Time for some science

[davef]

I have seen a lot of discussion about horizontally positioned MTM centers, with many consumers pointing to off-axis lobing issues that are clearly revealed in contour plots.

Contour plots, as generated by the Kippel NFS, are true anechoic measurements. They display each *individual* off-axis angle and indicate the amount of amplitude change using colors. They are a useful tool for a quick examination of the overall directivity of a speaker.

The problem is that they do not represent what we hear. We do not hear individual off-axis responses. For example, at 20 degrees off-axis, we do not just hear the response at 20-degrees, we hear a weighted summation of all of the off-axis angles.

Below is the vertical contour plot of the 340SE2, which would be the horizontal contour plot of the same speaker when positioned horizontally.


2616

You will note the frequency range of lobing is mostly between 800Hz to 2.8kHz. The contour plot shows this area being quite messy - to the inexperienced, it simply looks horrible.

But how does this translate into what we are hearing? As I mentioned above, we hear a summation of all off-axis angles, we do not hear a single angle.

Below is a comparison between the on-axis in-room response of our CMT-340SE2 center and in-room response of the same speaker with the mic at 20 degrees to the right. Microphone is at ear-level, positioned 8 ½ feet back from the center, with the center speaker positioned as most would place it. The mic was then moved over to the right by exactly 3 feet (which translates to an off-axis horizontal angle of 20 degrees)

I could not move the mic further to the right, as it gets much too close to that sidewall, which has a far more dramatic effect on the response than lobing would ever cause.


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Blue trace is on-axis, brown trace is the 20-degree measurement. BTW, that on-axis in-room response for a center looks fantastic and does indeed closely mirror the predicted in-room response of the 340SE2 center.

*Ignore the response below 300Hz as below this frequency, the response is dominated by room modes.

You will note that the frequency range of the off-axis lobing was well represented in the contour plot, as the off-axis response shows a dip in that same range. That dip is ~ 3dB. When you factor in that most rooms will create +/- 10 dB peaks and dips, actual audibility of this 3dB dip is suspect.

Is it ideal? Certainly not, however, all center speakers have major compromises and many simply can not fit a properly designed 3-way center due to the significant increase in speaker height.

Is this anywhere near as bad as many would conclude by looking at just the contour plot? That is a firm no. We are fast approaching nearly 10,000 CMT-340 centers out there, I honestly can’t recall even a single complaint about off-axis issues.

There have been questions thrown our way (and towards other manufacturers as well) as to why we don’t post a horizontal contour plot for the 340SE2 center. The reason is simple enough, contour plots are generally misunderstood – and, with regard to Ascend, we don’t need to.

Why don't we need to?

We post far more critical data as to the off-axis performance of the 340SE2 center, data that actually represents what a listener would hear in a listening environment. This data is both peer-reviewed and accepted and we spent a ton of time developing this unique measurement with some assistance from the designer of the NFS himself.

Below is our published CMT-340SE2 center Off-Axis Estimated In-Room Response:


2615


Note just how closely this unique measurement mirrors the actual on- and off-axis in-room measurements I took of the 340SE2 center using REW.

The green trace (20 degs off-axis) is 3dB down from the on-axis (black trace) in the exact same frequency range. Rather remarkable how closely they compare with one being anechoic and the other in what I would call a typical listening environment.

This measurement is quite difficult to generate though, I do not think it even possible to do without an NFS, and even with the NFS, it is complex. However, it is a FAR MORE accurate representation of off-axis performance compared to a contour plot, as I have just proven.

Once again, a quick look at just how accurate our predicted off-axis measurement is to actual:


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It is my hope that our off-axis EIR measurement will eventually become the standard to evaluate off-axis performance, as it is indeed a properly weighted summation of all of the off-axis angles we hear, with the listener being seated at different off-axis angles.

[rvsixer]

EXCELLENT post. Thank you for the time put into this :) .

[davef]

EXCELLENT post. Thank you for the time put into this :) .

My pleasure, well worth the time in showing real-world results on the accuracy of those predicted (estimated) in-room response measurements. I knew they would be close, but I honestly didn't expect them to be *that* close. It was also time for me to refresh myself a bit on REW ;)

[mikesiskav]

My pleasure, well worth the time in showing real-world results on the accuracy of those predicted (estimated) in-room response measurements. I knew they would be close, but I honestly didn't expect them to be *that* close. It was also time for me to refresh myself a bit on REW ;)

Hi Dave, didn't you have some acoustic treatments on the right wall?

[diesel79]

And it’s things like this why I will only buy Ascend speakers. Honesty. You know exactly what your are getting. great info!

