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Discussion Starter #1 (Edited)
Monoprice Polypropylene 2-way In-Wall Speakers​


Foreword:

I recently purchased a set of the Monoprice Polyprop 2.5 way in-wall speakers to use in my garage. I chose these particular speakers because polypropylene is more tolerant of the garage environment in the long term. Since there are no real objective measurements on these speakers, I thought it worthwhile to pursue and provide them myself for those who may be curious about their real performance. Therefore, the following will be a brief objective review on the performance of the speaker as a set, focusing on linear distortion and non-linear distortion.


Note on test setup:
In-wall speakers are typically installed in a manner that results in the speaker being crowded by insulation. All of my measurements are done on a flat, open baffle to emulate that of what is the industry standard. This allows you to view the data on its own without worry of how your particular insulation will effect the results if compared to another speaker or raw driver's results. Evaluate this on its own. While everyone's experience will vary from installation to installation, you can be sure that evaluating the speakers' performance on their own using this method will permit you to draw reasonable and (most importantly) meaningful conclusions as to the performance of the speaker.


Product Information:

These speakers are distributed and sold by Monoprice.com. The product details can be found here.

Specifications
6.5〞2-WAY IN-WALL SPEAKERS

Impedance: 8 Ohms
Frequency Response: 65Hz - 20,000 Hz
Power Handling Capacity: 40 Watts Nominal, 80 Maximum
Woofer: 6.5" PolyPropalene Cone Woofer w/ 10oz Magnet and rubber surrounds.
Tweeter: 1" Titanium Silk Membrane Dome (Pivoting)
Sensitivity: 87 +/- 2db (1.0M/2.83V)
Crossover: 24dB per Octave (with -3, -6 dB Switch)
Cut-Out Dimensions: 10.71" (Length) x 7.32" (Width)
Overall Dimensions: 12" (Length) x 8.7" (Width)
Mounting Depth: 3"

Contents:
2 - 6.5" 2-way In-Wall Speaker w/ grill
1 - Installation instructions
1 - Cutout template and paint mask
1 - Grill removal tool
1 - Grill putty


Worth noting, in my opinion are the following:
  • The tweeter is positionable. You can move the tweeter and aim it pretty freely within it's housing so you can direct the sound to your choosing.
  • The tweeter employs a waveguide which helps keep the response shape very similar in every axis.
  • The tweeter has a switchable attenuation circuit with 0dB, -3dB, and -6dB as options to tailor the HF response as desired.
  • The overall size is pretty small. I've played around with a few in-wall speakers and when these showed up, they were smaller than what I had figured.
  • Installation is really, really easy.
  • The edge of the trim ring is raised approximately 0.175 inches above the speaker drivers themselves which can cause some higher frequency diffraction. Ideally, you'd want the speakers to be entirely flush with the wall/baffle so there is no edge diffraction causing filtering effects.


Photos:

 

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Small Signal Parameters Measurements and Analysis​

The following testing is done with the tweeter level at "0". The tweeter level is adjustable between this value and -3dB and -6dB.

Measured Parameters:

  • Re 7.34 Ohm
  • K 0.045
  • n 0.4
  • Cmes 529 µF
  • Lces 8.23 mH
  • Res 11.78 Ohm
  • fs 76.3 Hz
  • Qtp 1.185
  • Qms 2.986
  • Qes 1.86
  • Qts 1.146





Small Signal Analysis:

From the above measured results, you can see the load on your amplifier/AV Receiver is just under 8 ohms. The woofer Fs is measured at 76hz and the impedance curve indicates the tweeter output level is about 2-3 ohms less than that of the woofer. This may be how the passive crossover was designed; as opposed to providing an increase in output, the network is configured so the tweeter output itself is higher than the woofer but can be attenuated by as much as 6dB to better mate with the woofer and/or subjective desires.
 

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Discussion Starter #3
Frequency Response Measurements and Analysis​

The following is a conglomerate of frequency response testing. First, I'll provide the standard 2.83v/1m measurements with the grille on and the tweeter level at 0dB measuring at 0, 30 and 60 degrees. This is the baseline test. Subsequent measurements will cover comparison testing consisting of:
  1. Grill on results vs Grille off
  2. Tweeter level attenuation and effect on frequency response



Baseline Frequency Response:
Grille on, tweeter level at 0dB. 2.83v/1m.






Comparison Measurement - Grille On versus Grille Off:
Tweeter level at 0dB. 2.83v/1m.






Comparison Measurement - Tweeter Level Attenuation:
Tweeter level at 0dB, -3dB, and -6dB. 2.83v/1m.

 

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Discussion Starter #4
Harmonic Distortion

The following test is a measurement of harmonic distortion at 96dB/1m equivalent. For what it's worth, 96dB at 1 meter is pretty loud for just one speaker.

 

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Discussion Starter #5 (Edited)
Overall impressions:

Frankly, the results are about what I would expect. The frequency response is not very linear. The high Q measured in the small signal analysis above looks to be the cause of the bump in low end frequency response. While it looks bad, one could view it as a plus as it would potentially make blending with a subwoofer easier (especially if your target curve is like most people's with a boosted low end relative to the rest of the spectrum). The overall smoothness of the response is ragged above 4khz. At first glance, this appears to be very, very bad frequency response. However, if you were to employ a 120hz crossover on the low end, the bump in response down low would smooth out and the overall linearity would benefit. That said, the high frequency raggedness concerns me; especially the bump in response near 7.5khz measured at 0 and 30 degrees. This bump suggests sibilance will be an issue and a quick listen certainly confirms this is the case.

One nice feature about this speaker is it uses a mini-waveguide for the tweeter. This helps to keep the high frequency response roughly the same shape at various listening points, just lower in output. This is evidenced by the response measurements at 0, 30, and 60 degrees. Notice how, for the most part, the response of the tweeter doesn't differ significantly in each axis' measurement. This is due to the waveguide.

Getting back to the crossover, you can see these speakers have a pretty steep natural rolloff below 100hz. If your goal is home theater, you're absolutely going to need a good subwoofer (or two) to mate with these. As is, they are reasonable solutions for a budget theater but don't expect to play them low by any means.


The distortion results actually look quite good as a whole. The overall THD is kept under 3% above 200hz and is mostly all comprised of only 2nd order distortion (whereas 3rd is considered to be more problematic). 3rd order distortion is kept below 0.5% above 200hz. It's worth noting that even and odd order distortion are separated fairly well with at least a 10dB gap between 2nd and 3rd order distortion in the midrange and up to 20dB separation above the midrange. In terms of high output vs distortion, I'd say using a crossover point of 150hz would be the best way to play it safe. If you want to go down to 100hz or so, you shouldn't have serious issues but keep it in mind. I wouldn't advise crossing too far below 100hz if you plan to use these as front mains in a loud oriented setup (and as noted above, you really won't get much out of them anyway below 100hz). Use the subwoofer for what it's meant to be used for.



Final thoughts:

Basically, what I'm seeing is a speaker that has impact on the low end and brightness on the top end with a subdued midrange; making this a 'forward' sounding speaker that will grab your attention at first but may be more fatiguing toward the end of your use. You can use the tweeter level attenuation to blend the midrange and tweeter response and I would recommend trying the -3dB option. Of course, the room and final application dictate final results. For the money, these are actually really nice. I have no problem recommending them at their current selling price of $55+shipping for the pair.

- Erin
 
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