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MTM vs Bookshelf for Center Channel

luft262

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*Disclaimer:

I am a huge fan of Audio Science Review, Erin's Audio Corner, Audioholics and audio science in general. This is my no means an attempt to tell people how to do things or a critique of anyone or anything in any way. I simply want to share my dilema, research, personal experimentation and thought process. This may lead to others giving me useful advice and or learning from my successes and mistakes. Thank you for taking the time to peruse my meandering, amateur experimentation.

Background:

About a year ago I started upgrading my home theater/music system. I slowly upgraded everything starting with the mains. I replaced my Pioneer SP FS 52 Towers with Focal Aria 926's, my Polk PSW 10 Subs with SVS SB 3000's, and my Onkyo TX-NR676 with a Denon X3700H. The last piece of the puzzle was the center channel. I wanted to replace the Pioneer SP C-22 center channel. In doing my research I ran across the following Audioholics article and Erin's video.



From The Research:

After doing some research I learned that speakers with horizontally oriented drivers can suffer from off axis problems, which could be a big problem for a center speaker, because one of its main jobs is to provide clear and audible dialog to all viewers at various angles and to deliver consistent and anchored audio at the center of the TV or viewing area. Although there are many different center speaker designs the most common are MTM (mid/tweeter/mid) driver designs. From the research I learned that the best speaker design with regards to horizontal off axis audio homogeneity would be a vertical speaker design. If a vertical speaker is too tall and would force the TV too high on the wall the best horizontal design would be a W(T/M)W (woofer(tweeter/mid)woofer) design or something with a coaxial driver, such as a KEF center channel design. This is because higher frequency sound waves need to come from a single driver location not from two drivers situated horizontally from each other to avoid "cold" pockets of sounds for off axis listeners.

My Course of Action:

I had reservations about using a bookshelf speaker for my center channel as it would force me to move my TV higher or implement some sort of short bookshelf stand mount in front of the TV and I didn't want my setup to look strange. My wife was also against using a bookshelf as the center channel... The horizontal channel that matches my Aria mains happens to be an MTM design and I was worried that it would not sound great, but I was also hesitant to buy a center channel with an W(T/M)W design from a different company as the center and main speakers would not match aesthetically and I was also worried about timbre.

I decided that since I had a pair of bookshelf speakers in my office area (ELAC Debut 2.0 B6.2) and vertical speakers give a better off axis response than horizontal speakers, generally speaking, I could use one of those and test it against the Aria 900c MTM center channel to see what I might expect from a W(T/M)W designed center channel speaker from a different brand, roughly speaking. If I found a major difference I could return the Aria 900c and look elsewhere. I understand that every speaker will be different, but I didn't want to buy 3, 4, or 5 different speakers from different companies, test them out, and return all but one of them so I thought this would be a decent compromise and experiment.

I hooked up first the Aria 900c and then the ELAC Debut 2.0 and turned Audyssey off. I used REW, ASIO, and a Umik-1 to run some graphs of each center channel at 0 degrees, 10 degrees, 20, degrees, and 40 degrees off axis. 40 degrees off axis is the furthest off axis any person could posibbly sit in my living room in relation to the center channel without moving chairs, couches, or sitting on the floor. On a side note about 95% of the time plus it is only my wife and I watching TV or listening to music in our living room and almost always I am sitting directly on axis and she is about 10 degrees off axis, for what that's worth.

*Highlighted Graph Is Always The Aria 900c

Aria 900c vs ELAC Debut 2.0 Fully On Axis
1647889790159.png


Aria 900c vs ELAC Debut 2.0 10 Degrees Off Axis
1647889911352.png


Aria 900c vs ELAC Debut 2.0 20 Degrees Off Axis
1647889964620.png



Aria 900c vs ELAC Debut 2.0 40 Degrees Off Axis
1647890030630.png


1647892419942.png


1647892477207.png


Personal Conclusions:

The thing that stuck out to me the most is how much the room, more than anything else, appears to affect the results. Here we have two completely different design types from different companies and price points using different drivers and materials. The results at every angle on or off axis are similar. I wold like to see more examples of different types of speakers in room responses in various rooms. Perhaps any given room is so impactful to the sound signature that various speakers will barely make a difference? I am also surprised the results are as close as they are given that the ELAC Debut 2.0 retails for about $400 a pair and the Aria 900c is about $900. However, I would say that despite it's potentially inferior MTM design the Aria still performed slightly better in the testing. From subjective listening tests I preferred the Aria center and my wife greatly preferred the Aria, but it was not a blind test so we could both be biased. I mostly felt that voices were clearer from the Aria. I'm not sure why.

