Hsu Research VTF-TN1 15" Subwoofer Review

Hsu Research gained a lot of attention recently when they announced a new subwoofer, the VTF-TN1. One of the reasons for that is that even though they are popularly known for their subwoofers, Hsu Research hasn’t actually released a new sub in quite a while, about 7 years (their last new sub release was the now sadly discontinued VTF-1 mk3). So it’s a big deal when Hsu Research, the original manufacture-direct subwoofer company and still a major player in home audio subs and speakers, announces a new release. Audio enthusiasts know to pay attention. The VTF-TN1 replaces Hsu Research’s previous flagship sub, the VTF-15h MKII. It has a lot in common with the former flagship, but it makes one big change that simultaneously enables greater performance yet lowers the pricing. This is what we will explore in today’s review of the VTF-TN1; how important enclosure and ports are to subwoofer performance. This is a sub that tries to give the user high performance at a low cost without skimping on the usual slate of features and post-purchase support that buyers in this segment have come to expect. We will be asking how the VTF-TN1 fares in such a highly competitive marketplace and what are its strengths and weaknesses as such a unique design in the subwoofer world.

Hsu Research VTF-TN1 Packing and Appearance

Needless to say, a large sub like the VTF-TN1 came in a large, sturdy box. Inside the box, the sub was completely covered with polyethylene foam blocks which is a step up from most subs which only have foam tops and bottoms. There are some very stiff edge protectors along the vertical edges. One interesting detail is that the corners of the polyethylene blocks have some metal corner protectors. Hsu tells me that this helps to diffuse the energy that hits the sub when it is dropped on a corner. Corner drops are one of the most common causes of shipping damage because all of the kinetic energy is focused on one point of the sub, and these corner guards should help to spread that out over a larger area. Inside the foam blocks, the sub came wrapped in a plastic back to protect against liquid spills and moisture, and underneath the plastic, it came wrapped in a soft foam sack to protect against scratches and scuffs. This level of packing should protect the VTF-TN1 against the rough shipping practices of the major parcel shipping services.

Once unpacked, we are met with a monolithic tome of a sub that only has the woofer and a Hsu badge at the lower edge to distinguish it. Outside of those distinguishing traits, it is a simple and minimal-looking piece of audio equipment. The satin black finish and rounded edges do help to soften its appearance, but they can’t hide the fact that it is a big subwoofer. This isn’t something that can be bought and hidden in a corner with the hope that other household occupants will not notice. The supplied grille can be used to hide the woofer for those who want to simplify its appearance even more, but users will need to accept its size (it is about 2.5 ft tall, 1.5 ft wide, and 1.5 ft deep). One aspect that makes it look so large is that it trades width and depth for height. Most subs and loudspeakers use depth to hide the true size of the enclosure, but Hsu opted to save user’s floorspace instead, so the VTF-TN1 was made to be more practical than eye-pleasing. I do prefer the aesthetic of the VTF-15h MKII with its interesting triangular ports. Nonetheless, as large subs, the VTF-TN1 is not bad-looking but a bit unusual compared to most subwoofers in this class.

Hsu Research VTF-TN1 Design Analysis

Let’s dig into the design analysis of the VTF-TN1 by starting with its driver. The cone is a fiberglass-impregnated paper cone with an inverted dustcap which is attached to the frame by a beefy nitrile-butyl foam surround. The basket is a cast aluminum design using 12 thick spokes that lead to the motor. The motor uses a 2” stack of two magnets that have a 6.75” diameter. The pole piece is undercut for a better magnetic field symmetry, and multiple shorting rings reduce induction effects which lessens even-order distortion as well as increases the driver’s bandwidth. Venting is done both underneath the spider and through the pole piece. It’s a capable driver and remains largely unchanged from what was used in the VTF-15h MKII.

It is powered by a 600-watt RMS class-AB amplifier that is one of the few in this segment that eschews DSP filters. It is an all-analog amp which brings some advantages as well as disadvantages. One disadvantage is that the amp controls can’t be as fine as what can be had with many DSP amps, especially those with app control. I don’t regard this as a big deal since most of the calibration of the subwoofer should normally be done through the receiver or processor end, not on the sub itself. On subs, I normally recommend users just set the phase to zero, low-pass filter to bypass, and the volume to a medium-to-high setting, and let the receiver/processor do the rest. There are exceptions for those who want to tweak their systems to perfection, but for typical users, that is a good standard practice. Another strength of DSP amps is that they can have much more sophisticated limiters during playback to ensure that the sub can’t be harmed from over-driving, thermal conditions, or poor electricity sources.

