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AN EMAIL COMPILATION FROM THE MEMBERS DURING
JULY & September, 1998
MAY, 1999
ALSO SEE:

  -----Original Message-----
From: paul janse <kaztam@xs4all.nl>
Date: Wednesday, July 29, 1998 6:39 PM

>Hi, Paul Janse here
>I would like to present some idea's on the form of the Djembe bowl :
>First of all,  with the Djembe standing, take a plane through the cental axis of the Djembe and consider the intersection of this plane with the bowl surface. In practice , the resulting curve will, to my eyes  very much resemble a part of a parabola !!!!
>Let us assume for the moment, that this is the form a Djembe bowl has.
>This brought me to the following thoughts :
>In the case of light , when you have a mirror of parabolic form,  the energy  of a parallel beam of light falling onto the mirror is concentrated in the focus That this focus is just one point in space is a result only of the parabolic form of the mirror. The proces involved is reflection of light. Maybe , this reasoning applies also to the sound waves produced by the skin of a djembe, that is : the propagation of sound waves in the Djembe bowl. What matters is the question how the sound waves  leave  the djembe -pipe, i.e.how to optimize this so, that the sound of the Djembe will be good.
>So, imagine a parallel beam of sound waves emerging vertically down from the skin
>into the bowl. When the sound waves follow the same reflection laws as in the case of light waves then in the case of a parabolic form of the bowl there must be a focus of energy too
>(lying on the central axis of the djembe). Off course, one could  now ask the question :  In the case of a djembe with parabolic bowl form , where should lie the focus so that the sound leaves the best way through the pipe. ???
>I think the answer is obvious : the focus should lie within the pipe , or at least in the centre of the circle being the intersection of djembe-bowl surface and pipe surface(waist). Now you can calculate a little on this idea , with the following result :
>
>Let  R be the radius of the Djembe's top edge (interior) circle and  r be the radius of the circle being the intersection of djembe-bowl surface and pipe surface(waist) Let  d    be the distance  between the two parallel planes formed by these circles Then  for the focus to lie within the pipe ( and thereby giving the sound waves the best possibility to leave the djembe) you have :
>
>R ^2  <  2rd +r ^2      or      r >  -d + ( d^2 + R^2 )^(1/2)               (*)
>
>So  :  R squared  smaller or equal to : two times r times d, plus r squared
>
>In the  case of equality the focus lies exactly in the centre of the circle being the intersection of djembe-bowl surface and pipe surface (waist).
>
>I  am still worried about the validity of the comparison with light wave reflection but if true  (*) will give a relationship between the easy measurable parameterrs R, r and d of a Djembe
>Cheers  !!
>Paul Janse
>
>P.S
>It is fun to do the calculation , even if the comparison should fail.

  -----Original Message-----
From: LR <lrowland@metz.une.edu.au>
Date: Wednesday, July 29, 1998 8:03 PM

>Paul Janse's post about the parabolic shape of the djembe bowl is interesting theoretically and pretty much outside my field of expertise. Nonetheless, I wanted to add a few thoughts.
>
>Consider that the maths invoked deals with perfect forms and we all know that traditional djembes are constructed using a minimum of precise measuring devices - and on the whole they seem to work fine. The one djembe we've all heard of that approaches perfect forms - circles/parabolas/thickness, etc - the Remo djembe, gets a pretty bad rap around here. And certainly the lathed djembes I've heard didn't stand out as being extraordinarily different to
>hand made instruments.
>
>Many of us have played instruments that were not perfectly round, flat on the bearing edge, uniform in thickness or 'ideal' in any number of parameters, but these were still perfectly satisfying instruments and while none of us pretend to sound like Mamady, at least we can approach the sounds he produces.
>
>A djembe, like any other musical instrument is a compromise, a balance between things like intonation, volume, treble and bass tone, physical size, available materials, etc. The typical djembe sounds fall within the realm of what is the culturally preferred sounds. In other words, the ideal djembe is what sounds good to West African ears and it is rather a dubious endeavour to try to come up with the physical parameters for the ideal/perfect instrument. And I feel it's rather dubious to think of African crafts being driven by the same development' forces as we find in the West. The djembe has probably undergone the most physical change in the last few years; more than in the previous century or so.
>
>Others on the list have described the bass of the djembe as being governed by the theories offered by Helmholtz. That is, for the bass, the djembe acts as a Helmholtz resonator. On the other hand, I regard the slap and tone as arising from the skin itself, with a minimum of influence from the djembe walls - they're usually so thick that they tend to absorb vibration rather
>than act as primary sources of sound.
>I suggest you will have to look to the physics of vibrating membranes and plates to get to the maths describing the way a skin vibrates.
>
>Many of the long timers here will probably back my statement that the sound of your djembe has much more to do with your technique than anything else. Your hands make the sound - not the djembe.
>
>It's a great privilege to live in a time when we have access to such a rich culture that allows us to dabble in its artefacts and to be able to buy handcrafted instruments realised by traditional crafts people. Let's not go down this road of vivisection and deconstructionism. Rather, let's just drum
>instead.
>
>Cheerz,
>Lynzz

