Ultimate Ears UE-11 Pro in-ear headphones Measurements
Keith Howard is writing an article for Stereophile about assessing the frequency response of headphones. Unfortunately, I lack the necessary hardware to follow his example. I did measure the electrical impedance of the Ultimate Ears UE-11 Pros, however. To ensure the correct acoustic loading, the review samples were inserted in Wes Phillips' ears. The results are shown in fig.1. I had understood that the UE-11s are easier to drive than the UE-10 Pros, which WP reviewed in October 2006; however, the '11's impedance at low frequencies averages 10.5 ohms compared with the '10's 13 ohms. The rise in impedance in the low treble, however, is considerably greater, reaching 18 ohms at 1kHz, as specified, and 43 ohms at 2.7kHz. This impedance peak is significantly higher in frequency than that of the Ultimate Ears UE-5c, which I reviewed in December 2004. The UE-11's dip to 10 ohms at 11kHz is similar to both the earlier Ultimate Ears models, however.
Fig.1 Ultimate Ears UE-11 Pro, electrical impedance (solid) and phase (dashed). (5 ohms/vertical div.)
Their impedance modulus will tend to make the UE-11 Pros sound rather bright with headphone amplifiers that have high source impedances. They will work best with amplifiers optimized for driving lower impedances, such as the various Ray Samuels Emmeline and HeadRoom models.—John Atkinson