Sunfire XTEQ 8 Subwoofer Review & Test
Full review and laboratory test of theSunfire XTEQ 8 Subwoofer by Australian Hi-Fi Magazine. Free download.
The following equipment review consists of a full subjective evaluation of the Sunfire XTEQ 8 Subwoofer written by Greg Borrowman, but omits the technical analysis.
If you would like to read the complete review, together with a complete set of independent laboratory tests and graphs conducted by Newport Test Labs and a test report written by Steve Holding, click on the graphic at the right, which is a downloadable pdf that is an exact replica of the original pages on which the review appeared in Australian Hi-Fi Magazine, January/February 2017 issue (Volume 48 Number 1).
Sunfire XTEQ 8 Subwoofer Review & Test
Many audiophiles, for reasons of domestic harmony, are obliged to listen to smaller loudspeakers than they’d like, which means that although they can usually enjoy superb midrange and treble, they miss out partially—or almost completely—on deep bass. Those same audiophiles, again for reasons of domestic harmony, are also unable to add a large subwoofer in order to deliver that bass.
If this sounds like you, fear not, for US manufacturer Sunfire has come to the rescue with its XTEQ 8 subwoofer, which is so tiny that you’ll be able to sneak it into the room under your jumper, install it by hiding it from sight under a chair or behind your equipment rack and then simultaneously rejoice in the sudden addition of deep bass to your music and the continuance of domestic harmony.
Sunfire is able to claim an amplifier power rating of 1,800 watts for the tiny XTEQ 8 subwoofer—far more power than would be possible if it used a conventional Class-AB amplifier—and quite possibly, even a Class-D amplifier—because it uses an unusual tracking down-converter amplifier developed by the famous US designer Bob Carver, who founded Sunfire.
The tracking down converter amplifier is a variant of the Class-H amplifier topology, and to understand how Class-H works, you need to understand that in amplifiers that use conventional power supplies, the designer uses a power supply with a voltage high enough to deliver the maximum power the amplifier is capable of delivering. So, for example, if the amplifier were to be rated at 100-watts per channel into 4Ω, the power supply would need to deliver 20 volts ( P=V2/R so 50 = 400/4). The problem is that when the amplifier is not operating at its maximum output, and instead is delivering, say, only 1-watt, which requires only 2 volts, the power supply will still be delivering 20 volts, so the remaining 18-volts is wasted (it’s dissipated as heat). This isn’t a problem with low-powered amplifiers, but as power output increases, the cost of building power supplies for them becomes prohibitively high, and it also becomes difficult and expensive to remove the increased heat that results from the increase in power (no matter whether you remove this heat using heat sinks, cooling fans or a combination of both).
In Class-H designs the voltage of the power supply is varied depending on the power output required at any given moment, so that if you’re playing at 1-watt, it would supply only 2-volts, since this is all that’s required. Then, when you turned the volume up to 4-watts, the power supply voltage increases to 4-volts. At an output of 50-watts, the power supply would deliver the full 20-volts. This means there’s no waste, very little heat (so no need for heatsinks and fans) and importantly that the power supply can be made relatively cheaply.
The difficulty in designing Class-H designs lies in the designer ensuring that the power supply always stays one step ahead of the output stage, otherwise it won’t be able to deliver the voltage required at the precise instant it’s required. Carver’s tracking down-converter was a innovative way of doing this inexpensively and with very few components… indeed it was sufficiently innovative that he was awarded a patent for it—US Patent #4,484,150. (Carver’s patent application cites more than thirty previous patents outlining previous similar approaches to the problem, so he didn’t ‘invent’ Class-H, but he did invent a unique and very practical implementation of it: one that’s been so successful that it’s still being used four decades later, often in preference to Class-D.)
But why would you want a 1,800-watt amplifier inside a subwoofer? The answer to that is partly physics and partly marketing. In order to extract good low-frequency extension, low distortion, and high volume levels from a subwoofer, you need a large enclosure. The problem is that very few consumers want large enclosures in their living spaces. So manufacturers build enclosures that are smaller than optimum, and whenever they do this, they have to compromise by making a choice between reduced low-frequency extension, increased distortion, or lower volume levels: in other words, ‘something’s gotta give!’
