Short answer: the Monoprice Monolith 16 THX Ultra on measured sound quality, the Monoprice THX 121456 on price. The Monoprice Monolith 16 THX Ultra ranks #18 of 110 subwoofers at $2300. The Monoprice THX 121456 ranks #109 at $899, $1401 cheaper.
What the Monoprice Monolith 16 THX Ultra offers: 16-inch ported driver and THX Ultra certification deliver 126.5dB CEA-2010-A average at a fraction of the price of the subwoofers ranked above it. Watch for: Heavy at 78 kg and ported design can interact with room acoustics.
What the Monoprice THX 121456 offers: Independent CEA-2010 testing records 94.6 dB at 20 Hz and 108.0 dB through 40-80 Hz. The subwoofer enclosure with 12” (305mm) driver delivers substantial upper-bass output for movie effects and music. 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. The 0.0H x 0.0W x 0.0D mm cabinet and 44.7 kg mass still require deliberate placement and calibration.
Buy the Monoprice Monolith 16 THX Ultra if sound quality matters more than the price. Buy the Monoprice THX 121456 if the price matters more than sound quality.
Skip the Monoprice THX 121456 if sound quality matters to you. It ranks near the bottom of the 110 subwoofers.
Want more options? Browse the full Subwoofers rankings.
Specifications Side By Side
| Monoprice Monolith 16 THX Ultra | Monoprice THX 121456 | |
|---|---|---|
| Price | $2,300 | $899 |
| Ranked | #18 of 110 in Large Home Subwoofers (Over 75 lbs) | #109 of 110 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | - |
| Output SPL at 15 Hz | 107.3 dB | 92.0 dB |
| Output SPL at 20 Hz | 118.4 dB | 94.6 dB |
| Output SPL at 25 Hz | 123.3 dB | 100.1 dB |
| Output SPL at 31.5 Hz | 125.1 dB | 103.2 dB |
| Output SPL at 40 Hz | 126.3 dB | 104.7 dB |
| Output SPL at 50 Hz | 126.5 dB | 107.3 dB |
| Output SPL at 63 Hz | 126.6 dB | 109.3 dB |
| Output SPL at 80 Hz | 126.8 dB | 110.5 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 | 108.0 dB |
| Dimensions | 25.6"H x 22"W x 28.1"D (650.2 x 558.8 x 713.7 mm) | 0"H x 0"W x 0"D (0.0 x 0.0 x 0.0 mm) |
| Weight | 171.5 lbs (77.8 kg) | 98.5 lbs (44.7 kg) |
| Warranty | 5 | - |
| Cabinet Color | black | - |
| Country | United States | United States |
| Measurement Source | Audioholics | Brent Butterworth |
| Drivers | 16" (406mm) driver | 12" (305mm) driver |
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Prices on this page were last checked September 16, 2026 at 12:41 AM 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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The Two Speakers In Full
Monoprice Monolith 16 THX Ultra: $2,300 eBay
Pros: 16-inch ported driver and THX Ultra certification deliver 126.5dB CEA-2010-A average at a fraction of the price of the subwoofers ranked above it.
Cons: Heavy at 78 kg and ported design can interact with room acoustics.
Notes: Product # 42031
Full Monoprice Monolith 16 THX Ultra review and specifications →
| CEA-2010-A Average (40-80Hz) | 126.5 dB |
|---|---|
| Cabinet Color | black |
| Country | United States |
| Dimensions | 25.6"H x 22"W x 28.1"D (650.2 x 558.8 x 713.7 mm) |
| Drivers | 16" (406mm) driver |
| Enclosure | ported, front |
| Measurement Source | Audioholics |
| Output SPL at 15 Hz | 107.3 dB |
| Output SPL at 20 Hz | 118.4 dB |
| Output SPL at 25 Hz | 123.3 dB |
| Output SPL at 31.5 Hz | 125.1 dB |
| Output SPL at 40 Hz | 126.3 dB |
| Output SPL at 50 Hz | 126.5 dB |
| Output SPL at 63 Hz | 126.6 dB |
| Output SPL at 80 Hz | 126.8 dB |
| Output SPL at 100 Hz | 127.2 dB |
| Output SPL at 125 Hz | 127.6 dB |
| Warranty | 5 |
| Weight | 171.5 lbs (77.8 kg) |
- Links
- Reviews, Comparisons and Sound Samples
- Independently measured by Audioholics; the published figures above come from this ASR subwoofer measurement thread.
- Head-to-Head Comparisons
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Monoprice THX 121456: $899 eBay
Pros: Independent CEA-2010 testing records 94.6 dB at 20 Hz and 108.0 dB through 40-80 Hz. The subwoofer enclosure with 12” (305mm) driver delivers substantial upper-bass output for movie effects and music.
Cons: 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. The 0.0H x 0.0W x 0.0D mm cabinet and 44.7 kg mass still require deliberate placement and calibration.
Notes: Product # 121456
Full Monoprice THX 121456 review and specifications →
| CEA-2010-A Average (40-80Hz) | 108.0 dB |
|---|---|
| Country | United States |
| Dimensions | 0"H x 0"W x 0"D (0.0 x 0.0 x 0.0 mm) |
| Drivers | 12" (305mm) driver |
| Measurement Source | Brent Butterworth |
| Output SPL at 15 Hz | 92.0 dB |
| Output SPL at 20 Hz | 94.6 dB |
| Output SPL at 25 Hz | 100.1 dB |
| Output SPL at 31.5 Hz | 103.2 dB |
| Output SPL at 40 Hz | 104.7 dB |
| Output SPL at 50 Hz | 107.3 dB |
| Output SPL at 63 Hz | 109.3 dB |
| Output SPL at 80 Hz | 110.5 dB |
| Weight | 98.5 lbs (44.7 kg) |
- Reviews, Comparisons and Sound Samples
- Independently measured by Brent Butterworth; the published figures above come from this ASR subwoofer measurement thread.
- Head-to-Head Comparisons