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

[Rick Sykora]

I can source a lot of them at dealer cost because this is a category of products for which Madrona is a dealer (we do custom installs of electronics).

May be a better differentiator for the Madrona brand then.

Since the target market is more of pro one, might be able to do testing as a subscription service and use ASR to tease one every now and then. May be a funding model that gets you some paid help too.

 

[eriksson]

Thanks Amir, that's interesting. I am a bit sceptical, or perhaps confused would be better description: We take $400 in wall speaker and stick it into a piece of plywood and it measures like good (more expensive) bookshelf speaker!?

Did you do listening test?

 

[617]

Thanks Amir, that's interesting. I am a bit sceptical, or perhaps confused would be better description: We take $400 in wall speaker and stick it into a piece of plywood and it measures like good (more expensive) bookshelf speaker!?

Did you do listening test?

The reason bookshelf stand mount speakers are small boxes on pedestals is due to convention and economy. Integrating speakers architecturally has serious merit from a sound perspective.

The wall acts like a 180 degree waveguide and a lot of diffraction is eliminated. Baffle step doesn't happen so crossover design is potentially a bit simpler. Speaker is radiating into half space so bass is 6db more efficient (never that simple of course).

Genelec makes a line of in-walls with gentle waveguides and a subwoofer which occupies an entire stud cavity. I would love to see that system in action. Genelec also makes soffit mounted systems for recording studios.

 

[DavidMcRoy]

Not only older. Every purpose built studio has a soffit mount main speaker. It is just that not many new studios are built these days.

Well, not “every.” That’s why I chose my language carefully.

 

[eriksson]

The reason bookshelf stand mount speakers are small boxes on pedestals is due to convention and economy. Integrating speakers architecturally has serious merit from a sound perspective.
[...]

Sure, but I wouldn't expect in-wall speakers to sound good if I put them in a something like 50x50cm piece of freestanding plywood, instead of a wall. I guess my confusion boils down to - does Amirs measurement reflect what the speaker does when in-wall? If I understand correctly the graphs we are seeing are calculated interpretation of measured data. I am wondering if Amir heard the same nice freq. response his Klippel gear is showing.

However, if something is wrong with the setup it would be strange to get good test results! Still, before testing many in-wall speakers I would be tempted to actually built a wall or create a hole in existing one for a speaker or two, and compare measurements from that setup with the plywood fixture.

 

[Francis Vaughan]

I guess my confusion boils down to - does Amirs measurement reflect what the speaker does when in-wall?

It does up to the limitations of the extent of the baffle. So bass radiation becomes less accurate. But that is no different to a boxed speaker. Bass response in both cases becomes controlled by the room. That is why bass management is so important. However an in wall speaker is less affected by the room so in terms of measurements reflecting reality what Amir shows is likely closer to reality than a box speaker when transferred to a real room.

 

[Francis Vaughan]

I do...

Do you hear the individual panels as defined by the studs or the entire wall? Stud walls will cheerfully vibrate as a whole and this action has important effects on the overall room response. Sometimes useful and sometimes really bad. Ceilings can be even worse. The elasticity of the studs and the mass of the wall being the defining properties. Interior walls behind the worst. For an in wall speaker I was referring to the single panel defined by the studs and noggings that the speaker is mounted in. No doubt it will be driven by the speaker but only the face of the effective box rather than the entire wall.
OTOH my own DIY in-wall speaker designs have their own braced enclosure separate to the wall. How much of a difference this makes I don’t know. I do it because I can. But the available depth is always a problem.

 

[amirm]

Thanks Amir, that's interesting. I am a bit sceptical, or perhaps confused would be better description: We take $400 in wall speaker and stick it into a piece of plywood and it measures like good (more expensive) bookshelf speaker!?

Did you do listening test?

I haven't yet since I don't have a setup to mount them on a wall. I will see if I can do something....

 

[Chromatischism]

Do you hear the individual panels as defined by the studs or the entire wall? Stud walls will cheerfully vibrate as a whole and this action has important effects on the overall room response. Sometimes useful and sometimes really bad. Ceilings can be even worse. The elasticity of the studs and the mass of the wall being the defining properties. Interior walls behind the worst. For an in wall speaker I was referring to the single panel defined by the studs and noggings that the speaker is mounted in. No doubt it will be driven by the speaker but only the face of the effective box rather than the entire wall.
OTOH my own DIY in-wall speaker designs have their own braced enclosure separate to the wall. How much of a difference this makes I don’t know. I do it because I can. But the available depth is always a problem.

It's hard to say what it is, but when I'm running Audyssey sweeps with the smartphone and I step just out of the room and to the other side of the wall, the drywall doesn't make pretty sounds. It's hard to describe and I can't say whether I can hear that at my seat. Maybe not. It's probably lost in the noise of reflections etc.

 

[redshift]

Can someone explain why resonances are not more of an issue? I would assume most are installing into drywall and resonances would be a huge deal. Also the cavity is often shallow (back reflections) and it's volume could be limited by fire breaks in the walls (horizontal 2x4 between studs).

My layman’s thoughts regarding this.

The inwall speaker suffers from the relatively thin materials (in most walls) in its cavity as it will cause the bass driver to vibrate the tweeter as it will shove the wall around and cause Doppler shifts.

This could be mediated by adding mass to either the inwall speaker or surrounding wall. Perhaps adding some internal bracing could mediate that as well. However, I’m not sure stiffness is the only way to go, but rather increased stiffness, perhaps additional damping and mass.

Sort of like stealth fighter jets uses MW dampening panels on the skin of the airframe to make the energy from Team Reds radars dissipate in that material.

