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 #139 (rated 3.4/5) for the Genelec HTS4B. If you want one new, the JTR Speakers Captivator 215PRO ranks #7 at $3,500.
The Monoprice Monolith 16 THX Ultra is the better-sounding option. 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 Genelec HTS4B does well: A 12 inch passive radiator subwoofer with XLR and RCA inputs and a link output, now discontinued. Watch for: Deep-bass output is more limited than the strong 40-80 Hz result suggests, so it is not the right choice when the lowest movie effects are the priority.
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. For a new speaker, start with the JTR Speakers Captivator 215PRO instead.
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 12 inch passive radiator subwoofer with XLR and RCA inputs and a link output, now discontinued.
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 | Genelec HTS4B | |
|---|---|---|
| Price | $2,300 Discontinued | $2,995 Discontinued |
| Ranked | #19 of 143 in Large Home Subwoofers (Over 75 lbs) | #139 of 143 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | passive radiator |
| Output SPL at 15 Hz | 107.3 dB | 92.1 dB |
| Output SPL at 20 Hz | 118.4 dB | 97.9 dB |
| Output SPL at 25 Hz | 123.3 dB | 100.2 dB |
| Output SPL at 31.5 Hz | 125.1 dB | 103.3 dB |
| Output SPL at 40 Hz | 126.3 dB | 107.3 dB |
| Output SPL at 50 Hz | 126.5 dB | 110.1 dB |
| Output SPL at 63 Hz | 126.6 dB | 111.6 dB |
| Output SPL at 80 Hz | 126.8 dB | 112.3 dB |
| Output SPL at 100 Hz | 127.2 dB | - |
| Output SPL at 125 Hz | 127.6 dB | - |
| CEA-2010-A Average (40-80Hz) | 126.5 dB | 110.3 dB |
| Dimensions | 25.6”H x 22”W x 28.1”D (650.2 x 558.8 x 713.7 mm) | 20.4”H x 19”W x 18.3”D (517.4 x 482.6 x 465.1 mm) |
| Weight | 171.5 lbs (77.8 kg) | 81.6 lbs (37.0 kg) |
| Warranty | 5 | 2(+3) |
| Cabinet Color | black | - |
| Country | United States | Finland |
| Measurement Source | Audioholics | Ilkka Rissanen |
| Drivers | 16” (406mm) driver | 12” (305mm) driver |
| Inputs | XLR, RCA, XLR out | XLR (in plus link-out), RCA (line-level) |
| 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 |
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