Well, it's good you record the pink noise on any device such as a good mp3 recorder on 320kbps, and use this as a external pink noise source, them plug the mp3 player on the line in of the soundcard and see if the pink noise of your source is accurate. Be sure to disable any equalizer or sound enhancement devices on the mp3 player to have the pink noise flat. Once you have your source of pink noise ready to go, plug off the soundcard and plug in on an amplifier. Now you put the mic on the mic input of the soundcard, (You can use a mixer between the soundcard and the mic but you will have to plug the mixer on the line in of the soundcard), and start testing. the mic must be at least 20cm of the speaker. If you want you can use a sealed box to make this test, than you can see the curve of frequency of your speaker on the trueRTA. Its a bit tricky to get it working for the first time and get the right parameters, you have to watch for the volume to not saturate the sound of the speaker, testing different volumes, you will get the idea how your speaker can operate in differents powers.
That's it. if you have any further questions I'm here to help
Best Regards