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.
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.
The Samsung Galaxy Buds are one of the best-scoring portable Bluetooth headphones Consumer Reports has ever tested. That’s all the more impressive given their “true wireless” design, meaning the model doesn’t have a cord connecting the left earbud to the right. That’s the same design scheme popularized by Apple’s AirPods, but our testers say the Galaxy Buds sound dramatically better.
The E25BT didn’t score quite as high for audio quality as other models on this list, and it lacks some features you’ll find on certain other models, such as water resistance and extended battery life. But if you want a pair of wireless headphones that provide decent sound at a fraction of the cost of its competitors, the E25BT is an appealing option.
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; 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. 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." 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. 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. though such practices have received mixed response from some segments of the buying who favor the personal choice of setting their own volume levels.
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.
This type combines advantages of earbuds and in-ear headphones – depending on the environment and requirements of the user, they provide passive noise reduction for quality mode (conversation or active music listening) or they give control over the sound environment around user in comfort mode (stand by or background voice/music listening).
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.