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Ascend CMT-340 SE Center Channel Speaker Review

amirm

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This is a review and detailed measurements of the Ascend Audio CMT-340 Signature Edition Center Channel Speaker. It is on kind loan from a member. The CMT-340 SE costs US $298 from the company plus $30 in shipping. It looks to be a design that was released 10 to 15 years ago but of course, speakers don't age like electronics.

The speaker is too big to put in my photo booth so here is a picture of it from the company:
Ascend Acoustics CMT-340 SE Center Home Theater Speaker Baloon  Audio Review.jpg

This is the classic "MTM" configuration which stands for Mid-woofer, Tweeter, Mid-woofer. These quickly became popular with the advent of home theater and the need for a not so tall speaker to put under or over the TV or projection screen. The second mid-woofer was added versus a 2-way design to get increased power capability as the speaker has to keep up with the Left and Right units. MTM configuration works fine as a vertical speaker but when placed on the side this way, creates off-axis radiation which has a cancellations varying distance between the drivers and listeners. We will see this in measurements.

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections. It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in ordinary rooms yet results that can be more accurate than anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room. All measurements are reference to tweeter axis with the grill removed.

Around 1000 points around the speaker were measured (from 20 to 20 kHz) which resulted in well under 1% error in identification of the sound field in all but the 8 to 10 kHz where the error is about 2% due to complexity of the soundfield (see the eye candy section). Final database of measurements and data is 1.4 Gigabytes in size.

Spinorama Audio Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker can be used. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:

Ascend Acoustics CMT-340 SE Center Home Theater Speaker CEA-2034 Spinorama Audio Measurements.png


Research says that on-axis, i.e. the sound that comes to you if you point the speaker directly at you (as would be the case in center speakers) should be as flat as possible. I have shown this in red arrow. We don't see that here with a dip in upper bass, followed by a peak around 1 kHz, then a dip and so on. Company talks about having compensated by the usually poor horizontal dispersion of MTM. I am wondering if the peak around 1 kHz is their attempt at such a fix.

We see our MTM problem clearly in Directivity Index:

Ascend Acoustics CMT-340 SE Center Home Theater Speaker CEA-2034 Spinorama Directivity Index A...png


Focusing on the blue dashed line, research says that should be smooth, i.e. no variations up and down. It can have some title though as I have indicated with my red arrow. We see a large deviation around 3 to 4 kHz. That says that the off-axis response varies a lot from on-axis. So the sound that bounces around the room versus the one coming at you directly have different tonality. Our poor brain then has to figure out what the sum of that mess is and likely thinks the sound is colored, with a suck out in that region. In a center channel speaker, you don't to see such a dip as that is the upper range for vocals.

This also means the speaker will have room dependence as what reflects from the environment changes it sound. Equalization cannot in theory fix any of this because it is before the speaker and whatever it does, changes both on-axis and off-axis at once so the difference between them remains (bad). Controlled listening tests though have shown that some improvement can be made by boosting that area. So you can try but best to listen before and after to make sure it did make things better.

We can put the whole recipe together and guestimate what sound you may get in your room:

Ascend Acoustics CMT-340 SE Center Home Theater Speaker CEA-2034 PIR Spinorama Audio Measureme...png


Ideal response again looks more or less like the arrow I have drawn. More bass than treble but otherwise smooth graph. We have the overall tilt so this speaker should not sound too bright but we don't want the variations we see. We also have a dip in bass frequencies which may take away "warmth" from the speaker. There, I used that subjectivist word! :D

We are done. The rest is for speaker nerds.

Basic Speaker Measurements
Impedance graph shows that this speaker is harder to drive than the company implies:

Ascend Acoustics CMT-340 SE Center Home Theater Speaker Impedance and phase Audio Measurements.png


There are also some "kinks" int he graphs that indicates presence of resonances but they are also visible in the spinorama measurements already sown.

I am trying to standardize the distortion measurements as the software always autoscales this graph:
Ascend Acoustics CMT-340 SE Center Home Theater Speaker Distortion Audio Measurements.png


I picked 5% as the upper limit. If I set that too low it will clip distortion peaks in other speakers. Let me know if you want something else and why.

And here is our waterfall which as noted is not anechoic measurements like spinorama is. As such, I have gated the response in time, reducing or ruining low frequency resolution.

