Guest Blogger "Professor Thump" of Klipsch Talks About the Challenges of Designing Headphones
10:31 AM PST, December 31, 2007
I have been a loudspeaker design engineer for over 20 years. Klipsch has been interested in getting into the headphone market for several years now, and when the president of Klipsch asked that I develop a line of headphones for the company, I knew I had my work cut out for me. Loudspeakers are one thing to design but “in-ear” speakers are a different beast.
I had the advantage (or disadvantage?) of starting from the beginning. There were no boundaries initially to what should be designed. This is the way I like it…no rules except the laws of physics. Getting smart real fast wasn’t going to be easy but I knew it could be done. When we first started out with initial concepts for the Klipsch IMAGE and Custom series of earphones we started prioritizing what we thought would be most important to the customer—the sound and the comfort.
The Challenge of Making a Big Sound Small
Early on we gathered the entire staff of Klipsch engineering gurus we quickly realized that comparing loudspeakers and headphones is like “apples and oranges.” A speaker radiating into a room has certain characteristics. Sound bounces off the walls and your body and then to one or both ears depending on the frequency. These are the effects of reverb and “Head Related Transfer Function” (HRTF). To make things more confusing, sound bounces off your pinna and concha (the flappy parts of your ears) and then makes a couple of corkscrew turns into your ear drum. We call this location at your eardrum the "earDrum Reference Position" or DRP.
What we soon realized is that the frequency response that you want to hear at the DRP is not flat.
What? Okay, think of it like this. When you design a speaker most people generally design it so the frequency response is flat, so nothing “colors” the sound coming out. But in designing earphones, things like the absence of room gain and master mixes need to be considered. When you switch back and forth between a loudspeaker and an earphone you notice right away that there are a lot of problems. First the “timbrel accuracy” or sound quality between the two is different. The two can be normalized to be identical using an equalizer but the envelope or dynamics will still be completely different. Besides other differences like Head Related Transfer Function (HRTF), ear canal gain and room gain, there are also dynamic differences in the envelope that are a result of the reaction capabilities of each source. In other words: diaphragms are heavy in loudspeakers but not in earphone armatures. As a result, we chose to add bass response at the DRP to create the “Klipsch Sound Signature”.
“It’s the Fit, Stupid”
When I first started researching earphone applications, I read a lot of patents. I came across one that was a big cylindrical hearing aid from the 60's, I believe. If the hearing aid didn't fit the patient (or victim), the doctor would literally take a drill to the ear canal! I thought, ”Egads, what are these guys thinking?” Well, technical advances since in microelectronics have allowed custom ear shells to be created which has made comfort an obvious improvement for hearing aids. But it made me realize that nobody was concentrating on the fundamental human need...comfort. So we started having ear impressions made of people. (Ear impressions are silicone that is injected into the ear to acquire the exact shape of that individual's ear canal.) With these impressions, 3D laser scans could be made to get digital data which could later be analyzed via computer. Every ear is different, but I noticed a similarity: If you look at the crossection of most people's ear canals you will find that the shape is generally oval, not perfectly round like most eartips currently on the market. Hey… why don’t we make an ear tip that is the shape of your ear? Now we have reduced tickle, firmer placement and the Holy Grail…a complete AIR SEAL (which is absolutely needed for bass output).
Guest blogger Mark Blanchard, aka "Professor Thump", is the Senior Acoustic Designer at Klipsch Audio in Indianapolis, IN.
Video: Professor Thump (aka Mark Blanchard) takes Amazon.com for a tour of Klipsch's anechoic chamber and research laboratory. See link for video:
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