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In Reply to: RE: Musings on true-ribbon roll-off points for 3-way Maggies. :-)) posted by andyr on October 22, 2009 at 03:44:44
Andy,
You made me curious, so I took a quick look at the 3.3 crossovers in the tweaks section. (For the "Lars" 3.3/R values.)
The Bass Filter is a third order Butterworth
L2+L3 = 4.8mH
C2= 275 uF
L4 = 1.7 mH
For a nominal 4 ohm bass panel this provides a 200 Hz, third order roll off.
The combined mid & high bass filter is actually difficult to analyze without computer tools (Spice or Matlab). Fourth-order polynomial equations are not fun!
However, a simple approach is to model the ribbon filters as a series of two second-order LC-filters. With the Filter frequency equal to 1/[2 x pi x Sqrt(L X C)]
First Filter (external x-over, mid & tweeter)
C1=90 uF
L1=8.5 mH
freq = 182 Hz
Second Filter (tweeter)
C4=20 uF
L7=0.397 mH
freq = 1,786 Hz
The band-bass configuration is somewhat odd. I'd really have to derive that one.
At any rate, it would seem without an exact soulution that the ribbon filter on this model 3.3R is likely much lower than 4,500 Hz.
regards,
Jim
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