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MP-65RT Bookshelf Speaker Measurements & Conclusion

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MP Ribbon outdoor testing

The Monoprice MP-65RT speakers were measured in free-air at a height of 7.5 feet at a 1-meter distance from the microphone, and the measurements were gated at a 8.5 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 1/24 octave resolution.

MP Ribbon response curves 

Monoprice MP-65RT response curves 

The above graph shows the direct-axis frequency response and other curves that describe the speaker’s amplitude response in a number of ways. For more information about the meaning of these curves, please refer to our article Objective Loudspeaker Measurements to Predict Subjective Preferences. The feature that leaps out the most in the MP-65RT’s response is the eruption of treble that occurs above 8 kHz. That certainly explains the speaker’s brightness. We see this elevated treble in in all of the power responses but the directivity indexes are smooth in that region, and that tells us that this large treble bump happens over a wide angle around the speaker. The good news is that this rise in high-frequency response doesn’t really get significantly hot with respect to the rest of the bandwidth until 9 kHz. That means that elevated treble largely escapes most of the harmonics of human voice and musical instruments, but it will have an audible effect. The narrower spike at 3.5 kHz may have a more significant impact, since it lies in a region that is far more heavily used in recorded content, but that spike is somewhat narrow and so may look more offensive in this graph than it would be heard. What is more, we see it as a feature on the directivity index curves unlike the 8 kHz+ treble eruption, so it doesn’t occur at nearly as wide of an angle over the space around the speaker. Below that 3.5 kHz spike, the response is relatively smooth. The bottom line here, as was heard in the listening sessions, is that ribbon tweeter is working overtime!

 MP Ribbon horizontal dispersion 3D

Monoprice MP-65RT Horizontal Response +/- 100 degrees: 3D view

MP Ribbon horizontal dispersion 2D

Monoprice MP-65RT Horizontal Response +/- 100 degrees: 2D view 

The above graphs depict the MP-65RT’s horizontal dispersion out to a 100-degree angle in ten-degree increments. In these graphs we get a look at how that upper-treble swell behaves at off-axis angles. While it does calm down as we move off of direct axis, it is still considerably hotter than the lower frequency band, so listening to the MP-65RT at an off-axis angle will still make for a bright sound, especially in a more reflective, reverberant environment. To truly take that treble, it would need to be equalized. In these graphs we can see how and why the 3.5 kHz peak crops up so prevalently on the directivity index; by the time it reaches a 90-degree angle off-axis, it has pretty much inverted into a dip. Ordinarily I would assume that kind of behavior to be the result of phase summation and cancellation between the woofer and tweeter, but in this case,  it may be the result of breakup behavior of the woofer. The most neutral overall response happens at the 50-degree angle; here is a graph the 50 degree angle versus the direct axis angle for a more distinct look at those two responses:

MP Ribbon direct axis vs 50 degrees 

Monoprice MP-65RT Horizontal Response: direct-axis versus 50 degrees off-axis

At 50 degrees off-axis, the response remains very steady until 6 kHz, and the treble eruption isn’t as severe as on direct-axis.

 MP Ribbon polar map

 Monoprice MP-65RT Polar Map of Horizontal Response

The above graph shows the same information that the preceding horizontal dispersion graphs do but depict it in a way that offers new insight regarding this speakers behavior. Instead of using individual raised lines to illustrate amplitude, 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. In the polar map of the MP-65RT that excess of treble energy really looms over the rest of the response. We do see that the midrange frequency has a very nicely controlled dispersion up to 4 kHz. Something that is interesting to see is slight lobing patterns from 4 kHz to 7 kHz, as the woofer and tweeter enter into different degrees of phase at various angles and distances. These lobing patterns are inevitable when the woofer is allowed to run full-range, but they are not severe on this model.

