Rhythm: Bass
The Afro-Cuban bassline, also called a tumbao, glues the piano montuno to the conga tumbao; mediating the space in between them, providing rhythmic integrity when both behave under tension. In this space beats the heart of the song.

Traditional Afro-Cuban tumbaos for son styles at their simplest comprise just four notes per clave phrase, but they must be well placed. A well played tumbao is unobtrusive in its support of both piano or guitar and conga - noticed least when present, noticed most by its absence. This one observation highlights the power of the bass in conveying its message, the groove, at near-subliminal levels when it is as much felt as it is heard.

The instrument
Better coverage of the pros and cons of acoustic versus electric, upright versus guitar are available elsewhere. Only the main considerations relative to playing salsa are mentioned below.

With acoustic bass instruments, it's simply a matter of physics. The lower frequencies have longer wavelengths and require larger resonating surfaces. The ideal would be the acoustic double bass, which would be flexible enough to be played pizzicato or bowed for the older genres like the danzón. Its surfaces could be played with the finger and thumb joints for percussive accents. There are few acoustic bass guitars that could get into the same region, and the best I've come across is the Guild B30E.

Then there's the electric upright or bass guitar; more portable, less fragile, and a plethora to choose from. I would tend towards a 5-string over a 4-string if my hands were large enough.

What to play
The most important single note to get right timing-wise is, by far, the bombó; located on the upbeat between beats two and three. It is key to getting the feel of rhythmic tension right in the groove. The second most important is the ponché which falls on beat four. Combining them both you get the traditional tumbao which is loaded towards the later half of each bar.

Recommended tumbaos to start with are (in order):

• Traditional tumbao (without clave orientation) - bombó and ponché
• Tumbao indicating clave orientation using a synchopated 2-side - beat 2, bombó and ponché on 2-side / bombó and ponché on 3-side
• Tresillo (without clave orientation) - beat 1, bombó and ponché

Two of the most useful pointers I received when I started playing Latin bass were:

1. "Less is more". The most effective bassline gives the most support with the fewest notes.
2. Mute the strings with the fingers of your dominant hand on beat two before you play the bombó. The "2" coincides nicely with the slap stroke of the conga and serves as a calibration point; then all you have to learn is the time interval from the slap to when the note on the bombó should be sounded.
    

Recommended Resources

Salsa Guidebook For Piano & Ensemble by Rebeca Mauleón. (External link)

The True Cuban Bass by Carlos Del Puerto & Silvio Vergara. From the same people who brought you "101 Montunos". A well planned book, the link is to the book and CD package. (External link)

The Latin Bass Book: A Practical Guide by Oscar Stagnaro & Chuck Sher. This is a weighty tome and must be the definitive work on playing Latin bass. (External link)