Monoprice Monolith THX-365T Mini-Tower and THX-365C Center Speaker Review

Monolith THX-365T Mini-Tower and THX-365C Center Introduction

Regular readers will know that Audioholics has closely followed Monoprice’s foray into higher-end audio with their ‘Monolith’ family of products. Among the Monolith products we covered were the K-BAS speakers, Air Motion speakers, and THX subwoofers. The Monolith line’s expansion into THX-certified products must have proven to be successful because Monoprice has recently rolled out a set of THX-certified loudspeakers to complement their subwoofer line. The Monolith THX certified loudspeaker set is comprised of a bookshelf speaker, a ‘mini-tower’ (really just a large bookshelf speaker), and a center channel speaker. In for review today, we have the mini-towers and center channel speaker, which are called the THX-365T and THX-365C, respectively. The THX-365T Mini-towers also come with an Atmos speaker built in the top portion, so those who want an Atmos height speaker in their system can also have that. This review will be focused on the Monolith THX speakers used as normal speakers, so we will not be looking at the Atmos speaker addition very closely, although we do discuss its construction in the ‘Design Overview’ section of this review, and we do take a glance at a couple of measurements of its performance in the ‘Measurements and Analysis’ section.

Monoprice THX-365T & Revel M126Be Reviews YouTube Discussion

What Does THX Mean?

Monoprice is banking on the THX-certification to add consumer appeal to these products. But, what does THX-certification really mean? The trouble here is that THX closely guards the exact performance characteristics needed to attain certification, but we do have some general guidelines that need to be followed for speaker manufacturers. Of course, a flattish response is needed, so that the speaker is accurate, and a smooth off-axis response is needed as well, so the speaker provides even coverage over a wide listening area. The speaker must be able to hit reference levels at the listening positions over certain spaces. In other words, the speaker has to get loud enough without running into distortion or compression based on its certification level. The speaker must be capable of 105 dB peaks and 85 dB continuous levels for the certifications outlined on the THX website.

Many people think that THX certification is simply a stamp of approval for a certain level of performance, but there is more to it than that. THX is intended to encompass the entirety of a listening/viewing experience, and the certification is a mark that the component will behave in a way that fits in with a THX environment. You can have a multitude of THX-certified components without having a THX-certified system or a THX-level experience, so an individual component such as a loudspeaker or amplifier is just one piece of that puzzle. The performance targets of a THX-certified speaker means that it will behave in a very predictable manner when installed in a THX system, and the whole experience will add up to what the artists intended. It’s a way of ensuring that you are experiencing what you are supposed to experience and eliminating variables that impede the intended experience.

That being said, even when not installed in a THX environment, THX certification is still a desirable attribute, in that you know you will be getting fairly accurate sound or video reproduction equipment. That is one of the aspects of the Monolith THX-365T and THX-365C that we will be looking at. What is the level of accuracy needed to secure THX certification? What are the performance metrics needed to acquire this piece of the THX puzzle? In other words, how good does a loudspeaker have to be for a THX experience?

Packing and Appearance

The Monolith THX speakers arrived at my home in a thick cardboard box packed in three tough polyethylene foam pieces: two that capped the speakers on both ends and one in the middle. The speakers were wrapped in a black cotton drawstring sleeve that should protect it from both scuffing and moisture. The packing is good enough that it should protect the speakers through rough shipping, and, from the look of the boxes that I received, did.

Once out of the packing, THX-365T and THX-365C speakers proved to have a rather elegant shape. They have a rounded cabinet that tapers off toward the rear. The angled top of the THX-365T is reminiscent of the speaker design from Sonus Faber, but Monoprice uses this shape for a far more practical reason; there is an embedded Dolby Atmos speaker at the top of the speaker, and the angled cabinet aims it such that ceiling reflections would be heard as Atmos ‘height’ channels. We will dig a little more into that in the design overview section of this review. The finish is a slick, semi-wood grain textured vinyl wrap that is sleek yet does not allow fingerprints to stand out. It’s a nice looking finish even though it is probably a low-cost one; I have seen it used on other budget speakers before.

