Short answer: the Monoprice Monolith 16 THX Ultra. It ranks #18 of 110 subwoofers by sound quality at $2300; the Harbottle Audio C18 L1 ranks #77 and costs $5331.56, which makes this an easy call rather than a real tradeoff.
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 Harbottle Audio C18 L1 offers: Published CEA-2010 specifications list 108.0 dB at 20 Hz and 118.5 dB through 40-80 Hz. The ported enclosure with 18” (457mm) driver has the headroom for demanding film bass in a large room. Watch for: The 670.1H x 578.1W x 460.0D mm cabinet and 39.0 kg mass make this a serious placement and moving commitment. Ported output does not solve room modes, so careful placement and calibration remain essential.
Buy the Monoprice Monolith 16 THX Ultra. It ranks higher for sound quality than the Harbottle Audio C18 L1 and costs less, so there is no real case for the other one.
Want more options? Browse the full Subwoofers rankings.
Specifications Side By Side
| Monoprice Monolith 16 THX Ultra | Harbottle Audio C18 L1 | |
|---|---|---|
| Price | $2,300 | $5,331.56 |
| Ranked | #18 of 110 in Large Home Subwoofers (Over 75 lbs) | #77 of 110 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | ported |
| Output SPL at 15 Hz | 107.3 dB | 102.0 dB |
| Output SPL at 20 Hz | 118.4 dB | 108.0 dB |
| Output SPL at 25 Hz | 123.3 dB | 112.0 dB |
| Output SPL at 31.5 Hz | 125.1 dB | 117.0 dB |
| Output SPL at 40 Hz | 126.3 dB | 119.0 dB |
| Output SPL at 50 Hz | 126.5 dB | 119.0 dB |
| Output SPL at 63 Hz | 126.6 dB | 118.0 dB |
| Output SPL at 80 Hz | 126.8 dB | 118.0 dB |
| Output SPL at 100 Hz | 127.2 dB | 117.5 dB |
| Output SPL at 125 Hz | 127.6 dB | 117.0 dB |
| CEA-2010-A Average (40-80Hz) | 126.5 dB | 118.5 dB |
| Dimensions | 25.6"H x 22"W x 28.1"D (650.2 x 558.8 x 713.7 mm) | 26.4"H x 22.8"W x 18.1"D (670.1 x 578.1 x 460.0 mm) |
| Weight | 171.5 lbs (77.8 kg) | 86 lbs (39.0 kg) |
| Warranty | 5 | - |
| Cabinet Color | black | black, white, red, blue |
| Country | United States | Canada |
| Measurement Source | Audioholics | Manufacturer |
| Drivers | 16" (406mm) driver | 18" (457mm) driver |
| Output SPL at 10 Hz | - | 93.0 dB |
| Output SPL at 12.5 Hz | - | 98.0 dB |
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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.
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Harbottle Audio C18 L1: $5,331.56 eBay
Pros: Published CEA-2010 specifications list 108.0 dB at 20 Hz and 118.5 dB through 40-80 Hz. The ported enclosure with 18” (457mm) driver has the headroom for demanding film bass in a large room.
Cons: The 670.1H x 578.1W x 460.0D mm cabinet and 39.0 kg mass make this a serious placement and moving commitment. Ported output does not solve room modes, so careful placement and calibration remain essential.
Full Harbottle Audio C18 L1 review and specifications →
| CEA-2010-A Average (40-80Hz) | 118.5 dB |
|---|---|
| Cabinet Color | black, white, red, blue |
| Country | Canada |
| Dimensions | 26.4"H x 22.8"W x 18.1"D (670.1 x 578.1 x 460.0 mm) |
| Drivers | 18" (457mm) driver |
| Enclosure | ported |
| Measurement Source | Manufacturer |
| Output SPL at 10 Hz | 93.0 dB |
| Output SPL at 12.5 Hz | 98.0 dB |
| Output SPL at 15 Hz | 102.0 dB |
| Output SPL at 20 Hz | 108.0 dB |
| Output SPL at 25 Hz | 112.0 dB |
| Output SPL at 31.5 Hz | 117.0 dB |
| Output SPL at 40 Hz | 119.0 dB |
| Output SPL at 50 Hz | 119.0 dB |
| Output SPL at 63 Hz | 118.0 dB |
| Output SPL at 80 Hz | 118.0 dB |
| Output SPL at 100 Hz | 117.5 dB |
| Output SPL at 125 Hz | 117.0 dB |
| Weight | 86 lbs (39.0 kg) |
- Links
- Reviews, Comparisons and Sound Samples
- These figures are manufacturer-specified rather than independently measured.
- Head-to-Head Comparisons