Harmonic Balance..... - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
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post #1 of 1 (permalink) Old 10-23-04, 05:31 AM Thread Starter
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Harmonic Balance.....

Now, just a quick lesson to get a grip on things,

1. 80Hz can be felt in the gut (I.e think bass guitar etc.)
2. 80Hz has a cycle rate of 80 cycles per second
3. a 360(deg) cycle refers to the sound moving foward (180deg) and back (180deg)
4. In electronic terms - foward may be "+", Backwards may be "-"

5. Phase is messured in (deg)
6. So for a sound to complete one cycle it must travel 360(deg), i.e 180 up, 180 down and back to the centre (0deg).

so when we have several noise sources, i.e a bad wheel balance (220hz), muffler noise (140Hz) and road noise at 100km/h (80Hz)

This is where harmonic phase shift occurs, i.e several wave cycles crossing each other at different points. this is know as a mode!.

A "mode" is where the cancellation of two freq (Hz) occurs. So with the above noise suffering a "mode" 80Hz might have a 3dB boost at 1.2 octaves, whilst 220Hz may have a complete cancellation (-89db) or (180deg in phase shit, in regards to the originall sound source).

My point -

No matter if were talking about sounds from cars, Speakers, Road noise, Sewing Machines, TV's or Bobs microwave nextdoor, a Freq(Hz) is just a freq.
No matter what the scale of the bandwith may be, 100Hz will always be low. 1Khz is the centre of all freq, lower than 0hz is know as microsub-waves (only available in space), yet above 40Khz we move in to the MHz Spctrum where video and UHF, VHF and other devices like to call home.

The "Auto Industry" does not have a bandwith, Sound re-inforcement does not have a bandwith, bandwith is a messured for a limited spectrum.

What does all this mean, No matter what you call high or low freq it can not be compared, 100hz is always going to 100hz no matter what industry you work in!

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