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HSU Research ULS-15 MK2

By Jim Wilson (theJman)

photo courtesy of HSU Research​

The subject of this review is the HSU Research ULS-15 MK2, a newly released upgrade of the MK1. If it seems like HSU deja-vu you're partially correct; in June of this year I published a review on another updated HSU subwoofer, the VTF-3 MK5. That proved very popular, and almost immediately the requests started coming in asking if I would evaluate the new ULS as well. One quick email to Dr. Hsu and a review unit was on its way to me.

The ULS-15 MK2 is an acoustic suspension subwoofer utilizing a single front-firing 15" driver. It's a perfect cube, measuring in at a tidy 18"x18"x18" (HWD), and weighing a mere 61 pounds. For me that was a refreshing treat, given that I haven't reviewed a subwoofer under 100 pounds in who knows how long. Finally, one I can pick up and carry around with ease. The amp is rated at 600 watts RMS with a massive 2000 watts peak. The stated frequency response is 20Hz-200Hz, but note that's within a very tight +/-1dB (a 2dB window, as opposed to the 6dB window when the specification is +/-3 dB). In other words, there is almost no variation in the frequency response for well over 3 octaves.

HSU Research is the quintessential ID (Internet Direct) company, selling everything from their own website. The ULS-15 MK2 has a retail price of $779. Add $69 for shipping in the continental US and the total package will run you $848. There is a 2 year warranty on the electronics and 7 years on the driver. Like all HSU Research products the ULS-15 MK2 comes with a 30 day in-home trial period.

Shipping protection for the ULS-15 MK2 was excellent; HSU utilizes one the best methods I've seen to date. Everything was double boxed, so damage during shipping would be difficult, but that's only the beginning. The outside carton had thick cardboard sleeves placed in each corner, adding additional structural rigidity. The thing which most impressed me though was the inner box was protected on the top and bottom with 1" thick sheets of soft foam. In essence, the carton which contained the subwoofer was protected as well as some companies protect the subwoofer itself.

Cutting open the inner box reveals a 2" thick custom molded piece of soft foam cradling the ULS-15 MK2 firmly in place. On the bottom was a matching piece of foam, replete with cutouts for the massive round rubber feet and the Accessory box (which held the power cord). The sub was inside a plastic bag which was neatly taped shut. To protect the painted finish HSU covered the entire subwoofer with a thin sheet of soft foam material. All-in-all this is an impressive setup, one that could easily be used as the yardstick for how products should be protected during shipping.

The review model came covered with black satin paint. You can also get it with genuine rosenut wood veneer for an extra $150. Cabinet finish and overall construction quality was typical HSU; in other words, outstanding. The paint application was impeccable, being both smooth and even, everything was screwed down securely, nothing was misaligned or out of place. Like the packaging, other companies can take a lesson from HSU with regards to how things should be done.

Documentation was standard HSU fare, which is to say exceptional. That's perhaps the third time I've used a variation of the same sentence - which is totally unlike me - but for some reason I simply can't come up with a more creative way of expressing my sentiments. After my experience with the ULS-15 MK2, and the VTF-3 MK5 before it, I have come to expect flawless execution from just about everything HSU Research does. This company is consistent if nothing else, consistently good. The owner's manual is complete, logically organized, well written and has everything one could possibly need to get the most from their subwoofer. You begin to wonder if these people even know how to make a mistake.

The cabinet is built using 1" MDF all around. There is a circular brace surrounding the driver that ties the horizontal and vertical walls together, forming a rigid structure. 1" thick black eggcrate foam is attached to all the interior surfaces, damping the backwave from the driver. The grill is also constructed from 1" MDF, smoothed over and painted black to match the exterior of the enclosure. It feels very solid and exhibits almost no flex whatsoever. The material is acoustically transparent and was attached to the frame meticulously. Centered at the bottom is a classy HSU logo. There are magnets in both the frame and front panel which are used for attachment points, so all you need do is position the grill within an inch or so of the sub and it hops on by itself. Since the grill is held on by magnets and not screws, should you choose to use it without there are no unsightly holes in the front panel to mar the appearance.

