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In Reply to: Using AJ-Horn to examine filter networks - how should certain things be viewed? posted by freddyi on February 17, 2007 at 08:42:49:
I didn't use AJ Horn, but while optimizong crossovers I noticed what a 2nd order LP filter does to a woofer, and incorporated it into my two latest projects. There are limits to its effectiveness. If you start with a horn that has high sensitivity and fairly flat response the filter is far less effective than with a horn with medium sensitivity and a rolled off high end. So while it does wonders with my OmniTops (short straighthorns) it's of no benefit with my DRs.
Follow Ups:
those "omni top" 12 & 15 graphs look good nuff for home midbass use - throat looks narrow - what advantages did that give you?here's sims with 80sq.in. throat for common midbass type with 2220H - top end would be more ragged than sims
short midbass ~like Bruce's "System 10"
0.8M imaginary horn w. 2220H
"those "omni top" 12 & 15 graphs look good nuff for home midbass use - throat looks narrow - what advantages did that give you?"Better sensitivity and pattern control. But the downside is the LP action of the large front chamber volume. I got around that with a filler that reduces the volume of the front chamber and the 2nd order LP filter. In the case of the version that uses a passive crossover and compression driver the LP filter was a necessity anyway, but since it does such a nice job of flattening out the midrange response I'm using it in all versions, bi-amped, piezo tweeter and even woofer only.
sounds like you hit good tradeoff - were your sims done with sawdust?
"were your sims done with sawdust?"Of course. I can't speak for AJ, but just like box programs McBean is only good at predicting the response of the cone, not the dome. Once you get above 800Hz or so there's only one way to find out what the things will do. You can't tell with a reflex box how independantly the cone and dome operate, but stick that driver in a horn and you find out.
Modeling programs assume the cone acts as a rigid piston, but this is only the case at low frequencies. When the cone enters breakup, it acts sort of like an array of smaller radiators, not a single rigid one.Breakup modes aren't confined to the (dome) voice coil cap. The entire cone has ripples across it when in breakup. The thing is the dome of the voice coil cap is centrally located, so when it's in a horn, that's what is exposed to the throat and so is naturally louder.
Another thing at issue is directivity. Sometimes people don't take collapsing DI into account, and look only at power response instead. If you see falling power response, but also have collapsing directivity, the on-axis response may be a flat line even though the power response droops.
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