With the grilles on, the Monolith THX speakers are inoffensive but indistinct rounded enclosures.  With the grilles removed, the speakers have a lot more character with the drivers exposed, and I think they look better. The dustcaps of the woofers and domes of the midranges and tweeters have a satiny, slightly glittery texture that gives them a subtle but noticeable distinction against the flat black of the driver frames. These are large speakers, but one aspect about them that softens their appearance is that there are few hard edges anywhere on them. It’s all circles and rounded organic shapes. This is in contrast to the Monolith THX subwoofers that have a more mechanical and angular masculine aesthetic. The Monolith THX speakers look much more refined than the Monolith THX subs.

Like the Monolith THX subs, these particular Monolith THX speakers are rather large. Monoprice calls the THX-365T a ‘mini-tower,’ but in reality, it’s just a large bookshelf speaker. That isn’t to undersell what it is, but it will be used in the same way as bookshelf speakers are, so there is no need for a new speaker type classification, in my opinion. Their large size might make them a non-starter for those looking for unobtrusive speakers, but their stylish design goes a long way toward making them ingratiating in a home setting. Speakers with the performance goals that the Monolith THX speakers have cannot really be placed in a small package, so anyone who wants THX Ultra certification has to be prepared to find a place for largish bookshelf speakers. Personally, I think they look very nice. Their size may preclude them from finding a place in a finely decorated living room, and they don’t have a luxury-class finish, but they shouldn’t be a problem in a family room, media room, office, or especially a home theater room.

Design Overview

The Monolith THX-365T and THX-365C are both rather heavy-duty three-way bookshelf speakers and center channel speakers. Both of them are THX Ultra certified, and that means they should be able to achieve THX Reference level loudness at a distance of 12 feet within a 3,000 cubic foot room, so they do need to be very capable speakers. The specs are on their side toward this end, however. They use two 6.5” bass drivers, a 2” midrange dome, and a 1” dome tweeter. Furthermore, the THX-365Ts have an Atmos speaker installed at the top, which gives them two channels of speaker in one cabinet. One thing I found is that the midrange driver is rather vulnerable. It uses a silk dome that is very soft and can easily be damaged by kids and rambunctious guests and pets. The speakers should be used with caution around pets and people who are not careful. Leave the grilles on in those instances.

The 6.5” woofers use long-fiber pulp cones in stamped steel baskets with some chunky ¾” x 4” magnets in the motor. The midrange and tweeter use silk domes and are each housed in their own enclosed space in a plastic enclosure. The structure of the midrange is much more like that of a traditional dome tweeter on a larger scale rather than a usual midrange cone. All of the drivers use shorting rings which reduce even-order distortion as well as extending their operational bandwidth. The drivers are crossed over at 550 Hz and 1.9 kHz using fourth-order slopes. The choice of a 1.9 kHz crossover seems like an unusually low crossover for a three-way speaker. While midrange driver can certainly handle higher frequencies than 1.9 kHz, I am told by the speakers’ designer that the crossover frequencies were chosen because they added up the the best performance overall when looking at on and off-axis response and distortion performance. Altogether the quality and quantity of drivers on the Monolith THX speakers seem to be unexpectedly good considering the pricing.

The Atmos Driver

The Atmos driver in the THX-365T is a coaxial driver that uses a 5.25” pulp fiber woofer with a 0.6” silk dome tweeter mounted in the center of the woofer cone. It’s internal cabinet space is closed off from the rest of the internal speaker space, so it has its own sub-enclosure. It uses a third-order crossover at 3.8 kHz. I would expect the reason for such a higher crossover is to have a narrower directivity. Wide dispersion sound probably isn’t a great idea for an Atmos-module type speaker since the listener should only be hearing reflected sound from the speaker and not direct sound. For those who don’t know, Atmos speakers try to simulate sound coming from above by bouncing sound off of the ceiling that hits the listener instead of just projecting sound directly to the listener. The wider the dispersion of the speaker, the more direct sound that will hit the listener instead of direct sound. If the listener hears too much direct sound coming from the Atmos speaker, that would create a mess out of the intended Atmos effect. For this reason, listeners using the Atmos module should listen to this speaker with ears level with or below the tweeter. The higher the listener is in elevation with respect to this speaker, the more sound they will hear directly from the Atmos driver which will degrade the intended effect.

