Hsu Research VTF-15H Mk2 Subwoofer Review

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Can You Improve on Near-Perfection?

Brent Butterworth

Hsu Research's VTF-15H subwoofer is something I thought might stay in the company's line for 10 years, or even longer. It was probably the least expensive subwoofer that I'd consider a "supersub" -- a subwoofer with so much output and such deep extension that it's hard to push it to its limits, much less past them. But at the 2014 Rocky Mountain Audio Fest, Hsu surprised me with the VTF-15H Mk2, a substantially modified and updated version.

The most important change was that the power was upped from 350 watts RMS to 600 watts RMS -- a difference that would give you an extra +2.3 dB more output, assuming the driver can handle it. To help handle that extra power, the driver has a magnet Hsu says is double the size of the one on the original VTF-15H. Pro-style XLR balanced stereo inputs were added, and a small heat sink was attached to the back panel.

The newer model was slightly altered in its dimensions. It's an inch shorter, which allowed Hsu to get a lower rate on shipping. The price of the sub went up, but shipping dropped, so the newer model actually ends up costing less.

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Hsu Research VTF-15H Mk2: Features and Ergonomics

Brent Butterworth

• 15-inch driver
• 600 watts RMS BASH (Class G) amplifier
• Five listening modes with EQ switch
• Two foam port plugs included
• 30 to 90 Hz crossover adjustment with bypass switch
• 0.3 to 0.7 Q control
• RCA and XLR stereo analog inputs
• Five-way binding posts for stereo speaker level input
• Dimensions: 24.5 x 17.25 x 28 in / 623 x 438 x 711 mm (hwd)
• Weight: 110 lb / 49.9 kg

As with the original model, the VTF-15H Mk2 has almost every feature I could want in a subwoofer. With the EQ switch and the ability to run it sealed, one port open or two ports open, you have five sound modes to choose from. (Why just five? Because you can't run it with both ports open in the EQ1 setting.)

Ported Max Output (2 ports open, EQ2)
Ported Max Extension (1 port open, EQ1)
Ported Max Headroom (1 port open, EQ2)
Sealed Max Extension (0 ports open, EQ1)
Sealed Max Headroom (0 ports open, EQ2)

It has plenty of inputs. It has no outputs, though, so you can't run a high-pass-filtered signal back to your main speakers. The high-pass function takes the bass out of your main speakers. You'll have to do the high-pass in your A/V receiver (all A/V receivers have built-in subwoofer crossovers), use an external crossover (of which there are sadly only a few available), or just run your main speakers full range and set the VTF-15H Mk2's crossover frequency to the low-frequency response limit of your main speakers.

To me, the VTF-15H Mk2 has only one real downside, and that's its form factor. At 28 inches deep, it sticks way out into a room. But of course, so do many other supersubs.

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Hsu Research VTF-15H Mk2: Performance

Brent Butterworth

I love the original VTF-15H, which I've used as a reference subwoofer for the last several years. I've found subs that exceed its measured output by a dB or two. I've found subs that sounded subtly tighter and better-defined. But they were all much more expensive models. To me, the VTF-15H Mk2 sounds basically the same. When I tried running them side-by-side for a comparison, I found that the slight position differences of the subs made more difference in the sound than switching the subwoofers. When I tried switching them out, the subs' >100-pound weight made the process so cumbersome that by the time I was done, my memory of the sub I'd just heard was starting to fade.

The one difference that I was confident I heard was that the VTF-15H Mk2 gave me more floor shake in Chapter 14 of , where the sub passes under the destroyer and emits extremely strong deep bass notes. It's actually a little scary sometimes what a supersub can do, and a supersub with about +3 dB more output is even scarier. The room doesn't just shake, it pressurizes. You can feel (and maybe even hear) the walls and ceiling move a little bit. Some audiophiles deride this level of bass reproduction, but at least for home theater, I think it's highly appropriate because it's so much more realistic than what a more modestly sized sub can deliver.

The VTF-15H Mk2 keeps one of the aspects of the original model that I loved: its tuneability. You can make it sound very tight and punchy by plugging both ports and turning the Q down. Or you can make the sound fatter and looser by running one or both ports open and maybe turning the Q up a bit. You're not stuck with just one sound or one type of sub.

In a couple of years of using the VTF-15H, and a couple of weeks of using the VTF-15H Mk2, I got wonderful results with all types of music. Even my all-time-favorite CD for jazz upright bass playing -- the Oscar Peterson Trio's We Get Requests -- really sang through the VTF-15H Mk2. It easily tracked bassist Ray Brown's fleet-fingered but always-tasteful playing without ever booming or bloating. With both subs on the same settings and placed in the same location, the new model sounded just a bit better defined. But that could be the result of the older model being much more broken in, or maybe a slight difference in the calibration of the controls.

I have heard at least one supersub that sounded slightly tighter and better defined -- more "musical," if you will -- than the original VTF-15H, and that's the SVS PC13-Ultra, which is almost twice the price of the VTF-15H Mk2. I imagine there are others; few subs with 15-inch drivers are known for their pitch definition. But the fact that a much more expensive 13-inch sub delivered only a subtle improvement in this area is a real achievement for the Hsu design.

