In this review, we will be comparing Gravis II 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 II 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 Sonus faber Gravis IIand KEF KUBE 8b have a single woofer setup however the Sonus faber Gravis II's woofer is 10-inch whereas the KEF KUBE 8b features a 8-inch woofer.
Frequency Response
Gravis II has a frequency range of 25-120 Hz whereas KUBE 8b has a frequency range of 34-140 Hz. With a minimum frequency of 25Hz, the Gravis II 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
The Sonus faber Gravis II has a Passive Radiator type cabinet. Passive Radiator type subwoofers sports a non-powered cone that moves in response to the main woofer to move air out in order to generate stronger bass in a smaller body compared to ported or sealed designs. On the other hand the KEF KUBE 8b have Acoustic Suspension type enclosure. 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 II's and KEF KUBE 8b's external dimensions. Sonus faber Gravis II has external dimensions of 407.0 x 358.0 x 435.0mm (16inch x 14-1/16inch x 17-1/8inch) 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 II is clearly the larger of the two speakers. Its body is 62mm wider, 113mm taller and 96mm 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 II needs about 55% more floor or shelf area. Sonus faber Gravis II is 96mm deeper, so it stands that much further out from the wall. Sonus faber Gravis II is 113mm 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 II is approximately 1557.3cm2 / 241.4inch2 and base area of the KEF KUBE 8b is approximately 1003.4cm2 / 155.5inch2. The Gravis II requires 55% 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 II weighs 21.50kg / 47.3lbs and the KEF KUBE 8b weighs 11.36kg / 25lbs. This makes the Gravis II 89% heavier than the KUBE 8b.
Here is a comparison of how Gravis II and KUBE 8b's weights compare with the average, max and min weights in Powered Subwoofer class.
Weight
All Subwoofer Speakers
What's in the Box of Sonus faber Gravis II?
Here are the items that are included inside the box of Gravis II:
- Powered subwoofer
- Grille
- 6-feet AC power cord
- 33-feet Speakon cable
- Owners Manual
- Environmental Information
What's in the Box of KEF KUBE 8b?
Here are the items that come with the KUBE 8b:
- Powered subwoofer
- 6.5-feet AC power cord
- Speaker-level input block
- User Manual
- Important Safety Information
- Warranty Information
 Woofer Size |
10 inches
vs
8 inches
|
Larger woofer |
| Low Frequency Response |
25 Hz
vs
34 Hz
|
Generates deeper bass |
 Passive Radiator |
2 x 10-inch
vs
None
|
Increases the bass performance |
 High Frequency Response |
140 Hz
vs
120 Hz
|
Generates higher frequency |
 Height |
294mm
vs
407mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
1003cm2
vs
1557cm2
|
Takes less floor space |
 Price per pair* |
600USD
vs
1499USD
|
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 II needs about 55% more floor area. Sonus faber Gravis II stands 96mm further into the room. Sonus faber Gravis II is 113mm taller.
| General |
Sonus faber Gravis II |
KEF KUBE 8b |
| Brand |
Sonus faber |
KEF |
| Speaker Type |
Powered Subwoofer |
Powered Subwoofer |
| Max Amplifier Output |
350 watts |
300 watts |
| Frequency Response |
25-120 Hz |
34-140 Hz |
Amplifier |
|
|
| Watts RMS (Continuous) |
350-watt RMS |
300-watt RMS |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
10" |
8" |
| Woofer Composition |
Treated Paper |
|
| Tweeter Size |
- |
- |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
n/a |
40-140 Hz |
| Firing Direction |
front |
front |
Physical Specs |
|
|
| Height |
407.0mm (16") |
294.0mm (11.6") |
| Width |
358.0mm (14.1") |
296.0mm (11.7") |
| Depth |
435.0mm (17.1") |
339.0mm (13.3") |
| Weight |
21.50kg (47.3lbs) |
11.36kg (25lbs) |
| Enclosure |
Passive Radiator |
Acoustic Suspension |
| Available Colors |
Piano Black,Matte White |
n/a |
| Grille |
Yes |
n/a |
| Moisture Resistancy |
No |
No |
Connections |
|
|
Other |
|
|
| Parts Warranty |
2 Yr/3 Yr registered |
2 Years |
| Labor Warranty |
2 Yr/3 Yr registered |
2 Years |
A passive radiator subwoofer against a sealed one. That is the most consequential line on this page: it decides how the bass rolls off, how it behaves in a small room, and how much output you get for the size of the box.
| Area | Better | Why |
|---|
| Bass depth | A | Sonus faber Gravis II goes deeper - 25Hz against 34Hz. That gap covers the lowest notes of a five-string bass and a concert bass drum. |
| Amplifier power | evenly matched | Much the same amplifier (350W vs 300W RMS) - under 1dB apart. |
| Driver area | A | Sonus faber Gravis II moves more air: 10" against 8" is 1.56x the cone area, not the 1.25x the diameters suggest. More area means the same output with less excursion, and less distortion with it. |
| Enclosure | depends | Sonus faber Gravis II is passive radiator - a passive radiator behaves like a port without the pipe noise, and suits a slim cabinet; KEF KUBE 8b is sealed - a sealed box rolls off gently and is usually the easier one to integrate in a small or awkward room. Neither is better in the abstract; ported tends to suit films and sealed tends to suit music, and both generalisations have exceptions. |
| Speaker-level inputs | A | Sonus faber Gravis II 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. |
| Driver placement | depends | Sonus faber Gravis II fires front/down and KEF KUBE 8b fires front. A down-firing driver is more forgiving of a grille-less look and of a hard floor; a front-firing one is the safer choice on a thick carpet or a suspended timber floor. |
| Cabinet size | depends | KEF KUBE 8b is about 53% 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 $1,499, about 60% less. |
A Sonus faber Gravis II 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 II measures better, KEF KUBE 8b costs about 60% less. In a normal room, placement will make a bigger difference than the gap between these two. Films or music? If this is mainly a home cinema, Sonus faber Gravis II will hit harder for the money; if it is mainly for music in a normal-sized room, KEF KUBE 8b is usually the easier one to make sound right. Check your amplifier first: if it has no subwoofer or preamp output, Sonus faber Gravis II is the only one of these two you can connect at all.
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.