Monolith 12" THX Ultra Subwoofer Review

Manufacturer & Model
Monoprice Monolith 12” THX Ultra Subwoofer
MSRP
$799
Link
https://www.monoprice.com/product?p_id=24457
Highlights
Competitively priced, in-room performance below 20Hz, dual tunable ports, THX Ultra certification, tight and punchy output, excellent entry into high-end bass performance, edgy eye-catching styling.
Summary
The Monolith 12” THX Ultra Subwoofer is one of three new THX certified Monolith subs designed to offer high-end performance without a hefty price tag. Overall build quality is impressive, as is the size of the subwoofer, which weighs nearly 100-lbs. The rear plate amp offers an impressive array of controls and connectivity options, while dual front firing ports are tunable via included foam plugs. Sound quality is excellent, featuring tight and powerful in-room performance that hits well below 20Hz, making the Monolith 12” THX Ultra a shortlist worthy subwoofer.
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Monoprice couldn’t help itself. First, it successfully became the Internet’s go to source for reasonably priced AV cables and interconnects. Now, it’s attempting to crack the foundation of a rather insulated top-end AV marketplace with seductively disruptive gear that’s priced right. Today, we’re shining a spotlight on the company’s brand-new Monolith 12” THX Ultra Subwoofer, a ridiculously fun subsonic cannon that offers head-turning performance for a mere $799 (plus shipping).


Monolith Has Arrived
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If you’re not familiar with Monoprice’s relatively new Monolith badge, then it’s time to take notice. The company is actively leveraging healthy sales of its widely varied Monoprice branded products to deliver a range of audio gear – from headphones and speakers to amps and DACs – loaded to the brim with design elements typically found on products costing 20- to 40-percent more. The name of the game is high-performance and cost consciousness – and from my exposure (including in-home experience) with several Monolith products, Monoprice is poised to give the competition fits by servicing price savvy buyers that want more than just budget gear.

Monoprice’s three new ported Monolith subwoofers (featuring single 10”, 12”, and 15” drivers) were officially announced just months ago at CEDIA 2017, with final labeling awaiting approval from the labs of THX. The original hope, according to Monoprice’s Hobie Sechrest (Senior Product Manager, Monolith), was for the 12” design to receive a THX Select rating. Instead, the hefty middle model was anointed THX Ultra status, independently establishing itself as performance ready for rooms up to 3,000 cubic feet. Combine that kind of rating with a sub-$800 price tag, and it’s entirely impossible not to be curious about the 12” THX Ultra subwoofer’s true real-world performance capabilities.


The Guts Of Glory
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(Monoprice)

The 12” THX Ultra subwoofer (along with its 10” THX Select and 15” THX Ultra brethren) has been percolating in Monoprice’s labs for the last several years, during which significant R&D capital was spent fine tuning the “guts and engineering” of the sub. According to Sechrest, Monoprice wanted to ensure top-line performance capabilities first and foremost (which, in the case of the 12” THX Ultra, equates to clean in-room performance hitting well below 20Hz).

The man behind the curtain, so to speak, is a Claridy 500 Watts RMS (900 Watts peak) Class D amplifier managed by a Texas Instruments 48-bit DSP engine. The exterior of the amp features multiple controls, including Crossover, Phase, Gain, EQ (THX vs. Extended), and Power (On vs. Auto). It also houses an informative multi-color LED light that indicates the sub’s operational status. Connectivity wise, users have access to dual unbalanced RCA inputs along with single XLR balanced input and pass-through ports.

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The sub’s custom front-firing driver looks impressive, stamped dead-center with a Monolith logo and sporting a rather substantial surround formulated by NBR (Nitrile Rubber-acrylonitrile-butadiene copolymer). The “hybrid” high-excursion cone (>80mm peak-to-peak) is comprised of long fiber pulp and fiberglass for lightweight action while maintaining overall stiffness. And the motor structure is beefy to the eye, featuring a 60mm voice coil and a 9-lb magnet aided by spider and cone venting that lends to advanced cooling and reduced distortion.

Overall output is tunable via dual front mounted 3.5” ports. The port mouths are flared with smooth black plastic surfaces. Monolith ships the sub with two firm foam plugs that measure 3.75” T x 3.75” W. Both are easy to insert and remove.


