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Reviewed by
Jeff Fritz

25-31PC-Plus Subwoofer

Features SnapShot!


Model: SVS 25-31PC-Plus

Price: $775 USD
Dimensions: 32.5"H (with integral base) x 16" diameter
Weight: 70 pounds

Warranty: Three years parts and labor; 45-day money-back guarantee

  • TC Sounds 12" aluminum-cone woofer
  • Strontium-ferrite magnet assembly (woofer)
  • Aluminum former with a 2" voice coil (woofer)
  • Dual-stacked mirrored-image spiders with sewn-in tinsel leads (woofer)
  • 1" Santoprene surround (woofer)
  • 525W BASH amplifier
  • Three 3" Tri-Power ports
  • 1.5" birch end caps
  • Adjustable crossover (40Hz to 120Hz)
  • Damped metal grille
  • Black fabric exterior

The state of the art in digital components has been pushed forward dramatically in the last few years. You can buy an excellent DVD player -- many with advanced capabilities such as progressive scan, DVD-Audio, and SACD -- for surprisingly few dollars. The case for excellent boom-for-the-buck subwoofers is equally compelling. The LFE (low-frequency effects) tracks on DVD movies require subwoofers that will play louder, lower, and with greater impact than ever before. This puts the demand for high-performance subwoofers at an all-time high. Scan the product lineup for most speaker manufacturers and you’ll see a selection of subwoofers just not available a few years ago. And they come in all sizes, shapes, and performance levels.

To take it a step further, there are companies that produce only subwoofers -- no itsy-bitsy midrange or tweeter drivers to be found around these companies’ warehouses. SVS -- the self-proclaimed "Bass Authority" -- is an Internet-direct company based in Ohio that stands at the forefront of this business model. They make subwoofers, period. Their offerings consist of a comprehensive lineup of big, bad, monster bass speakers. Their subwoofers start at a surprisingly affordable $599 and go up to about $3500. I decided to test the 25-31PC-Plus, which retails factory-direct from SVS for $775 USD.

Subwoofer design, the SVS way

SVS is an engineering-based subwoofer manufacturer. They reportedly research and test their products extensively, measuring frequency response, distortion levels, compression, and other variables that tell them how their subwoofers perform. The fruit of this research is the end product, of course, but perhaps an even more significant byproduct is the wealth of knowledge they’ve gained on how subwoofers actually work. SVS’s principle owners, Ron Stimpson and Tom Vodhanel, have substantive data that, according to them, proves there is a right way and a wrong way to design a high-performance subwoofer.

When you look at SVS subwoofers in either their cylindrical or conventional box-type configurations, you notice they’re big. According to SVS, if you want truly great bass, you need to get past the size. Vodhanel says there are some compelling reasons to make subwoofers big: "In the mid 1960s, Anthony Hoffman [the "H" in KLH, by the way] developed a mathematical equation that we now call Hoffman's Iron Law. This law states that the efficiency of a bass system is directly proportional to its enclosure volume." There are ways around the size, but the folks at SVS will say that the "ways around it" are inherently compromised.

"But Jeff, what about the little cubes that seem to play so low?" I hear you thinking. Ah, there are reasons they can do this, starting with equalization and power. Vodhanel goes on: "Within the circuitry of the amplifier in this example [of a small box], you would be forced to use ‘EQ boost’ to flatten the nominal response of the design." For example, if the subwoofer is down 12dB at 25Hz, you add 12dB of gain at that frequency, essentially flattening out the response curve. But at what cost? According to SVS, there are several: distortion caused by excessive heat build-up in the voice coils of the drivers; greatly reduced headroom in the driving amplifier; and, of course, the cost to overcome these obstacles. Even with the massively overbuilt drivers needed to take this abuse, and the prodigious power needed to produce the desired output, the laws of physics can only be pushed so far. SVS reports that some of the small cube-type subwoofers have distortion measurements approaching a whopping 40% to 50% when played at home-theater-approved levels!

