How do sound-isolating earphones work?

I'm frequently asked about sound-isolating earphones, how they work and what they're good for, and quite frankly I think they're something many people would benefit from using. For the benefit of all concerned, I felt it was time for the definitive, easily accessible guide to the pros and cons of this type of portable headphone.

What is sound-isolation?
Sound-isolating earphones are normal earphones, except that they're inserted deeper into the ear canal. In addition they utilise tips -- usually made from silicone or foam -- that form a seal in the canal, thereby isolating sound within the ear and passively blocking out external noise.

'Passive blocking' simply means there are no electronics involved in the reduction of the noise surrounding the listener, and it works in exactly the same manner as the conventional earplugs you might wear on a plane or when working with drills.

There are several other advantages to sound-isolating earphones. Firstly, by reducing the amount of ambient noise that enters the ear when listening to music, it's possible to have the music playing at a lower volume. Your tunes needn't be turned up to better drown out the sound of chattering on a bus or the rattling of the train racing along its tracks. This is much safer for your ears.

A typical sound-isolating earphone

Secondly, when there's a good seal between the silicone or foam tips of the earphone, the bass and low-end frequencies of music are typically enhanced. This not only helps music sound meatier, but it can also make it sound warmer and more natural.

Since there are no batteries involved in the process, you needn't worry about heavy battery compartments, bulky headsets or costly battery replacements in future. But remember, sound-isolating earphones won't be able to block out the excessive low-end rumble you might hear on a plane, for example. For that, you'll want noise-cancelling headphones that actively annihilate that noise.

The only other disadvantage of sound isolation is that noise created by the movement of the cable -- when you're walking along, for instance -- is conducted into the ear. This means if you use your earphones when you're walking to work or exercising, for example, you'll hear plenty of rustling, depending on how much the cable moves around. One solution to this is to select a pair of silicon tips that are slightly looser. You'll lose a little in sound quality and bass conductivity, but it will reduce the distraction of the rustling.

A great first pair of sound-isolating earphones are Sennheiser's CX 300s, or the slightly more costly -- but much more impressive -- CX 500s.