So what then is the advantage of an analog amp? Lower-cost analog amps tend to be more reliable than lower-cost class-D amps. Analog amps can also have more headroom than a similarly rated Class D w SMPS amp. Furthermore, analog amps have no delay in the signal chain. DSP-controlled amps will always have some delay due to the processing that has to occur. While they have become much better than early generations of DSP amps, they still have a delay that must be compensated for in the calibration process. Usually, this delay makes the A/V processor ‘see’ the sub as being much further in distance than it actually is. Sometimes users will think that is an error and ‘correct’ that distance setting by inputting the physical distance of the subwoofer, but that would be a mistake. It’s always best to pull measurements with the sub and main channels to ensure proper time alignment is achieved.

Hsu’s amp is a BASH design that combines some of the efficiency strengths of class-D designs with the fidelity of class-AB designs (although that description is a simplification). Connectivity consists of a pair of RCA inputs, XLR inputs, and speaker-level inputs. XLR inputs allows it to easily be integrated into higher-end systems or pro-audio systems that usually use balanced connectivity. Speaker-level inputs enable it to be easily used in very simple two-channel systems that don’t have bass management.  

In addition to the usual controls of a volume knob, phase switch, and low-pass filter (30Hz to 120Hz), the VTF-TN1 has an operating mode switch which is important when changing the port tuning. The operating mode switch has an ‘EQ1’ setting, which is what the sub should be set to where only one port is open, and an ‘EQ2’ setting where the user can run the sub with both ports open, one port sealed, or both ports sealed. Make sure that one of the ports is sealed when running the sub in ‘EQ1’ mode as that mode’s filter can NOT fully protect the driver when both ports are open. Configuring the sub to ‘EQ1’ with a single port open enables the sub to achieve the deepest bass, and using ‘EQ2’ with both ports open will allow more port-generated output around its tuning frequency. While sealing both ports is an option, it’s not one I recommend, because why buy a large ported sub if you aren’t going to take advantage of the ports?

The enclosure is an unusual one in that it trades depth and width for height. Most subwoofers use depth as the dimension to increase internal space, and that can make the unit look more innocuous and furniture-like, but it does use a larger footprint. The VTF-TN1 is a tall boy. One advantage of the TN1’s smaller footprint is that it makes it easier to facilitate a multi-sub system since there may be more places that the subs can go in more circumstances. As regular readers know, Audioholics strongly advocates for multi-sub setups wherever possible since the acoustic destructiveness of room modes can be mitigated by the optimal placement of multiple subwoofers. For those who want to know more, Audioholics has many articles on the subject, but a good introduction can be read here: Room Modes and Standing Waves.

Another advantage to a taller sub is that it can have down-firing ports that do not need bends to increase port length. Many ported subs with very low tuning frequencies have bending in their ports to achieve such deep tuning, but those bends have to be handled very carefully to not dramatically increase port turbulence. The ideal is to simply not have bends. The VTF-TN1’s design allows it to attain this ideal as well as have the advantage of down-firing ports. By using down-firing ports, the VTF-TN1 gains additional loading from the confined floor space underneath the sub that may increase its lower-frequency output even more. Down-firing ports are also great at masking unintended port artifacts such as chuffing should that occur, so it reduces the audibility of any port related misbehavior.

The port tuning frequencies are 15Hz for a single port open, and 18Hz for both ports open. These are unusually low port tuning frequencies, especially at this price point. That could make the VTF-TN1 a very compelling choice for those who are chasing deep bass on a limited budget.

The enclosure is made from MDF and uses a 1 ¼” thick front baffle. There is a top and bottom brace as well as two mid braces shoring up the side panels’ strength. There is also corner bracing lining the enclosure edges. Sheets of acoustic stuffing line the interior panel sides. The feet are some tall rubber cones that look to give the ports enough breathing room to operate well, even in thick carpeting. The ports are heavily flared on both sides and have a 4” diameter with a 25” length. They are some of the larger ports I have seen on a subwoofer. Some small polyurethane pucks are included to provide an air-tight seal for those who want to plug the ports. The grille attaches to the enclosure via grille guides onto some metal tabs; the metal tabs are nice since plastic tabs have a habit of snapping off.

