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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: passive crossover vs. active crossover posted by Metro_Noam on October 1, 2005 at 01:20:35:
If all you want is a simple 6dB highpass filter for the tweeter then all this is (in terms of a PLLC) is a cap in series at the input of your tweeter amp. I'm not sure of the equation but for 'f' you take the -3dB frequency you want for this highpass filter and for 'R' you take the input impedance of the amp.BTW, the same equation holds true for a "normal" speaker-level passive crossover except that for 'R' you take the driver impedance ... ie. 4 ohms ... 8 ohms ... whatever!!
HOWEVER, to do a good job of this crossover:
1. you really need to know what the corresponding -3dB point is of the Vifa 12dB lowpass rolloff slope, AND
2. you need to know where the resonance point of the low frequency rolloff of the tweeter is. This should be at least an octave below the -3dB frequency you select for the tweeter (which is derived from the roll-off frequency of the Vifa).ALSO, in a "normal" speaker-level passive crossover, a 6dB slope is achieved by a cap in series with the driver. This protects the tweeter against "power-on thumps" made by the amp.
If you instead use a PLLC - ie. a small cap in series with the input of the amp - the tweeter is directly connected to the amp with no "protection" ... so you need an amp with no power-on thump! BTW, there are such amps ... in my 3-way active system, my very fragile Maggie ribbons are directly connected to my AKSA ss amp.
Regards,
Andy
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Follow Ups
- Re: passive crossover vs. active crossover - andyr 02:20:09 10/01/05 (1)
- Re: passive crossover vs. active crossover - Metro_Noam 23:38:24 10/01/05 (0)
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