3. Tuning the Pitch of a Cylindrical Drum
‘Cylindrical drums’ are those us drummers are most used to playing – cylindrical shells with two drumheads, on the batter and resonant sides. No matter how they are tuned, all cylindrical drums have a sonic ‘pitch’, which basically means the frequency which the drum vibrates at and which we hear. If you make the drumhead tighter the pitch goes up, looser and the pitch goes down. It’s no different to a guitar or violin – you tighten a string, the sound goes up in pitch, loosen the strings and the pitch goes down.
You might have seen the previous blog post about the vibration modes of a drum – well, we mentioned that the most powerful vibration of a drum is when we hit it in the centre and that’s when the drum’s pitch is really obvious to hear. Hitting the drum in the middle causes the drumhead to vibrate up and down at a certain frequency based on the tension of the drumhead. This vibration causes a very small amount of air compression inside the drum, which translates onto the bottom drumhead, and ultimately the bottom drumhead moves up and down too at the same frequency as the top one, making a really powerful vibrating system with a sound we know as that of a popular drum.
OK, so what is the pitch range of a drum? Well, imagine the drum has just had two new heads put on and they are both at the point where they are really loose, but just tightened so that they can vibrate when hit. I.e. all the slackness is taken out of the drumheads, but it is as loose as possible without sounding broken. Since the pitch is related to the two drumheads vibrating together, if we tighten either drumhead, the pitch will go up. If we tighten both drumheads it will go up more, so imagine tightening both to the point where the two drumheads really cannot be tightened any more, or they will snap and break; OK, that’s now the highest pitch of the drum. In reality, these two low and high settings both sound a bit extreme, and there’s certainly a sweeter sounding range somewhere in the middle.
BUT, the range is quite big and it’s possible to experiment with this range to decide what pitch you want your drum tuned to, to give the best sound for your kit, the best sound for the style of music you are playing, and for your personal performance style and preference too. Look, here’s a video of a 13-inch tom being tuned all the way from completely slack, to the first good reading at 79 Hz, and then tuned all the way up to 138 Hz, which is not far off a whole octave on the music scale.
The drum sounds good at all stages in this zone, but obviously some frequencies will sound better with some styles of music than others. There are no rules here, but it’s valuable to get an understanding of where you like to tune your own drums in. terms of pitch.
As mentioned in the previous post, there are lots of frequencies given off when the drum is hit, but this ‘fundamental’ frequency which is heard when the drum is hit in the middle is the one that really defines the overall pitch of the drum, and we refer to the fundamental frequency as F0 for shorthand.
It’s not uncommon for Jazz drummers to use relatively high pitch tuning (nearer the tight end of the range), and Rock drummers often go for something lower pitch and more powerful (nearer the slack end of the pitch range). The benefit of using iDrumTune here is to take a reading of the pitch and identify what frequency you prefer for each of your drums. Then you can make sure your drum is always tuned to this frequency every time you play, or if you play in different bands you might use different tunings for different music genres, so the app helps you quickly get the sound you need at any moment in time. It's also useful if changing drumheads, or to make a record of the tunings used in a recording session.
You probably know that every note on the piano has a corresponding frequency, so if you want, you can tune the drum's fundamental pitch to be on the musical scale - for example 98 Hz is note G2 on the piano, 110 Hz is A2 on the musical scale, C3 is 130.8 Hz - these musical frequencies are also indicated and described in the iDrumTune app. Here’s a diagram of every note on the piano within 50 - 400 Hz, showing what each frequency is for each musical note:
You can also use this frequency to setup the intervals between the different drums in your kit. So, as you play a drum roll around the kit, you go up (or down) in frequencies at well-spaced intervals. If you tune to musical pitches then you can start to develop really musical phrases around the kit and your fills will sound pretty cool.
Some suggested frequency ranges are shown here for standard drums, with Rock sounds tending to be towards the lower end and Jazz sounds tending to be towards the higher end or each suggested range. Of course, the size of the drum makes a difference too, so a 16-inch floor tom will generally have a lower tuning range than a 14-inch floor tom.
Now, we mentioned something a little controversial earlier - that the top and bottom drumheads vibrate at exactly the same fundamental frequency. This is true and is a fact of physics, however, that doesn’t mean they sound exactly the same when hit with a drumstick. They sound different because the overtones on the top batter head are completely different to those on the resonant head, even though the fundamental pitch is identical. We can prove it actually, by taking a reading with iDrumTune at the center of the top and bottom heads and you should see, if you hit it quite gently, that the fundamental frequency is identical (see video below!). So the drumheads must be vibrating together, in unison, connected and coupled by a mass of air trapped in between within the drum. It’s not a huge issue or one to worry about for tuning, but it’s a cool acoustics fact all the same!
In fact, you don't have to just take our word for it, much of this percussion theory was first written about by probably the most incredible expert in musical acoustics, Professor Thomas Rossing of Stanford University, who has published over 15 books and 400 peer reviewed articles on the subject. In particular, the basic theories on drumhead vibration and cylindrical drums is covered in his excellent, though very technical book, Science of Percussion Instruments, which is previewed own Google Books here. Our very own Professor Rob Touslon took this knowledge and developed it into a more practical set of strategies and theories for specifically tuning cylindrical drums, which was demonstrated fully to a packed audience of music and acoustics experts in a 90 minute tutorial at the 2009 Audio Engineering Society Convention in New York - there will be a future blog post own the history of the research and development that resulted in the iDrumTune app later, for this who are interested!
In the next post we’ll discuss overtones in more detail and explain the process for analysing the F1 (edge) overtone to ensure that the drumhead vibrates evenly and smoothly. In future posts we’ll also show more drum kits tuned to musical pitches and make some sense of what is often regarded as the most confusing aspect of tuning; the resonant drumhead!