Center Channel Design Questions

[jhollander]

The FRDs can be taken as an average then adjusted down by about 6 dB (I don't have the exact formula in front of me) but the total combined response needs to match the measured combined response. Once you have the individual driver responses (ZMAs are not required) you can derive the Z.

As the Ms are likely in the same cabinet you need to break out he ZMA's using a modeling program. The benefit of all the extra work is to be able to use PCD to move off axis and look at the response.

The short answer is with all the drivers in the same cabinet you should tie together and test, long answer above is why you might want to break out the responses.

[Chris Roemer]

If you DON'T need to see response off-axis (instead, take the easy way out), 4 woofers (wired series/parallel) should be the same FR as a single unit (but +6dB), and should have the same Z as a single unit (modified on the bottom (box rolloff) end - although that "box modified" impedance shouldn't really have an effect on your XO design - except for whatever you're doing for BSC, maybe).

[weinstro]

Thanks guys.

If this were a vertical format I would consider pursuing the design on-axis only, but I would still be curious about the impact on vertical directivity.

However, this design is a horizontal oriented center channel to be installed in a wide room, so off-axis behavior is something I need to at least examine.

The sealed chamber for the W4-1757SB splits the vented enclosure for the Ms in 2. Each side has the same volume and an adjustable length slot port to allow adjustment of the box frequency for each pair independently. You could think of this as two (FR)MM with 2.5 way cross, mirrored horizontally about the full range driver.

[jhollander]

With a split chamber for the M's you can design as two woofers. Use the point between the two M's as your x measurement in PCD. if you are doing a 2.5 you are back to breaking out the zma's and reducing the frd's spl.

Having done a similar center I found no advantage to a .5 x-o with a 3 inch woofer. My opinion would be to take the extra SPL from the M's and make a 2-way.

[Mayhem13]

A horizontal WWTWW works IF the tweeter XO is low enough.....the RS28 and the SB26ATC can do 1khz in a typical home setting.