Sunfire Atmos XT Series Subwoofer Review

Introduction
Sunfire is no stranger to the home theater arena and has been testing the limits of compact, high-powered subwoofer performance for years now. The Atmos XT has been designed for excellent output and sound quality, but within what is arguably one of the most extreme size constraints. For some, no-compromise bass performance can be achieved with huge drivers, large enclosures, and very high powered amplifiers. For others, there are many factors that require performance compromises in the interest of aesthetics (or a peaceful marriage). Sunfire has targeted consumers facing these limitations. Like you probably did, I made appearance-based judgments of the sub before hearing it, and my expectations began low. However, I value fair and unbiased product reviews, so I intend to give you just that. Sunfire has packed some great technology into this heavy little cube and it may be just the thing you are looking for.


Design, Build Quality, and Aesthetics
Sunfire has chosen a dual opposed driver configuration for the Atmos, which helps to maximize output from the small enclosure and keeps things nicely balanced. The 6.5" diameter woofers are designed for long throw in order to deliver solid output at the lowest audible frequencies. The thickness of the woofer surrounds change as they get closer to the center of the driver to promote long travel and low distortion. A 1400 watt amp is crammed into this tiny little enclosure (which is already cramped by the beefy magnet on the back of the woofer). Sunfire's engineers have made use of a one-piece aluminum structure to contain the power-packed system. The ends that house the woofers are capped with decorative plastic trim to hide the fasteners. A set of four "anti-resonate" feet are fastened to the bottom of the aluminum cabinet to prevent the Atmos from walking due to vibration while operating at high levels.

UPDATE
Upon the completion of the review it was brought to my attention that the Atmos has one powered driver and one passive radiator, contrary to what is stated in the specs published on Sunfire's website (dual powered woofers). Although it does not effect my subjective evaluation of the subwoofer, I do not want my slightly misinformed explanation of the design and operation to mislead anyone. Be sure to check out the review discussion thread and post any questions you may have!
At first glance, the Atmos XT appears well designed and constructed. The Aluminum enclosure gives it a premium look. Everything fits together squarely and snugly. Despite its size, it is quite heavy. That is generally a good thing when it comes to subwoofer design. The amp is sized to fit just within the boundaries of the back panel of the sub, and sits nice and flush with the back surface. Controls and connections on the amp are well marked and laid out, considering the amount of space available. The knobs and connectors have the look and feel of good quality. The crossover frequency knob seemed finicky around the upper range/bypass setting. This could be due to a dirty pot or maybe just the nature of its behavior when turned to the bypass setting. It may very well be an isolated problem, and it did not affect performance unless I was physically moving it back and forth.

I would venture to guess that one of Sunfire's major goals with the Atmos was to make it blend well with existing decor and even completely disappear under some circumstances. In my opinion the physical design of the sub is very tasteful and attractive. It would certainly be easy to hide in all but the tiniest rooms. Even in plain site, it is very inconspicuous. The aluminum cabinet is unique and interesting to look at, while the exposed drivers seem to say "don't underestimate me". The sides are bowed as opposed to flat, which makes it look less, well, less boring. The matte black finish is pretty standard, but definitely a safe bet for a sub that needs to blend in with existing furniture or other A/V gear. It could pretty easily be hidden by a potted plant or even a large lamp but I wouldn't mind it being visible, even in a small space.


Setup and Operation
Here is where the size of the Atmos becomes a real advantage. Whether you do the "sub crawl" or move the unit to various locations in your room, this compact sub makes the process easy. After trying my typical spots with the assistance of REW, I decided to do my evaluation with the sub on the front wall, below my display. It still suffers a bit from a couple of room modes at the main listening position, but provides the best compromise of output and response between the front and back rows. The corner location was the clear winner in terms of room gain, but added a large peak which I do not currently have the means to correct. For reference, the graph section below contains a comparison of frequency response sweeps at three different positions within my room.