The cabinet uses ¾” high-density fiberboard (HDF) paneling all around. Most speakers in this class use MDF instead of HDF. The advantage of HDF in speaker construction is that it will be less resistant to moisture effects than MDF and is a stiffer, denser material. The disadvantage is that is doesn’t damp acoustic resonances as well. The curvature of the cabinet should help to reduce internal standing waves which will help to eliminate resonances. There is also a window brace in the middle of the cabinets which will help to keep the panels inert. The cabinet is filled with stuffing which will help damp internal acoustic energy. The THX-365T uses some small rubber dimples as feet, and the THX-365C center speaker uses a flat rubber mat. Both use five-way binding posts that protrude from a rear-mounted plate.

Both speakers use sealed designs so there are no ports Sealed designs are preferred by THX (although not required) in order to achieve the 12dB/octave slope needed for a THX speaker/subwoofer crossover, because a sealed design has a natural 12dB/octave slope low-end rolloff that is much more difficult to achieve in a ported design, and a sealed design has a much more predictable phase response. Given that THX specifies an 80 Hz crossover, I wouldn’t expect the Monolith THX speakers to have very much bass output below that point. These speakers are intended to be used with subwoofers, and I would expect the low-end rolloff to occur around 80 Hz.

The Monolith THX speakers use an 11-element crossover with some reasonably solid-looking components. Taking a peek at the crossover for the regular non-Atmos part of the speaker, we see two iron core inductors, three air-core inductors, two electrolytic capacitors, four film capacitors, and three largish resistors. Monoprice’s crossover spec claims fourth-order slopes, and the plethora of crossover elements plus the acoustically sealed drivers should be able to add up to such steep filters.

There is a lot that I like about the design of the Monolith THX speakers. One thing is the arrangement of the tweeter and midrange on the center speaker. By relegating only the bass drivers to horizontal alignment, this center speaker should be mostly free of the off-axis lobing that occurs with traditional ‘MTM’ center speaker design which simply places a tweeter between two woofers (the problems with that design approach can be read about in our article detailing the difference between horizontal vs vertical speaker designs and in our article about center channel design considerations. I like the three-way design of the THX-365T speakers; that can do a better job of controlling directivity and it should have a wider dynamic range with better power-handling versus an ordinary two-way bookshelf speaker. I like the idea of putting dual woofers in the THX-365Ts, and furthermore, the placement of the second woofer above the tweeter; this placement pushes the Atmos speaker above the ear height which should help to keep all of that sound as acoustic reflections where they belong. Spacing the woofers apart helps to mitigate ground-bounce cancellation a bit as well, and it does better at keeping the acoustic center of the speaker squarely around the tweeter and midrange where it should be. All in all, the THX-365T and THX-365C are a lot of speaker for the money. But are they too good to be true for the price? Let’s take a listen to hear what they can do...

Listening Sessions

In my 24’ by 13’ (approximately) listening room, I set up the speakers with stand-off distances between the back wall and sidewall, and equal distance between speakers and listening position. The speakers were set up to face the listening position directly. Listening distance from the speakers was about 9 feet. Amplification and processing were handled by a Pioneer Elite SC-55. No room correction equalization was used. Subwoofers were used for all content since these speakers were designed to be used with subs.

