I hung the tuning fork by a thread and hit it with a knife and listened to the frequencies with my computer I analyzed the tuning fork in the free-free conditions. In free-free condition, the part has many vibration modes and is not damped by being held or fixed at any location. For us, dangling under gravity is close enough to approximate free-free analysis in Elmer. A free-free part in real life would be floating in space not subject to a gravity. The case we will analyze is called free-free, where the object is not rigidly held at all. (It is also slightly higher because the tension has been increased a little bit). The note is mainly higher because its length is shorter. When you pluck the string again you hear a higher note. When you press the sting onto the neck of the guitar you shorten the length of string that can vibrate. When pluck a guitar string you hear a certain not. How you hold something changes which frequencies can be excited. I’ll examine these factors in depth below. I assume my model is very close to the real life part.īased on my previous work, I’m using 2nd order tetrahedral elements, which gave answers accurate to within 2% of predicted hand calculations in my previous post, Calculating the Vibration Frequency of a Cantilevered Beam.ģ-5) Boundary Conditions, Mesh Density, ad Material Properties My model used average measured dimensions. 1 mm, thicknesses in the forks of the prong only varied by +/. I measured my tuning fork with some vernier calipers, accurate to 0. Material Properties – Is your material correct?.Mesh density – Is the mesh fine enough to give you an accurate answer?.Boundary Conditions – Is the way you’re holding the part in the model the same as the way you’re holding it in real life?.Element types – Did you use elements which will give you an accurate answer?.Geometry – Is your CAD model accurate vs the real part?.When you’re making a model of a part a number of inputs impact your answer. Hardware: Ruler + Vernier Calipers (to measure the tuning fork).Hardware: Microphone/headset microphone (allows you to record audio when you hit tuning fork in real life, I could also have used a cell phone).Software: Audacity (audio analysis/recording, analyzes the frequencies in an audio file).Software: Libreoffice/Excel (spreadsheet, conversion of FEA eignevalues into frequencies).Compare the calculated to actual results.Ping test the part in real life to find the actual frequencies.Import mesh into Elmer (Finite Element Analysis (FEA) software), solve for frequencies in Elmer.So I bought a tuning fork off and compared the Elmer analytical frequencies to the real life free-free frequencies. 5% of the frequency depending on temperature, barometer and other natural conditions so no way around that.I’ve shown that Elmer accurately calculates a cantilevered beam’s lowest natural frequency, but I wanted to test Elmer on a real part. This is because the frequency of the best quality tuning fork will still vary by.

17Hz difference between 7.83 and 8 does not really matter with tuning forks. All three of these forks are based on the Schumann resonance, the Earth's frequency. So that is how the Otto 32, Otto 64 and Otto 128 were derived. The C note after 16 hz is 32 hz hence, the Otto 32. The next C is 16 hz, still too low to be heard. When we say that we are octavizing a frequency, we are just going to the next set of white keys on the piano. The note following B is C, same note just a higher octave. On a piano the notes of the white keys are C, D, E, F, G, A & B. You can read more about octaviztion here. If you want to make frequencies based on the Earth frequency, we would need to octavize 8Hz which essentially means doubling the frequency. So the if the frequency of the Earth is 8 hz, then why not an Otto 8 hz? Its because the lowest frequency we can sense is around 20Hz.

17Hz difference is not really a problem and I'll explain why shortly. For the purists reading this, know that the. The Earth frequency, also referred to as fundamental, is 7.83Hz which has been rounded to 8 hz. Schumann determined that the wave length or frequency of Earth was 7.83Hz but lets just say he knew what he was talking about. I could go into the scientific details on how Dr.

Ever wonder why the most popular Otto Weighted Tuning Forks are the 32Hz, 64Hz and 128Hz? It has to do with the Schumann resonance.

Tuning fork frequencies