Taking a long view, the VTF-TN1 is a subwoofer that places function over form. The decision to exchange depth for height is probably going to alienate buyers who are chiefly concerned with aesthetics, but those prioritizing clean deep bass at high output levels look to have a great choice here. But let’s see that for ourselves in some real-world listening…

Hsu Research VTF-TN1 Listening Sessions

The best placement for a single sub in my room gives me a relatively flat response for an un-EQ’d single subwoofer, with a window of +/- 4 dB from 25 Hz to 100 Hz with no broad dips in important ranges. This location trades low-end room gain for a relatively flat response, a worthwhile trade for my tastes. The receiver used was a Marantz AV7705. The crossover was set to 80Hz. The speakers used were some Philharmonic 1802G Custom Reference speakers.

As always, I will note here that since room acoustics have a huge effect on low frequencies, the way these subwoofers sound in my room at my listening position is not necessarily going to be the way they sound anywhere else for anyone else, so readers would do well to keep that in mind, and not just for this subwoofer in this review but for any subwoofer in any review.

Music Listening

As usual, I gave the review subwoofer a spin on a pipe organ recording, and for the VTF-TN1, I found a banger entitled “Organ Fantasies: Masterworks by Bach, Liszt, and Reger.” The music of this 2023 release was performed by Felix Hell, and the instrument was the Weiwuying Concert Hall Organ in Taiwan, the largest pipe organ in Asia. This mammoth organ has 9,085 pipes and 127 stops and can easily dig down into infrasonic frequencies. Hell has selected five spirited pieces from the famed composers in the album’s title to show off this organ’s capabilities. With some 32’ pipes, the organ should be a good match for a system capable of the VTF-TN1’s purported 15Hz tuning. I streamed this album on Qobuz.

Felix Hell isn’t known for shying away from the low-frequency potential of pipe organs, so he is a good fit for demonstrating what such a tremendous instrument as the Weiwuying Concert Hall Organ is capable of, and together, they are a good fit for demonstrating what a powerful subwoofer is capable of. The VTF-TN1 proved to be very capable indeed. The subwoofer was able to convey the immense scope of this instrument as well as the enormous venue it was situated in. Most of these tracks had seriously low bass notes, and I am sure that is no accident from Felix. However, not all of the bass was of the ‘sturm und drang’ variety, and on pieces where the bass is gentle such as track 2, “Adagio in D Flat Major” by Lizst, the VTF-TN1 could relay the presence of those notes without overdoing them. Polyphonic bass passages were also easy to discern, and the sub was also to communicate more complex notation without trouble. And when these tracks needed thunder, such as in track 3, Reger’s “Fantasia and Fugue,” the TN1 delivered in spades. On the lowest notes I could not only hear but also feel the individual cycles of the waveform. Bach’s “Toccata and Fugue,” a staple of pipe organ pyrotechnics, also made an appearance, and the crescendos roared with gusto with this subwoofer. The VTF-TN1 was an excellent vehicle for this style of full tilt pipe organ music. Most subwoofers don’t dig down to 16Hz, but some pipe organs do, and I normally excuse their inability to fully catch those lowest notes by saying most pipe organ performances don’t have content that digs that low, but the VTF-TN1 needs no excuses. It can reproduce the lowest notes of these massive organs with exuberance.

One of the few other instruments that can take advantage of a subwoofer is the double bass, and a terrific jazz album I found that centers around this instrument is “Conversations With Christian” by bassist Christian McBride. McBride is joined by other instrumentalists for duets and trios from track to track, but his double bass is the focus of this album. This laidback album features tracks that are mostly covers but some are original pieces by McBride as well. The virtuoso McBride uses both bowed and plucked playing techniques. Plucked double bass playing has to be one of the best ways to gauge the transient character of the bass of a sound system since the attack happens so quickly. The mutes are also good for the same purpose since the cessation of the instrument’s sound occurs just as quickly. I streamed this album in a 96kHz/24-bit resolution from Qobuz.

