Product Review

SVS B4-Plus Subwoofer with Four 12" Drivers

September, 2003

John E. Johnson, Jr.



● Type: Four 12" Drivers Arranged in Dual Push-Pull Configuration
● MFR: 25 Hz - 125 Hz 3 dB; Adding Foam Plugs Extends Low Response to 16 Hz at Expense of SPL Output
● Nominal Impedance: 4 Ohms
● Power Handling: 2,500 Watts Continuous, 10,000 Watts Peak
● Size: 26" H x 32" W x 25" D
● Weight: 190 Pounds
● MSRP: $3,499 with Crown K1 Power Amplifier and BetterCables Interconnect ($2,499 w/o Power Amp)

SV Subwoofers


SV Subwoofers (SVS) is a purveyor of subwoofers only on the Internet, although they may be selling at dealers soon.

Their products are notorious for great sound, great build, and fine value.

For a couple of years, SVS's subs were cylindrical tubes covered by a sock, the driver mounted at the bottom, with the port at the top.

As their subs got more and more powerful, it was only a matter of time before they decided to build a statement piece that could blow the walls out. Because multiple drivers would be employed, it was necessary to move into a box design, rather than the tube.

The SVS B4-Plus is the result of that effort.

The Design

The B4-Plus is definitely a box, a very big box. It has four 12" long throw drivers, each with a 2" voice coil and large strontium ferrite magnet (photo shown below).

The drivers are configured as dual push-pull, with two drivers mounted facing outward on the left and right sides, and two drivers facing inward, mounted in a center chamber (bottom photo below). Four very large ports are mounted on one of the sides (photos shown below). The enclosures come in gloss maple veneer, with other colors as options. I thought it might not be very spouse acceptable, because of its size, but my wife commented on how beautiful it was, so maybe she is getting used to big speakers around our house.

A set of speaker binding posts are mounted underneath the left side of the rear enclosure panel (just to the left of the logo in the left-hand photo shown above). The opening to the center chamber is covered by a grille, shown in the right-hand photo above.

The Amplifier

The B4-Plus can be purchased with or without a power amplifier. Since you will need a big amp to drive this, and since SVS supplies power amplifiers at a very good price (about half MSRP), it is prudent to order the B4-Plus with a power amp.

In our case, we obtained the B4-Plus with a Crown K1 fully balanced stereo power amplifier, rated at 1,500 watts RMS into 4 Ohms, in bridged mode. The front of the K1 is shown below. It has an on/off toggle and dual volume controls. When in bridged mode, you just use the volume control on the left. There are several LEDs on the front, which light up when there are various overload issues. These amplifiers are used by rock groups in concerts, and they likely overdrive the amps, so that is why there are so many protection indicators.

The rear panel of the K1 has Balanced XLR as well as 1/4" phone jack inputs for each channel. There are slider switches to select the input sensitivity, bridged mode, and to have a single input go to both channels. For our review, we used bridged mode and 1.4 V input sensitivity. Bridging requires that you use the two red + binding posts shown in the photo, to drive the subwoofer. The - binding posts are not used in this case. Channel 1 input is used in bridged mode.

The Listening

From my listening experiences with the B4-Plus, it is obviously the most powerful subwoofer ever constructed for consumer use. It plays loud and deep. Movies such as "Pearl Harbor" just explode into the room. Not only explosions from bombs and torpedoes, but the low frequencies from machine guns have tremendous impact.

One of my favorite home theater gadgets is an Audio Control Phase Coupled Activator. It takes a low frequency and creates a sub-harmonic at half that frequency. So, if the sound track has some 40 Hz explosion sounds, the PCA adds in some 20 Hz. This drives some subwoofers crazy, since not all of them can handle material down around 20 Hz, but the B4-Plus did not flinch.

"Daylight" is another of my favorite movies to test a subwoofer, even though it is not a very good movie in itself. The scene where explosions occur in the tunnel can bring many subs to their knees. But, the B4-Plus, being the standup fellow it is, just blew through all of them. I am surprised someone has not tried to use the B4-Plus as a termite exterminator, because I think any that were in my walls took a long hike after that test.

I watched rental movies using the B4-Plus, along with other movies from my collection such as "Patriot Games", "Air Force I", and "Phantom Menace". All were enjoyable, with no boominess from the B4-Plus. At sane volumes, it just coasted along. Because the Crown K1 does not have a crossover built-in, I used a 50 Hz crossover setting in my Theta Casablanca. SVS can supply a Rane electronic crossover if you need one.

On the Bench

I tested the B4-Plus with no foam plugs, since this product is made for high SPL. With foam plugs inserted into the ports, the B4-Plus will play deeper (16 Hz), but not as loud. I took these measurements outdoors with the microphone at 1 meter from the side with the ports.

At 15 Hz and 100 dB SPL, THD was quite high. This is because the B4-Plus, without foam plugs, has extension to 20 Hz, but not lower.

At 20 Hz, THD was a lot more manageable at a little over 3%. I was able to get 110 dB at this frequency before the amplifier shut down for a few seconds. Keep in mind that because I tested this subwoofer outdoors, there is no "room gain". So, if the sub were in a room, you could likely expect another 10 dB maximum SPL. This means that you would not have to turn the volume up as much, so the distortion would be even lower than shown here.

At 25 Hz, THD is coming down. I got a maximum of 115 dB here, before the amp shut down.

At 31.5 Hz, THD was less than 2%. I got 121 dB at this frequency at maximum volume control setting, but the amp did not shut down. The B4-Plus obviously could take more power, but the K1 "only" delivers 1,500 watts. The K2 is rated at 2,500 watts if any of you dare to use it. The B4-Plus is rated at 2,500 watts continuous, so it could handle the K2. SVS has even used a Crown 5,000 watt amp with the B4-Plus, and found that, finally, the could determine the sub's limits.

40 Hz at 100 dB produced only 1.2% THD. Maximum output was 122 dB, and the amp did not shut off.

At 50 Hz, THD was less than 2% at 100 dB output. I got 122 dB at this frequency with the volume control turned all the way up. The B4-Plus wanted more.

Quasi-anechoic frequency response showed a maximum at about 60 Hz, with steady roll-off down to 20 Hz, using a 60 ms MLS window. The impulse response, shown at the bottom, has three initial peaks, representing the delay between the driver facing the microphone, the one on the front, and the one on the other side of the enclosure. The large long peak at 16 ms is probably cabinet resonance. The 16 ms corresponds with 60 Hz, and the frequency response shows the peak at that frequency. The resonance could probably be tamed by placing a rubber pad on the top of the enclosure and then sitting the power amplifier on top of the pad.


SVS has done it again. For anyone who wants to have the Darth Vader of subwoofers, the B4-Plus is it. With almost unlimited power and low distortion, the B4-Plus is definitely one of the Masters of the Universe.


- John E. Johnson, Jr. -

Related to the article above, we recommend the following:

Primer - Speakers



Copyright 2003 Secrets of Home Theater & High Fidelity

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