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How Bad are those MTM Center Speakers in Practice in Reality? Revel C25 Content Inside

Do we objectively make too much of horizontal MTM designs in real-world applications?

  • Yep

    Votes: 9 36.0%
  • Nope

    Votes: 16 64.0%

  • Total voters
    25

Steve Dallas

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As I read through the reviews of 2 way MTM center channel speakers and contemplate their dismal horizontal directivity in context with the application of the Revel C25 in my media room, I cannot help but wonder how much it matters and whether we are making too much of it. I love audio science, but I love practical application perhaps a bit more.

In this thread, I will throw out a bunch of measurements of my real-world application of such a speaker (Revel Concerta2 C25 reviewed here) for contemplation and discussion.

Starting with the room... It is absolutely terrible, but it is what I have to work with. It is nearly a cube at nearly 13' x 13' x 10.5'. I did the best I could with it in terms of layout, and I treated it with tasteful broadband absorption to make up for some of its deficiencies. This is how it is laid out, although the sofa ended up ~1' back from where depicted due to WAF opinion:

Room Designs.png



Here is the AMROC for the room:

AMROC for Media Room.PNG



Here are standard and wide angle photos (with dog butt where appropriate):

20201224_125259.jpg



20201224_125317.jpg


If we invert the listener triangle shown in the first diagram and apply measurements, we have 84" to the center listener's center headspace, 87" to each side listener's headspace, 48" between the centers of the side listeners' headspaces, and a dispersion angle of ~32 degrees.

To measure the response of the center channel speaker, I plugged the left channel speaker lead into the center speaker, then plugged my laptop into the Peachtree Nova 300 via USB. I used REW to take sweeps of the left channel only, followed by RTA measurements using the MMM with unfiltered pink noise.

Let's start by looking at the center position sweep and what it tells us about the speaker and the room:

Revel C25 Center Position Sweep Frequency Response.png


Revel C25 Center Position Sweep Reverb Time.png


Revel C25 Center Position Sweep Waterfall.png


My goal in treating this room was to achieve fairly even decay averaging around 300ms, and I missed that by about 50ms, which is something I can adjust, but it otherwise looks decent for what it is.

The center seating position sweep is less than ideal to be sure. Here it is again compared to the left and right seating positions:

Revel C25 LCR Sweeps Positions Overlay.png


That looks terrible--especially against my Harman-ish target. Judging by the sweeps, a listener definitely wants to be in the center seat.

Much of the over-brightness is explained by table bounce, which has to be there due to having children and dogs in the house. Fortunately, there is not usually much useful content up there in film and television content. The rest... Well... No wonder we hate MTM horizontal designs! Maybe...

There is some good news, however. A crossover frequency of 80-100Hz is appropriate with this speaker, which is what we expect in a normal home theater. Human vocal fundamentals range from ~150 to ~1000Hz, and that range is clearly room-influenced here, although the center seating position does fare better at the dip centered at 700Hz. Above 1KHz... Who am I kidding? This is mostly bad. OK, terribly, horribly bad.

The better news is, we do not listen to sweeps at a fixed location. We listen to an excited room with many frequencies playing and reflecting and cancelling at the same time, and we move around a bit. Perhaps things get better with pink noise and the Moving Mic Method? (To measure this, I used REW's RTA to record unfiltered pink noise for ~30s or ~60 samples while moving the mic around in a ~16" headspace in each position.) (So sorry I was too lazy to make the colors match the sweeps, so you will have to read the legends.)

Revel C25 LCR MMMs Positions Overlay.png


And with 1/3 octave smoothing for legibility:

Revel C25 LCR MMMs Positions Overlay 1-3.png


Hmmm... This looks somewhat better.

That 700Hz dip is now equally experienced by every position, proving it is room-influenced. (Assume DRC up to at least 1KHz to help clean up the uneven bass.)

Above that, the center seat still experiences the flattest frequency response up to 3KHz, but the largest difference is less than 3dB at 2KHz. At the upper limit of the female human voice fundamental however, we see maybe 1.5dB difference in SPL.

We are now focusing on 1KHz to 3KHz cancellation, where only extreme fundamentals and overtones of vocals exist (except for screaming, which quickly blends across the seating positions). The rest of the human vocal spectrum is subject to the room and potentially DRC if available, which it is in my system.

The largest worrisome discrepancy is centered at 2KHz. What is there, and do the side listeners care? We care from a data POV, but do listeners actually care?