 

[bigjacko]

My layman’s thoughts regarding this.

The inwall speaker suffers from the relatively thin materials (in most walls) in its cavity as it will cause the bass driver to vibrate the tweeter as it will shove the wall around and cause Doppler shifts.

This could be mediated by adding mass to either the inwall speaker or surrounding wall. Perhaps adding some internal bracing could mediate that as well. However, I’m not sure stiffness is the only way to go, but rather increased stiffness, perhaps additional damping and mass.

Sort of like stealth fighter jets uses MW dampening panels on the skin of the airframe to make the energy from Team Reds radars dissipate in that material.

I have read some threads on box construction and CLD. I think the conclusion is for low frequency increase stiffness is better, at high frequency increase mass is better, at resonance frequency damping is better.

 

[bigjacko]

The reason the speaker measured here has such a wide directivity well into the upper mids is simply that there isn't a baffle edge reflecting the energy back. What you see is the natural directivity and response of the driver.

I don't really understand this part. Can you please elaborate on why reflecting energy back will cause narrow directivity? What is the reason behind it? Thanks in advance.

 

[GWolfman]

I am game pursuing this unless someone sees any serious issues here which I don't.

Your poor microphone!

Have you figured out how to prevent it from running into your baffle/wall?

 

[amirm]

Have you figured out how to prevent it from running into your baffle/wall?

I have a guess as to the cause. Will troubleshoot on the next one I measure.

 

[redshift]

I have read some threads on box construction and CLD. I think the conclusion is for low frequency increase stiffness is better, at high frequency increase mass is better, at resonance frequency damping is better.

That seems reasonable since the inertia of the bass driver is rather large shoving the wall around instead of creating lovely sound pressure waves, with the tweeter suffering from whatever shenanigans from the bass driver as Doppler shift, due to short wavelength and a “cabinet” that “flaps” around. Then some (resistive) dampening (in-wall) to cancel zeros in the room causing some bass to be “sucked” out.

Shopping list (gym plates for some mass):

In-wall Dampening (3M bitumen):

And some braces

(Yes, I’m the worlds worst and bodgiest speaker designer)

I’m sure a well-designed mechanical all-pass filter with a nice Q factor for that critically damped step response would sort out most of that in a hurry? An Atkinson-style accelerometer would sort that out in a hurry?

In walls are slick and discreet. I can imagine that in a competently executed setup, the lovey sounds just appears out of nowhere.

 

[redshift]

One can not argue it is quite slick with inwalls.

 

[Francis Vaughan]

I don't really understand this part. Can you please elaborate on why reflecting energy back will cause narrow directivity? What is the reason behind it? Thanks in advance.

It is messy. At the frequencies we are concerned about here, the wavelengths are still not too small. The edge of the baffle is a step and the sudden impedance change at the step causes some of the wave to radiate out, as if the edge itself was radiating. So in the listening position you see some energy coming not just from the driver, but from the baffle edge. So (handwaving furiously, and I'm not taking phase into account here) you can imagine that the extent of the driver becomes effectively wider. This effect changes with wavelength of course. Which is why we see ripples and oddities in the polars at these wavelengths as well. But without the presence of the baffle edge there is no diffraction effect, and the effective width of the driver is defined by the driver, not the box. As the wavelength gets smaller things get more complex. Eventually the driver becomes directive enough by itself that the baffle ceases to matter.
With a large extent baffle clearly eventually a boundary is reached, but this (ideally) is the room corner, or some other boundary, one that is much less well defined than the cabinet edge. So effects on directivity are lost into the morass of general room reflections.

 

[moonlight rainbow dream]

I think I read somewhere that this “elephants ear” takes care of early reflections of the back wall that otherwise causes distortion.

Not sure if this is relevant with infinite baffle / in wall designs.

In-wall = no SBIR effects from the "rear" wall (I prefer front wall)

On-wall = you still have SBIR due to the distance from the driver to the rear wall, but it is pushed up higher in frequency such that you can use relatively thin absorption panels to negate the effect. I think this is the strategy shown in your photo

 

[hex168]

Why in-wall, when you can go on-wall for the practicality of moving and measuring the speaker before you bolt it on the wall?

(Shameless Carlsson plug coming)
View attachment 141739

FR in the listening position (no EQ):
View attachment 141741

Details explained in:
https://www-carlssonkult-se.transla...x_tr_tl=en&_x_tr_hl=sv&_x_tr_pto=ajax,nv,elem

Stig Carlsson’s ‘ortho acoustic’ speaker design principles has a (well deserved?) cult status in Sweden.

I haven’t seen (much) measurements and listening reviews on ASR of unconventional speaker designs, as in ‘not-a-box-on-the-floor-some-distance-from-the-walls’.

Reminds me of:
http://directacoustics.com/
Winslow Burhoe's design.

 

[redshift]

In-wall = no SBIR effects from the "rear" wall (I prefer front wall)

On-wall = you still have SBIR due to the distance from the driver to the rear wall, but it is pushed up higher in frequency such that you can use relatively thin absorption panels to negate the effect. I think this is the strategy shown in your photo

Yes, I consider it an impedance mismatch between the room and speaker. The dampener panel outside and flow resistance internally in the speaker provides resistance that moves the poles (standing waves) and zeros (cancellations) to a more favorable region. That is probably why these small cabinets can deliver bass to 34Hz in a 16L volume.

It doesn’t exactly gives itself off as a boomy and “uneven” speaker when I shove some frequency sweeps and electronica through them (without the panels).