W-frame openings question

[Gargoyle]

I want to build dipole woofer with two 15"s per side (Eminence Beta) in W-frame. For aesthethic reasons I need make the frame smaller and round off. This inevitably leads to openings area reduction. Is there any rule how big the openings should be? Phoenix has openings cca. 50% of related cone area. Further reduction to half (1/4 of cone area) helps me much.
Thank for your response in advance. ;x(
GG

[JonMarsh]

As you reduce the opening area, it changes the "Q" in the upper bass frequencies, and reducing the opening size will alter the response above 100Hz- more peaking. This would have to be compensated in the crossover design. As you notice, for W frame woofers you need one roll off pole just to compensate for this rise. See SL's site for more info.

~Jon

[Gargoyle]

If I understood SL correctly, the quaterwave resonance peak is removed with notch and in my case it should be probably deeper and more narrow.
A new question arises in my mind. In my intended project I want to cross W-frame to the single 8" (L22RN4X) and it seems to be inevitable to set up the xo freqency in the 120-150 Hz region. Does it mean the possible (phase related and/or any other) irregularities with NF in xo region (or 1 octave above) could cause me a serious problems? Even with LR4 and about 3 meter wavelenght?
SL remarks it, but overcomes it with xo at one third of peak/notch freq.

[Davey]

GG,

The W-frame design is sort of asymmetric in that one side has a single opening and the other side two openings. Each of these openings is approximately the same size and roughly equivalent to the Sd of a single 12" woofer. Your 50% number is based on two woofers radiating from the single output on one side?

It's an interesting question because I've taken nearfield measurements from both sides of a W-framed woofer and they are essentially similiar. This tells me that the size differences (asymmetry) in the opening area are not sufficient to adversely effect the responses. I haven't experimented with reducing the size of W-framed baffles, but I would imagine there will be a fairly defined point this becomes more of a problem.

However, I'm not sure why you would compromise your design for aesthethic reasons.

Cheers,

Davey.

[Gargoyle]

However, I'm not sure why you would compromise your design for aesthethic reasons.

Part of the game.

50% number was based on smaller one of rear openings of Phoenix woofer 3"x13". There are also bigger ones, 4.25" and 5.25" if remember correctly, but seems for assembling. I also see no reason for asymmetry caused mismatch, if "sensibly" sized. The question was more about the air speed limit in reduced opening.

What about xo one octave below peak?

GG

[Dennis H]

You're asking questions no one can answer. As SL noted, using the same enclosure but changing the drivers changed the frequency of the resonant peak because the different magnet/basket structures gave a different acoustic impedance. We don't know anything about your drivers so you'll just have to mount them and measure them yourself.

[Gargoyle]

You're asking questions no one can answer.

I didn't expect the exact answer. I was just afraid of something like "never ever try this" or "the filtering will be extremely complex and tricky to reach sufficent result" and so on.

We don't know anything about your drivers so you'll just have to mount them and measure them yourself.

This is the words which encourage me.
Thanks to all for their responses.