Build Box Cajon: Size and Tone
dustin gooding
and is made of 3/4" MDF (awesome for speakers, etc) and 1/8" baltic
birch for the head... it has a 7.6" hole (using an equation i found
online) and it sounds AMAZING... super low bass, with excellent
sustain...
my question is this... my drum currently has a 20"x20" head... it's
lowest note is a G (two octaves lower than middle C)... now, if i
wanted to make a another drum out of the same materials, how would i
make it so that new drum's lowest note was an exact octave higher?
things that i know: to make the next octave G, i need the new drum to
resonate with a frequency twice that of the current drum... but how?
i would like to only change the size of the head (for various reasons
that may not interest you)... i would think that if you wanted twice
the frequency, you would half the size of the drum head (but in what
direction, if not both?)...
to double the frequency of a 20"x20"x20" (head length X head width X
box depth) drum, which of the following do i do?
a) 10"x20"x20" (half length, half area, different shape)
b) 10"x10"x20" (half length and width, quarter of area, same shape)
c) 14.14"x14.14"x20" (half area, same shape)
d) other
i know that i will end up just trial and erroring until i find the
right answer, but if anyone can point me in the right direction,
please do... thanks alot !!
-dustin
bja...@users.iwaynet.net
> i recently built my first box cajon. it's rather large (20"x20"x20")
> and is made of 3/4" MDF (awesome for speakers, etc) and 1/8" baltic
> birch for the head... it has a 7.6" hole (using an equation i found
> online) and it sounds AMAZING... super low bass, with excellent
> sustain...
Sounds like a cool project!
> my question is this... my drum currently has a 20"x20" head... it's
> lowest note is a G (two octaves lower than middle C)... now, if i
> wanted to make a another drum out of the same materials, how would i
> make it so that new drum's lowest note was an exact octave higher?
What about using those on-line equations you used to build the first one?
> things that i know: to make the next octave G, i need the new drum to
> resonate with a frequency twice that of the current drum... but how?
> i would like to only change the size of the head (for various reasons
> that may not interest you)... i would think that if you wanted twice
> the frequency, you would half the size of the drum head (but in what
> direction, if not both?)...
> to double the frequency of a 20"x20"x20" (head length X head width X
> box depth) drum, which of the following do i do?
> a) 10"x20"x20" (half length, half area, different shape)
> b) 10"x10"x20" (half length and width, quarter of area, same shape)
> c) 14.14"x14.14"x20" (half area, same shape)
> d) other
How about "none of the above"? The pitch of a cajone is not determined
by the the head or tuning like a drum or string. It's determined
by the volume of the box and the size of the hole sort of like a
guitar body.
If you want to calculate, go look up the formula for a Helmholtz
resonator. It basically consists of a volume of air connected
to a tube of a certain length and diameter. For your purposes
a hole in a plate acts as if it is a tube the diameter of the
hole which is about a hole diameter long. That's only
approximate but should get you in the ball park.
> i know that i will end up just trial and erroring until i find the
> right answer, but if anyone can point me in the right direction,
> please do... thanks alot !!
> -dustin
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dustin gooding
Those were rigged to work with bass-reflex speaker enclosures. When I
hit the cajon without a hole, I found out what frequency that was, and
cut a hole the appropriate size (given volume, hole diameter, hole
length)... this changed the frequency that the cajon made... which
is explained by:
> If you want to calculate, go look up the formula for a Helmholtz
> resonator. It basically consists of a volume of air connected
> to a tube of a certain length and diameter. For your purposes
> a hole in a plate acts as if it is a tube the diameter of the
> hole which is about a hole diameter long. That's only
> approximate but should get you in the ball park.
and calculate it, it did!! i played with the helmholtz formula a
little bit, trying the get "my frequency" to come out... i found that
the port length that was needed was in fact the RADIUS of the hole,
not the diameter... i may be doing something wrong, but I will be
testing these results this week sometime... i'll be sure to post the
results...
the reason for this whole mess is that i want to create a *single*
box, with multiple chanbers inside, all having their own head... i
also want these individual drums (all in one neat tidy box) to be a
root, 3rd and 5th... if the helmholtz equation is all it's cracked up
to be, this project just got a LOT easier... any suggestions or hints
on this? does it matter if the volume is in an akward shape (L or T,
to allow for smaller chambers in the same box) ???
also, should i do root-3-5 or root-4-5 ??
bja...@users.iwaynet.net
> and calculate it, it did!! i played with the helmholtz formula a
> little bit, trying the get "my frequency" to come out... i found that
> the port length that was needed was in fact the RADIUS of the hole,
> not the diameter... i may be doing something wrong, but I will be
> testing these results this week sometime... i'll be sure to post the
> results...
Yes. RADIUS! I remember now. That does sound correct!
> the reason for this whole mess is that i want to create a *single*
> box, with multiple chambers inside, all having their own head... i
> also want these individual drums (all in one neat tidy box) to be a
> root, 3rd and 5th... if the helmholtz equation is all it's cracked up
> to be, this project just got a LOT easier... any suggestions or hints
> on this? does it matter if the volume is in an akward shape (L or T,
> to allow for smaller chambers in the same box) ???
Generally I don't think the shape of the volume matters TOO much. But
I do think it needs to be fairly compact and not long and skinny
like a pipe. (Think djembe, conga, guitar) Also I think it's important
to have a pretty good transition place at the hole. In other words a
decent volume of air around the hole to feed it. I mean a guitar
is kinda of a flat oddball shape and works OK. Basically you don't
want the volume of air being forced into smaller spaces where acoustic
resistance could kill the resonance. Optimum is a pipe attached to a
sphere, but one rarely sees that except in physics demos. A djembe
is close though. (usually a hemisphere or close to it)
> also, should i do root-3-5 or root-4-5 ??
I think it would be cool to start with just a dual chamber
version and tune them a fourth apart like traditional
conga tuning. No?
Might want to think about how one plays this. You sit on it
and then maybe hit left and right sides? Or maybe have 2
panels on the front each feeding a different chamber?
Cool idea!
Benj