Drum Science - Part 2

Welcome to this podcast series on the science of drums, where we’re exploring everything related to drum acoustics, drum kit setup and approaches to drum recording and production. I'm Professor Rob Toulson. I've studied the science of popular drums for over 20 years and in this series I'm discussing some of the scientific theory on drums in a practical way so that it can be useful to all drummers and studio engineers. In this episode, I'll be discussing how some of the scientific theory on drums relates to a real world scenario, where a drummer or producer is looking to get the absolute best sound out of a drum kit, either for a live performance or a recording session. We'll refer to this as optimising the sound of the drum kit, though in reality the term optimal is quite subjective. More importantly, we're interested in considering how musicians can control and modify their drum sound to achieve exactly the style and nuances that they are looking for. So it often comes down to a personal preference, but having a knowledge of what changes are possible and what modifications result in which particular sound characteristics allows you to get to a desired result quicker and more repeatably. 01:09 - Drum Heads When we talk about manipulating the sound of drums, no single aspect of the drum sound can be personalised more so than by the choice of drum heads. A good choice of drum heads and knowledgeable tuning can make a cheap and simple drum kit sound far better than an expensive kit that hasn't been set up properly. So the type and size of drums you choose have a big influence on the sound of a kit, but nothing comes close to influencing the sound as much as the drum heads you choose and the way you tune them. So investing in and experimenting with different drum heads is a necessary requirement for all drummers and I would say it's a valuable learning exercise for all sound engineers too. 01:44 - Mersenne’s Laws Let's just cover some of the acoustics principles of drumheads before we start comparing different types. Now as with most acoustics concepts, there's a scientific theory and a mathematical equation that relates to the physical properties of a drumhead. In fact, it's possible to see that the drumhead equation, as we might call it, is very similar to a famous acoustics equation called Mersenne's equation that relates to the musical strings which we see on the guitar, piano and violin. The factors relating to the pitch or frequency of a string are the tension of the string, the length of the string, and the thickness or weight of the string. We know practically that tightening a string makes its pitch go up, shortening the string makes its pitch go up and thinner strings have higher frequencies too. So next time you're at a guitar, take a look. Tightening the string with the headstock makes the pitch go up. Reducing the length of the string by moving to a higher fret also makes the pitch go up. You can also hear that the thinner strings vibrate at higher frequencies or with a higher pitch, even though they're roughly the same length and have similar tension. So exactly the same principles apply to drum heads too. When we tighten the drum head, its vibration frequency increases. When the drum head has a smaller diameter, it has a higher pitch. And drum heads that are thinner allow higher pitches too. So with this in mind, we control the pitch and frequencies of our drum kit. If we want a low tuned kit, then we should use thicker drum heads and larger diameter drums tuned with relatively low tension. If you want higher sounding pitches in the kit, then use smaller drums, thinner drum heads and tuned to higher tension. Of course, there are lots of options here. You can also have different combinations. Thick drum heads on small diameter drums tuned low, or big drums with thin drum heads tuned to a medium tension. There are so many permutations, all you can really do is experiment to find what combinations suit you best. So it's no surprise that drumheads come with different thicknesses to allow you to find the right thickness for your own preference. 04:05 - 1 and 2 Ply Drum Heads Generally, there are two ways in which thickness or weight of a drumhead can be increased. One method is to add a coating, which makes the drumhead heavier and the other is to add a second layer of drumhead, known as a 2 ply drumhead and this makes the membrane twice as thick and twice as heavy as a 1 ply drumhead. Let's take a listen and compare drumheads with two identically tuned drums. So first we'll compare single ply clear and coated drumheads. Both of these drums are identical, they're 13 inch drums and they're both tuned to a fundamental frequency of 98 hertz. with an overtone frequency of around 1.5 times the fundamental. First let's hear the clear drum head, followed by the coated drum head and let's hear some alternation between clear and then coated. It's really quite subtle, but hopefully you can hear that the coated drum head sounds like it has slightly more low frequency energy, with less powerful overtones, and a slightly crisper attack caused by the stick hitting the harder surface of the coated drum head. The clear drum head has subtly more overtones and a slightly longer decay time and you can hear a little bit of pitch bend as the stick makes contact with the drumhead. The pitch bend is caused by the fact that for a fraction of a second the stick contact causes the drumhead to stretch, giving a momentarily higher frequency that settles after the contact between the stick and the drumhead ends. The pitch bend is less apparent with the thicker coated head, which doesn't stretch as easily as the clear drumhead. 