And I don't mean the slope of a line, but a crossover slope. I know how to set the slope on my HU so that it sounds good to ME, but I still have a tough time visualizing this concept. Here is how I see it. Let's say on my HU I have my mids crossed at 100 Hz with a 12 db/octave slope. Then that means for every octave ABOVE 100 Hz, the decibal level decreases 12 db/octave? That's how I read it. Maybe I am over or under simplifying it. Sorry for the noob question, but it bugs me to not truly know what this means.
That's exactly what it means. 12 db/octave, is exactly as it says. For every octave above or below the set frequency it decreases by tht much, depending on whether it's a HP or LP. for example, a 18 db/octave HP is decreases 18db for every octave below the set freq. And the exact opposite for LP.
Let's say I have my mids crossed at 100 Hz and the slope set at 12 db/octave. By the time you hit those high frequencies, like 10K Hz and above, it seems like you'd lose a lot of volume if you had a slope of 12-24 db/octave. I think that is where I am getting things confused.
Slope = rate of attenuation. Usually the slope of attenuation is divisible by 6 (6, 12, 18, 24, etc.). And it's quite literally what its name implies. A 12 dB slope on your high pass filter (set to 100 hz, for example) will result in output below 100 hz dropping at a rate of 12 dB's per octave. So, at 50 hz, output has dropped 12 dB's. At 25 hz, it has fallen another 12 dB's...This all takes into account whether your speaker can play frequencies above/below you crossover point. You can HP your tweeter at 3.15 khz at 12 dB/oct, but that doesn't mean it will still play 30 hz at a greatly reduced spl level (it won't go that low to begin with). LP your sub at 30 hz also doesn't mean it will play 15 khz at some greatly reduced rate. With the exception of true full range speakers, which aren't used in car audio, most speakers have a limit as to how high/low they can play. At some point, even when no xover is used, output just plummets...sometimes in a "brick wall" fashion. Also, when you high pass a set of (passive) components, you're really only high passing the mid being used. As said above, your mid isn't playing (or even capable of playing) 10 khz at any level...that's what your tweeter is for Output from the tweeter won't be affected by the HP filter of your component set amp or HU hp filter.
Ohhhhhhhhhh, the slope pertains to the output BELOW the crossover frequency (in the case of a high-pass xover) and the output ABOVE the crossover frequency (in the case of a low-pass xover). Now it all comes together. Thanks for the clarification - I feel enlightened now!
Another couple basic, but on-topic concepts: An octave - Just like in music class... a tone one octave higher than another tone will be the same note, just one octave higher. Every time you double or halve your frequency, you traverse one octave. For example, 50hz is one octave higher than 25hz, and 16,000hz is one octave higher than 8000hz. Fun with octaves - The Audiocontrol Epicenter (and Epic150 and Epic160) are fun toys. They take certain tones out of the music (something like 50hz-160hz, although I don't remember exactly), and mathematically divide them in half, creating artificial tones exactly one octave lower (if I'm right on the frequency guess, that would be 25hz-80hz). It gives you a knob, to give you control over how loudly you wish this artificial bass to be mixed in with the original music. Fun toy. B) Slope - rate of attenuation, or rate of cut/boost, or rate of rolloff... just depends on what you are talking about. For example, if you had a low-pass crossover on a subwoofer, let's say you had selected a crossover point of 80hz: If you had a 12dB/octave filter - that means that one octave higher - 160hz - it would be attenuated by 12dB. One more octave - 320hz - it would be attenuated by 24dB. One more octave - 640hz - it would be attenuated by 36dB, etc. If you had a 24dB/octave filter - that means that one octave higher - 160hz - it would be attenuated by 24dB. One more octave - 320hz - it would be attenuated by 48dB. One more octave - 640hz - it would be attenuated by 96dB, etc. Crossovers never work like "walls", just blocking frequencies - there is always a rate of attenuation like this... and as you can see, it can be dramatic. A 6dB/octave crossover is very shallow (but dirt cheap!), while a 24dB/octave slope or better really attenuates off fast, as you can see. B)
Really good stuff Geo - just like any discipline or area of interest, knowing the terms and the basics is important. This really helps.
