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 #71 (rated 4.2/5) for the Monoprice Monolith M-15 V2.
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.
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Specifications Side By Side
| Monoprice Monolith 16 THX Ultra | Monoprice Monolith M-15 V2 | |
|---|---|---|
| Price | $2,300 Discontinued | $1,500 Discontinued |
| Ranked | #19 of 143 in Large Home Subwoofers (Over 75 lbs) | #71 of 143 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | ported, front |
| Output SPL at 15 Hz | 107.3 dB | 106.3 dB |
| Output SPL at 20 Hz | 118.4 dB | 112.6 dB |
| Output SPL at 25 Hz | 123.3 dB | 116.6 dB |
| Output SPL at 31.5 Hz | 125.1 dB | 119.5 dB |
| Output SPL at 40 Hz | 126.3 dB | 120.9 dB |
| Output SPL at 50 Hz | 126.5 dB | 120.6 dB |
| Output SPL at 63 Hz | 126.6 dB | 120.0 dB |
| Output SPL at 80 Hz | 126.8 dB | 118.7 dB |
| Output SPL at 100 Hz | 127.2 dB | 120.1 dB |
| Output SPL at 125 Hz | 127.6 dB | 120.2 dB |
| CEA-2010-A Average (40-80Hz) | 126.5 dB | 120.0 dB |
| Dimensions | 25.6”H x 22”W x 28.1”D (650.2 x 558.8 x 713.7 mm) | 28.7”H x 17.7”W x 26.8”D (729.0 x 449.6 x 680.7 mm) |
| Weight | 171.5 lbs (77.8 kg) | 132.9 lbs (60.3 kg) |
| Warranty | 5 | 5 |
| Cabinet Color | black | black |
| Country | United States | United States |
| Measurement Source | Audioholics | Manufacturer |
| Drivers | 16” (406mm) driver | 15” (381mm) driver |
| Inputs | XLR, RCA, XLR out | XLR, RCA |
| XLR Input | Yes | Yes |
| RCA Input | Yes | Yes |
| TRS Input | No | No |
| Optical Input | No | No |
| Coaxial Input | No | No |
| USB Input | No | No |
| HDMI Input | No | No |
| AES Input | No | No |
| Aux Input | No | No |
| Output SPL at 12.5 Hz | - | 91.0 dB |
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