Your help please - Simple X-over for spare drivers

[SoundQuest]

I have a pair of 4" Vifa drivers (no model number as they were a buyout sold through Parts Express--were used in a JBL setup). They are 8ohm. For tweeters I have a pair of 8ohm Sonance 1" textile dome tweeters (sold through Apex Jr.). I am trying to build a very simple, and I mean simple (nothing fancy), X-over for this combo with a X-over point of about 4500k. I can figure out the correct resistance for tweeter volume through trial and error so I'm mainly looking for someone to tell me what values for cap and coil I will need for a simple X-over. Any input would be greatly appreciated. I realize this is a bit hard to do without model numbers or graphs but it's all I have at the moment. Thanks in advance.

[Cal Weldon]

Here's a calculator for after you (hopefully) find out more about the drivers. It's really hard to guess what the impedance of the drivers might be at the XO point.

I recommend starting with a first order (6dB) configuration and if you find that doesn't work, meaning you don't like the overlap of the two drivers, find someone in your area who knows about XO's. When you venture into a second order (12dB) or zobels or BSC's things start to get tricky.

Are the two drivers matched in their sensitivity or efficiency? If you have to add a resistance network to the tweeter, that gets calculated into the equation.

http://www.mhsoft.nl/spk_calc.asp

[SoundQuest]

Thanks for the calculator, I used one similar and ended up with different values. Question for you on adding resistance in line on the tweeter for volume attenuation--you mentioned that this too needs to be calculated into the equation. So if I add 3 ohms of resistance to the tweeter you are saying when I calculate the xover I need to make the tweeter read 11ohms total instead of 8ohms? Thanks.

[Cal Weldon]

Yes if you are using 8 ohms as the value at the XO point. Keep in mind it's not likely to be 8 ohms as that is a nominal rating only. It varies with frequency.

Also, you can add a resistor across the leads as a by-pass. For example: If you start with an 8 ohm driver and add 8 ohm resistance in series and also add 16 ohm across the leads in parallel, you have come a full circle and still have 8 ohms. This will allow for 1/4 of the original power to the driver or an attenuation of about 6 dB.