Monolith by Monoprice 12in THX Ultra Certified 500-Watt Powered Subwoofer (EU plug)
Rated 3.5/5 based on 11 customer reviews

Monolith by Monoprice 12in THX Ultra Certified 500-Watt Powered Subwoofer (EU plug)

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Monolith THX Select Subwoofer

The Monolith™ THX® certified subwoofer sets the standard for bass output, low distortion, and affordability. With chest thumping bass that plays down to well under 20Hz, the Monolith subwoofer unleashes cinema level volume, with the ability to convey and articulate the subtle nuances of music.

THX Ultra Certified
500 Watt Amplifier

THX Ultra Certified
500 Watt Amplifier

THX Ultra Certified: THX® engineers completed hundreds of different scientific tests to ensure the highest audio performance possible. The tests ensure the speaker can reach the high volumes necessary to achieve THX Reference Level without creating audible distortion or artifacts. THX Certified Ultra products are for large sized rooms, up to 3,000 cubic feet (85 m³) in size, with a 10-12 foot (3.5 m) viewing distance from the screen.

12" Woofer: The Monolith™ 12" (30 cm) driver was developed from the ground up, with a design focus on achieving output, accuracy, dynamics, and linearity, while minimizing distortion. Enclosed in a cabinet made from HDF material, massive internal bracing, and outfitted with dual ports that can utilize a foam plugs to run the subwoofer in a sealed mode.

500 Watt Amplifier: The 500W RMS amplifier is built around a Texas Instruments™ 48-bit data path (with 28-bit filter coefficients) and DSP engine. Each amplifier's transfer function, power output limiting and thermal protection are monitored to the millisecond and are customized for each individual driver. The high efficiency Class D amplifier modules are based on a proven topology that has been continuously refined over the past 4 years. The amplifier has vast reserves of power for highly accurate, deep bass for your home theater or music system.


Performance Class


THX Ultra


THX Certified Ultra products bring the cinematic experience to large home theaters, 3,000 cubic feet in size, with a viewing distance of 12 feet or greater from the screen.*

* Previously known as Select2


Anatomy of a Subwoofer

12-inch Subwoofer

Cabinet and Internal Bracing

HDF (High Density Fiberboard), not MDF, was utilized resulting in a sonically inert cabinet. Internal bracing has been strategically placed to increase overall cabinet strength and limit unwanted panel vibrations that would cause discoloration and distortion. The strong cabinet and bracing combine to ensure you hear massive amounts of bass, not cabinet resonances.

Ports and Grille

The 12" model uses a single 88.5mm port with inner and outer flares. Multiple ports are used to ensure high SPL capability at low frequency (fb=21Hz). The dual flares help reduce turbulence and asymmetrical distortions. Additional adjustments can be made by sealing one or more ports with the supplied plugs. The "floating" grille is made from non resonant MDF to provide rigidity, while the entire structure is offset from the cabinet to maximize air flow of the woofer and ports.

12-inch Driver

10-inch Subwoofer

Every part of this driver has been developed from the ground up and customized to deliver high output, low distortion, and accurate bass. Our unique hybrid cone combines long fiber pulp and fiberglass, taking advantage of the pulp's superior stiffness with the additional rigidity and lightweight properties of fiberglass, to deliver a driver of massive durability and excursion. The result is a cone that achieves optimal motion at all frequencies it is asked to produce and beyond.

1. Lower Suspension

FEA (Finite Element Analysis) modeling and Klippel laser based optimizations were used to design a cone that is capable of astounding >80mm peak-to-peak excursions. The lower and upper suspensions are designed together with the motor structure. The lower suspension is critical for maintaining very low levels of distortion at high excursions, which are required for high SPL at low frequencies.

2. Spider and Cone Venting

The spider is made from multiple layers of NOMEX® with integrated tinsel leads hand stitched in place for low mass yet high strength and durability. The purpose of these vents are twofold -- first, they allow convective air flow to cool the voice coil and, second, they reduce asymmetrical compliance due to air compression under the cone/spider, which would appear as unwanted distortions.

3. Woofer Surround

FEA (Finite Element Analysis) modeling and Klippel laser based optimization were utilized to create this durable, high profile surround that’s made from a unique formulation of NBR (NITRILE RUBBER-acrylonitrile-butadiene copolymer). This formulation was developed after months of modeling and prototyping to ensure the highest levels of excursion, without sacrificing linearity or distortion.