The first track features a duet between a female vocal and McBride’s double bass. The rapid plucked playing relayed the dense notation of this composition, and the VTF-TN1 was able to delineate the low frequency melody of this track with aplomb. The second track was a virtuoso display of McBride’s talents as he alternated from plucked playing to bowed playing; the richer harmonics of the bowed double bass needs a sub that can integrate well with the speakers, and the TN1 demonstrated this ability. Most of the tracks featured plucked playing, and the subwoofer reproduced the acuteness of the attacks with a hi-fi immediacy. However, the attacks of a double bass are mostly the main speakers talking, and I have always thought that the mutes are what subs need to do well to exhibit fidelity, and on this count, the VTF-TN1 does remarkably well. There was no lingering energy or overhang in the abrupt halts of the strings’ vibration. Similarly, on bowed playing, the sub also tracked the much more gradual attack and decays of the strings with a delicacy that allowed it to disappear in the overall presentation. “Conversations with Christian” nicely illustrated the VTF-TN1’s abilities with an acoustically recorded instrument, and double bass enthusiasts should definitely check this album out with a capable sound system.   

Taking a stark one-eighty from the breezy jazz of Christian McBride, I loaded up a dark ambient album titled “Humanoid Dystopia” by Kristof Bathory. This album has a bit more going on than mere atmospherics; in fact, there are some fairly strong rhythms throughout the tracks here. However, the overall intent is to paint a futuristic but dismal soundscape, and the music sounds like the soundtrack to what might happen if Clive Barker wrote a science fiction movie. As you might imagine, that leads to lots of bass, and this genre of music uses low-frequencies in a number of different ways. But even among this genre, “Humanoid Dystopia” is fairly bass-heavy and has an abundance of deep bass to keep woofers busy.

In the first track, “Exiled From Human Life,” a pulsating bass rhythm rides over a drone and creates a portentous atmosphere. The VTF-TN1 juggled these low-frequency elements well and seamlessly blended into the foreboding soundscape conjured by the artist. The second track utilized a highly textured drone sound that was finely defined with help from the sub. Further on, we get a track that is underlined with a fluctuating rumble, and the minute shifts in its pitch was audible on the TN1. Thunderous kettle drums were given a startling thump by the sub which made me realize that this album was compositionally a bit busy to be labeled ‘ambient,’ even if on the heavier end of the genre. It felt much more like a movie score, and the VTF-TN1 helped to realize this album’s cinematic quality due to its seemingly endless low-frequency extension. I don’t think that Hollywood is still capable of creating a movie that could match the cold futurism and bleak imagery suggested by this album (maybe an adaptation of “Blindsight” by Peter Watts?) However, the imagery projected by the mind’s eye will never be matched by any hack screenwriter or army of CGI animators. This music provides a color pallet for the imagination’s brush strokes, and that pallet is given a wider color gamut by a potent sound system. The extremely deep frequency bandwidth and dynamic range of the VTF-TN1 certainly expands that color gamut and helps to create a more vivid picture intimated by the music.

For something to see how the VTF-TN1 would react when pushed hard, I selected “Mission 02,” a 2022 compilation of electronic bass music from the always-interesting Vision Recordings label. The music ranges over a multitude of sub-genres, from drum’n’bass, trap, dubstep, techno, and a lot in between. This massive album has 28 tracks that stretch over a 106-minute runtime and features tunes by established artists such as Forbidden Society and Current Value to promising talent that aren’t as well known. The one thing that all of these tracks have in common is that they want to punish bass drivers, and, at a high enough loudness level, most subs would make their own shortcomings apparent.

I queued the album and cranked the volume, and I quickly found that the sub was willing to play louder than I was willing to endure. Aside from my own discomfort, I have an aging cockatiel that I didn’t want to scare to death even though it was on another floor of my home. I knew that a powerful sound would be able to make its way to my bird at the kind of output this sub was capable of. The VTF-TN1 was able to throw a concussive blow for every kick drum hit. It had plenty of chest punch power to bring the bass into the realm of physical as well as audible sensation. I could almost swear I could feel the different pitches of the basslines resonate different areas of my body. “Reason” by Subtension had a loud and rapidly oscillating bassline that was an absolute blast to listen to on the TN1. “Skatepark” by ET Finger had delightfully syncopated percussion along with a more melodic bassline that recalled old school drum’n’bass. Forbidden Society’s contribution was expectedly dark but unusually lower tempo for them, and the weight that the VTF-TN1 gave to its bassline made it sound like a wrecking ball. Some other highlights for bass fiends: “Space Bass” by Mono-Poly, “I/O U” by Secret Tape, “Quicksand” by TANTRON, and the bizarre “THAT U” by HOST, among others. Lovers of electronic music ought to give “Mission 02” a listen with a subwoofer as potent as the VTF-TN1.

