Build your own sound with Repercussion patented Bessel vented snare.

• Choose vent characteristics : we will print out spacers fitting exactly your needs to parameter the ported vent.
• Choose top and bottom shell independently (Height, thickness, material)
• Change the shell as easily as changing a head
• All mechanical elements on the chassis (snare strainer and butt plate – not represented below)
• Want to change your sound ? get some new spacers printed from us and/or change one or two shells ! Mix and match metals / woods/.. to tailor the sound colour to your exact needs –
• Build it yourself : No drilling, No adjustment, as simple as a Swedish furniture.

Oh and of course, like all other drum makers you can have it in any colour or finishes – once you found your sound.

See samples in True sound tailored Drums

Soon issued : full drum kits !

Construction of the patented Bessel vented snare drums – heads and tension rods are not shown, they bolt into the fully threaded M12 stainless steel bolt, threaded on both sides, which holds the whole chassis together.

Further considerations on the simulation results lead to think that – as always in simulation – the results are limited to the modelled physics. We still don’t understand the presence of a low frequency component (100 Hz) only found in Repercussion Bessel vented snares testing , where model shows a “Helmhotz resonator” behaviour for standard vented snares at 50 Hz (see Shell depth , Venting & admittance) not heard nor seen in the testing…

Could this be coming from a lack in our model ? In our case, we considered infinitely rigid shell and studied the behaviour of two stretched membranes coupled by a cavity – practically this means that the transfer of energy from the stuck top membrane to the bottom one would be done solely by the air within the shell.

In reality, mechanical waves are transmitted to the shell structure, and transferred to the bottom membrane. As the stiffness of the shell “axially” is considerably higher than the one of the air in the cavity, and as velocity of sound within material is higher than in the air, it is very likely that in reality, the sound wave coming from the top head hits a membrane that is already in motion due to structure borne transfer…

Does it mean that when we split the shell in halves we kill this transfer ? what consequences for the sound ?

Let’s get back to testing where various shells material and construction were tested in the lab with calibrated stick hit, and vibration of top and bottom head recorded : let us look at the ratio of those over the range of the 6 snares tested.

It seems there is a global trend that makes sense : intuitively, a steel shell is stiffer along its axis (that is traction/compression waves), then the fairly thick and stave built oak shell that would channel the sound wave faster to the bottom head, then the repercussion 10 slots which is the only prototype that actually was NOT splitting completely the maple shell (only slots), then the standard snare that features U shaped beams of aluminum to hold the two half shells apart, finally the Orchestral snare, with a fully split shell and tubelugs of small cross section to space the two 12mm maple shell.

Close up of the Repercussion 10 slot vent

Close up of the Orchestral snare

Inside the standard radial vented snare prototype

Finally, the mahogany snare, which would mean that this type of material either damps the energy or that the relative thin shell bending takes over the axial transmission. 

Sound velocity for various material used for snare shell / In comparison with our testing : Steel is the fastest, the Maple before Oak, but in our case Oak is thicker and built in staves / for reference sound in air is 340m/s so the waves in the shell material would travel at least 10x faster.

Conclusion :

“at first glance” there might be some correlation between the shell presumed stiffness and the level of vibration seen on the bottom head, however material and construction seem to play a stronger role than the fact of splitting the shell, and the effect on the perceived sound is yet to be documented. Keep in mind that radial venting does enhance top head vibration and sound as presented in The snare was killing batter head sound !

First results of numerical simulation indicates that on a dual membrane drum, the first mode of the membrane is actually more influenced by the shell depth than the tension itself. This is a direct consequence of the heavy coupling occurring in drums : the first membrane mode ((1,0) with one nodal circle being the edge of the membrane for both membranes, in phase) being volume conservative, the volume of air between the two membrane is mass-loading this mode.

The graph below illustrates how the first membrane mode shifts in frequency for standard shells (3,5 to 10″) and a purely simulated 60 inch shell.

The frequency shift follows well the square root of the depth, indicating a mass behaviour. The system is alike one mass between 2 springs representing the stiffness of the membranes.

Then simulation of opening in the shell, corresponding to the standard venting (one single vent hole) and to the patented Repercussion radial venting system have been conducted.

The mechanical mobility – or admittance- has been computed : this quantity is the ratio of the velocity of the head for 1N applied (at its center). The greatest this quantity, the “easier” it is for the membrane to vibrate, and the more energy is likely to be transmitted to the instrument (and not reflected back into the stick).

One very significant phenomenon occurs as soon as an opening is made in the shell : a resonance “Helmhotz-like” with maximum velocities in the vent appears around 50Hz.

in practice, this phenomenon is very likely not to be heard nor felt, because of the poor radiation efficiency (small surface) of the vent and because of the very heavy damping that will be caused by air flow & turbulence.

Picture of the 1st “mode” maxima (the two heads are one phase opposition)

The second effect of venting is the slight raise (10%) from low frequency of the mobility : the air can now flow outside of the drum and compression added stiffness disappears.

The third major effect is, in the case of the patented Repercussion radial venting system only, the increase of the mobility at a lower frequency (the pitch drops down to the one of a 25″ shell – 4x the physical depth of the shell) and a 25% increase on the max mobility.

What does it mean for the player ?

• A more evenly distributed sound around the shell (radial venting) with a very strong low end giving “in your chest” punch.
• A way more present sound for the audience and musician around (the sound “flows” out of the drum very efficiently
• A drum easier to play : more motion for the force injected : More sound, less force, less chances for injuries.

A major step has been made in the understanding of drums acoustics thanks to the Laboratoire de Vibration et D’ Acoustique (Vibration & acoustics lab) of the National Applied Science (INSA) engineering school in Lyon.

Two students have been modelling a snare drum with the intent of :

1. Understanding how the air loading (coupling) was influencing the  membrane behaviour in the case of 2 membranes instruments
2. How the venting characteristics influenced the membrane vibrations
3. Quantifying the mechanical mobility of a snare as a function of its venting system

Congratulations to INSA LVA for those progress !

Repercussion is devoted to innovation in the field of musical instruments, linking acoustics and structural dynamics developments with musical instrument crafting in order to propose innovative concepts to performers.

Today, a major step has been done as Repercussion filed a patent for the “Bessel vented drum system” after month of lab research and feedback from users.

Sound tailoring of drums is now a reality thanks to patented Repercussion technology.

More for your eyes and for your ears soon !

Thomas ANTOINE

 

 

Today is a great day for Repercussion drums !

All prototypes have been properly badged … what would be a drum without a badge anyway ?

I would have never imagined how a tiny part of metal would change the global feel and look of my drums !