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Monolith Air Motion Cinema 5 Bookshelf & Center Channel Speaker Measurements

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The Monolith Air Motion speakers were measured in free air at a height of approximately 9 feet and gated at 14 ms. At this window gate, some resolution is lost below 140 Hz, and accuracy is completely lost below 70 Hz and so that range should be ignored. The microphone was placed 1 meter away from the speaker at a height level with the tweeter. All measurements are unsmoothed.

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Monoprice Air Motion Cinema 5 bookshelf speaker response curves 

The Air Motion speakers measure well up to 2.5 kHz, but the tweeter shows some spikiness above that point, especially on axis. Off-axis, the tweeter calms down significantly. The spike at 6 kHz suggests that the speaker would have a sibilant character, but in my listening sessions I didn’t hear anything that I would consider to be notably sibilant. It may be that the peak is so narrow that sibilance wouldn’t come out except in particular cases. The dip centered around 3.5 kHz would be more concerning, although that is something an automated room correction equalization routine like Audyssey can help out with, since it occurs all around the speaker’s axis and so is not a diffraction problem. The directivity indexes show that at high treble frequencies, the Air Motion speakers become a very directional speaker, meaning the acoustic energy becomes more focused in front of the speaker instead of widely dispersing. The tweeters higher directivity may be another reason why I didn’t hear it to be especially sibilant, since much of the treble energy was confined to a tighter beam instead of reflecting all over the room. For more information on what all the difference curves mean in this graph, we refer the reader to this Audioholics article: Objective Loudspeaker Measurements to Predict Subjective Preferences.

One feature the Air Motion bookshelf speakers has in common with the K-BAS speaker is that the bass response is relatively flat. Most bookshelf speakers in this range seem to have a mid bass boost, but the Air Motion speakers keep the bass relatively neutral. A flat bass response and a slightly elevated range from 500 Hz to 2.5 kHz would suggest a somewhat more ‘forward’ sounding speaker rather than a laid-back or ‘warm’ speaker. This sound character can bring out a detailed sound but at the risk of being fatiguing over long listening sessions, although I did not find them to be fatiguing myself. All told, I would wish for a flatter response over the entire range, but the flaws that this graph suggest didn’t seem pronounced when I was listening to the speakers themselves.

In investigating the cause of the jagged treble response, we swapped tweeters from the center channel speaker, which measured to have a much tamer response in the 6 kHz to 10 kHz region. The response in the bookshelf speakers remained the same, so it seems that the tweeter itself is not the cause of the problem, or at least is not the sole cause. When we took a measurement with the tweeter disconnected, the problem became apparent; the woofer was clearly running into breakup modes, and the low-pass filter was not sufficiently suppressing the woofer’s misbehavior. We would have thought that since the crossover uses a third-order low-pass slope on the woofer at 2.8 kHz, cone breakup should be significantly reduced in this region. In A/B comparisons with speakers we had on hand that had a more neutral response in this frequency range, the Air Motion speakers were notably ‘edgier’ in character, surely a byproduct of the cone breakup. 

It should be noted here that the measurements seen here for both the Air Motion bookshelf speakers and center speaker were performed with the grille off. The grille did not improve matters above 5 kHz, because the grille frame caused some diffraction that led to more jaggedness in the upper frequencies. The Air Motion speakers perform best without the grille on. 

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Monoprice Air Motion Cinema 5 Bookshelf Speakers horizontal frequency response +/-90 degrees from axis: 3D view

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Monoprice Air Motion Cinema 5 Bookshelf Speakers horizontal frequency response +/-90 degrees from axis: 2D view 

Looking at the Air Motion’s dispersion graphs in 10-degree increments, we can more explicitly see some off-axis behaviors. We can more clearly see the beaming of the response after 10 kHz. There looks to be a cancellation effect from the tweeter itself off-axis at about 12 kHz, but that is not likely to be audible, so that shouldn’t be a cause for concern. Looking closely, we can see the 20 degree and 30 degree angles lose most of that higher frequency on-axis irregularity. For those who want a less forward sound, they might try aiming the speakers off the listening position outside of a 20-degree angle, whether toed in or toed out. That would go a long way toward reducing any ‘brightness’ of the speaker. The 30-degree response angle looks to be the most linear, at least out to 15 kHz. Dispersion is fairly wide and mostly uniform up to 12 kHz. The Air Motion speakers would offer relatively good coverage over a wide area. This is a speaker that might work well when facing straight ahead as well as toe-in angles aiming at the listening position.

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Monoprice Air Motion Cinema 5 Bookshelf Speakers Polar Map 

The above polar map of the horizontal dispersion of the Air Motion speakers depict the same information as the two graphs above it, but tells the story in a different way that can offer further insight regarding its behavior. We can see fairly reasonable dispersion out to 40 degrees, and outside of that the response becomes quite a bit more uneven. As seen on the other horizontal dispersion graphs, 20 degrees to 30 degrees maintains the smoothest response from these angles. As we move up the frequencies, we see a tightening of dispersion until we hit 6 kHz where we encounter a flare up of acoustic energy, which rapidly recedes again after 10 kHz. The 6 kHz irregularity is more evidence of the cone breakup to be certain, but it isn’t so severe as to make the speaker extraordinarily bright. Those who want a bit more high frequency detail would be advised to listen on the direct axis of the Air Motion speakers, but, as mentioned above, those who want a less forward sound would be better off at a 20 to 30 degree angle off direct axis.