-----Original Message-----
From: Saberalla@aol.com <Saberalla@aol.com>
Date: Wednesday, July 29, 1998 8:35 PM

><< It's a great privilege to live in a time when we have access to such a rich culture that allows us to dabble in its artefacts and to be able to buy handcrafted instruments realised by traditional crafts people. Let's not go down this road of vivisection and deconstructionism. Rather, let's just drum
> instead.  >> Why can't we do both? Mathematics as you know also had it's origens in African.
>Don't you think that Africans employed some type of scientific basis ? I would like to see more research in this area, especially in Nigeria where I'm told they used a host of number systems for their spiritual rituals. Maybe someone can elaborate on this.
>Olushola

  -----Original Message-----
From: Robert Feuer <rfeuer@bcn.net>
Date: Wednesday, July 29, 1998 10:39 PM

>Paul,
>
> Following your theory re: parabolic reflection, all light falling on a parallel reflector is sent out the top of the parabola in lines parallel to its central axis. In the analogy of light to sound waves, all sound waves reflecting off of the inside of the djembe "parabolic" bowl would try to leave the djembe in lines parallel to the bowl's central axis and through the skin. Traditionally, the concept is not that we beat the sound down into the drum, but that we bring the sound up out of the drum. If you bend your neck and head forward while playing your djembe, you can hear the sound of your drum better. This implies that the "parabolic reflector" under the skin, the djembe bowl, is sending most sound made within the bowl out the top of the drum in parallel lines, i.e. focusing the energy. Perhaps the pipe is merely allowing the air within the drum to breathe the air outside the drum, so that the head can vibrate more fully.
>
> Note we also play not in the middle of the skin, but away from the skin's center. Perhaps this sends sound waves down to the inside of the bowl's walls for better reflection. Waves originating in the center of the head, might not get reflected due to the hole at the top of the pipe. So center strokes sound deader that strokes made away from the center.
>My $0.02
>
>Bob.

  -----Original Message-----
From: Robert Feuer <rfeuer@bcn.net>
Date: Wednesday, July 29, 1998 10:47 PM

>>         Following your theory re: parabolic reflection, all light falling on a parabolic (sic) reflector is sent out the top of the parabola in lines parallel to its central axis. In the analogy of light to sound waves, all sound waves reflecting off of the inside of the djembe "parabolic" bowl would try to leave the djembe in lines parallel to the bowl's central axis and through the skin. Traditionally, the concept is not that we beat the sound down into the drum, but that we bring the sound up out of the drum. If you bend your neck and head forward while playing your djembe, you can hear the sound of your drum better. This implies that the "parabolic reflector" under the skin, the djembe bowl, is sending most sound made within the bowl out the top of the drum in parallel lines, i.e. focusing the energy. Perhaps the pipe is merely allowing the air within the drum to breathe the air outside the drum, so that the head can vibrate more fully.
>>
>>         Note we also play not in the middle of the skin, but away from the skin's center. Perhaps this sends sound waves down to the inside of the bowl's walls for better reflection. Waves originating in the center of the head, might not get reflected due to the hole at the top of the
>> pipe. So center strokes sound deader that strokes made away from the center.
>> My $0.02
>>
>> Bob.
>

  -----Original Message-----
From: Denis Robinson <dj.robinson@auckland.ac.nz>
Date: Wednesday, July 29, 1998 11:42 PM