Connections are very simple and straightforward. The Atmos has left and right line level RCA inputs and RCA outputs with a [bypass-able] 85Hz high-pass filter. There is also a slave input/output section for use with multiple Atmos XT subs. The slave/master connection is nifty in that it applies the EQ, level, crossover, etc settings from the master unit to the slave unit, meaning the adjustments only have to be made once. Having an operational sub is as simple as plugging in the power cord, connecting an RCA cable from your receiver's sub output to the left or right input and setting the volume ('0' is a good place to start). From there, phase, crossover, and EQ adjustments can be made as needed/desired, all from the rear panel of the sub. For the duration of the review, I set the built-in crossover to "bypass" and used the receiver's crossover set to 80Hz. The controls are easy to use, especially if you are already accustomed to making these types of adjustments on typical consumer subs. My one complaint about the controls and inputs is that they are cramped, but I guess that is the price you pay for such a small form factor. With the sub in place and levels set, I have not found myself fiddling much with the controls anyway, so this is a very minor issue by all practical measures.

The Atmos comes with a built-in auto-EQ program and a microphone which can be placed at your listening position. This works similarly to the auto-EQ and room correction programs found in many modern A/V receivers. The manual provides instructions for starting the auto EQ program, and it takes less than a minute once you have everything hooked up and your mic is placed at the listening position. It outputs tones at four different frequencies and uses measurements from the microphone to make adjustments. I was intrigued by this option and gave it a try. It was pretty quick and simple to complete the process and it is a potentially great feature for those who do not own receivers with built-in correction. I will discuss my results in the next section.

By default, the Sunfire has an auto on/off feature like many other self-powered subs. Within moments of sensing a signal, it will start playing, following two subtle relay clicks. After what seems to be a short amount of time without a signal, the Atmos will enter standby mode. I have found the delay to be too short, especially when doing REW measurements, and find myself frequently having to "wake it up" before running a test sweep. Alternatively, the Atmos also has a 12v trigger input, which is a very handy feature I wish more subs had. As much as I like the feature, I have not tested it on this particular unit - mostly due to the fact that I've been too lazy to run the wire from my rack to the sub. Still, nice to see it there.


General Impressions and REW Results
The Atmos XT is certainly small, and does indeed produce some respectably loud bass. I appreciate the benefits of the small size and the history of Sunfire subwoofer design. What we are after here though is, how it really measures up to the competition. Sunfire has clearly targeted much larger subs, and suggests that the Atmos matches or even beats their performance. That is a bold claim, considering what is available today. To me, it seems unfair to compare this sub to something with, say, a 12" driver. For reference, a pair of 6.5" woofers have a combined surface area of only about 60% of a single 12" woofer. Now, I know there is more to sub design than woofer size (and that cones have different surface area than circles), but driver diameter is definitely a major factor. While the size comparison may seem unfair, when we consider the price we should expect it to perform as well as other subs in the $2000 range right? Well, yes, but I will talk value later. For now, let's talk strictly performance. The Atmos is rated for frequency response between 30 and 100 Hz. That is not particularly outstanding, but the sub does perform well throughout that range in a moderately sized room. Measurements (see below) confirm pretty even response in the 30-100Hz range, despite some peaks and dips courtesy of my room. When pushed to higher levels the Atmos can definitely add some rumble during movies, and fill out the lower octaves needed for good music reproduction. Push it harder though, and you will begin to reach its limits before achieving reference levels during bass-intensive movie soundtracks. It makes a valiant effort but unless you are in a closed, compact space it just cannot rattle your bones like a bigger sub will. Within its limits of clean performance, the Sunfire sub does a nice job of producing rich, full bass for music playback, and can definitely add a nice foundation to an action-packed movie soundtrack that bookshelf speakers and sound bars cannot provide on their own. I am not trying to bash this sub - it has a niche and can perform very nicely in the proper environment.

Having said that, I do want to single out one of the features here that has been somewhat of a disappointment. While the auto-EQ on the Atmos XT is, to me, a premium feature for a home theater subwoofer, it just does not seem to do much. The changes it has made are very subtle and not likely to be detected by the ears of most listeners. I tried it in multiple locations and was similarly unsatisfied each time. The graphs section has a plot of the frequency response before and after EQ, with the sub located at the front wall of my HT. Note that once the EQ has been set, it can be turned on or off via a switch on the back of the sub.

Ok, now for some real world data. The first plot shows the in-room response at the main listening position for three different sub locations. Based on these sweeps, I chose the front wall as the final location for the sub. The second plot shows the response at the front row (main listening position) and the back row, with the sub placed at the front wall. Ironically, the back row response is beautiful compared to the somewhat sloppy-looking response in the front row. Finally, the third graph compares the before and after EQ response in both rows. For reference, the auto EQ was performed with the mic placed at the main listening position (front row). You can see now that the EQ had very little effect on the measured in-room response. The final plot is the Atmos blended with my mains. Not too bad aside from a couple of dips which are unfortunate characteristics of my room.


