A pair of headphones are useful in many circumstances for a sound engineer, whether in the studio or on location. Headphones are available with many different specifications and to the novice it may seem difficult to make the right choice. This AudioCourses article will outline the basic specifications of headphones available today.
Before we go any further it must be noted that we will be talking about circumaural headphones with dynamic drivers/transducers. Circumaural headphones enclose the ear and are the choice in studios all over the world. Alternative forms such as In-Ear and Supra-Aural, are generally not suitable for serious audio work although they are fine connected to an iPod or Walkman for casual listening.
It should also be said that mixing on headphones is undesirable, and headphones should only be used as a reference rather than a replacement for studio monitors.
Closed vs Open
The choice between closed and open is probably the most important decision. Both have their pros and cons so the decision should focus on the environment in which they will be used.
Closed back headphones, such as the Beyer DT 100 excel at both preventing spill from the headphones into the microphone when recording, and also preventing outside noise from reaching the wearer. This means they are the logical choice for musicians when tracking as the lack of spill ensures a cleaner signal and also makes feedback less likely to occur when nearer the microphone. In a live sound environment closed headphones are invaluable. As very little sound is let in from the outside world it allows the engineer to listen to a different source than the FOH mix – for instance the engineer can solo channels and try to identify any rogue signals. For location recording, DJs and broadcast usage, closed headphones are preferable due to the aforementioned reasons.
This type of headphone will often appear to give a good representation of low frequencies but this is tempered by the coloration to the sound that placing a diaphragm in a closed environment incurs. The fit of the headphone onto the ear is also important as to fully benefit from the advantages of closed back headphones a good seal must be made between the cushioned earpiece and the ear. If this seal is not satisfactory acoustical isolation in both directions is lost.
Open back headphones, such as the Beyer DT 990 Pro, do not offer the same level of isolation as their closed back counterparts. Open headphones usually look similar to closed back headphones but with a ‘grille’ on the rear of the enclosure (as can be seen in the picture of the DT 990 Pro). The presence of a grille allows freer movement of sound both in and out of the earpiece. This makes open designs unsuitable in recording situations as spill into the microphone will be excessive and the likelihood of feedback (‘howlaround’) is increased. These characteristics also make open designs unsuitable for most broadcast and location recording.
The area in which the open design excels however is the sound quality. Although the low end may not appear as well defined as closed designs, the reproduction of other frequencies is likely to be more accurate as there is less coloration from the design of the earpiece. These characteristics make open back headphones suitable for critical listening in quiet environments, such as the control room. As mentioned earlier, mixing should not be attempted with headphones, but for analytical listening headphones are very useful during mixdown for finding rogue noise or checking reverb tails.
This figure details the range of frequencies that the headphones can reproduce. The average humans hearing range is 20Hz-20,000Hz. You will often see headphones will frequency responses that stretch beyond either of these limits. What is critical in interpreting these figures is variation in level over the frequency response. If the headphones can produce 10Hz-40,000kHz but dip or peak in level by 10dB above 10,000Hz then they are not particularly suitable. For serious audio work peaks and troughs should be less that 3dB – this is often represented by a figure such as +/-3dB or ±3dB at the end of the frequency response i.e. 10Hz-30,000Hz +/-1dB.
The Impedance of headphones is measured in ohms (Ω ) and is, crudely speaking, how hard the amplifier must drive the headphones. Most dedicated headphone amplifiers such as the Samson S-amp will be capable of driving most headphones satisfactorily. If you are connecting headphones to equipment such as a mixing console or DJ mixer then you should read the technical specifications to ensure you buy headphones with the correct impedance. Some headphone manufacturers offer a number of different impedances for a given model. The DT 100 mentioned earlier is an example of this.
There are some other criteria not relating to sound quality that should also be considered when purchasing headphones.
Many high end microphones offer a modular design which ensures that repairs are cheap and parts are plentiful. Non modular headphone designs are often difficult or financially unviable to repair.
The comfort of the headphones is also important and if possible you should try as many designs as you can to find the best balance of sound quality and comfort.
Most headphones terminate into a stereo 1/4″ jack (sometimes with a minijack underneath a 1/4″ adaptor), but some manufacturers produce models with an XLR connector. It is wise to determine which kind of connections are present in your studio and make your choice based on that. Most studio equipment and headphone amplifiers accept 1/4″ jacks, but when using stage boxes there are often XLR’s provided for returns.