When Axel Grell, engineer at German company Sennheiser, chose the music to test what he thinks is the world’s best headphone, he turned not to Teutonic hi-tech sounds from Kraftwerk or Paul van Dyk, but instead used some good old blues records. “John Lee Hooker is my favourite testing artist,” says Grell, an acoustics developer who is nicknamed the Headphone Pope by his colleagues. “I simply know every note and every distortion on these records. I know how the music is supposed to sound.”

This sums up his firm’s down-to earth approach towards its products. Over the years Grell and his team have been working towards one goal – to build headphones that reproduce music as close to the original as possible. “We leave colourful designs and ever-changing fashion statements for other brands,” says Frank Hermann, director of marketing communications at Sennheiser.

For connoisseurs in the premium market Sennheiser produces headphones such as its new HD 800 (a €1,000 affair that comes in a satin-lined box), handmade at the company’s headquarters in the small town of Wennebostel near Hannover. The headphones took Grell more than 10 years to develop, a process he says costs over €1m. The firm’s founder, Dr Fritz Sennheiser, once ­famously said that his engineers needed ­­­­­ to fool around in order to be creative. So fool around Grell did.

Developing a new headphone usually begins with drawing ideas on a piece of paper, says Grell, then moves on to a 3D model of the transducer – the headphones’ speakers. Grell talks at length about ­oscillations, modes and swaying coils, but his aim is simple – to achieve the lowest possible amount of what experts call “total harmonic distortion”. That means no unnaturally high-pitched voices and no booming hip-hop bass.

Before the HD 800 is finally boxed and ready for shipment, one of the 22 female manufacturing technicians painstakingly dusts off the hardware with a small clothbrush. “Most people in my country have no idea how positive the image of ‘Made in Germany’ is all over the world,” says Frank Hermann.

Increasingly, customers seem to like this dedication. Total sales for the family-owned company have risen from €229m in 2002 to €385m in 2008. Almost 30 per cent of the revenue comes from headphone sales; wireless microphones rank second at 26.2 per cent, and other products, such as wired microphones, conference and tour guide systems and aviation headsets, each account for less than 10 per cent of sales.

After the headphones, most professionals know Sennheiser for its high-quality ­microphones – in 1946, they were the second item added to the company’s product list (the first being Fritz Sennheiser’s 1945 tube voltmeters). The launch microphone was the DM 1 and innovations soon followed thick and fast. Sennheiser built the first noise-compensated microphone in 1949 and the first interference tube microphone for the film and television industry in 1954. It introduced its wireless microphone in 1957, unveiled the baby monitor in 1962 and the clip-on microphone for RF wireless transmission in 1968. In 1983 the company boasted a new creation – the smallest ever studio clip-on microphone – and in 2000 it launched MKH 80, the first studio condenser microphone to fully utilise the wider frequency range of the new digital audio formats.

In 1991, Sennheiser acquired Georg Neumann – which for many is the standard-setting manufacturer that leads in studio microphones. Neumann products, such as the new and versatile TLM 67, receive rave reviews from experts and combine cutting-edge technology with a tasteful retro design.

But is this kind of German engineering ethic an anachronism in times when most people listen to compressed versions of music on their iPods? Does Sennheiser cling to a long-lost ideal of authenticity? Grell thinks not. “Each decade had its own sound,” he says. “The music of the 1970s with its record players and tape machines was warmer than the ‘cold’ digital sound of the 1980s coming from CDs and synthesizers.”

But for the engineer, one is not better than the other. Both are, again, just types of “distortion” – as is the compressed and radio-friendly tones of the 1990s or the harsh, artefact-rich MP3 sound of today. Grell’s job is simply to reproduce each one as perfectly as possible.

Sennheiser is a medium-sized enterprise acting globally: more than 80 per cent of its turnover is generated outside Germany. It has more than 2,100 employees, more than half of whom work in the small town of Wennebostel near Hannover but research is also conducted in Palo Alto, California and Singapore, and headphone production is mostly in Ireland. Microphones as well as headphone- and microphone-capsules come out of the German headquarters.