Hsu Research VTF-3 powered subwoofer:
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Improving the linearity of the subwoofer's response turned out to be easier than I'd anticipated. A very slight downward adjustment of the VTF-3's volume control left the frequency response in the crossover region intact, but reduced both the 40-38Hz and 22-20Hz peaks by about 4dB. There was still a rise from 24Hz down to 20Hz, but now it was 5dB rather than 10dB. Overall variation from 100 to 20Hz was within ±3dB, which is quite good for in-room response without equalization or room treatment.

These measurements and subsequent tweaking were done with the VTF-3 set to Maximum Extension. I then repeated the measurement with the sub in Maximum Output mode (foam plug removed, toggle switch in the 25Hz position). From 63Hz up there was no difference, but the 26-56Hz output was about 2dB higher than in Maximum Extension mode, peaking again in the 38-40Hz region. That's more or less as expected. What I found surprising was that the response stayed flat between 20 and 26Hz, with no indication of a rolloff at 20Hz, and less overall frequency-response variation from 20 to 100Hz.

I also did a brief test of the VTF-3's frequency response below 20Hz with a Hewlett-Packard sinewave generator (the R.A.B.O.S. test signals don't go below 20Hz). This showed that Maximum Extension mode did result in greater response below 20Hz, with strong response evident down to 16Hz (albeit with some doubling), but the cost of the increased extension was a peak in the response at 20Hz.

Back in December 1999, my comparison of the VTF-2's Maximum Extension and Maximum Output modes showed that sub dropping sharply below 31Hz in Maximum Output mode, which led to my recommending use of Maximum Extension. In the case of the VTF-3, the situation was reversed: At least in my room and with my subwoofer placement, Maximum Output mode resulted in more even response and still-excellent low-end extension, even down to 16Hz. This is better than Hsu Research claims, and it may represent a fortuitous augmentation of the subwoofer's response by a room resonance.

Listening Low
While these measurements are technically rather crude, their implications were generally confirmed by my listening tests. I spent some time comparing the Maximum Output and Maximum Extension modes using the deep-bass CD-R music compilation provided by Hsu Research as well as some of my own bass torture-test CDs and DVDs.

One test that I find most telling is in chapter 6 of Jumanji. In that scene, the children—including babe-to-be Kirsten Dunst—run upstairs to look for the source of the throbbing sound that seemingly only they can hear; at one point, the sound turns into a loud thud that can be scary in its impact. With the VTF-3, it was scary. Comparing the Maximum Output and Maximum Extension modes, my initial impression was that this impact was greater, more room-shaking, in Maximum Extension mode. But, as I listened some more, it became apparent that the bass was actually tighter, crisper, with less overhang, in Maximum Output mode. The only subwoofer that I've heard in my system that did better on this test was the Bag End Infrasub-18 ($1650), which reached even further into the nether regions.

Although the VTF-3 performed well in Maximum Output mode, at times I felt that the bass, while clean, was not as powerful as it should have been. As calibrated, the explosions in the pre-title sequence of Tomorrow Never Dies (my favorite James Bond movie with Pierce Brosnan) were just a bit on the wimpy side. Rather than switching to Maximum Extension—which involves having to fiddle around at the back of the sub—I used the Anthem AVM-20 pre-pro's subwoofer level control. This worked well, a 5dB boost providing the impact that was missing. (I just had to remember to restore the original subwoofer setting afterward.)

My preference for the Maximum Output mode held up for music as well as home-theater material. Mickey Hart's Planet Drum (Rykodisc RCD 10206), with its variety of drum sounds and occasional low-bass synthesizer note, is a good test of a subwoofer's extension, power, and integration with the rest of the range. The VTF-3 did very well on this test, making its presence felt in a way that did not draw attention to the low-bass range except when required by the music.

New King of the $1000 Sub Market?
In my review of the $899 Infinity IL120S in November 2001, I said that, with the R.A.B.O.S. settings optimized, this was the subwoofer to beat in the under-$1000 category. Although I no longer have the IL120S around for direct comparison, I feel comfortable in saying that its performance has been conclusively bettered by the $849 Hsu Research VTF-3. The VTF-3 goes much lower (the Infinity is good down to just below 30Hz, whereas the Hsu has strong response to 20Hz and even as low as 16Hz), and it plays louder without strain.

The IL120S R.A.B.O.S. equalization is very effective in controlling a peak in a subwoofer's response. I wish that something like it was part of every subwoofer's design, including the VTF-3's. There was an uncorrected peak in the VTF-3's response in my room, but its magnitude was low enough that whatever negative impact it had on the subwoofer's performance was more than compensated for by the VTF-3's greater extension.

The Hsu VTF-3 offers a significant improvement over the $499 VTF-2, itself an outstanding product in its price range, and provides a challenge to subwoofers in the $1500-$2000 range.