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

amirm

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A couple of weeks ago I post the measurements of the Monoprice THX-365IW. For that, I built a leaky back wall in an attempt to approximate the actual application. Alas, that provided such messy measurements that I thought I start over using a new methodology/system. Klippel NFS has a module for measuring drivers in a baffle. It is a combination of a special baffle and different measurements system where only the surface of the baffle is scanned. I asked for an evaluation license for the module which normally costs more than 4,000 Euros. The baffle is even more expensive so I decided to build my own. First attempts were total failures as the module assumes you have their fixture and its special alignment points. I made a second try and almost succeeded:

Monoprice THX-365IW measurements.jpg


I say almost as the software performs an alignment check and complained that accuracy was not as good as it should be. It was right: it pushed the microphone into the baffle at some point. :( Still, the results are much cleaner and I thought I share this with you and make a collective decision if we need to keep going this way.

As a way of background, Klippel NFS scanner makes measurements in a semi-hemisphere. This way, it doesn't matter what radiates in the back. To the extent any of that reflects from the walls, NFS computationally eliminates it. Furthermore, since edge diffraction occurs outside of the scanned area, it is able to eliminate that as well. Fort his to work though it requires a lot of distance between the "driver" and the sides of the baffle and hence the wide width you see. The width is also dictated by the height of the in-wall speaker which is naturally much taller than what Klippel had in mind with a single round driver.

Measuring and cutting the baffle was one thing. Getting it to mount and stay stable on a 5 inch stand was another! In addition to this, you have to be mindful of any resonances in the baffle being captured and reported as part of the speaker response. You can't see the back side of my baffle but I managed to deal with these effectively as well.

Monoprice THX-365IW Measurements
Before I show you the spin graph, let's view the radiation pattern at 1 kHz so you get oriented correctly on how we are measuring:

Monoprice THX-365IW Baloon Radiation Pattern Baffle Frequency Response Measurements In-wall Sp...png


This would be looking into the left side of the baffle. All energy is naturally directed forward.

Here is our spin graph now:

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


Remarkably clean, isn't it? We just have one resonance around 3.8 kHz or so but otherwise, speaker is doing well as is the measurement scheme.

I should note that this is a much higher resolution measurement than normal by accident. I was playing around and forgot to change the chirp signal to what I normally use. So if you are processing the exported data, be mindful of this.

Back to our spin, we see perfect directivity because there is no back radiation and what is facing forward is quite broad. You can see it better in beam width:

Monoprice THX-365IW horizontal Beam width vs Frequency Response Measurements In-wall Speaker.png


And horizontal directivity:

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


Note that we are now correctly bound by ±90 degrees due to measurement scheme and how the speaker is used.

Early window response now puts the "rear wall" response right on top of the rest:

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


Predicted in-room response is very nice as well:

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


Of course the math for this is for normal speakers in rooms. The angles may need to be adjusted. I welcome our mathematicians suggesting what should be changed.

Back to directivity, here is our vertical:
Monoprice THX-365IW vertical directivity vs Frequency Response Measurements In-wall Speaker.png


Grill or no Grill; That is the Question
For these measurements, I decided to not use the grill as to get the core measurements right and not worry about its effects. Once done though, I went back and made a couple of in-room measurements with and without the metal grill:

Monoprice THX-365IW with and without grill Frequency Response Measurements In-wall Speaker.png


As expected, the effect is small. What I don't know however is whether it will impact NFS more in the way it causes diffractions.

Conclusions
The new measurement system gives us a much more close to real life results. The cost is an afternoon to build a precision baffle for every in-wall speaker to measure and thousands of dollars in software licensing. I am game pursuing this unless someone sees any serious issues here which I don't.

------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Attachments

  • Monoprice THX-365IW Baffle Wall.zip
    67.5 KB · Views: 32

Rick Sykora

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Thanks for the effort!

Not sure how many people use in-wall speakers, but certainly puts a premium on front ending the room design. So, not for me (although my wife likes). ;)
 
Last edited:

Doodski

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I imagine shipping in-wall speakers is much easier than regular box speakers. :D
 

JDS

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A couple of weeks ago I post the measurements of the Monoprice THX-365IW. For that, I built a leaky back wall in an attempt to approximate the actual application. Alas, that provided such messy measurements that I thought I start over using a new methodology/system. Klippel NFS has a module for measuring drivers in a baffle. It is a combination of a special baffle and different measurements system where only the surface of the baffle is scanned. I asked for an evaluation license for the module which normally costs more than 4,000 Euros. The baffle is even more expensive so I decided to build my own. First attempts were total failures as the module assumes you have their fixture and its special alignment points. I made a second try and almost succeeded:

View attachment 141716

I say almost as the software performs an alignment check and complained that accuracy was not as good as it should be. It was right: it pushed the microphone into the baffle at some point. :( Still, the results are much cleaner and I thought I share this with you and make a collective decision if we need to keep going this way.

As a way of background, Klippel NFS scanner makes measurements in a semi-hemisphere. This way, it doesn't matter what radiates in the back. To the extent any of that reflects from the walls, NFS computationally eliminates it. Furthermore, since edge diffraction occurs outside of the scanned area, it is able to eliminate that as well. Fort his to work though it requires a lot of distance between the "driver" and the sides of the baffle and hence the wide width you see. The width is also dictated by the height of the in-wall speaker which is naturally much taller than what Klippel had in mind with a single round driver.