Out Of The Box
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Monoprice’s subwoofer packaging experience is a mixture of both good and bad, with a strong emphasis on good. The sub arrived double boxed using double wall corrugated cardboard; the interior box was reasonably protected from its journey across the country. Internally, thick custom foam blocks and black cloth sacks more than adequately protected the sub, its grille, and the included power cord (a physical manual isn’t provided). That’s the good. The bad is a lack of any kind of unboxing instructions (which are typically included with gear weighing in the 100-lb range). That led to a guessing game consisting of flipping, sliding, and hoping my way to revealing the sub. Through the magic of film, the unboxing (video link below) looks rather easy, but I’m inclined to mention that I had several moments of stalled frustration. Of course, the experience didn’t present anything unsurmountable, but Monoprice should consider adding printed or on-box instructions as the Monolith line matures. Editor’s Note: Monoprice appreciates the feedback and says it will consider options for future packaging.

Click on the video below to watch the entire unboxing process.


The Monolith 12” THX Ultra subwoofer is a beast in the hands, weighing a smidge less than 100-lbs, and looks great to the eye with sharp lines and a unique edgy styling. Its 22.8” T x 16.7” W x 23.6” D HDF cabinet passes the knuckle wrap test with flying colors and truly handles like a brick. The exterior is covered in a low-sheen Black Ash high-grade vinyl that has the general appearance of wood veneer – it’s quite impressive. Overall fit and finish is spot-on, with excellent craftsmanship (yes, even the back side of the cloth grille is clean and well put together). As for exterior durability, my assumption is the 12” THX Ultra’s cabinet is perfectly fine for home theater duty (i.e., unbox and place), but that more frequent handling should be done with care.

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The plate amp’s knobs all turn with a gratifying smoothness paired with a pleasant amount of resistance, switches are crisp, and the grille cover (including its ¾” standoffs) fits firmly in the cabinet’s strategically placed grille mounting points. Again, considering price, Monoprice has given the 12” THX Ultra some nice little touches that elevate the user experience when interacting with the speaker. Color me impressed.


Set Up
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Moving the Monolith 12” THX Ultra into place was a two-person operation, largely due to its weight and overall length. It was placed in a carpeted 2000-cubic foot dedicated home theater room at the front wall’s left quarter-point. The sub’s small rubber feet seemed to provide decent stability on the carpet, but are probably best suited for hard surfaces.

Following roughly 30-hours of break-in, the sub was equalized with Audyssey MultEQ XT32 via a Marantz SR7012 AVR and paired with a 7.x.4 arrangement comprised of SVS Ultra and Prime Elevation speakers (system wide crossover = 80Hz). Other associated gear included an OPPO UDP-205 4K Blu-ray player, an Emotiva XPA5 amp, and – integrated later in the review – a Yamaha RX-A3050 AVR.

Final subwoofer settings were as follows: Gain +0dB, Phase 0°, and THX EQ engaged. THX EQ asks the sub to perform within THX certification parameters, while the Extended mode is designed for slightly louder output with a minute uptick in distortion (Monoprice says measurable distortion in Extended mode remains within an inaudible threshold). My Room EQ Wizard (REW) measurements didn’t show a significant in-room performance difference between the two modes (response wise), hence I chose to leave THX EQ engaged.

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Post-calibration in-room measurements: Purple = Sealed, Blue = Two Ports, Green = One Port

Following a variety of listening tests and frequency response measurements, I opted to run the sub with one port open. As you can see in the figure below, in-room output for both sealed and single port open modes of operation was excellent, digging deep into infrasonic frequencies. And I felt the one port open mode sounded tight and controlled, with more apparent depth and impact.

It’s worthy to note that I – purely through personal choice – opted to run the 12” THX Ultra subwoofer cooked slightly hot (channel leveled at 79dB vs 75dB for other speakers in the system), but also experimented with dialing back the sub's output. Overall, I had zero complaints about system blending.


