HSU Research VTF-15H MK2 Subwoofer Review

The Best Deal in a Super Subwoofer Gets Even Better

HSU Research's original VTF-15H subwoofer was probably the least expensive subwoofer that could be considered a super sub—a subwoofer with so much output and such deep extension that it was hard to push it to its limits, much less past them. However, at the 2014 Rocky Mountain Audio Fest, HSU Research surprised everyone with the VTF-15H MK2, a substantially modified and updated version of the company's powerful subwoofer.

The power was upped from 350 watts RMS to 600 watts RMS—a difference that gives 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 that HSU Research 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 is slightly altered in its dimensions. It's an inch shorter, which allows HSU Research to get a lower rate on shipping. The price of the sub went up, but shipping cost dropped, so the newer model ended up costing about the same as its predecessor.

01
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HSU Research VTF-15H MK2: Features and Ergonomics

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Brent Butterworth

 The features and ergonomics of the VTF-15H MK2 are impressive:

• 15-inch driver
• 600 watts RMS BASH (Class G) amplifier
• Five listening modes with EQ switch
• Two foam port plugs included
• 30 to 90 Hertz 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
• Weight: 110 pounds / 49.9 kg

As with the original model, the VTF-15H MK2 has almost every feature you 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. (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)

The subwoofer has plenty of inputs, but it has no outputs, 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, use an external crossover, or just run your main speaker's full range and set the VTF-15H MK2's crossover frequency to the low-frequency response limit of your main speakers.

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 so do many other super subs.

02
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HSU Research VTF-15H MK2: Performance

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Brent Butterworth

Users of the original VTF-15H love it. A few subs exceed its measured output by a dB or two, and a few sound subtly tighter and better defined, but they are all much more expensive models. The VTF-15H MK2 sounds essentially the same as its predecessor. In a side-by-side comparison, the slight position differences of the subs made more difference in the sound than switching the subwoofers. Subs with a greater than 100-pound weight made the process so cumbersome that the memory of the sub it was tested against was starting to fade.

The VTF-15H MK2 gives more floor shake where the sub passes under the destroyer and emits extremely strong deep bass notes. It's a little scary what a super sub can do, and a super sub 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, 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 users 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.

One super sub that sounds slightly tighter and better defined—more "musical" —than the original VTF-15H is the SVS PC13-Ultra, which is almost twice the price of the VTF-15H MK2. A 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 Research design.

03
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HSU Research VTF-15H MK2: Measurements

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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

This chart 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). These measurements were taken by close-miking the driver using an Audiomatica Clio 10 FW audio analyzer and MIC-01 measurement microphone. The Ported Max Output result was normalized to peak at +3 dB, and the other measurements were scaled 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 are happy to see that the VTF-15H MK2 plays down to 17 Hz in Ported Max Extension mode. The -10 dB response is 14 Hz. Very little material has much content below 30 Hz.

CEA-2010A measurements were made 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 (limiter) and not by exceeding the CEA-2010A distortion thresholds. Averages are calculated in pascals. The output is measured in the three modes that should deliver the most output with the subwoofer on its side. This seemed closest to the CEA-2010 prescription to measure equidistant from the driver and port.

A couple of quick measurements of the output of the new vs. the old VTF-15H models at 40 Hz ensured that the conditions during the measurement tests were 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

The VTF-15H MK2 averages +3.1 dB more output than the original VTF-15H calculated in pascals. This is to be expected given the almost twice as powerful amp and the beefier driver.

04
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HSU Research VTF-15H MK2: Final Take

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Brent Butterworth

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. This big black sub doesn't do its job with much style, but it does it incredibly well.

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