i'm confused about caps and coils

I read the diagrams on 2nd order caps and coils. I think thats what Im after. I'm trying to cut the low end and volume to my dash speakers, more so the volume. There 4 ohm 4x6 speakers. There running parallel with the kick panel components off the amp, which is set to 100 hz high pass. The amp is 2 ohm stable in stereo. To figure on the right cap I need to know the impedance. Is the impedance the speaker rating, 4 ohms? or the load rating, which I guess would be 2 ohms. I've got my head in a knot over this.

The impedance is going to be 4 ohms.  You want the cap in series with the dash speaker only.  Door speaker directly to amp.  Cap or coil only in the path to dash speaker.

Will a cap actually drop the volume level as well? Or am I misunderstanding the idea of 1st, 2nd and 3rd order? thanks

jetmech_jt8 wrote: Will a cap actually drop the volume level as well? Or am I misunderstanding the idea of 1st, 2nd and 3rd order? thanks

No. The caps and coils ONLY perform crossover functions, not broadband attenuation. For that, you need either a padding network or a simple attenuating resistor IN FRONT OF the crossover. The preferred method is the padding network, but there are additional calculations required for those. There are additional calculations required for the resistor, as well, but they are easier to implement, and require fewer components. The order numbers you are asking about describe how fast the crossover slope affects the output of the frequencies below the crossover point. First order = 6dB/octave rolloff Second order = 12dB/octave rolloff Third order = 18dB/octave rolloff ...And so on, with each order equaling 6dB/octave faster rolloff than the previous order.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Just what I needed, more complexity, oh well, something new to learn that's all. Now where would I start with trying to figure out what resistor I want? Are these just standard resistors that go in line with the cap? I'd like to drop the volume by 50% to the dash speakers.

Ok, I looked up an L-Pad, it appears to basically be a reostat. The one I found is a 15 watt stereo L-Pad with 3 connections on it. How do I go about hooking this up? I assume both the dash speakers will tap into this and the one volume knob will turn them both down.

Well, in simplest terms, 50% is 3dB. A 3dB drop on a 4 ohm driver would be a 4 ohm resistor. This is the fixed resistor value. The rheostat, if it is a stereo rheostat, would be able to adjust both speakers, yes. If it is not, then you must have one for both speakers - one each. You said it has 3 terminals; I am going to guess (fairly safely) that this is NOT a stereo 'stat. Your amplifier positive will go on one of the outside terminals. Your amplifier negative AND the speaker negative go on the other outside teminal. The speaker positive then connects to the center terminal - the wiper. If you turn the knob in the "up" direction, and it gets quieter, you need to reverse the three wires (the amp positive, and the amp/speaker negative) on the outside connections, but leave the center one alone. Connect them first, without soldering, to make sure you can move wires easily after testing.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Thanks, great explanation.  It could very well be a four point unit, I was looking at a stock photo.  As far as frequencie goes, if I want to cap at 500 Hz, would I just add that in the positive wire after the Pad?

The pad is directly before the speaker;  the crossover occurs before the pad.  That's the usual scenario, anyway, in a passive design.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.