4. Motor Structure

The motor is made of CNC milled low carbon steel in the modified undercut "T" pole assembly to focus the magnetic flux. Dual aluminum shorting rings are used to cancel eddy currents, further stabilizing the magnetic flux and significantly lowering distortion. The precision wound, high temperature, all aluminum bobbin (which has a lower thermal compression than copper) enable the voice coil to remain cool. The motor and suspension design is extremely critical for maintaining control of the driver's displacement over a very wide range of input signals, allowing the subwoofer to reach maximum performance and output levels while keeping distortion to a minimum.

All Amp'd Up

12-inch Subwoofer


The Monolith™ subwoofer amplifier has an extraordinarily high power output of 500 watts RMS (900 watts peak), which can deliver massive amounts of power when needed. Each Class D amplifier is built around a Texas Instruments™ 48-bit data path (with 28-bit filter coefficients) DSP engine, allowing virtually unlimited design flexibility with the assurance of no signal degradation. Each amplifier's transfer function, power output limiting, and thermal protection are monitored to the millisecond and are customized for each individual woofer and cabinet air volume combination. This state-of-the-art Class D amplifier technology ensures maximum headroom capability, excellent transient response, high output, and very low distortion when driving the Monolith 12-inch THX® Select certified subwoofer.

CEA-2010 SPL Measurements @ 2 meters

12-inch Subwoofer

12-inch Subwoofer

Ported (2 ports)

  SPL @ 2m Distortion
Hz Peak (dB) RMS (dB) THD% 2nd
16 99.7 96.7 8.1% 3.9% 6.5%
20 108.3 105.3 9.5% 3.4% 8.0%
25 112.3 109.3 5.7% 1.3% 5.2%
31 113.6 110.6 4.3% 2.6% 2.9%
40 114.2 111.2 4.0% 2.4% 3.1%
50 114.6 111.6 2.7% 1.5% 2.2%
63 115.0 112.0 2.6% 1.1% 2.3%
80 115.4 112.4 1.6% 0.8% 1.0%
100 115.9 112.9 1.2% 0.7% 0.8%
125 116.3 113.3 1.2% 0.7% 0.6%

Ported (1 port)

  SPL @ 2m Distortion
Hz Peak (dB) RMS (dB) THD% 2nd
16 101.8 98.8 9.2% 1.3% 8.5%
20 106.3 103.3 11.7% 5.5% 8.7%
25 108.5 105.5 8.0% 4.6% 4.5%
31 110.8 107.8 4.7% 3.2% 2.4%
40 111.5 108.5 3.6% 2.6% 2.1%
50 111.9 108.9 2.5% 0.8% 2.1%
63 112.6 109.6 2.3% 1.3% 1.2%
80 113.6 110.6 3.3% 1.7% 1.4%
100 114.3 111.3 1.9% 1.1% 1.5%
125 115.0 112.0 1.3% 0.8% 0.9%


  SPL @ 2m Distortion
Hz Peak (dB) RMS (dB) THD% 2nd
16 95.0 92.0 15.3% 2.4% 13.5%
20 100.3 97.3 17.1% 3.1% 15.4%
25 105.4 102.4 12.7% 4.3% 9.9%
31 108.1 105.1 3.5% 2.0% 2.3%
40 109.9 106.9 2.9% 1.4% 2.1%
50 110.9 107.9 2.2% 0.7% 1.2%
63 112.1 109.1 2.1% 0.9% 0.9%
80 113.1 110.1 2.6% 1.1% 1.2%
100 113.9 110.9 2.1% 1.1% 1.7%
125 114.8 111.8 1.4% 1.0% 0.8%

Support Files:

Monoprice™, Monolith™, the Monolith logo, and all Monoprice logos are trademarks of Monoprice Inc.

THX® and the THX logo are trademarks of THX Ltd., registered in the U.S. and other countries. The THX Ultra logo is a trademark of THX Ltd.

Texas Instruments™ is a trademark of Texas Instruments.

DuPont™ and Nomex® are trademarks or registered trademarks of E.I. du Pont de Nemours and Company or its affiliates.

Updated Jan 21, 2021

How long will it take for my order to arrive?

After the order has been placed, shipping takes about 3-4 business days.

How much do I have to pay for shipping?

Free shipping for orders from 30.

What are the returns policy?

You can return your items to us within 14 days without giving a reason. We expect the items to be in their original condition upon return.

How does the return work?

If you do not like an article, you can return it to us within 14 days of delivery. Please contact us at to receive a return label. Please print the return label, stick it on the carefully sealed package and hand it over to your local post office. Please keep the document with the tracking number carefully.

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