Choosing a good pair of headphones
I spend much of my working day listening to audio through my headphones. Sometimes I listen to Dolby Audio with a spatial virtualiser and other times I’m listening to Spotify to mask that annoying sound coming from the air-conditioning duct. The headphones are almost always on my head, so it’s not surprising that I’m picky about my headphone specifications. Here are the features I take into consideration.
The most common drive unit in headphones is the dynamic driver design. It consists of a static doughnut-shaped magnet mounted in the plastic and a coil of thin wire attached to a stiff diaphragm is suspended within its magnetic field. When the varying current of an audio signal is passed through the coil, it interacts with the magnetic field causing the attached diaphragm to vibrate. The vibrating diaphragm pushes on the air to produce sound waves.
The quality (and price) of the headphones is largely dictated by the materials used for the coil and diaphragm. The diaphragm is typically made of cellulose, polymer, carbon material or paper.
There are many modifications to be basic design with many marketing buzzwords. Double-sided spiralling coils allow twice as many conductors to be placed within the magnetic field, which leads to higher sensitivity, better damping, and better drive force.
A problem with the dynamic drive unit design is the non-linear distortion caused by the distorting shape of the diaphragm as it vibrates. This is particularly true at higher volumes.
Another design, called planar magnetic, consists of a relatively large membrane with an embedded wire pattern. This membrane is suspended between two sets of permanent, oppositely aligned, magnets. When the varying current of an audio signal is passed through the embedded wires, it interacts with the magnetic field causing the membrane to vibrate and provide sound.
The planar magnetic drive unit design produces a uniform driving force across the membrane. This results in reduced audio distortion and excellent transient response. Although these drive units may be slightly heavier and have less bass response.
Listening to audio over headphones is different to listening over speakers. When listening on speakers, both ears hear the left channel from the left speaker and the right channel from the right speaker. This effect is called inter-aural crosstalk. The subtle variation of the volume and phase of each channel heard at both ears allows the brain to perceive the localised direction of the sound. When listening over headphones, the left ear hears only the left channel and the right ear hears only the right channel. There is no inter-aural crosstalk which means the audio can appear “within the head”. For Dolby Audio, the location of the centre channel can be perceived as lost. Panning sounds between the left side and right side will sound different and hard-panned sounds will be heard only in one ear rather than from one side. Listening to audio like this for long periods can be fatiguing.
Spatialisers are algorithms that apply audio processing to the left and right channels so that the audio is perceived as bigger or more spatial. The audio appear to “out of the head”. The algorithms do this by filtering and combining the left and right channels to each of the left and right ear. They artificially create the inter-aural crosstalk that would be present when listening over speakers. For this reason, these algorithms are sometimes called speaker virtualisers. Of course, the algorithms are a little more complicated than what I’ve explained and Dolby has been developing and improving algorithms in this area for a long time.
Some people love spatialisers and others don’t. It’s a personal choice since the way we perceive audio and it’s direction is different for everyone. It also depends on the audio. If the audio already has effects applied or are binaural recordings, then the combination of the algorithms might produce bad results. It’s worth seeing if it works for you.
OVER EAR HEADPHONES
Over-ear headphones are definitely the way to go. They provide good sound isolation and plenty of bass. Earbuds become painful after many hours. On-ear headphones also tend to be uncomfortable after a few hours, but may be the best option if you wear glasses or concerned about messing your hair!
Over-ear headphones also tend to provide the best sound production. They can provide a larger drive unit that is capable of producing better bass and a flatter frequency response. Look for a frequency range between 10Hz and 25kHz. However, significant response at less than 20Hz is unlikely. Support for lower frequencies will allow you to hear the LFE channel of Dolby Audio.
Over-ear headphones can be closed-back (aka closed can) or open-back (aka open can) design. There are endless arguments archived forever on the internet espousing personal preferences for one over the other. Open-back headphones have vents in the cups to allow the pressure to equalise and prevent the sound waves bouncing off the closed plastic back. They tend to be more comfortable and provide more natural, precise sound without distortion. Most headphones are open-back design.
Pay attention to the weight of the headphones too. If you’re wearing them all day, you don’t want heavy headphones, but you do want them to be robust. Around 250g is reasonably comfortable. Wireless headphones will contain batteries which make them heavier and provide less space for good drive units. I’m not convinced that wireless headphones provide a good solution.
If you take your work on the road, then noise-cancelling headphones could be a good option. Although most people associate noise-cancelling headphones for use on planes, I’ve found that my noise-cancelling headphones successfully eliminate that annoying vibration from the air-conditioning duct! And I use them on the plane too. Definitely worth considering if you can find a pair at a good price.