Short answer: the WW Speaker Cabinets X21 - B&C 21DS115-4. It ranks #3 of 143 subwoofers by sound quality (rated 4.6/5) at $3,995 and is still sold new; the Monoprice Monolith 16 THX Ultra ranks #19 (rated 4.4/5) and is discontinued, so it is only an option used.
The case for the Monoprice Monolith 16 THX Ultra: A THX Ultra certified 16 inch ported subwoofer with huge output for far less money than most rivals, now worth finding used. The tradeoff: Heavy at 172 lbs (78 kg) and ported design can interact with room acoustics.
The case for the WW Speaker Cabinets X21 - B&C 21DS115-4: A passive 21 inch ported subwoofer with enormous output, made for big home theater rooms. The tradeoff: Premium $3995 price, massive 114.6 lbs (52 kg) cabinet, and ported room gain dependency.
Buy the WW Speaker Cabinets X21 - B&C 21DS115-4. It is rated higher for sound quality, and the Monoprice Monolith 16 THX Ultra is discontinued, so it is only available used.
Looking for alternatives? See the complete Subwoofers rankings.
A THX Ultra certified 16 inch ported subwoofer with huge output for far less money than most rivals, now worth finding used.
A passive 21 inch ported subwoofer with enormous output, made for big home theater rooms.
Prices on this page were last checked October 29, 2026 at 4:42 PM UTC. Product prices and availability are accurate as of that date/time and are subject to change; the price and availability shown on Amazon at the time of purchase will apply to the purchase of this product.
As an eBay Partner, we may be compensated if you make a purchase.
Specifications Side By Side
| Monoprice Monolith 16 THX Ultra | WW Speaker Cabinets X21 - B&C 21DS115-4 | |
|---|---|---|
| Price | $2,300 Discontinued | $3,995 Passive |
| Ranked | #19 of 143 in Large Home Subwoofers (Over 75 lbs) | #3 of 143 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | ported, front |
| Output SPL at 15 Hz | 107.3 dB | 111.9 dB |
| Output SPL at 20 Hz | 118.4 dB | 121.9 dB |
| Output SPL at 25 Hz | 123.3 dB | 120.8 dB |
| Output SPL at 31.5 Hz | 125.1 dB | 122.5 dB |
| Output SPL at 40 Hz | 126.3 dB | 126.7 dB |
| Output SPL at 50 Hz | 126.5 dB | 129.2 dB |
| Output SPL at 63 Hz | 126.6 dB | 132.9 dB |
| Output SPL at 80 Hz | 126.8 dB | 136.3 dB |
| Output SPL at 100 Hz | 127.2 dB | 139.0 dB |
| Output SPL at 125 Hz | 127.6 dB | 140.1 dB |
| CEA-2010-A Average (40-80Hz) | 126.5 dB | 131.3 dB |
| Dimensions | 25.6”H x 22”W x 28.1”D (650.2 x 558.8 x 713.7 mm) | 24”H x 32”W x 32”D (609.6 x 812.8 x 812.8 mm) |
| Weight | 171.5 lbs (77.8 kg) | 115.1 lbs (52.2 kg) |
| Warranty | 5 | - |
| Cabinet Color | black | - |
| Country | United States | United States |
| Measurement Source | Audioholics | Data-bass |
| Drivers | 16” (406mm) driver | 21” (533mm) driver |
| Inputs | XLR, RCA, XLR out | - |
| XLR Input | Yes | - |
| RCA Input | Yes | - |
| TRS Input | No | - |
| Optical Input | No | - |
| Coaxial Input | No | - |
| USB Input | No | - |
| HDMI Input | No | - |
| AES Input | No | - |
| Aux Input | No | - |
| Passive | - | Yes |
| Output SPL at 12.5 Hz | - | 96.2 dB |
Related Speaker Comparisons
More top alternatives to WW Speaker Cabinets X21 - B&C 21DS115-4:
- Pro Audio Technology LFC-24sm vs WW Speaker Cabinets X21 - B&C 21DS115-4
- JTR Speakers Captivator S2 vs WW Speaker Cabinets X21 - B&C 21DS115-4
- JTR Speakers Growler (2015) vs WW Speaker Cabinets X21 - B&C 21DS115-4
- Danley Sound Labs DTS10 vs WW Speaker Cabinets X21 - B&C 21DS115-4
- Reaction Audio PV-15X vs WW Speaker Cabinets X21 - B&C 21DS115-4