Passive crossover/filter question - diyAudio
 Passive crossover/filter question
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 Multi-Way Conventional loudspeakers with crossovers

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 26th January 2010, 02:19 AM #1 diyAudio Member   Join Date: Jan 2004 Location: Canada Passive crossover/filter question I searched the site and many other places with no luck. Just one simple question... A second-order LC filter (high- or low-pass) has a specified cutoff or resonant frequency (f3). At this frequency the output of the connected driver is down 3 dB as compared to its output without the filter connected. Let's say that f3=500 Hz and we're dealing with a low-pass filter. In theory, what would be the amount of attenuation at 1000 Hz? Would it be 12 dB or 15 dB? While we're at it, what would be the theoretical attenuation at 2 kHz? 24 dB?
 26th January 2010, 02:57 AM #2 diyAudio Member     Join Date: May 2003 Location: Saskatchewan 1st order filters have a 20 dB/decade (or 6 dB/octave) slope. 2nd order filters have a 40 dB/decade (or 12 dB/octave) slope. 3rd order filters have a 60 dB/decade (or 18 dB/octave) slope. etc... An octave is x2 the frequency A decade is x10 the frequency. __________________ The power of Science compels you!
 26th January 2010, 03:00 AM #3 diyAudio Member     Join Date: May 2005 Location: SoCal slopes of filters are determined by the order except close to the cutoff. For figuring attenuation at least an octave or greater away the cutoff freq is calculated as the reference ie at O dB. so for your example the answer is 12 dB. we use an asymptote for filter slopes. http://upload.wikimedia.org/wikipedi..._High-Pass.PNG 1st 6 dB/octave 2nd 12 dB/octave 3rd 18 dB/oct 4th 24 dB/o __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

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