The ULS-15 MK2's driver is based on the same platform as the VTF-3, so the two share many characteristics, but they are not the same. Both utilize a large half roll high density foam surround and a reinforced paper cone topped by an inverted dustcap made from a composite material. The motor uses a pair of 1" magnets and multiple shorting rings which are anchored to a black 12 spoke powder coated metal basket.

HSU's BASH amp is becoming universal in their product line, but in this day and age - where programmable DSP's are all the rage - you can get away with that and still custom tailor the output to fit the specific alignment. The amp contains dual balanced (XLR) and unbalanced (RCA) inputs, along with high level connectors featuring 5 way binding posts. That pretty much covers all the bases right there, making it such that you can connect this subwoofer to anything you have. There are dials for volume, crossover and Q Control. The Q Control allows you to make the sound 'lean' or 'thick', depending upon your preference. A Q setting of 0.3 tends to work well for music (lean), while 0.7 is often the choice for movies (thick). Because I enjoy both I left the dial at 0.5, which is essentially the midway point. HSU includes toggle switches for the Phase - 0 or 180 degrees only - along with one that enables/disables the crossover dial. There's also the typical power switch, with settings for Off/Auto/On. The 4th switch is for the EQ mode, and similar to the Q Control it's used to contour the output to your individual tastes. EQ 1 adds some boost to the bottom end, extending the response flat to just below 20Hz. EQ 2 virtually eliminates the boost and creates a curve which mimics the natural roll-off profile that this subwoofer would probably have in the first place.

As was the case with the VTF-3, I had a little trouble with the Standby functionality. It would often go to sleep while watching sporting events, and on occasion even while viewing a movie if the volume was low. I ended up leaving it in the On position - because it is football season after all, so I'm watching a lot more TV now - and that solved the problem. Thankfully the amp runs cool and generated no appreciable heat, even after being left On for several weeks straight.

My living room is 13x17x8 (1768 ft^3), so it's not terribly large. The main seating position is approximately 11 feet from the subwoofer. All testing was done after the unit had been broken in for at least 25 hours.

I sometimes find it difficult to write this section of a review. Realistically speaking, how does one accurately quantify the overall sound quality of something in a paragraph or two? Try it with a product you already own and you'll soon come to realize it's not that easy. Thankfully it's pretty obvious on occasion, and when that occurs an image appears and presents itself in a manner impossible to ignore. With the HSU ULS-15 MK2 it was very evident almost from the get-go because in my head I kept hearing the phrase "it just works". However, putting that into words proved to be a challenge.

Although "it just works" may sound trite and somewhat simplistic it's actually quite the opposite. Every single person reading this has owned something - and hopefully more than one something - that just worked with no fuss, no hassle. A car that went well beyond 200,000 miles without needing anything but routine maintenance, a refrigerator which lasted 25 years and never failed to keep things cold, a t-shirt you wear every weekend that still fits perfectly even though you've gained a few pounds along the way. Perhaps it's a cooler you've owned since high school, your faithful friend that has seen more camping trips, BBQ's and sporting events then you can actually remember. Whatever it is, you know what I'm referring to. Ol' faithful, as it were.

Having lived with the ULS-15 MK2 for over 2 months I can tell you it's that rare breed of product which just goes about its business without drawing attention to itself, unless the situation warrants. The anti-Paris Hilton, if you will. Are you just watching TV? No problem because this subwoofer will hang in the background and merely augment the soundtrack. Maybe you switched to a bass-heavy movie. If so, the ULS-15 MK2 will spring to life and make its presence known. This subwoofer is able to seamlessly morph into the perfect companion for whatever the occasion calls for. I like that, and yet I don't at the same time. What on earth does that mean? It's complicated.

This review was supposed to be published weeks ago but I simply couldn't get the words out of my head and into a document. I rewrote three entire sections - one of them several times - because it just wasn't coming to me. I would type paragraph after paragraph, but then delete them because I wasn't satisfied they depicted my sentiments accurately. I started to get very frustrated until it finally dawned on me what the problem was; because the ULS-15 MK2 works so well I was at a loss for how to explain what I was hearing. How do you honestly say "this thing just does what it's supposed to all the time" without coming across as vapid, or resorting to worn-out clichés? Confused? Join the club. It's akin to describing the color blue to a person who has never been able to see. What do you use as a reference? How can you relate that to someone who has no concept of colors in general? I certainly would struggle trying to do it, but that's exactly what it felt like when typing up this review. Ultimately I decided not to fight it and instead acquiesced, going with the "it just works" theme. That may not make any sense to you, but buy a ULS-15 MK2 and you'll come to realize exactly what I mean.

