Audio and Video

How MEMS speakers enable better two-way headphone designs

17 June 2024
Source: xMEMS

Today, even the smallest, cheapest, most rudimentary bookshelf speakers have multiple drivers. Thanks to improved driver design over several years and sufficient room inside the speaker chassis, manufacturers leverage multi-driver designs to separate the highs and mids from the bass and deliver a clearer, cleaner, more detailed listening experience.

However, headphone manufacturers have long struggled to enable the same level of performance, even in the most advanced, single-driver designs. Until now.

I’ve spent years in headphone R&D, so I took notice when I heard my son was less than impressed with the performance of his gaming headphones. At times during online sessions, he had difficulty making out what his friends were saying. But turning the volume up only made things louder and not clearer.

It goes without saying that headphone designers have many tools at their disposal for optimizing audio performance. For example, in my previous job at a major headphone manufacturer, we included a multi-band EQ that users could manipulate, maintain several presets and load into their headphones.

Depending on the preferred listening experience, those who design and manufacture headphones often leverage components like 50 millimeter drivers, larger-than-usual coils, bigger magnets, and graphene or carbon fiber diaphragm materials — each included to mask the core issue: it’s quite difficult to make a single driver sound great.

But what if this became no longer necessary? What if it was possible to design two-way headphones that mirror what we see in bookshelf speakers? Advances in solid-state MEMS speaker technology are the answer.

Solid-state possibilities

Much like the rise of solid-state microphones over the last decade, solid-state MEMS speakers are uniquely positioned to redefine personal audio. These miniature speakers allow us to realize a two-way headphone design in which highs and mids are rendered precisely by the MEMS speakers as a tweeter, while bass is reproduced through a smaller-than-usual, 35 or 40-millimeter dynamic driver.

The benefits for headphone designers include improved mid- and high-end frequency rendering, for cleaner vocals and spatial imaging; less weight, for better-wearing comfort; and much simpler back-volume acoustic tuning, for faster time to market. And, amazingly, having the latest in solid-state technology doesn’t automatically mean an increased financial burden on the manufacturer. In fact, brands can actually save money when replacing graphene or other exotic material dynamic drivers with this two-way design.

I was first introduced to solid-state speakers when working in my previous role overseeing headphone R&D. My first thought was: “What can I do with this tiny, little speaker?” It’s hard to be adventurous and explore when faced with tight engineering resources, budgets and product timelines. So, I started looking into the technology in my free time. And here’s what I found:

What struck me immediately was how much clearer the solid-state speaker sounded. Because they are driven by voltage and not current like traditional coil speakers, solid-state speakers are capable of a much faster impulse response, removing any of the sound coloration introduced by traditional transducers.

They also have nearly zero phase shift, which means the sound stage or stereo image is incredibly accurate, which greatly helps with clarity whether you are listening at low, medium or high volumes.

And because of their unique semiconductor manufacturing process, solid-state speakers also have a near perfect phase consistency. The benefits of this are twofold: lessening the calibration required to match left and right speakers in each earcup and improving sound resolution and accuracy for spatial audio.

Building a two-way design

Spurred on by the potential of solid-state speakers, I’ve since worked on the creation of a headphone reference design that combines a dynamic driver with a solid-state tweeter, resulting in a device that produces fantastic sound quality in the full frequency range (20 Hz to 20 kHz).

Acoustic tuning is simplified because the dynamic driver now only needs to be tuned between 20 Hz to 4 kHz, speeding up time to market. Furthermore, the solid-state speakers eliminate the need for an acoustic chamber on the back of the earcup to tune the high frequencies, reducing weight and time spent on assembly.

The lack of an acoustic chamber also means more flexibility for designers if they want to add larger batteries or go the other direction and make smaller, sleeker products while maintaining audio quality.

In creating this design, we’ve brought to headphones what bookshelf speaker companies have done for decades — a separation of highs and mids from the bass, enabling clearer, high-resolution sound and faster, cheaper manufacturing.

Market-changing opportunities

What’s truly disruptive about a two-way headphone design concept is that it can support virtually any headphone format.

Such flexibility will prove industry-altering going forward as brands can more efficiently and cost-effectively debut new product variations that sound better than what came before.

Whether open-back, closed-back, wired or wireless, two-way headphones today have the capability to improve performance, boost design flexibility and reduce cost — all thanks to solid-state MEMS technology.

About the author

Neal Breitbarth is audio applications director at xMEMS, the inventors of the world’s first solid-state True MEMS speakers for TWS earbuds, headphones and other personal audio devices. Before joining xMEMS, Breitbarth was Director of Research at Turtle Beach, where he spent over eight years in headphone R&D.

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