How to Build a Better Two-Way Headphone

Two-way headphones are considered an advantage for users because of their improved sound quality, hands-free communication, and comfort. But up to now, two-way headphones have been difficult to design, mainly due to properly squeeze multiple components into a tight space.

A MEMS technology company called xMEMS recently unveiled a reference design for two-way True Wireless Stereo (TWS) earbuds, while the other is for audiophile-level full-range in-ear-monitors (IEMs).

The Harding 2-way TWS earbud design delivers superior high-frequency response and clarity featuring Cowell, the world’s smallest solid-state micro speaker. Cowell serves as the tweeter for highly realistic mids and highs and is paired with a custom-designed 9-mm dynamic driver woofer that delivers thumping bass. This ANC-ready (Active Noise Canceling) design embeds a Qualcomm Bluetooth Audio SoC and three microphones per earbud for noise canceling.

Design News recently caught up with xMEMS' Neal Breitbarth, Audio Applications Director, to discuss the advantages of two-way headphones and how their MEMS technology can expedite the design of these products.

DN: What is the premise behind two-way headphones? How does the MEMS technology make this possible?

Solid-state micro speaker technology enables a 2-way headphone design in which the highs and mids are precisely rendered by a MEMS speaker serving as a miniature tweeter, while the low end is handled through a smaller less expensive- 35 or 40-millimeter, dynamic driver.

Related:MEMS and Ultrasound Tech Team to Reinvent Audio Speakers

Solid-state speakers are voltage-driven, not current-driven like traditional coil speakers, so they’re capable of ultra-fast impulse response, without any of the sound coloration of traditional transducers.

The benefits for audio brands include improved frequency rendering, cleaner vocals, almost perfect phase between the left and right earcups for an improved sound stage and spatial imaging; less weight, and simpler back-volume acoustic tuning for faster time to market. Additionally, despite using the latest solid-state technology for a 2-way design, the overall cost can actually be less expensive for medium and high-end headphones.

DN: What previous attempts have been made to develop two-way headphones? Why have they failed?

There have been a few tries at two-way headphones but it’s tricky to have multiple coils and magnets in a small space, especially if you're trying to do a wireless headphone. Most of the two-way systems that were tried ended up being extremely heavy with very large earcups that typically had phase issues. The xMEMS Cowell MEMS tweeter is magnet-free and weighs only 56 milligrams. Also, at just 3mm x 6mm and 1 mm thin, it is a fraction of the size of the dynamic driver and can be easily placed in front of it without any impact to the headphone mechanical design dimensions.

DN: What specs on noise levels, frequencies, etc. are obtainable using this technology for the headphones? How do they compare with speakers?

This 2-way design produces exceptional sound quality from 20Hz to 20kHz, with a crossover at 3.5 kHz. Notably, the xMEMS Cowell tweeter easily reaches 40kHz with no drop in SPL. It’s also easier to tune acoustically since headphone designers only need to tune the dynamic driver in the 20Hz to 4kHz range, accelerating time to market.

Additionally, in most cases, there is no need for an acoustic chamber to be added to the back of the ear cup to tune left and right high frequencies which helps to reduce weight and assembly time.

DN: When will products using the technology start appearing on the market? Are there discussions underway with consumer audio companies?

2-way solutions using xMEMS technology are already on the market in the form of True Wireless Stereo (TWS) earbuds, from the vendors such as Creative and Noble Audio. As for headphones, we expect the first projects with xMEMS inside to launch toward the end of 2024.