         MP Ribbon vertical dispersion 3D

Monoprice MP-65RT Vertical Response +/- 100 degrees: 3D view

The above graph depicts the MP-65RT’s frequency response behavior on 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. The valleys that occur above and below the zero-degree axis are very common in conventional loudspeaker design. They are the result of the tweeter and woofer playing the same frequencies but out of phase, so they are not synchronous. They are usually only fully synchronous directly ahead of the speaker. The lateral response matters far more than the vertical response, since most listeners will be on roughly the same height and also since the ear is much more sensitive to side-wall reflections than floor or ceiling reflections, so the ragged response off the direct axis shouldn’t be a cause for too much concern. The tweeter itself seems to exhibit some odd lobing patterns as the angle moves off direct-axis. It also swiftly loses amplitude off direct-axis, very much unlike its horizontal response. This is all predicted by its narrow width relative to its height. The story here, as with most two-way bookshelf speakers, is that the MP-65RTs should be listened to with your ears at speaker height, not above or below the speaker.

MP Ribbon Impedance 

Monoprice MP-65RT Impedance and Phase Response

The above graphs show the electrical behavior of the MP-65RT speaker. This should be a relatively easy load for any amplifier to drive, with a minima at 6 ohms and soft phase angles at those points. All steep phase angles occur at high impedances. It can be seen that the resonant frequency of the woofer happens just under 100 Hz due to the impedance spike and sharp phase change. There are ripples in the impedance and phase curves that are evidence of cabinet resonances, and this is not surprising given the minimal cabinet construction. Monoprice specifies the MP-65RT as a 6 ohm speaker, and this is a conservative rating. I measured the sensitivity at 86.1 dB at 1 meter for 2.83v which is respectable for a sealed bookshelf speaker of this cost. That closely matches Monoprice’s spec of 87 dB for 1 watt at 1 meter. This speaker does not need a lot of power to get loud, which is good because it wouldn’t be able to handle a lot of power anyway. A 15 to 30-watt amplifier would make this speaker sing nicely.

 MP Ribbon bass response

Monoprice MP-65RT Low-frequency Response

The above graph shows the MP-65RT’s amplitude response in bass frequencies. It was captured by using groundplane measurement techniques. The bass response here is overall quite good, considering the cost of the speaker. The response above the resonant frequency near 100 Hz is relatively flat and even. The bass is slightly bumped up around resonance, but it is a mild enough rise that it should not register as ‘boomy.’ It does start to roll-off at a relatively high frequency, but it does so at a more gradual 12 dB/octave slope than what would be seen were this speaker ported. The good news about this kind of gentle slope is that it will get more reinforcement below the resonant frequency than a steep slope and so is likely to get more assistance from room gain and boundary gain. However, for content with heavy bass or deep bass, a subwoofer should be used, since that budget 6.5” woofer isn’t likely to have a lot of excursion.

Conclusion

Loudspeakers have to make compromises between price and performance. The price of the MP-65RTs is particularly low, so the compromises that it must make are particularly stiff. The question is, did Mnoprice make the right compromises to achieve its pricing? I believe that they did. It is not a perfect loudspeaker, but no loudspeaker at anywhere near its price will be perfect. The compromises it makes are many: minimal enclosure construction, the absence of a real crossover circuit, a tweeter with a sensitivity that doesn’t quite match the woofer (thus the elevated treble), lack of any aesthetic flare, relatively low power-handling, and so on.

But with a speaMP Ribbon pair 2ker like this, it is more reasonable to focus on what it does right; the MP-65RTs sound creditably good. By creditably good, I mean they can make a recording sound natural and clear, and, in the end, enjoyable. Their imaging abilities are far better than I had anticipated. Their chief audible sin is bright treble, but most systems have something like a tone control with a treble level that can bring the brightness down. Furthermore, most of that treble elevation occurs above 10 kHz which is not a heavily used range in most recorded content, so while the response in that range is lifted very high, its actual audible consequence isn’t nearly as severe as it looks on a graph. After equalization, I can attest that this speaker can sound pretty smooth.

The bottom line is that the MP-65RTs can be made to sound good. The flaws of this speaker are not insurmountable: subwoofers help, toed-in listening angles help, and some EQ on the highs help.