One thing I feel is lacking in too many reviews I've read over the years is a recognition that the person doing the evaluation had a true understanding of what the product in question is actually capable of. To me it's impossible to get a feel for any piece of audio equipment unless you live with it on a day-to-day basis for an extended period of time, experiencing what a 'normal' person would if they happened to own it themselves. That's not to say everyone in this business is like that - because they aren't - but too often after reading something I come away wondering if they did much more than watch 2 or 3 movies and played a few songs. That's partially why my reviews take so long to publish; I live with something for a month before jotting down most of my notes. I'm of the mind you can't truly understand the essence of a product unless you do have that level of familiarity.

With the HSU ULS-15 MK2 what I found was a faithful companion, a subwoofer refusing to draw attention to itself unless the situation warranted. What exactly does that mean? It means the ULS spoke in a hushed manner, never raising its voice unless it needed to get a point across. You could almost forget it was there until the soundtrack got challenging, at which point the thing would rise up and announce its presence in no uncertain terms.

Dark Knight Rises (blu-ray)
For this review I chose Dark Knight Rises mostly because it starts off with a bang; a few minutes after the opening credits disappear from the screen there is some content in the soundtrack which dips below 5Hz. No that's not a misprint, the sound engineers really threw in material that drops deep into single digits. I knew the ULS-15 MK2 wasn't going to be able to hit those notes, but I was curious to see what it would do when confronted with such punishing material. I made sure to crank it up as well, just to be sure and stress the limiters (sometimes it can be fun to play with other people's toys).

When the movie begins we find the main protagonist, a fellow by the name of Bane, deliberately getting himself and a few of his cohorts captured by the CIA in order to get onto the same transport plane as Dr. Pavel, a person he fears may have told them all his secrets. As the scene unfolds there is an ominous low-level rumble designed to heighten a sense of impending doom. The ULS-15 MK2 played its part expertly, creating a palpable sensation of imminent destruction. And destruction is what occurs; once Bane gets the answers he came for the rest of his crew begins wreaking havoc, repelling down from a trailing plane onto the transport. They proceed to lock the planes together with steel ropes, blow off the transports tail, flip the thing perpendicular to the ground and then watch as the wings get sheared off by the force of the wind. While all this is happening there are the requisite deep rumbling sounds from the engines of both planes, along with the occasional explosion for good measure. During all this the ULS-15 MK2 kept pace, pumping out subterranean content in a very believable manner.

Feeling satisfied this subwoofer was up for a challenge I then switched to scene 5. This one doesn't have bass anywhere near as deep as what you'll find in scene 1, but what it does have is an incredible amount of material between 25Hz and 150Hz. What I'm talking about here is peg-the-needle amounts, lots and lots of output. Combined, these scenes provided me an ideal opportunity to evaluate two very distinct qualities of the ULS-15 MK2; how it manages really deep bass, along with pushing the envelope in octaves most people consider the "punch to your chest" range. If you think I was intentionally trying to trip up this subwoofer you would be correct because, quite frankly, I love pushing the limits. I'm afraid my 'acid test' didn't work out as planned though because I never did throw the ULS-15 MK2 off its game.

The music score in this seen was omnipresent, yet it was never obnoxious. That's a really fine balancing act for a lot of subwoofers to pull off, but it proved no challenge here. When Batman's flying bat-cycle emerges from the alley I noticed the driver undulating wildly, yet juxtaposing that was the fact I felt almost no vibration when my hand was placed on the cabinet. I did get a sense of resonance as the engine of his craft pulsated on takeoff, but that was due to the frequency it was playing at and how it coupled to my room. Truth be told, the ULS-15 MK2 wasn't really struggling.

