For passive, and even now some active loudspeakers, very much so.

Links for passives: sites.google.com/site/undefinition/diy www.zaphaudio.com www.madisoundspeakerstore.com/speaker-kits/ (etc)

Active speakers are usually things like this and use commercially available parts with commercial software. But if you want you can build a DIY DSP and DAC and DIY amplifier. Note that there are tons of other designs for both available.

The DIY audio community is very vibrant. [There](www.diyaudio.com/community/] are tons and tons of forums collaboratively iterating. You can build [DIY headpy](github.com/ploopyco/headphones] and DIY headphone amplifiers. Hell, you can even build [DIY speaker drivers].

Anything I missed was not an intentional omission, lol.