For most, a smartphone, a streaming music service subscription and a pair of headphones is sufficient for listening on the go, so why would someone consider an external amp and what benefits might they offer? This article, the first in a new mini-series looking at dedicated, external amplifiers, will explore the reasons why someone might choose to pick up an extra device for their portable audio setup.
So, in what circumstances would you need a headphone amplifier?
External amplifiers are designed to bypass or augment the performance of the internal amplifier found in the audio source device, so to determine why one might be needed, we need to explore why someone might want to go around, or improve upon, the amplifier already inside their phone or laptop.
The first and simplest reason to consider an external headphone amplifier is to improve the sound quality of your audio. For most device makers, sound quality is a low priority compared to other specifications. This is particularly true for mobile devices, where portability is crucial, and features such as the overall size of the product and battery life are higher priorities for general users, and therefore the manufacturers. To save money, space and potentially battery power, many manufacturers use cheap, low quality amplifier chips, or rely on amplifiers integrated into multi-purpose components which prioritise quantity of function over quality. These components can output poor quality and distorted sound. A dedicated, external amplifier can sometimes offer a better sound quality than using headphones directly from the source device by offering quality amplifying components which bypass the cheap internal chips.
The second reason to consider a dedicated amplifier is power. Not only offering poor sound quality, the cheap amplifier chips inside mobile devices can be incapable of driving enough power into certain types of headphones to achieve an adequate sound pressure level (volume) for comfortable listening. Many modern headphones, especially in-ear models, are optimised for use with mobile devices and generally don’t need the additional power provided by a dedicated amp, however more specialist headphones may need more than a mobile device can provide on its own.
The two key headphone specifications to pay attention to in relation to power are impedance and sensitivity, the combination of which will give an indication of the headphone’s efficiency; how much power is needed to comfortably generate sound. As a rule of thumb, headphones with a low sensitivity (below 93dB) and a high impedance (above 80 ohms) will generally benefit from the power provided by a dedicated amplifier. These numbers can vary depending on other factors, including the technology used for the headphone driver, distortion and damping, which we’ll explore in a later blog. For headphones with lower impedances and higher sensitivities, generating the sufficient volume required from a phone, tablet or laptop is generally not a problem. However, a dedicated amplifier might still improve sound quality for many headphones, especially if the unit combines the amplifier with a dedicated DAC, another component which will be discussed in a later blog.
As a case study, consider the RHA MA750i and CL750 – two products similar in aesthetics but with different driver configurations. The MA750i is optimised for use with mobile devices, featuring a three-button remote and microphone for use with Apple® products; it has a high sensitivity of 100dB and a low impedance of 16 ohms, numbers which are typical to mobile-friendly headphones. In contrast, the ultra-wideband transducer configuration of the CL750 has a lower sensitivity of 89dB, a higher impedance of 150 ohms and is therefore better suited to use with a dedicated amplifier to achieve sufficient volume and a higher sound quality than that of the smartphone-friendly MA750i. To answer the question posed at the beginning, those listening with the MA750i may receive some benefit from using a headphone amplifier depending on their source device, whether they also use a dedicated DAC component and their quality of music files; those with the CL750 will be sure to miss the full benefits of its specialist technology without one.
So having considered the above and having decided that you need a dedicated, external amplifier, we will discuss what to look for in an amplifier and how to pick one that’s right for your portable audio setup in the next part of the series.
[UPDATE: minor edits were made to this blog on 23/11/16 to reflect updated information, links and products]