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experimenting? costs?And, is it the -6db point or the -3db points we want to match?
It is a valid point that a high-pass power level capacitor where calculated from theory with the tweeters Z at the freq. - 'to match the existing acoustic low-pass' on the mids may NOT give a good blend, giving an audible notch OR a forward hump. leading to more expense, esp. if using better thru to 'expensive' caps
But if you designed a passive line level R& C 1st order filter knowing these relatively more stable source and inputs z's. might this be MORE likely to give a good match. With lower costs for experimentation / matching? And,
How important is 'quality' of R and C in such conditions? IE will a Holco or a VISHAY sound a LOT better than a 1 watt 1% Philips MF?
And,
Can we add a knob to trim the result?
TIA
WarmestTimbo in Oz
The Skyptical Mensurer and Audio ScroungerAnd gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm
Edits: 03/07/08Follow Ups:
Timbo, mate,
A 1st order series line-level cap will IMO sound much better than the equivalent spkr level cap. However, this requires a separate amp for the tweeter, right - ie. bi-amping! :-))
For a 1st order filter, the equations give you the -3dB point. However, you don't want the -3dB frequency for the tweeter HP to be the same as the LP -3dB frequency ... you need to spread them apart a bit, to get it reasonably flat across the XO region.
And, yes, component quality is just as important here as in all other applications. So some caps will sound much better than others. However, whether Holco sounds better than Vishay sounds better than Beyshlag sound better than Phillips ... is something I cannot comment on. However, *definitely* some reses sound better than others! :-))
If you are using reses in series (to tame the tweeter) then I would recommend the hugely expensive Duelund - based on feedback from a USA mate of mine who mods Maggies for a living. He tried out a lot of reses.
Reses in parallel are perhaps not so critical?
Regards,
Andy
The only problem I had was that my calculations were most of the time off the mark. But adjusting L and C values with spot frequencies and SPL meter allowed good matching without bumps or suckouts.
Drivers for such XO should have as extended and smooth usable frequency range as possible. It is easy to match a woofer that goes up to 6K with tweeter that goes down to 1 K.
Quality of parts is important, but that does not mean esoteric parts. It always pays to test a variety of inexpensive caps, some $1-2 polypro or mylar caps can be amazingly good. With coils, avoid iron cores, use as thick wire as you can, and encase wound coils in epoxy. Resistors are better avoided altogether, match driver sensitivity if you can. White coffin is the worst kind of resistor for XO use.
Perhaps I wasn't as clear as I wanted to be!I was asking - in relation to simple FIRST order High-Pass-only to a tweeter designs, and of the two means mentioned, which ......
is the most economically adjustable - to good / excellent / acceptable, both audibly / measurably! ?
So, what I need/want to do is - come up with a good blend to the acoustic-only midrange roll-off, but to get there as economically as possible.
I want to use, a FIRST-order-only high-pass xover, around 3.5k theoretical - plus or minus what ever it takes - to get the right blend.
knowing - as I now do - that the tweeter's REAL Z under drive, it's size and dispersion, let alone the room/set-up, will affect what I finally settle on.
Either a series spkr-level capacitor, OR
an R&C network on the input to the pre-amp, noting that here, the values for output Z and input Z are easy to measure - AND, don't shift much under dynamic conditions!
And, MIGHT I may be able to use a pot / vane-cap, in the line-level prototype filter, to vary things. And then settle on the fixed values to use!
So, I can't see how we got, from there, into power resistors OR to inductors at ALL!!!
Summing up, your post is not of much use, to me.
try again!?
WarmestTimbo in Oz
The Skyptical Mensurer and Audio ScroungerAnd gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm
For me with my limited knowledge, a single capacitor & a variable L-pad as high pass filter & attenuation on tweeter would be easiset to implement sorta satisfactorily. I say sorta because I've been frustrated many months sometimes experimenting this way & that. Anyway, the L-pad can be measured each side to replace with fixed value R's once level is determined (or it can be left in place against future system placement changes). I'd start with a cap value an octave above my desired crossover per the resistance reactance formula results. C = 160,000/(R X Frequency) gets you in the ball park; IOW when using this formula double the Frequency over what you want to shoot for. I round off to 160,000 so's I can do the math in my head & the end result is close enough per frequency as to not matter vs using the acurate 159,xxx.xxx or whatever that # is.
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