Monoprice Monolith THX-365T Bookshelf Speaker Review

  • Friday, Apr 8, 2022

Foreword / YouTube Video Review

These speakers were loaned to me by Monoprice. They did not see the review before publication.

The review on this website is a brief overview and summary of the objective performance of this speaker. It is not intended to be a deep dive. Moreso, this is information for those who prefer “just the facts” and prefer to have the data without the filler. The video below has more discussion.

Information and Photos

Some specs from the manufacturer can be found here.

  • Main Woofer Drivers: 2x 6.5” long fiber pulp cones with FEA optimized nitrile butadiene rubber (NBR) surround and aluminum shorting ring
  • Main Midrange Driver: 2” silk dome midrange with Neodymium magnet and aluminum shorting ring
  • Main Tweeter Driver: 1” silk dome tweeter with Neodymium magnet and copper shorting ring
  • Main Frequency Response: 65Hz ~ 24kHz
  • Main Sensitivity: 89.5dB (2.83V@1m)
  • Main Crossover Frequencies: 550Hz (24dB Linkwitz‑Riley) and 1.9kHz (24dB Linkwitz‑Riley)
  • Main Impedance: 4 ohms
  • Atmos® Woofer Driver: 5.25” long fiber pulp cone with FEA optimized nitrile butadiene rubber (NBR) surround
  • Atmos Tweeter Driver: 0.6” silk dome tweeter with Neodymium magnet
  • Atmos Frequency Response: 120Hz ~ 20kHz
  • Atmos Sensitivity: 86.0dB (2.83V@1m)
  • Atmos Crossover Frequency: 3.8kHz (18dB Butterworth)
  • Atmos Impedance: 4 ohms
  • Recommended Amplifier Power: 80 ~ 250 watts
  • Cabinet: Sealed, 5 layer HDF with horizontal shelf bracing and 5‑way binding posts
  • Dimensions (without grille) (LxWxH): 10.8” x 9.7” x 22.9” (275 x 246 x 581 mm)
  • Dimensions (with grille) (LxWxH): 11.4” x 9.7” x 22.9” (290 x 246 x 581 mm)
  • Weight: 28.4 lbs. (12.9 kg)

The current price is approximately $449 USD per speaker ($900 for the pair).

CTA-2034 (SPINORAMA) and Accompanying Data

All data collected using Klippel’s Near-Field Scanner. The Near-Field-Scanner 3D (NFS) offers a fully automated acoustic measurement of direct sound radiated from the source under test. The radiated sound is determined in any desired distance and angle in the 3D space outside the scanning surface. Directivity, sound power, SPL response and many more key figures are obtained for any kind of loudspeaker and audio system in near field applications (e.g. studio monitors, mobile devices) as well as far field applications (e.g. professional audio systems). Utilizing a minimum of measurement points, a comprehensive data set is generated containing the loudspeaker’s high resolution, free field sound radiation in the near and far field. For a detailed explanation of how the NFS works and the science behind it, please watch the below discussion with designer Christian Bellmann:

The reference plane in this test is at the tweeter.

Measurements are provided in a format in accordance with the Standard Method of Measurement for In-Home Loudspeakers (ANSI/CTA-2034-A R-2020). For more information, please see this link.


The On-axis Frequency Response (0°) is the universal starting point and in many situations it is a fair representation of the first sound to arrive at a listener’s ears.

The Listening Window is a spatial average of the nine amplitude responses in the ±10º vertical and ±30º horizontal angular range. This encompasses those listeners who sit within a typical home theater audience, as well as those who disregard the normal rules when listening alone.

The Early Reflections curve is an estimate of all single-bounce, first-reflections, in a typical listening room.

Sound Power represents all of the sounds arriving at the listening position after any number of reflections from any direction. It is the weighted rms average of all 70 measurements, with individual measurements weighted according to the portion of the spherical surface that they represent.

Sound Power Directivity Index (SPDI): In this standard the SPDI is defined as the difference between the listening window curve and the sound power curve.

Early Reflections Directivity Index (EPDI): is defined as the difference between the listening window curve and the early reflections curve. In small rooms, early reflections figure prominently in what is measured and heard in the room so this curve may provide insights into potential sound quality.


