Short answer: both are discontinued, so this only matters if you are buying used. Used, the Monoprice Monolith 16 THX Ultra is the better pick: it ranks #19 of 143 subwoofers by sound quality (rated 4.4/5), against #45 (rated 4.2/5) for the Paradigm Defiance X15.
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 catch: Heavy at 172 lbs (78 kg) and ported design can interact with room acoustics.
What the Paradigm Defiance X15 does well: A 15 inch ported subwoofer with strong, deep bass for movies in a large room, a solid value pick used. The catch: The 625.3H x 588.8W x 625.3D mm cabinet and 91.9 lbs (41.7 kg) mass make this a serious placement and moving commitment.
Buy the Monoprice Monolith 16 THX Ultra only if you find one used in good condition; both are discontinued, and it is the better rated of the two.
Still deciding? The full Subwoofers rankings cover every ranked option.
A THX Ultra certified 16 inch ported subwoofer with huge output for far less money than most rivals, now worth finding used.
A 15 inch ported subwoofer with strong, deep bass for movies in a large room, a solid value pick used.
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.
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Specifications Side By Side
| Monoprice Monolith 16 THX Ultra | Paradigm Defiance X15 | |
|---|---|---|
| Price | $2,300 Discontinued | $1,499 Discontinued |
| Ranked | #19 of 143 in Large Home Subwoofers (Over 75 lbs) | #45 of 143 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | ported, bottom |
| Output SPL at 15 Hz | 107.3 dB | 102.8 dB |
| Output SPL at 20 Hz | 118.4 dB | 109.2 dB |
| Output SPL at 25 Hz | 123.3 dB | 112.2 dB |
| Output SPL at 31.5 Hz | 125.1 dB | 116.2 dB |
| Output SPL at 40 Hz | 126.3 dB | 121.3 dB |
| Output SPL at 50 Hz | 126.5 dB | 123.4 dB |
| Output SPL at 63 Hz | 126.6 dB | 123.8 dB |
| Output SPL at 80 Hz | 126.8 dB | 123.1 dB |
| Output SPL at 100 Hz | 127.2 dB | 121.9 dB |
| Output SPL at 125 Hz | 127.6 dB | 121.2 dB |
| CEA-2010-A Average (40-80Hz) | 126.5 dB | 122.9 dB |
| Dimensions | 25.6”H x 22”W x 28.1”D (650.2 x 558.8 x 713.7 mm) | 24.6”H x 23.2”W x 24.6”D (625.3 x 588.8 x 625.3 mm) |
| Weight | 171.5 lbs (77.8 kg) | 91.9 lbs (41.7 kg) |
| Warranty | 5 | 3 |
| Cabinet Color | black | black |
| Country | United States | Canada |
| Measurement Source | Audioholics | Audioholics |
| Drivers | 16” (406mm) driver | 15” (381mm) 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 | - |
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