Manifold design: from tilting bass reflex speaker...

Hi, i have a simple question... i have seen bass many reflex design with tilted speaker facing BR duct:

manifold reflex.jpg


Now my question is: is not a full horn, but is still not more a reflex... depending to speaker angle.
How response change? how can i simulate it pratically ?
Someone can help me to understand this design?
 
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Does a little bit of something at ‘horn’ shaped 1/4 wave resonator multiples of its length (way above the passband ) and sort of changes the shape of the bandwidth with a little different pressure on the other side of the driver?

(My example is a lot ‘longer’, so I could see what might be happening at lower frequencies in horn response )
 
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(My example is a lot ‘longer’, so I could see what might be happening at lower frequencies in horn response )
It is a normal reflex, the excessive flare would hardly do anything.
The driver would be 20 to 30 degrees off axis. And with a ground plane the response is flatter.
That sim shows resonance of a typical fart tube. Or a port that is too long.
looks like wrong alignment for the woofer shown, and not modeling leakage with the excessive Q in the lowend response.

Assuming the vent would be a everyday slot port, sharing 3 walls, end correction would be the usual 2.27
which would just make the needed length slightly shorter like any other slot port
 
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This is just diffraction of a 12" on baffle, with a ground/floor plane added

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This is 40 degree Vertical tilt ( Blue) with 0 degree overlay( Orange) with ground plane.
So I correct myself 40 to 60 degree is ideal.
Just putting the driver response off axis, plain and simple.

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Assuming most use a basic 2nd order crossover.
This would make a dirt simple 1st order more feasible with high crossover points.
Otherwise dont do dingle.
People insist that being " 4 feet" from a side wall is some magic science.
Actually makes things worse. So again high crossover point with 1st order
helps rid sidewall barf.
 
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Adding a ground plane and a sidewall at 4 feet (1200mm)
reflection is rather evident.
(Orange) 0 degree ( Blue ) 40 degree.
And showing dirt basic 12" speaker response full space ( DC300-8)

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But if we look at the real world bandwidth below 300 Hz

The baffle step is flatter,
(Blue) 40 degree ( Orange Overlay) 0 degree
And you slightly gain back about 1 dB of losses to full space at the low end.
Crossover region around 250 / 300 Hz be flatter.

So pretty generic 45 degree tilt be more than fine.

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am I wrong or does it seem to me that building subwoofers with this "inclination" is not so effective for performance... I'm thinking of PAs, for example many 2 x 18" where the reflex is in the center and the woofer is inclined 20-30 degrees looking at itself... ok, the response does not seem much improved in the low range due to the effort of transporting a subwoofer deeper than 20-30 cm... what am I missing?