Monoprice Monolith 16 THX Ultra vs Rythmik F18

Last updated: August 9, 2026

Short answer: the Monoprice Monolith 16 THX Ultra for the higher ranking, the Rythmik F18 for the lower price. The Monoprice Monolith 16 THX Ultra ranks #13 of 97 subwoofers at $2300. The Rythmik F18 ranks #60 at $1850, $450 cheaper.

On the Monoprice Monolith 16 THX Ultra side: 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. Set against that: Heavy at 78 kg and ported design can interact with room acoustics.

Buy the Monoprice Monolith 16 THX Ultra if the ranking matters more than the price. Buy the Rythmik F18 if the price matters more than the ranking.

Specifications Side By Side

Monoprice Monolith 16 THX Ultra Rythmik F18
Price$2,300$1,850
Ranked#13 of 97 in Large Powered Home Subwoofers (Over 75 lbs)#60 of 97 in Large Powered Home Subwoofers (Over 75 lbs)
Enclosureported, frontsealed
Output SPL at 15 Hz107.3 dB102.0 dB
Output SPL at 20 Hz118.4 dB106.2 dB
Output SPL at 25 Hz123.3 dB110.9 dB
Output SPL at 31.5 Hz125.1 dB114.3 dB
Output SPL at 40 Hz126.3 dB117.1 dB
Output SPL at 50 Hz126.5 dB119.1 dB
Output SPL at 63 Hz126.6 dB120.5 dB
Output SPL at 80 Hz126.8 dB121.2 dB
Output SPL at 100 Hz127.2 dB121.4 dB
Output SPL at 125 Hz127.6 dB121.4 dB
CEA-2010-A Average (40-80Hz)126.5 dB119.5 dB
Dimensions25.6"H x 22.0"W x 28.1"D (650.2 x 558.8 x 713.7 mm)20.5"H x 20.5"W x 21.0"D (520.7 x 520.7 x 533.4 mm)
Weight171.5 lbs / 77.8 kg115.1 lbs / 52.2 kg
Warranty55/3
Cabinet Colorblackblack
CountryUnited StatesUnited States
Measurement SourceAudioholicsData-bass
Drivers16" (406mm) driver18" (457mm) driver
Output SPL at 10 Hz-93.7 dB
Output SPL at 12.5 Hz-97.4 dB

The Two Speakers In Full

Monoprice Monolith 16 THX Ultra: $2,300

Monoprice Monolith 16 THX Ultra ranking card

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

CEA-2010-A Average (40-80Hz)126.5 dB
Cabinet Colorblack
CountryUnited States
Dimensions25.6"H x 22.0"W x 28.1"D (650.2 x 558.8 x 713.7 mm)
Drivers16" (406mm) driver
Enclosureported, front
Measurement SourceAudioholics
Output SPL at 15 Hz107.3 dB
Output SPL at 20 Hz118.4 dB
Output SPL at 25 Hz123.3 dB
Output SPL at 31.5 Hz125.1 dB
Output SPL at 40 Hz126.3 dB
Output SPL at 50 Hz126.5 dB
Output SPL at 63 Hz126.6 dB
Output SPL at 80 Hz126.8 dB
Output SPL at 100 Hz127.2 dB
Output SPL at 125 Hz127.6 dB
Warranty5
Weight171.5 lbs / 77.8 kg

Rythmik F18: $1,850

Rythmik F18 ranking card

CEA-2010-A Average (40-80Hz)119.5 dB
Cabinet Colorblack
CountryUnited States
Dimensions20.5"H x 20.5"W x 21.0"D (520.7 x 520.7 x 533.4 mm)
Drivers18" (457mm) driver
Enclosuresealed
Measurement SourceData-bass
Output SPL at 10 Hz93.7 dB
Output SPL at 12.5 Hz97.4 dB
Output SPL at 15 Hz102.0 dB
Output SPL at 20 Hz106.2 dB
Output SPL at 25 Hz110.9 dB
Output SPL at 31.5 Hz114.3 dB
Output SPL at 40 Hz117.1 dB
Output SPL at 50 Hz119.1 dB
Output SPL at 63 Hz120.5 dB
Output SPL at 80 Hz121.2 dB
Output SPL at 100 Hz121.4 dB
Output SPL at 125 Hz121.4 dB
Warranty5/3
Weight115.1 lbs / 52.2 kg

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Product prices and availability were last checked August 9, 2026 at 6:57 AM UTC 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.