A Chat With One Of The World's Top Headphone Engineers

Sennheiser makes some of the best headphones in the world regardless of whether you want to pay $70 or $US1500. Today, we're lucky enough to have Sennheiser Senior Acoustic Engineer Axel Grell here to answer a few of our questions.

Amongst Grell's many accomplishments are the designs for Sennheiser's super high-end HD 800 over-ear headphones and the new badass IE 800 in-ear monitors. To kick things off, we asked Grell to answer a few questions about the design of these beauties.

Q: The HD 800's 56mm transducers -- I believe that this is the largest dynamic driver in any headphones right now? As far as I know: yes!

Q: What design challenges does such a big driver pose? When just the diameter of a traditional transducer is increased the diaphragm will make unwanted movements in the audible frequency range. These movements cause dips and peaks in the frequency response and a decrease of high frequency reproduction. The solution is the usage of a wideband ring radiator: The diaphragm is glued to an inner rim, the 40mm voice coil (this is more than double the diameter of the average voice coil diameter of full size headphones!), and the outer rim. The distance to a controlling element is even smaller than it is in a traditional transducer. It leads to a very clean reproduction even in the high frequency range and above ( the last is only interesting for bats ;-) ).

Q: And why driver size is important in headphones? The larger the moving area of a transducer, the less movement he needs to make to produce a certain Sound Pressure Level. The less movements a transducer needs to make the lower is the THD. A second aspect: The natural sound field takes up a very large area around the head. To create a natural impression of the "room" it is necessary to radiate the sound as similar to the natural sound field as possible. This is the second reason for the big diameter and the angled position of the transducer.

Q: What's was the biggest challenge in designing the new IS 800s? IE 800? The biggest challenge was to design a transducers that covers the whole frequency range from 5Hz to 46,500Hz. But it was definetely worth the work. It reproduces the sound without time differences what happens when you use a multi driver solution. The other thing is how to avoid the resonance that occurs when you put a earphone in your ear canal. The solutions is the dampened two-chamber absorber. It leads to a smoother high frequency reproduction. Now you can hear real heights instead of a peak at 7500Hz!

Q: Earbuds tend not to be very durable... what have you done to ensure that these will last long enough to justify the $US1000 price tag. Do you see people using these on the go or at home? They are definitely designed for the use on the go -- but you can use them at home as well. We have thought a lot about the durability of this earphone: we made the housing out of ceramics, build special easy to change easy to clean ear adaptors, build in two meshes to protect the acousics against ear wax and used a special very durable cable. We found that most of the defects of standard earphones are caused by broken cables. The defect is located close to the 3.5mm connection plug. So the lower part of the cable, from the plug to the divider is exchangeable.

Q: One of the things we really love about Sennheiser is that some of the less expensive headphones are so fantastic... We know how music sounds. A lot of Sennheiser employees are DJs, musicians, sound engineers or Tonmeisters. We have a lot of a experience with the right tuning of headphones. We know how a headphone should sound and we know it better than some gangsters ;-) It is possible for us to make a good sounding headphone even when inexpensive components, but of course in direct comparision you will hear the difference to a top class headphone.

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