I guess I'm posting this because I spent some time on this and I thought the results might be interesting to others. I also want to opine that there is a lot going on inside of a speaker box and just because a center channel is an MTM design doesn't necessarily mean is will sound bad or that it can't be the best option for your setup. Like others I want to learn more about speaker design and have more access to graphs and information, but in my case an MTM speaker design was my best option in terms of TV placement and aesthetics. Subjectively it sounds great and objectively it appears to measure as well or better than a decent bookshelf speaker both on and off axis. I'm sure there are other examples of this as well and I'm not 100% convinced that timbre isn't a thing and matching the mains with the center isn't important. When listening to voices with the ELAC there did seem to be more of a difference from the mains, but I don't know how to measure that or if such a measurement would be possible.

If this was helpful or if you agree or disagree fell free to chime in and let me know what you think.

Thanks for reading.
 
OP
luft262

luft262

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Did you measure off-axis? Because on-axis it’s the same MTM or not.

If you didn’t measure off-axis the difference won’t be so clear (for a microphone).
Yeah, on axis, 10, 20, and 40 degrees off axis.
 

ernestcarl

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Reflections in the room could be helping elevate the off-axis performance of the 900c. While we have the individual directivity curves for the 906 as measured by Amir, we do not have it for the 900c -- so direct comparison of their anechoic off-axis directivity curves in the range specified (10-40 degrees) is not possible, yet. You could take gated measurements and/or outdoors to find out for yourself.
 
OP
luft262

luft262

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OP
luft262

luft262

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luft262

luft262

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How many people use the center channel at teh same time?
Is it just you, and the Brady Bunch, or something in between?

1,2,3,4,5,6,?
It's a good question (although I believe I answered it in my post already ;). 95% of the time plus it's just my wife and I watching. I sit in the middle of the couch, on axis, and she sits on my right about 10 degrees off axis. I understand that if sitting on axis there is no difference. I was just seeing how much of a difference off axis would make with an MTM design compared to a bookshelf and in this case it didn't appear to be much if any.
 

Holmz

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It's a good question (although I believe I answered it in my post already ;). 95% of the time plus it's just my wife and I watching. I sit in the middle of the couch, on axis, and she sits on my right about 10 degrees off axis. I understand that if sitting on axis there is no difference. I was just seeing how much of a difference off axis would make with an MTM design compared to a bookshelf and in this case it didn't appear to be much if any.

My Haus Boss and I are also the only ones to watch.

I bought a center channel, but I am 95% convinced that for you and I (and respective partners) that a 4.x.x or 6.x.x would be better than using a center channel that had any chance of a timbre mismatch.

The main point of a center channel is to get the dialogue there and anchor the sound. But it is already there in a phantom image, and you do not need it until you have people way off axis.
Combine that with the fact that many center channels do not have a good spread, means that at some budget level on is better off with 2 good L/R channels over mediocre L/C/R.

Basically I would make sure you try 2.x.x and 4.x.x before you get a center channel, and if you get one, then make sure you compare 3.x.x to 2.x.x (and/.or 5.x.x to 4.x.x or 7.x.x to 6.x.x)
I was surprised… the center channel is basically a waste of funds without listeners way off axis.

Or how do you know if you even need a center channel?
 
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luft262

luft262

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My Haus Boss and I are also the only ones to watch.

I bought a center channel, but I am 95% convinced that for you and I (and respective partners) that a 4.x.x or 6.x.x would be better than using a center channel that had any chance of a timbre mismatch.

The main point of a center channel is to get the dialogue there and anchor the sound. But it is already there in a phantom image, and you do not need it until you have people way off axis.
Combine that with the fact that many center channels do not have a good spread, means that at some budget level on is better off with 2 good L/R channels over mediocre L/C/R.

Basically I would make sure you try 2.x.x and 4.x.x before you get a center channel, and if you get one, then make sure you compare 3.x.x to 2.x.x (and/.or 5.x.x to 4.x.x or 7.x.x to 6.x.x)
I was surprised… the center channel is basically a waste of funds without listeners way off axis.

Or how do you know if you even need a center channel?
Before getting the center channel I was mostly using a 4.1 system for a few months. I agree that a phantom center is an option and a good one at that. I think I will put the mic in the center and run a frequency response graph with just the mains vs the mains and the center. I'm not sure if that would completely represent what to expect in terms of dialog in a movie, though. In my subjective opinion having the center channel makes dialog much easier and clearer. My wife noticed an immediate difference vs just using the mains. I'm not sure why, IMHO, the phantom center did not produce as good of sound for movies, especially in terms of dialog, but I am of the opinion that the most important piece of any system are the mains, then probably the subs, then the center, then the quality of the receiver (assuming basic functionality has been met), and last, but not least the surrounds.
 