However, there is a ‘work-around’ to the getting bass out of a small cabinet, and it’s one that hinges around the fact that the one reason the volume drops off when a cone is mounted in a small enclosure is that the amplifier has to work harder to push that cone, which requires more power… lots more power. In the past, it was not practical to include a sufficiently high-powered amplifier in small subwoofers—they simply cost too much to build. But Carver’s tracking down-converter amplifier was the first one to break the rules: it could deliver enormous amounts of power very cost-effectively, and it was this that enabled Sunfire to build such small subwoofers… and this new Sunfire XTEQ 8 is certainly small… indeed at just 267×315×270mm (HWD) it’s the smallest model in the XTEQ range. (There are two larger models, the XTEQ 10 and XTEQ 12.)
As with all products Sunfire builds, the model numbers of the XTEQ 8 actually mean something. The ‘XT’ stands for eXtended Throw, because the roll-surrounds fitted to the drivers in these models have Sunfire’s so-called ‘Asymmetrical Cardioid Surround’ geometry, which the company says: ‘enables them to travel over a very long throw without distorting.’ The ‘EQ’ stands for Equalisation, except that in this case, the equalisation is automated. Each subwoofer comes with its own microphone and has a signal generator and measurement circuitry built in that can be used to measure the output of the subwoofer in your room, after which it can then automatically adjust the frequency response of the subwoofer for best performance in that room. It does this at four frequencies: 35Hz, 49Hz, 64Hz and 84Hz. (And if, for any reason, you don’t like the result of the automated circuitry, you can over-ride it, and instead set the equalisation ‘by ear’.)
There have been several improvements to Sunfire’s automatic equalisation circuitry over the years it’s been available, the most significant of which is to my mind that this latest iteration is by far the easiest and the fastest to use. However, another significant improvement was the switch from analogue to digital circuitry, which made the calibrations and equalisation more precise.
As for the final number in the model name—the ‘8’—that’s good ol’ imperial inches, showing that the XTEQ 8 has an 8-inch (203mm) diameter bass driver. And yes, that’s driver singular… there is only the one driver, and it’s on the left side of the subwoofer as you’re looking at it from the front. The circular thing that looks like a driver on the opposite side to the woofer (that is, on the right side of the subwoofer as you’re looking at it from the front) is actually a passive radiator—that is, although it has a cone and suspension, it does not have a voice coil or a magnet: its motion comes about entirely in response to air pressure variations inside the cabinet caused by the movement of the other side-firing bass driver: which is the reason some people call passive radiators ‘drone cones’. (They’re also known as auxiliary bass radiators, or ABRs). Whatever you decide to call them, Sunfire is at least honest enough to point out that it is a passive radiator: Some manufacturers don’t mention it at all, presumably hoping you’ll think you’re getting multiple drivers.
The rear panel of the Sunfire XTEQ 8 has both unbalanced (via RCA) and balanced (via XLR) inputs as well as two line-level outputs. The line-level outputs can be a simple pass-through (unaffected by any of the subwoofer’s settings) or high-passed through an 85Hz high-pass filter, using a switch located between the left and right output terminals. There’s also ‘Slave Input’ and ‘Slave Output’ terminals, which allow you to link multiple XTEQ 8 subwoofers together. By using the ‘Slave’ links to do this, all the settings you make on the ‘Master’ subwoofer will be replicated on the ‘Slave’ subwoofers, which greatly simplifies operation if you are using two or more subwoofers. Using dual subwoofers is a classic way to solve issues you may have with room modes, plus it’s also an easy, efficient, and cost-effective way of increasing bass levels in larger rooms.
A rotary control is used to adjust crossover frequency, and is adjustable from 30Hz to 100Hz, plus there’s a ‘Bypass’ setting at the extreme clockwise setting of the control. The phase control—also rotary—is continuously adjustable between 0° and 180°. The level control is rotary, with calibration markings only for ‘Min’, ‘0dB’ and ‘Max’. There are several fittings for use with the automatic equalisation circuitry, including an EQ LED, a ‘Start’ button, an EQ on/off switch and a microphone input. The other controls are a 12V d.c. trigger for remote power switching, a power LED and a mains power switch. Although the mains power switch has only two positions (off and on) the XTEQ 8 is fitted with a signal-sensing circuit that will turn the subwoofer off after a period of time during which it does not detect an audio signal. If you then apply an audio signal, it will switch on automatically. (I prefer three-position power switches—Off, On, Auto—but for no particular reason… it’s just an idiosyncratic personal preference.)