05:45 - Damping Systems As we've heard, different drum heads also resonate for longer and shorter times depending on their design. Many rock drummers tend to like their drum sounds to decay quickly, so drum heads with built in damping systems have also been developed. The most common is an edge control system built around the edge of the drum, which causes the overtones of the drum head to decay quicker than they would normally. Let's hear a comparison between a clear drum head and a clear drum head with overtone control. Again, both are identical 13 inch drums tuned to a fundamental of 98Hz and an overtone frequency of around 1.5 times the fundamental. Let's hear the clear drumhead, followed by the edge control drumhead and some alternation between clear and edge control. Now hopefully you can hear that the edge control drumhead still has the overtones you'd expect to hear from a clear drumhead, but they decay quicker and allow the lower fundamental pitch to remain as the most powerful sound characteristic. Now there are lots of combinations and permutations too. We've got clear, coated, single ply, double ply, and many different approaches to edge control, so you need to test different designs and different manufacturers methods in order to find exactly the sound you are looking for from your drumheads. 07:10 - Center Dot Drum Heads Another common type of drumhead is the Center Dot. This adds extra mass to the centre of the drumhead and also provides some extra durability for hard hitters. The Center Dot is another way of dampening the drum. Adding mass to an object usually causes its natural frequency to reduce and also creates more inertia, meaning that a vibration comes to an end sooner. A Center Dot is quite suitable for a snare drum, because it benefits from the extra durability, and many drummers like a heavily damped snare drum too. Let's hear a snare drum tuned with and without a Center Dot drum head. For this we'll use a steel drum tuned to a fundamental of 185Hz. First let's hear a standard drum head without the Center Dot and now the Center Dot drum head and some alternation between the standard snare head and the one with the Center Dot. Again, the difference is subtle, but the Center Dot adds just a bit of extra damping to the snare, which satisfies most drummers that don't like excessive ringing. As you know, the snare is a really important instrument in modern music of all styles, so the snare sound is something that drummers give a lot of thought and attention to. So while we're here, let's take a listen to this steel snare drum with the Center Dot drum head, at a few different tuning frequencies. First we'll tune it to the lower end of its range. And here we have the drum tuned to a fundamental frequency of 155Hz, which is about a D sharp on the musical scale. We've now tuned the drum to 175Hz, which is an F note and now we take the drum to around the top of its tuning range, to 196Hz, which is a G. So let's just hear those three tunings again. First low, then medium, then high. So you can hear that we have a lot of options with a single drum just through tuning. Taking it from a low frequency to a high frequency and those different sounds will suit different genres of music and different projects. 09:27 - Choosing Your Timbre Now as we turn our attention to snare drums, it makes sense to introduce another musical acoustics concept, which we call Timbre or Timbre. By definition, Timbre is the word we use to group together all the other sound aspects that can't be described by volume and pitch. The drummer determines the pitch and frequency by tuning, and the volume is related to how the drum is hit or performed. So the Timbre relates to all the other sound characteristics that aren't controlled through tuning or performance. So with reference to other instruments, If a guitarist plays the same chord in the same way on two different guitars, the timbre is what defines the difference between the two sounds. A soft middle C note on both a trumpet and a clarinet differs by the timbre of the sounds. The difference between the sound of two singers holding a single note is predominantly from the difference in the timbre of their voices. And in the same way, two drums tuned to exhibit the same fundamental and overtone frequencies differ in sound by their timbre. So the timbre of a snare drum is affected in a number of different ways. Firstly, by choosing the drum head, which we've already heard examples of. Secondly, the shell material. Third, setting the snare wires on the underside of the snare and also by controlling the damping of the batter drum head. Furthermore, different manufacturing methods and the shape of the bearing edges of the drum can make a difference to timbre and the design and material of the hardware attached to the drum shell itself can also influence the overall sound and timbre. Now we'll talk about the shell material in a moment, but first there are a couple