Looking at crossovers with the Spectrum Anylizer

[thewire]

Using REW and looking at the crossover can be complex. Espicially when looking at mulitple crossover sources such a CD player, receiver, pre/pro, external crossover. Which one do we use and how do we look at it under a microscope?

First you need to hook up your source to the input of your soundcard.

example: Receiver right channel out connection with RCA cable - Soundcard right channel in connection with RCA cable.

This means you connect the line out that you want to look at into the right input of the soundcard. Then connecting the right line out from your soundcard to the input of your source. If there is no input at your source generally speaking for most players a CD can made from the generator to substitue the soundcard by clicking "save PN to WAV file". White PN is equal power at all frequencies which is good because we are wanting to look at a voltage reading inside the source with which in this case will be with the crossover engaged. Then we can check the sound in the room to see what happens. A correct phase between the subwoofer and mains will give the highest output level at the crossover area. If you are unsure it is correct you can examine this by measuring with REW which way works best, or standing leaning back and forth between the speakers with a THX optimizer disc you may have. The out-of-phase will seem less localized and the in-phase will seem focussed with some difference in spaciousness as you move side to side, should you choose to do that.

It is important to disable the soundcard calc file if one is loaded in the settings window. This will be added back when you measure with the mic again.



Now going into the Spectrum Anylizer, open the generator (that's the icon that says generator above) and go to the White PN. Set this to -20dB FS. Check your source is at the correct level if that is not done already, then press the record button bellow. Note that the setting mode says Spectrum and not RTA.



Pressing the green arrow in the generator starts the playback, or press play on the source. When you have a signal wait a moment then press the save button next to the record button.

Now you can go into the filters window. First add smoothing to the response you took in the trace adjustments tab area. I used 1/1 smoothing. and select the output crossover you wish to look at. Lets say we are looking at a subwoofer with an 80Hz crossover in this example. You select the "subwoofer" and make sure it is set to "80" in the tab that says target settings. Your measurement might not show so try adding something near 30 in the trace offset by highlighting it, typing in the number, and pressing enter. Whatever way you preffer you to do, get the offset to match the REW target line in blue as close possilbe to your target crossover.



Now you can do this for the other output from your source, this time one of the mains. You will need to select "bass limited" this time instead of the subwoofer.



Now you have two traces similar to the ones in REW. Now it is time to see what the speakers are doing and if the crossover is working the way we want.

Connecting the right input of the soundcard this time to your mic, place it at the location you want to measure. Make sure that you go back to the settings and load the mic calc file.

Soundcard right connection out with RCA (or other cables you may be using), to the input of your mic pre amp or mic.

Now take a measurement of both the main speaker and the subwoofer independently. Turn off the mains to measure the subwoofer, or turn off the mains to measure the sub.

Going into the measured tab you can now overlay your crossover to see how this compares to each of your results testing the source.





That is how I like to sometimes look at the crossover, espicially if I want to know how it causing interaction in my measurements between multiple inputs and outputs, or with other various equipment with filters.