Mini Review: Monoprice Monolith K-BAS Reference Series Bookshelf Speakers

Monoprice Monolith K-BAS Reference Series speaker

The search for great bookshelf speakers leads down many paths, thanks to the vast selection of designs. In this mini-review, I look at the K-BAS Reference Series bookshelf speaker ($250 each) from Monoprice, a company known for offering rock-bottom prices on a wide variety of products including AV gear and accessories.

It’s an open secret that Monoprice often relies on existing designs for its products. For example, the company’s Monolith amplifiers are built by ATI here in the US. The K-BAS (Kinetic Bass Amplification System) technology used in these speakers is no different; it’s actually an H-PAS (Hybrid Pressure Acceleration System) design that’s licensed from Atlantic Technology.

K-BAS schematic
This schematic shows what’s going on inside the Monolith K-BAS bookshelf.

K-BAS is said to provide bass performance that exceeds what’s typical for speakers of this size. Read on to find out if the Reference Series bookshelf speakers deliver what they promise.


The K-BAS Reference Series bookshelf is a 2-way design featuring a 1″ titanium-dome tweeter and a 5.25″ poly/mica woofer. Its 7.2″ (wide) x 15.6″ (high) x 13.0″ (deep) enclosure weighs 14 pounds.

Power handling is spec’d at 50 watts RMS and 150 watts peak. The sensitivity of the speaker is 87 dB/W/m with an anechoic frequency response from 39 Hz to 20 kHz, +/-2.2 dB. The crossover point is 3 kHz, and impedance is rated at 6 ohms nominal, 4.2 ohms minimum. The company touts the use of quality components in the crossover, which uses a parallel first-order low-pass/second-order high-pass design.

K-BAS crossover
Here’s a close look at the crossover.

This model comes in a durable matte-black finish. The rear-mounted binding posts are all-metal, easy to access, and accept banana plugs.


Great bass response is one of the headline features of the K-BAS design. Consequently, I opted to evaluate them in a 2-channel configuration—sans subwoofer. I used NAD’s excellent C 368 hybrid DAC/amp (80 watts/channel RMS) to power them.

I placed the speakers atop 24-inch stands positioned several feet from the front wall and six feet apart from each other, with a slight toe-in. During listening sessions, I sat about seven feet back from the speakers, forming an audiophile-approved triangle. I used 10-foot lengths of Monoprice 12-gauge OFC speaker cable to connect the speakers to the C 368.


This is a mini-review, so let’s get right to the point: This model offers great sound but limited peak output. Thus, depending on your needs, it may not represent the best value for the dollar in a market filled with competent yet affordable 2-way bookshelf designs.

The combination of qualities in the Monolith K-BAS Reference Series bookshelf speakers make them a solid choice for an apartment or condo system. The aural pleasures they provide are evident at moderate listening levels—great if you have neighbors that you don’t want to disturb while enjoying a genuine deep-listening experience. But, if you are looking for a speaker to use in a high-impact home-theater rig, or for playing music at anything approaching concert levels, I suggest looking elsewhere.

The good news is these speakers can be counted on for accuracy. The transparency they offer makes them suitable for use as budget-friendly studio monitors. The primary performance limitation is modest peak output, which is unsurprising for a low-sensitivity speaker with 50-watt RMS power handling.

Despite my criticism, these speakers may offer a desirable tradeoff for someone seeking affordable, high-performance bookshelf speakers. They don’t require a sub to sound full-bodied at modest listening levels.

Basic in-room frequency response measurements jibed well with the speaker’s specs. Treble extended past 20 kHz, response was smooth, and bass reached down to 39 Hz. However, while measuring bass extension, I noted an issue that has not been a problem in many reviews: port noise. When I played sine waves through the speakers at moderate to high levels, the K-BAS port exhibited audible chuffing. On the other hand, this chuffing only occurred while playing sine waves at frequencies below 55 Hz; it was not an issue when playing music. Nevertheless, I feel it’s important to mention.


“Turquoise Hexagon Sun” from Boards of Canada’s Music Has the Right to Children showed off the clarity and excellent imaging these speakers can achieve. Boards of Canada will put sounds behind your head if you let them, such is their production wizardry. At modest volume levels, the speakers teased out many subtleties buried in the group’s multilayered mix.

My reference for belting out taut deep bass is Daft Punk’s “Disc Wars” from the Tron: Legacy soundtrack. True to form, at lower volume levels these speakers rendered the track in a satisfying manner. The orchestral and synthesizer sounds stayed distinct, with rich texture.

While listening to Disc Wars, I read what I wrote about the track when I reviewed ELAC’s Debut B6 speakers ($280/pair): “The album did lose some measure of its deep-bass impact when compared to subwoofer-equipped systems, but I have to give credit to the B6s, they managed to get the room shaking. Notes that are totally absent on some speakers—even some costlier floorstanders—came through as guttural growls, with nary a hint of distortion. It was a heroic effort that reaffirms my conviction that these speakers don’t need a sub to please bass-loving listeners.”

The rub here is that the Debut B6s are the best-performing inexpensive bookshelf speakers I heard in 2016. The ELACs play louder and dig a bit deeper than the K-BAS speakers, getting down to 34 Hz in-room without audible chuffing.

At this point, you might be wondering if the ELAC B6s are the outright better-sounding speakers. In my subjective opinion, not at the lower levels where the Monolith K-BAS thrive. But once you turn up the volume—even with a modest amp or AVR—you’ll eventually reach the point where the Monoprice speakers can’t deliver the dynamics that the ELACs can.

I’m hesitant to make a value judgment here, because the Monoprice speakers do offer notable fidelity that will please critical listeners—until you bump up against their output limitations.

The positive attributes of this system were evident when auditioning program material that demands delicacy, such as jazz, bluegrass, and folk recordings. Feed them a solo vocalist playing a guitar and they are happy to deliver an audiophile-quality performance.

Ultimately, this is not an ideal speaker system for fans of rap, dubstep, death metal, rock, or other hard-hitting genres who habitually turn the volume up to “11.” However, I suspect that the Monoliths would elicit a positive response from attendees at high-end audio shows thanks to their finesse.


The Monolith K-BAS Reference Series bookshelf speakers are worth considering if what they offer clearly matches your needs and expectations. Used in a system that eschews subwoofers, a pair can deliver an engrossing listening experience if they are not pushed too hard. As with many other competent bookshelf speakers, adding a good sub results in a 2.1 system that offers much more visceral satisfaction, but negates the purported advantage of K-BAS technology.

Clean, deep bass along with smooth response and precise imaging at modest output levels are the headline feature here. If that sounds like what you’re looking for in a bookshelf speaker, be sure to give the Monolith K-BAS Reference Series a listen.