Center vs. Mains-as-Center (1 Viewer)

[mackie]

The typical center channel design of midrange, tweeter, midrange has developed in large part to marketing pressure.

It is best to use 5 identical speakers if possible.

A lot of typical center channels suffer off axis response problems due to comb filtering which is basically frequencies canceling each other out because of the location of the two mid ranges in close proximity. As long as you're in the sweet spot it's not a problem, but it becomes more of one as you move off axis. To test it out use pink noise and sit in the sweet spot then move to either side and see how much it changes. Do this with one of your mains and you shouldn't notice as big a difference as you move off axis.

Some speaker companies address this better than others, but its still a problem.

BTW I use a Paradigm Studio 470 CC. I couldn't see having a Studio 40 on top of my TV

 

[ChrisWiggles]

The correct advice in a nutshell.

 

[RichardH]

It's not so much the dual midbass drivers in close proximity that is causing the problem, but rather the tweeter being sandwiched directly between the midbass drivers. You get severe lobing of the high frequencies off-axis to the left and right.

e.g. there are some centers by Atlantic Technology where the two woofers are pushed together in the center w/ the tweeter on top of them. That is a much better design for a center as far as lobing goes.

 

[John Garcia]

Huh? The tweeter isn't the problem. Tweeter's response normally drops off quickly off axis, as the highs tend to "beam" due to their shorter wavelengths. It isn't playing the same frequencies as the other drivers and the driver interaction isn't as great. Combing comes from the fact that the two midbass drivers tend to cancel each other out off axis. It is the interaction between the two drivers playing the same thing that creates the lobing - peaks and dips in response, normally in the midrange, not the highs.

I agree that having the tweeter above the axis of the midbass drivers can help in some cases, but it all depends on what the designer intends to achieve. A properly designed D'Appolito config can be made to work just fine. My speakers are all D'Appolito and they have very good response off axis both vertically and horizontally. Response doesn't take a noticable dip until 40 degrees off axis in both directions.

 

[ChrisWiggles]

I think John is known enough to be trusted around here, but just backing up this explanation because it is, indeed, correct. Although, through the crossover range (which may be significant) there can be some added phase problem off axis if you consider the tweeter and the bass/mid-bass drivers are playing the same thing as well, but even if the tweeter is nonfunctioning you get some nasty combing as you move off-center because of the typical MTM arrangement. As mentioned, it doesn't matter for on-axis listening, but for everywhere else you've got combing problems. This is why it's ok to be selfish as an audiophile and relegate your guests to the off-axis seating position!