>Paul,
>
>Without knowing the numbers involved, I fear that your analogy between light and sound waves isn't going to work very well (in the way you are applying it).
>
>When you start operating at distances which are small relative to the wavelength of light you start getting effects not easily described in terms of straight-line rays transmitting, "bouncing", etc. The wave character of light becomes dominant and "diffraction" effects come in. Even looking at a
>CD you can see the pattern of colours formed by interference between light rays reflecting from adjacent strips of reflective material: this is not simple reflection.
>
>The point is, the wavelength of sound is so much longer than the wavelength of light, that ordinary distances are comparable with the wavelengths of musical sounds. Indeed I believe it was while reading in the back archives of djembe-l on FindMail (fascinating experience) that I saw somone saying that the wavelength of the fundamental frequency of a dejmbe bass would be comparable with the dimensions of a room (hey folks!! don't flame me if this is out by an order of magnitude ... I said I didn't know the numbers). This manifests in the fact that you can set up standing waves in a room, experienced as follows. Often, if you stand in one place and play the bass, while someone else moves around the room, in certain places they will hear the sound very loudly, in other places hardly at all. This is because of the standing-waves pattern. Standing waves are an interference effect like CD diffraction colours are.
>
>If this is right then the beam- reflecting- at- equal- angles- from- a -flat- surface- model will be quite inappropriate for many of the interactions between soundwaves and the bowl of the djembe. Just supposing a room is 16 feet across and that's the wavelength of a bass note, and a
>djembe bowl is one foot across: then a note four octaves higher than the bass (doubling the frequency and halving the wavelength, four times) would have the same wavelength as the diameter of the bowl. So such a sound would interact in some complex way with the bowl as a whole, rather then separate "beams" of sound reflecting off the bowl surface in a nice simple way.
>Three octaves higher still would get you down to a wavelength of about one a a half inches. So *just possibly* it's only when you get to sounds 6 or 7 octaves higher than the bass note fundamental pitch that you start to get the equivalent of a parabolic reflector: only then would the wavelengths get small relative to the size of the bowl.
>
>I hope someone who *does* know the numbers will set me straight on all this if it's wrong in general drift, or in details for that matter. Any acoustic engineers out there?
>
>I just did some rough calculations based on my vague memory of the speed of sound, and if they're right a sound-wave with a frequency of about 2 octaves below middle C would have a wavelength of about 16 feet. I would expect the bass of a djembe could be even lower, hence longer.
>
>Hope someone finds this somehow helpful or illuminating, And let's give thanks to those who developed the djembe for all the accumulated practical knowledge and sensitive listening which must have gone into getting it *right*!!
>
>Cheers,
>
>Denis

  -----Original Message-----
From: paul janse <kaztam@xs4all.nl>
Date: Thursday, July 30, 1998 1:34 AM


>>         Following your theory re: parabolic reflection, all light falling on a parabolic (sic) reflector is sent out the top of the parabola in lines parallel to its central axis. In the analogy of light to sound waves, all sound waves reflecting off of the inside of the djembe "parabolic" bowl would try to leave the djembe in lines parallel to the bowl's central axis and through the skin.
>
>For a lot of incoming rays the energy is directed downwards, into the pipe  not backwards up  through the skin I must admit that the energy of ray's situated near the central axis is
>directed upwards,but when will that happen ? It depends solely on the curvature of the parabola
>In fact when the ray is coming in under an angle of 45 degree's the energy of the ray is directed horizontally I know that the bottom of the bowl of an actual djembe can be quite flat shaped, so in this area the energy of incoming rays is certainly directed upwards.
>But, for what percentage of the incoming rays this is the case ??
>
>I must emphasize that I do'nt want to be cocky, I had my serious doubts about my idea but I like to think the consequences of it to an end
>Tanks
>Paul
>
>
> Traditionally, the concept is not that we beat the sound down into the drum, but that we bring the sound up out of the drum. If you bend your neck and head forward while playing your djembe,
>> you can hear the sound of your drum better.
>
>This make  surely sense, yes
>
>This implies that the "parabolic reflector" under the skin, the djembe bowl, is sending most
>> sound made within the bowl out the top of the drum in parallel lines, i.e. focusing the energy.
>
>I wonder, after produced within the bowl back through the skin ???
>
> Perhaps the pipe is merely allowing the air within the drum to breathe the air outside the drum, so that the head can vibrate more fully.
>
>At least for the bass you know that closing the end of the pipe has a dramatic effect on the quality of sound ! Because of this I was thinking of the following : What would happen to the sound of a Djembe when you glued the end of the pipe rigidly to a surface but leaving the opening at the bottom intact  ???
>
>        Note we also play not in the middle of the skin, but away from the skin's center. Perhaps this sends sound waves down to the inside of the bowl's walls for better reflection.
>
>Whether you play in the middle or at the edge of the Djembe in any case the skin is to a very high extent only vibrating vertically So it is not strange to say that the sound waves are produced
>only vertically down, as far a the skin movement is concerned. Only there is more to the sound production as the vertial movement of an isolated skin only, thats for sure.
>Paul

