Wanted: acoustic "noise" source

[dewardh]

Originally Posted by RevMen

maybe someone might wander along that could use . . . information

You might address that better by going back and "correcting" your links to "member only" resources and four and five digit price "equipment" catalogs.

Actually useful information generally falls in the range between the blatantly obvious and the practically inaccessable . . .

[RevMen]

I'm starting to realize you have trouble with reading comprehension, so I'll go ahead and explain again that the reason I posted links to reference sound sources was to show that I was wrong when I said they are no longer made. I find it interesting that I can admit that I was wrong and post links to the proof that I was wrong, yet still draw criticism from you about the links that I posted. You seem to be impossible to please.

I pointed out that they're very expensive, but if you wanted to find one for yourself at a price an average person might be able to afford, there's a chance you could find a used one on the auction site (from time to time premium equipment turns up there, sold by people who don't know what it is). In no way did I suggest that anyone on this forum should consider purchasing a reference sound source from B&K or LD.

In what world is a procedure to measure and calculate sound power, complete with appropriate equation, "blatantly obvious?" I think that you're projecting your vast knowledge onto the rest of us. Do you really have the hemi-anechoic relationship between Lw and Lp memorized?

Somewhere between blatantly obvious and very expensive I posted a full set of steps, including math, for choosing and measuring your very own DIY reference sound source. I gave you reference data for every fan type you're likely to come across. Earlier in the thread I explained that, with current processing power, there's no real need to use a reference sound source and explained how to work without one. You have all the information you need and more to accomplish your goals. Is there really no useful information in there?

Also, there are still some unanswered questions I'm waiting to hear answers on. It seems my understanding of signal processing is flawed, and I hope you don't mind sharing some of your knowledge with me so that I can work towards correcting that. Let's recap.

Originally Posted by dewardh

The whine of a jet engine or the hum of a refrigerator is called "noise" in some circumstances, and at least parts of it may be deconstructed to a sum of continuous tones. That is not the kind of "noise" we are talking about here . . .

Originally Posted by RevMen

So what determines what kind of function can be broken down into sines and cosines? In other words, which parts of the jet engine whine are eligible for Fourier transform and which are ineligible?

If it's not possible to break down acoustic noise into pure tone components, what is a sound level meter showing me when I look at the RTA display?

You never answered the first question. Could you go ahead and do that?

The second question you answered with

Originally Posted by dewardh

A statistical average. If there are "pure tone" components to the noise a spectrum analyzer (using FFT) will separate them out and display them as separate peaks in the frequency domain . . .

A statistical average, as opposed to a non-statistical average? I'm not sure what you mean here. What averaging operation can transfer time domain sound pressure information into the frequency domain? What needs to be averaged?

I'm also interested to learn how FFT separates out pure tone components and displays them as peaks against... against what? What is all of that other information in the FFT display under the peaks? How did it get into frequency domain?

You also started this thought:

Originally Posted by dewardh

I suspect that you are confusing "sines and cosines" as mathematical functions with continuous waves. Not the same . . .

Could you go ahead and finish that for me? It might be blatantly obvious to you, but I'm having trouble following.

Thanks for your time.

[Ron E]

Originally Posted by dewardh

Well that's certainly . . . useful . . .
Now, back to the question in the OP . . .

Wow! There are three commercial alternatives to your crazy fan noise source and you aren't interested? I like the tap box, myself. I think you could diy a tap box pretty easily.

Interesting that reading about room measurements with modern software is now on your radar.... even if the quote is so banal and obvious. MLS "noise" gets turned into an impulse! Holy crap, when did that get invented?

[dewardh]

Originally Posted by RevMen

It seems my understanding of signal processing is flawed.

Could be. The "quality" of your advice would certainly suggest so. But it is not my job to fix it.

About low cost broadband noise sources . . . got anything useful to offer?

[dewardh]

Originally Posted by Ron E

I like the tap box, myself. I think you could diy a tap box pretty easily.

Good. Go for it. I look forward to seeing your results . . .

[RevMen]

Originally Posted by dewardh

Could be. The "quality" of your advice would certainly suggest so. But it is not my job to fix it.

I thought so.

About low cost broadband noise sources . . . got anything useful to offer?

You mean, other than telling you exactly what to get and how to use it? I guess not.

[dewardh]

Originally Posted by dewardh

got anything useful to offer?

Originally Posted by RevMen

I guess not.

Oh, good . . . something we can agree on . . .