fEARful High-pass L-pad and resistor values for 18sound tweeter

[Oobly]

I have been studying the high pass circuit and trying different values in the L-pad calculator found here: Crossover Design Calculators

None of the values I get in the calculator will match what the 8ohm L-pad gives. Is it better to build a fixed value L-pad for the 18sound tweeter (XD125) when using it with the 18sound mid (6nd410) and 15" woofer (3015LF) and what values should I use to get a very balanced (hifi) sound without the highs being too hot or soft?

My unprofessional attempt at working this out:

From the curves it looks like the tweeter is a little more sensitive across the desired frequencies than the mid driver (looks like around 105dB from 6k to 15k compared to around 102dB from 1k to 4.5k). So I assumed a little more attenuation (about 3dB more at 6k and 2dB at 10k) should be applied to the tweeter. The mid has around 3dB attenuation (with the 15/6 Cheap But Good crossover). If I put 8.1ohm and 6dB (roughly the values of the tweeter at 6k) into the calculator I get resistor values around 4ohm series and 8ohm parallel. With 9ohm and 5dB (values at 10k) it gives 4 and 12ohm. I am guessing that 4 and 10ohm would give about the same SPL as the mid unless I am going about this the wrong way.

Is this a valid calculation or am I barking up the wrong tree here?

[dhomer]

The fEARful crossovers have been painstakingly refined to the point if you build the xovers to GB's specs, you will not have any issues. Those online calculators are a bit too generic. I would suggest posing the question on the fEARful forum

fEARful

[Oobly]

Thanks, got a reply on the fEARful site.. best to just stick to the designs there.

[Foz]

Well - sorta... my understanding of the advice you got was if you want a fixed horn Lpad just use the variable until you know where it lines up best with the choice of compression driver/horn you made and your listening tastes - then measure the series and shunt values of that variable at that setting and replace the variable with fixed value resistors. Which would be a waste of time cause the variable works fine for horns [not so good for mids].

I read that to mean you are invited to mod away and make a fixed horn Lpad if it pleases but probably not really beneficial.

FWIW the measurements I have taken of fEArfuls suggest that pulling the variable out altogether is pretty close to flat above 6k Hz [maybe an avaerage of 4 dB up] - so you might try it without. The easiest mod evah!

If you want to explore the matter further download and dink around with the passive crossover designer excel sheet linked in Greenboy's FAQ.

Have Fun!