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Old 3rd December 2009, 08:08 PM   #1
cuibono is offline cuibono  United States
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Default WWYD? Higher order acoustic slopes and lower order targets

This may be an amature question, but also complicated - at least too much for me.

I'm working on an active dipole/open baffle crossover. I'm using two small neo tweeters, back to back, wired out of phase to make a dipole tweeter. They normally have a second order HP character (f3 of about 2000Hz). Used dipole, this becomes 3rd order due to dipole roll off. I've blown my prior pair of tweeters (from switching/static, not music), so now I'm going to include protection - a cap at the crossover point. This gives a total acoustic roll off of -24dB/oct (fourth order) at 2000Hz.

Here is my issue - I want a 2nd order acoustic roll off, but I also need to attenuate the LF content before it hits the tweeter, right? I would minimally want to HP the signal hitting the tweeter at 12dB/oct, before it hits the tweeter? How do I do this?

The only way I see is to put a 2nd order passive filter between the amp and tweeter, then boost the lows in the active XO to get a 2nd order acoustic HP filter. There must be an easier way...
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Old 3rd December 2009, 10:22 PM   #2
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When all is said and done, turning a 3rd order native acoustic response into a final 2nd order acoustic means you are boosting the lows, not cutting them, no matter how you get there electrically.

What is your desired Fc? If it's high enough, say 4K or above, you could tailor the response so it's 2nd order for a while and then rolls off much steeper at a lower frequency, say below 2K.
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Old 3rd December 2009, 10:34 PM   #3
badman is offline badman  United States
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No filters are symmetrical for infinitely long. Usually 2 octaves of target rolloff is considered sufficient for most filters.

What's your target crossover point? Why are you decided upon a 2nd order target function?
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Old 3rd December 2009, 11:36 PM   #4
cuibono is offline cuibono  United States
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Thanks for the input. I guess I'm being too particular - I wanted to get things 'perfect', but that definitely isn't possible. I guess I'll try and cross at about 3.2kHz, although I'm not happy with that - my previous tweeters were crossed at 1700Hz without problem, but these need to be crossed much higher...
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