Music Performance
Enya - The Longships (Watermark, ALAC/CD)
There are some very deep bass notes in this song and unlike some of the music manufactured specifically for deep bass, this is actually enjoyable to listen to. Of course, that is just my opinion. With a good sub, the deep drums accompanying this song can make your room rattle. A sloppy sub can make them hang on a bit long, and sound overly boomy, breaking up the otherwise smooth bass line of the song. The Atmos definitely reaches down into the range required to reproduce the drums, and adds a bit of feel to them beyond the capability of an average floorstanding speaker. Despite some respectable depth capability, the little Sunfire is not quite as tight as I would like, and adds a hint of boom while it recovers from each drum strike. At high levels, the sub overpowers itself and begins to exhibit some audible distortion and even attempts to relocate itself. At casual listening levels though, it does a nice job of adding a desirable amount of depth to the range of my system overall.

Ian Tracey - Widor Organ Symphony No. 6 (Bombarde! French Organ Classics, ALAC/CD)
I like organ music for subwoofer testing because of the deep bass capabilities of very large pipe organs. The effect of a massive pipe organ in a huge cathedral can be challenging to reproduce, and maybe an unfair feat to expect of such a small sub. Fair or not, you'd better believe I am going to give it a try. The deepest of bass notes (as low as 16-20Hz on an organ this size) could be heard, but not at a realistic level. Again, at casual to moderate listening levels, the Atmos does a nice job here of augmenting the low frequency output of even somewhat large floorstanding speakers, but when pushed to real world levels it begins to strain to keep up. I do not frequently listen to music at extremely high volume, so most of the time this sub would work nicely for me, but it does not give me confidence that it has the headroom needed to really deliver when called upon.

Deadmau5 - Some Chords (4x4=12, 320kbps streaming)
After listening to Enya and some pipe organ music, I needed something with a little more punch. Electronic/Dance/Club/whatever-you-want-to-call-it music is a fun way to get your subs moving, but I can only take so much of it. The repetitive nature of many of these songs can become tiresome and a poorly designed sub can compound the effect, bringing me quickly to my threshold of tolerance. The Sunfire gives me the kick I'm looking for here, making the room thump, so to speak. When I am in the mood for this style of listening, that punch and that thump are exactly what I want to hear and feel. Even when cranked, the Atmos does not get too boomy. It seems to like the relentless driving beat. This song does not dip quite as deep into the frequency range, allowing the sub's built-in amp to divert more clean power to the range in which it was designed to perform optimally.


Movie Performance
The Hitchhiker's Guide to the Galaxy (DVD)
There is some notably deep bass content in this movie that can challenge subs much larger than the Sunfire Atmos XT. Although I did not expect it to reveal every bit of it, I thought it would be worth hearing how well it could handle the soundtrack overall. Throughout the movie, the soundtrack includes the low hum of space ships, the occasional planet explosion, and all manner of sci-fi space travel sound effects. Just a few minutes into the movie, Earth is destroyed by a fleet of alien ships. The explosion is accompanied by a nice deep rumble from the Atmos, though it is not quite tactile. Shortly after Earth is blown up and just before the main characters are subject to some horrific alien poetry, a rather elaborate microphone support descends from the ceiling with a boom. Again, the effect can be heard, but it leaves me wishing I could feel it just a little bit more.

Olympus Has Fallen (Blu-Ray)
This is just a good old American action movie. Guns, explosions, fistfights, jets, tanks, well... you get the idea. It is the perfect opportunity for a bone-rattling soundtrack. Not far into the movie, the fighting begins, and it does not stop until the end. Kicks, punches, gunshots, and explosions are all accompanied by deep thumps. Planes crashing and buildings crumbling are made more dramatic by deep, hearty rumbles. We started the movie at a moderate level as the kids were still up. The Atmos did a nice job of supplementing the main and surround speakers without being overly boomy or obtrusive. Even without the volume cranked, there was a strong rumble that I could feel as the Washington Monument fell to the ground after being struck by the diving plane. After the little ones had passed out and been placed in their cribs, I gradually brought the volume up in small increments throughout the rest of the movie. The Sunfire sub kept up fairly well with the action. While the bass sounded full and balanced, it was still missing the impact I would have liked to have felt.

