Below is a typical HD system using "Pro Drivers " and a MICRO4v2 "Bridged Stereo/Mono".
This shows the CORRECT method to do that and to set the crossovers, gains, and filters , etc. (Double click it to open...OR....right click the image and you can download a high resolution PDF to make it easier to see it)
The tweeter "attenuation" circuit is there to help set levels up between the Horn Tweeter (Which is 107dB 1W/1M sensitivity) and the MidBass driver (which is usually about 95-97 dB) That is a 10dB difference in output. A BIG deal.
We recommend that you attenuate the tweeter to make your system more "balanced" and "musical". Resistors are the "Sand" type and 10 watt version (Parts Express has these as does MCM) It is just a suggestion. You'll notice that the circuit is not simply a resistor in series but an ACTUAL attenuation circuit. Resistor is series with a resistor to ground. This is the CORRECTmethod of attenuation.