Now you know why SVS builds ‘em big -- no crazy amounts of equalization or power -- but why do they build some of them round? Simply stated, it costs less. A round, tube-type enclosure is easier to manufacture than a box of equal size and performance. Subwoofer boxes need rigid enclosures, which mean thick walls and lots of cross-bracing. This increased cabinet complexity translates into lots of money spent in the wood shop. Cylinders don’t behave the same way boxes do, according to SVS; the round enclosures work against the tendency to flex. SVS is therefore able to get increased air volume and the performance of a big, rigid enclosure without the cost of building it. The lighter construction also means less shipping cost, which is not inconsiderable for a large subwoofer.

The SVS 25-31PC-Plus subwoofer

The SVS 25-31PC-Plus contains a TC Sounds-sourced aluminum-cone 12" driver that fires from the cylinder’s bottom face downward onto a base plate. The base plate is separated from the driver via three cylindrical legs. Instead of spikes, the sub sits on the floor via "compliant disks" -- small mat-like feet safe for floors of all types. The driver itself features a Santoprene surround, a strontium-ferrite magnet assembly, and a 2" voice coil. The woofer and the opposing three ports on the top end of the cylinder are mounted in inch-and-a-half-thick solid-birch end caps. A removable metal grille hides the ports on top, while the rest of the enclosure is wrapped in a black, velvet-like material. A "plate" amp rated at 525W is flush-mounted into the tube’s side. This amplifier is a digital-switching design based on a BASH circuit, and reportedly operates at a high efficiency level. Features on the amplifier module include adjustable gain, crossover, and phase, as well as a crossover enable/disable switch that lets your processor handle those functions. There is also a four-position subsonic filter that will help you customize the sub (more on that below).

The model numbers of the various SVS subwoofers indicate two important specifications: The first two digits refer to the practical low-frequency extension (for the 25-31PC-Plus that means useful output to 25Hz) while the second number is the enclosure’s height (31" in this case). The low-frequency extension is somewhat adjustable, however. "Tuning" options are available to end-users via what SVS refers to as "port blockers" -- foam inserts that fit into the subwoofer’s ports. With all three of the subwoofer’s "Tri-Power" ports open, the tuning is set to the stock 25Hz level. Closing one port with one of the supplied foam plugs lowers the frequency response by 5Hz to 20Hz, while blocking two ports takes the response down to an ultra-low 16Hz. The subsonic-filter function mentioned above is adjusted to work with the port blockers. There is no free lunch though; you’ll lose absolute output capability in the upper bass when you block the ports. But hey, SVS gives you the choice between absolute extension and output capability. This is a very nice design touch.

There was not much drama when it came to setting up the 25-31PC-Plus. I dialed in an 80Hz crossover level on the BASH amp and placed the cylinder in the front corner behind the right speaker and away I went. I did experiment with positioning throughout the review, but could not better my initial placement.

SVS bass

No self-respecting home-theater reviewer should be without a collection of bass-filled test material to push subwoofers to their limits. I’ve got a pretty good selection of woofer-rattlin’ DVDs and CDs that can jar the nails out of the walls. Starting with the DTS track on the Gladiator DVD, I listened to the impact of the fireballs hitting the trees behind the opposing army in the opening battle scene. The bass in this scene is hard-hitting and percussive, not the sustained rumble of indistinct bass. The SVS 25-31PC-Plus smacked me in the chest with authority, displaying excellent speed, weight, and slam. I was hearing the kind of bass that shifts furniture and makes the hair on the back of your neck stand up. SVS’s initial volley was jolting. Frankly, I wasn’t prepared to experience what I was hearing and feeling.

"OK Mr. SVS subwoofer, let’s see how you like this," I said to myself as I loaded The Lord of the Rings: The Fellowship of the Ring (Special Extended Edition) into my player. Again cueing up the DTS track, I played chapter 36, "The Bridge of Khazad-dm," and waited for the results. I was overwhelmed with low-end grunt when the Balrog pursued the movie’s protagonists, so much so that I feared for the surrounding walls. The crushing footsteps of the devilish beast sounded as if they were crushing my floor. Talk about wicked bass -- I was impressed, but I couldn’t help thinking that I was near the SVS’s limits. So, with a hesitant hand I inched the volume control up a couple more notches. By this time I had my Radio Shack SPL meter out to see just what kind of sound-pressure levels I was hearing/feeling at the listening position. I was also prepared to quickly ramp down the volume level in case the subwoofer driver started to cry uncle. The SVS responded to my challenge by producing even more bass, easily hitting 107dB cleanly. I was astounded.