  -----Original Message-----
From: paul janse <kaztam@xs4all.nl>
Date: Thursday, July 30, 1998 1:51 AM

>Denis Robinson wrote:
>
>> Paul,
>>
>> Without knowing the numbers involved, I fear that your analogy between light and sound waves isn't going to work very well (in the way you are applying it).
>>
>> When you start operating at distances which are small relative to the wavelength of light you start getting effects not easily described in terms of straight-line rays transmitting, "bouncing", etc. The wave character of light becomes dominant and "diffraction" effects come in. Even looking at a
>> CD you can see the pattern of colours formed by interference between light rays reflecting from adjacent strips of reflective material: this is not simple reflection.
>>
>> The point is, the wavelength of sound is so much longer than the wavelength of light, that ordinary distances are comparable with the wavelengths of musical sounds. Indeed I believe it was while reading in the back archives of djembe-l on FindMail (fascinating experience) that I saw somone saying that the wavelength of the fundamental frequency of a dejmbe bass would be
>> comparable with the dimensions of a room (hey folks!! don't flame me if this is out by an order of magnitude ... I said I didn't know the numbers)
>> . This manifests in the fact that you can set up standing waves in a room, experienced as follows. Often, if you stand in one place and play the bass, while someone else moves around the room, in certain places they will hear the sound very loudly, in other places hardly at all. This is because of the standing-waves pattern. Standing waves are an interference effect like CD diffraction colours are.
>>
>> If this is right then the beam- reflecting- at- equal- angles- from- a -flat- surface- model will be quite inappropriate for many of the interactions between soundwaves and the bowl of the djembe.
>
>If this is true, which I fear it is,  this is a strong argument against my idea'sof reflection. It would be a convincing argument !!
>
>> I hope someone who *does* know the numbers will set me straight on all this if it's wrong in general drift, or in details for that matter. Any acoustic engineers out there?
>>
>> I just did some rough calculations based on my vague memory of the speed of sound, and if they're right a sound-wave with a frequency of about 2 octaves below middle C would have a wavelength of about 16 feet. I would expect the bass of a djembe could be even lower, hence longer.
>
>Yes please, anyone who has this numbers   ???
>
>Thanks very much
>
>Paul

  -----Original Message-----
From: R Clark <clark@acceleration.net>
Date: Thursday, July 30, 1998 3:01 AM

>Paul,
>Following your theory re: parabolic reflection, all light falling on a parabolic (sic) reflector is sent out the top of the parabola in lines parallel to its central axis. In the analogy of light to sound waves, all sound waves reflecting off of the inside of the djembe "parabolic" bowl would try to leave the djembe in lines parallel to the bowl's central axis and through the skin. Traditionally, the concept is not that we beat the sound down into the drum, but that we bring the sound up out of the drum.
>If you bend your neck and head forward while playing your djembe, you can hear the sound of your drum better. This implies that the "parabolic reflector" under the skin, the djembe bowl, is sending most sound made within the bowl out the top of the drum in parallel lines, i.e. focusing the energy. Perhaps the pipe is merely allowing the air within the drum to breathe the air outside the drum, so that the head can vibrate more fully.
>
>Note we also play not in the middle of the skin, but away from the skin's center. Perhaps this sends sound waves down to the inside of the bowl's walls for better reflection. Waves originating in the center of the head, might not get reflected due to the hole at the top of the pipe. So
>center strokes sound deader that strokes made away from the center.
>My $0.02
>
>Bob.
>
>R Clark@acceleration.net wrote:
>
>Hail Bob,
>
>IMHO you are on to something here. I am thinking the high notes are emitted by the ‘skin side’ too. I might add that I feel that a lot of the bass sound exits the pipe. I have often noticed when turning around with the drum strapped on that should there be a surface behind me that reflects the
>sound back to me IE a wall, that the bass notes sound more pronounced to me.
>There is my 2%. ;^ )>
>
>Thanks and Praises JAH
>I’n’i Love to Talk about DRUM
>Blessed Be
>In Time
>R

