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Monoprice THX-365IW Review (In-wall Speaker)

amirm

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This is a review and detailed measurements of the Monoprice THX-365IW THX Ultra certified, 3-way in-wall speaker. It was kindly purchased new by a member and drop shipped to me for testing. It costs US $400 from the company direct.

This is the first in-wall speaker we are measuring so I had to go through some prep to test it. Between the owner and I, we decided to build a back box using 2x4 American studs. The THX-365IW is made to hold on to drywall or plywood so I built the latter from scraps I had in my woodshop:

Monoprice THX-365IW Review In-wall Speaker.jpg


As you can see, the baffle is wider than the frame I built to give it some (small) approximation of it mounting on full wall. Clearly this is a compromise as making this much bigger would make it much heavier and harder to measure. I chose to not seal the back box enclosure as in typical application of it just mounted to a well, it enjoys a very large space behind it. I figured allowing leakage would reduce the back pressure on the driver. Good or bad decision? I let you all comment. I confirmed during testing that copious amount of air was leaking around the 2x4 framing.

In addition, I made the executive decision to use the metal, magnetically attached grill as I doubt anyone would use such with exposed drivers. Speaking of which, this is a 3-way design with dual woofers:

Monoprice THX-365IW Drivers In-wall Speaker.jpg


Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in ordinary rooms yet results that can be more accurate than an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

I performed over 1000 measurement which resulted in error rate of less than 1% below 10 kHz. Above that error shot through the roof so that area of the response is likely not reliable.

Reference axis was the tweeter center. I also tested it with mid-range being such but it did not make much of a difference.

Monoprice THX-365IW Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker is and how it can be used in a room. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:

Monoprice THX-365IW Frequency Response Measurements In-wall Speaker.png


The graph is pretty unsettling at first blush. The low frequency variations though I believe due to leaky back box. Actual response in room will be different both because of that and room variations. Its level is higher than the rest of the response. Company produces its own measurements which we can compare:

1624591059650.png


Alas, they don't list any conditions as to how the test was done. The low frequency response is indicated as "near-field" which tells me is not anechoic. There is decent correlation between theirs and mine in higher frequencies including the bump around 3.5 kHz and peaking at the end.

We can look at my near-field measurements for how the crossover responds (these were done WITHOUT the grill):

Monoprice THX-365IW near field Frequency Response Measurements In-wall Speaker.png


Overall integration of drivers seems fine to me. The main issue I see is the non-flat response of the tweeter.

Back to our spin data, my measurements are 360 degrees so we have our usual graphs even though some of it such as rear wall reflections are not appropriate here:

Monoprice THX-365IW Early Window Frequency Response Measurements In-wall Speaker.png


If we took that out, the tilt would be less. The same applies to predicted in-room response:

Monoprice THX-365IW Predicted in-room Frequency Response Measurements In-wall Speaker.png


This looks good to me.

Impedance graph shows the issues in bass with respect to enclosure leakage:

Monoprice THX-365IW Impedance and phase Measurements In-wall Speaker.png


Ignoring that, I am surprised at the very low impedance of just 2.9 ohm. I compared that to the company measurements and it matches. So whatever amp you are going to use these is going to work hard as far as current delivery and may even shut down if you use these as your fronts in home theater application.

Distortion graphs look good considering the vagaries of the backbox I built:

Monoprice THX-365IW THD distortion Measurements In-wall Speaker.png


Monoprice THX-365IW THD percentage distortion Measurements In-wall Speaker.png


Beamwidth seems to be nice as delivered by the mid-range and some of the tweeter:

Monoprice THX-365IW horizontal beamwidth Measurements In-wall Speaker.png


I don't have an explanation for heavy beaming of the tweeter above 10 kHz other than it being impacted by measurement error. Anyone has other ideas?

Note that anything past 90 degrees is of no consequence in real use which is also noted in the directivity graphs:

Monoprice THX-365IW horizontal directivity Measurements In-wall Speaker.png


Figuring out what is going on in the vertical directivity plot would probably takes weeks of research. :)

Monoprice THX-365IW vertical directivity Measurements In-wall Speaker.png


I did not have time to listen to the thing. I got bruised up building the box in my unfinished wood shop so decided to just publish the measurements.

Conclusions
There are a ton of factors here relative to how we are testing and how the speaker will be used. If we take the approximation as presented, performance seems reasonable. Most in-wall speakers are built to a price and have horrible performance. Such doesn't seem to be the case here.

I am open to suggestions of how to vary or improve the setup for future testing. In-wall speakers are a huge category and would be good to have a standardized method of testing them that is reasonable, defensible and not very time consuming to build.

------------
As always, questions, comments, recommendations, etc. are welcome.