Tron: Legacy (blu-ray)
I decided to put some additional effort into unnerving the ULS-15 MK2, and there are few movies able to do that more effectively than Tron: Legacy. Not only does this soundtrack contain some very deep bass - and for long periods of time - it is also recorded on the hot side. That's like the Bermuda Triangle for a subwoofer, but it makes for a lot of fun when you're pushing the limits like I was. Let me cut to the chase; if I really cranked the volume the ULS-15 MK2 struggled a little with a few sections, almost as though the soundtrack was coming at it faster than it could keep up with. But that was only a couple of times during extreme sessions; if I kept the volume just below the threshold of pain then all was good and this HSU subwoofer churned out oodles of deep bass.

Scene 4 starts with our hero, Sam Flynn, getting sucked into the alternate world that constitutes the Grid. In an instant he goes from the real thing to a parallel universe, the same one his father never returned from years earlier. As he begins to assess the situation a Transporter descends upon him. These are airborne vehicles that roam his new world, picking up 'strays' who have refused to be subsumed. As the rocket boosters of the Transporter kicked in I detected a bit of droning. To be honest I think the only reason I even noticed is because everything else was so clean and precise that any deviation became pretty apparent. The presentation was certainly potent though, with a distinct rumbling that was unmistakable.

The subsequent scene (Games) is rather long, but it's certainly a treat for the ears if your subwoofer can render it correctly. The HSU-15 MK2 did that very thing, producing an intense and captivating performance. The first time I ran through this scene I did so with the grill on, and in spite of the crazy amount of bass it was never in jeopardy of getting kicked off. I played it a second time without the grill because I was getting an awful lot of bass and I wanted to see precisely what the driver was doing. The short answer is 'a lot'; this thing was gyrating wildly, pumping back and forth in a manner reminiscent of a piston from an internal combustion motor. Yet no matter how far it traveled there was never any unpleasant mechanical sounds - it never bottomed or hit a limit. You could definitely tell the driver was working its tail off but it didn't object to the abuse.

Hurt Locker (blu-ray)
After pummeling the ULS-15 MK2 with Dark Knight Rises and Tron: Legacy I opted to back it off and watch something that wasn't quite so strenuous, but what should I choose? How about a movie almost completely opposite of the previous two? What about something where the subwoofer was hardly ever used? At first glance that may seem counterproductive when you're evaluating a sub, but is it really? Some of us - including yours truly - like to watch movies that aren't necessarily going to show up on anyone's 'best of the bass' list. I also enjoy flicks featuring solid characters with only the occasional soundtrack passage that requires your subwoofer to activate. Hurt Locker is one such movie, and it happens to be a particular favorite of mine because of the first rate acting. It afforded me the chance to see if the ULS-15 MK2 could stay out of the way and only make its presence known when it was time to supplement a story, as opposed to dominate one like is necessary during an action movie.

This is one of the few movies I use for subwoofer testing that I actually watch from start to finish, instead of playing just a few select clips to punish the unit in question. As a matter of fact there are long stretches where the subwoofer contributes little, so it's definitely not the prototypical movie in that regard. Lots of down time in the action meant the director was free to flesh out the characters, and it's perhaps this aspect which attracts me the most.

Hurt Locker is centered around Sargent William James (Jeremy Renner), an Explosive Ordnance Disposal hotshot who is stationed in Iraq. James is a virtuoso when it comes to defusing bombs, but the pressure associated to the job has taken a toll and he begins to lose his grip on reality. Instead of avoiding dangerous situations he starts intentionally courting them, and that puts him at odds with his team; Sargent JT Sanborn (Anthony Mackie) and Specialist Owen Eldridge (Brian Geraghty). Sanborn and Eldridge have but one job, and that's making sure Sargent James is protected and out of harm's way while he goes about the business of disarming bombs. This dynamic between them ensures all three men are tied at the hip, dependent on each other for their very survival. Since Sargent James is becoming unhinged that reliance presents a problem because Sanborn and Eldridge want very much to survive their tour of duty, but as things progress it becomes increasingly apparent Sargent James may not feel the same way.

During portions of the movie you do catch a glimpse of why James is such a sought after individual, in spite of the increasingly erratic behavior. His leadership and calm demeanor comes into the fore while the 3 of them are on a scouting mission in the desert. They stumble upon a handful of mercenaries who are hunting the enemy, but unfortunately they got a flat tire and don't have the correct lug nut wrench. While the trio of soldiers are helping them out enemy snipers open fire, killing several of the mercenaries in the process. M16's ring out in the still desert air and the ULS-15 MK2 provided a solid underpinning for the action, with each shot having weight to it.