In Use and Performance
When it comes to getting the ultimate performance from a subwoofer it is essential that you position it in the optimum acoustic position in your room before you do anything else at all. Sunfire’s manual has excellent advice, but for perfect placement, follow the instructions here: www.tinyurl/subwooferplacement
Sunfire’s manual also contains excellent advice about how to best set the crossover, volume and phase controls, but you’ll get far better performance if you take a more technical approach, using the system outlined here: www.avhub.com.au/sub
Using the approach outlined in the link will require a small financial outlay of around $30 (for an app for your phone and a test CD) but I guarantee the results will be worth it.
You will also need to calibrate the XTEQ 8 using its own automated calibration routine, which is as simple as positioning the supplied microphone in the listening position, pressing the ‘EQ Start’ button and waiting around 15–18 seconds, after which the job is complete. For best performance, I would recommend running the automatic equalisation process BEFORE you do your external calibration.
As is my custom, the very first thing I played was Jean Guillou playing the great organ in the St Eustache church in Paris (Dorian DOR-90134). The playback of Bach’s Toccata and Fugue in D Minor (BWV 565) proved to me that despite its small size, the Sunfire XTEQ 8 is easily the equal of many larger subwoofers, and it was able to reproduce the very lowest notes in the audible spectrum. Sure, it wasn’t able to do this at quite the same volume level as I recall being able to achieve when I reviewed the XTEQ 12, but it was still able to play the lowest notes it was able to reproduce at surprisingly high volume levels… and, thanks to the use of a passive radiator rather than a bass reflex port, there were no unwanted ‘chuffing’ sounds, as there can be when driving a bass reflex subwoofer at high levels.
However, since almost all the bass you hear when listening to music actually falls between 30Hz and 100Hz, this is the region in which you want a subwoofer to deliver its best performance, and the Sunfire XTEQ 8 was happy to oblige in this respect, delivering a very uniform response across this frequency band, with a very pure tonality, so that the notes it reproduced had a very musical sound quality, with no unwanted harmonics or overtones. Distortion was also very low.
One problem with small subwoofers is their tendency to move along your floor when they’re delivering low bass at high levels, though frankly the XTEQ 8 is so heavy (it weighs 19.4kg) that the fact it could possible move at all is testament to the power of the driver it contains. Nonetheless, to prevent this happening the four feet underneath it have what Sunfire calls an ‘Anti-Walking Tread Design.’ I have absolutely no idea how this is supposed to work, but I can say that it must, because my review sample stayed exactly where I positioned it throughout the auditioning sessions, and did so when I tried it in other rooms with different floor surfaces. (Carpet, wood and tile, if you’re interested.)
Size (both cabinet volume and driver diameter) certainly helps when it comes to subwoofer performance but, as I explained at the start of this review, today’s technologies enable many workarounds that make it possible to extract big bass from small subwoofers.
However, once you are using this technology to level the playing field—as Sunfire is doing with its XTEQ series—the fact remains that the subwoofers with the larger cabinets and the bigger bass drivers will still deliver more—and deeper—bass than the smaller ones. The only thing you won’t be able to do with the big ones is hide them from sight, whereas you can do this very easily with the XTEQ 8.
So my conclusion must be that if you have a smaller room and are desirous of great bass—and domestic harmony—Sunfire’s tiny XTEQ 8 would be a great choice. # greg borrowman
Sunfire XTEQ 8 Subwoofer
Model: XTEQ 8
Category: Powered Subwoofer
Warranty: Two Years
Distributor: Qualifi Pty Ltd
Max volume limit
Deep bass extension
Limited colour choice
the LABORATORY REPORT which is in the pdf version of this review. (Click the RED box above).
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