The Sound
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(Lionsgate Films)

Question: If someone handed you a bazooka at a proving ground, would you (A) fire it at a cardboard cutout of a pine tree, or (B) take aim at a scrapped military tank loaded with TNT? If you consider “B” to be the obvious answer, pat yourself on the back and hop into my world. The Monolith 12” subwoofer, you see, is a bazooka and I had no choice but to immediately fire it at the biggest target I could find. In review terms that means Blu-ray movies, specifically movies laced with devastating bass widely celebrated to hit low and hard.

As I combed through my media library, I selected three films capable of challenging the 12” THX Ultra’s prowess: Edge of Tomorrow (Blu-ray), Deepwater Horizon (4K UHD Blu-ray), and Interstellar (4K UHD Blu-ray). And because I wanted immediate results, Edge of Tomorrow was the first disc to spin.

Edge of Tomorrow’s Blu-ray release is legendary for its first scene bass attack that cycles through several brutal subsonic and infrasonic tones. If you’re unfamiliar with the opening sequence, approach it cautiously. It can cripple less than capable gear. Being responsible, I kept close tabs on the volume control, easing the 12” THX Ultra into the Edge of Tomorrow’s challenging waters. I quickly found no hand-holding was necessary, as the sub confidently dished-out punishing bass without any hint of unpleasantry. I pushed output levels to near reference, and the sub didn’t flinch, filling my dedicated room with pulsating bass (yes, even the opening scene’s 10Hz thunder). The remainder of the film was a delightful listen, layered with tight and nuanced LFE that graced the audio presentation with a weighty texture and impact. Everything from the subtle rumble of aircraft engines to the powerful thuds of explosions and falling debris was present and devoid of bloated or loose playback. And the smaller impacts of bass bursts associated with weapons firing were quick and tight.

Suffice to say, the 12” THX Ultra passed its first challenge.

Phase two of the evaluation introduced more explosions, this time at the hands of Deepwater Horizon. Deepwater is loaded with a variety of LFE, including tension building pulsations that match the intensity of the film’s storyline, and the 12” THX Ultra obliged with a buttery smooth presentation. The sub’s transient capabilities were on full display during the crews’ helicopter ride to the oil platform, as sound associated with the copter’s blades was tight and textured. But the beef of the film’s bass is paired with the Gulf’s cracking seafloor and the resulting explosive chaos that occurs on the surface of the water. The 12” THX Ultra didn’t disappoint. The sub injected powerful rumbles into my theater room – shaking seating – as the Horizon was lost. I even noted subtle bass drops that floated with controlled character. From start to finish, I was thoroughly impressed as the 12” THX Ultra met the film’s demands with thunderous composure.

My experience with Interstellar was much the same, with notable performance output experienced during the film’s incredibly challenging big bass moments (namely the worm hole and black hole scenes). The 12” THX Ultra kept pace with grace, never showing signs of wilting under pressure as volumes were advanced to reference levels. Most importantly, the resulting bass maintained character, devoid of any bloated or loose output that you might expect from an inferior party-pounder.

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(Jon Bellion / Capitol Records)

Moving onto music, I re-experimented with various port tunings and – once again – confirmed a preference for operating with one port open. After thrashing my theater room with hard-hitting film content, I was eager to explore the 12” THX Ultra’s musical capabilities. First, I took a journey into Thundercat’s bizarre world of Drunk (TIDAL). Musical tastes aside, Thundercat’s bass guitar exposé and kick drum beats make for great sub demo material. “Captain Stupido” sounded phenomenal, loaded with quick bass notes that blended perfectly with my system’s Ultra Tower mains. The character of Thundercat’s bass guitar was high-level in its presentation. And the tightness of bass in “A Fan’s Mail” was rich and pleasing to the ear. As eluded to earlier, the 12” THX Ultra’s output fell in line with what I’d expect from well-regarded gear.

Next up was Jon Bellion’s Human Condition (CD), an album layered with low-end fun that likes to run smooth and long. Shorter bursts of bass heard during “80’s films” were tight and punctuated, and the song’s subtle background bass drops maintained clean character as they fell into the lower depths of hearing. A very similar low-end experience graced Bellion’s “Overwhelming,” which has plenty of pop that hits tight and then smoothly slides away. The 12” THX Ultra kept pace, once again relying on its ability to punch without looseness. This particular track allowed the sub’s confident musicality to shine right to reference volume levels.

