In this review, we will be comparing ISW4 and IW Sub Reference, two Passive In-wall speakers from Bowers Wilkins and Definitive Technology. Let's have a brief look at the main features of Bowers Wilkins ISW4 and Definitive IW Sub Reference 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.Bowers Wilkins ISW4 and Definitive IW Sub Reference have a totally different setup: the Bowers Wilkins ISW4 features 2 x 8-inch drivers whereas the IW Sub Reference features 1 x 13-inch drivers.
Frequency Response
ISW4 has a frequency range of 25-222 Hz whereas IW Sub Reference has a frequency range of 14-200Hz. With a minimum frequency of 14Hz, the IW Sub Reference can go significantly deeper on the low side and provide stronger bass compared to the ISW4's min frequency of 25Hz.
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 In-wall class in our database.
Low Frequency
In-wall Speakers
Definitive IW Sub Reference
High Frequency
In-wall Speakers
Definitive IW Sub Reference
Input Type and Bi-Amping / Bi-Wiring
ISW4 features Spring post type posts and IW Sub Reference has a Spring post type posts. None of these speakers feature bi-amping/bi-wiring.
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 Bowers Wilkins ISW4's and Definitive IW Sub Reference's external dimensions. Bowers Wilkins ISW4 has external dimensions of 1406.5 x 346.1 x 85.7mm () whereas Definitive IW Sub Reference has external dimensions of 639.0 x 366.0 x 102.0mm (25.1250-inch x 14.3750-inch x 4.0000-inch).
Bowers Wilkins ISW4 is 19.9mm narrower and 16.3mm less deeper than Definitive IW Sub Reference but it is also 767.5mm taller.
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 Bowers Wilkins ISW4 weighs 9.62kg / 21.2lbs and the Definitive IW Sub Reference weighs 11.79kg / 25.9lbs. This makes the IW Sub Reference 23% heavier than the ISW4.
Here is a comparison of how ISW4 and IW Sub Reference's weights compare with the average, max and min weights in Passive In-wall class.
Weight
All In-wall Speakers
Definitive IW Sub Reference
 Nominal Impedance |
8 ohms
vs
4 ohms
|
Less selective with amplifiers |
 Number of Woofers |
2
vs
1
|
More woofers |
 High Frequency Response |
222 Hz
vs
200 Hz
|
Generates higher frequency |
 Base Surface Area |
296cm2
vs
373cm2
|
Takes less floor space |
| Woofer Size |
13 inches
vs
8 inches
|
Larger woofer |
| Low Frequency Response |
14 Hz
vs
25 Hz
|
Generates deeper bass |
 Passive Radiator |
1 x 13-inch
vs
None
|
Increases the bass performance |
 Height |
639mm
vs
1406mm
|
Easier to fit in smaller spaces |
 Price per pair* |
1499USD
vs
2400USD
|
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.
Definitive IW Sub Reference needs about 26% more floor area. Definitive IW Sub Reference stands 16mm further into the room. Bowers Wilkins ISW4 is 768mm taller.
| General |
Bowers Wilkins ISW4 |
Definitive Technology IW Sub Reference |
| Brand |
Bowers Wilkins |
Definitive Technology |
| Speaker Type |
Passive Subwoofer |
Passive Subwoofer |
| Impedance |
8 ohms |
4 ohms |
| Frequency Response |
25-222 Hz |
14-200Hz |
Drivers |
|
|
| Woofer Quantity |
2 |
1 |
| Woofer Size |
8" |
13" |
| Woofer Composition |
|
|
| Tweeter Size |
- |
- |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
Physical Specs |
|
|
| Height |
1406.5mm (55.4") |
639.0mm (25.2") |
| Width |
346.1mm (13.6") |
366.0mm (14.4") |
| Depth |
85.7mm (3.4") |
102.0mm (4") |
| Weight |
9.62kg (21.2lbs) |
11.79kg (25.9lbs) |
| Enclosure |
|
In-wall |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
n/a |
No |
Other |
|
|
| Parts Warranty |
5 Years |
5 Years |
| Labor Warranty |
5 Years |
5 Years |
Different price classes - Bowers Wilkins ISW4 costs roughly 1.6x what Definitive IW Sub Reference does. Before paying it, read the note below about two smaller subwoofers.
| Area | Better | Why |
|---|
| Bass depth | B | Definitive IW Sub Reference goes deeper - 14Hz against 25Hz. Under 20Hz is felt more than heard - the bottom of a pipe organ and the bottom of a film mix. |
| Driver area | B | Definitive IW Sub Reference moves more air: 13" against 2 x 8" is 1.32x the cone area, not the 1.15x the diameters suggest. More area means the same output with less excursion, and less distortion with it. |
| Cabinet size | depends | Definitive IW Sub Reference is about 43% 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 | Definitive IW Sub Reference costs less - $1,499 against $2,400, about 38% less. |
A Bowers Wilkins ISW4 B Definitive IW Sub Reference
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?
Definitive IW Sub Reference is the easier recommendation: it leads on most of the measured areas and costs less. Take Bowers Wilkins ISW4 if one of the "depends" rows describes your room. 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 $1,499 each, two Definitive IW Sub Reference cost about $2,998 against $2,400 for one of the other, which is worth a thought. If placement is the constraint - a corner, behind a sofa, under a desk - Definitive IW Sub Reference 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.