Measuring and cutting the baffle was one thing. Getting it to mount and stay stable on a 5 inch stand was another! In addition to this, you have to be mindful of any resonances in the baffle being captured and reported as part of the speaker response. You can't see the back side of my baffle but I managed to deal with these effectively as well.

Monoprice THX-365IW Measurements
Before I show you the spin graph, let's view the radiation pattern at 1 kHz so you get oriented correctly on how we are measuring:

View attachment 141717

This would be looking into the left side of the baffle. All energy is naturally directed forward.

Here is our spin graph now:

View attachment 141718

Remarkably clean, isn't it? We just have one resonance around 3.8 kHz or so but otherwise, speaker is doing well as is the measurement scheme.

I should note that this is a much higher resolution measurement than normal by accident. I was playing around and forgot to change the chirp signal to what I normally use. So if you are processing the exported data, be mindful of this.

Back to our spin, we see perfect directivity because there is no back radiation and what is facing forward is quite broad. You can see it better in beam width:

View attachment 141720

And horizontal directivity:

View attachment 141721

Note that we are now correctly bound by ±90 degrees due to measurement scheme and how the speaker is used.

Early window response now puts the "rear wall" response right on top of the rest:

View attachment 141722

Predicted in-room response is very nice as well:

View attachment 141723

Of course the math for this is for normal speakers in rooms. The angles may need to be adjusted. I welcome our mathematicians suggesting what should be changed.

Back to directivity, here is our vertical:
View attachment 141724

Grill or no Grill; That is the Question
For these measurements, I decided to not use the grill as to get the core measurements right and not worry about its effects. Once done though, I went back and made a couple of in-room measurements with and without the metal grill:

View attachment 141725

As expected, the effect is small. What I don't know however is whether it will impact NFS more in the way it causes diffractions.

Conclusions
The new measurement system gives us a much more close to real life results. The cost is an afternoon to build a precision baffle for every in-wall speaker to measure and thousands of dollars in software licensing. I am game pursuing this unless someone sees any serious issues here which I don't.

------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
I set up my HT with in-wall speakers (KEF coax) for SAF reasons, so I'm happy to cheer you on from the sidelines to splurge on the software.

And I am very encouraged by the measurements you just provided. If they hold up, it would seem that in-wall can deliver some real advantages.
 

Steve Dallas

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Thanks for the effort!

Not sure how many people use in-wall soeakers, but certainly puts a premium on front ending the room design. So, not for me (although my wife likes). ;)

I use in-walls for surrounds, but I let Audyssey have its way with the whole FR, so as long as directivity is decent...
 
Last edited:

Beershaun

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Great stuff. There is a substantial cost for anyone building an Atmos ht system and in wall is definitely a path to getting astetic approval from our significant other. So knowing which are worth the money
 

DavidMcRoy

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In-wall or “soffit-mount” installation is something I‘ve seen in older recording and mastering studios but I’ve never had any personal experience with it. I’m following closely because a new house on the horizon brings such an approach into feasibility.
 
OP
amirm

amirm

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Rick Sykora

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I use in-walls for surrounds, but I let Audyssey have its way with the whole FR, so as long as directivity is decent...

yes, I can see the use for surrounds or atmos speakers, but use as mains requires more upfront planning to do well.
 

BillH

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This makes me wonder if in-wall speakers have an inherent advantage in terms of directivity, enclosure resonances, etc
 

Bear123

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This is great work, thanks Amir. And rather unique info as I don't see ANYone else publishing good data for in walls. Arguably even more important to have data like this for in walls vs box speakers as once you cut your walls and install them, your stuck with em. Can't demo like box speakers. And there are not only aesthetic advantages, but potentially big sonic advantages as well assuming the wall cavity construction doesn't cause major issues. I mean, holy cow, the horizontal dispersion is unbelievable! Talk about hearing the same thing no matter where you sit……..at least for most of the frequencies that cover almost all music i.e. below 7KHz. And no SBIR. So many wins.
 

dfuller

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In-wall or “soffit-mount” installation is something I‘ve seen in older recording and mastering studios but I’ve never had any personal experience with it. I’m following closely because a new house on the horizon brings such an approach into feasibility.
Aside from a very few, that's not really the same as these in-wall types. Those are just normal boxes in soffits. But yes, they are good, if the speakers are appropriate (must be either sealed or front ported). They essentially entirely eliminate SBIR which simplifies acoustics in the room a lot.
 

DavidMcRoy

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Aside from a very few, that's not really the same as these in-wall types. Those are just normal boxes in soffits. But yes, they are good, if the speakers are appropriate (must be either sealed or front ported). They essentially entirely eliminate SBIR which simplifies acoustics in the room a lot.

Yes, I understand.
 

Francis Vaughan

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I am game pursuing this unless someone sees any serious issues here which I don't.
Brilliant . The results speak for themselves.
I have grown to the opinion that a continuous baffle and wall with its elimination of a raft of diffraction and reflection problems is almost always going to be a superior answer. It is just too difficult in many domestic settings.
Being able to characterise these speakers in an accurate and meaningful way is going to be a big win.
Probably time for me to make another monetary contribution to the cause.
 
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