Let me start by thanking Audioholics for the time, effort, and expense in getting this all together. I've known Gene for a long time, and he is a good guy. Please allow me to provide some feedback on the addendum.
Let's start with subjective listening impressions. When listening to two channel music with the subwoofer placed in the middle of the room at or near maximum output levels, the VTF-15H with both ports open will have substantially less output compression compared to some of the other subs tested. This may make the sound too deep bass heavy in comparison. During development of the VTF-15H, we noted that a less deep bass heavy sound may be perceived as "tighter" with music, due to accentuation of mid-bass frequencies. So this is one of the reasons why we included support for a wide variety of operating modes (including various ported and sealed modes) in addition to continuously adjustable Q. The VTF-15H has more flexibility in terms of operating modes and adjustable Q vs. any of the other subwoofers tested here. This flexibility makes it practical to get good sound quality, irrespective of room size, playback levels, listening preferences, etc. I'm sure that the VTF-15H would have been perceived as very tight sounding under the previously mentioned listening conditions if using one of the other operating modes.
Regarding measurements with the enclosure on it's side vs. upright, it's a little bit hard to compare Paul's graphs because the Y axis scale has changed from 5dB per major division in the original review to 4dB per major division now. In our own testing with Paul's review unit, we measured a 2dB advantage at 20Hz with the enclosure upright vs. on it's side. This is significant. I personally feel that the most accurate measurement is done with the enclosure in the upright position, for two reasons. One is that each port contributes equally to the deep bass output (which is not the case when the enclosure is on it's side). Two is that the microphone need not be moved when switching from two port open to one port open mode, as the distance from mic to port centroid stays the same for each operating mode (which is not the case when the enclosure is on it's side). The only tradeoff is that the port centroid ends up being about 10% closer to the mic than the center of the driver, but it is a worthwhile tradeoff given the two advantages noted above.
As some of you may know, we measured an outdoor frequency response of +/- 2.5dB from 20-200Hz (ie. 5dB down at 20Hz relative to 50Hz) for Paul's VTF-15H review unit in the upright position with 2 ports open and EQ2. So there is still a 3dB difference between our frequency response measurement vs. Paul's. We really don't know exactly why there is a difference between the two data sets. We may never know. Do note that we have already measured the frequency response of VTF-15H many times, in several different locations, with two different microphones too, and we have always gotten results that are consistent with this +/- 2.5dB range. In the near future we will take very extensive measurements of the VTF-15H at the park which should result in nice ripple free curves that are about as accurate as we can hope for. I am looking forward to providing a wealth of data on the VTF-15H, far more than has ever been provided before.
On to the frequency response sweeps done with 1 port open, operating mode set to 'EQ1', and Q = 0.7. These settings are not recommended for high playback levels. We mention this in the VTF-15H owner's manual on page 5 here: http://www.hsuresearch.com/products/...HSubmanual.pdf
. This operating mode should be used for low-to-moderate levels only, where a rising in-room response may be preferrable due to the lower sensitivity of the ear at increasingly low frequencies at low-to-moderate listening levels. The 'EQ1' operating mode is certainly not for "making great curves for sales", and we don't appreciate that remark. If one wants to listen at high playback levels, it is better to run with operating mode switch set to 'EQ2', whether using 1 port open or 2 ports open. That said, with real world program material, there should be no issues with the woofer reaching it's excursion limits in any of the operating modes, including 1 port open with 'EQ1'. In fact, I have yet to hear from even a single VTF-15H owner who has bottomed out the driver in any of the operating modes. Based on the customer feedback, the overload behavior on this subwoofer has proven to be quite excellent, and the limiters and subsonic filtering appear to be working well.
Next, let's talk about the sealed operating modes. We intentionally aimed for a rolled off (NOT "droopy") low frequency response in the sealed modes. This response shaping works quite well in small-to-moderately sized rooms that are well enclosed and have significant room gain to boost the low end response, and also works quite well for customers who are looking for a less deep bass heavy sound in any given room.
Regarding the BASH amplifier used on the VTF-15H, we are very happy with it, and feel that we achieved a very balanced result for end users. As I have mentioned before, this is a very powerful and high headroom amplifier, runs cool to the touch, has very low noise, and has conveniently located switches and controls. The performance and reliability of the VTF-15H amplifier has been exceptional so far.
As you may know, we released CEA2010 data on maximum clean peak output many months ago. There is a 2-3 dB difference between our max clean peak output measurement vs. Paul's, at all frequencies, with 2 ports open and 1 port open mode. Again, we really don't know why there is a difference between the two data sets, and again, we may never know. In our upcoming measurement session in the park, we will measure max clean output upright vs. on side, 2 port open vs 1 port open, etc. using an SPL calibrator before the measurements are taken in order to take into account any temperature/humidity effects on the day of the measurement.
Having spent countless hours over the last two years measuring the VTF-15H, listening to the VTF-15H, and getting customer feedback and impressions on the VTF-15H, I am quite confident that this subwoofer performs as advertised. In our experience, the maximum output capability is very strong all the way down to 20Hz, the frequency response linearity is exceptionally good with true 20Hz extension (within a +/- 2.5dB window based on our recent measurements), the output compression is very low even at very high sweep levels (in max output and max headroom modes), and the limiters and subsonic filtering seem to work extremely well to keep the unit sounding clean with real world program material. The customer feedback has been overwhelmingly positive too. I am very proud to call the VTF-15H our most flexible, most capable, and most innovative subwoofer design ever.
Thank you again to everyone for the support. It makes the occasional long and sleepness nights well worth it!