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Hsu Research VTF-15H Mk2: Measurements

Brent Butterworth

Frequency Response
Ported Max Output: 22 to 447 Hz ±3 dB
Ported Max Extension: 17 to 461 Hz ±3 dB
Ported Max Headroom: 22 to 485 Hz ±3 dB
Sealed Max Extension: 28 to 485 Hz ±3 dB
Sealed Max Headroom: 29 to 485 Hz ±3 dB

Crossover Low-Pass Rolloff
-18.5 dB/octave

Max Output (Sealed Max Headroom mode)
                            CEA-2010A           Traditional
                             (1M peak)              (2M RMS)
40-63 Hz avg        117.8 dB                108.8 dB            
63 Hz                    118.2 dB L             109.2 dB L
50 Hz                    117.8 dB L             108.9 dB L
40 Hz                    117.3 dB L             108.3 dB L
20-31.5 Hz avg     107.4 dB                98.4 dB
31.5 Hz                 111.8 dB                102.8 dB
25 Hz                    106.1 dB                97.1 dB
20 Hz                    101.1 dB                92.1 dB

Max Output (Ported Max Headroom mode)
                            CEA-2010A           Traditional
                             (1M peak)              (2M RMS)
40-63 Hz avg        117.8 dB                108.8 dB            
63 Hz                    125.8 dB L             116.8 dB L
50 Hz                    125.1 dB L             116.1 dB L
40 Hz                    124.3 dB L             115.3 dB L
20-31.5 Hz avg     107.4 dB                98.4 dB
31.5 Hz                 122.8 dB L             113.8 dB L
25 Hz                    120.4 dB                111.4 dB
20 Hz                    114.1 dB                105.1 dB

Max Output (Ported Max Output mode)
                            CEA-2010A           Traditional
                             (1M peak)              (2M RMS)
40-63 Hz avg        117.8 dB                108.8 dB            
63 Hz                    127.0 dB L             118.0 dB L
50 Hz                    127.1 dB L             118.1 dB L
40 Hz                    126.7 dB L             117.7 dB L
20-31.5 Hz avg     107.4 dB                98.4 dB
31.5 Hz                 124.4 dB L             115.4 dB L
25 Hz                    119.3 dB                110.3 dB
20 Hz                    111.5 dB                102.5 dB

The chart above shows the frequency response of the VTF-15H Mk2 with the crossover frequency set to maximum, in each of the five modes: Ported Max Output (blue trace), Ported Max Headroom (red), Ported Max Extension (green), Sealed Max Headroom (purple) and Sealed Max Extension (orange). I did this measurement by close-miking the driver, using an Audiomatica Clio 10 FW audio analyzer and MIC-01 measurement microphone. I normalized the Ported Max Output result to peak at +3 dB, and scaled the other measurements by the same amount, so the differences you see in the graph are what you'll get in your room when you change modes. Measurements were made using ground plane technique, with the microphone on the ground 2 meters from the sub and results smoothed to 1/6th octave. The sub was placed upright, as it would normally be used.

Deep bass freaks will be happy to see that the VTF-15H Mk2 plays down to 17 Hz in Ported Max Extension mode. BTW, the -10 dB response is 14 Hz. Very little material has much content below 30 Hz.

I did CEA-2010A measurements using an Earthworks M30 measurement microphone, an M-Audio Mobile Pre USB interface and the freeware CEA-2010 measurement software developed by Don Keele, which is a routine that runs on the Wavemetrics Igor Pro scientific software package. These measurements were taken at 2 meters peak output, then scaled up to 1-meter equivalent per CEA-2010A reporting requirements. The two sets of measurements presented -- CEA-2010A and traditional method -- are the same, but the traditional measurement (which most audio websites and many manufacturers use) reports results at 2-meter RMS equivalent, which is -9 dB lower than CEA-2010A reporting. An L next to the result indicates that the output was dictated by the subwoofer's internal circuitry (i.e., limiter), and not by exceeding the CEA-2010A distortion thresholds. Averages are calculated in pascals. I chose to measure the output in the three modes that should deliver the most output. I measured the sub on its side, which seemed closest to the CEA-2010 prescription to measure equidistant from the driver and port.

While I was set up, I went ahead and ran a couple of quick measurements of the output of the new vs. the old VTF-15H models at 40 Hz. This way I could be assured that the measurements condition were exactly the same. Here are the results:

CEA-2010A @ 40 Hz
                                               VTF-15H          VTF-15H Mk2
Ported Max Output mode          123.2 dB          126.7 dB                
Ported Max Headroom mode     121.2 dB          124.3 dB
Sealed Max Headroom mode     119.2 dB          121.8 dB

Thus, the VTF-15H Mk2 averages +3.1 dB more output than the original VTF-15H (again, averages calculated in pascals). Which is about what you'd expect given the almost twice as powerful amp and the beefier driver.

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Hsu Research VTF-15H Mk2: Final Take

Brent Butterworth

I'll keep my wrap-up simple. I thought the VTF-15H delivered the most bang for the buck of any subwoofer on the market. Now the VTF-15H Mk2 delivers even more bang for about the same bucks. No, this big black sub doesn't do its job with much style, but it does it damned well.