Things were getting serious. I decided to throw the SVS a curve by playing a couple of bass-heavy CDs that require not just low bass, but tight, clear bass. The Crystal Method’s Vegas [Outpost recordings OPRD-30003] is better known as the "horsepower" CD around here because if your system doesn’t have some serious power under the hood, you’re just spinning your wheels. The SVS rocked like a muscle car on a Saturday night on "Cherry Twist." The bass was completely void of extraneous noises such as cabinet rattles and port chuffing. I could hear and feel what seemed to be effortless and clean low frequencies engulfing the room. The bass was not just filling the room, but controlling the room with iron-fisted authority.

A few words about the scale of what I heard through the SVS: There’s a point where a subwoofer doesn’t seem to be fighting against the internal volume of the room, but actually seems to move the room from its foundation up. This kind of bass quality, coupled with prodigious output capability, is rare in my experience. I’ve heard subwoofers that exceed the 25-31PC-Plus’s level of performance: Wilson Audio’s XS can pull the same trick and then some, controlling an entire house, but then again it’s $18,500 without a crossover! I certainly have not heard this kind of bass from a sub-$3000 subwoofer, ever -- and the SVS 25-31PC-Plus is $775!

Massive Attack’s Mezzanine [Virgin 7243 8 45599 2 2] is a low-frequency-challenged speaker’s worst nightmare, and I wanted to finish up this test with a ringer. So much of this disc’s content is subwoofer territory that you’d miss much of the music if your system cannot reproduce it properly. The SVS 25-31PC-Plus completely pressurized the room with the methodical, rhythmic bass sound of "Angel."

The SVS 25-31PC-Plus blended quite well with either the Polk Audio RTi150 or the Dynaudio C2 speakers I paired it with. The bass from the SVS was so clean, powerful, and agile that I can’t imagine a user having a problem blending it in a system, as long as the crossover point and room placement are both optimized.


I couldn’t help feeling I was bringing the lamb to slaughter when I asked a close friend to bring his Pinnacle Baby Boomer over to my house to compare it with the SVS 25-31PC-Plus. This small cube-style subwoofer sports two 8" drivers in a 10" cube. It’s priced at $799 and has a rated frequency response down to 25Hz (-3dB).

The Pinnacle actually surprised me right off the bat with bass output that belied its small size. It gave a firm foundation and fair extension to the music of Massive Attack -- much of which the Polk Audio speakers missed on their own. I could see someone whose space is limited really appreciating what this subwoofer does in a small room. The sound was not boomy, but not quite able to punch through the air with authority either.

Simply put, the SVS 25-31PC-Plus outperforms the small Pinnacle by a considerable margin in every category you care to name. It’s cleaner, plays deeper and louder, is tighter and faster, and just plain sounds better. I found this to be true with music or movies. What else is left to say?


The SVS 25-31PC-Plus is a groundbreaking subwoofer in the under-$1000 price category. In fact, I have not heard a better subwoofer at several multiples of its price. Rarely do I get so excited about a product that I call my buddies to tell them about a new find. This case was different: "You’ve got to hear this sub. It is blowing my mind," I told my bass-freak friends. So now you -- the bass-addicted readers of Home Theater & Sound -- know too.

Review System
Speakers - Dynaudio Confidence C2 (mains), Polk Audio RTi150 (mains), CSi40 (center-channel), RTi38 (surrounds)
Amplifiers - Krell FPB-700cx, Coda System 100, Adcom GFA-545 II
Preamplifier - Orpheus Labs Two
Sources - Technics DVD-A10 DVD player, Teac/Esoteric DV-50 universal audio/video player
Cables - Nordost
Monitor - Sony WEGA direct-view TV

Manufacturer contact information:

SV Subwoofers LLC (Business Office)
365 Stone Harbor Road
Holland Michigan, 49424
Phone: (703) 845-1472
Fax: (330) 793-8183

E-mail: sales-svs@svsubwoofers.com  
Website: www.svsubwoofers.com  


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