Using headphones at a sufficiently high volume level may cause temporary or permanent hearing impairment or deafness. The headphone volume often has to compete with the background noise, especially in loud places such as subway stations, aircraft, and large crowds. Extended periods of exposure to high sound pressure levels created by headphones at high volume settings may be damaging to hearing;[25][26] Nearly 50% of teenagers and young adults (12 to 35 years old) in middle and high income countries listen to unsafe levels of sound on their personal audio devices and smartphones.[27] however, one hearing expert found in 2012 (before the worldwide adoption of smartphones as the main personal listening devices) that "fewer than 5% of users select volume levels and listen frequently enough to risk hearing loss."[28] The International Telecommunication Union recently published "Guidelines for safe listening devices/systems" recommended that sound exposure not exceed 80 decibels, A-weighted dB(A) for a maximum of 40 hours per week.[29] The European Union have also set a similar limit for users of personal listening devices (80 dB(A) for no more than 40 hours per week) and for each additional increase of 3-dB in sound exposure, the duration should be cut in half (83 dB(A) for no more than 20 hours, 86 dB(A) for 10 hours per week, 89 dB(A) for 5 hours per week and so on. Most major manufactures of smartphones now include some safety or volume limiting features and warning messaging in their devices.[30][31] though such practices have received mixed response from some segments of the buying who favor the personal choice of setting their own volume levels.
Dale: There are so many types of amplifiers (and DAC’s with amplifiers) that there is no shortcut for studying all of the options, unless you settle for the most generic approach. Important things to consider are power – if you don’t have enough power for your headphone and the dynamics in the music, clipping will result. Sometimes the clipping is “soft” and not readily noticed, but eventually you would discover that much of the detail goes missing or gets veiled with limited dynamics. Another consideration is whether to use a DAC, which may be a separate DAC or built into the same enclosure as the amp. Most DACs will improve the sound over the DACs that are built into computers, but when a DAC is available to replace the DAC built into most cellphones and low to mid-priced music players, you can usually expect a much greater improvement.

Just a few hours of burn-in today – I don’t expect much change with Tesla-quality drivers etc. The treble is recessed almost as much as the Philips M1 I had, kind-of a worst-case scenario. So I took out my most minimal non-peaky non-bright non-sibilant headphone – the B&O H6, and even though it doesn’t sound the same as the T51p because of the H6’s “light” midrange, I wanted to get a sense of how much the T51p was recessed below a very minimal treble. My Foobar2000 settings were +2 at 2.5, +4 at 3.5, +2 at 5, +4 at 7, +6 at 10, 14, and 20 khz. Normally I wouldn’t do the dip at 5 khz, but the T51p has a nasty 10 db peak around 5 khz, which makes it difficult for portable use without a customizable equalizer. Without a treble boost it sounds very boomy as well as muffled. I can understand Beyer going to a darker sound with more bass – in fact I thought it was a move in the right direction. But they need to cut that (resonant?) peak around 5 khz. I compared to several other headphones and none of those were anything like that.
The iPhone will drive the headphone fine and make a very nice sound, but the amp will make a big improvement in harmonic extension and soundstage. Use the amp whenever possible. Both Headfonia and I concur that the E07k is a great amp, and probably the best thing you can get for up to twice the price. I’m familiar only with the E07k, the E17, and the E12. I think the E07k beats the E17 (and both are also USB DACs), while the E12 is just an amp, and has a darker sound but with more power for inefficient headphones. The Philips is not inefficient.
Hi. I have more or less decided that the Philips Fidelio L1s are the ones for me. I plan to use them on my commute paired with an iPhone or the iPad as the source. I listen to a mix of pop, rock, blues and jazz so I’m not after boosting bass but I might want to fiddle with the dial on the treble and mids. Which brings me to my question. You state in your review that the L2s pair well with the Fiio e17 which lets you independently adjust treble and bass. Could the same effect be achieved lower down the $$ curve via a combination of say a Fiio E6 (for signal amplification) and a Dirac or Accudio app for equalisation?

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.

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.