Hit It Like It Owes You Money! Batala Drums Go BOOM
By Andy Dehaney-Steven, Batala London Fundo player and drum fixer
Where do we get our Batala drums?
Batala drums are made for us in Salvador, Bahia (Brazil). That’s also where a lot of the other bits that make Batala look and sound like Batala are made. The people who make the straps and baquetas, paint the drum skins, sew the costumes, make the belts and print our fabric are all based there.
How are our drums made?
The anatomy of our drums is very simple. There’s a steel cylinder (a shell) of a specific diameter which will take commercially manufactured drum heads (the ‘head’ is the bit you hit). Then we have a couple of rings, again made of steel, with small lugs evenly spaced around the circumference. The diameter of the ring is slightly more than the diameter of the shell and slightly less than the diameter of the head.
A head goes on each end of the shell and the rings go over them. M6 threaded rods go through the lugs between the two rings and are tightened to tune the drum.
Now we have a thing to hit.
We all know, “Hit drum, drum goes BOOM!” That’s all well and good but what actually happens?
First, what is sound anyway?
This is the science bit, pay attention at the back.
Sound is vibration travelling through a material such as air, water, wood or metal. In air, it moves as a wave of changing pressure: regions where air molecules are pushed slightly closer together are followed by regions where they are slightly farther apart. The air itself does not travel all the way from the drum to your ear. Individual air molecules mostly jiggle back and forth around their usual positions. What travels is the disturbance¹: the pattern of high and low pressure.
What reaches the ear is this travelling pattern of pressure changes. The frequency of the vibration determines the pitch, the amplitude determines the loudness and the mixture of frequencies gives the sound its tone or character.
Frequency is how many vibrations happen per second. Higher frequency means higher pitch. A small, tight drumhead tends to produce higher frequencies; a large, looser head tends to produce lower ones.
Amplitude is how large the pressure changes are. Greater amplitude means louder sound, because the air is being compressed and expanded more strongly.
Wavelength is the physical distance between one compression and the next. Low notes have long wavelengths; high notes have short wavelengths.
Speed is how fast the pressure wave travels through the medium. In air at room temperature, sound travels at roughly 343 metres per second. It travels differently in water, wood, metal and other materials because their particles interact differently.
You’ll hear us coming before you see us.
How does the drum go BOOM?
When a drum is struck, the stick pushes the top drumhead out of shape. The tension in the head pulls it back, so it begins vibrating up and down.
That motion compresses and expands the air inside the drum. The changing air pressure reaches the bottom head (or resonator), causing it to vibrate as well. The bottom head then affects the enclosed air and the top head in return, so energy passes repeatedly between:
the top head
the air inside the drum
the bottom (resonator) head
and, to a lesser extent, the shell
It is not quite a single shock wave simply travelling down, bouncing off the bottom and coming back. It is better thought of as a set of coupled vibrations and pressure waves². The waves reflect inside the drum and interfere with one another, forming resonant patterns.
Each drumhead has natural frequencies determined mainly by its diameter, tension and mass. The air cavity and shell also have resonant frequencies. When the drum is tuned so its vibrations work well together, energy is reinforced rather than quickly cancelled or absorbed. The drum then rings longer and more strongly: it resonates³.
The sound heard outside comes mainly from the vibrating heads pushing the surrounding air.
Our bass drums (Fundos) are large and have a lot of air to get moving. They need a good hard thump.
Andy, our long-term Fundo player and drum fixer, is often heard encouraging new players to:
“Hit it like it owes you money.”
In plain English
1. Disturbance | Think of a Mexican wave. The people stay roughly where they are, but the wave itself travels around the stadium. Sound moves through air in a similar way.
2. Coupled vibrations | Different parts of the drum are vibrating together and affecting each other, rather than each part behaving independently.
3. Resonance | When vibrations reinforce each other, allowing the drum to ring more strongly and for longer.