Movie Watching

I had not yet seen the 2023 actioner “John Wick: Chapter 4,” but I knew I would get around to it when I had a piece of seemingly-capable audio equipment in-house. If its sound mix held with its predecessors, it would surely have loads of low-frequency effects with which to show off a subwoofer’s chops. I enjoyed the other ‘John Wick’ outings, so I felt that this fourth installment was such a safe bet that I hadn’t bothered to watch the trailers and didn’t know what to expect story-wise, except that it would involve a boatload of shooting and fistfights.

“John Wick Chapter 4” had a multiplicity of epic action scenes, and the VTF-TN1 gave the action a sense of heaviness and force. It turned out to be the perfect movie for a good sub since I felt as if the sound mix had given the gunshots a bit more thump than normal. Every bullet discharge had a palpable thud, even from handguns. Shotguns have always had a privileged status in the “John Wick” franchise, and this entry continues that tradition by having a bravura long-take sequence shot overhead where Wick uses shotguns loaded with ‘Dragon’s Breath’ shells where the pellets are made from burning magnesium. The resulting carnage is quite spectacular, both in sight and sound, and should be seen on a system that can do both sight and sound reproduction justice. The VTF-TN1 was definitely game for delivering oomph to the shotgun blasts. A car chase around the Arc de Triomphe gave the subwoofer moments to shine in the many crashes and collisions with human bodies. Another terrific action scene involved a shootout and fistfight in a club where Wick encounters a heavy-set man who just might be his match. The subwoofer drove the scene with the bassline of the techno music and brutally realized the blows that Wick and his hefty opponent were inflicting on each other. I enjoyed “John Wish Chapter 4,” but its nearly three-hour runtime of bombastic fight scenes left me a bit fatigued by the end. That is one of the dangers of such a capable subwoofer; if the content demands it, it won’t tire of dealing out a beating to the listener regardless of the listener’s state. 

I also hadn’t come around to seeing “Dune: Part 2” yet, but with the VTF-TN1 in-house, it was time to rectify that mistake. As a long-time Dune fan, I loved what Denis Villeneuve has done for Frank Herbert’s book in the first movie, so I was excited to see how that story was continued. The first movie was a total bass-fest, and I had to wonder if it didn’t single-handedly drive up sales for potent subwoofers by itself. I expected the series' penchant for deep bass to continue in part 2, especially where Paul Mua’dib’s Fremen warriors would collide with the Harkonnon’s forces. It should give any subwoofer a real workout.

“Dune: Part 2” continued the first movie’s penchant for heavy-duty deep bass, so it was a good thing I had the VTF-TN1 on hand to reproduce the full spectrum of this sound mix. The bass in “Dune: Part 2” could plunge into infrasonic frequencies that were more felt than heard. Of course, the sandworms were the star here, where their presence could be felt as a rumble from their approach, and the VTF-TN1 signified that as a shaking sensation in my seat. Other scenes with massive bass featured the space harvesters, especially when they were getting blown out of the sky. Their sounds were given a rumble that was positively visceral. The scenes set on Giedi Prime also had a tremendous amount of deep bass, and the VTF-TN1 delivered those scenes with a terrifying reality. Hans Zimmer’s score also bubbled with deep bass elements, as one would expect from Zimmer, and the music alone would be enough to justify a serious subwoofer. The VTF-TN1 realized the score with a surfeit of dynamic range, and it always kept the bass from the music distinct from effects sounds. Movies like “Dune: Part 2” are why subs like the VTF-TN1 exist. They use deep bass to effect an epic feel and can dig into the fringes of humanly audible frequencies. Most subwoofers don’t really dive into frequencies below 20Hz, but the VTF-TN1 does. While you don’t need to have a sound system with infrasonic playback abilities to enjoy movies like this, the ability to do that does add a tension and gravity that wouldn’t be there otherwise. The VTF-TN1 unquestionably accomplishes this. I am glad I waited to watch “Dune: Part 2” with such a potent subwoofer on hand.

