Monoprice Monolith 16 THX Ultra vs JBL 4645C

Last updated: September 14, 2026

Short answer: the Monoprice Monolith 16 THX Ultra. It ranks #18 of 110 subwoofers by sound quality at $2300; the JBL 4645C ranks #24 and costs $4999, which makes this an easy call rather than a real tradeoff.

Monoprice Monolith 16 THX Ultra vs JBL 4645C

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 JBL 4645C offers: Independent CEA-2010 testing records 98.9 dB at 20 Hz and 127.3 dB through 40-80 Hz. The ported, front enclosure with 18” (457mm) driver is best suited to upper-bass support in a modest room. Watch for: Deep-bass output is limited relative to its midbass result, so it is not the right choice for the lowest movie effects. The 1009.6H x 673.1W x 450.8D mm cabinet and 62.6 kg mass still need deliberate placement and calibration.

Buy the Monoprice Monolith 16 THX Ultra. It ranks higher for sound quality than the JBL 4645C and costs less, so there is no real case for the other one.

Looking for alternatives? See the complete Subwoofers rankings.

Specifications Side By Side

Monoprice Monolith 16 THX Ultra JBL 4645C
Price$2,300$4999 Passive
Ranked#18 of 110 in Large Home Subwoofers (Over 75 lbs)#24 of 110 in Large Home Subwoofers (Over 75 lbs)
Enclosureported, frontported, front
Output SPL at 15 Hz107.3 dB-
Output SPL at 20 Hz118.4 dB98.9 dB
Output SPL at 25 Hz123.3 dB114.0 dB
Output SPL at 31.5 Hz125.1 dB118.7 dB
Output SPL at 40 Hz126.3 dB122.0 dB
Output SPL at 50 Hz126.5 dB123.7 dB
Output SPL at 63 Hz126.6 dB129.7 dB
Output SPL at 80 Hz126.8 dB133.9 dB
Output SPL at 100 Hz127.2 dB135.1 dB
Output SPL at 125 Hz127.6 dB135.8 dB
CEA-2010-A Average (40-80Hz)126.5 dB127.3 dB
Dimensions25.6"H x 22"W x 28.1"D (650.2 x 558.8 x 713.7 mm)39.7"H x 26.5"W x 17.7"D (1009.6 x 673.1 x 450.8 mm)
Weight171.5 lbs (77.8 kg)138 lbs (62.6 kg)
Warranty55/3/2
Cabinet Colorblackblack
CountryUnited StatesUnited States
Measurement SourceAudioholicsData-bass
Drivers16" (406mm) driver18" (457mm) driver
Passive-Yes

More worthwhile head-to-heads for Monoprice Monolith 16 THX Ultra:

Prices on this page were last checked September 14, 2026 at 1:47 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.

As an eBay Partner, we may be compensated if you make a purchase.

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 →

JBL 4645C: $4999 Passive eBay

JBL 4645C ranking card

Pros: Independent CEA-2010 testing records 98.9 dB at 20 Hz and 127.3 dB through 40-80 Hz. The ported, front enclosure with 18” (457mm) driver is best suited to upper-bass support in a modest room.

Cons: Deep-bass output is limited relative to its midbass result, so it is not the right choice for the lowest movie effects. The 1009.6H x 673.1W x 450.8D mm cabinet and 62.6 kg mass still need deliberate placement and calibration.

Full JBL 4645C review and specifications →

CEA-2010-A Average (40-80Hz)127.3 dB
Cabinet Colorblack
CountryUnited States
Dimensions39.7"H x 26.5"W x 17.7"D (1009.6 x 673.1 x 450.8 mm)
Drivers18" (457mm) driver
Enclosureported, front
Measurement SourceData-bass
Output SPL at 20 Hz98.9 dB
Output SPL at 25 Hz114.0 dB
Output SPL at 31.5 Hz118.7 dB
Output SPL at 40 Hz122.0 dB
Output SPL at 50 Hz123.7 dB
Output SPL at 63 Hz129.7 dB
Output SPL at 80 Hz133.9 dB
Output SPL at 100 Hz135.1 dB
Output SPL at 125 Hz135.8 dB
PassiveYes
Warranty5/3/2
Weight138 lbs (62.6 kg)
Search eBay for JBL 4645C →