I have been using 2-way center for some time and always had some doubts about the performance. Firstly, it just sounded small compared to the front speakers I am used to listening to music on. Secondly, I had noted some peculiarity when listening to the center from the sidemost positions in the room. Now having changed to 3-way center, I thought I would share some experiences.
The system is a 7.1 Monitor Audio previous-generation Silver series, powered by a Denon X4500H. The wall behind the TV isn't very wide but the room opens up to adjacent large spaces and is long, and there's a couple of spread-out sofas and couches. An off-center TV position is a living room compromise. The system is used a bit more for stereo music but we often also watch movies. In this speaker series generation, there was only one center speaker, the Silver Center. It's rated 8 ohms nominal impedance, 90 dB sensitivity, and 45 Hz low-end. Weight is 10 kg or 21 lbs and it has two 6" mid/bass drivers, one on each side of the tweeter. In the current, 6th generation Silver series, there's a smaller center which is a 2.5-way design, the C150, and a larger 3-way center, the C350, which is what I have got now. The C350 is rated 8 ohms, 90 dB and 40 Hz low-end. It's 15 kg or 32 lbs and has a 4" midrange driver under the tweeter and two 6" bass drivers.
I ran the AVR's calibration feature, the Audyssey XT32 with the C350 installed. The AVR picked 60 Hz as ramp-down frequency for the center. I then figured that I could swap back and forth with the centers with acceptable comparison results since they seem to have similar impedance and sensitivity, without having to recalibrate the AVR every time. I then picked a few dialogue scenes as test material and got started comparing. Here's the 2-way setup:
It was immediately quite clear that the C350 has a "fuller" range, with a deeper bottom, making a more natural sound. The 5th generation Silver Center is not a very small speaker and its sound isn't particularly weak, but the difference to the larger speaker was clearly noticeable even when I couldn't do immediate back-and-forth comparisons because I had to pause to do some speaker replacement and re-wiring between the test scenarios. Here's the 3-way setup, where you may also see that I had to modify the TV bench by heightening it in order to fit the larger speaker:
However, the frequency band width wasn't my only concern with the old center. I had also noted that there was some kind of sound degradation when listening not perpendicularly straight in front of the speaker. There are several listening positions in the room and some are well off that central line. I can't identify what exactly happens but it sounds slightly lower or muddier, sort of more the further away from the center line. The effect isn't huge and certainly doesn't make dialogues incomprehensible, but it's there. A reservation: My test scenes had quite clean and isolated dialogues. If there's simultaneous music or sound effects in the scene then the "off axis" issue might be bigger. I have learned that this type of issue isn't uncommon with 2-way centers, and that an explanation would be that the midrange sound, where human voices are found, is sent from two midrange drivers rather than from one - and if listening from the side of a room then the distance two those two drivers is different.
With the C350, which has a single midrange driver, I couldn't hear any "off axis" issue at all, no matter where I listened or how far away from the center line.
So the C350 solved two issues and it's definitely a keeper for me. Now, I can't help but thinking how I would perceive a center speaker with even wider range. For instance, if I installed a third Silver 10 speaker, as center and laying under the TV - would that be even more awesome? Not sure I will ever go there though, not perceiving drawbacks with the C350 like I did with the old speaker. The C350 doesn't sound "just small" compared to the front tower speakers like the smaller speaker did. I can't guarantee that such feeling will not develop over time though - but I hope it won't.
: The 3-way speaker has better sound consistency between listening positions, and unlike the 2-way speaker it doesn't lose sound quality when listening off the perpendicular axis from the speaker. Also, this particular 3-way speaker being bigger than the compared 2-way speaker, it has a fuller and more natural sound in general.
Bonus mini review: Dual center speakers
Before getting the C350, my system actually had two Silver Center speakers - one under the TV and over the TV. The purpose was to locate the dialogue where the picture is rather than outside of the TV. It's an issue I perceived especially in the listening positions closer to the TV. When getting the C350 center, I thought I would start with getting only one and do some tests before potentially getting a second C350. Another, lazy reason was that I wasn't sure that the current top center shelf would hold a heavier speaker.
I have been running the two center speakers in parallel, creating a 4 ohms load for the AVR. That hasn't seemed to be a problem. So now I put the C350 under the TV and connected one of the old centers in parallel. Opposite to having two older centers of the same type, there's now two different speakers which means that the center sound is now composed of two different sound flavors. However, when I tested the two speakers against each other I didn't notice any other "flavor" difference than one of them reaching deeper bass. That makes me think that the speakers could work quite well in a dual setup even though they aren't the same model.
Ahead with testing. Here's the setup:
First, I stayed at the height right between the two center tweeters and moved left and right to see if I could hear the old center's off axis issue. I did actually not hear it, which I understand as the C350 masking the shortcoming of the 2-way center quite well. I am sure the issue to some extent technically is there though, and I assume that some suitable laboratory equipment or person with more sensitive ears would reveal it.
Then I moved up and down to see what impressions that gave. It was clear that the apparent location of the sound source moves when moving the listening position up and down. To make it easier to hear the differences, I also did the same thing with my eyes closed. Of course that's not how you watch movies, but it did make it clearer how the perceived sound source location actually moved. It turned out that the perceived sound source moved pretty much like I moved my head up or down. With the ears right between the tweeters, the sound appears to come from the middle of the screen, or from the actors. But moving only a few inches up or down clearly makes the apparent sound source also move, about as much or even a bit more. Moving even further up or down, I could start hearing the different speaker flavors take over. Further down, closer to the larger speaker, the sound became fuller, and further up, the sound became thinner. Going really close to the TV and listening closely to each speaker intermittently, their sound profile difference became very clear. For example, I could now hear that the difference is a bit bigger with male voices but also audible with female voices. But shouldn't there be some type of sound degradation of the type I heard from the 2-way center when moving away from that speaker's perpendicular axis? I think there should, however I did not identify such thing. I suspect one reason may be that the off axis distance wasn't very big, and another that the difference in sound flavor masked any other difference. I did hear a difference, but can't be sure how much was a result of the speakers being different and how much may have been due to an off-axis phenomenon. In any case, the height which is right between the two tweeters is in my case about the same as the listening height when sitting in the different sofas and couches in the room which makes the question less relevant.
I did also experiment with tilting the center speakers so that they were directed towards me, by wedging the lower speaker up and the upper speaker down. I could not hear a difference from doing that, just like I couldn't hear a difference from only the 3-way speaker when moving left-to-right. I suspect that means that the drivers radiate quite evenly to different directions, at least within reasonable angles.
So what is then the sound profile right between the speakers - is it a "half fuller" range or what? Well, it certainly sounded more like the 3-way center than the 2-way version, perhaps since I am after all hearing the larger speaker's deeper range. But is it just like listening to only the larger speaker? No, I wouldn't say that. But perhaps not very far from it.
The question in the end perhaps becomes: What's worth more - moving the dialogue to the screen at the expense of sound consistency, or maximizing sound consistency at the expense of sound location? I am going to keep both centers connected at least for now. To be honest, an additional drawback of the dual centers is the somewhat weird look of it from a furnituring point of view - my room is primarily a family living room and at least as much a music listening space as a home theater. But I am thankful that the family likes the speaker system and have no objections. Actually, it's not uncommon that guests who have no speaker interest or knowledge exclaim something like "Oh, nice speakers!".
: If you are sometimes distracted by the sound not coming from where the picture is, it may be worth trying a dual center setup. Maybe you would like it, and find the benefit outweighing the peculiarities.