An hours long sniper battle ensues, with Sanborn returning fire using a 50 caliber rifle while James calls out coordinates for him. Every time he pulled that trigger the subwoofer responded with a sharp blast of bass. Given that the lead up to this scene is nothing but dialog I had the volume raised, perhaps a bit more than I realized though because when the first 50 cal shot rang out it startled me. In that moment I realized I got the exact test I was hoping for; this subwoofer was inconspicuous until it was time to not be inconspicuous. When called upon it roared to life, and then fell silent when there was nothing for it to do. That's just as it should be.

Of course there's the quintessential menacing soundtrack playing at various points, and the ULS-15 MK2 didn't disappoint there either. An ominous tone was generated by this rumbling little beast, completing the experience and making the whole thing quite enjoyable. Between the soundtrack and the rifle blasts, it was impossible not to get drawn into the action. Again, just as it should be.

After all the testing had concluded I checked the amp to see how hot it had gotten, but the thing was barely more than warm. If a pounding like this wasn't enough to make it break a sweat, then it's hard for me to imagine how anyone could push the ULS-15 MK2 over the limit.

The order of the various sections in my reviews is not necessarily indicative of how I evaluated a product; just because a segment appears before or after another doesn't mean that's how I went about things during my evaluation. This section is a perfect example - I am always listening to music. Without tunes my world is upside down, so they're my constant companion, yet this part is at the end of every review. Why? I'm not sure really. Perhaps I'm saving the best for last, or maybe I want to hold off until the end to ensure I get it right, but whatever the reason I probably spend more time fine tuning my notes about music than I do anything else. Without question, I spend more time listening to music than everything else. By extension that also means I'm more critical of music reproduction, so I was quite chuffed to find out this subwoofer is a master in that regard.

Motor City Madhouse, Ted Nugent (CD)
Time for some old school rock from the Motor City Madman himself. Ted Nugent exploded onto the music scene with his 1975 self-titled album which spawned not only Motor City Madhouse but Stormtroopin', Just What The Doctor Ordered, Hey Baby, Snakeskin Cowboys and of course the 8 1/2 minute epic Stranglehold. At that time Ted was a virtual unknown in spite of the fact he had been the Amboy Dukes frontman for several years. No worries though because all that was about to change.

Uncle Ted, as he likes to be known, is an outspoken person who has rubbed many people the wrong way. Love him or hate him, there's no denying he owned the last half of the 70's from a musical standpoint. The band released an album every year for 6 straight years and churned out classics such as Dog Eat Dog, Free-For-All, Writing On The Wall, Hammerdown, Cat Scratch Fever, Death By Misadventure and Out Of Control. Touring relentlessly, this band built a diehard following. I've seen Ted Nugent perform live 5 times. The man puts on quite a show, that's for sure. The lineup for this album is my favorite of any he had, featuring Derek St. Holmes (guitar, vocals), Cliff Davies (drums) and ex-Amboy Dukes bandmate Rob Grange (bass).

Motor City Madhouse can best be described as an off-beat tune, somewhat bizarre even. With a fast-paced tempo it demands to be turned up, something I happily complied with. The ULS-15 MK2 supported this song brilliantly, creating a rolling wall of sound as Davies and Grange go crazy trying to keep up with the manic Ted Nugent. You can't see it but as I type this line I'm bobbing my head up and down in my easy chair while the ULS-15 MK2 handily goes about its business. Yes, I'm enjoying it that much. And no, I'm not taking any pictures.

Monkey Wrench, Foo Fighters (CD)
Dave Grohl was initially known as the drummer in Nirvana, and for some musicians that would have been enough to call it a career. After Kurt Cobain's suicide Nirvana disbanded and few would have faulted Dave had he chosen to leave the industry entirely. He didn't though, and about a year later he resurfaced with a group called the Foo Fighters. Actually 'group' might be a misnomer because on that first album Dave sang, played every instrument, did the recording and even produced it! For someone who can't play even a single instrument - that would be me - this man's talent is the stuff of jealousy. Once past my envy though I'm in awe of a person who can do so much.