Hsu Research VTF-TN1 Subwoofer Measurements

Testing on the Hsu Research VTF-TN1 was conducted with the microphone facing the woofer at a 1-meter distance with measurements scaled back to a 2-meter distance by subtracting 6dB. The temperature was recorded at 60F degrees with 90% humidity. The subwoofer’s gain was set to maximum, the phase was set to zero, and the low pass filters were set to bypass.

The above graph shows the measured frequency responses for the Hsu Research VTF-TN1 subwoofer. The shown responses are measured from both ports open and one port sealed with the Q control set to 0.7 for both. The responses are ruler flat from port tuning all the way up to 200Hz. These measured frequency responses are nearly ideal, and Hsu did not need to resort to DSP equalization to acquire them. This is what happens when you put a good driver in an optimal enclosure with carefully tuned port design. Something to note is the upper-frequency extension out past 200Hz. This allows higher than typical crossover frequencies which can better help to address room modes in multi-subwoofer systems. It also gives the system more dynamic range in mid-bass frequencies.

The above CEA-2010 measurements are short-term bursts that show the subwoofer’s clean peak SPL before heavy distortion sets in. Our measurements have been referenced to 2-meter RMS, which is 9dB down from the standard requirement for the measurements to be shown at 1-meter peak. However most publicly available CEA-2010 measurements are shown at 2-meter RMS, so we followed that convention.

The VTF-TN1 puts out some impressive numbers with some real low-frequency output combined with a lot of mid-bass punch. Both operating modes measured here exceed 100dB at 16Hz, but the single port ‘max extension’ configuration allows cleaner deep bass and more output at port tuning at such a deep frequency. With both ports open and sub set to ‘max output,’ 20Hz to 25Hz performance is improved. Above that range, the headroom is about even, although we are seeing a bit more distortion in single port mode at the highest drive level. These numbers are largely a match with Hsu’s own reported numbers give or take a decibel or two depending on frequency. The tremendous mid-bass output is a good argument for experimenting with the higher-than-typical 80Hz crossover frequency, especially in a multi-sub system. 118dB and higher is pretty prodigious output and is definitely something you can feel in your chest. These numbers certify the VTF-TN1 to achieve our Bassaholics ‘Extreme’ room rating meaning it should be able to handle a room of up to 6,500 cubic feet in its ‘max output’ mode (2 ports open), and it gets our ‘Large’ room rating in its max extension’ (1 port open) mode. 

To learn more about Audioholics’ Bassaholics Room ratings, please look at this article: Bassaholic Subwoofer Room Size rating Protocol.

Testing for long-term output compression was done by first conducting a 20-second sweep tone where 50Hz hit 90 dB with the subwoofer 1 meter from the microphone (graph has been scaled to 2 meters for easy comparison with our other review measurements). We then conduct further 20-second sweeps by raising the gain by 5dB until no more output could be wrung out of the subwoofer. These tests show us the long-term continuous headroom that the subwoofer is capable of.

Both operating modes of the VTF-TN1 permit a great deal of output with most of the bandwidth exceeding 112dB continuously, but on the whole, the ‘max output’ mode with both ports open does offer more headroom overall. We can see how halving the port volume reduces port generated output, and the sub compresses output more at port generated frequencies when one of the ports has been sealed. With a single port open, the highest two sweeps compress on the low end, but with both ports open, the TN1 only compresses the response shape at the last few dB. It’s no surprise that leaving the ports open enables the greatest dynamic range. Use the sub with both ports open and the EQ control set to ‘2EQ’ for the most punch.

The above graphs show the corresponding total harmonic distortion to the long-term output graphs. Essentially, they depict how linear the subwoofer remains for the corresponding drive level seen in the long-term sweeps. The quantity being measured is how much of the subwoofer’s output is distortion and is shown here as a percentage.

