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In Reply to: RE: Wall treatment for close listening position? posted by BDP24 on January 31, 2017 at 10:57:15
As usual, Satie's comments are confusing.
The IV-A and IV crossover are different in that a delay network is used in the high-pass section of one.....but not in the low-pass.
However, he mentioned the low-pass section (apparently on his speakers only) adding a 2ft electrical delay.
Dave.
Follow Ups:
I'm confused alright, but I attribute that to my lack of technical knowledge. Like they say, a little bit of knowledge is dangerous thing! Another apropos expression is "I know enough to get me into trouble, but not enough to get me out". I'll be doing some reading (going back years here on PSA) as I try different set-ups and x/o settings.
You can take the delay figures from Neo's spreadsheets it is inside the calculation portion - aim at matching the relative delays of the mid an octave above the HP and bass an octave below the LP to the driver offsets.
Or you can use the magnepan suggested offsets for the staggered configuration as the guide and use the same offset when putting the bass panels ahead of the mids.
Thanks Satie. Above you differentiate between reversing the phase and reversing the polarity, in regards to bass panels in front versus in back. Reversing polarity I understand (swapping red and black speaker cable leads to both subs), but not phase. Could you explain for me?
I am talking about aligning phase vs. aligning the drivers for time coherence. and I don't remember what the OEM polarity should be so I suggested to flip it so that you hear it in both polarities. IIRC the staggered positioning from the maggie manual requires flipping the polarity to compensate for some 60-120 deg phase difference turning into 180 deg at some portion of the XO range between 250hz and 400 hz and thus a big dip in FR at a critical portion of the F spectrum. That since the 2'ish ft offset of the bass in back introduces another 1/4 wave of phase.
That as opposed to time alignment (bass ahead) where you are reducing phase by that same 1/4 wave. In this case you risk having a lump in the FR at the lower mids or a suckout when polarity is reversed.
Thanks Satie, I know just enough to now understand! I'll be trying every configuration possible---the standard Magnepan panel alignment and x/o settings; your equidistant panel/1st order filter arrangement; bass panels behind m/t and visa versa, with the Magnepan x/o settings. The T-IV manual does not include related info for split panel operation, but the T-IVa manual does, I believe.
This is why I got myself a First Watt B4 crossover, which will do pretty much any textbook filter you need (in 25Hz increments). Fun awaits me!
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