of valuable points to make about snare tuning. So with a snare drum, the snare wires on the underside tend to add damping to the fundamental frequency more than they do the edge overtone. Because they limit the amount the drum head can vibrate through the center. As a result, the overtone becomes much more prominent, and if you are tuning a snare to be in key with a song, you may want to focus on the overtone frequency for tuning instead of the fundamental that we would generally listen to with tom tuning. Additionally, there are many ways to set up the snare wires but in most cases, it's good to find the right balance that gives a tight, connected sound, but without choking the drum and stopping the drumheads from vibrating naturally. Of course, you can always add extra damping and weights to the snare batter drumhead too, but if a heavily damped sound is what you're aiming for, personally I would recommend trying a damped drumhead style, with edge control and or a center dot first. 11:44 - Selecting Your Drum Shells Now let's turn our attention to the drum shells. Let's hear the difference between two snare drums that have the same drumheads installed. They're both 14 inch diameter and 5.5 inch deep, and they're tuned to exactly the same fundamental and overtone frequencies. In this instance, both are tuned to 175Hz with the snare wires disengaged. The first drum is a steel snare and the second drum is an oak snare. So let's hear an alternation between steel, then oak. It might be surprising that the difference between the sounds is extremely subtle. It's clear that far more influence on the drum sound can be made by drum head selection and tuning than by the drum shell itself. Now before moving on to talk about tuning the whole drum kit, let's talk about the shell vibration in a little more detail first. So as the drum heads both vibrate up and down, they force the shell to vibrate too. But owing to it being a cylindrical shape, the shell's most prominent vibration, see, is in the perpendicular axis to the drum heads. To visualise the shell vibration, imagine looking down on the drum. As the shell vibrates, its shape deforms from a perfect circle into a slightly oval shape with a greater radius in one direction. Then it vibrates back towards its start position. It overshoots and deforms with a slightly shorter radius, and continues back and forth until eventually all vibration energy is lost. Now much of this vibration is constrained by the hoops and the drum heads themselves, which attempt to keep the shell in a perfect circular shape. So as a result, the influence of the shell on the drum sound is quite minimal in comparison to the choice of the drum heads and the tuning. I'm often asked about tuning the drum heads to match the shell frequencies, but the natural vibration frequencies of the shell change completely when we add hardware and drum heads, so there's no real value in tapping bare shells to see how they sound, or trying to tune the drum heads with reference to the sound of the drum shell itself. One area where the drum shell can make a big difference is in the depth of the drum. With deeper drums, the acoustic connection between the two drum heads is weaker and that decoupling results in lower frequency vibrations. So deeper drums allow you to tune to lower frequencies, so if you want low sounding drums you can either use bigger diameter drums, or deeper drums, or both of course. Equally, shallower drums have a stronger coupling between the two drum heads. This gives them a higher fundamental frequency, which explains why a 14 inch snare can be tuned higher than most 10 or 12 inch toms. Shallower drums are also a bit more sensitive to tension changes and hence trickier to tune, and the strong drum head coupling can make them ring for longer also. 14:25 - Optimising The Whole Kit Now let's consider optimising the drum kit as a whole and for specific genres. It's generally accepted that rock and metal drummers tend to tune to lower frequencies and jazz and funk drummers tend to tune to higher frequencies, with pop and fusion drummers tuning somewhere in between. So if you want to have drums that give deep low frequencies and are tuned to be powerful and bass heavy, then it makes sense to have larger diameter drums. The opposite applies too, so if you want to play drums that sound bright and tuned high, then it makes sense to have smaller diameter drums in your kit. You can have some fun with this theory though, experimenting with your own style and preference. It's well known that John Bonham of Led Zeppelin had a strong musical influence from the jazz world, but he also wanted to contribute powerful and identifiable drums to a song. Bonham's approach to the drum sound was therefore to use quite large diameter drums, yet with drum heads tuned to a fairly high tension. Now this gave a relatively high fundamental pitch to his drums but with a clearly defined and powerful sound for each drum, which many drummers try to emulate. Now drummer Terry Bozzio, who's played with Frank Zappa and Herbie Hancock and Korn, has pioneered approaches towards musical tuning of drums. He has a big kit, which he takes on tour, including 26 toms, each tuned to a different musical pitch. Now he uses 14 8 inch piccolo toms, tuned over an octave range from C#5, which is 