Elliot Sound Products has a useful calculator for L Pad attenuation. (scroll down the following page a bit)
https://sound-au.com/articles/l-pad-calc.htm
The 2.2 series and 10 parallel with the 6 ohm tweeter attenuates about 4 dB, while maintaining the nominal 6 ohm load.
https://sound-au.com/articles/l-pad-calc.htm
The 2.2 series and 10 parallel with the 6 ohm tweeter attenuates about 4 dB, while maintaining the nominal 6 ohm load.
Thank you! This makes perfect sense, and helps me understand the woofer circuit calcs as well.
And it confirms to me that the original tweeter should be 6ohms impedance, so perfect.
At least I got a good deal when I bought this center. Basically paid for the aesthetics of the box. I am perfectly happy turning it into a rehab project.
4 db makes sense. I think the original tweeter was 90-91db, and the two 12-16ohm poly woofers were much lower efficiency. Maybe 84db? Doubled up woofers make 87db then.
Two methods, sort of.
(1) If the XO frequency f is known -- say 2khz -- the simplest 2nd-order has mH*uF~(5khz/f)^2 so woofer~0.5mH and tweeter~1.8mH (not aircore).
(2) Using alligator clipped wire, and a capacitor of known uF, build up a parallel notch filter mH||uF->(any)driver+ at unknown frequency f~5khz/sqrt(mH*uF) and listen to a tone sweep; the notch f should be obvious and its minimum trough audibly precise to <0.1khz; f is independent of driver impedance (notch depth isn't) so mH can now be calculated.
A notch filter is a 1st-order low-pass and high-pass both connected to a single driver, their filter frequencies (160hz*ohm)/mH and (160khz/ohm)/uF pulled apart so their geometric center (inversely related to square-root of mH*uF) is the notch frequency; the impedances cancel out (assuming near each other).
I use a free Android app Frequency Sound Generator and a fullrange driver of known flat response in the region tested for the notch.
(1) If the XO frequency f is known -- say 2khz -- the simplest 2nd-order has mH*uF~(5khz/f)^2 so woofer~0.5mH and tweeter~1.8mH (not aircore).
(2) Using alligator clipped wire, and a capacitor of known uF, build up a parallel notch filter mH||uF->(any)driver+ at unknown frequency f~5khz/sqrt(mH*uF) and listen to a tone sweep; the notch f should be obvious and its minimum trough audibly precise to <0.1khz; f is independent of driver impedance (notch depth isn't) so mH can now be calculated.
A notch filter is a 1st-order low-pass and high-pass both connected to a single driver, their filter frequencies (160hz*ohm)/mH and (160khz/ohm)/uF pulled apart so their geometric center (inversely related to square-root of mH*uF) is the notch frequency; the impedances cancel out (assuming near each other).
I use a free Android app Frequency Sound Generator and a fullrange driver of known flat response in the region tested for the notch.
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It doesn't really confirm anything. Nor is there anything you can be certain of gaining if you continue with a different 6 ohm tweeter. You'll go through a process of adjustment regardless.
True. I was just excited that 6 ohm seems to be a good fit with this crossover. I will add the new tweeter, then if it sounds good, leave it. If it doesn't, build a new crossover (I have ample nice caps on my shelf...would just need to either use these existing inductors or source new ones and pick up appropriate wirewound resistors.).
Here is one way you can get a estimate with calipers.
1. Using calipers get the winding length, diameter, awg of the inductor wire.
2. Measure the dc resistance of the coil.
3. Head over to any multilayer aircore calculators and input the data for length, diameter and gauge.
4. Then just try changing inductance till it matches the resistance measured. When it matches you have your L value.
1. Using calipers get the winding length, diameter, awg of the inductor wire.
2. Measure the dc resistance of the coil.
3. Head over to any multilayer aircore calculators and input the data for length, diameter and gauge.
4. Then just try changing inductance till it matches the resistance measured. When it matches you have your L value.