Music Listening

One album loaned to me as good demo material for speakers was ‘Time Out’ by The Dave Brubeck Quartet. I am not a jazz aficionado, so I didn’t realize this quintessential album’s place in music history, although I have recognized some of the tracks played as demo music from various sound system exhibits over the years. At first, I was skeptical that this recording, made in 1959, had a sufficiently good sound quality to be useful as speaker demo music, but I was pleasantly surprised at the realism of the sound in the recording. ‘Time Out’ is an instrumental jazz album featuring a quartet of a piano, alto saxophone, bass, and drums, and it is known for its innovation using uncommon time signatures. The album I used is the 1997 remaster of this classic recording. The Monolith THX-365T speakers played this album splendidly. It sounded so good that I checked the liner notes to make sure it was actually recorded in 1959 and was not some recently recorded cover. Listening closely, there were some tells that it was an older recording, such as hearing an analog hiss in the background during some quieter moments, but this 60-year-old recording was beautifully reproduced on these speakers and brought this musical moment alive as though it were happening in the present. All of the instruments sounded crisp and their positions in the soundstage were clear and distinct. The tonal balance of the sound seemed to be quite even with everything sounding natural with no notable tonal aberrations. I have heard these tracks played on far more expensive speakers, but I didn’t get a sense that this presentation was lesser in any way. As I said, I am not a jazz guy, but I still quite enjoyed ‘Time Out’ as replayed by the Monolith THX speakers; this music doesn’t show its age at all.

An orchestral album that I gave a spin with the Monolith THX speakers was a compilation entitled ‘Sounds of the Sea’ that I pulled from a larger box set of albums called ‘In Classical Mood.’ ‘Sounds of the Sea’ is a collection of classical pieces with a sea-faring theme such as ‘The Flying Dutchman: Overture’ by Richard Wagner and ‘H.M.S. Pinafore: Overture’ Arthur Sullivan. There are other tracks by Debussy, Berlioz, and Rimsky-Korsakov as played by esteemed orchestras such as the Royal Philharmonic Orchestra and the London Symphony Orchestra. Individual tracks are taken from different sources, but the production quality is high throughout, so this is a good album to demo classical music on account of the diversity of venues, recording techniques, and instrumentalists. The Monolith THX speakers proved to be adept with the large scale orchestral pieces in this album they were with a small jazz ensemble in ‘Time Out.’ They managed to throw a large soundstage befitting of these epic pieces of music. Imaging was generally excellent with orchestral section positions readily identifiable. It’s easy to imagine a listener mistaking the listening room for a much larger venue where they were listening to these speakers in a darkened space. I did not hear any wrongdoing in instrumental tonality, and the timbral balance sounded very even on the whole. The Monolith THX speakers were not lacking in dynamic range either; crescendos hit with a palpable force and weight. That is no surprise given the THX Ultra certification and oversized three-way bookshelf speaker design. Another aspect of their design that really helps here is they do not try to tackle lower bass frequencies, and that allows the design of the bass drivers to attack midbass bands that much more competently. To be honest, I wish more bookshelf speakers would forego chasing after bass below 80 Hz, as these do, since most users will have subwoofers anyway. After listening to ‘Sounds of the Sea’ on the Monolith THX speakers, I do think they will satisfy the craving of almost any classical music enthusiast.

For something with more emphasis on vocals, I dug out the 1995 release ‘Songs of Sanctuary’ by Adiemus. The music is primarily female choral but with some solo vocals provided by singer Miriam Stockley. The voices are backed by traditional orchestral instruments provided by the London Philharmonic along with other instruments and music styles pulled from around the globe. This is an album of vaguely ethnic world music that was a popular new-age style back in the ’90s. It’s not exactly challenging music to listen to but it is pretty. It can almost be described as something Enya would do but with more weighted with traditional orchestral elements. With so much singing, I thought ‘Songs of Sanctuary’ would be a good album with which to evaluate human vocals. On the Monolith THX speakers, this album sounded better than I can ever recall hearing it before. Miriam Stockley’s often soaring vocals were rendered with detail in a larger-than-life soundstage where studio recording techniques expanded the choral elements to be a virtual wall of sound. The Monolith THX speakers didn’t seem to add or subtract anything, and I can’t help but think this is very close to what this album is supposed to sound like. That brings to mind the fact that if a THX experience was closely governed in every component from recording to playback, then theoretically THX-certified home audio speakers should serve as well as studio monitors as they do in home audio applications, at least in a controlled setting. 