Early Reflections Breakout:

Floor bounce: average of 20º, 30º, 40º down

Ceiling bounce: average of 40º, 50º, 60º up

Front wall bounce: average of 0º, ± 10º, ± 20º, ± 30º horizontal

Side wall bounces: average of ± 40º, ± 50º, ± 60º, ± 70º, ± 80º horizontal

Rear wall bounces: average of 180º, ± 90º horizontal


Estimated In-Room Response:

In theory, with complete 360-degree anechoic data on a loudspeaker and sufficient acoustical and geometrical data on the listening room and its layout it would be possible to estimate with good precision what would be measured by an omnidirectional microphone located in the listening area of that room. By making some simplifying assumptions about the listening space, the data set described above permits a usefully accurate preview of how a given loudspeaker might perform in a typical domestic listening room. Obviously, there are no guarantees, because individual rooms can be acoustically aberrant. Sometimes rooms are excessively reflective (“live”) as happens in certain hot, humid climates, with certain styles of interior décor and in under-furnished rooms. Sometimes rooms are excessively “dead” as in other styles of décor and in some custom home theaters where acoustical treatment has been used excessively. This form of post processing is offered only as an estimate of what might happen in a domestic living space with carpet on the floor and a “normal” amount of seating, drapes and cabinetry.

For these limited circumstances it has been found that a usefully accurate Predicted In-Room (PIR) amplitude response, also known as a “room curve” is obtained by a weighted average consisting of 12 % listening window, 44 % early reflections and 44 % sound power. At very high frequencies errors can creep in because of excessive absorption, microphone directivity, and room geometry. These discrepancies are not considered to be of great importance.


Horizontal Frequency Response (0° to ±90°): specs

Vertical Frequency Response (0° to ±40°): specs

Horizontal Contour Plot (normalized): specs

Vertical Contour Plot (normalized): specs

“Globe” Plots

Horizontal Polar (Globe) Plot:
This represents the sound field at 2 meters - above 200Hz - per the legend in the upper left. specs

Vertical Polar (Globe) Plot:
This represents the sound field at 2 meters - above 200Hz - per the legend in the upper left. specs

Additional Measurements

Impedance Magnitude and Phase


Response Linearity and Sensitivity


Step Response


Group Delay


Harmonic Distortion

Harmonic Distortion at 86dB @ 1m: specs

Harmonic Distortion at 96dB @ 1m: specs

Dynamic Range (Instantaneous Compression Test)

The below graphic indicates just how much SPL is lost (compression) or gained (enhancement; usually due to distortion) when the speaker is played at higher output volumes instantly via a 2.7 second logarithmic sine sweep referenced to 76dB at 1 meter. The signals are played consecutively without any additional stimulus applied. Then normalized against the 76dB result.

The tests are conducted in this fashion:

  1. 76dB at 1 meter (baseline; black)
  2. 86dB at 1 meter (red)
  3. 96dB at 1 meter (blue)
  4. 102dB at 1 meter (purple)

The purpose of this test is to illustrate how much (if at all) the output changes as a speaker’s components temperature increases (i.e., voice coils, crossover components) instantaneously.


Parting / Random Thoughts

As stated in the Foreword, this written review is purposely a cliff’s notes version. For details about the performance (objectively and subjectively) please watch the YouTube video. But a few notes:

  • Mid-High frequency sounds boosted; sometimes sounding ‘brittle’ or ‘sharp’. Notably there is sibilance in the upper octaves but also I noticed a peaking in the 2-4kHz region on various tracks. Looking at the estimated in-room response backs up what I heard pretty readily.
  • “Soft” on the midbass. Looking at the data I see a bump around 110-120Hz but a rolloff below this with an F3 = 84Hz.
  • I noted that in my listening I heard resonance. I thought this was in the 200Hz region but I see no signs of this. Looking at the data I see the bump around 110Hz (mentioned above) and wonder if that’s what I was hearing. The bump indicates a mild-Q from what is possibly a slightly-undersized enclosure. Based on my experience, I’m tempted to say this is more likely the culprit of the resonance I heard. Though, it could have very well been a room mode.
  • Tons of SPL. The compression data shows a similar issue as the center channel version (reviewed here).

Given the overall price, I don’t know that my qualms are dealbreakers, per se. But they are definitely audible anomalies that I feel are worth pointing out to would-be consumers. In my opinion, EQ is necessary with this speaker to smooth the tonal balance and luckily, other than the 1kHz region, this speaker should take well to EQ. Ceiling absorption and carpeting on the floor would be one way to help remedy this due to the narrowing of the two midbass drivers meeting the midrange where the midrange is now wide in directivity at this region (see: Early Reflections graphic). Though, this is anecdotal and your results may vary.

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