This is how Audyssey XT32 measured this speaker with 8 averages around the seating positions:

Screenshot_20220118-203506_MultEQ.jpg


Above 3KHz, it is much less accurate, but in the 1KHz to 3KHz region, it is pretty close.

If I let DRC correct this speaker up to 3KHz, do I need to obsess about less than 3dB cancellation in an area not terribly critical for dialog? What if I just let it own the whole FR? Unfortunately, I cannot measure that difference without upgrading my laptop. I very much wish I could.

What if I always get the center seat, and none of my family members care about any of this stuff?

What if my 9 year-old bounces around all over the place, and my wife falls asleep after 30 minutes of whatever we are watching?

The horizontal directivity of this speaker is not so bad in my environment that I feel terribly compelled to care much about it. If I had room, I would use an M105 or M106 in vertical orientation instead, but I do not, and this compromised design is fine for us.

Having said that, I ran the home theater without a center for a few months while waiting for the dealer to get one in stock, and NO ONE MISSED HAVING A CENTER CHANNEL SPEAKER. I had a solid phantom center image, and my family members did not notice anything missing nor care. So there is that also.

It is my opinion this objectively flawed design is perfectly, subjectively workable in my situation, and a very high percentage of people are in the same situation with similarly acceptable results.

Discuss.
 
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Holmz

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  • If the room correction is using all three positions, then on average it should be better.
    • The 2 kHz and 700 Hz would be too high or too low, but should be only half as bad as it was without.
  • The person in the middle will also be in the golden seat if the on-axis correction is perfect.
  • Whether or not the people on the sides care is person dependent.
    • Maybe ask the 9 year old?
 

thewas

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We should keep in mind though that human perception is different than a static frequency response measured by an omnidirectional microphone at the listeners position (also when MMM is used), namely we perceive more the direct sound at higher frequencies, a reason why also loudspeaker correction based on such measurements is usually problematic.
 

HooStat

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I have gone back and forth on this for a long time. If you go 2-channel, you can get active speakers and dispense with an AVR. And my family did this for years. I think it depends on the room to some degree. I think most dialog intelligibility problems are from the recording, and possibly the down-mixing, so those factors get in the way of making an evaluation too. We have had a cheap KEF Q150 for over a year to test the idea of a center and I am still not sure what I like best.
 
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Steve Dallas

Steve Dallas

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I have gone back and forth on this for a long time. If you go 2-channel, you can get active speakers and dispense with an AVR. And my family did this for years. I think it depends on the room to some degree. I think most dialog intelligibility problems are from the recording, and possibly the down-mixing, so those factors get in the way of making an evaluation too. We have had a cheap KEF Q150 for over a year to test the idea of a center and I am still not sure what I like best.

When I purchased the F206s, the dealer threw in a C205 at no charge on top of the discount I negotiated with him. As of a few months later, he was unable to deliver that speaker and offered a C25 plus $300 instead. I looked at the spins here and saw the C25 is an objectively better speaker in many ways and accepted his offer. It took a few more months for that speaker to arrive in stock.

The point is, we went at least 5 months with no center channel, and no one seemed to miss it. I, too, cannot decide whether we even need it. I am tempted to turn it off and see if anyone notices anything missing after having it turned on for 6 months or so.

On the other hand, no one seems to notice the horizontal MTM is a flawed design either. It could be that DRC is "halving" the problem area between 1KHz and 3KHz, making it a perfectly acceptable difference.

After seeing these measurements, I am tempted to let XT32 have its way with the entire FR of this speaker, instead of limiting it to 3KHz. No one has noticed it being overly bright, however, possibly due to diminished content in the upper bands in the center audio channel?
 

abdo123

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We should keep in mind though that human perception is different than a static frequency response measured by an omnidirectional microphone at the listeners position (also when MMM is used), namely we perceive more the direct sound at higher frequencies, a reason why also loudspeaker correction based on such measurements is usually problematic.
That's a strange statement to say when the direct sound has a hole in it once you sit off-axis. If anything you're making the case for not having a compromised center.

If your intention was the complete opposite then I apologize.
 

thewas

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That's a strange statement to say when the direct sound has a hole in it once you sit off-axis. If anything you're making the case for not having a compromised center.