[davef]

Hi Dave, didn't you have some acoustic treatments on the right wall?

Yes, took them down to better mimic a typical room. We designed that room so that we can easily hang or remove the 4" thick acoustic foam panels.

I did also take measurements with them up, the differences were (surprisingly) very minimal and only in the very top end. I was too lazy to put them back up, but we have a demo tomorrow and another on Friday so I have to set the demo room back up.

Mike - I used a Surface Pro 7+ (windows 11) with REW and I was surprised at how well it worked. I have had some issues with REW on other laptops, but this combo worked really well.

[rvsixer]

Yes, took them down to better mimic a typical room. We designed that room so that we can easily hang or remove the 4" thick acoustic foam panels.

I did also take measurements with them up, the differences were (surprisingly) very minimal and only in the very top end. I was too lazy to put them back up, but we have a demo tomorrow and another on Friday so I have to set the demo room back up.
Yes with 4" panels it's expected mostly mids/highs will be affected. Broadband absorbers (6" min. and better at 8" +) will cover bass/mid/highs.
Space your 4" ones up to 4" off the wall creating an air gap, they will dig a little deeper (any further than this, and they start to become more reflective and less absorptive).

Info (not foam tested here, but same results/trends would come with foam of similar gas flow resistance):
https://jhbrandt.net/wp-content/uploads/2023/01/Broadband-Absorption.pdf
https://jhbrandt.net/wp-content/uploads/2023/01/Fluffy-vs-703.pdf

[davef]

Yes with 4" panels it's expected mostly mids/highs will be affected. Broadband absorbers (6" min. and better at 8" +) will cover bass/mid/highs.
Space your 4" ones up to 4" off the wall creating an air gap, they will dig a little deeper (any further than this, and they start to become more reflective and less absorptive).

Info (not foam tested here, but same results/trends would come with foam of similar gas flow resistance):
https://jhbrandt.net/wp-content/uploads/2023/01/Broadband-Absorption.pdf
https://jhbrandt.net/wp-content/uploads/2023/01/Fluffy-vs-703.pdf

rvsixer, not to sound condescending (that is not my intention) but we do no know a bit about about absorption. We are certainly not looking to absorb bass or even mids. Our panels were purposely built and installed by us to absorb slap echo in our demo room, as it was quite a lively room due to a very large section of glass on the opposite wall. Ultimate goal was to dramatically improve RT60, which it does, while *not* absorbing too much in the way of reflections so as to reduce actual spaciousness.

My previous comment regarding absorption was a positive one, I expected more high frequency absorption due to the panels compared to what we measured, which I was pleased about. It means the panels are doing exactly what our goal was for them :)

[rvsixer]

rvsixer, not to sound condescending (that is not my intention) but we do no know a bit about about absorption. We are certainly not looking to absorb bass or even mids. Our panels were purposely built and installed by us to absorb slap echo in our demo room, as it was quite a lively room due to a very large section of glass on the opposite wall. Ultimate goal was to dramatically improve RT60, which it does, while *not* absorbing too much in the way of reflections so as to reduce actual spaciousness.

My previous comment regarding absorption was a positive one, I expected more high frequency absorption due to the panels compared to what we measured, which I was pleased about. It means the panels are doing exactly what our goal was for them :)My apologies, was not my intention to imply you didn't know about absorption, decay time improvement, etc.

I suppose I misinterpreted the 'surprisingly' minimal measurement differences you found between panels up and panels down, whereas in my own experience that would be the expected result of typical 4" foam panels. Great your customized panels/treatment met your goals.

Again, my apologies for the misinterpretation. Sometimes too easy to do over forums. Now on to measuring my own new room and getting ideas on the treatment needed; I am expecting RT60 times WAY up there as it's all tile floors, a big window on one side, etc.

[davef]

Again, my apologies for the misinterpretation. Sometimes too easy to do over forums. Now on to measuring my own new room and getting ideas on the treatment needed; I am expecting RT60 times WAY up there as it's all tile floors, a big window on one side, etc.

Yeah, our demo room was initially a disaster. Tile floors, bare walls, a huge glass wall section... We put down a large thick shag rug, it looks ridiculous but it is effective. That combined with our panels throughout the room, and bass traps in the corners have turned this room into my personal listening space when I need a break from work and need to just enjoy music. Spent 3+ hours in there yesterday with a glass of scotch and some Jeff Oster:

https://jeffoster.com/

[N Boros]

I have seen a lot of discussion about horizontally positioned MTM centers, with many consumers pointing to off-axis lobing issues that are clearly revealed in contour plots.