I wanted to push the Monolith THX speakers harder to see how they handled louder and more aggressive music played at high levels, and toward this end, I selected Blank Banshee’s ‘Metamorphosis.’ Blank Banshee is an artist who has been doing something unique in his corner of the electronic music world that is not easy to pigeonhole in a particular genre. It’s percussion-heavy and bass-heavy, but the rhythms are unusual and the sound is idiosyncratic. His music is said to be somewhere between Trap music and Vaporwave, but it isn’t quite either. ‘Metamorphosis’ is a recently released 18-minute long epic single that is sprawling over a rich, diverse array of sounds, melodies, and rhythms; it begs to be played at a loud level. It uses a punchy kick drum underneath a host of synthetic bells, vocal pads, and plucked strings, but the sound is constantly evolving throughout the track’s duration. The Monolith THX speakers showed that they can rock very nicely with ‘Metamorphosis.’ The music was vibrantly and cleanly reproduced even at high loudness levels. I never sensed any compression, congestion, or distortion. These speakers can hit hard, and I think they could handle a house party if they were asked to. They may be just bookshelf speakers, but they are some of the most robust bookshelf speakers that I have yet encountered. Which again, is not surprising given their design.

Movie Watching

THX is popularly associated with high dynamic range movie experiences, so I looked for a movie that could take advantage of such capable speakers. I had not seen the 2011 science-fiction film ‘Real Steel’ before and guessed that it would make an appropriate demo of wide dynamic range speakers since it is about boxing matches between large robots. ‘Real Steel’ is what happens when you combine two Sylvester Stallone movies, ‘Over the Top’ and ‘Rocky,’ but use robots instead of people in the competitive sport. Seriously, Stallone should have been given story credit for ‘Real Steel’ because it does not deviate much from the plots of these previous films where he did help to write the stories. Hugh Jackman plays a down-on-his-luck boxing manager for robots, and he is tasked with taking care of his 11-year old son for a summer for whom he had been an absentee father. The kid turns out to be gifted in working with fighting robots, and they bond while the kid helps the father make a career comeback with a special underdog robot boxer. It’s fairly predictable stuff, but the robot fights look and sound quite spectacular, which is what speakers like the Monolith THX series are made for. Indeed, the robot fights crackled with aural energy, and not just from the gladiating steel hulks battering each other but from the bombastic music, excited audience, and the human characters’ constant exhortations for the robots to “get up” when they were knocked to the ground. You know how in movies when a boxer’s team pleads with them to get up on their feet again when they are knocked down? That happens a lot in ‘Real Steel,’ but it’s not as if emotional pleas will invigorate the will of a robot to accomplish any task. I beg my computer to snap out of it when a program locks up, but it has never done any good so far. But hey, it’s just a movie and a crowd-pleasing one at that. As cliched as ‘Real Steel’ was, it sounded terrific on the THX Monolith speakers. I played this movie at a loud level and did not detect any fault in the speakers’ ability to reproduce its lively sound mix. Many people will be purchasing these speakers for the purpose of having blockbuster movies sound as large and dynamic as a commercial cinema experience, and on that count, I can happily say that the Monolith THX speakers deliver.

Like so many others, I binged-watched the third season of ‘Stranger Things’ not long after it was uploaded on Netflix. This mega-popular series sounded better than ever thanks to Netflix’s recently improved sound quality which now streams at 640 kbps. That resolution should put it above the threshold of human hearing, so Netflix programming is certainly worthy of a great sound system for those who have one available. ‘Stranger Things’ season 3 once again puts the plucky young heroes of the series against bizarre cosmic horrors in the backdrop of 1980’s suburbia, complete with a spread of some of the big pop music hits of the day. The sound mix is as high quality as any major Hollywood production, and the sound effects, dialogue, and music are mixed with all of the polish that you would expect from a no-expenses-spared production. The show is filled with growling monsters, shrieking teenagers, and synth-heavy music, and the Monolith THX speakers brought all of this action to life without any audible weaknesses. Regardless of the volume level, the Monolith THX speakers rendered a crystal clear soundscape no matter how frantic the scene. One highlight was the rich vintage synthesizer-driven music score provided by the duo Kyle Dixon and Micheal Stein; anyone who has seen the show can easily recall the arpeggiated bass line overlayed with the haunting electronic leads of the show’s opening theme. The music throughout, whether by Dixon and Stein or taken from some other source, gives the show such a memorable atmosphere that it is difficult to imagine that the ‘Stranger Things’ series would have gained such popularity with a more conventional score. The Monolith THX speakers made this propulsive retro-futuristic score blaze with the analog synth sounds so thick that they could be cut with a knife. ‘Stranger Things’ season 3 is best watched at a high loudness level when speakers as good as the Monolith THX line is used. This show will sound as good as the system it is played on. 

