Comment: The future of headphone design will be solid-state

Even the most basic, compact, affordable bookshelf speakers have multiple drivers. This allows manufacturers to separate the highs and mids from the bass to deliver clearer, cleaner, more detailed listening experiences.

Now, the same technology is coming to headphones which, historically, have only featured a single driver.               

Of course, headphone designers have a lot of tools for optimising audio. For example, 50mm drivers, larger-than-usual coils, bigger magnets, graphene, and carbon fibre materials are common — each introduced with the goal of trying to make a single driver sound great.

But what if it didn’t have to be this way? What if technological advances allowed headphone wearers and manufacturers to enjoy the benefits of multi-driver design? Solid-state speaker technologies hold the key.

The power of solid-state speakers

Printed in a single piece of silicon, solid-state speakers can support the creation of 2-way headphone designs where highs and mids are precisely rendered by a MEMS speaker serving as the tweeter, while the low end is reproduced through a smaller-than-usual dynamic driver.

The benefits for audio brands include improved mid- and high-end frequency rendering, for cleaner vocals and spatial imaging; less weight, improved comfort; and simpler back-volume acoustic tuning for faster time to market. And, despite including the latest solid-state technology, the cost of materials may actually decrease when exotic material dynamic drivers are replaced with this simple 2-way system.                         

When I was first introduced to MEMS speakers after years in headphone R&D, I thought, “What can I do with this tiny speaker?” It’s always difficult for brands to explore new technologies under tight engineering resources and timelines. So, I started independent research on weekends and here's what I found: the solid-state speaker sound is clearer. They’re driven through voltage, not currents like the coil speakers inside most headphones today, meaning they can produce an ultra-fast impulse response without any coloration of the sound.

They’re also capable of near-zero phase shift, which means the sound stage or stereo image has incredible accuracy while improving clarity across low, medium and high volumes.

Certain manufacturing processes can make their phase consistency near perfect, minimising the calibration required to match left and right speakers, and ensuring enhanced sound resolution and accuracy in spatial audio applications.

2-way headphones reference design

Inspired by the potential of solid-state speakers, I participated in developing a reference design for 2-way headphones, utilising a micro speaker. The 2-way design produces exceptional sound quality and is easier to tune acoustically. In separating the highs and mids from the bass, the result is clearer, high-resolution sound and faster, potentially cheaper manufacturing.

Since there are many 35-40mm dynamic drivers that have an excellent response from 20Hz-4kHz, the 2-way system design is smaller and doesn’t require an acoustic chamber, so headphone designers can choose bigger batteries or other electronics. Or they can make lighter, sleeker, and more brand-defining designs while delivering a better audio experience.

Future possibilities

This modular 2-way headphone can be plugged into pretty much any headphone style and, as a long time R&D guy, I’ve been trying that a lot lately. With the 2-way module installed, tuning the EQ takes hours instead of months. For example, I swapped out a graphene driver for the 2-way module and achieved better response through tuning in only four hours.

That speed and flexibility will disrupt the future of headphones. Imagine a future where headphone designers can quickly and cost-effectively roll out new products as the market demands, or create line ups of modular open and closed-back headphones with earcups that users swap depending on what they’re listening to.

By delivering such rich, clear sound quality up to 40kHz, distinctions among studio, gaming, and consumer headphones fade. No matter the design, 2-way headphones can sound better without large drivers; no exotic, expensive materials; no giant earcups. The future of headphone design will be solid-state.

Neal Breitbarth, audio applications director, xMEMS