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The Center, Measured

As some may remember last year I embarked on a new active center channel project. Partly inspired if not suggested by Troel’s Gravesen’s huge and expensive Illuminator Center. I’m pleased with the final results, but since the topic of off-axis response has come up I wanted to share with you what I thought was excellent off-axis performance and the troubles of getting that in a 2-way or center channel speaker.

It’s also important to note that if I had to do this as a passive speaker I would have probably compromised somewhat in the performance in large part because I would not have used 4th order filters, or been able to add some subtle EQ.

Yes, of course it’s easy to criticize the frequency response, but I hope you’ll ignore the foibles and focus not on the on-axis response but on what it takes to get excellent off-axis response as well.

As a speaker builder this is what I shoot for and when I see very expensive multi-way speakers that can’t get there I do have to scratch my head.

I post this in the spirit of discussing pros and cons of design choices. I hope you please keep that in mind. :)

 

erik_squires
erik_squires OP
16,303 posts
 

Thanks, @audiokinesis - I think the foundation for this is that 4" midrange. Gravesen’s center channel designs get excellent off axis performance as well.

The center speaker format for homes (vs. theaters) really is a challenge. Consider in a theater the three speakers behind the screen are identical. The purpose of the center, as you point out correctly, is to center dialogue and effects no matter where in the listening field a person sits, which would be well served by a vertical 3-way speaker or large coaxial.

The physical challenge for homes is height. My own center is 12" tall, which while small compared to mega-centers like the Wilsons, is very tall for many home entertainment centers. The compromise is usually to create a 2-way center.

Less common alternatives are 3-way’s with tiny mids and/or tweeters, and coaxials.

If I were forced to downgrade this center and reduce the height to say 8" tall I’d probably change everything except the midrange which is the key to the off-axis response. I’d use a "low profile" tweeter with much smaller diameter body, and 5" mid-woofers. This would reduce dynamic range and bass, also small diameter tweeters tend to be less smooth sounding, perhaps small prices to pay for greater livability. :)

terry9
2,353 posts
 

I turned a Quad 2905 ESL on its side - utmost clarity. Seamless with an otherwise all-magnepan HT system.

erik_squires OP
16,303 posts
 

@terry9  Nice idea.  Did you use room correction?

terry9
2,353 posts
 

No. We sit in the near field with an old friend, a Kuro plasma display. 

deep_333
1,520 posts
 

A concentric driver can do very good in a center channel application, depending on the design.. The woofers in the coupled cavity design of my speaker crossover at 200 hz into the mid/tweet concentric, which handles the rest. (Elac Adante AC61 from Andrew Jones).

The woofers are inside coupled to external radiators, the latter also serving as an acoustic filter...i.e., you'll also hear some of the cleanest bass that may/may not otherwise only happen with very expensive drivers.

I struggled for years to find a design that nullifies the typical problems of center channel speakers. The guy literally gave away TAD type of performance at a fraction of the cost.

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