Headphone Earpad Selection
Earpads tend to be one of the most misunderstood components of a headphone design. The earpad obviously affects comfort and styling but is often not recognised as a key contributor to audio performance. In fact earpads have a massive influence on the audio character of a headphone. A poorly performing headphone can be completely transformed to something that sounds great just by getting an earpad that compliments the rest of the headphone design.
Earpad are most commonly built with a foam block interior covered with an outer material. The most common foams are open celled, that means means that air can move freely in and out of the foam. These types of foam tend to be more springy and have a lighter feel and a generally low cost. Memory foams, although technically open celled, do not share the same characteristics as the common open celled foams, these are not springy and instead change shape relatively slowly. Memory foams are higher density and therefore heavier. The advantage of memory foams is that they tend to form a better seal on the head and block more external noise. Memory foams are normally the way to go for noise cancelling and noise isolating headphones. The disadvantage is that the memory foam earpad will tend to make ears hotter and trap in any perspiration making it less comfortable for long wear periods.
The go to choice for earpad surfacing is artificial leather (leatherette). These materials can be made very soft and have a real leather look. Ironically real leather is not often used for headphone earpads because it is not soft enough. There are a few forms of animal skin that are soft enough but these are often prohibitively expensive for headphones and have inconsistent supply. The quality of artificial leathers vary dramatically, some will look and feel great for many many years, others will disintegrate in less than a year. A normal range of abrasion and soak testing will discriminate the good from the bad here. Velour is another popular choice having fantastic comfort and better breathability than leatherette.
The cheapest and most common type of earpad is sewn with a top, bottom and lip. The earpad hooks onto a matching lip on the headphone. This type of construction works well enough for a lot situations but does result in a fairly flat earpad. The thickness is limited by the foam hardness and surfacing stretchiness.
Increasingly a 4 part earpad construction is being used. In this style the front face is cut as a doughnut, then inner and outer walls are built separately. Finally the front face, walls and rear surface are sewn together. This style of construction has become popular because it allows for thickness without increasing the foam hardness. In fact this type of construction allows for more variety of shapes in general.
The earpad affects the acoustics of the headphones front chamber in profound ways. An earpad that has a relatively high degree of acoustic transparency can serve as a damping mechanism for unwanted resonances, however misuse of this property can lead to significant energy loss and loss of SPL, especially in the mid range. For best results the earpad design must be matched to the rest of the acoustic system.