Ascend Acoustics CMT-340 SE Center Home Theater Speaker CSD waterfall Audio Measurements.png


Advanced Speaker Measurements

Ascend Acoustics CMT-340 SE Center Home Theater Speaker CEA-2034 Spinorama Horizontal Audio Me...png


Ascend Acoustics CMT-340 SE Center Home Theater Speaker CEA-2034 Spinorama Vertical Directivit...png



Ascend Acoustics CMT-340 SE Center Home Theater Speaker CEA-2034 Spinorama Full Horizontal Dir...png

Ascend Acoustics CMT-340 SE Center Home Theater Speaker CEA-2034 Spinorama Full Vertical Direc...png


Ascend Acoustics CMT-340 SE Center Home Theater Speaker CEA-2034 Spinorama Early Window Audio ...png


Notice the narrow angle after which, response falls apart horizontally:

Ascend Acoustics CMT-340 SE Center Home Theater Speaker Horizontal Contour Audio Measurements.png


Ascend Acoustics CMT-340 SE Center Home Theater Speaker Vertical Contour Audio Measurements.png


Eye Candy Measurements
I was surprised that the measurement system had a hard time in the region of 8 kHz, sampling the soundfield despite 1000 point measurement system. So i zoomed there and found this:

Ascend Acoustics CMT-340 SE Center Home Theater Speaker Baloon  Audio Measurements.png


Frequencies below and after show simple sound fields as we would expect. At 8 kHz though, we have countless sound sources. I suspect both woofers are still playing and we have diffraction from all corners of the speaker combining.

Conclusions
I don't expect many of you to have interest in this speaker but reviewing it is good because it shows all the classic issues with MTM speakers. There are ways to optimize them better than we see here but ultimately the (near) best solution is to add a mid-range to it. See my measurements of the Revel C52 with that addition: https://www.audiosciencereview.com/...el-c52-speaker-review-and-measurements.10934/

People normally think only the dialog comes out of the center speaker in movies but that is not so. The center channel carries vast majority of burden including sound effects as it represents the center of the image on screen where the action is. So whatever you do, don't skimp on center speaker. Get the best one you can. In the case of MTM, see if you can place them vertically. That is what I did with my first dedicated theater.

So overall, despite the reasonable price, I would not recommend this center speaker.

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As always, questions, comments, recommendations, etc. are welcome.

Don't make me tell you another bad joke to get you to donate money. Do it on your own by using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

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MZKM

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This is sold for both purposes so I calculated both.

Upright Preference Rating
UPDATE: Dave confirmed the Mains version is different, it doesn’t have the “Extended Baffle Compensation” and doesn’t rely as heavily on bass reinforcement, and is thus more linear.
Center Preference Rating
SCORE: 3.4
SCORE w/ subwoofer: 6.2

BD2A020F-0D1D-4D6E-A828-3AC9A5DDDAB0.jpeg
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Ascend also posts measurements and I can compare them (they have the dip at 2500Hz but not the peaking at 1kHz).
 

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LTig

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It definitely needs a sub. Is this typical for center speakers?
 

aarons915

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Just curious this speaker is also marketed as an LCR speaker so it can be used vertically as the L/R Channel. Is it easy to flip the horizontal and vertical axes and show the spin for the vertical configuration or is that not possible without re-measuring?
 

MZKM

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Just curious this speaker is also marketed as an LCR speaker so it can be used vertically as the L/R Channel. Is it easy to flip the horizontal and vertical axes and show the spin for the vertical configuration or is that not possible without re-measuring?
I calculated it as both (I manually had to compute the early reflections, listening window, and in-room; I left sound power alone, not sure if that is right).
 

aarons915

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So would a pair of JBL 305p mk2, placed on their sides, tweeters together, form a better center channel than most of a similar price?

A pair wouldn't sound good due to cancellations but a single 1 would work fine, I always use 3 identical bookshelf for my LCR and it sounds fine. Of course now I have 3 LS50 so the response is fine in all directions anyway but even a typical 2-way bookshelf sounded fine.
 
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amirm

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So would a pair of JBL 305p mk2, placed on their sides, tweeters together, form a better center channel than most of a similar price?
It wouldn't have enough power for movie applications.
 

