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What capacitor values?

I have custom-made 3 way sealed box speakers with 12" Hokutone paper woofers run full range (wired directly to the speaker terminals).
The 5 1/2" Scanspeak Woofer/Mid has 1 capacitor with no coils, inductors or resistors.
The 1" silk dome Scanspeak Revelator tweeter has 1 capacitor with no coils, inductors or resistors.
What value capacitors would you suggest for the Mids and the Tweeters?
The existing capacitor values may not necessarily be ideal?
halcro
rodman99999
6,206 posts
 
If the sound has been excellent with the existing values, why would you change them? Keep in mind- When the new caps are installed, it will take a number of hours(perhaps 200+) for them to sound right.
halcro's avatar
halcro OP
2,664 posts
 
The reason I may change them is that the Scanspeak Mid/Woofers and Tweeters were substituted a year ago for the original Hokutone drivers.
Whilst they sound OK, their characteristics (eg impedance and X-over frequencies are almost certainly different.
Does 200uF for the Mid/Woofers and 1.766uF for the Tweeters sound reasonable?
rodman99999
6,206 posts
 
If those speakers are 8ohm: the 200uF cap will cross at 100Hz and the 1.76uF over 10kHz. If they are 4ohm drivers: 200uF= 200Hz, and 1.766uF=somewhere over the rainbow, I mean- over 20kHz. I seriously doubt the mid-range actually has the ability to reproduce that range of frequencies accurately. If it does, I'll buy a truckload of 'em from you! If the tweeter is a nominal 16ohm piece, it would come in at 5kHz, but the cap on the mid might as well not be there at 16ohms. Or are those the values you were thinking about substituting? Most people use 8ohm drivers when building their own systems. It would be good to know with what you're dealing. Do you have a multimeter? Here's the formula for capacitance per your impedance and cut-off desires(for a 6db/oct slope): C1(in uF)= 1,000,000/6.283 X speaker impedance X desired x-over freq.
halcro's avatar
halcro OP
2,664 posts
 
Thanks Rodman,
The Tweeter is 6 ohm and the Mid/Woofer is 4 ohm.
The Tweeter at the moment has a 2.2 uF cap and the Mid I believe has a 10 uF cap.
Should I stick to these values?
rodman99999
6,206 posts
 
Well- That would bring your tweeter in a little above 10kHz, and your mid- right about 4kHz. The mid isn't doing much midding that way. I'd say 80uF on the mid(500Hz) and about 5.5uF on the tweeter(about 5kHz). I suppose if you were to go with an iron core inductor on the woofer, you wouldn't have as much insertion loss(though it may become non-linear at high input levels). If I were doing it, I would use either Solo or Alpha-Core air core inductors(very low insertion loss and phase shift, very transparent). The value of the coil would depend on the impedance of course(8ohm=2.5mH, 4ohm=1.27mH for 500Hz). I suppose a .13mH to roll off the mid at 5kHz wouldn't hurt either. You may find yourself having to pad the tweet and/or mid to match their outputs with the woofer.
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