Introduction: Tune the Pitch of Your Homemade Tin-can Made Dan Moi
I will quote myself: "Since my first instructable on the dan moi jew harp, I grow up from the technical point of view", which is true, but I noticed that some people would like to know more on how to tune the pitch of their homemade dan moi.
The 'tables things you can find following the link below:
Another point: buying a dan moi made by Dr Froggy
If anybody is interested I may sale some dan moi on order. You can contact me. It will be not cheap most probably because of the shipping costs. but I will charge you for a unique working dan moi and the work around it... for about 50 dollars without the shipping costs. This is clearly more expensive than a vietnamese dan moi. But if you are interested. let me a message...
I will maybe only do that for maximum 20 buyers then I will stop.
Each will be made out of oldtimer tin can boxes I need to find and buy, and I have my own costs and so on. It takes time to make several tests prior to make your very own. I make sure that the dan moi design will not move to much and is buzzing right.
Now I have a working process, I will not get rich dudes but I consider every work must be rewarded, I am more interested to see how many of you may be interested for such art!
What are the strategies to tune your homemade bass dan moi tin-can made into higher pitches?
I will try to give you the points for that.
I can only recommand reading the book of John S. Hopkin on musical instrument makings: Musical Instruments Design . One picture is highly inspired from one scheme of his book regarding the free reed design.
I added some further details to improve further the comprehension. And I hope it will help some of you.
Just a mention on the contents of this instructable-->attribution non commercial sharealike. You can re-use my texts and my pictures, modify or whatever, if you do so please cite the author, my work or even better put a link to this instructable. I would appreciate your cooperation :) In addition if you have any comment or improvement that you would like to share with me please do it. Last but not least, Share with me the metal homemade danmoi you made. I will probably add a gallery for your danmoi later on.
important notice/ safety issue
Step 1: Further Details About the Tin-Can Material
Back to the pitch tuning
I realized that once you made it you may want to tune the pitch. From my experience sofar, I can get a pitch between 20 to 60 Hz which is low but allow you to play high tunes (get the playing instructions given by Mr Robert Vandre on his website rvandre [dot] com)
Lately I was able to prepare a single 120 Hz one, I have to repeat this to confirm it
Why not higher pitches?
one great restriction comes from the material used for making those jew harps. Tin-can metal is quite soft, very little elastic and extremely plastic compared to brass traditionnally used by Dan Moi Makers in Vietnam. This material is choosen for good reasons.
Just to make you understand:
brass is an alloy used for piping, it is stiffer than copper (also it contains some copper) and is not brittle. It is used for brass wind instruments because of his extraordinary mechanical properties and its workability.
In front of that... Do not try to make piping and tubing out of tin can metal....it will blow up and be torn apart under water pressure... And for a wind instrument....it will not be possible to keep it in shape... I mean I found out a lot of trick (mostly folding) to rigidify the whole system.
But to make a bugle out of this material will be more than challenging.
Someone wants to say "Challenge accepted!"? :D
So If you want to get higher pitch, it is actually possible but ... you obtain a very very short and not lasting tone. Which is not the idea when you get a jew harp, it must vibrate. Otherwise, it is a very poor instrument. You obtain even better by clacking your tongue in your mouth...
Step 2: Jew Harp Configuration
This paragraph is dedicated to the various Jew harp building blocks.
A Jew Harp is basically a free reed instrument which reed vibrates after plucking/hitting a tail or a pluck part. The whole is part or is firmly attached to a rigid frame: the jew harp body.
It is necessary to get a long lasting vibration. This motion is enabled when the energy is transmitted to the system through hitting it. The elastic par of the spring takes actively a role into the vibration. It feeds the vibrating motion of the reed with energy during a longer period of time.
At the same time it oscillates and consume energy as well.
But this vibration is allowed to last by three main phenomenons:
The energy stored in the spring part
The energy stored in the reed
The energy stored in the frame
in other terms, if you want to get a long lasting vibration you need to avoid any damping behaviour, This is the key issue.
So we have seen the main subcomponents of a jew harp.
The tail, the reed, the spring and the frame.
The order of those three elements are differents in the presented configurations.
You can easily see the difference of the original Dan Moi version and the homemade tin can made dan moi.
The given configuration has been developped to enable a satisfying playing experience. As this configuration allows to modulate the mechanical properties of the used material to obtain a locally stiffer one.
Just think about the origami technology, which allows a piece of pape to withstand high loads, that otherwise will fail doing so for instance.
Step 3: Rules for Modulating the Pitch of a Free Reed
Here the various strategies for tuning a free reed are summarised on this picture.
However, this looks much simpler and effective as it is and especially if you want to verify those dogmes.
free reed tuning can be achieved by:
playing on the length of the reed
(shorter reeds will get higher pitches, but will store less energy and will not last long)
playing on the width of the reed
(wider reeds will get higher pitches - but it can be counterbalanced by extra damping in that case)
adding a load on the reed
(the closer to the end the lower the pitch AND the heavier the weight is the lower the pitch)
playing on the stiffness of the reed
(rigidity can be obtained by folding, however you want to avoid folding close to the end of the reed, little improvement will be achieved, clearer changes are obtained closer to the basis of the reed) Ideally folding the whole reed will cause a significant increase of pitch.
