In this review, we will be comparing SB17 Ultra R Evolution and KUBE 8b, two Powered Subwoofer speakers from SVS and KEF. Being Powered subwoofers, they both have built-in amplifiers so you don't need an external power amp or an integrated amp to power them. Let's have a brief look at the main features of SVS SB17 Ultra R Evolution and KEF KUBE 8b first before getting into our more detailed comparison.
The sections below take each area in turn: driver and amplifier, frequency response, physical size and connectivity.
Drivers
The efficiency of a subwoofer is directly proportional to the total radiating are squared hence the woofer quantity and diameter.Both SVS SB17 Ultra R Evolutionand KEF KUBE 8b have a single woofer setup however the SVS SB17 Ultra R Evolution's woofer is 17-inch whereas the KEF KUBE 8b features a 8-inch woofer.
Frequency Response
SB17 Ultra R Evolution has a frequency range of 15-320 Hz whereas KUBE 8b has a frequency range of 34-140 Hz. With a minimum frequency of 15Hz, the SB17 Ultra R Evolution can go significantly deeper on the low side and provide stronger bass compared to the KUBE 8b's min frequency of 34Hz.
Below graphs depict how these two speakers compare with the max, min and average values of the Min and Max Frequencies of other speakers in the Subwoofer class in our database.
Low Frequency
Subwoofer Speakers
SVS SB17 Ultra R Evolution
High Frequency
Subwoofer Speakers
SVS SB17 Ultra R Evolution
Physical Specs
The size of a speaker can sometimes be an important decision factor due to space constraints or in some cases purely for esthetic reasons. In this section, we are going to compare SVS SB17 Ultra R Evolution's and KEF KUBE 8b's external dimensions. SVS SB17 Ultra R Evolution has external dimensions of 508.0 x 495.3 x 539.8mm () whereas KEF KUBE 8b has external dimensions of 294.0 x 296.0 x 339.0mm (11-9/16 x 11-5/8 x 13-5/16inch).
SVS SB17 Ultra R Evolution is clearly the larger of the two speakers. Its body is 199.3mm wider, 214mm taller and 200.8mm deeper than KEF KUBE 8b.
Base Surface Area Comparison
Base surface area of a loudspeaker may become a determining factor when the space in your room or desk is limited.
The base surface area of the SVS SB17 Ultra R Evolution is approximately 2673.6cm2 / 414.4inch2 and base area of the KEF KUBE 8b is approximately 1003.4cm2 / 155.5inch2. The SB17 Ultra R Evolution requires 166% more surface area than the KUBE 8b which gives it a small disadvantage on placement in tight spaces.
Weight Comparison The weight of a subwoofer may become an important factor if you need to move and reposition the unit often to find the optimal positioning, also known as 'Subwoofer Crawling'. The SVS SB17 Ultra R Evolution weighs 56.25kg / 123.8lbs and the KEF KUBE 8b weighs 11.36kg / 25lbs. This makes the SB17 Ultra R Evolution 395% heavier than the KUBE 8b.
Here is a comparison of how SB17 Ultra R Evolution and KUBE 8b's weights compare with the average, max and min weights in Powered Subwoofer class.
Weight
All Subwoofer Speakers
SVS SB17 Ultra R Evolution
 Woofer Size |
17 inches
vs
8 inches
|
Larger woofer |
| Low Frequency Response |
15 Hz
vs
34 Hz
|
Generates deeper bass |
 High Frequency Response |
320 Hz
vs
140 Hz
|
Generates higher frequency |
 Height |
294mm
vs
508mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
1003cm2
vs
2673cm2
|
Takes less floor space |
 Price per pair* |
600USD
vs
2700USD
|
costs less (*prices may change depending on the seller, location and time) |
Size, drawn to scale
Both subwoofers and both views share one scale, so everything here is directly comparable. Hover a box for its dimensions.
One scale for both, standing on the same floor and pushed back to the same wall, so the bigger one visibly takes more of the room.
SVS SB17 Ultra R Evolution needs about 166% more floor area. SVS SB17 Ultra R Evolution stands 201mm further into the room. SVS SB17 Ultra R Evolution is 214mm taller.
| General |
SVS SB17 Ultra R Evolution |
KEF KUBE 8b |
| Brand |
SVS |
KEF |
| Speaker Type |
Powered Subwoofer |
Powered Subwoofer |
| Frequency Response |
15-320 Hz |
34-140 Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
2800-watt RMS |
300-watt RMS |
| Watts Peak (Max) |
6000-watt RMS |
n/a |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
17" |
8" |
| Woofer Composition |
|
|
| Tweeter Size |
- |
- |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
n/a |
40-140 Hz |
| Firing Direction |
n/a |
front |
Physical Specs |
|
|
| Height |
508.0mm (20") |
294.0mm (11.6") |
| Width |
495.3mm (19.5") |
296.0mm (11.7") |
| Depth |
539.8mm (21.3") |
339.0mm (13.3") |
| Weight |
56.25kg (123.8lbs) |
11.36kg (25lbs) |
| Enclosure |
|
Acoustic Suspension |
| Moisture Resistancy |
No |
No |
Connections |
|
|
Other |
|
|
| Parts Warranty |
5 Years |
2 Years |
| Labor Warranty |
5 Years |
2 Years |
Two quite different sizes of subwoofer. Room volume decides this more than anything else on the page: a big driver in a small room is wasted, and a small one in a large room is worked to death.
| Area | Better | Why |
|---|
| Bass depth | A | SVS SB17 Ultra R Evolution goes deeper - 15Hz against 34Hz. Under 20Hz is felt more than heard - the bottom of a pipe organ and the bottom of a film mix. |
| Amplifier power | A | SVS SB17 Ultra R Evolution has the bigger amplifier - 2800W against 300W RMS, about 9.7dB more on tap. In a large room that is headroom before the DSP starts limiting. |
| Driver area | A | SVS SB17 Ultra R Evolution moves more air: 17" against 8" is 4.52x the cone area, not the 2.13x the diameters suggest. More area means the same output with less excursion, and less distortion with it. |
| Enclosure | evenly matched | Both are sealed designs, so they roll off in much the same way. |
| Cabinet size | depends | KEF KUBE 8b is about 78% smaller by volume. In a subwoofer that is a real trade rather than a preference: box volume is how you get output low down without a bigger amplifier. |
| Warranty | A | SVS SB17 Ultra R Evolution carries 5 years on parts against 2 years. A subwoofer amplifier works harder than anything else in the system, so this is not a throwaway line. |
| Price | B | KEF KUBE 8b costs less - $600 against $2,700, about 78% less. |
A SVS SB17 Ultra R Evolution B KEF KUBE 8b
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both subwoofers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
The usual trade-off: SVS SB17 Ultra R Evolution measures better, KEF KUBE 8b costs about 78% less. In a normal room, placement will make a bigger difference than the gap between these two. Two small subwoofers beat one big one in most rooms - a pair evens out the room modes in a way no single box can, whatever its specs. At $600 each, two KEF KUBE 8b cost about $1,200 against $2,700 for one of the other, which is worth a thought. If placement is the constraint - a corner, behind a sofa, under a desk - KEF KUBE 8b is the one that will actually go there, and a well-placed small subwoofer beats a badly-placed big one every time.
One thing outweighs everything above: where the subwoofer stands. Room modes can add or remove 10dB or more at a given seat, which is far larger than any difference on this page. Before spending more, try the sub in two or three positions - the crawl test, where you put it in the listening seat and crawl the room to find where the bass sounds best, costs nothing and usually beats an upgrade.