Hello All

[vibrationtest1985]

I created a profile because the following post really "Disturbed" me:

http://www.eng-tips.com/viewthread.cfm?qid=126607#post

Particularly:

phanikumar (Mechanical)
17 Jun 05 11:04
In my defense
"Octave
An octave is a frequency interval having a ratio of two. It is called an octave from the music tradition where an octave spans eight notes of the scale. The second harmonic of a spectral component is one octave above the fundamental. In acoustical measurements, sound pressure level is often measured in octave bands, and the center frequencies of these bands are defined by the ISO. Vibration measurements are seldom expressed as octave band levels, but the US Navy has used 1/3 octave band analysis for vibration measurements on submarines for a long time. "
Source:

http://www.vibinst.org/vglos_f-o.htm#o

I hope you know what a vibration institue is

I am not ashamed to say "I dont know when I dont know" b'cos being an engineer I know its always being on a learning curve. Octave is seldom used in vibrations its associated with acoustics, since a lot of times acoustics and vibrations go together, definitions are interchanged easily.

This statement is very, very WRONG. Octaves are used EXTENSIVELY in vibration testing. It is used not only to define the sweep rate of a sine vibration test, but also to express the slope of both random vibration spectral curves and Sine Vibration profiles (dB/Oct).

So, the term octave is NOT seldomly used it is used A LOT if you are actually involved in vibration analysis and vibration testing!

 

[IRstuff]

You may wish to review the fact that the thread in question is over 7 years old. Moreover, the posting was from someone who wasn't even necessarily an engineer.

TTFN
faq731-376

 

[electricpete]

Good points by IRstuff... not much point in responding to that particular post.

But, now that you've signed up... Welcome to the forum!
Stick around and read/contribute on some of the current threads.

=====================================
(2B)+(2B)' ?

 

[amanuensis]

Nevertheless, I think that octaves are less important in vibration than in acoutics. Indeed, octaves mimic a physiological aspect of the ear, that is the fact that it is easier to hear two tonal sounds at low frequencies than to the high frequencies.
In vibration, it is just a convenient way to get a straigh line/ slope using a log-log plot.

 

[IRstuff]

The straight line is a consequence of the log-log itself, and not related to whether you are using octaves or decades. What makes octaves and decades convenient is that the slopes come out at multiples of 3 dB/octave or 10 dB/decade, which are convenient values to remember. Moreover, since it used to be common to have taken some sort of music lessons, people immediately recognize octave as a scale factor.

TTFN
faq731-376

 

[amanuensis]

Are you saying, M. IRstuff, that it is impossible to have a slope of 4dB/Oct (for example)?
Could you tell me what is the reason for that?

 

[IRstuff]

For classical LCR circuits, there are integer powers of poles and zeros.

TTFN
faq731-376