In this review, we will be comparing Gravis VI and KUBE 8b, two Powered Subwoofer speakers from Sonus faber 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 Sonus faber Gravis VI 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.Sonus faber Gravis VI and KEF KUBE 8b have a totally different setup: the Sonus faber Gravis VI features 2 x 12.5-inch drivers whereas the KUBE 8b features 1 x 8-inch drivers.
Frequency Response
Gravis VI has a frequency range of 18-120 Hz whereas KUBE 8b has a frequency range of 34-140 Hz. With a minimum frequency of 18Hz, the Gravis VI 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
High Frequency
Subwoofer Speakers
Cabinet Type
Both Sonus faber Gravis VI and KEF KUBE 8b have Acoustic Suspension type cabinets. Acoustic Suspension aka Sealed type subwoofers have enclosures that are sealed hence no ports or holes exists on the cabinet. Sealed designs helps to provide more accurate and tight bass responses compared to ported designs.
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 Sonus faber Gravis VI's and KEF KUBE 8b's external dimensions. Sonus faber Gravis VI has external dimensions of 616.0 x 448.0 x 585.0mm (24-1/4 x 17-5/8 x 23-1/16inch) 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).
Sonus faber Gravis VI is clearly the larger of the two speakers. Its body is 152mm wider, 322mm taller and 246mm deeper than KEF KUBE 8b.
Size, drawn to scale
Both speakers 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 surface and pushed back to the same wall, so the deeper one visibly sticks out further.
Sonus faber Gravis VI needs about 161% more floor or shelf area. Sonus faber Gravis VI is 246mm deeper, so it stands that much further out from the wall. Sonus faber Gravis VI is 322mm taller.
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 Sonus faber Gravis VI is approximately 2620.8cm2 / 406.2inch2 and base area of the KEF KUBE 8b is approximately 1003.4cm2 / 155.5inch2. The Gravis VI requires 161% 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 Sonus faber Gravis VI weighs 52.00kg / 114.4lbs and the KEF KUBE 8b weighs 11.36kg / 25lbs. This makes the Gravis VI 358% heavier than the KUBE 8b.
Here is a comparison of how Gravis VI and KUBE 8b's weights compare with the average, max and min weights in Powered Subwoofer class.
Weight
All Subwoofer Speakers
 Woofer Size |
12.5 inches
vs
8 inches
|
Larger woofer |
| Number of Woofers |
2
vs
1
|
More woofers |
| Low Frequency Response |
18 Hz
vs
34 Hz
|
Generates deeper bass |
 High Frequency Response |
140 Hz
vs
120 Hz
|
Generates higher frequency |
 Height |
294mm
vs
616mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
1003cm2
vs
2620cm2
|
Takes less floor space |
 Price per pair* |
600USD
vs
6500USD
|
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.
Sonus faber Gravis VI needs about 161% more floor area. Sonus faber Gravis VI stands 246mm further into the room. Sonus faber Gravis VI is 322mm taller.
| General |
Sonus faber Gravis VI |
KEF KUBE 8b |
| Brand |
Sonus faber |
KEF |
| Speaker Type |
Powered Subwoofer |
Powered Subwoofer |
| Max Amplifier Output |
1700 watts |
300 watts |
| Frequency Response |
18-120 Hz |
34-140 Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
1700-watt RMS |
300-watt RMS |
| Watts Peak (Max) |
2400-watt RMS |
n/a |
Drivers |
|
|
| Woofer Quantity |
2 |
1 |
| Woofer Size |
12.5" |
8" |
| Woofer Composition |
Honeycomb sandwich |
|
| Tweeter Size |
- |
- |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
Continuously adjustable |
40-140 Hz |
| Firing Direction |
n/a |
front |
Physical Specs |
|
|
| Height |
616.0mm (24.3") |
294.0mm (11.6") |
| Width |
448.0mm (17.6") |
296.0mm (11.7") |
| Depth |
585.0mm (23") |
339.0mm (13.3") |
| Weight |
52.00kg (114.4lbs) |
11.36kg (25lbs) |
| Enclosure |
Acoustic Suspension |
Acoustic Suspension |
| Grille |
Yes |
n/a |
| Moisture Resistancy |
No |
No |
Connections |
|
|
Other |
|
|
| Parts Warranty |
|
2 Years |
| Labor Warranty |
|
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 | Sonus faber Gravis VI goes deeper - 18Hz 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 | Sonus faber Gravis VI has the bigger amplifier - 1700W against 300W RMS, about 7.5dB more on tap. In a large room that is headroom before the DSP starts limiting. |
| Driver area | A | Sonus faber Gravis VI moves more air: 2 x 12.5" against 8" is 4.88x the cone area, not the 2.21x 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. |
| Speaker-level inputs | A | Sonus faber Gravis VI takes a speaker-level connection as well as line level. That is what lets it work with an integrated amplifier or a vintage receiver that has no subwoofer output at all. |
| Cabinet size | depends | KEF KUBE 8b is about 82% 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. |
| Price | B | KEF KUBE 8b costs less - $600 against $6,500, about 91% less. |
A Sonus faber Gravis VI 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: Sonus faber Gravis VI measures better, KEF KUBE 8b costs about 91% less. In a normal room, placement will make a bigger difference than the gap between these two. Check your amplifier first: if it has no subwoofer or preamp output, Sonus faber Gravis VI is the only one of these two you can connect at all. 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 $6,500 for one of the other, which is worth a thought.
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.