PERFORMANCE
Arguably, the most important aspect of a headset is how well it attenuates noise. The DC ONE-X manages noise suppression via active and passive means.
The passive noise attenuation is simply accomplished via the physical shape and materials choice of the headphone’s earcups and ear seal.
Consistent with David Clark’s website, their active noise cancellation is called Hybrid Electronic Noise-Cancelling, or Hybrid ENC. This system utilizes 2 microphones which send the signal to the digital signal processing, or DSP for short, so that it can reduce the noise signature with the headset’s speakers. Peak ENC attenuation is reported at 30 dB at 150 Hz, with an overall ENC effective range from 20 Hz to 1 KHz. This is accomplished while keeping an extremely low total harmonic distortion, or THD, of < 1% from 300 Hz to 3,000 Hz.
While the company does report a frequency range from 12 – 15,000 Hz for the speakers, do not focus too much on these numbers. I have experience with studio work and professional grade headphones and subwoofers. I conducted several tests with professional grade gear, in a controlled studio environment, and the results were really interesting. While the audible low end of the speakers starts at 25 Hz, the overall dB normalizes only above 31.5 Hz. However, I assure you that post DSP, the low end is closer to 150 Hz. The DSP of the ONE-X aggressively eliminates the low end of the incoming wired signal. However, when listening to the same test soundtracks via wireless Bluetooth, the DSP does not eliminate the low end and allows for a more balanced music listening experience. The overall sound quality is good; however, I am not confident that full spectrum (20 – 15,000 Hz) THD would remain low due to sound dynamics, driver size, and R&D cost. When evaluating a tool, I always keep in mind its main purpose. As an aviation headset, the sound quality is great.
Microphone performance is arguably the most difficult to evaluate. I do have an idea of how to test it, however, I do not have any professional testing equipment to provide you with empirical data for the microphone. I can, however, shine light on the relationship between the microphone and DSP interaction. As it turns out, whenever you initiate a transmission from the cockpit, you “open” the microphone. When that occurs, the microphone’s sound signature and overall noise floor can be heard via the headset. Here is what I have observed: there is an increase in the noise floor of the headset whenever you transmit to ATC or when you communicate via intercom. While I find that the change in noise floor with ATC to be normal, the intercom fluctuation is not normal. Other headsets that I have used over the years did not present a significant change to the noise floor while utilizing the intercom. The overall increase is of only a few dB ~3-5, and the frequency change occurs from 500 – 1500 Hz. With all that stated, I have never received any negative feedback about this microphone’s quality while transmitting. In fact, every time that I have checked, the answer is always: “crystal clear”.
As a final note in the performance category, I would like to bring up the observed electromagnetic interference, or EMI. I am currently operating the Boeing 737 aircraft. This platform provides an excellent testing environment due to the loud flight deck and the electromagnetic field’s interference with the headset. Perhaps most interestingly, is the fact that the EMI signature changes significantly from tail number to tail number. Additionally, there is also tremendous variance in the intercom sound signature between the different tail numbers. This observed behavior is likely due to the variance in wiring configurations from airplane to airplane. All in all, I cannot determine why this headset experiences the EMI while others do not. I am simply relaying to you my observations during live operations.
Please keep in mind that, I am still rather young, with full spectrum hearing. I am also extremely attentive to all nuances as I utilize this instrument. Most of my colleagues are not aware of the described behaviors here stated.