Getting killed around the house with various chores. The stupid dryer decided to break its own trim mount resulting in two hours of cursing to remove the trim, glue it back up to assemble later. By then it was hot but I had no choice to go in the yard and deal with all the damage done to our corn plants by rabbit or some other animal. The darn think ate the stock right at the ground and left 99% of the plant to die. :( Noticed racoons are going after our prized cherries so have to go out now at 8:30 pm and harvest what I can before they eat them all tonight!!!

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

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JohnBooty

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Nice. This is an exciting new avenue for reviews as you don't see many in-wall speakers seriously reviewed. Thanks for your hard work and bruises!

Performance here looks pretty decent... tolerable, at least. Maybe more relevantly, dispersion looks pretty reasonable so it should be amenable to EQ right? I assume the average customer for these is doing home theater where calibration is (hopefully) the norm.

In-wall subwoofers are a thing too, if anybody is curious like I was since bass performance seems pretty light. You can go for budget units from Monoprice or something a little more ambitious. A few years back I saw an absolutely awesome in-ceiling subwoofer install that used 24" woofers or something like that. Could probably be used to break up your kidney stones before they become a problem as well.

By then it was hot but I had no choice to go in the yard and deal with all the damage done to our corn plants by rabbit or some other animal.

I'm not a knowledgeable gardener by any means but we grow some decent tomatoes and such here in NJ. They used to be ravaged by rabbits and such. Every. Single. Year.

BUT, last year we planted marigolds between the tomato plants. Absolutely massive reduction in the number of fruits we lost to the critters. Apparently the smell of the marigolds keeps four-legged pests away. I wonder if anything like that might work for you.

(As bonus, we have a bald eagle nesting nearby this year. That should help control the rabbit population as well :p)
 
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617

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I'm not sure if the NFS is up to the task of measuring speakers like this. I do think your conclusions are mostly on the money - better than most of the garbage out there, but distortion and impedance not very impressive. Directivity is nice and wide due to the small midrange. For side and rear speakers these would be great; lots of HF energy creating ambience in the room. I'd get something better for LCR.

The baffle extension you made effectively becomes...a baffle, and I think a lot of the HF waviness you see is actually due to the diffraction. Half space speakers (and even wide baffle speakers) can avoid baffle diffraction issues at high frequencies, so I would expect this speaker to sound better than the measurements indicate. Having said that, the individual driver contributions seem to indicate a not very sophisticated crossover.

Overall tonality may not be as important in a product that will in all likelihood be powered by an AVR doing all kinds of filtering and room 'correction'.

I don't know if $400 is a lot of money for this segment; this is one of those speakers I think most people would be happy with but not really for a hifi enthusiast.
 

Francis Vaughan

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I figured allowing leakage would reduce the back pressure on the driver. Good or bad decision? I let you all comment. I confirmed during testing that copious amount of air was leaking around the 2x4 framing.

This is an interesting question. As you say, in real use, the actual drivers will very likely see leakage. I have always assumed that most in-wall speakers would be designed assuming little to no rear loading, so essentially an infinite baffle. But there will be all manner of weird issues, leakage through cracks are resistive losses. It may be a better plan to actually seal the cavity on the basis that a high quality installation would seek to to do this, and at least you are working from a known position, whereas random leakage isn't providing a usefully controlled measurement, and is thus hard to reproduce and reason about. The cavity should adhere to the standard stud-noggin spacing expected in a built to spec house. The test rig may be too short, and thus incorrectly loading the bass.

But here leakage is more of a problem as the leakage of sound is picked up by the test system, whereas in a real in-wall installation it would remain on the other side of the wall. This is going to make the measured bass response invalid. It won't be what a real world user of the speaker would see. So, this further supports sealing the cavity.

The CEA2034 results are of course not really valid. There needs to be a proper half space version of the processing applied in order to correctly predict in-room response.
 

hardisj

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Random bits:
Per the CTA-2034:




I understand building a 2m by 2m baffle isn't really feasible. Just pointing out this is indeed covered in the standard before someone comes rolling in all half-cocked.

That said, you can get an idea of the baffle step by simply calculating the frequency equal to the width of the baffle. I don't know the size "baffle" you created but I'm looking at it and estimating something around 562mm wide by 657mm tall (guesstimate). That likely explains the rolloff ~200Hz we are seeing here. I threw it in to VCAD and came up with the below for the estimation of baffle diffraction.

1624594212321.png





All that said, the size of the baffle is more important than the "sealed" aspect. The sound can't get around the baffle if it is "infinitely" large, like you would get in a room on a real wall.

