As the title says, I'd like to know at what tempo should J.S.Bach's fughettas be played. I specifically speak about BWV 704 Fughetta: Lob sei dem allmächtigen Gott, but I believe it's applicable in general. For this one I have seen two printed versions and none of them mentions any tempo. And for instance here it's played at c. 1/2 = 80, but my intuition would be to play it quite more slowly:
Is there any consensus on the proper tempo or proper tempo feeling of such a piece?
Tempo assignments and the tempi of performances by others are not normative.
If you consider a slower or faster tempo as more reasonable or more adequate you can always choose another tempo. Mind there will always be people who find it should have been different.
I cannot find online manuscripts of Bach's fughettas, but manuscripts are available for the Well Tempered Clavier and the 15 Two Part Inventions. Manuscripts are the actual scores written out by Bach himself.
Those two manuscript sources do not have tempo indications. Certainly no metronome markings but also not even expression markings like "allegro."
At that time musicians had a general understanding about how something should be performed based on meter and the rhythmic value of notes, and also basic genres. As an example, a sarabande in 3/2 meter with lots of half notes was understood to played properly at a slow tempo. But a courante in the same 3/2 meter with lots of quarter notes and shorter values would be played at a brisk tempo. A lot of that was just understanding the conventions of those dance genres, but I think the performance of those dances probably informed the performance of other musical genres with similar meters and rhythm values.
This doesn't mean their were absolutely no tempo/expression markings. Plenty of baroque music would indicate 'vivace', 'gave', etc between musical sections or movements. But it's important to understand many pieces have no indication and there are assumed performance conventions.
I have an Alfred edition of Bach's Inventions which includes an index of metronome markings from about a dozen different previous editions. Some of those tempos differ by double!
I think it's perfectly acceptable for you to try a wide range of slow tempos. Given the title you want gravitas not sprightly (IMO.)
The tempo choice is often up to the performer. It's not clear what tempi are meant even if an indication is used. This article has some discussion: http://www.pianosociety.com/pages/bachsnotationoftempo/
Tempo may have to be varied depending on venue acoustics. A place with a long reverb time sometimes requires a slower tempo than does a place with short times. One has to experiment (if there's time) and rely on your own musical taste.
I did read (somewhere) that composers often start using the usual Italian phrases (allegro, adagio, etc.) then try metronome markings, then return to Italian phrases. It's not an exact science (but teaching a judgement to a computer is even harder that teaching it to incoming freshmen).
