Great center speaker choice

You should pick a center speaker of the same brand and same line, within the brand. Manufacturers match the speakers with the same components, so you get an even, and balanced sounding front stage.

If you mix and match, you'll likely notice uneven or unbalanced audio from your front speakers, due to different cabinet design, components, crossovers, drivers, etc...

You can, usually, get away with different surround speakers, but 99% of users on these forums will tell you that matching the front three is very critical.

Best CC for the SM-55 is... another SM-55.

The new SMs have new drivers that haven't yet been incorporated into a CC speaker. While they'll probably sound fine with an existing DefTech CC like the 8040, another 55 would be a more perfect match. Three identical speakers are almost always the best option if you can manage it.

Or, if it's a small room with a single listening position, you might find a Phantom Center provides the best sound of all. That's an experiment that costs nothing to try.
Edited by rdclark - 1/8/13 at 1:18pm

+1

I recommend the Cambridge Audio S50.

The Def Tech 55, with its top passive radiator, will be a crappy center speaker. The design is 100% wrong, and if you contact a Def Tech speaker designer, he will tell you so.

Call them and ask them what model they recommend.

There is nothing about the content of a center channel signal that requires a loudspeaker to be designed differently in order to reproduce it. The SM55 is a great sounding speaker that will sound great whatever channel you connect it to.

There may be placement issues that dictate that a CC speaker can't be identical to the mains, but that has nothing to do with sound.

And if the overall excellent sound quality of a design is due in part to its incorporation of a passive radiator, that excellence will be evident wherever you use it.

Finally, the CC speaker that DefTech recommends for use with the SM55 is the $500 CS-8040 -- which has a passive radiator on top.

My only initial hesitation in recommending a third SM55 was the radiator on top - depending on how close the speaker is to your TV I wondered about extra reflections from the top radiator that may not be present in the LR mains. But when I (also) checked and saw that the DefTech recommended center also has a radiator on top I recommended the third SM55 sans hesitation.

Three identical speakers across the front vs a dedicated, horizontal center speaker is often debated in the forums - just search/read some other threads on the subject if it will help ; )

To be honest in the past I've not been a fan of most DefTech speakers - I thought they sounded fine for HT but sub par for music (and seemed overpriced to me). That changed with the SM series, the 350's and 450's sounded surprisingly good to me, and, I think DT nailed it with the new SM's - 45, 55 and 65.