The name Foo Fighters seems rather silly, even by the absurd standards of the music industry, but it actually has a true meaning. Rumor has it the term "foo fighters" was used by pilots during World War II to describe UFO's and alien crafts that supposedly were seen over active European theaters. I'm not certain what a "foo" is, or what they may have been fighting, but in the context of band names it is one of the more amusing (nonsensical?) out there. If nothing else, it is memorable.

Monkey Wrench is a typical Dave Grohl song, in that there's a frenetic pace to it. Oh yea, and Dave screams out his lyrics (a hallmark of virtually all Foo Fighter's songs). This one has quick changes, a driving rhythm section and is well recorded. The ULS-15 MK2 ate it up, treating me to a rousing version of the song.

Taylor Hawkins is the bands drummer, but this song was recorded before he came on board so it's actually Grohl you hear. No matter how fast he played the subwoofer effortlessly kept up, never lagging behind. Nate Mendel's energetic bass lick could have caused a problem for a subwoofer lacking in transient response - often referred to as "quick bass" - but that wasn't the case here. Similar to Grohl's drumming, no matter how complex the rhythm this thing shrugged it off. I added some volume when I listened to Monkey Wrench the third time, yet even with that the ULS-15 MK2 never lost composure. Quite the contrary, because it seemed to be having as much fun as I was.

Rooster, Alice in Chains (Streaming)
Rooster is from Alice in Chains second release, their wildly successful 1992 album Dirt. For any Alice fan this is a must-have disc; it spawned 5 songs that made it to the radio, most of which you are probably familiar with (Rooster, Would?, Them Bones, Angry Chair and Down in a Hole). Not too shabby, especially when you consider there were just 13 songs on the album. 23 years after the initial studio release, Rooster still sounds as fresh as it ever did.

Written by guitarist Jerry Cantrell as an ode to his father's time during the Vietnam war, this one is Jerry's interpretation of what he experienced during his tour of duty. The title is derived from his father's nickname, frequently attributed to his unkempt hair as a youth (the name stuck with him even as an adult). Like pretty much every Alice in Chains song, this one is dark and brooding. When the ULS-15 MK2 was confronted with Mike Starr's lazy opening bass lick it responded by sounding both muscular and precise, with dynamics aplenty. Changes in pitch or intensity were easily handled, making it a treat for my ears. One part of this song in particular caught my attention, and that was during the middle section where the tempo slows down. Starr's bass and Sean Kinney's kick drum are more prominent here and they blended perfectly, effortlessly creating the power that's needed to convey the overall tone of this song. So enthralling was ULS-15 MK2 that it was almost begging to be cranked up, so naturally I obliged. Even when pushed to the extreme I heard no untoward noises or sounds of distress. It seemed to be relishing this song and the elevated volume.

Taken as a whole, the HSU Research ULS-15 MK2 may be the best value going in the 15" subwoofer market. At less than $850 shipped it represents an amazing bargain, yet it's not just the low price that makes it stand out. This subwoofer was executed to near perfection by HSU; from its appearance to the obvious attention to detail - and of course the magnificent sound quality - they nailed every aspect. You realistically couldn't ask for more from a subwoofer that costs what this one does. With all the changes the company has recently made to their product line it seems HSU Research may have grown weary of being an also-ran in the ID (Internet Direct) market. It's evident they want to be on top of the heap now, and if my experience with the ULS-15 MK2 is any indication they have every right to be. Make sure HSU is on your short list the next time you go shopping for subwoofers. You can thank me later.

Please use the HSU Research ULS-15 MK2 Discussion Thread for questions and comments​

The driver picture is a stock photo from HSU's website. After removing the screws from the one in the review unit I was still unable to get the driver out as it was adhered with what appeared to be some type of bonding agent. Because this is not my subwoofer I was reluctant to do anything that might cause damage, so I didn't proceed further.

These measurements were taken using an Omnimic measurement system. The ULS-15 MK2 was positioned in the center of my listening room with the microphone 1 foot from the dustcap of the driver. The gain was at 3:00, 0° Phase, Q Control 0.5 and the Crossover defeated. Frequency response smoothing was 1/12 octave. Operating Mode - EQ1 or EQ2 - is noted accordingly.

Overall frequency response, EQ1

Spectrograph, EQ1

Overall frequency response, EQ2

Spectrograph, EQ2
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