The Dark Knight Rises (Blu-Ray)
There seem to be mixed opinions about the use of bass on this soundtrack. Some love it, others feel it is a bit overdone. At times I tend to agree with the latter group, but overall it is an excellent movie and soundtrack in my opinion. A couple of moments stand out to me while watching it with the Sunfire sub. The first is the chase scene following Bane's attack on the stock market. Batman chases down one of the hackers who had fled with a hostage and eventually finds himself cornered in an alley by Gotham's police force. To the dismay of the acting commissioner, Batman flees the scene in "The Bat". The high-tech hovering machine blasts out of sight with a ground-shaking rumble, leaving Gotham's finest in a cloud of dust and trash. The sub does surprisingly well here at higher volumes. My HT's signature room rattles were activated and there was a tactile element to The Bat's takeoff. Another moment handled nicely by the Atmos is the descent of the office floor that lowers Mr. Fox and Miranda to the reactor below the river. When the platform reaches the bottom of its ramp, there is again a very deep rumble that can be felt. At higher (although not extreme) levels, the sub appears to reach its mechanical limits, producing some audible distortion and rattle (rattle from the sub, not the room this time). Again, this is probably another case of the Atmos doing its best to reproduce tones that are simply beyond its intended range of operation. Overall it did well with this movie, but appeared to be near its limit on several occasions well below reference listening levels.


Overall Value
Back to my earlier question - if it does not seem fair to compare the performance of such a small sub to much larger ones, is it fair to compare it to a sub of any size that costs the same? The MSRP for the Atmos is $2000. That is pretty high by most people's standards, and with so many internet-direct companies offering high performance subs at reasonable prices, you can get a lot of sub for $2000. For that matter, you can get a lot of sub for half as much. Does the little wonder from Sunfire measure up? In my opinion, no. So, where can we find value in the Atmos XT? Well, I look at it this way: say you have a huge budget for a home entertainment system, but you are extremely limited by space or WAF (wife acceptance factor). If you are forced to purchase compact components, you might as well find the best small components available, right? Of course! And this sub certainly beats the others I have heard in the below 8" driver size category. However, others in that category typically cost a fraction Sunfire's asking price for the Atmos, so that alone does not necessarily define it as a good value. To go a step farther, I cannot say that I am aware of many (or any) other subs that aim to offer such performance in such a small overall package. So, if the Atmos XT is basically the only product that meets this need, then it could be considered a good value at its sticker price, provided there is enough demand. Bottom line, if you have the cash, but you are not restricted by space, consider a larger sub for the best performance. If you just cannot go any bigger, but you are willing to make an investment, give this little Sunfire sub a chance. Take your time to set it up properly and get it nicely integrated with the rest of your speakers and you are likely to be happy with the results.


Conclusions and Recommendations
Sunfire markets this as a sub that will keep up with the big dogs, and I would say that is a bit of a stretch. By now, it should be pretty clear that I don't quite fit into the category of consumers that truly needs a sub like this, for a couple of reasons. First, the list of suitable subs for my HT is not limited much by physical size. Second, I do not have the budget required for a single Atmos XT. But as I try to do with all of my reviews, let me conclude by stating what I do like about it, and why it should not be disregarded simply because of its size. It is a well designed and well constructed sub with some good technology built in. There are obvious benefits to the small size. The high-power amp and dual opposed driver configuration certainly make the best of the small box. It does play nice and loud for its size. It has some great features such as the 12v trigger, slave/master connections, and auto-EQ (has potential, and hopefully performs better for others than myself). To me, the Atmos is ideal for people looking to add a sub to a soundbar in a small room, or maybe handling bass duties in an office, bedroom, or small den. A pair of them could work nicely in a medium-sized room where aesthetics still prohibit the use of a larger sub. It will not blow your socks off, but it could surprise you if you start with appropriate expectations. Although epic action movie soundtracks will present substantial challenges for the Atmos XT, it handles most types of music well. For casual listening, it can be a great companion to wall mounted or bookshelf speakers with limited bass response. The sound quality is respectable when used within its specified range of operation. I think it will beat just about any other sub that could fit within half of a cubic foot.


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