Holmz

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Before getting the center channel I was mostly using a 4.1 system for a few months. I agree that a phantom center is an option and a good one at that. I think I will put the mic in the center and run a frequency response graph with just the mains vs the mains and the center. I'm not sure if that would completely represent what to expect in terms of dialog in a movie, though. In my subjective opinion having the center channel makes dialog much easier and clearer. My wife noticed an immediate difference vs just using the mains. I'm not sure why, IMHO, the phantom center did not produce as good of sound for movies, especially in terms of dialog, but I am of the opinion that the most important piece of any system are the mains, then probably the subs, then the center, then the quality of the receiver (assuming basic functionality has been met), and last, but not least the surrounds.

Thanks for the feedback @luft262 .
The whole reason I got the center channel for the Haus-Boss and the dialogue.

Now that I got the cable and connectors, I can get it wired up and try for myself.
 
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luft262

luft262

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luft262

luft262

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When I try to attach that file it doesn't let me. It doesn't show up as a supported file time. Not sure if there is a work around. Sorry.
 

F14B

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*Disclaimer:

I am a huge fan of Audio Science Review, Erin's Audio Corner, Audioholics and audio science in general. This is my no means an attempt to tell people how to do things or a critique of anyone or anything in any way. I simply want to share my dilema, research, personal experimentation and thought process. This may lead to others giving me useful advice and or learning from my successes and mistakes. Thank you for taking the time to peruse my meandering, amateur experimentation.

Background:

About a year ago I started upgrading my home theater/music system. I slowly upgraded everything starting with the mains. I replaced my Pioneer SP FS 52 Towers with Focal Aria 926's, my Polk PSW 10 Subs with SVS SB 3000's, and my Onkyo TX-NR676 with a Denon X3700H. The last piece of the puzzle was the center channel. I wanted to replace the Pioneer SP C-22 center channel. In doing my research I ran across the following Audioholics article and Erin's video.



From The Research:

After doing some research I learned that speakers with horizontally oriented drivers can suffer from off axis problems, which could be a big problem for a center speaker, because one of its main jobs is to provide clear and audible dialog to all viewers at various angles and to deliver consistent and anchored audio at the center of the TV or viewing area. Although there are many different center speaker designs the most common are MTM (mid/tweeter/mid) driver designs. From the research I learned that the best speaker design with regards to horizontal off axis audio homogeneity would be a vertical speaker design. If a vertical speaker is too tall and would force the TV too high on the wall the best horizontal design would be a W(T/M)W (woofer(tweeter/mid)woofer) design or something with a coaxial driver, such as a KEF center channel design. This is because higher frequency sound waves need to come from a single driver location not from two drivers situated horizontally from each other to avoid "cold" pockets of sounds for off axis listeners.

My Course of Action:

I had reservations about using a bookshelf speaker for my center channel as it would force me to move my TV higher or implement some sort of short bookshelf stand mount in front of the TV and I didn't want my setup to look strange. My wife was also against using a bookshelf as the center channel... The horizontal channel that matches my Aria mains happens to be an MTM design and I was worried that it would not sound great, but I was also hesitant to buy a center channel with an W(T/M)W design from a different company as the center and main speakers would not match aesthetically and I was also worried about timbre.

I decided that since I had a pair of bookshelf speakers in my office area (ELAC Debut 2.0 B6.2) and vertical speakers give a better off axis response than horizontal speakers, generally speaking, I could use one of those and test it against the Aria 900c MTM center channel to see what I might expect from a W(T/M)W designed center channel speaker from a different brand, roughly speaking. If I found a major difference I could return the Aria 900c and look elsewhere. I understand that every speaker will be different, but I didn't want to buy 3, 4, or 5 different speakers from different companies, test them out, and return all but one of them so I thought this would be a decent compromise and experiment.

I hooked up first the Aria 900c and then the ELAC Debut 2.0 and turned Audyssey off. I used REW, ASIO, and a Umik-1 to run some graphs of each center channel at 0 degrees, 10 degrees, 20, degrees, and 40 degrees off axis. 40 degrees off axis is the furthest off axis any person could posibbly sit in my living room in relation to the center channel without moving chairs, couches, or sitting on the floor. On a side note about 95% of the time plus it is only my wife and I watching TV or listening to music in our living room and almost always I am sitting directly on axis and she is about 10 degrees off axis, for what that's worth.