Monoprice Monolith THX-365T and THX-365C Measurements & Conclusion

The Monoprice Monolith THX speakers were measured in free-air at a height of 7.5 feet at a 2-meter distance from the microphone, and the measurements were gated at a 9-millisecond delay. In this time window, some resolution is lost below 250 Hz and accuracy is completely lost below 110 Hz. Measurements have been smoothed at a 1/12 octave resolution.

Outdoor Measurement Platform with Monolith THX-365C Speaker

The above graph shows the direct-axis frequency response and other curves that describe the speakers’ amplitude response in a number of ways. For more information about the meaning of these curves, please refer to our article Understanding Loudspeaker Measurements Part 1. While the responses that I measured don’t exactly match the responses that are seen on the product pages for these speakers, they are nonetheless good overall. The responses are fairly neutral, but they do have a very slight downward slope; that will be their chief audible distinction from perfect neutrality. The THX-365T Mini-Towers do have a minor peak centered around 9 kHz, but that won’t be very audible. These speakers may have a slightly warm or laid back sound compared to many other speakers because there is a bit more energy in the woofer and midrange dome bands than the tweeter’s band. We can see that these are both relatively wide dispersion loudspeakers because the early reflections curve tracks the on-axis response and listening window response very closely until upper treble frequencies. This can also be seen in the directivity indexes; the dispersion of these speakers will begin to narrow above 5 kHz. For the most part, however, both speakers provide a very good response and should sound great to most ears except maybe for those listeners who are looking for a bright sound.

The above graphs depict the Monolith THX speakers’ lateral responses out to 100 degrees in five-degree increments. More information about how to interpret these graphs can be read in this article: Understanding Loudspeaker Review Measurements Part II. Once again, we see how well behaved these speakers are, but these graphs show us how well the horizontal off-axis response correlates with the on-axis response in greater detail. As the directivity indexes suggested, these speakers hold a nicely uniform axial response up to 5 kHz where the tweeter does roll-off quite a bit more at farther off-axis angles. We do see a slight amount of off-axis cancellation from the woofers in the center speaker, but it is extremely mild compared to what occurs in most two-way center speakers. This response from this center speaker is very good and places it among the best center speakers we have measured to date.

The above polar map graphs show the same information that the preceding graphs do but depict it in a way that can offer new insight regarding these speakers’ behavior. Instead of using individual raised lines to illustrate amplitude, these polar maps use color to portray amplitude and this allows the use of a purely angle/frequency axis perspective. The advantage of these graphs is they can let us see broader trends of the speaker’s behavior more easily. For more information about the meaning of these graphs, we again refer the reader to Understanding Loudspeaker Review Measurements Part II. In these graphs, we can better see the breadth of dispersion of the Monolith THX speakers. Again, we see a very wide dispersion pattern out to 80-degrees that extends up to 5 kHz, but here we also get a better look at the width of dispersion at the top end of the treble response. Listening is best done within a 30-degree angle from the front axis, but that is pretty much within the range of most people’s normal listening positions anyway. There are some directivity mismatching issues with the center speaker at around 1.5 kHz and below that are inevitable byproducts of aligning two woofers on a horizontal plane but then spacing them apart, but it is mild in this design compared to most other center speakers. 

The above graph shows the Monolith THX speakers’ response behavior along its vertical axis where zero degrees is directly in front of the tweeter, negative degree values are below the tweeter, and positive degree values are above the tweeter. It should be said here that the vertical response isn’t nearly as critical as the horizontal response, so an imperfect vertical dispersion is much less of a problem. The responses seen here are unusually good for this type of speaker. There are lobing nulls caused by conflicting drivers off-axis, but they are very moderate compared to what is normally seen. These speakers actually have a relatively wide vertical angle off-axis where no severe nulls occur. They will probably never be listened to at an odd vertical angle, but it doesn’t hurt to have a good off-axis vertical response due to the consistency in sound from the acoustic reflections from the floor and ceiling.