The VTF-TN1 can be made to produce significant distortion but only at very high drive levels. At nominal drive levels, distortion products are essentially nonexistent, even at very low frequencies. As would be expected, distortion crops up at the lower frequencies first when the sub is starting to be pushed hard. Using the sub with both ports open and set to ‘2EQ’ offers the most clean headroom. Were DSP available, limiters could be set up to prohibit output levels and frequencies where distortion occurs but only at the expense of headroom. The good news is that users will rarely drive this sub to levels where distortion as a percentage runs above single digits. It is only at the last 5dB where distortion starts rising across the bandwidth as we approach a continuous 110dB of output. Up until the highest drive levels, the VTF-TN1 is an extremely clean subwoofer.

The above graphs depict measurements of the constituent harmonics from the long-term output sweeps and are what the total harmonic distortion measurements are composed of for the 2nd and 3rd harmonics. These individual harmonics can give us a clue as to what might be the cause of some quirk or non-linearity. We are only showing the 2nd and 3rd here because they more or less reflect the higher even-order and odd-order behaviors, although higher-order harmonics tend to be much further down as a percentage of distortion compared to the second and third.

In order not to deluge the readers with graphs, we will only show the harmonic distortion components for one operating mode, since the ratio of odd-to-even harmonics is largely the same for any ported operating mode of the VTF-TN1. In this ‘max extension’ mode with a single port open, the distortion generated is a mixture of even and odd harmonics. As the driver hits its maximum excursion limits, the way it begins to ‘clip’ the output results in a complex mixture of distortion products. This isn’t bad or good, and every driver will produce distortion when pushed hard, but some will veer toward even or odd harmonics as the main bulk of distortion output whereas the VTF-TN1 produces a bit of both. Because of this complexity, these graphs are mainly of academic interest, and pretty much the only way they will result in anything relatable to audible experience is if the user blasted a sine wave at maximum drive levels.

Group delay is the measurement of how much time it takes for individual frequency bands of an input signal to be produced by the speaker. It can indicate that some frequency components are developing slower than others or are taking longer to decay. It is generally thought that 1.5 sound cycles are needed for group delay to be audible at bass frequencies, although there is an argument that group delay should remain under 20ms to be completely unnoticeable, but that is likely meant for mid and upper bass frequencies.

The group delay shown by the VTF-TN1 is quite good, and it doesn’t even pass our ‘worst case scenario’ of 20ms until below 40Hz which is well below the frequency range of the vast majority of music content. The sub sounds sharp and it measures likewise. Plugging a port does bring the group delay down a bit from about 18Hz to 50Hz, but I doubt that will translate into anything even remotely audible. Running it in sealed mode will bring group delay down in that range a bit further, but I would discourage anyone from running the TN1 in a sealed operating mode since it sacrifices a lot of deep bass output for a small decrease in group delay. The TN1 does not exceed a cycle of group delay until very deep bass frequencies, which is expected given its very low port tuning frequencies. Those looking for a sub that has good transient behavior as well as big deep bass have a great choice here.

Hsu Research VTF-TN1 Subwoofer Conclusion

Before bringing this review to a close, I will briefly go over the weaknesses and strengths of the product under evaluation, and, as always, I will start with the weaknesses since I am the kind of person who always wants the bad news first. There isn’t much to complain about regarding the Hsu Research VTF-TN1. The only aspect that some might find problematic is its shape. By exchanging depth for height, it becomes a tall sub and that makes it a bit more visually conspicuous. The satin black finish and rounded edges help to soften its appearance, but it won’t be easy to hide in a typical living room or family room. Lower profile subs are less conspicuous even though they have a larger footprint. I don’t think the VTF-TN1 looks bad, but those who want a more inconspicuous sub will probably opt for something that has a more traditional shape for a home audio subwoofer.

Some might complain that the VTF-TN1 doesn’t really push Hsu’s design forward much over the VTF-15h MK2 since all it really does is redo the ports and enclosure. However, that more serves to highlight a strength rather than a weakness since the VTF-15h MK2 was and still is a very high-value and competitive subwoofer in its class (see our 15” ported sub round-up YouTube discussion: Battle of the 15” Ported Subwoofers), and Hsu has made something that plays deeper bass at a lower price and increase the electronics warranty to 5 years of coverage. In a time where prices are increasing, who can fairly complain that one of the best bang-for-the-bucks in subwoofers actually lowered pricing for their flagship product?

