Short answer: the RBH Sound Unrivaled 21-SF/R, if you are buying new. The Monoprice Monolith 16 THX Ultra ranks higher than it (#19 vs #91 of 143 subwoofers, 4.4/5 vs 4.1/5) but is discontinued, so only consider it used; the RBH Sound Unrivaled 21-SF/R is still sold new at $11,995.
The Monoprice Monolith 16 THX Ultra is the better-sounding pick. A THX Ultra certified 16 inch ported subwoofer with huge output for far less money than most rivals, now worth finding used. Watch for: Heavy at 172 lbs (78 kg) and ported design can interact with room acoustics.
What the RBH Sound Unrivaled 21-SF/R does well: A colossal sealed subwoofer with a 21 inch carbon fiber driver and extraordinary deep bass output for the biggest home theaters. The catch: At about 151kg (333 lbs), moving or placing this cabinet is a multi-person job.
Buy the RBH Sound Unrivaled 21-SF/R if you want one new; the Monoprice Monolith 16 THX Ultra is discontinued, so only look for it used.
Want more options? Browse the full 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 colossal sealed subwoofer with a 21 inch carbon fiber driver and extraordinary deep bass output for the biggest home theaters.
Prices on this page were last checked October 31, 2026 at 7:11 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 | RBH Sound Unrivaled 21-SF/R | |
|---|---|---|
| Price | $2,300 Discontinued | $11,995 |
| Ranked | #19 of 143 in Large Home Subwoofers (Over 75 lbs) | #91 of 143 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | sealed |
| Output SPL at 15 Hz | 107.3 dB | - |
| Output SPL at 20 Hz | 118.4 dB | 112.3 dB |
| Output SPL at 25 Hz | 123.3 dB | 117.2 dB |
| Output SPL at 31.5 Hz | 125.1 dB | 120.1 dB |
| Output SPL at 40 Hz | 126.3 dB | 119.5 dB |
| Output SPL at 50 Hz | 126.5 dB | 118.7 dB |
| Output SPL at 63 Hz | 126.6 dB | 118.4 dB |
| Output SPL at 80 Hz | 126.8 dB | 118.7 dB |
| Output SPL at 100 Hz | 127.2 dB | 119.2 dB |
| Output SPL at 125 Hz | 127.6 dB | - |
| CEA-2010-A Average (40-80Hz) | 126.5 dB | 118.8 dB |
| Dimensions | 25.6”H x 22”W x 28.1”D (650.2 x 558.8 x 713.7 mm) | 27.3”H x 43”W x 21”D (692.2 x 1092.2 x 533.4 mm) |
| Weight | 171.5 lbs (77.8 kg) | 332.9 lbs (151.0 kg) |
| Warranty | 5 | 10/3 |
| Cabinet Color | black | - |
| Country | United States | United States |
| Measurement Source | Audioholics | Manufacturer |
| Drivers | 16” (406mm) driver | 21” carbon fiber 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 | - |
| Output SPL at 10 Hz | - | 91.3 dB |
| Output SPL at 12.5 Hz | - | 97.7 dB |
| Output SPL at 14 Hz | - | 100.8 dB |
| Output SPL at 16 Hz | - | 105.5 dB |
| Frequency Response | - | 12-80Hz, ±3dB |
| Power Handling | - | 4000W thermal power handling |
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