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By futurepotus
#39320
Hello everyone,

Let me preface this post by saying that I am a prospective drum builder. I have acquired some large chunks of North American hardwood that I intend on carving into Djembe inspired hand drums.

I'm quite interested in the inner design of the Djembe, and how the shape of the bowl and neck affect the sound characteristics of the instrument. I understand that the proportions play quite a big part in the overall sound of the Djembe. There are other factors of course, such as thickness and tightness of playing surface, thickness of shell material, density of shell material. However, in this discussion I would like to focus on how neck design affects overall sound. (The "neck" being the bottom tube that goes from the bowl to the ground.)

If I understand correctly, a Djembe is a Helmholtz resonator.
A Helmholtz resonator or Helmholtz oscillator is a container of gas (usually air) with an open hole (or neck or port). A volume of air in and near the open hole vibrates because of the 'springiness' of the air inside. A common example is an empty bottle: the air inside vibrates when you blow across the top
(Source: https://newt.phys.unsw.edu.au/jw/Helmholtz.html

So when we strike a Djembe, the air in the neck of our drum acts as a spring between the bowl of the drum and the outside world, causing a pleasing vibrational frequency in the form of BASS.

From my research on this forum, I can conclude that a smaller neck hole results in lower bass, and a longer neck tube will result in lower bass. (Source: viewtopic.php?f=3&t=2824)

The djembe follows the same principle that a ported subwoofer does. Which makes me wonder: Does the bowl of a Djembe need to be tapered into the neck hole? Why does the bowl "funnel in" to the neck? A subwoofer does not depend on any sort of tapered or angled geometry to funnel air into the port, so why does a Djembe?

It seems to me that this funnel shape that we often see in the bowl of a Djembe is unnecessary. Consider this:
One thing that it seems we all agree on is the importance that a squared off "shelf" at the bottom of the bowl plays. Though our shells have a smaller over-all bowl, you will find that the inside of the bowl is always intriquately "shelfed out". This in our opinion is a key factor for responsiveness, definitive seperation between bass, tone and slap, and projecion. Without this "shelf" the sound would simply slip through the drum and all dynamics would be lost.
(Source: DrumSkull Drums - Tue Nov 02, 2010 10:24 pm in viewtopic.php?f=3&t=2407)

My hypothesis is as such: Any sort of tapered or angled geometry in the bowl which "funnels" towards the neck hole only serves to reduce tonality and responsiveness of the drum. This is due to the taper or angle reducing the size of the flat surface on the bottom of the bowl, which seems to coincide with pleasant acoustic features. Ideally, the bottom of the bowl should be flat with the neck hole flush to this flat surface as if it was drilled rather than carved.

Additionally, I would like to call into question the bottom of the neck tube which traditionally flares out. Consider the following comment:
The bass comes pretty much exclusively from the foot. You can feel the pressure if you hold your hand in front of the opening while hitting a bass.
(Source: michi - Sun Mar 20, 2011 12:43 am in viewtopic.php?f=3&t=2824&start=15)

Does the geometry of a flared neck at the bottom offer much in terms of amplifying the sound, or will it simply cause the bass to sound muddier?

Please let me know your thoughts.