In citing its strengths, sound performance has to be its foremost asset. It has real output down to infrasonic frequencies as well as a solid punch in mid-bass frequencies. Even in large rooms, users will get serious output below 20hz. I do recommend using it in its ‘max extension’ mode in large rooms since it will play louder and stay cleaner at higher output levels. It has a ruler flat response with extremely low distortion up until its highest drive levels. Its time-domain behavior is terrific as well with all mid-bass frequencies staying under 10ms of group delay and deep bass never even touching 1.5 cycles of delay. That shows proper ported subwoofer design, and those who think ported subs sound laggy or slow should hear a VTF-TN1 in a properly calibrated setup.

Outside of the sound quality, a major advantage is its footprint: it doesn’t eat up more floor-space than most sealed 15”s. So if you want ported subwoofer-level deep bass but don’t have a lot of floorspace to give up, the VTF-TN1 is one of the best solutions out there, especially at its pricing. That also makes it a great candidate for a multiple sub system where space is more at a premium. Multiple VTF-TN1s run in ‘max extension’ mode would produce pretty gob-smacking deep bass. Also adding to its usability and accessibility is that it doesn’t weigh a ton and is easy to move around which is not something that many of its competitors can claim. This doesn’t mean its build quality is lacking either but rather the internal bracing is thoughtful rather than going for the brute-force approach of adding sheer mass. The ability to move the VTF-TN1 around easily may not be something that some users will care about who will only need to get it into place once, but I do greatly appreciate it when moving a sub doesn’t have to be a multi-person chore. Lifting it should still be done by two people, but walking it into position is easily done by a single person.

Its feature set is good for the segment. While it doesn’t have all the intricate adjustability of app controls, it does have variable port tuning, XLR inputs, speaker-level inputs, and a Q control. The variety of inputs allow it to be easily integrated in a wide range of systems from typical home audio, high-end home theater, pro-audio, and old school two-channel. Per its variable tuning, as was mentioned before, I would advise users who are looking for maximum dynamic range to run it in its ‘max output’ mode with both ports open. That still gives plenty of deep bass extension, and users will still get a strong in-room response below 20Hz but with more thump and clean output. ‘Max extension’ mode with one port sealed would be my choice for a smaller room or multi-subwoofer systems. The room gain that would come in a smaller room from a sub with a 15Hz anechoic extension would be pretty tremendous. And, as was said before, I do NOT recommend that the VTF-TN1 be used with both ports sealed. The main advantage of a sub like this is its port design, and sealing the ports negates all of that. If you want a comparable sealed sub, look at its sealed brother, the ULS-15 mkII.

HSU vs the Competition

Outside of the VTF-TN1 itself, we have to mention pricing as an advantage here. The VTF-TN1 is priced at $1.2k not including shipping, and shipping will be $99 for the lower 48 states (shipping is available to the non continental US and Canada at greater cost). Most of the subwoofers that it’s competing against in the ported 15” class are closer to $2k than $1k. They may be more conventional looking and have a higher ‘spouse approval factor,’ but few of them dig as deeply in low bass. There are a few subs that can dig below 20Hz that can be had for less than the VTF-TN1, namely the VTF-2 mk5, the Speedwoofer 12s, and the BIC Acoustech PL-300, but none of them are in the same output class as the TN1. Within its caliber of subwoofer, there are not many that have such a deep low-frequency extension, and they all cost significantly more than the VTF-TN1 and are also significantly larger and heavier. The Hsu Research VTF-TN1 is a singular design that brings with it some unique advantages.

In the end, I greatly enjoyed my time with the VTF-TN1, and I think it is an extremely strong contender in its price class. At the time of this writing and at its present price point, it would be my first pick. I would understand if someone needed something a bit more visually subdued and decided on something else within its price class, however, there isn’t anything else that can quite match its overall performance for the cost. And when you consider its feature set, warranty (5-year electronics, 7-year driver), a true satin black finish, Hsu’s terrific post-purchase support, and its relatively small footprint, that all adds up to being an exceptional value proposition. I believe that it deserves consideration even among more expensive subwoofers. 

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

• — Excellent
• — Very Good
• — Good
• — Fair
• — Poor

Metric	Rating
Bass Extension
Bass Accuracy
Build Quality
Fit and Finish
Ergonomics & Usability
Features
Dynamic Range
Performance
Value