On many snare drums, a “venting hole” is made “to ease the motion of the heads” avoiding too high pressure rise inside the shell. While it is a common practice to drill one or many holes in the shells, some manufacturers prefer none, and some other are rally imaginative when it comes to “venting the drum”.
The studies on Timpani, showed that strong coupling occurred between the membrane normal modes and the cavity (closed in the case of a timpani bowl). That coupling explained how a non-harmonic system (the normal modes of a membrane) became nearly harmonically tuned (with a distinctive pitch) sometimes up to the 5th partial as some modes would change frequency depending on their mode shape.
Back to snare drum, that venting hole is defined as a sign of some “zero hertz” coupling: static pressure inside the shell linked to membrane deformation (and we will see that we mostly speak of the (0,1) mode being not volume conservative) causes flow out of the drum. But how does this work at higher frequencies? and how a axisymmetric venting opening would better accommodate the axissymetry of the instrument rather than a single hole ? What about using this opening as a radiating element and maximizing its efficiency through a “ported” profile ?
Lab tests :
Those questions have led Repercussion to develop a number of prototypes, and take them to the lab after positive subjective appraisal coming from professional percussionists. The snares studied are of widely different construction from the personal collection of Repercussion:
- 13×7 Stave Oak : is a 13” diameter, 7” deep drum, and has a shell built by stave technique : alike barrels, pieces of wood are beveled and assembled together then lathed to perfect roundness. This is said to minimize the amount of glue vs ply shells and therefore, the damping of the shell and the sustain of the sound.
- 14×6,5” “Free Floating” : is a 14” Diameter,6,5” deep drum with a rolled sheet metal steel shell (thickness = 1mm). The particularity of this drum is to feature no tensioning devices (lugs) or strainer on the shell itself, hence letting the shell « free to resonate » as claimed by the manufacturer.
- 14×6,5” Mahogany : is a 14” diameter, 6,5” deep drum, with a shell made out of mahogany plies. 4 layers of mahogany are glued together, and reinforcement rings at the top and bottom of the shell guarantee roundness and strength.
- Repercussion Orchestral snare : is a 14” diameter, 6,5” deep prototype drum, with a 15 ply maple shell (11mm thickness). Its main feature is a radial ported vent in its center resulting in a “split shell” architecture (2 half shells).
- Repercussion 1O slots vent : is a 14 “ diameter, 6,5” deep prototype drum with a 8 ply (6mm) maple shell, featuring ported vent close to the top head, between each lug.
- Repercussion Standard Snare radial vented : is a 14” diameter, 6,5” deep drum with a radial ported vent, made from a 8 ply (6mm) maple shell.
A “gravity operated” arm has been developed to provide exactly the same kinetic energy to a drumstick, while controlling the trajectory to avoid multiple strokes. Vibration and acoustic measurement have been performed in anaechoic room, using lab grade equipment.
A very distinctive element of a snare drum is the snare itself. This is a somewhat tricky element seen from the NVH engineer, as it is basically closer to one infamous “squeak and rattle” source. It is stretched across a membrane and would therefore rub and clatter against that membrane, depending on the adjustment of the membrane and the snare itself…In a nutshell : a very nonlinear element. The measurements below have been made with snares “on” and “off” to understand their contribution to the sound.
With a first membrane mode (0,1) located in the 200Hz third octave band for all the drums, it is noticeable that the snare Adds quite a lot of energy in the 1kz-1kHz band, and on “standard vented” (holes) drums, tend to “chop off” the first membrane modes up to 500 Hz by 10-12 dB.
Same as above, but seen up to 1kHz, with a narrowband spectrum.Note the presence of a lower component in the 120 Hz range on Repercussion snares, that will be discussed in another page.
On repercussion snares, the fundamental motion (1,0);(1,1);(2,1) modes and first partials are kept intact from the snare action, on all other standard drums those components of the sound are chopped off.
This is due to the loss of energy in the friction of the snares against the batter (resonant) head bringing some heavy damping to the top head : the smaller the venting, the strongest the coupling between the two heads, and the stronger the damping of the top head first modes. The snare is bringing heavy damping to the top head if the venting is not decoupling them enough.
So Repercussion vented drums keep the low end, all right, what about the high end of the spectrum ?
On the left: the loss in the fundamental third octave band : 11 to 12 dB loss for standard drums, 2 to 5 dB maximum loss for Repercussion.
On the right, global gain in the high frequency range (1kHz – 10kHz) ranging from +24 to + 32 dB
On Repercussion « Bessel vented drums » the sound is perceived with greater presence by the player, and quite notably by the audience a few meters away – One might think, in the constant « WYSIWIG » mindset it is because of the larger opened surface of the vent, drawing more sound around the drum. Although it is true that a ported vent radiates way more efficiently than a standard hole, for the particular motions of the head at low frequency responsible for that feeling of « presence », it is really that freedom from the damping mechanism of the snares that helps build this « in your stomach » sound perception.