  -----Original Message-----
From: paul janse <kaztam@xs4all.nl>
>Hi, Paul Janse
>As I said, I had my doubts about the sound reflecting ideas and the post of Denis Robinson was quite convincing but I still have a remark and a question :
>1.     For an actual Djembe  the focus of reflected energy lies in the center of a circle which is quite near to the bottom of the bowl.
>        The reason is that  only quite deep in the bowl the incoming rays are in 45 degrees with the bowl surface
>        So the majority of rays (and thereby the energy) are reflected downwards.
>2.     I know of two situations in which there seems to be a focus of sound energy due to  a spatial form :
>       In the railway station of my home town Arnhem there is this dome-shaped roof of about   6 meters in diameter at a height of about 4 meters
>       I do'nt know if the dome is spherical or parabolic but when I clap my hands the intensity of the sound is so much greater in the center of it   !!!!!
>       When you go out of the center the sound intensity drops very fast. It is so much fun that I allways tap my foot when passing under it
>
>       The same experience I have in a park called "Sonsbeek park" in Arnhem both the effect is weaker
>       There is a podium for the performance of music. They build it as a circular upstanding wall of about 1.5 meters high
>        The radius of the circle must be something like 10 meters
>        Again, only in the center you experience the sound as " amplified" when clapping your hands
>        I think this has to do with the reflection of sound Anyway it seems consistent with the post of Denis  ?? :
>        The greater the dimensions of a spatial form (here meters instead of cm's) become compared to the wavelength  the more important  reflection becomes
>
>Paul

  -----Original Message-----
From: Peter E. Carels <carelspe@muohio.edu>
To: Djembe drumming/hand percussion <djembe-l@u.washington.edu>
Date: Thursday, July 30, 1998 10:09 AM
Subject: Re: Form of the Djembe bowl

>
>>R Clark@acceleration.net wrote:
>>
>>Hail Bob,
>>
>>IMHO you are on to something here. I am thinking the high notes are emitted by the ‘skin side’ too. I might add that I feel that a lot of the bass sound exits the pipe. I have often noticed when turning around with the drum strapped on that should there be a surface behind me that reflects the
>>sound back to me IE a wall, that the bass notes sound more pronounced to me.
>>There is my 2%. ;^ )>
>
>
>On a related matter, here's two more cents worth --  and some of this could be based on something I read a long time ago on the list, maybe related to Albert Prak's studies.
>
>Anyway, to demonstrate to the kids how the S and T differ from the B sounds emanating from a djembe, I stand the djembe up on three small 1"+ cubes of wood which have been placed in an equilateral triangle in the middle of a tray (e.g. baking sheet) containing about 1/8" of fine, dry sand, spread as smooth and even as possible.  Then play a slap.  Lift off the drum.  Little
>or no change in sand underneath.  Repeat for tone.  Same result.  Once again, now play a bass.  You will see a distinct pattern in the sand.
>
>Pete
>

  -----Original Message-----
From: LR <lrowland@metz.une.edu.au>

>>
>> Whether my idea is completely useless or not I do'nt agree with this
>> The sound of the djembe is determined by what is potentially in the "material"
>> Has nothing to do with the player's :
>> The player is just "the instrument" that makes physics work
>> Paul
>>
>
>I'm not suggesting your idea is completely useless - that's a cynical position
>for anyone who values thought. Afterall, the pretence for most academic
>research is that the ultimate value of such investigation cannot be judged.
>
>Hmmmm, I disagree with your latter assertion. The 'preferred' djembe timbres
>are only a subset of what is possible on such an instrument. For example, a
>doumbek is very similar in form to a djembe, only smaller. The range of
>sounds employed in typical traditional playing are much greater than that
>invoked on a djembe in a similar context. Furthermore, a couple of times
>each week, every week, emperical evidence presents itself to me indicating that
>technique is far more important than djembe form.
>
>I have to question why I find 'scientific' speculation - as opposed to
>analysis - worrisome. It occurs the me that in general, such ideas tend to
>generate a lot of air without any valuable assessment of the issues at hand
>and a spate of unscientific hypothetical scenarios. I don't condemn such
>mental gymnastics, but I suggest that if we ignore the recent work of our
>colleagues, such as Ben Sibson and Albert Prak, we are discounting their
>research - certainly not a wise thing.
>
>The other thing I find worrying is that notions of ideal proportions promote
>a search outside ourselves for the perfect instrument. Just about anyone who
>has played in rock bands will have experienced the syndrome. You know, the
>guitarist who turns up each week to a gig with some new electronic device
>or a different guitar and who still sounds the same, only louder. They still
>can't be relied upon to hold down a steady rhythm, but they sure are engrossed
>in the idea that the look and sound a whole lot better.
>
>I'm not trying to prevent your discussion, I'm only concerned that it focuses
>issues away from the fact that the music that comes out of a djembe
>arises solely from what we know and feel - and that is a perfect instrument.
>So, instead of pondering the physics of reflected waves, I have more of the
>precious moments left to me to be actively in awe of the timbres, rhythms,
>music, etc possible on my very imperfect djembe.
>
>Cheerz,
>Lynzz

