount of power they can provide. To ensure an even frequency response, adequate damping factor, and undistorted sound, an amplifier should have an output impedance less than 1/8 that of the headphones it is driving (and ideally, as low as possible). If output impedance is large compared to the impedance of the headphones, significantly higher distortion is present. Therefore, lower impedance headphones tend to be louder and more efficient, but also demand a more capable amplifier. Higher impedance headphones are more tolerant of amplifier limitations, but produce less volume for a given output level.
Electrostatic drivers consist of a thin, electrically charged diaphragm, typically a coated PET film membrane, suspended between two perforated metal plates (electrodes). The electrical sound signal is applied to the electrodes creating an electrical field; depending on the polarity of this field, the diaphragm is drawn towards one of the plates. Air is forced through the perforations; combined with a continuously changing electrical signal driving the membrane, a sound wave is generated. Electrostatic headphones are usually more expensive than moving-coil ones, and are comparatively uncommon. In addition, a special amplifier is required to amplify the signal to deflect the membrane, which often requires electrical potentials in the range of 100 to 1000 volts.
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A: What you plug your headphones into can significantly affect their sound, and the quality of the amplifiers built into portable CD/MP3 players is generally awful. It's not their fault: the little guys have to power their electronics and their internal amplifier using a few puny volts. Even some of the better home AV receivers' headphone jacks offer highly variable sound quality.
The usual way of limiting sound volume on devices driving headphones is by limiting output power. This has the additional undesirable effect of being dependent of the efficiency of the headphones; a device producing the maximum allowed power may not produce adequate volume when paired with low-efficiency, high-impedance equipment, while the same amount of power can reach dangerous levels with very efficient earphones.
Pairing high sensitivity headphones with power amplifiers can produce dangerously high volumes and damage headphones. The maximum sound pressure level is a matter of preference, with some sources recommending no higher than 110 to 120 dB. In contrast, the American Occupational Safety and Health Administration recommends an average SPL of no more than 85 dB(A) to avoid long-term hearing loss, while the European Union standard EN 50332-1:2013 recommends that volumes above 85 dB(A) include a warning, with an absolute maximum volume (defined using 40–4000 Hz noise) of no more than 100 dB to avoid accidental hearing damage. Using this standard, headphones with sensitivities of 90, 100 and 110 dB (SPL)/V should be driven by an amplifier capable of no more than 3.162, 1.0 and 0.3162 RMS volts at maximum volume setting, respectively to reduce the risk of hearing damage.
Transducer technologies employed much less commonly for headphones include the Heil Air Motion Transformer (AMT); Piezoelectric film; Ribbon planar magnetic; Magnetostriction and Plasma-ionisation. The first Heil AMT headphone was marketed by ESS Laboratories and was essentially an ESS AMT tweeter from one of the company's speakers being driven at full range. Since the turn of the century, only Precide of Switzerland have manufactured an AMT headphone. Piezoelectric film headphones were first developed by Pioneer, their two models used a flat sheet of film that limited the maximum volume of air movement. Currently, TakeT produces a piezoelectric film headphone shaped similarly to an AMT transducer but, which like the Precide driver, has a variation in the size of transducer folds over the diaphragm. It additionally incorporates a two way design by its inclusion of a dedicated tweeter/supertweeter panel. The folded shape of a diaphragm allows a transducer with a larger surface area to fit within smaller space constraints. This increases the total volume of air that can be moved on each excursion of the transducer given that radiating area.
However, the Bose 700 earphones have a much slimmer profile when folded up, and they have a few updated elements, including more integration with digital assistants, touch controls, and sensors for Bose’s “augmented reality” apps. Bose has kept some of the best-loved features from its older models as well, such as adjustable levels of noise cancellation, a monitoring mode to let in sound from your environment, and an advertised 20-hour battery life. According to Bose, call quality is improved as well, though CR doesn’t test call quality in headphones.
EQ controls: Equalization, more commonly referred to as EQ, controls the different aspects of sound that come through your headphones, and some headphones come with custom apps that let you adjust the EQ in granular detail. With the right EQ controls, you can add more treble, bump up the bass, or just create a sound profile that’s suited to your tastes. If you’re into customizing how your music sounds, look for headphones that work with an EQ app.
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.