when I can actually
see how it sounds ...
For that it might not be necessary to by a mic. In low frequency many phone mics are pretty good. And you might find a spectrum analyser app that works with sufficient resolution.
I just did a quick and dirty test for the FR of an homepod with an old iphone7 in my kitchen.
1. A sweep with Umik (REW) Hanning window
2. The live view of periodic white noise (from generator in REW: 32k sequence and custom filtered BU2, 20-1000Hz) in iphone app "Audio Spectrum" from Pawel Krzywdzinski (you have to make an investment of 99ct) with Window set to 65536 and Hanning.
3. Then the overlay of both.

That should be close enough to get quite a good view of bass performance.
For Android there might be similar apps.
It's fun to see the FR change in real time when moving the phone around in the room. White noise above 1kHz gets rather nasty though.