  -----Original Message-----
From: paul janse <kaztam@xs4all.nl>

>LR wrote:
>
>> >
>> > Whether my idea is completely useless or not I do'nt agree with this
>> > The sound of the djembe is determined by what is potentially in the "material"
>> > Has nothing to do with the player's :
>> > The player is just "the instrument" that makes physics work
>> > Paul
>> >
>>
>> I'm not suggesting your idea is completely useless - that's a cynical position
>> for anyone who values thought. Afterall, the pretence for most academic
>> research is that the ultimate value of such investigation cannot be judged.
>>
>> Hmmmm, I disagree with your latter assertion. The 'preferred' djembe timbres
>> are only a subset of what is possible on such an instrument. For example, a
>> doumbek is very similar in form to a djembe, only smaller. The range of
>> sounds employed in typical traditional playing are much greater than that
>> invoked on a djembe in a similar context. Furthermore, a couple of times
>> each week, every week, emperical evidence presents itself to me indicating that
>> technique is far more important than djembe form.
>>
>> I have to question why I find 'scientific' speculation - as opposed to
>> analysis - worrisome. It occurs the me that in general, such ideas tend to
>> generate a lot of air without any valuable assessment of the issues at hand
>> and a spate of unscientific hypothetical scenarios. I don't condemn such
>> mental gymnastics, but I suggest that if we ignore the recent work of our
>> colleagues, such as Ben Sibson and Albert Prak, we are discounting their
>> research - certainly not a wise thing.
>>
>> The other thing I find worrying is that notions of ideal proportions promote
>> a search outside ourselves for the perfect instrument. Just about anyone who
>> has played in rock bands will have experienced the syndrome. You know, the
>> guitarist who turns up each week to a gig with some new electronic device
>> or a different guitar and who still sounds the same, only louder. They still
>> can't be relied upon to hold down a steady rhythm, but they sure are engrossed
>> in the idea that the look and sound a whole lot better.
>>
>> I'm not trying to prevent your discussion, I'm only concerned that it focuses
>> issues away from the fact that the music that comes out of a djembe
>> arises solely from what we know and feel - and that is a perfect instrument.
>> So, instead of pondering the physics of reflected waves, I have more of the
>> precious moments left to me to be actively in awe of the timbres, rhythms,
>> music, etc possible on my very imperfect djembe.
>>
>> Cheerz,
>> Lynzz
>
>  Hi Lynzz
>Thank you for your post
>I just want to say that to me there is no contradiction involved
>If my assumptions were correct my gymnastic exercices could really
>add something to the understanding  of the sound of the djembe
>To me there  is no contradiction with the other things you say
>My assumptions seem not to be correct but that is  beside the point
>Greetings
>Paul