The above graphs show the Monolith THX speakers’ low-frequency responses that I captured using groundplane measurements (where the speaker and microphone are on the ground in a wide-open area). While I included the responses of both the Mini-Tower and Center Channel Speaker, I didn’t need to since they both measure almost exactly the same. That is not surprising given the similarities in design for low-frequency output. The low end here is pretty much textbook THX bass response with a 12 dB/octave roll-off occurring just above 80 Hz. As was mentioned before, the sealed enclosure provides for a much more predictable phase response in this region which makes it a lot easier for a THX processor to blend the subwoofer with the speakers at the crossover. The bass response here is beautifully flat out to 400 Hz. This speaker is behaving exactly how one would hope for and expect in this range.

The above graphs show the electrical behavior of the Monolith THX speakers. Again, there is not much point in posting both graphs since they are so similar, but we have done so any way to demonstrate their similarity. Monoprice specs these as 4-ohm speakers, and in that they are correct. The impedance never dips down below 4 ohms, but the steep phase angle at the impedance minima between 100 Hz and 200 Hz may be a tough load for cheaper amps. Budget amplifiers should be OK with this load if it isn’t played loud, but who buys THX speakers to only be played at soft volumes? Outside of a small but important frequency band between 100 Hz and 200 Hz, the electrical load is fairly easygoing. I wouldn’t task an entry-level AVR amp with running these speakers, but a mid-level AVR should be OK.

I measured both the Center Speaker and the Mini-Tower’s sensitivity at 91.0 dB for 2.82v at 1 meter. That is certainly an above-average sensitivity for a bookshelf speaker but not so surprising for large and powerful speakers such as these. While the lower impedance does play a role in that, this higher sensitivity will help alleviate the electrical load that these place on amplifiers. These are relatively sensitive speakers and don’t need a lot of electrical power to get loud.

Atmos Speaker Measurements

For those who are curious about the performance of the Atmos speaker, the above image contains a couple of measurements to give an idea about their behavior. These were taken with microphone at a 1-meter distance and cover the vertical axis, but with a coaxial driver like this, the horizontal axis measurements should be very similar. We see a surprisingly well-controlled on and off-axis response out to 5 kHz. The on-axis response does get a bit peakish from 6 kHz to 7 kHz, although the off-axis response holds pretty steady out to 8 kHz. The lack of upper treble is not likely a serious issue here since this speaker banks on reflected sound, and high treble would get the most severely attenuated by reflections anyway. The electrical impedance measurements didn’t contain anything worrisome, and sensitivity was measured at 87.9 dB at 1 meter for 2.83v, which is fine.

Editorial Note On Atmos-enabled Speaker Frequency Response

The Dolby Atmos-enabled speaker is supposed to employ a complex 7-element crossover network to shape its response using a HRTF to enhance the height effect. The peakiness in frequency response noted in the measurements may be a deliberate design attempt to accomplish this goal. Research has found this may NOT be necessary since each individual has their own unique HRTF response and artificially mimicking this in a loudspeaker design can be hit or miss as a result.

For more information, see: Are HRTF really necessary in Dolby Atmos Speakers?

One possible concern that a response like this could cause is that it is a relatively wide dispersion response. The problem is one we mentioned before; in a top-mounted Atmos speaker, the listener ideally shouldn’t be hearing any sound directly from this speaker. The sound heard from this channel should only be arriving at the listener as an acoustic reflection from the ceiling, but, with such a wide dispersion pattern, if the listener is at a slightly high listening angle with respect to the speaker, they could be hearing a significant amount of direct sound from the Atmos speaker which could ruin the intended effect of sound coming from above. To ensure that this doesn’t happen, make sure that the listener’s ear height is below the top front edge of the cabinet. Ideally, the listener’s ears should be level at a height somewhere around the tweeter’s or midrange driver’s elevation. If used at the correct height, the measurements here indicate that this speaker should be able to do its job well as an Atmos height speaker that uses reflections within the limits of such designs.