Contour plots, as generated by the Kippel NFS, are true anechoic measurements. They display each *individual* off-axis angle and indicate the amount of amplitude change using colors. They are a useful tool for a quick examination of the overall directivity of a speaker.

The problem is that they do not represent what we hear. We do not hear individual off-axis responses. For example, at 20 degrees off-axis, we do not just hear the response at 20-degrees, we hear a weighted summation of all of the off-axis angles.

Below is the vertical contour plot of the 340SE2, which would be the horizontal contour plot of the same speaker when positioned horizontally.


2616

You will note the frequency range of lobing is mostly between 800Hz to 2.8kHz. The contour plot shows this area being quite messy - to the inexperienced, it simply looks horrible.

But how does this translate into what we are hearing? As I mentioned above, we hear a summation of all off-axis angles, we do not hear a single angle.

Below is a comparison between the on-axis in-room response of our CMT-340SE2 center and in-room response of the same speaker with the mic at 20 degrees to the right. Microphone is at ear-level, positioned 8 ½ feet back from the center, with the center speaker positioned as most would place it. The mic was then moved over to the right by exactly 3 feet (which translates to an off-axis horizontal angle of 20 degrees)

I could not move the mic further to the right, as it gets much too close to that sidewall, which has a far more dramatic effect on the response than lobing would ever cause.


2612

2613

2614

Blue trace is on-axis, brown trace is the 20-degree measurement. BTW, that on-axis in-room response for a center looks fantastic and does indeed closely mirror the predicted in-room response of the 340SE2 center.

*Ignore the response below 300Hz as below this frequency, the response is dominated by room modes.

You will note that the frequency range of the off-axis lobing was well represented in the contour plot, as the off-axis response shows a dip in that same range. That dip is ~ 3dB. When you factor in that most rooms will create +/- 10 dB peaks and dips, actual audibility of this 3dB dip is suspect.

Is it ideal? Certainly not, however, all center speakers have major compromises and many simply can not fit a properly designed 3-way center due to the significant increase in speaker height.

Is this anywhere near as bad as many would conclude by looking at just the contour plot? That is a firm no. We are fast approaching nearly 10,000 CMT-340 centers out there, I honestly can’t recall even a single complaint about off-axis issues.

There have been questions thrown our way (and towards other manufacturers as well) as to why we don’t post a horizontal contour plot for the 340SE2 center. The reason is simple enough, contour plots are generally misunderstood – and, with regard to Ascend, we don’t need to.

Why don't we need to?

We post far more critical data as to the off-axis performance of the 340SE2 center, data that actually represents what a listener would hear in a listening environment. This data is both peer-reviewed and accepted and we spent a ton of time developing this unique measurement with some assistance from the designer of the NFS himself.

Below is our published CMT-340SE2 center Off-Axis Estimated In-Room Response:


2615


Note just how closely this unique measurement mirrors the actual on- and off-axis in-room measurements I took of the 340SE2 center using REW.

The green trace (20 degs off-axis) is 3dB down from the on-axis (black trace) in the exact same frequency range. Rather remarkable how closely they compare with one being anechoic and the other in what I would call a typical listening environment.

This measurement is quite difficult to generate though, I do not think it even possible to do without an NFS, and even with the NFS, it is complex. However, it is a FAR MORE accurate representation of off-axis performance compared to a contour plot, as I have just proven.

Once again, a quick look at just how accurate our predicted off-axis measurement is to actual:


2615

2614

It is my hope that our off-axis EIR measurement will eventually become the standard to evaluate off-axis performance, as it is indeed a properly weighted summation of all of the off-axis angles we hear, with the listener being seated at different off-axis angles.

This thread warrants a sticky, so that people can see it for years to come. Excellent information here with the measurements.

[billy p]

Yea...it should be a sticky.

AAMOF...over at avs...lots of folks...question even, if it's not from the same brand...timber matching is moot or not using one all together[ ie: phantom]...I'm in the camp of just buying the best available design(2 or 3way)... for your mains, permitting you have no restrictions...to avoid any regrets down the road.

[davef]

This thread warrants a sticky, so that people can see it for years to come. Excellent information here with the measurements.


Yea...it should be a sticky.

I agree -- it is now a sticky :)

Thanks!

