Hey there carlvigg! It truly depends on the device and your willingness to work with third party apps. Some ringtone services that you can download on the Play Store claim to have this kind of functionality (I've never personally tested them). With some devices, you can work around using an app by setting a default ringtone, placing your contacts into groups and assigning each group a ringtone. Then all unknown numbers will ring with the default. What kind of phone are you using?
Happy Sunday! Just touching base to see if you were still looking for a way to accomplish this. We're happy to help if you're still in need - or if you were able to resolve this, please let us know what worked! Thanks!