Hi everyone... For anyone not familiar with my project, I'm building what are, essentially, Big-Mal mains... I say essentially because, instead of a totally horizontal woofer layout, I'm doing a 2x2 configuration. I realize this gives up the wide horizontal directivity benefit of the Malcolm designs, but I'm willing to deal with that. I originally planned on doing a basic 2.5-way crossover, but can't get an impedance curve I'm happy with using that layout; I can't get the impedance for the midrange below 10 ohms, and I don't want to give up the extra power (technically, the 4 ohm-ish midrange of the Big-Mal is lower than my HK AVR is spec'd for, but I've been running 6 ohm mains forever on it, and I'm sure if you looked at their impedance curve it dips down that low, and I don't think the Big Mal's impedance is that low for much of the frequency range). My question is concerning the shunt capacitor that goes across the outer woofers in a Malcolm design... I budgeted for a Dayton poly cap (actually capS, I was going to use 3 50uF caps, since the xover has a 50uF already in it, if I use 3 50s I need a total of 12 and get the 10+ discount at PE), but I took a look at the standard Malcolm's crossover, and it specs a NPE. It seems like a capacitor in this location is in a fairly critical location and would benefit from a better cap (if you subscribe to that school of thought), was a NPE spec'd in the Malcolm simply for budget concerns? I don't know ANYTHING about that type of crossover, nor can I really play around with it since I can figure a way in PCD to sim that style (thanks to bwaslo for explaining the theory behind that topology to me). I'm sorta figuring, since I planned on using a poly in that spot and budgeted for it, that I will probably go that route, but thought it was worth asking.
The capacitor works at a pretty low frequency, so I doubt a mylar would be audibly different from an NPE. The biggest issue with NPEs (IMO) is the tolerance and stability of the value. But this capacitor doesn't affect any sharp transitions, it just slowly shunts out a couple of woofers, so its value isn't at all critical. But, yeah, NPE chosen for cost but I don't see any reason to spend $$ on film caps there.
Thanks for the advice... I always get turned around reading the schematic for the Big Mal for some reason... I forget that the 2 pairs of woofers are in series and get it stuck in my head that the shunt capacitor effects the inner woofer pair as well. I just noticed that the 50uF in the schematic is also an NPE, not a polypropylene... I'll likely just go the NPE route, ALTHOUGH I'm also considering buying a mess of the 10uF mylars on closeout at Madisound for $0.50 each (since I'd need so many) just to set my mind at ease. Going that route, it'd cost about 2x as much as NPEs, which isn't nearly as ridiculous as >10x the cost, especially considering I'm using $9 woofers. My next project is refurbishing a vintage console record player that was my Grandma's... Was plainning a pair of EOS-8+DNA-350s, a pair of B&C 6" woofers, and a pair of the Series II Dayton 12" subs. I'm TOTALLY going active this time!
AVR power... I don't have any interest in off-board amps, that was my main reason building decently high sensitivity speakers in the first place (the Big Mal should be solidly in the mid 90s, IIRC bwaslo stated around 94dB). That, and I've always liked horns. I greatly prefer high sensitivity to high power (my car is the same way, only 800-900W with a 3-way active front stage and 2 IB subs) and these should hit "stupid" loud off just the AVR, and sound pretty good doing it.