One final audio test came at the hands of an old-time favorite that makes for fantastic demo material: Meat Beat Manifesto’s Now EP (CD). This rare audio gem is loaded to the brim with raw and punishing electronic bass that’s repetitive and unrelenting. The EP’s second remix track, “Paradise Found,” opens with a heartbeat-like bassline that bleeds into a mesmerizing drum beat. The 12” THX Ultra delivered pure and tight bass with composure right to reference levels and beyond. The EP's third track, “Paradise Now,” contains an equally punishing bass guitar rhythm that also played cleanly right to reference. Again, these are incredibly challenging audio tracks that present brutal bass expectations at high volume levels. It was a pure power show of super tight and explosive bass. In fact, during later testing sessions involving these songs, the bass output dislodged a glass candle holder and a framed mirror (in an adjacent room) from their resting places and sent them crashing to the floor.

The Monolith 12” THX Ultra is a beast after all.


Conclusion
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The Monolith 12” THX Ultra subwoofer is a super intriguing entry on numerous levels, and Monoprice deserves a high-five for bringing such high caliber performance to market at a budget friendly price point. For $799, an enthusiast can fetch nearly 100-lbs of sub with an amp/driver combination that produces high-level bass output. Forget raw and boomy power, the 12” THX Ultra has the composure of high-class gear. It can punch and lower the boom with a clarity and powerful tightness that allows for natural and controlled playback, all the while fully carrying the load of a system’s low-end output. Add to that three possible variations of port tunings, and the sub presents quite a bit of room-friendly flexibility. This is definitely a sub worthy of shortlist status – cost-conscious buyers take note, the 12” THX Ultra is your gateway to serious home theater performance.


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Monolith 12" THX Ultra Subwoofer Specifications
  • Model: 24457
  • Woofer: 12" cone
  • Cone Material: 2 layer long fiber pulp/glass fiber cone
  • Voice Coil: 60mm with high temperature aluminum wire and black anodized aluminum bobbin
  • Surround: FEA optimized NBR (nitrile budadiene rubber)
  • Motor: FEA optimized, 2 aluminum shorting rings, undercut T-pole focused field
  • Magnet: Ceramic Y35, 2 pcs total 144 oz.
  • Xmax: 18mm (one-way)
  • Xmech: 80mm (peak-to-peak)
  • Enclosure: Sealed or vented HDF cabinet with horizontal and vertical bracing
  • Finish: Black Ash
  • Amplifier: Class D 500Wrms
  • Frequency Response: (-6dB) Sealed Vented (1 port) Vented (2 ports)
  • Extended EQ: 26-200Hz 19-200Hz 18-200Hz
  • THX EQ: 29-200Hz 23-200Hz 20-200Hz
  • Harmonic Distortion: <1% 20-100Hz (90dB @ 1m)
  • Variable Level Control: +15/-20dB
  • Crossover: Inline/Bypass variable 40-160Hz
  • Inputs: RCA (2), XLR
  • Outputs: XLR
  • Signal Turn On: Selectable always on/auto
  • Auto Turn Off: 30 minutes
  • Dimensions: (H x W x D) 22.8" x 16.7" x 23.6" (580 x 425 x 600mm)
  • Net Weight: 98.5 lbs. (44.7 kg)
  • Gross Weight: 125.7 lbs. (57 kg)
 
Last edited:

Tony V.

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So do you think this sub or one of the larger 15" models would be a good pair up with an older SVS PB13u?
 

Todd Anderson

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Hmmm... I thought someone might chime in with a question like that! To be honest, Tony, you don't want to take a chance of introducing anything that might be the limiting factor on that PB13u. While you can see the in-room measurements I recorded were impressive for 1 port and sealed, the bass head inside of me wants to tell you to consider the 15" to match what you already have.
 

tripplej

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Thanks for the review. Very well done. Nice video as well. :)
 

Matthew J Poes

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Great review Todd! This seems like a real value. I can't think of any other subwoofers in the same performance category for that kind of price.
 