Conclusion

As always, before wrapping this review up, I will briefly go over the pros and cons of the product under review, and I will start with the cons-- but the Monolith THX speakers are such a well-designed and well-conceived product that the ‘cons’ are few. One con might be that the THX-365T Mini-Towers are essentially very large bookshelf speakers and might be a bit too large in certain instances that a normal bookshelf might work. However, that is the price that must be paid to get this level of performance. A smaller speaker would have a lesser dynamic range. If a smaller speaker is needed but with a similar level of fidelity, Monoprice also has the THX-265B speaker that is THX Select certified. This isn’t really a criticism of the Mini-Towers since what they are doing can’t physically be done in a smaller enclosure; it is just a caveat for those circumstances where size is a consideration. 

Another disadvantage might be their lack of low bass output. However, their low-end response is a deliberate design goal of these speakers, and they would not work as well otherwise. Besides that, if they did have a deeper bass response, that would lower their sensitivity which is not a trade-off worth making for high dynamic range speakers that are intended to be used with subs. So again, this isn’t a criticism so much as it is a notice for those who are looking to their speakers to handle full-range sound: these are not the speakers for that application.

Something else that could be said is that the finish of the Monolith THX is not the slickest and that other similarly priced speakers do have higher-end finishes. That’s true, but these speakers are much more about performance for the price and adding a nicer finish would drive the cost up significantly thereby sending these into a price range beyond the reach of many potential buyers. While these don’t look bad in my opinion, the decision to keep costs down by using a serviceable but standard finish was a correct decision. I do wish Monoprice would offer a version of the 365T sans the Atmos driver for those that don't need that feature. This could potentially shave a couple of hundred dollars off the price of a pair.

Now let’s talk about the strengths of the Monolith THX speakers. First and foremost is their performance; it is exceptional, as one would expect from a THX Ultra certified product. They are speakers with a very linear response, great dynamic range, and very good dispersion characteristics. They sounded terrific with everything that I threw at them over a very wide range of loudness levels. They are a touch warm on the side of total neutrality, and I doubt that many people would have a gripe about their tonality except for those who prefer searing hot treble for the extra ‘detail.’ One aspect I particularly like is that they bring to market an affordable three-way center speaker as an alternative to the many two-way MTM center speaker designs that inevitably have severe off-axis lobing interference. The THX-365C Center Channel Speaker is an affordable, powerful, tonally balanced center speaker that largely avoids the problems associated with that compromised design.

Another strength is the build quality of the Monolith THX speakers; they are very nicely put together and have some very good components with sensible cabinet. They might not cost a fortune to buy, but they are not a ‘cheap’ construction. One does see a little bit of cost-cutting in the finish, but, as was said before, the finish is in line with the goals of this speaker, and it doesn’t look bad. The use of a rounded cabinet does give the speakers a far more attractive appearance than that of an oblong box that they could have had.

The overall story of the Monolith THX speakers is much the same as was told by the Monolith THX subwoofers: here, for maybe the first time, one can get THX Ultra certified components for a very affordable price. These are high-performance speakers for $500/ea (365T) and $400 (365C), respectively. I can’t remember any THX Ultra certified speaker that was priced so low; all of the ones that I can think of were at least four-figure items. It used to be that you needed big bucks to put together a THX home theater system, and in many ways, it still does, but at least the subwoofers and now the speakers can be had without breaking the bank. But beyond THX certification, these are just plain-old good speakers and a bargain at their pricing. While they are intended for home theater, I think anyone shopping in this price range for high-fidelity speaker should give these a hard look so long as the performance attributes are understood, i.e., they do need a subwoofer. Even if their wide dynamic range is not needed, the baseline performance at lower levels is so good that these would also be great for a two-channel music system with a subwoofer (or two—or more). They reproduce sound very well and do so for an extremely reasonable cost given the level of performance.  Highly recommended!  

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

• — Excellent
• — Very Good
• — Good
• — Fair
• — Poor

Metric	Rating
Build Quality
Appearance
Treble Extension
Treble Smoothness
Midrange Accuracy
Bass Extension
Bass Accuracy
Imaging
Dynamic Range
Fit and Finish
Performance
Value