If your intention was the complete opposite then I apologize.
You misunderstood what I wanted to say, namely that a typical non-gated omnidirectional mic measurement at the listeners position rather hides the dip of the direct sound when sitting not in the middle. Also even when sitting in the middle the reflected sound from the side walls will have the dip, while such a measurements will partially hide it.
 

nerdoldnerdith

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When I purchased the F206s, the dealer threw in a C205 at no charge on top of the discount I negotiated with him. As of a few months later, he was unable to deliver that speaker and offered a C25 plus $300 instead. I looked at the spins here and saw the C25 is an objectively better speaker in many ways and accepted his offer. It took a few more months for that speaker to arrive in stock.

The point is, we went at least 5 months with no center channel, and no one seemed to miss it. I, too, cannot decide whether we even need it. I am tempted to turn it off and see if anyone notices anything missing after having it turned on for 6 months or so.

On the other hand, no one seems to notice the horizontal MTM is a flawed design either. It could be that DRC is "halving" the problem area between 1KHz and 3KHz, making it a perfectly acceptable difference.

After seeing these measurements, I am tempted to let XT32 have its way with the entire FR of this speaker, instead of limiting it to 3KHz. No one has noticed it being overly bright, however, possibly due to diminished content in the upper bands in the center audio channel?
It looks like you could fit an M106 under your TV. That would work best as a center channel and not have the problems of the C205 or C25.
 
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Steve Dallas

Steve Dallas

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It looks like you could fit an M106 under your TV. That would work best as a center channel and not have the problems of the C205 or C25.
Although we are planning to replace the furniture in this room, and we could go lower with the equipment rack, the wife has ideas that will not accommodate a vertical bookshelf. I actually have an M105 in reserve, just in case...

However, the M105 is >14" tall. The available space is around 10" as of now, so it is not close to fitting. It might be interesting to set in place and take more measurements, however.
 

NateB

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This is super interesting! Thanks for diving into it a little further.
I'm considering moving from my stereo setup to giving surround sound an earnest attempt for once, but the center channel issue is a big sticking point.

It seems like they're reasonable functional, but it really is hard to justify buying one of these more expensive options when the design is fundamentally broken. I'm considering having a non-matching center channel, but that has its own potential issues I guess.
I wonder which tradeoff is worse? Is it better to have a center with better directivity and not matched, or have worse directivity and a matched center...

Im really hoping someone does a review of one of the cheaper kef center channels. Those look like they might be best middle ground but I don't know enough to say
 

Nwickliff

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This is super interesting! Thanks for diving into it a little further.
I'm considering moving from my stereo setup to giving surround sound an earnest attempt for once, but the center channel issue is a big sticking point.

It seems like they're reasonable functional, but it really is hard to justify buying one of these more expensive options when the design is fundamentally broken. I'm considering having a non-matching center channel, but that has its own potential issues I guess.
I wonder which tradeoff is worse? Is it better to have a center with better directivity and not matched, or have worse directivity and a matched center...

Im really hoping someone does a review of one of the cheaper kef center channels. Those look like they might be best middle ground but I don't know enough to say
I went with a KEF Q100 as my center and I'm enjoying it thus far. The LR are Klipsch RP600m's with Crossover mods. The placement alone is enough to change the timbre of the speaker, Just listen to the levels pink noise test...even the exact same speaker omit completely different tonality depending on where they are in the room. Furthermore, if your mains are MMT or MT or WMT and your center is MTM is it really a "matched" center?
 

krabapple

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View attachment 180072




If I let DRC correct this speaker up to 3KHz, do I need to obsess about less than 3dB cancellation in an area not terribly critical for dialog? What if I just let it own the whole FR? Unfortunately, I cannot measure that difference without upgrading my laptop. I very much wish I could.

What if I always get the center seat, and none of my family members care about any of this stuff?

What if my 9 year-old bounces around all over the place, and my wife falls asleep after 30 minutes of whatever we are watching?

The horizontal directivity of this speaker is not so bad in my environment that I feel terribly compelled to care much about it. If I had room, I would use an M105 or M106 in vertical orientation instead, but I do not, and this compromised design is fine for us.

Having said that, I ran the home theater without a center for a few months while waiting for the dealer to get one in stock, and NO ONE MISSED HAVING A CENTER CHANNEL SPEAKER. I had a solid phantom center image, and my family members did not notice anything missing nor care. So there is that also.

It is my opinion this objectively flawed design is perfectly, subjectively workable in my situation, and a very high percentage of people are in the same situation with similarly acceptable results.

Discuss.