  -----Original Message-----
From: Robert Hartman <hartman@informix.com>

>Hoo boy, you've got me thinking.  Always a dicey idea!
>
>I have noticed that the sweet spot varies from drum to drum, and now
>I'm wondering which is more important, the size of the waist hole or
>the contour of the bowl.  That will take some pondering.  I do tend
>to think that every drum will have a sweet spot, and that finding it
>and strking it consistently is a matter of technique more than shape.
>
>A parabola doesn't reflect everything back in parallel lines, only
>those rays that originate near its focus.  Car headlights use
>parabolic reflectors to keep the light pointed toward the road
>instead of radiating out in all directions, and each bulb is placed
>at or near the focus of each reflector.
>
>When you feed parallel rays into a parabola, they are all reflected
>back to the focus.  (Angle of incidence equals angle of reflection.)
>The sound waves that are produced by the head travel pretty-much in
>parallel until they hit the sides and are reflected back.  Each point
>along the wavefront travels in a line that is parallel with the lines
>of travel for all the other points in the wave-front.  If the shell was
>a perfect reflector, the skin perfectly rigid and flat, and the shape
>of the bowl a perfect parabola, the cumulative sound pressure produced
>by the movement of the head would be concentrated on a single focal
>point inside the drum.  If you could put a microphone at that point,
>the sound would be very loud indeed.
>
>However, none of those materials are perfect, which means that the
>skin produces interference patterns that can either be reinforced or
>dampened by the shell depending on where you strike it, the shell
>absorbs some of the energy from the sound pressure, the hole at
>the waist relieves some of the sound pressure inside the bowl and
>creates some harmonic distortion, and the stem does too.
>
>The hole and stem will alter the location of the focal point for the
>drum.  But I'm not sure how much or in which direction (up or down).
>
>I'm also not sure about where the focus _should_ be in relation to the
>hole for the best sound.  To get the loudest sound, the focus should
>probably be right at the waist hole.  However, that might not produce
>the best tone quality.  It may be that the "thunk" of a really good
>tone comes from the focus being higher up in the bowl rather than at
>the waist or somewhere down the neck.  On the other hand, I would
>imagine the brightest slap tones would come from the focus being in the
>same plane as the rim of the waist hole.  I'm also not clear on how you
>would alter the focal point except by removing material at the rim to
>make the bowl shorter with respect to its rim diameter.
>
>> From: ElenaEF@aol.com
>> Subject: Re: Plea to move useless DumbDrum debate to private e-mail
>>
>> I beleive the request was for people who get into a back and forth situation
>> on the list to please do it privately.I choose to delete or not delete.That is
>> a freedom we all have.I'm also free to express my opinions without having to
>> tell the everyone my country of origin,my ethnicity,my spiritual beliefs or my
>> gender(though I guess my name gives that away)in order to make them more
>> legitimate.
>> Anyway this is about DRUMS,right?
>> Peace,Elena
>
>It's about drums and drumming.  Issues of racism affect the history
>and traditions of drumming, and the ways that drums are being played
>and appreciated (or not) right now.
>
>I do agree that sniping and name-calling are inappropriate and a
>waste of bandwidth.  If I were going to make a suggestion I would
>ask people to just talk about their own experience and their own
>views, and refrain from trying to categorize, rebut, or characterize
>the views of others--especially those with whom they disagree.
>
>They say that good fences make good neighbors.  The glue that holds any
>community together is a willingess among the members to honor principled
>disagreements.  Which is more important, that we support each other or
>that we agree about everything?  If there is someone here who can't
>stand to be disagreed with about anything, that person can't really be
>a member of any community, let alone this one.  That isn't our problem,
>and it's not our fault if such a person can't get along with the rest
>of us.  Shy of that, we each have an opportunity to make this decision
>on a daily basis?  Do I need this person's agreement, or is their
>support good enough?
>
>If you read something here that provokes an emotional reaction in you,
>it might make more sense to explore that reaction than to try to make
>the other person take back or "pay for" what they've said, or to try
>to get others to dismiss them in favor of you.  It isn't about you,
>its about drums and drumming.  Remember?
>
>If you say something I don't like, or you say it in a way that I
>don't like, is that your problem or mine?  Unless you've called me a
>name or libelled me, chances are that it's my problem.  I can handle
>my problem responsibly, by looking at my reaction and where it comes
>from, or irresponsibly by calling you names and trying to shout you
>down.  If I check it out and it looks like there's a response I want
>to make, I can do that in a way that makes my views clear without
>trashing anybody.  If I'm too upset to say my part without trashing
>anybody, then I am probably too upset to post.  I would do better to
>send it to myself, and rewrite it for posting when I've settled down
>and have some perspective.
>
>Elena is absolutely right in saying that she shouldn't have to put
>up with it if you choose to handle your reaction irresponsibly by
>barfing it out the list just because you happen to have an emotion.
>
>On the other hand, if I choose to be deliberately provocative in how I
>present something, I should not be shocked or dismayed when my hostile
>approach draws a negative reaction from people.  Does that mean that
>the people who react against my approach are reactionaries or bigots if
>they happen to be of a different background than mine?  It is possible,
>but it is also quite possible that I've been abusive and owe those
>people some amends for baiting them.
>
>There are 630 of us so far out of a world of 6 billion or more.  We all
>have something in common.  We also have differences.  We can use the
>differences to divide ourselves against each other, or we can use what
>we have in common to support one another.  So if Lillian wants to do
>battle against racism, more power to her.  If I don't join her at the
>barricades on a daily basis, does that mean that I am a hypocrite or
>that I am against her?  Of course not.
>
>Even so, these drums do come with some history and cultural baggage
>that it would be outrageous and completely irresponsible to ignore.  So
>if Lillian wants my support in raising the issue of racism, why should
>any of us begrudge her that?  What possible good could that do us?
>
>If you've got something to say, say it.  But don't shove it in my
>face.  If you've got something to say in response, respond!  But any
>response that can be boiled down to "you're stupid, get lost,"
>that isn't much of a response and it really doesn't belong here.
>
>Thank you for listening,
>
>-r