554Hz, down to C4 at 262Hz. He also has a 12 inch snare tuned at B3, which is 247Hz then has a range of other eight to 14 inch diameter drums, which cover the lower pitches from A3, so that's 220Hz down to E2 at 82.4Hz.. This allows Terry Bozzio to perform extremely musical phrases on the drum kit, and you can see images and watch videos of his kit being played at his website, terrybozzio.com. So what frequencies should you choose to tune the drums in your own kit? Well, there's no real answer. In fact, you just need to experiment and decide what tunings suit you best. There's no perfect preset or single approach. It makes sense to have fairly even intervals between each drum, so a drum roll around the kit goes from low tones to high notes and vice versa. The intervals could be grouped closely together in the low range or closely together in the high range, or you may prefer wider intervals which start low and go to quite high. It all depends how many drums you have in the kit and what style of music you play, and personal preference too. The best advice is to experiment and to reflect on the results. Well let's hear some examples. Here we have a 5 piece drum kit with coated drum heads. We have a 22 inch kick drum, 10, inch toms, and a 14 inch snare. In the first example, the drums are tuned relatively low. The kick is tuned to a fundamental frequency of 61.5Hz, which is a B, 16” floor tom is tuned to 73.5Hz which is a D, 12” rack tom is tuned to 87Hz which is an F. The 10” rack tom is tuned to 110 Hz which is an A and the 14” snare is tuned to a fundamental of 174Hz which is an F. Let's hear a groove and some fills with that setup. In the second example, exactly the same drums are tuned to a medium tuning range. The kick is tuned to a fundamental frequency of 69.5Hz which is a C#. The 16” floor tom is tuned to 82.5Hz, which is an E. The 12” rack tom is tuned to 98Hz, which is a G and the 10” rack tom is tuned to 123.5Hz, which is a B. We keep the snare at the same frequency as previously. And let's hear a similar performance with tom fills. In the third example, the drums are tuned up further to become relatively high. The kick is tuned to a fundamental frequency of 73.5Hz which is a D, 16” floor tom is tuned to 92.5Hz, which is Gb, 12” rack tom is tuned to 123.5Hz, which is a B. The 10” rack tom is tuned to 147Hz, which is a D. We keep the snare the same again. Now let's hear the high tuning. Okay, now let's move quickly between the three tunings, just to hear the difference. Here's the low tuning and the medium tuning and the high tuning. Back to the medium tuning and back to the low tuning. We kept the snare tuned the same each time because it's quite independent of the tuning of the toms. It seems that all styles work well sometimes with a low tuned snare or a high tuned snare, so it's an additional variable when tuning the kit as a whole, and doesn't have to follow the low, medium, high tuning approach which we used for the toms in this instance. 19:41 - Tuning The Kick Drum Finally, let's discuss the tuning of the kick drum. In modern music the kick is generally heavily damped, almost to the point where you can find it hard to identify its pitch or frequency. So if you want a heavily damped kick drum then a good suggestion is to buy a heavily damped kick drum head. These can sound fantastic. If you use a damped drum head and tune the kick as if it were a large tom drum, it can be quite simple to get a good sound. Something less simple is to add blankets or pillows into the kick drum. These actually make very little difference to the drum sound, unless some part of the material is in contact with one or both drum heads. The challenge is in getting the same drum head damping each time you set up the drums, because the blanket or pillow will inevitably move in transit, and you'll have a different sounding drum every time you take it out of the case. Now, in the previous drum tuning examples, we had the kick drum tuned with a damped drum head and experimented with low, medium and high frequencies, which were 61.5Hz, 69.5Hz and 73.5Hz respectively. Let's listen to those again, here's the low kick, 61.5Hz, medium, 69.5Hz and high, 73.5 Hz. The kick drum sounds tight and tuneful at each frequency and these sounds were achieved by simply tuning both drum heads to finger tight, and then adding small turns to each tuning rod until the desired frequency was achieved. I hope you have fun and can expand your knowledge of drum sound further by experimenting with drum heads and by trying different tunings on the complete Drum Kit. Hopefully you can develop your listening skills too, by listening for the nuances of timbre and the subtle characteristics of the different drum designs and shell materials. In the next podcast we'll look in detail at how you can optimise the drum setup in a recording studio and capture exactly the sounds you're aiming for. I'm Professor Rob Toulson and this has been an RT60 Ltd podcast production for Sound On Sound. Thank-you for listening and be sure to check out the show notes page for this episode where you'll find further information along with web links and details of all the other episodes. And just before you go let me point you to the soundonsound.com/podcasts website page where you can explore what's playing on our other channels.