Short answer: the Rythmik FV18, if you are buying new. The Monoprice Monolith 16 THX Ultra ranks higher than it (#19 vs #60 of 143 subwoofers, 4.4/5 vs 4.2/5) but is discontinued, so only consider it used; the Rythmik FV18 is still sold new at $2,670.
What the Monoprice Monolith 16 THX Ultra does well: 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.
Why pick the Rythmik FV18: An 18 inch ported subwoofer with deep, powerful bass for large rooms and flexible balanced and RCA inputs. The tradeoff: The 838.2H x 533.4W x 558.8D mm cabinet and 160.1 lbs (72.6 kg) mass make this a serious placement and moving commitment.
Buy the Rythmik FV18, since the Monoprice Monolith 16 THX Ultra is discontinued and only worth hunting down 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.
An 18 inch ported subwoofer with deep, powerful bass for large rooms and flexible balanced and RCA inputs.
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 | Rythmik FV18 | |
|---|---|---|
| Price | $2,300 Discontinued | $2,670 |
| Ranked | #19 of 143 in Large Home Subwoofers (Over 75 lbs) | #60 of 143 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | ported, front |
| Output SPL at 15 Hz | 107.3 dB | 109.5 dB |
| Output SPL at 20 Hz | 118.4 dB | 114.3 dB |
| Output SPL at 25 Hz | 123.3 dB | 117.6 dB |
| Output SPL at 31.5 Hz | 125.1 dB | 119.2 dB |
| Output SPL at 40 Hz | 126.3 dB | 120.4 dB |
| Output SPL at 50 Hz | 126.5 dB | 121.3 dB |
| Output SPL at 63 Hz | 126.6 dB | 121.7 dB |
| Output SPL at 80 Hz | 126.8 dB | 121.9 dB |
| Output SPL at 100 Hz | 127.2 dB | 122.4 dB |
| Output SPL at 125 Hz | 127.6 dB | 121.9 dB |
| CEA-2010-A Average (40-80Hz) | 126.5 dB | 121.3 dB |
| Dimensions | 25.6”H x 22”W x 28.1”D (650.2 x 558.8 x 713.7 mm) | 33”H x 21”W x 22”D (838.2 x 533.4 x 558.8 mm) |
| Weight | 171.5 lbs (77.8 kg) | 160.1 lbs (72.6 kg) |
| Warranty | 5 | 5/3 |
| Cabinet Color | black | black |
| Country | United States | United States |
| Measurement Source | Audioholics | Data-bass |
| Drivers | 16” (406mm) driver | 18” (457mm) driver |
| Inputs | XLR, RCA, XLR out | XLR (2), RCA (line/LFE) |
| 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 | - | 102.0 dB |
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