# First diy, crossover design difficulties

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#### cocojakes

Hey, I'm brand new here, currently in the middle of building my first diy speakers, a small pair of 2 way bookshelves. I'm trying to keep things as simple as possible, and just have a first order crossover. I'm using the Dayton Audio ND25FA-4 tweeter paired with their TCP115-4 woofer. My crossover right now consists simply of a 0.23mH inductor in series with the woofer, and a 15MFD capacitor on the tweeter. The real issue though is that the tweeter is substantially louder than the woofer (by about 5db according to their spec sheet graphs) but as a beginner, on a mac, I haven't been able to find any software I can use to properly work out my crossover, and instead used a simple online calculator to work out the 1st order crossover. I know I can bring down the tweeter with a resistor, but don't know the math to figure out what size resistor I'll need to buy.

Any help from someone with a bit more experience, or access to proper software would be greatly appreciated.

#### cocojakes

Okay, so I would switch to a 7.5MFD capacitor, in series, and add an 8ohm resistor in parallel (after the capacitor?). Any chance you could give the equation for working that out? That or if its a standard concept I could look up, so that in the future if I need to adjust a speaker by 2db or 6db or whatever, I can do the math myself? I'm trying to figure out how much of this I can do by hand since none of the software will run on my computer.

Thanks for the quick reply though!

#### Galu

Here's a useful source of information on all things crossover: The Crossover Design Cookbook

P.S. The resistor goes in series with both the capacitor and the tweeter.

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#### Galu

The 8 ohm resistor and 4 ohm tweeter form a simple voltage divider.

Voltage Dividers - learn.sparkfun.com

The signal voltage is divided up in the same ratio as the resistances - in this case 2:1

So, the voltage (V2) which reaches the tweeter is only one third (0.33) of the full signal (V1).

You can convert to dB using this calculator:

Voltage to dB Converter

e.g. V1 = 1V and V2 = 0.33V gives -9.63dB

#### Galu

P.S. The resistor goes in series with both the capacitor and the tweeter.
Like this!

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• Tweeter Resistor.png
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