More on Drums, Part 1

This article is titled “More On Drums” and if you say it out loud – – say it now – – it sounds like “Moron Drums”, which could be said for the drummer but definitely not the drum. Drums are very complex instruments and this was underscored for me recently when I revisited a book titled “The Acoustical Foundations of Music” by John Backus. Some of the information I’m about to write about deserves repeated credit to John and his book and it took several readings by this moron drummer to understand it.

Drumheads

Most of the sound we hear when a drum is hit comes from the drumhead. The shell and other factors play into its tonal qualities. Don’t believe it? A Roto Tom (a metal frame drum without a shell) makes a drum-like sound when hit, and in this case, it’s the entire sound. When a drumhead is coupled to the shell via the bearing edge, energy is transferred to the shell and the characteristics of the shell tonally combine with the drumhead(s). It’s at this point that the type of wood used, number of plies, how the bearing edges are cut and other factors combine to make the ‘sound’ of different drums and even the sound of an entire drum company. But it all starts with the drumhead.

In his book, John analyzed the physics of striking a circular membrane and what happens with the sound, especially the overtones. John analyzed tympani because drums with two heads are infinitely more complex to measure. We are assuming the head is evenly tensioned and tuned. Circular membranes vibrate with several modes when struck. A mode is a line where tonal amplitude is at its peak. There are many modes when a drumhead is hit but John writes that beyond six basic modes, others don’t supply enough musical content to be concerned with. An initial hit produces a fundamental tone from the entire head surface, which we’ll call the first mode.  In the second most-useful mode (designated by the black hash line in the photo) the head divides in half and the two sides vibrate opposite of one another, out of phase; that is, one half the head moves up while the other side moves down.  (No console phase button for that.)

In the next mode (blue hash lines) the head divides into ‘quarters’ and these sections also vibrate opposite one another. Next (red hash line) there’s a modal line in the shape of a circle about half the size of the head; next the head divides into six pieces (purple hash lines) and finally another circle mode with a mode that again divides the head in half (green hash lines).  As you would expect, these modes are not the fundamental tone but actually overtones (light bulb moment) that are not harmonic. I’ll say that again – they – are – not – harmonic. The lowest tone that lasts the longest is the second mode, (black hash line) the one where each half is vibrating out of phase. The following mode’s frequency is 1.42 of  the second mode pitch, the next is 1.53 of the second mode pitch and so on, thus explaining the basic difficulty in tuning drums to begin with and the futility of tuning a drum to a ‘note’. Remember, this is a tympani, a drum that that should be tuned to a note. John again states that two headed drums are way more complex because of the vibrating second head, space between heads, air volume inside the drum, tuning, etc.

The initial strike moves the most air on the fundamental (mode one) but dies out quickly. You can demonstrate this yourself by lightly hitting a drum dead center and you’ll notice a ‘drier’ quick fading tone but if you strike off center the drum will have more sustain. The fundamental mode provides the ‘thump’ but the other modes supply the sustain and quality of the tone. This has to be repeated; the other modes supply the sustain and quality of the tone. Dampen these modes too much and you’ll will get a boxy sound (hello Eagles). Tune the drum evenly, let the head freely ring and you will have more sustain and better tone.

Here’s a way to check out the second modal line (the one with the most tone, which is a straight line across the drumhead). Back in the day, I would find the place to put the tape using this method (I know, yes I too liked dead snares then).  I still use this technique today to find the spot to put a touch of moon gel to cut a little overtone. Take your snare (with the snares off) and tap the drum lightly in the center while moving your finger around the drumhead about an inch from the rim. If you very lightly touch the drumhead as you move it around, you will hear a point where the ringing is less. That is the second modal line that runs across the drumhead and where you place the dampening material.

Here’s a video link where you can see 4 of the 6 useful modes: http://www.youtube.com/watch?v=v4ELxKKT5Rw&feature=related

Modern drumheads are made of plastic and are manufactured to exacting standards, so your results from head to head can be quite consistent. If you prefer a particular head, every time you replace the head you can expect a similar result, something impossible in the days of calf skin heads. When I started playing, white single-ply coated heads were just about all we could buy. We wanted clear heads so we would scrape the white coating off with a razor blade. Ugly for sure but we could see our shoes through the drum as we marched! As rock music came in full force, drumhead companies started introducing all manner of heads with multiple plies, dots, rings and colors. Musically driven? I don’t know. But I guess they introduced reinforced dots because drummers were playing harder and couldn’t afford to replace heads often, dual plies to darken the tone and eliminate the ring, colors for visual flair and so on.  And today, wow, there are several companies with all kinds of formulations and combinations.  Here is why all this is so important. If you understand fundamentally what happens to a head when it’s hit, you should be able to match your style of playing with the type of music you are playing with your particular drum set and choose a head that will give you the sound result you are expecting. Once you get good at this, you can even look at a kit and heads and know the sound it will make even before someone plays it.

So what is the best drumhead?  That depends on the music, but the drumhead that will allow the drum to “speak the most” is a single-ply clear head. All other heads dampen modes one way or another. Understanding how they dampen will allow you to alter the tonal qualities of your drums if that is what you’re looking for. Some heads are made for durability in live situations or if you play hard and can’t afford to change heads often. Some heads reinforce the initial ‘thump’ while making the head more durable. Some are designed to dampen the ‘ring’ a little. Some are just marketing gimmicks to lure the uninformed, which may possibly be the largest group of head types.

What I’ve noticed in the studio is when drums are tuned for maximum tone and sustain, they sit better in the final mix and feel more musical to me. Keeping the drums in this heightened state while playing hard will mean head changes as the sessions progress. It’s amazing how quick a head will ‘go dead’ in the studio with a hard-hitting drummer. Plastics also break down and harden over time. Do old heads, whether top or bottom, dampen modes, thus affecting tone?  Yes. This also explains why new drum heads, top and bottom, give you more sustain and tone. Even though you don’t hit the bottom head, over time, after countless vibrations, the plastic hardens and self-dampens. Take your favorite credit card and bend it and see what happens.

Once you understand drum heads and basic modes, you begin to think through your drum sound and will possibly think outside the box a little. For example, does it make sense to have a bass drum beater strike dead center on the head where the fundamental dies quickly and overtones are minimal?  No, unless all you want is smack and in some music it’s all about the kick smack. If you want a little more tone from the kick adjust the beater so it doesn’t hit dead center.

This is a lot of info to think about without discussing shell woods, plies, bearing edges, coverings, hardware, rims and sticks. And, actually, I have covered very little about heads, but hopefully enough to understand why drums sound the way they do.

In Part 2, I’ll write about the drum itself.

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