Ear bud headphones jam lots of complexity in a tiny package - Embedded.com

Ear bud headphones jam lots of complexity in a tiny package


I don't think I've ever done a Tear Down of a product that didn't contain its own active power. In most cases, that power comes from a battery, but occasionally I work on equipment that's line powered. But if you had told me there was a significant amount of technological innovation inside a pair of ear-bud headphones, I probably would have laughed at you.

The Logitech Ultimate Ears 700 earphones

I'm not laughing any more. I ran into Paul Manfrini, a director of product development for Logitech a few months back, while he was out showing off one of his latest products—the Ultimate Ears 700 noise-isolating earphones. The ear buds are a hot button for me, as I've been told I have “irregular ears.” Before your imagination starts wandering, I'll explain. Most people have an ear canal that goes straight. Mine goes around a curve.

For an ear bud-type headphone, that presents two problems. One is that the sound has to navigate around a curve. The second, and the more problematic one for me, is that the buds generally don't stay in my ears. As a runner, with lots of jostling around, that's a problem for me.

When I explained my dilemma to Paul, he told me that he had a solution for me. First, he confirmed my ear irregularity, then told me to try the UE 700. Because of the earphone's foam outer shell, the buds did stay snugly in my ear. But what really got my attention, and why I wanted to take these earphones apart, was the amazing sound quality.

Paul explained to me why the tiny devices we able to produce such great sound. It comes from the fact that Ultimate Ears, which was acquired by Logitech in the Summer of 2008, has a reputation for producing professional-quality earphones. In fact, Paul told me a few tales about some of the musicians he had worked with. Funny stuff, but this likely isn't the place to tell those tales.

The UE 700 consists of dual speakers (also known as drivers) in a single package. In general, two types of miniature speakers are used for in-ear monitors. One is a diaphragm and one is an armature, which is what's used in the UE 700. The round diaphragm is typical of what you'd see in a home speaker.

The armature speaker originated from the hearing aid industry, and it's specifically designed to work inside of an ear in a closed compartment that doesn't need a lot of air. The diaphragms need more air to work properly. Usually the diaphragm product is rounder because of the shape of the diaphragm and there's often some kind of venting so air can get in and out. Hence, there's usually a hole or slot present. The diaphragm is generally used in lower cost products as it's a less expensive product to build.

One of the design challenges to be overcome by Ultimate Ears was that the original armature designs, those intended for hearing aids, were very limited in their frequency range, around 500 to 4000 Hz. That's because they were mainly intended to capture voices. Now, thanks to the designers at Ultimate Ears, they can handle from 20 Hz up to 20 kHz.

In the armature design, as shown in the figure, the audio filter shapes the sound for maximum detail. In systems with at least two speakers, it helps dampen the sound for better balance.

This blowup shows all the components that are squeezed into a tight space.

“Where you position that filter will have an effect on the sound signature and that's part of our secret sauce,” says Manfrini. “We're pretty exacting in that area and we have patents on tube lengths; we pick certain filters for certain reasons, and there are all kinds of configurations at that point.”

The filter has a metal can around it. It's like a rolled metal mesh, then placed inside a compartment. The densities and different configurations of that metal mesh have different effects on the sound.

The sound comes out of the “spout” on the end of the speaker. That tube effects the sound signature and it's why there's a need for filtering. From there, the sound goes straight into your ear.

The foam tip is used for noise isolation. This was designed specifically for the UE 700, but will appear on future products as well. The elliptical shape of the tip lends itself better to most ears, as opposed to the round shape that's used on competitive products.

The concept of noise isolation is simple—block out as much external noise as possible.

All in all, for around $200, you get some great sound, in a product that stays put.

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