Product Review

SVS 25-31 PCi Powered Subwoofer

December, 2002

John E. Johnson, Jr.



12" Driver: Downward Firing - Ported
320 Watt Built-In Amplifier
Tuned to 25 Hz
MFR: 25 Hz 100 Hz 3 dB
Dimensions: 32 1/2" H x 16" D
Weight: 50 Pounds
MSRP: $549 Plus Shipping



I am not sure why I am writing this review. So many people are already purchasing the 25-31 PCi, maybe I am just wasting space. OK, let's assume there are a few of you out there who don't know how good a sub this is. That way, I can justify the effort. However, if you just want to hurry out and buy the sub, I can summarize here by saying that I have never seen a sub less than $1,000 - from any company other than SVS - that performs like this.

SVS is not a new company. It is not an old company. But, it is a company that has taken the consumer subwoofer market by storm. Yeah, yeah, they sell only on the Internet. So, what's so special about that? There have been lots of startups coming and going, mostly going, who are Internet-only marketers.

SVS is unusual in that (1) its products are very low in price for what you get, and (2) they are terrific quality.

Here is how they do it: (1) be obsessed with the technology (of subwoofers); (2) put the money into the product instead of into expensive offices and warehouses; and (3) put the product design money into the performance instead of into expensive enclosures and veneers.

I am obsessed with quality too, but I am not an engineer, so I can't design and build this stuff. I have to wait until I find a company that makes things to my standards of performance. SVS appears to be one of those companies. Their main offices are at their homes, like most entrepreneurs (including yours truly), and when they run tests, they have the staff over for a barbeque in their back yard, being careful not to spill the beer on the microphones and laptops. Hey, I can dig it. This is my kind of organization.

In the case of the 25-31 PCi, as with most of their subs, the product is basically a heavy cardboard tube, with the driver mounted at the bottom, facing downward, and a huge port at the top, with a perforated metal plate over the entire top end. The tube is covered with a cloth sock on the sides. As a result, most of the expense can go for the driver, in this case, a very heavy 12" driver, and a nice amplifier, in this case, a 320 watt BASH amp. Photos of the driver are shown below. It is very well built, with a large frame and magnet.

The amplifier is mounted on the side of the enclosure (shown below). It is full featured, with volume, phase, auto on/off, line-level in-outs, speaker-level in-outs, and detachable power cord. It also has a switch so that you can disable the 40 Hz - 120 Hz variable low-pass crossover, which is what I did for the bench tests.

The round column shape of the 25-31 is a problem for wives. Let's face it, this is not something that fits into an average decor. However, the shape is actually one of the best for speakers, because the non-parallel sides attenuate internal standing waves. So, there is more to this sub than just the fact that some standard tubing can be cut to 31" long, put in the driver plate and port plate, and amplifier to finish its construction and keep the cost down. There are engineering reasons too. Personally, I don't have an issue with the looks, but I am not a bachelor.

The only concern I have with the design at all is that the port is open at the top through the perforated metal plate, and you could spill something into the subwoofer. So, I would suggest putting it somewhere that a guest is not likely to place a wineglass on it, and do not put it under any shelves that have potted plants on them. Over-watering the plants could result in spillover right into the subwoofer.

The Sound

I tested the 25-31 in a home theater setting, using a McIntosh MVP851 DVD Player, Theta Casablanca II Processor, Cinepro 3k6 SE Gold Power Amplifier, Threshold ES-500 Electrostatic Speakers, Monitor Audio Studio 20 SE Speakers, Krix Esoterix I MkII Speakers, Nordost Cables, BetterCables, Sony 10HT Projector, and Stewart Grayhawk Screen.

My favorite movies for video are also my favorite for sound.

For example, "Star Wars I" has the Pod Race, and there are plenty of very deep engine sounds that will show what a good subwoofer can do. Not only that, but I run the bass through an Audio Control unit that generates sub-harmonics at 1/2 the frequency of the original. The SVS handled all those sounds beautifully. If there is much distortion, the sound will be boomy. Nope, nothing but the deep rumble of the engines here. And loud enough to wake up a parking meter too.

The attack scenes in "Pearl Harbor" are the best depiction of this tragedy that have ever been filmed. From the first torpedo explosion to the USS Arizona coming apart with ammunition storage being detonated, it is just one jaw dropping moment after another. Again, the 25-31, which looks a bit like a torpedo itself, sailed along with the special effects, never sounding overdriven. I just wish I could saddle the hurricane coming out of the SVS port to be part of the special effects somehow.

On the Bench

Here are the reasons the 25-31 does so well. Even at 20 Hz, which is a killer for many subwoofers, the SVS only produced 3.37% THD, at 100 dB, 8" from the port. There appeared to be about the same amount of even-ordered as odd-ordered harmonics. By the way, I found that up to about 35 Hz, the SVS moves most of its air from the port. At 40 Hz and above, it comes out of the base where the driver is. So, I placed the microphone accordingly.

To show you how this performance ranks in comparison to other products, here is Subwoofer "X", 20 Hz, 100 dB, 8". This subwoofer has an MSRP of more than $1,000 and a very powerful amplifier. As time goes on, we will have a large database of spectra from various speakers and subwoofers for you to look at and compare.

At 31.5 Hz and 100 dB output, again, the 25-31 has very low distortion. This is sooooo important to getting a natural sensation of what is in the film, rather than what is in the subwoofer enclosure.

It's even less at 40 Hz, and this frequency is still very much in the domain of subwoofers rather than main speakers.

At 50 Hz, it's still a piece of cake, although higher than at 40 Hz.

The frequency response shows a smooth roll-off from the peak at 75 Hz. Remember, this is a very conservative measurement (quasi-anechoic). The actual in-room response is always much better. Even my reference Velodyne 18" servo-feedback subs have a roll-off similar to this. What I look for is smoothness in the parabolic curve, and no bumps or dips. But, the really important thing is how much distortion the subwoofer produces, and the 25-31 has less distortion than some subs costing several times its price. Frankly, it is almost beyond belief what this thing does for $549.


SVS has set standards to beat with its product line, and the 25-31 is certainly a blockbuster for $549. If you or your spouse don't have issues with the round appearance, getting one of these is a no-brainer. It has powerful, deep output at low distortion, and would be a killer addition to any home theater, especially an entry-level system which tends to have subwoofers in this price range, but not even in the same league as to performance.


- John E. Johnson, Jr. -

Related to the article above, we recommend the following:

Primer - Speakers

Copyright 2002 Secrets of Home Theater & High Fidelity
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