*Highlighted Graph Is Always The Aria 900c

Aria 900c vs ELAC Debut 2.0 Fully On Axis
View attachment 194207

Aria 900c vs ELAC Debut 2.0 10 Degrees Off Axis
View attachment 194208

Aria 900c vs ELAC Debut 2.0 20 Degrees Off Axis
View attachment 194209


Aria 900c vs ELAC Debut 2.0 40 Degrees Off Axis
View attachment 194210

View attachment 194216

View attachment 194217

Personal Conclusions:

The thing that stuck out to me the most is how much the room, more than anything else, appears to affect the results. Here we have two completely different design types from different companies and price points using different drivers and materials. The results at every angle on or off axis are similar. I wold like to see more examples of different types of speakers in room responses in various rooms. Perhaps any given room is so impactful to the sound signature that various speakers will barely make a difference? I am also surprised the results are as close as they are given that the ELAC Debut 2.0 retails for about $400 a pair and the Aria 900c is about $900. However, I would say that despite it's potentially inferior MTM design the Aria still performed slightly better in the testing. From subjective listening tests I preferred the Aria center and my wife greatly preferred the Aria, but it was not a blind test so we could both be biased. I mostly felt that voices were clearer from the Aria. I'm not sure why.

I guess I'm posting this because I spent some time on this and I thought the results might be interesting to others. I also want to opine that there is a lot going on inside of a speaker box and just because a center channel is an MTM design doesn't necessarily mean is will sound bad or that it can't be the best option for your setup. Like others I want to learn more about speaker design and have more access to graphs and information, but in my case an MTM speaker design was my best option in terms of TV placement and aesthetics. Subjectively it sounds great and objectively it appears to measure as well or better than a decent bookshelf speaker both on and off axis. I'm sure there are other examples of this as well and I'm not 100% convinced that timbre isn't a thing and matching the mains with the center isn't important. When listening to voices with the ELAC there did seem to be more of a difference from the mains, but I don't know how to measure that or if such a measurement would be possible.

If this was helpful or if you agree or disagree fell free to chime in and let me know what you think.

Thanks for reading.


Horizontal 2-way MTM center channel designs are one of my most hated things in HT. Full-stop, it's a terrible utilization of a great design (D'Appolito).

Vance Dickason detailed the numerous errors with utilizing this physical-electrical arrangement many years ago in his Loudspeaker Design Cookbook.

Your Elac uses one method (physically raising the tweeter) of minimizing the off-axis combing involved with horizontal mtm's. That isn't to minimize your point about room interactions. Particularly where it concerns your average home listening environment. However, in an acoustically well designed room, I think your measurements differences wouldn't be quite so suttle of axis.

Personally, I prefer identical speakers for the five main channels because more uniform speaker timbre and tonality are more immersive imo.
 

valerianf

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The measurement of the high frequencies respons of the Aria are far better than the one from the Elac.
Did you tried to configure the center to Small?
It will enlarge your center sound field as the Phantom center will add strength to the center speaker.
This will happen only if the passive crossovers do not induce too much phase rotation.

Regarding the center speaker technology, I strongly recommend to test a speaker designed with a coaxial tweeter and midrange.
It can be designed with 2 small woofers on each side to increase the low frequencies.
 

Spennis

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What about using a bookshelf speaker oriented horizontally? I'm wondering because all high-end center channels that would make a good match with my front towers are too big to fit in or on top of my media cabinet. There are however small high-end bookshelf speakers (which I use as surrounds) that are a great match. Has anyone tried this?
 

Vacceo

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What about using a bookshelf speaker oriented horizontally? I'm wondering because all high-end center channels that would make a good match with my front towers are too big to fit in or on top of my media cabinet. There are however small high-end bookshelf speakers (which I use as surrounds) that are a great match. Has anyone tried this?
Erin did that in his review of the KEF R2c and you can check the data. Unsurpsisingly, the speaker does not change much in response; that´s the nature of concentric-coaxial drivers, as they provide a fairly symetric dispersion on the vertical and horizontal axis.

That said, I wonder how the Perlisten center speakers work. They provide the data, but I´d rather see tests done by an outise source. Their driver array with a vary small mid, tweeter and mid does seem to offer a quite different result than a conventional MTM. In fact, I´m quite surprised the Perlistens show a frequency graph so similar to a KEF...
 
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