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  1. Vibac

    (Mis)Understanding How My SPL Meter Sums Spectral Amplitudes

    One thing to be aware of: The meter's broadband value may come from a (broadband) RMS detector, and not the summation of the 1/3-oct bands. Sometimes the RMS detector operates on a slightly broader freq. range, which would lead to a higher level.
  2. Vibac

    Foundational understanding in mathematics for studying honors

    Make sure to check out the YouTube channel 3Blue1Brown. It has fantastic presentations on a lot of medium to advanced math topic. I find it really worthwhile!
  3. Vibac

    Modal Impact Test Question

    Adding to GregLocock's comment, I suggest reading this nice paper by B&K, which compares different methods: https://www.google.com/url?q=https://www.bksv.com/doc/bv0044.pdf&sa=U&ved=2ahUKEwj9yLj2hMHjAhUBPVAKHY0pAF4QFjAAegQIBBAB&usg=AOvVaw3B8rY8z8pzzN3uDnV-vxUD
  4. Vibac

    Sound Insulation Testing Setup?

    I fully support the idea of empirical testing. However, keep in mind that there is quite a lot of analytical expressions available for sound transmission loss, even for multi-layer panels. See eg Beranek's classic text books. And, if you don't want to implement these, I recommend commercial...
  5. Vibac

    Complex Mode Shapes

    For modal analysis using Matlab, take a look at http://abravibe.com/toolbox.html Haven't used it myself, but it seems really useful.
  6. Vibac

    Curve fitting noisy experimental FFT response (transfer function) data of resonace

    ... Also: The way I see it traditional modal analysis works best with "deterministic", controlable measureable excitation. On the contrary, OMA methods work best in situations with stochastic excitation, random in both time and space. Hence the alternative name Ambient Modal Analysis. So, what...
  7. Vibac

    Curve fitting noisy experimental FFT response (transfer function) data of resonace

    ... but if the system is naturally like this then there is little that can be done (e.g. resonance of a structural element in water, such as vibration of a rudder of a boat while fully immersed in a body of water. Eatfood, are you familiar with Operational Modal Analysis (OMA), aka Ambient...
  8. Vibac

    measirung excitation forces

    Amenuensis, Using your mobility and velocity based approach, wouldn't you miss the energy corresponding to rotation around the three axes? I wonder in which cases this might still be a fair approximation?
  9. Vibac

    Software for test-analysis correlation

    Check out FEMtools: www.femtools.com Not exactly freeware nor cheep, but some call it state of the art of validating/correlating/updating FE models from measurement data.
  10. Vibac

    How to determine the sound power from a night club?

    May I add a word of caution: Noise from a night club is probably due to music, and might have a strong low-frequency content. Precise measurement of low-frequency noise/intensity (say, below 100 Hz) is not an easy task in outdoor conditions...
  11. Vibac

    Rayleigh Damping Coefficients of a plate

    Hi ghazwansaud Also, try googling the paper "Computation of Rayleigh Damping Coefficients for Large Systems" by Chowdhury and Dasgupta. I havn't had to use it myself, but I guess it might be helpful to you.
  12. Vibac

    Damping Measurement: Shaker Table vs Ping Test

    Rob45, just a comment: Modal analysis covers a wide range of different algorithms. Some are more appropriate for certain conditions than others. As an example, frequency domain based algorithms/methods may tend to exaggerate the damping ratio estimate for low frequencies (and or low damping...
  13. Vibac

    Human excitation frequencies

    Thank you all for your input. 70AARCUDA, could you give me a hint as to where to look for military/NASA medical test publications? Tried nasa.gov but got kind of lost...
  14. Vibac

    Human excitation frequencies

    Hi all Can anyone direct me to statistical descriptions of common excitation frequencies for walking, running, dancing, etc.? I'm think of eg. mean frequency with standard deviation for each activity. Would be very useful if you have a building deck with natural frequencies known from mobility...
  15. Vibac

    Natural frequency of expansion joints

    Thanks everybody for your input.
  16. Vibac

    Natural frequency of expansion joints

    No, I didn't post it anywhere else. What I had in mind was a simple assumtion of two rigid masses separated by a spring. From the top of my head this gives a natural frequency 1/(2pi)*sqrt(k*m1*m2/(m1+m2)). The masses would be the pipesections on each side of the joint,and k the stiffness of the...
  17. Vibac

    Natural frequency of expansion joints

    A general question: How do you estimate the natural frequency of an expansion joint mounted on a pipeline? For a simpel SDOF approximation I can get the expansion joint's stiffness (spring rate) from the manufacturer, but how about the oscillating mass? Any better idea than summing the mass of...
  18. Vibac

    ARTeMIS Modal Software

    As far as I can see the ArtemiS of Head Acoustic doesn't have anything to do with OMA (Operational Modal Analysis), whereas ARTeMIS from Structural Vibration Solutions is a dedicated OMA software package. I've been using ARTeMIS for a couple of years by now and is quite satisfied with it. We...
  19. Vibac

    cross-spectrum question

    When used to describe TBLs the cross-spectrum contains information about both the frequency content and the lenght-scale content. BobM3 just explained the frequency part. If eg. the TBL is convected above a plane surface you typically use two length-scale parameters: One (x1) in the direction of...
  20. Vibac

    Conversion to PSD?

    In other words: Divide the power spectrum by the measurement resolution including a correction for the data window: 1.5 for Hanning window and 1.0 for no window.

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