https://www.birmingham.gov.uk/directory_record/98083/helen_lloyd
http://www.oralhistoryconsultancy.co.uk/profile.html
Helen Lloyd of the Oral History Society 'The speaker plays and talks about extracts from her audio recordings for the National Trust Back to Backs and from her CD “Memories of Back to Backs”'
She would certainly be able to advise you.
I do not think you will find any sound recordings before 1900 of working people. From the 20C there are sound tracks to films made of the Back-to-Backs, but as far as I know there are not tape recordings or records. Even the films feature a middle class narrator with a condescending attitude.
It also depends what you propose to do with the recordings. This is why oral historians like to record the voices of now older people who can tell you about life in the Back-to-Backs when they were children. The recordings you hear in the Back-to-Backs were made in this way.
I hope this is helpful.