Physics of hitting a rim shot?

[azwethinkweizm]

Can anybody here give a good attempt to describe the physics of hitting a rim shot and why it is so loud?

[gbass598]

A rim shot is no different than any other stroke with the exception you are striking a metal rim at the same time you hit the drum head. This causes the metallic vibration in the drum that pierces the ear more than a regular stroke.

[snarescience]

I started an extensive discussion about this exact topic here: http://www.drumlines.org/threads/showflat..../0/fpart/1/vc/1

I am convinced that it has very little to do with drum (shell and / or rim) vibrations, and more to do with how the stick is reacting to hitting the rim. I believe that the bead of the stick gets 'whipped' into the head as a result of striking the shoulder of the stick on the rim.

There is evidence against the drum vibration theory: I have a marching snare with the top free floating section removed from the rest of the drum (i.e. there is no shell). When I hit rimshots on this, it is just as loud as on a regular drum.

[Slow Adam]

I think there are 3 things that combine to make a rim shot louder than a regular stroke. How much each of these things contribute, I am not sure.

1. Stick flex / whip as noted by Ryan. Increased impact velocity = increased volume.

2. Duration of impact. Anyone who has played a rim shot knows it doesn't rebound with the same velocity, or rebound height as a regular stroke. Impact is not an instantaneous event, it happens over a period of time. My guess would be that the amount of time the stick is in contact with the head is significantly longer for a rim shot.

3. Modified stick harmonics. There are two parts to every sound we hear: Frequency and Amplitude (Pitch and Volume). Every physical object has what's called a natural frequency i.e. hit it and it vibrates at a certain frequency. Drop a drumstick on a hard floor and you will hear it's natural frequency (Throw it at the floor and you will hear the same frequency, only louder). When you play a rim shot a small piece of the stick is isolated by forcing a node on the stick at the point of contact with the rim. The small length of stick will vibrate at a higher frequency than that of the entire stick.

Now when you hit a drum there are 4 things that vibrate: the stick, top head, bottom head and the guts, and each has it's own natural frequency (head and gut frequency is dependent on tuning obviously, and guts don't really add volume, just texture). Both the top and bottom heads are tuned (usually) at a higher pitch than the natural frequency of a typical snare stick, so in playing a rim shot you are exciting the heads at a frequency closer to where they are tuned.

So, combining 1+3+2 you get: increased impact velocity with a stick vibrating at higher frequency for a longer period of time.

Again, I'm not sure the degree to which each of these things contributes to the overall sound produced...it sure would be nice if someone with access to some software and more knowledge in the subject could do up an FEA model *cough* Tristan *cough* :)

Edited June 8, 2007 by Slow Adam

[MarimbasaurusRex]

Here's my take on what makes a rim shot sound like it does.... The rim, being very rigid, produces a very sharp attack with a lot of energy behind it, but without a resonator it just sounds like a rim click. The stick transmits that high impact energy of the rim attack directly to the head and into the cavity of the drum, engaging it momentarily as a coupled resonator. Normally, what happens on the rim stays on the rim because the edge of the head is a vibrational node and won't transmit the rim sound. The stick carries the rim sound to the center of the head where it is amplified along with the rest of the drum sound.

[Tristan]

My gut feeling says it's a combination of Marimbasaurus Rex's and Slow Adam's posts. Marimbasaurus Rex brings up a good point about the head amplifying the vibration.

I don't think it is stick flex, for two reasons: 1) the stick is stiff enough that the whip motion after hitting the rim (assuming it hits the rim just before the head) would actually be slower, as the stick is beginning to accelerate upwards. 2) Were this actually the case, gocks would tear up the sticks much faster than they already do (think freshmen in high school on Ralph Hardimon sticks torn up).

Here's my theory--

Rim knocks are much louder than rim clicks too because the butt of the stick is against the drum head, making it vibrate--like a speaker cone vibrates because it is attached to the magnetic driver. When you hit the rim with your stick alone, you get a lot less rebound than when you hit the head with the tip. Your stick also vibrates a lot more--try it with a really loose grip and you'll see what I mean. All that energy of vibration gets transferred to the head during a rimshot, and the head amplifies the vibrations of the stick.

A quick illustration proving this is to compare the sounds of a full-stick gock (center), a pang (1/2) and a ping (as close to the edge as possible. The pitch of the sound changes. There are only two things that can change the pitch of a drum sound: changing the tension in either of the heads or the guts, changing the length or the thickness of the stick. When you change between these three different kinds of rimshots, you are changing the length of the stick, thus shortening the vibrational area and changing the pitch.

As far as the stick being in contact with the head longer, that causality relationship is actually reversed. Normally your stick rebounds because only a small percentage of the energy of the stroke goes into making the drumhead vibrate. The rest of it is used to redirect the stick back where it came from. A rimshot, however, being much louder, extracts more energy from the stick as vibration, giving it far less rebound energy. In other words, it's rebounding less because it's louder, not the other way around. If you were to force the stick to be in contact with the head longer, you would actually get a quieter sound, because the stick would effectively dampen the response.

[Snapettes Mom]

I marched with a guy who was a snare in BAC. He said they would spend hours at rehearsal working on rimshot technique. He had the best I heard. I also believe BAC plays them better than anyone else in the Biz. I'll give a nod to SCV for having the loudest smacking rimshots for sure.

Mom

[Aaron Guidry]

I have no explanation for the physics of it all, but try this:

Use your other stick in place of the rim.

In other words, if you are playing the rim shot with your right hand, position your left stick under your right hand, and play the rim shot as you normally would, but instead of hitting the rim, hit the left hand's stick. That stick is serving as the 'rim.' It might take a little practice to get it right, but when you do, it produces an audible sound equal to a rim shot.

So, one could potentially conclude (in modest of terms) that it has nothing to do with the rim at all.

Where do we go from there? Not sure, but that's just some more food for thought.

Aaron

edit: to be clear, I'm not talking about producing a 'stick shot' where the bead of the left stick is on the head. the left stick would have no contact with the head at all with is altered 'rim shot' technique.

Edited June 22, 2007 by Aaron Guidry

[Tristan]

I think that would confirm that the added sound is actually the vibration of the stick being transfered into and amplified by the drumhead. That's also why you have almost no rebound when you do a gock.

[Stryfe]

I do think that the rim may have some effect, but whether or not there's a rim has no effect on the volume. Case in point, grab a textbook. (Er, one with... no rims. I'm pretty sure they don't come with rims.) Hit it normally. Hit it like a rimshot (more stick contact). This alone demonstrates that just the movement of the stick itself causes the rimshot to be naturally louder. (More stick may not always hit the drum as in the textbook example, but it is hitting more surface (drumhead + rim), which probably accounts for the volume?) What effect that has on the pitch is unclear to me, since textbooks give very poor indication of pitch. :P And I have little idea to theorize the actual physics of it. But I do know that I think of rimshots to not only be louder (which I mostly consider a side-effect) but mainly to be a different pitch, which I feel is more important in its use.

Or I could be very wrong. I have a feeling I am. But this is an interesting discussion, and I'll contribute what I can.