Todd Anderson

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Thanks, Matt. I’m curious to read owner reviews/reactions as these subs start to trickle into homes.

I didn’t note in the review, that duals can be purchased for $1500 (plus shipping)... I’d imagine that would put the out the door cost near $2k.
 

Matthew J Poes

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Thanks, Matt. I’m curious to read owner reviews/reactions as these subs start to trickle into homes.

I didn’t note in the review, that duals can be purchased for $1500 (plus shipping)... I’d imagine that would put the out the door cost near $2k.
It will be interesting. There are a few more of these in the hands of other reviews, but the reviews are awaiting SPL testing. I'll be curious to see how they perform. My guess is that this 12" model will perform similarly to the 13" sub from Outlaw Audio. They both have the same THX rating. While THX is very tight lipped on their specifications for THX certification, it would not be unreasonable to guess that the Outlaw audio represents roughly the limit. If that is true, then their distortion threshold is actually much lower than CEA-2010 for their range of concern, meaning a THX certified sub will typically have much lower distortion at a given passing CEA-2010 frequency than would a non-THX sub (obviously this isn't a given, anyone can make a low distortion sub, but the THX sub is guaranteed). The outlaw audio subwoofer is WAY more expensive, which is why I think this may be a real value.

There are non-THX subs that likely play at similar peak outputs but I have a feeling their distortion performance won't be as good and most are more expensive. The 15 may have more competition, but again, distortion.
 

Todd Anderson

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Look forward to seeing what others have to say...:T
 

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Thank you Todd for such a great review. It is impressive to see a sub with a 12" driver dig as low as 10 Hz based on your graph.
I too can't wait till people have it in their homes to see what they think.
 

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I didn’t note in the review, that duals can be purchased for $1500 (plus shipping)... I’d imagine that would put the out the door cost near $2k.
I have a bass black hole room, it is simply difficult to pressurize my open floor plan living room. That said, with the factory and review specs given, dual 12 THX Ultra would top my list of prospective candidates.
 

Matthew J Poes

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I have a bass black hole room, it is simply difficult to pressurize my open floor plan living room. That said, with the factory and review specs given, dual 12 THX Ultra would top my list of prospective candidates.
You could also try three, with one located very near you.
 

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Impressive... nice review too Todd... looks like a winner here. :T
 

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You could also try three, with one located very near you.
I have dual 18s running now, with a third waiting to be built out, ala Geddes, but without one above the room centerline.

Three of the 12 THX Ultra would be quite the treat!
 

Matthew J Poes

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I have dual 18s running now, with a third waiting to be built out, ala Geddes, but without one above the room centerline.

Three of the 12 THX Ultra would be quite the treat!
What you can’t mount an 18 in the ceiling?

I’ll be honest when I’ve experimented with height I’ve not found it to make much difference. I also believe Geddes never made that an absolute. It was more of a recommendation. His approach was/is a holistic systems approach that relied on a bunch of factors to be true. Things that made sense in his ideal system but are very inconsistent with most speaker systems. He runs his mains full range and uses them as additional Lf sources. His Mains are Summas, meaning they each have a high output 15” driver in a sealed enclosure. In total he typically ran a setup that would have at least 4 but as many as 6 LF sources, each of which could put out extreme SPL.

I say all this because if you don’t meet that criteria where you are sharing the Lf load across the front speakers then already you are doing it drastically different from him. Better to be consistent with the spirit of the idea rather than the specifics once you start to drift.

Three of these 12’s would be great for anyone but if their mains are being high passed at 80hz you would actually prefer at least one more.

And for others reading this, that may seem excessive but this is not about bass output. You actually don’t gain much output this way. It’s about bass smoothness and bass quality. The increased Lf sources reduces deviation and this LF linear distortion. The small increase in headroom also reduces non-linear distortion some.
 

tesseract

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What you can’t mount an 18 in the ceiling?
I dunno, will you ask my landlord for me? :p

I’ll be honest when I’ve experimented with height I’ve not found it to make much difference. I also believe Geddes never made that an absolute. It was more of a recommendation. His approach was/is a holistic systems approach that relied on a bunch of factors to be true. Things that made sense in his ideal system but are very inconsistent with most speaker systems. He runs his mains full range and uses them as additional Lf sources. His Mains are Summas, meaning they each have a high output 15” driver in a sealed enclosure. In total he typically ran a setup that would have at least 4 but as many as 6 LF sources, each of which could put out extreme SPL.