 

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Monoprice Air Motion Cinema 5 Bookshelf Speakers vertical frequency response +/-90 degrees from axis: 3D view 

The above graph exhibits the Air Motion’s vertical response. This might look rough, but it isn’t nearly as important as the horizontal response. In this graph, we see things are going fine until 3 kHz where lobing nulls are created by the woofer and tweeter cancelling each other out off of the direct axis. Very few speakers with separately placed drivers on a vertical plane (ie. most speakers) have a pretty vertical response off of the direct axis. If we look closely off axis above 6 kHz, we see some comb filtering develop about 60 degrees off axis above 6 kHz. This would be a product of the tweeter itself, perhaps an inherent quality of AMT designs- but this is simply an interesting little artifact in the data, and it will not adversely affect the sound unless the listener is strangely positioned more than 60 degrees above or below the tweeter. The overall message of this graph is that, as with every other conventional speaker, the Air Motion speakers are best listened to at an ear height level with the tweeters.

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Monoprice Air Motion Cinema 5 Bookshelf Speakers Electrical Impedance and Phase 

The Air Motion Cinema 5 speakers impedance profile shows it to be a very friendly speaker to any amplifier. At no point does the impedance dip below 7 ohms, and all the steep phase angles happen at high impedance points. These speakers do not need a heavy-duty amplifier at all, and even an entry-level AVR could run them easily. The Air Motions easily qualify for the 8-ohm rating they are specified at by the manufacturer. With regards to their sensitivity, I measured them to be 84.9 dB sensitive for 2.83v at 1 meter. They are specified by Monoprice to be 87 dB sensitive, but Monoprice does not say if that is 1 watt or 2.83v or the conditions that sensitivity spec was measured at (ie. in-room or anechoic). 84.9 dB is very typical for this type of design and is not abnormally low. Any conventional AVR or amplifier should be able to drive them to very loud volumes without much problem. By their maximum rated amplification load of 100 watts RMS, they should be able to hit 105 dB, which will be more than loud enough for most people in moderately sized rooms.

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Monoprice Air Motion Center Channel Speaker horizontal frequency response +/-90 degrees from axis: 3D view

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Monoprice Air Motion Center Channel Speaker horizontal frequency response +/-90 degrees from axis: 2D view

The above graphs depict the Air Motion Center Channel Speaker’s horizontal response. One thing to note is, while the 5 kHz to 10 kHz range on axis is not perfectly smooth, it is much smoother than the Cinema 5 bookshelf speakers. Overall, this bears a flatter response on axis then the Air Motion bookshelf speakers. As with their bookshelf counterparts, the dispersion diminishes rapidly after 12 kHz. One significant difference is the 500 Hz to 2 kHz dip off axis that occurs past 40 degrees. In an acoustically lively room, that may give this speaker a more forward character, since the 2 kHz to 5 kHz region has a wider dispersion. This off-axis dip may be due to the woofers interfering with each other. A more accurate design may simply been to have only used one woofer, but Monoprice has followed convention, since a center speaker with only one woofer might have raised some eyebrows simply for defying the norm, and sales would have suffered as a result. Imperfect though the horizontal dispersion might be, I didn’t hear any serious problems with the Air Motion Center Speaker in my time with them, although I only listened to them on the direct axis. The additional woofer does provide more output so we feel it's a good trade off anyways.

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Monoprice Air Motion Center Channel Speaker Electrical Impedance and Phase

Our own impedance measurement curve looks to be slightly more benign than the impedance graph on the product page for the Air Motion center. This speaker is listed as an 8-ohm nominal speaker in Monoprice’s product specs, which seems to be fair, although there is a dip that nearly touches 4 ohms from 130 Hz to 200 Hz, clearly due to the two woofers being wired in parallel circuit. The phase angle in that region isn’t the friendliest either, however, it occurs in such a narrow band that no amplifier should have problems with that, unless the user blasted test tone in that region specifically. The dips below 80 Hz shouldn’t be of concern since this speaker is unlikely to be run much below that point in most systems employing bass management. Sensitivity was tested at 89.3 dB for 2.83v at 1 meter, in a rare instance of sensitivity measuring higher than manufacturer’s specs.

 

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Recent Forum Posts:

panteragstk posts on May 16, 2017 01:57
Pogre, post: 1187468, member: 79914
Ah, so there are distinct differences. I wish brick and mortar stores were still around for hifi audio. I'd love to get out and listen to more.

They are, just depends on where you are…and if you are willing to drive.
Pogre posts on May 15, 2017 18:55
shadyJ, post: 1187452, member: 20472
Hey Pogre,

AMTs and ribbon tweeters are not the same at all, at least in design. AMTs use a folded membrane, and it collapses and expands the folds to squeeze air in and out of these folds. It does so at a frequency determined by the voltage signal. Ribbon tweeters oscillates a light film back and forth as a whole. AMT tweeters tend to be more robust, but they can range in quality from good to blah. I have heard very good AMTs and also very good ribbon tweeters.
Ah, so there are distinct differences. I wish brick and mortar stores were still around for hifi audio. I'd love to get out and listen to more.
shadyJ posts on May 15, 2017 17:52
Pogre, post: 1187439, member: 79914
How does the AMT tweeter compare to a Raal? I have very little experience listening to ribbon tweeters.
Hey Pogre,

AMTs and ribbon tweeters are not the same at all, at least in design. AMTs use a folded membrane, and it collapses and expands the folds to squeeze air in and out of these folds. It does so at a frequency determined by the voltage signal. Ribbon tweeters oscillates a light film back and forth as a whole. AMT tweeters tend to be more robust, but they can range in quality from good to blah. I have heard very good AMTs and also very good ribbon tweeters.
zieglj01 posts on May 15, 2017 17:32
They look like they have potential, however for now I will wait and see if they improve the tweeter response. First order on the tweeter at this price point disturbs me.
Pogre posts on May 15, 2017 16:55
How does the AMT tweeter compare to a Raal? I have very little experience listening to ribbon tweeters.
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