When inbuilt it is usually called a rumble filter or subsonic filter, just a HPF by a different name. If you are TC it is robustly ignored in all literature as it is very much higher than everyone else's non adjusting HPF.
Afaik Genzler, Mesa, and one or two very boutique brands chocka with onboard processing, are the only ones with adjustable HPF.
If you can push your string and watch the speaker move there is no filter.