vxla wrote:A good reference for this discussion is
The Science of Percussion Instruments by Thomas D. Rossing. More specific pitches will only be heard when a good, solid fundamental is produced by using the fleshy portion of hand (with fingers closed) between the edge and center of the drum head. On page 36 of the aforementioned book, an example of the sound spectra of various strokes is shown. The book can be previewed on Google Books (and page 36 is available) here:
The Science of Percussion Instruments.
Vxla, nice reference, thanks. That book is out of print, and the percussion chapters of Fletcher and Rossing are less detailed regarding congas.
The frequency by amplitude spectral graph (Figure 4.11 on p. 36 in the Rossing link you posted) shows graphically exactly what both Leedy2 and I agree on, that there are lots of frequencies present in the sound of a conga tone. It also shows that there is one loudest frequency peak that is the perceived tone of the drum at its current tuning. What Leedy2 is calling distortion is actually a mix of many different harmonics from the different vibrational modes of the vibrating membrane/plate that is the skin, plus the resonant responses from the shell cavity. There are many fundamental frequencies emitted by an uneven skin, each with its own set of harmonics, so the overall harmonics are extremely complex as shown in the spectral plot. Where I disagree with Leedy2 is that I would call the fundamental frequency peak, which is many times louder than any of the other frequencies, the main tone of the drum as tuned. He seems to be saying that there is no main tone and no frequency can be identified as the pitch of the drum. Leedy2, I know you will speak up if I have misstated what I understand your opinion to be. If I interpreted your previous statements incorrectly, please explain what you mean by an untuned instrument. The spectral plot directly refutes that interpretation, as the fundamental frequency peak at 240 Hz is a single identifiable pitch that is many decibels louder than all the other frequencies that are produced by the drum. This is most clear for the tone, but can also be seen in the bass, albeit the amplitude difference between the fundamental and the harmonics is much less clear.
Also, whoever played the conga for the spectral analysis in Figure 4.11 must have played a very sloppy open slap that sounded almost like a tone, since the slap graph has the same fundamental ((0,1) mode) peak at around 240 Hz as the tone, and it is almost as loud. You can damp the (0,1) mode by pressing a finger in the center of the skin to stop vibration of the center of the skin. This will greatly change the sound of the open tone and open slap, but has little effect on the closed slap.
The bass note is also very sloppy, as the harmonic at 280 Hz is almost as loud as the fundamental at 70 Hz. Poor technique, or the drum was not tipped optimally or mounted on a stand to let the bass be heard clearly.