Ultimate Ears UE900 part3: In-depth analysis

Continued from part 2.

Introduction

Ultimate Ears UE900 set the definition of Logitech's new reference in IEM acoustics: Low distortion, wide bandwidth, and linear impedance characteristic. More importantly, there are never-seen-before technologies implemented as well.

1. A pinhole bore
2. Knowles TWFK damping
3. Logitech: The pioneer of triple-bore technology?


A pinhole bore

Perhaps the most intriguing part of UE900 lies in its unique dual-bore configuration, with the large bore dedicated to the tweeter (Knowles TWFK), and the small bore dedicated to the woofer(Possibly Knowles CI-22955? Possible candidates are Knowles DTEC variants or Sonion 3300/3700/3800, according to one of my blog readers, Tom). My initial assumption is that the pinhole bore has something to do with an acoustic constriction action, which is a widely used low pass filtering technique in audiology for taming the frequency range above 5 kHz; the thinner the bore, the less output in the high. Moreover, as long as the bores are separated, the technique may help further eliminate any type of phase interference issues which may arise when a high frequency transducer is connected to a low frequency transducer in parallel.

from Wikipedia

So I did some constriction action calculation with that in mind.

However, the calculation attempt fails to yield anything valid- the measurement just does not match the numbers at all. Rather than cutting the high frequency, the pinhole actually amplifies the low frequency. What's going on?

So upon close examination of the frontal nozzle cap of UE900, I figure those four transducers actually share the same acoustic chamber within the nozzle. Thus, the dual bores do not really act as bores, but more as an acoustic enclosure with two ports working as Helmholtz resonators. (I guess the phase offset correction has been implemented only physically, by shifting the distance of the transducer from the outlet) Since the larger bore only affects the high frequency range due to its size(wavelength), the working principle of the pinhole is more of a concern here.

With so many acoustic filterings along the sound transduction path, no wonder the polarity of UE900 is so skewed up! Still, this approach is the first of this type of IEMs, so I shall give some credit to Logitech.


Knowles TWFK damping

There have been some speculations of UE900's high frequency transducer unit being a Knowles TWFK within the community. Even the damper configuration is identical, though UE900 uses 2200-Ohm red dampers instead of brown ones. Regardless, since there is enough room for a damper to be inserted on the larger bore, here you go:

Even with a slightest acoustic impedance drop, UE900 will lose all the frequency response above 16 kHz, since it is amplified by the larger bore's high pass filter, just like any other TWFK equipped IEMs. Try not to clog this bore with your bodily fluid!


Logitech: The pioneer of triple-bore technology?

Now we all know the dual-bore configuration techniques that are implemented on Triple.Fi 10 Pro and UE900 come from US7263195 & US7317806, issued on August 2007. While going through a bunch of research materials, I stumbled upon a patent document, US8116502, issued on February 2012. This patent deals with Logitech's all-new triple-bore & multi-layered bore configuration, both for generic and custom IEMs.

And it literally means that all of the custom & generic IEM manufacturers will have to acquire a permission from Logitech in order to manufacture devices with such bore configurations. You may call Logitech monopolizing the industry, but I know many companies haven't got the license, and made products anyway. Hopefully this will effectively eliminate whole bunch of random IEM companies with no objective design philosophy in mind.


In conclusion

Ultimate Ears UE900 is a well-made, class-defining product. It is free from the effect of electric damping, low in harmonic distortion, and reaching up to 20 kHz. Ultimate Ears really got their homework done, thinking about how bad Triple.Fi 10 was in those criteria.

The only thing UE900 is missing is the diffuse field linearity, and..

If someone is interested in a neutral tonality from UE900, hook up a 100-ohm adapter, block the pinhole, and insert the IEM nice and deep. That will yield the flattest, and widest frequency response, on par with electrostatic headphones! Really? Try it for yourself!




Appendix


There has been quite a talk going on in regards to this data. Perhaps it would not hurt to mention that Innerfidelity's data are in good agreement with mine, under a very specific circumstance.