This is a $50 per pair speMP Ribbon grille vs no grille 6aker (as low as $40/pair on sale)  that is not just passable, but actually enjoyable in a range of recordings. For anyone who is looking for a cheap upgrade over their built-in TV sound, the MP-65RTs are a terrific choice.They can be used as a simple two-channel system in a room where it isn’t going to play at blazing levels, as desktop PC speakers, or as surround speakers, to name a few other uses. The MP-65RTs would be a good starter speaker for someone who wants to get into hi-fi but is particularly cash-strapped. It would also be a good project speaker for anyone who wanted to look at DIY improvements since the speaker’s component parts and fundamental design seem to be of high enough quality that it’s worth the effort to upgrade. Some relatively simple additions like a true crossover circuit or cabinet bracing might be enough to push these to another level of performance.

I wasn’t expecting to enjoy the MP-65RTs as much as I did, and I can say that anyone on a very low budget would do well to consider a pair. I would also say any loudspeaker enthusiasts who are not limited by budgetary concerns should listen to a pair so they can see how good a speaker can sound when made from such modest, low-cost components- I think they will be surprised.

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

  • StarStarStarStarStar — Excellent
  • StarStarStarStar — Very Good
  • StarStarStar — Good
  • StarStar — Fair
  • Star — Poor
MetricRating
Build QualityStarStarStar
AppearanceStarStarStar
Treble ExtensionStarStarStarStar
Treble SmoothnessStarStar
Midrange AccuracyStarStarStar
Bass ExtensionStarStarStar
Bass AccuracyStarStarStarStar
ImagingStarStarStarStar
Fit and FinishStarStarStar
PerformanceStarStarStarhalf-star
ValueStarStarStarStarStar
About the author:

James Larson is Audioholics' primary loudspeaker and subwoofer reviewer on account of his deep knowledge of loudspeaker functioning and performance and also his overall enthusiasm toward moving the state of audio science forward.

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Recent Forum Posts:

Gmoney posts on May 06, 2020 06:05
shadyJ, post: 1388766, member: 20472
Most tower have bass going down to around 30 to 40 Hz. The woofer sizes can still matter if you like to listen at loud levels. Towers can play deeper but they also can have more headroom versus bookshelf speakers.
Those are the reasons I choose Tower’s over bookshelf speakers.
beezer73 posts on May 06, 2020 05:38
Kingnoob, post: 1388749, member: 89775
How low of bass do the towers make? 30hz?
If you have a dedicated or good sub does front speaker woofer size matter??

Sent from my iPhone using Tapatalk


27hz….why?
shadyJ posts on May 05, 2020 23:38
Kingnoob, post: 1388749, member: 89775
How low of bass do the towers make? 30hz?
If you have a dedicated or good sub does front speaker woofer size matter??

Sent from my iPhone using Tapatalk
Most tower have bass going down to around 30 to 40 Hz. The woofer sizes can still matter if you like to listen at loud levels. Towers can play deeper but they also can have more headroom versus bookshelf speakers.
Kingnoob posts on May 05, 2020 22:27
beezer73, post: 1386038, member: 91502
Everybody does 6.5“ woofers, that's find if you use a dedicated sub. But how about some dual 8”s, some good ones with rubber surrounds and vented coils, and MUST have better crossovers than these capacitors, these are making the woofers full range, they need to have cutoffs. If you have to ad a midrange, ad a midrange. The crossover and adding a midrange only add about $5 to your bottom line, and I have no problem paying extra for them.

Dayton Audio is the only ones I know of (in my pricerange) offering dual 8“, actually it's FOUR 8”s, two are passive, but they cost twice as much as these.

How low of bass do the towers make? 30hz?
If you have a dedicated or good sub does front speaker woofer size matter??

Sent from my iPhone using Tapatalk
beezer73 posts on April 24, 2020 07:30
Everybody does 6.5“ woofers, that's find if you use a dedicated sub. But how about some dual 8”s, some good ones with rubber surrounds and vented coils, and MUST have better crossovers than these capacitors, these are making the woofers full range, they need to have cutoffs. If you have to ad a midrange, ad a midrange. The crossover and adding a midrange only add about $5 to your bottom line, and I have no problem paying extra for them.

Dayton Audio is the only ones I know of (in my pricerange) offering dual 8“, actually it's FOUR 8”s, two are passive, but they cost twice as much as these.
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