LightninBoy

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The irony is that center channels are supposed to provide a center image for those sitting to the sides. Yet the typical center speaker design's off axis response is inherently compromised.
 

MZKM

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Ascend’s own measurements track very well expect for the 1kHz peaking and the bass response, the +/-15° vertical response (when upright; so +/-15° horizontal when used as a center) is also different.

I can’t post the super-imposed comparisons of the on-axis as I’m on mobile, but:
340SE_offaxis_uns.gif
A4A8CF82-8715-47C1-8AF6-944E5A6FE7C7.jpeg

Their own measurement is anechoic down to 250Hz (green bar).

@amirm, I just averaged to get the 5° and 15°; I know you said you have this data but in another format, what software is needed to decode it?
 
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GabrielZM

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People normally think on the dialog comes out of the center speaker in movies but that is not so

I think you meant the front left and right speakers amirn. Thanks again for another review.
 
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amirm

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I think you meant the front left and right speakers amirn. Thanks again for another review.
THanks. I meant to say "only" instead of "on." Corrected in the review.
 

Cahudson42

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Begs for these MTM to be run, $179 the pair:
Polk Audio Monitor 40 Series II Bookshelf Speaker (Black, Pair) - Big Sound, High Performance | Perfect for Small or Medium Size Rooms https://www.amazon.com/dp/B0071MSYEE/

'So many speakers, so little time'...
 

Francis Vaughan

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It is really hard to make an MTM work on its side. Checking the Ascend web site the centre speaker is not exactly the same as the sides - it appears that the crossover has been tweaked a bit - which can help. What is interesting is that Ascend suggest that the midrange response has been deliberately tweaked to take into account the likely physical location of the speaker. http://www.ascendacoustics.com/pages/products/speakers/cmt340c/cmt340ctech.html
This is arguably pretty important. A centre speaker has a miserable life as it is placed directly next to a TV screen. Thus the basic spinorama results are not an accurate representation of the final response. One would need to model the effects of the screen. Ascend claim their tweaked response mitigates these issues.

The crossover looks to be a 2nd order design, so it would not be expected that the woofers were emitting much at 8kHz. But clearly something is unhappy. I'm curious about the phase plugs on the woofers. They look awfully like cosmetic phase plugs - ie dustcaps made to look like phase plugs and simply glued onto the cone.
No matter what, the horizontal directivity is miserable, and close to unusable. Especially if there is more than one person watching.
 

MZKM

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It is really hard to make an MTM work on its side. Checking the Ascend web site the centre speaker is not exactly the same as the sides - it appears that the crossover has been tweaked a bit - which can help. What is interesting is that Ascend suggest that the midrange response has been deliberately tweaked to take into account the likely physical location of the speaker. http://www.ascendacoustics.com/pages/products/speakers/cmt340c/cmt340ctech.html
This is arguably pretty important. A centre speaker has a miserable life as it is placed directly next to a TV screen. Thus the basic spinorama results are not an accurate representation of the final response. One would need to model the effects of the screen. Ascend claim their tweaked response mitigates these issues.

The crossover looks to be a 2nd order design, so it would not be expected that the woofers were emitting much at 8kHz. But clearly something is unhappy. I'm curious about the phase plugs on the woofers. They look awfully like cosmetic phase plugs - ie dustcaps made to look like phase plugs and simply glued onto the cone.
No matter what, the horizontal directivity is miserable, and close to unusable. Especially if there is more than one person watching.
You may be right. However, the crossover photos and the on-axis measurements of both are the identical file, so hard to say unless Amir gets his hands on the upright version to measure.
I just emailed them to see if they can clarify (last time I did it took 4 business days for them to reply).
 
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MZKM

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People normally think only the dialog comes out of the center speaker in movies but that is not so. The center channel carries vast majority of burden including sound effects as it represents the center of the image on screen where the action is.
For most television shows and low-budget movies, basically every single thing comes out of the center except the soundtrack/score. So, unless you listen to a lot of stereo content, spend a lot more on your center compared to the mains. People talk about timbre matching, and to my knowledge that just means a similar distortion profile (tonal balance will be altered by room correction), and I wouldn’t say it’s such a large issue that it warrants spending less on the center.
 
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