Ultrasone HFI-780 and S-Logic

Disclaimer: I am finally down to Danganronpa's second last pair!! Oh you have no idea how bad I wanted to talk about this manufacturer.. 

Ever since Ultrasone introduce their proprietary technology, S-Logic™, the legitimacy of their claim has been disputed quite heavily within the headphone enthusiast community.

"...In studying the past, it is clear that S-Logic is the only way to influence stereo or channel tone signals to produce a 3-dimensional auditory event without any digital, binaural processing..." from http://ukrtech.com/root/faqfileref/27049.pdf

According to the manufacturer, S-Logic™ is an acoustic passive filter that promotes a front-localized surround sound. In short, this is done by creating an accurately controlled acoustic passage through an opening at the bottom part of the front baffle, and the reflected sound wave originated from the port yields directional pinna notches along the frequency spectrum.

B&K 4128C's HRTF characteristic: 0° / 45° / 90° / 135°

Since conventional headphone auralization techniques, such as Focusrite VRM, Creative CMSS, WaveArts Panorama, or even ToneBoosters Isone involve with actively simulating a specific HRTF target acquired via different head & pinna models, Ultrasone's approach seems rather passive and dull, like that of a simple cross-feed network.

PRO: HFI-780 sounds quite spatially open, though the sensation is a bit too artificial.

CON: There's a good amount of linear distorton in the treble due to a lot of baffle reflections.

ON SECOND THOUGHT #1: According to Ultrasone' patent documents and their white papers, the goal of S-Logic™ is quite simple: It is to create a front-localization. Dr. Florian M. König of Ultrasone thinks the in-head localization of headphones is located at the 45° above the listener's sagittal plane, and once it is brought down to the front subjectively, an effective front-localization is achieved.

By placing the driver(or the acoustic port) downwards, at about -35° of the sagittal plane of the pinna, Dr. König assumes the in-head localization is shifted closer to the front.

Ultrasone S-Logic™ in action on two different individuals

And on actual human pinnas, Ultrasone's proprietary surround technology creates a distinctive directional notches at 6 kHz & 11 kHz, along with resonances at 2 kHz, 4 kHz, and 8 kHz. According to Blauert's famous directional band model, amplitude increase at the following frequency bands promotes a sense of directionality.

Front: 260 Hz-550 Hz, 2.5 kHz-6 kHz

Rear: 700 Hz-1.8 kHz, 10 kHz-13 kHz

Above: 7 kHz-10 kHz.

Thus, it can be assumed that while S-Logic™ certainly has pinna notches for spatial enhancement, it doesn't necessarily mean the resulting sound is imbued with a front localization characteristic which is universally applicable.

ON SECOND THOUGHT #2: Since HFI-780 is equipped with S-Logic plus technology as well, its effect can easily be examined. Interestingly, the headphone has a pinna notch at 2.2 kHz, and is missing a notch above 10 kHz. Rather, the frequency response now resembles the conventional free-field reference, which has been proven to be highly ineffective in 1986. However, since HFI-780 still seems to be diffuse-field oriented as seen below, the peak at 10 kHz is most likely a linear distortion.

ON SECOND THOUGHT #3: If Ultrasone let go of the frontal localization and pump up the mid-range, the sound shall be very close to the headphone reference target suggested by Dr. Sean Olive.


References

J. Blauert, "Sound localization in the median plane," Acustica, vol. 22, no. 4, pp. 205-213, 1969-1970.