Short answer: the JTR Speakers Captivator 4000ULF. It ranks #6 of 139 subwoofers by sound quality (rated 4.5/5) at $5,699 and is still sold new; the Monoprice Monolith 16 THX Ultra ranks #18 (rated 4.4/5) and is discontinued, so it is only an option used.
Buy the JTR Speakers Captivator 4000ULF. It is rated higher for sound quality and still sold new, while the Monoprice Monolith 16 THX Ultra is discontinued.
Looking for alternatives? See the complete Subwoofers rankings.
Specifications Side By Side
| JTR Speakers Captivator 4000ULF | Monoprice Monolith 16 THX Ultra | |
|---|---|---|
| Price | $5,699 each | $2,300 Discontinued |
| Ranked | #6 of 139 in Large Home Subwoofers (Over 75 lbs) | #18 of 139 in Large Home Subwoofers (Over 75 lbs) |
| Enclosure | ported, front | ported, front |
| Output SPL at 10 Hz | 111.0 dB | - |
| Output SPL at 12.5 Hz | 115.3 dB | - |
| Output SPL at 15 Hz | 119.3 dB | 107.3 dB |
| Output SPL at 20 Hz | 122.3 dB | 118.4 dB |
| Output SPL at 25 Hz | 126.1 dB | 123.3 dB |
| Output SPL at 31.5 Hz | 129.3 dB | 125.1 dB |
| Output SPL at 40 Hz | 130.7 dB | 126.3 dB |
| Output SPL at 50 Hz | 131.2 dB | 126.5 dB |
| Output SPL at 63 Hz | 130.9 dB | 126.6 dB |
| Output SPL at 80 Hz | 130.6 dB | 126.8 dB |
| Output SPL at 100 Hz | 130.5 dB | 127.2 dB |
| Output SPL at 125 Hz | 129.5 dB | 127.6 dB |
| CEA-2010-A Average (40-80Hz) | 130.8 dB | 126.5 dB |
| Dimensions | 41”H x 20.5”W x 39.5”D (1041.4 x 520.7 x 1003.3 mm) | 25.6”H x 22”W x 28.1”D (650.2 x 558.8 x 713.7 mm) |
| Weight | 265 lbs (120.2 kg) | 171.5 lbs (77.8 kg) |
| Warranty | 5/3 | 5 |
| Cabinet Color | black, custom | black |
| Country | United States | United States |
| Measurement Source | Data-bass | Audioholics |
| Drivers | 2x 18” (457mm) driver | 16” (406mm) driver |
| Inputs | XLR, RCA | XLR, RCA, XLR out |
| XLR Input | Yes | Yes |
| RCA Input | Yes | Yes |
| TRS Input | No | No |
| Optical Input | No | No |
| Coaxial Input | No | No |
| USB Input | No | No |
| HDMI Input | No | No |
| AES Input | No | No |
| Aux Input | No | No |
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Prices on this page were last checked October 7, 2026 at 9:25 PM 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
JTR Speakers Captivator 4000ULF: $5,699 each JTR Speakers eBay
Pros: Independent CEA-2010 testing records 122.3 dB at 20 Hz and 130.8 dB through 40-80 Hz. The ported, front enclosure with 2x 18” (457mm) driver has the headroom for demanding film bass in a large room.
Cons: The 1041.4H x 520.7W x 1003.3D mm cabinet and 120.2 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 JTR Speakers Captivator 4000ULF review and specifications →
| AES Input | No |
|---|---|
| Aux Input | No |
| CEA-2010-A Average (40-80Hz) | 130.8 dB |
| Cabinet Color | black, custom |
| Coaxial Input | No |
| Country | United States |
| Dimensions | 41”H x 20.5”W x 39.5”D (1041.4 x 520.7 x 1003.3 mm) |
| Drivers | 2x 18” (457mm) driver |
| Enclosure | ported, front |
| HDMI Input | No |
| Inputs | XLR, RCA |
| Measurement Source | Data-bass |
| Optical Input | No |
| Output SPL at 10 Hz | 111.0 dB |
| Output SPL at 12.5 Hz | 115.3 dB |
| Output SPL at 15 Hz | 119.3 dB |
| Output SPL at 20 Hz | 122.3 dB |
| Output SPL at 25 Hz | 126.1 dB |
| Output SPL at 31.5 Hz | 129.3 dB |
| Output SPL at 40 Hz | 130.7 dB |
| Output SPL at 50 Hz | 131.2 dB |
| Output SPL at 63 Hz | 130.9 dB |
| Output SPL at 80 Hz | 130.6 dB |
| Output SPL at 100 Hz | 130.5 dB |
| Output SPL at 125 Hz | 129.5 dB |
| RCA Input | Yes |
| TRS Input | No |
| USB Input | No |
| Warranty | 5/3 |
| Weight | 265 lbs (120.2 kg) |
| XLR Input | Yes |
- Links
- Reviews, Comparisons and Sound Samples
- Independently measured by Data-bass; the published figures above come from this ASR subwoofer measurement thread.
- Head-to-Head Comparisons
- JTR Speakers Captivator 4000ULF vs JTR Speakers Captivator 215PRO
- JTR Speakers Captivator 4000ULF vs Power Sound Audio (PSA) TRIAX
- JTR Speakers Captivator 4000ULF vs Power Sound Audio (PSA) T18
- JTR Speakers Captivator 4000ULF vs JTR Speakers Captivator S2
- JTR Speakers Captivator 4000ULF vs JTR Speakers Orbit Shifter LFU
- JTR Speakers Captivator 4000ULF vs JTR Speakers Orbit Shifter PRO
- JTR Speakers Captivator 4000ULF vs Reaction Audio PV-15X
- JTR Speakers Captivator 4000ULF vs Monoprice Monolith M-215
- See all 15 comparisons
Monoprice Monolith 16 THX Ultra: $2,300 Discontinued eBay
Same family: the Monoprice Monolith 12 THX Ultra (smaller subwoofer, ranked lower, rated 3.8/5), the Monoprice Monolith 13 THX Ultra (smaller subwoofer, ranked lower, rated 4.2/5) and the Monoprice Monolith 15 THX Ultra (smaller subwoofer, ranked lower, rated 4.2/5).
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. Discontinued.
Notes: Product # 42031
Full Monoprice Monolith 16 THX Ultra review and specifications →
| AES Input | No |
|---|---|
| Aux Input | No |
| CEA-2010-A Average (40-80Hz) | 126.5 dB |
| Cabinet Color | black |
| Coaxial Input | No |
| 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 |
| HDMI Input | No |
| Inputs | XLR, RCA, XLR out |
| Measurement Source | Audioholics |
| Optical Input | No |
| 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 |
| RCA Input | Yes |
| TRS Input | No |
| USB Input | No |
| Warranty | 5 |
| Weight | 171.5 lbs (77.8 kg) |
| XLR Input | Yes |
- 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
- Monoprice Monolith 16 THX Ultra vs Harbottle Audio C24 L2
- Monoprice Monolith 16 THX Ultra vs Funk Audio Ultra 21.0LX
- Monoprice Monolith 16 THX Ultra vs Funk Audio Classic 18.0
- Monoprice Monolith 16 THX Ultra vs JTR Speakers Captivator 2400
- Monoprice Monolith 16 THX Ultra vs Reaction Audio PV-15X
- Monoprice Monolith 16 THX Ultra vs Harbinger V2218S
- Monoprice Monolith 16 THX Ultra vs Danley Sound Labs DTS10
- Monoprice Monolith 16 THX Ultra vs Rythmik FV25HP
- See all 88 comparisons