Monoprice Monolith 16 THX Ultra vs RBH Sound Unrivaled 21-SF/R

Last updated: September 16, 2026

Short answer: the Monoprice Monolith 16 THX Ultra. It ranks #18 of 110 subwoofers by sound quality at $2300; the RBH Sound Unrivaled 21-SF/R ranks #75 and costs $11995, so there is not much of a tradeoff to weigh.

Monoprice Monolith 16 THX Ultra vs RBH Sound Unrivaled 21-SF/R

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 RBH Sound Unrivaled 21-SF/R offers: Manufacturer-supplied CEA-2010 data records 112.3 dB at 20 Hz and 118.8 dB through 40-80 Hz, with a passing result down to 10 Hz. The 21” carbon fiber driver and 4,000W thermal power handling gave this sub the first Extreme Bassaholic room rating on record. Watch for: At around 333 lbs, moving or placing this cabinet is a multi-person job, and the price puts it well outside typical home theater budgets.

Buy the Monoprice Monolith 16 THX Ultra. It ranks higher for sound quality than the RBH Sound Unrivaled 21-SF/R and costs less, so the other one has nothing left to offer.

Want more options? Browse the full Subwoofers rankings.

Specifications Side By Side

Monoprice Monolith 16 THX Ultra RBH Sound Unrivaled 21-SF/R
Price$2,300$11,995
Ranked#18 of 110 in Large Home Subwoofers (Over 75 lbs)#75 of 110 in Large Home Subwoofers (Over 75 lbs)
Enclosureported, frontsealed
Output SPL at 15 Hz107.3 dB-
Output SPL at 20 Hz118.4 dB112.3 dB
Output SPL at 25 Hz123.3 dB117.2 dB
Output SPL at 31.5 Hz125.1 dB120.1 dB
Output SPL at 40 Hz126.3 dB119.5 dB
Output SPL at 50 Hz126.5 dB118.7 dB
Output SPL at 63 Hz126.6 dB118.4 dB
Output SPL at 80 Hz126.8 dB118.7 dB
Output SPL at 100 Hz127.2 dB119.2 dB
Output SPL at 125 Hz127.6 dB-
CEA-2010-A Average (40-80Hz)126.5 dB118.8 dB
Dimensions25.6"H x 22"W x 28.1"D (650.2 x 558.8 x 713.7 mm)27.3"H x 43"W x 21"D (692.2 x 1092.2 x 533.4 mm)
Weight171.5 lbs (77.8 kg)332.9 lbs (151.0 kg)
Warranty5-
Cabinet Colorblack-
CountryUnited StatesUnited States
Measurement SourceAudioholicsManufacturer
Drivers16" (406mm) driver21" carbon fiber driver
Output SPL at 10 Hz-91.3 dB
Output SPL at 12.5 Hz-97.7 dB
Output SPL at 14 Hz-100.8 dB
Output SPL at 16 Hz-105.5 dB
Frequency Response-12-80Hz, ±3dB
Power Handling-4000W thermal power handling

How Monoprice Monolith 16 THX Ultra compares with other leading options:

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

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

Full Monoprice Monolith 16 THX Ultra review and specifications →

CEA-2010-A Average (40-80Hz)126.5 dB
Cabinet Colorblack
CountryUnited States
Dimensions25.6"H x 22"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)
Search eBay for Monoprice Monolith 16 THX Ultra →

RBH Sound Unrivaled 21-SF/R: $11,995 eBay

RBH Sound Unrivaled 21-SF/R ranking card

Pros: Manufacturer-supplied CEA-2010 data records 112.3 dB at 20 Hz and 118.8 dB through 40-80 Hz, with a passing result down to 10 Hz. The 21” carbon fiber driver and 4,000W thermal power handling gave this sub the first Extreme Bassaholic room rating on record.

Cons: At around 333 lbs, moving or placing this cabinet is a multi-person job, and the price puts it well outside typical home theater budgets.

Full RBH Sound Unrivaled 21-SF/R review and specifications →

CEA-2010-A Average (40-80Hz)118.8 dB
CountryUnited States
Dimensions27.3"H x 43"W x 21"D (692.2 x 1092.2 x 533.4 mm)
Drivers21" carbon fiber driver
Enclosuresealed
Frequency Response12-80Hz, ±3dB
Measurement SourceManufacturer
Output SPL at 10 Hz91.3 dB
Output SPL at 12.5 Hz97.7 dB
Output SPL at 14 Hz100.8 dB
Output SPL at 16 Hz105.5 dB
Output SPL at 20 Hz112.3 dB
Output SPL at 25 Hz117.2 dB
Output SPL at 31.5 Hz120.1 dB
Output SPL at 40 Hz119.5 dB
Output SPL at 50 Hz118.7 dB
Output SPL at 63 Hz118.4 dB
Output SPL at 80 Hz118.7 dB
Output SPL at 100 Hz119.2 dB
Power Handling4000W thermal power handling
Weight332.9 lbs (151.0 kg)
Search eBay for RBH Sound Unrivaled 21-SF/R →