I say all this because if you don’t meet that criteria where you are sharing the Lf load across the front speakers then already you are doing it drastically different from him. Better to be consistent with the spirit of the idea rather than the specifics once you start to drift.
Depends on placement, the mains rolloff, mains enclosure alignment and crossover slope. I ran mains wide open, rolling in the subs at the bottom end for many years, out of necessity, way before bass management systems were widely available.

I'd go more into specifics (60 Hz roll off vs. 80Hz, 2nd order slopes vs. 4th order), but would be veering this thread far off topic.
 

Asere

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Quick question and I apologize if I should not be asking on the Monolith page here but considering we are talking about subs I guess its ok. When there is a really low frequency is it normal to hear the driver flap/vibrate hard or it does that only because the subs are trying to keep up?
 

bkeeler10

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Todd, when I saw that you had flat bass down to nearly 10 Hz, I went searching for your room size. I'm guessing it's a fairly small room and you're getting a fair bit of room gain, but still - that's crazy from a ported sub. Wonder what they tuned the ports to . . .

Looks like a great sub at a great value. Thanks for sharing.
 

tesseract

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Quick question and I apologize if I should not be asking on the Monolith page here but considering we are talking about subs I guess its ok. When there is a really low frequency is it normal to hear the driver flap/vibrate hard or it does that only because the subs are trying to keep up?
A subwoofer that is not broken or being pushed beyond its limits should not be making any untoward noises, no.
 

Asere

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A subwoofer that is not broken or being pushed beyond its limits should not be making any untoward noises, no.
Mine is ok. It's just that when there's a really low frequency I can hear the cabinet vibrate and the driver go crazy. What you are telling me is. Even with a really low frequency it should sound normal like when there is not a low note?
 

Michael Scott

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Mine is ok. It's just that when there's a really low frequency I can hear the cabinet vibrate and the driver go crazy. What you are telling me is. Even with a really low frequency it should sound normal like when there is not a low note?
sounds like you're pushing it too hot and it's causing some over travel on the cone. I'd check your clip lights to see if it's clipping (could be some of the cause of the noise) and try turning the gain down on either the amp or the receiver. You very well could be pushing it past it's limits
 

Asere

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sounds like you're pushing it too hot and it's causing some over travel on the cone. I'd check your clip lights to see if it's clipping (could be some of the cause of the noise) and try turning the gain down on either the amp or the receiver. You very well could be pushing it past it's limits
How do you check the clip lights?
 

Michael Scott

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Asere

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Panamax M5300 PM, Monster HTS 3600
what sub do you have?
Duo Kreisel DXD 12012. The avr trim is -3.5 for each and gain set to reference (green dot on these subs)
It could also be that I have DEQ engaged although DEQ starts to disengage on its own the closer you get to reference.
 

Michael Scott

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Front Speakers
Cheap Thrills Mains
Center Channel Speaker
Cheap Thrills Center
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Volt 10 Reach Surrounds
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Volt 6 Overheads
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2x Marty subs (full size with SI 18's)
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Draper Cineperm M1300 119 inch Static Screen
that green light on your amp. Let her rip with a good low bass tone where it starts distorting and if it's flickering red, then it's clipping the amp.
 

Asere

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Parasound HCA 1500A
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Oppo 103D
Front Speakers
SVS Prime Towers
Center Channel Speaker
SVS Prime
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SVS Prime Satellites
Front Height Speakers
Proficient
Rear Height Speakers
Proficient
Subwoofers
Dual Kreisel DXD 12012, PSA S3000i
Video Display Device
Samsung PNF8500
Screen
60"
Remote Control
Harmony Ultra
Other Equipment
Panamax M5300 PM, Monster HTS 3600
that green light on your amp. Let her rip with a good low bass tone where it starts distorting and if it's flickering red, then it's clipping the amp.
Thanks! I am also considering running them as one vs split. I should have more headroom as one don't you think?
 
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