However, if you tune the free reed only, you will be disappointed. Those points are in fact more important for the design of the reed (getting the direction). You can play a little on those to tune the free reed itself alone.
BUT the reed design is only one component of the Dan moi free reed vibration.
Hence you really need to play on other subcomponents! The tail, the spring and the frame modulated greatly the motion as well°!!! This is why it is quite tricky.
Hopefully a not annoying demonstration:
I remember looking at different dan mois I noticed that the spring part was not allways of the same proportions. The makers shape the dan mois free reed and then sand off the brass sheet close to the basis of the reed to get a thinner part there. This part becomes the spring part and the tail is although sand off to play on the load at the extremity). Actually this is normal, if you take a look into the spring+load simulation, you will easily see that a heavy load on a spring will oscillate on a longer period of time than a normal load. The elastic behaviour plays a role as well but this is the trick, if you get a too thick spring part it will requires a heavier load to oscillate long. However, you need to pay attention that the load will not modify the shape of the spring... Which means the ratio between load and spring constant is not optimal and you will get a too soft and not lasting instrument. Instead of oscillating it will get unshaped and bent. Bending will consume the energy and instead of getting restored by the spring, the vibration will be terminated sooner as expected.
Step 4: Focus on the Proposed Modified Dan Moi Configuration
I have tested several configurations as one can see from my previous instructables.
I found out a further quick and dirty method for making my dan moi design.
Why? because I wanted to go fast and test quickly.
The Electro Chemical Machining is very fine and give wonderful and reliable results but I needed to test several modulations fast.
I will share this method in a later instructables. ;)
Here, I wanted to show you that the position of the basis of the reed and the basis of the tail may influence greatly the mechanical properties of the jew harp leading and a fortiori also the motion of the reed.
In the case C on the picture, the tail is placed over the reed part it acts similarly as the pluck part in a bow shaped jew harp.
However, If we want to stick to the dan Moi we need to place the tail on the spring part more like shown on the dan moi indicated with a A).
I cannot identify the best choice between the three versions up to now. but A) will result in a bigger tail part compared to others.
Step 5: Experimentation: Using Audacity to Find the Fundamentals and Detecting the Key Modifications
The picture depicted the software audacity used to record with your microphone the sound of the free reed.
If the free reed of your dan moi oscillate without touching the edges of the frame, it will be possible to define the fundamental of this free reed.
you need to place the free reed facing the microphone of your computer (very closely placed). you must place it sothat the sound may be recorded by the microphone. To be sure of the orientation of the free reed pluck the dan moi close to your ear. You must hear a buzzing sound. Once you understood how to get the best sound you can go on.
With audacity, a freeware, you need to select 5 or more signals (each time you plucked the dan moi until it has reached its steady state = a signal)
Those signals look like a sinusoidal that dimished as a function of the time.
Then you go to the analyse menu, and select "spectrum". you will have to select in one menu numbers 514/1024/2048/4096/8192. choose 2048 minimum, 4096 gave more precise results.
Select logarithmic scale for the frequencies.
The highest signal (or highest "summit") gives you the fundamental value.
here we can read the values 42Hz and 56Hz on those two examples which correspond to "bass" free reed.
This particular case illustrates the modification that sofar affects the most the pitch:
Folding the spring part.
Step 6: Possible Modifications
Following what was presented On the previous slide,
I have shown you that one can increase the pitch by folding the spring part (here the case A- also it seems that the frame is fold... but this fold affects the spring heavily--> it creates great tension on this part, which means enhancement of the elastic behavior! it will act more like a spring and less energy will be wasted through signal damping)
The second possibility is to reduce the length of the tail by folding it like a zig zag like on B. This folding will improve the rigidity of the tail and of will act more like a spring too. but also its amplitude will be reduced (the mass is closer to the basis of the tail, meaning shorter amplitude... shorter amplitude means less energy wasted)
I carried out the same experiment several time on dan moi I made of different sizes. I noticed a slight enhancement of pitch. For instance, I obtained a shift from 43Hz to 51Hz by playing only on this part)
The third possibility consists in playing on the original length of the the tail. Mass/load distribution must be taken in account to get optimal oscillating behaviour.
One point about the frame: it must be rigid at least at the same level as your reed.
Step 7: How to Get a More Elastic Behaviour
the fold carried out on the spring part is very similar of the one used by the hair clip makers.
I actually got the idea from it. I discussed long time ago after my first instructables with a friend to who I gave one homemade dan moi. I already noticed that but he told me the same, sosad that we cannot build a dan moi from those hair clip. Those are really efficient ant oscillate nicely when plucked!
So lately I came back with this idea, because in the proposed configuration such a folding that can create tension in the frame. Those tensions are responsible of the elastic behaviour improvement I noticed.
On my trials on smaller reeds that were not able to oscillate, with such modifications enables sufficient oscillations: I got a dan moi with a fundamental around 120 Hz with comparable oscillating period!