UK audio gear company Advanced Communications Solutions (ACS), founded by Andy Shiach, has been supplying musicians with custom-made in-ear monitors and ear protection since 1995.

Bands such as U2 shell out £649 for its T1 monitors for the breadth of sound and noise isolation while on stage, but audiophiles with deep pockets are also enthusiastic. A post on headphonehaven.com enthuses: "T1s have more oomph and sound more organic."

As Mathew Jones, Acs managing director, explains, the product is like the difference between buying off the peg and tailor-made. Because the sleeve on an ACS in-ear monitor is custom-moulded using silicone to fit the shape of your ear, he says, you'll never have a set of headphones as comfortable.

Customers swear by the superior sound, he adds. "Our technicians have spent five months developing the new incarnation of the T1. Trying to beat the quality we already have is hard, but they've done it."

Now the business is casting its net wider by selling £90 custom sleeves to fit over other manufacturers' earphones. It has started the ball rolling through a partnership with Apple and Etymotic Research.

Jones explains: "Every Etymotic earphone sold through the Apple store has the option to custom-sleeve the tip and that's really driving sales. We're launching worldwide, so we'll sell through Apple stores in every territory."