[drewface]

So now horizontal MTMs are as good as proper 3way centers and we should all strive for crippled designs?
What we hear is a mix of on and off-axis indeed thus you dont want a speaker with very bad off-axis because then even if it has good on-axis, it is going to affect you in most cases.
I understand the sacrifices needed in terms of size or price of a 2-way vs 3-way and some people is fine with the former. BUT it is still a compromise in performance for anyone but the person in the MLP (depending on distance to speaker of course and how off-center plus specific speaker) no matter how anyone tries to sugar coat it.
Are you telling me that I wont hear a difference in terms of dispersion and getting the same sound experience across a wider area of chairs between one of your 3-way Sierra centers against your 340 (which I had version one and sold because as a center it didnt do it for me.)?

I don't think that's what Dave is saying at all. I think his point was that the criticisms of MTM centers are often blown way out of proportion and in many cases may not even be audible to many listeners. In particular, he discussed how horizontal contour plots for these speakers are often used to claim "horrible" off-axis performance but a real-world measurement shows it to be not that bad. He admits that it is certainly not ideal but ultimately has a relatively minor impact compared to other factors such as room effects.

He also compared his real-world measurement to the "Estimated In-Room Response" graphs Ascend publishes for their speakers and noted how similar they are as evidence that those graphs are a far more reliable indicator of speaker performance. With that in mind, comparing the CMT-340SE2 to the Horizon V2 clearly shows that the Horizon's 3-way design has better off-axis performance (the lines are practically on top of each other) so if that is an important factor in your setup the choice is obvious.

[davef]

So now horizontal MTMs are as good as proper 3way centers and we should all strive for crippled designs?
What we hear is a mix of on and off-axis indeed thus you dont want a speaker with very bad off-axis because then even if it has good on-axis, it is going to affect you in most cases.
I understand the sacrifices needed in terms of size or price of a 2-way vs 3-way and some people is fine with the former. BUT it is still a compromise in performance for anyone but the person in the MLP (depending on distance to speaker of course and how off-center plus specific speaker) no matter how anyone tries to sugar coat it.
Are you telling me that I wont hear a difference in terms of dispersion and getting the same sound experience across a wider area of chairs between one of your 3-way Sierra centers against your 340 (which I had version one and sold because as a center it didnt do it for me.)?


Hello Luis,

Why are you posting here using a fake username?


So now horizontal MTMs are as good as proper 3way centers and we should all strive for crippled designs?

Did you actually read my post? At what point did I state this or have I ever stated this? Hint, I have never stated this so please don't present any strawman arguments here.


What we hear is a mix of on and off-axis indeed thus you dont want a speaker with very bad off-axis

Thank you for agreeing with me... What we actually hear is precisely what is being discussed and the measurements of which are posted in this thread. We do not hear a contour plot, we "hear" a summation of all of the angles, and as such - since you believe in the science, you then must also believe in the measurements posted in this thread. You can't pick and choose what aspects of the science you wish to agree with.

I am sorry if our original CMT-340 center didn't work for you. We have no records of any purchases from you, ever, although we have had many discussions in the past, including an original 340 center back in 2007.

FYI, for transparency purposes, this poster is the same poster who started this massive thread on AVS Forum:

https://www.avsforum.com/threads/my-quest-for-a-center-speaker-my-impressions-of-many-center-speakers-i-tested-for-my-jbl-590s.3245316/

Luis, here's the thing, and something I have learned in my now almost 40-years of being a professional in this industry. Consumers who are hardcore to the far left or far right of a particular argument tend to generally meet somewhere in the middle over time.

We now have Amir actually recommending an MTM center (don't get me started on the measurements of *that* speaker) as well as Audioholics easing up on toppled (horizontally oriented) centers.

This thread has presented actual facts with objective data backing up those facts. And I'll present yet another.

Since we started selling 340SE2, we have only had 1 pair returned to us, and that was from a customer who has purchased and returned nearly every product we manufacture, so can't really count him. We have had not even one return request for 340SE2 center. From the standpoint of customer satisfaction, this is remarkable.

Now, if our customers were your typical Best Buy consumers, maybe it could explain as to just how well our 340SE2 center is loved. However, our customers are among the most knowledgeable and experienced audio consumers on this planet. They read everything, analyze everything, draw their own conclusions - do A/B comparisons with competing products...

I'll repeat this, in 5 months of selling 340SE2 centers, not one return or even a complaint. I am sure that will eventually change but the actual facts laid out clearly and objectively speak for themselves in this thread.

I know your history, we have dozens of correspondences dating back to your AV123 days, and it is interesting reviewing those to see just how your own opinion on many things has changed :o

[davef]

At the request of Luis, because he wishes to remain anonymous, I have deleted his posts.

[billy p]

At the request of Luis, because he wishes to remain anonymous, I have deleted his posts.

That's very kind of you Dave...nobody wants to get the wrong impression about LGG.:D