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  • Users: Hatch
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  1. Hatch

    Using accelerometer for FFT of guitar soundboards

    Interesting article on this topic by Bruel & Kkaer. See link. http://www.bksv.com/NewsEvents/Waves/Waves_2014_1/07-guitar-evolution
  2. Hatch

    Steel rolling mill chatter marks

    As I said before, its a complex situation and not normally solved in a few days. Items 3 and 5 are related. In our mill we found that older work rolls were consistently involved when we had chatter. One solution was to use all newer work rolls when we had chatter. For some critical products...
  3. Hatch

    Steel rolling mill chatter marks

    Its been years since I did Chatter investigations on a 4 stand Cold Mill. There are many conditions which cause the mill to go into Chatter but it takes time and measurements to sort it out. Some observations and comments I have are: 1) Its interesting that the work rolls do not show chatter...
  4. Hatch

    Interpretation of vibration spectrum

    Not much information to work with so I have questions. Is the vibration problem on the compressor or is it the support beam? What is the overall vibration at the compressor? Higher or lower than the support beam? I agree with StrykerTech that frequency info is required. Taking a shot at...
  5. Hatch

    Time Domain vs. Frequency Domain Acoustic Analysis

    Just a quick comment. Time Domain Analysis has been around a lot longer than a few years. It just had a different name but is the same thing. It was called the "Chart Recorder". You got amplitude versus time. Faster paper speed equals more resolution. Chart recorders were around long...
  6. Hatch

    Is it possible to convert from sound power to sound pressure level?

    The basic equation is in "Noise and Vibration Control Engineering" by Beranek and Ver. A simplified form is below. Lp = Lw - 20 log (r) + DI -11 Lp = sound pressure level. Lw = sound power level r = distance from source to receiver DI = directivity index. Use 3 for free field (outdoors)...
  7. Hatch

    Is it possible to convert from sound power to sound pressure level?

    The short answer to your question is Yes. You need to make/determine a few parameters. 1) Distance to the sound pressure level point, (usually 3 feet or 1 metre). 2) Is the measurement point indoors or outdoors. Most contracts just assume outdoor conditions or "free field conditions". i.e...
  8. Hatch

    Vibration of a recip. air compressor

    In the past where there are multiple degrees of freedom, I have used wire rope isolators. I used it in reverse to protect a computer system on a locmotive engine and also to isolate a fan system which was shaking a roof. See: http://www.enidine.com/Industrial/WireRopeIsolators.html Just make...
  9. Hatch

    PC's in U.S. for acoustical louver design

    Do you mean specify or design. I don't see why you have to design a new louvre unless you are talking a new product. There are quite a few suppliers of off-the-shelf acoustical louvres out there which can also be made to fit. Most louvres are 6" to 12" deep and provide a maximum 12 dB...
  10. Hatch

    Noise Measurement of Vacuum Pump

    Somptinguy, I looked up the solution for a Helmholtz resonator and the equation is: helmholtz resonance freq = v/2PI * sqrt (A/Vo L) The v in the equation is the speed of sound in a gas so do you have another equation where the speed of sound is not required?
  11. Hatch

    Noise Measurement of Vacuum Pump

    Interesting Question here are my thoughts: 1) In my experience the noise comes from the vacuum pump itself and the motor. The pipe noise is not usually a problem. 2) OK assuming the pipe noise is an issue, the inlet pipe is operating in a vacuum. What speeed of sound do you use to design the...
  12. Hatch

    A typical pressure drop for large silencers... ?

    The basics of silencer selection are as follows: Higher Insertion Loss = higher pressure drop. Longer Silencer = higher pressure drop. Higher low frequency performance = Longer Silencer Higher blockage = Higher velocities in silencer (passage velocity) Higher Passage Velocity = higher pressure...
  13. Hatch

    Inches per second to Mills

    A mil is a thousandth of an inch, (0.001 inches). Or... 1000 mils = 1 inch.
  14. Hatch

    Excess hotwell pump vibration

    You don't mention the frequency(s) of the high vibration, which can provide a significant clue to your problem. However, I have seen the follwing items cause high to severe vibration: 1) Pump shaft runout. 2) Motor overload due to motor damage or pump impeller wear, or a system change (they...
  15. Hatch

    Noise attenuation due to elbows in ducts

    The answer to your question should be covered in the paper: "Explicit formulas for the calculation of regenerated noise in ducts" by Tim M Marks The entire paper is available online. Do a google search and you should find the downloadable paper. The link is below but I find that long links...
  16. Hatch

    vibration isolation

    Wire rope isolators have several advantages over conventional single axis rubber or spring isolators. 1)They are not affected by extreme heat or cold (within reason of course,) nor oils or other corrosives which destroy rubber or neoprene isolators. 2)They can be mounted in any attitude...
  17. Hatch

    Calculating noise level of sonic flow in a pipe

    In a typical industrial setting, the steam flow in a pipe rarely generates problem noise levels. High noise levels are actually generated upstream at a valve or orifice. The turbulent flow/sound is then propagated down the pipe and out as noise. If you want to start somewhere then look up the...
  18. Hatch

    Spectrum tolerance

    Over many years, I have never actually hit a bearing defect frequency dead on (i.e. spectrum peak differs from defect frequency). Even if my FFT resolution is OK, there always seems to be a small 1 to 5 Hertz differnce. In fact if you calculate the bearing defect frequencies from the standard...
  19. Hatch

    Removing bubble from 200um holes via excitation

    How about doing it the other way. Ultrasonic cleaners excite the liquid so it cleans parts thoroughly. Maybe you can apply an untrasonic exicter to the tank so that the liquid will flow into the voids better and bubbles might be dislodged at the same time.
  20. Hatch

    Attenuator for Proximity Probes

    I am not sure about your set-up, but with my proximity probes, a DC voltage is first applied to the probes (excitation voltage?) on one set of terminals and the gap voltage (varying DC signal = AC signal if the gap is changing)is generated on the second set of terminals (output). The base gap...

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