FWIW, you might be better off using Klippel's baffle option and just doing a half-space measurement since a full-space, 360° isn't applicable here. Worth a shot to try it out.
 
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hardisj

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FWIW, I did a review of another monoprice in-wall speaker back in 2013 (wow... I feel even older now) for HomeTheaterShack. Might be fun to compare against the newer stuff.

My pictures aren't part of the review but you can find them, which I did via a search and have posted here.
https://www.hometheatershack.com/th...ene-2-way-in-wall-speakers.67181/#post-608615


First image turns sideways for some reason:
1624593981411.png


You can see the baffle there. I don't recall the exact size but I want to say it was close to 1.5 x 1.5 meters. That's off memory so it could be smaller or larger.


1624594025016.png



1624594034009.png



1624594057245.png



1624594066638.png




1624594072394.png



1624594106369.png


1624593955669.png
 

B4ICU

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What is different this morning from the rest of the days?
No listening!
Who cares how a speaker sounds, its all about measurements. Seriesly.
As so, No recommandation, No EQ, No verdict.
 
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amirm

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No listening!
When you become an audio reviewer, you are more than welcome to cut out a hole in your room and mount these speakers to listen.
 
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amirm

amirm

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But here leakage is more of a problem as the leakage of sound is picked up by the test system, whereas in a real in-wall installation it would remain on the other side of the wall.
It wouldn't though. Bass will cause resonances in the drywall so will transmit back.

I am wondering if a practical test setup may include rolling off the bass with 80 Hz filter. This is how they will be universally used anyway so I don't see much benefit in quantifying their performance otherwise. This would relax the requirements for bass frequency measurements, back box, etc. What say you?
 

Beershaun

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Thanks Amir for looking at in-wall speakers. @joentell recently shared a video where he was able to acquire a box for testing from a company with a set of pre-cut inserts. If you continue on this journey maybe building a big enough box that has some standard opening where you can swap in adapters for different shape an size speakers. Or maybe we can all pitch in and donate for you to have something made to spec. :)

For those of us looking to build an Atmos home theater setup we are keen to understand if there is a correctly engineered set of reasonably priced in-wall and in-ceiling options for people looking to buy 16 channels worth of speakers! trying to hang 16 Elac DBR62s will not pass my minimum aesthetic requirements much less my better half! :)
 
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amirm

amirm

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FWIW, you might be better off using Klippel's baffle option and just doing a half-space measurement since a full-space, 360° isn't applicable here. Worth a shot to try it out.
It is not "worth" a shot at 13,000 euros plus shipping! It is also rather small since it is made for driver testing, not tall in-wall speakers. I am just not seeing the value of it.
 

YSC

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Actually looked remarkable considering the “wall” you made. And though looked jagged, I believe even it’s like that irl we can’t perceive that
 
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amirm

amirm

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Thanks Amir for looking at in-wall speakers. @joentell recently shared a video where he was able to acquire a box for testing from a company with a set of pre-cut inserts. If you continue on this journey maybe building a big enough box that has some standard opening where you can swap in adapters for different shape an size speakers. Or maybe we can all pitch in and donate for you to have something made to spec. :)
Ah, let me know if you have the link. I don't think these speakers are standardized though.

I do have a CNC machine so once I have my workshop back together, I can easily cut out custom inserts. This one was done with portable tools and was crude and dirty.

Then again, messing with fixture takes time away from testing other products.
 

Francis Vaughan

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It wouldn't though. Bass will cause resonances in the drywall so will transmit back.
Yeah, that is a further complication. Even the section of wall you mount it in has that problem. Resonances are not going to have an easilly charaterised phase relationship with the forward radiation either, so it isn't going to be easy to have much luck predicting the outcomes. This was why I suggested that sealing it at least gets you a reproducible result. Any in-wall installation is going to be a bit of a crap shoot. If the measurements are at least reproducible there is something to go along with. Otherwise it becomes garbage in garbage out.

I am wondering if a practical test setup may include rolling off the bass with 80 Hz filter. This is how they will be universally used anyway so I don't see much benefit in quantifying their performance otherwise. This would relax the requirements for bass frequency measurements, back box, etc. What say you?
Yeah, I think that might be a good approach for a range of reasons. Still, I would still think about sealing the gaps, just to eliminate a variable.
 

B4ICU

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When you become an audio reviewer, you are more than welcome to cut out a hole in your room and mount these speakers to listen.

What that has to do with listening and a recommendation?
I assume no one forced you (band your hand behind your back) to test an in wall speaker.
Some fields, like HP require some fixtures. In wall speakers might need one too. If you wish to test in wall speakers, you might need some preparations. Or you may skip in wall. It is up to you.
I'm just saying, it is missing on your report. I thinks it is important.
 
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