Your room has similar dimensions to mine. So it's interesting to me to see how you've dealt with its acoustically suboptimal dimensions. My main LP is about where your couch center is (pre-WAF).

Perhaps the reason why no one missed the center is because you aren't sitting that far from the source, nor very far off center axis. And too maybe with the center sitting way back on the table, with the inherent table bounce, perhaps a phantom actually sounds a little better?

Couldn't you move the center to the front edge of the table when viewing, listening? (And then back when not)?

Why are there two sets of front L/R speakers?
 

Trell

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You should have a third poll option: It depends.

In my small living room I sit quite a bit off axis when slouching in the sofa on one side. Using a bookshelf improved the dialogue intelligibility.

Here is a picture of the living room and slouching in the right side corner puts me almost as far right as the front right.


1642627070076.png
 
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JonK99

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I also have this speaker as part of a Concerta2 suite (F36 front and M16 surround). It was chosen knowing the compromise involved, but 95% of the time it's just two of us on the sofa and I'm the only one who cares. On my longer term project list is to do some REW testing with the C25 stood on end on a low stand in front of my AV cabinet and angled up slightly. If that seems promising I could save an Audyssey setup for this arrangement to be used on the rare occasions I have more friends over for a "movie night" where seating on either side of the main sofa would be used.
 

sdiver68

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Ive generally come to the conclusion-

1) No 1 else in the house cares about HiFi
2) I set up for MLP only and sit there myself
3) Thus, no reason for center channel (phantom)
4) If I had a reason for center channel, it would either be a bookshelf set vertically or a 3 way horizontal.
 
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Steve Dallas

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Your room has similar dimensions to mine. So it's interesting to me to see how you've dealt with its acoustically suboptimal dimensions. My main LP is about where your couch center is (pre-WAF).

Perhaps the reason why no one missed the center is because you aren't sitting that far from the source, nor very far off center axis. And too maybe with the center sitting way back on the table, with the inherent table bounce, perhaps a phantom actually sounds a little better?

Couldn't you move the center to the front edge of the table when viewing, listening? (And then back when not)?

Why are there two sets of front L/R speakers?

I applied broadband absorbtion to the back and side walls to kill the flutter echo, help with the room modes, and bring the RT60 down to manageable levels. I may actually remove 4 panels and measure again to improve WAF and make room for whatever decorations she prefers to have rattling on the walls in there.

There are 2 sets of front L/R speakers because I took that photo when I was reviewing the roadshow pair of BMRs.

If table bounce may be helping matters, why would I want to move it to the front of the table? Also, it is piano black, therefore care must be taken to move it to avoid smudges.

I think the reason we do not miss the center when it is absent is the wide dispersion of the front pair.

I also still think the reason we do not hate the center (other than the reasons previously mentioned) is that the area of most diversion is above the fundamental of the human female voice., and we mostly focus on voices at the center location. Add to that DRC, which I have set to EQ up to 3KHz, which probably halves the difference, although I cannot measure that using the same methodology without a laptop with 5.1 capabilities.

Revel C25 LCR MMMs Positions Overlay 1-3 - Curtains.png
 
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gbrnole

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long time lurker and a first time poster. this is a well timed thread since i've been pondering the similar myself. ideally i would use a 3-way center speaker but as ever i have space limitations and WAF to contend with. differently though, and chief to my space limitations, is that i refuse to elevate my tv to make room for a vertical speaker. i'm a bit neurotic about my eyes being a particular height above the bottom of the tv.

my couch is set back 12'-6" from the center speaker and widest seating positions are 48" either side of the MLP which equates to ~plus/minus 18 degrees horizontal. as you noted we're hard pressed to find an MTM that can throw 36 degrees horizontal.

i have also resigned myself to prioritizing the MLP and diverted my attention to looking at speakers that can get the most benefit out of room correction, preferably in the sub 500hz level but i'm comfortable stretching that out to 1khz so have been spending my time digging up the center channel information for speakers that benefit the most sub 1khz with EQ that if that unicorn exists, can project up to 30 degrees total horizontal.
 

Holmz

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my couch is set back 12'-6" from the center speaker and widest seating positions are 48" either side of the MLP which equates to ~plus/minus 18 degrees horizontal. as you noted we're hard pressed to find an MTM that can throw 36 degrees horizontal.

A plot showing, say 25 degrees, is greater than +/- 18 degrees.
(I.e. You do not need to double the values as it is relative to being “off of the centerline”.)
 
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