  -----Original Message-----
From: Robert Hartman <hartman@informix.com>

>When you feed parallel rays into a parabola, they are all reflected back to the focus.  (Angle of incidence equals angle of reflection.) The sound waves that are produced by the head travel pretty-much in parallel until they hit the sides and are reflected back.  Each point along the wavefront travels in a line that is parallel with the lines of travel for all the other points in the wave-front.  If the shell was a perfect reflector, the skin perfectly rigid and flat, and the shape
>of the bowl a perfect parabola, the cumulative sound pressure produced by the movement of the head would be concentrated on a single focal point inside the drum.  If you could put a microphone at that point, the sound would be very loud indeed.
>
>However, none of those materials are perfect, which means that the skin produces interference patterns that can either be reinforced or dampened by the shell depending on where you strike it, the shell absorbs some of the energy from the sound pressure, the hole at the waist relieves some of the sound pressure inside the bowl and creates some harmonic distortion, and the stem does too.
>
>The hole and stem will alter the location of the focal point for the drum.  But I'm not sure how much or in which direction (up or down).
>
>I'm also not sure about where the focus _should_ be in relation to the hole for the best sound.  To get the loudest sound, the focus should probably be right at the waist hole.  However, that might not produce the best tone quality.  It may be that the "thunk" of a really good tone comes from the focus being higher up in the bowl rather than at the waist or somewhere down the neck.  On the other hand, I would imagine the brightest slap tones would come from the focus being in the
>same plane as the rim of the waist hole.  I'm also not clear on how you would alter the focal point except by removing material at the rim to make the bowl shorter with respect to its rim diameter.
>

From: Manos, Mike <mmanos@netatlantic.net>
>> anyone have any suggestions on how to bore out a single hole, maybe 2 or 3
>> inches wide, through the entirety of the 25"  long piece of
>
>I am just finishing up making a small kenkeni, my very first carving experience, so 4 weeks ago I was asking the same questions as you.  I carved a 20" cherry log, and it's looking pretty good.  To bore down the middle, I didn't drill at all;  I used an 8mm spoon gouge.  The "spoon" angle on the
>end allowed me to hammer straight down, yet scoop out the wood all the way down the middle.  I also got a bent gouge (a much longer, gentler scoop than the spoon gouge) that allowed me to chisel straight down the insides of the log.
>
>For the outside, I used an adze and the bent gouge.  I got everything from the Woodworkers catalog and at an outlet near me.
>Adze - $50
>Spoon gouge ("swissmade" brand) - $28
>Bent gouge ("swissmade" brand) - $35
>
>I also am treating the log every day with boiled linseed oil.  Let me know if you need more info.
>
>--Mike Manos
>  mmanos@uhd.com
>  301/926-8000
>
From: Adamrugo@aol.com <Adamrugo@aol.com>

>Hi,  Tim,
>
>I'm in the final stages of carving a maple djembe myself!  The piece I have
>had been eaten through the center by termites,  so I had a head start.
>
>Cutting a hole through the center of the log is definitely the first step.  I
>have seen a video (at SJI '98 - yeah!) of a Malian craftsman using a long-
>headed axe to chop through the core.  If you use a drill,  you could use a
>long wood boring bit,  but it doesn't need to be deep enough to reach through
>the log on one pass.  If you measure where the exact center is,  you can drill
>halfway from each side and meet in the middle.  (I've gotten bits like this
>from Builder's Sq.)  Or make a series of holes in each side and knock through
>a larger chunk of wood.
>
>For the shaping,  you can use chisels and maul (a woodcarving mallet),  but
>it's a slow process.  I've made chisels out of six foot lengths of heavy
>plumbing pipe.  You can use the weight of the tool to help on each stroke.  I
>saw a trick that some Native Americans do for carving their cylindrical log
>drums.  After getting a hole through the middle,  they use a chainsaw to make
>radial cuts every few inches.  Then you'd knock out the wood tongues with a
>heavy tool,  like my pipe-chisel.  You can even use this chainsaw technique to
>shape the outside of the djembe.  Just remember:  be conservative!  And make
>many,  small cuts,  rather than try to do it all in a couple of strokes.
>
>Hope this helps!
>Peace,
>Adam.
>
>P.S.  Keep the log wet as you work.  Either soak it in water between carving
>sessions or wrap it in something soaking wet.  Or,  you could paint the ends
>of the log with hot wax,  which helps control the moisture loss.  Leave the
>bark on as long as you can - it helps keep the moisture in,  too.
>A. 
>

ALSO SEE:

Volume 9c -  Making djembes / ashikos - bowl shapes, lathe   designs,
                                           bearing edges
                       Volume 9c1  Table Of Drum Dimensions and Descriptions
                                              Volume 9c3    Ashiko Construction