Frequency Spectrum

[Tod Gilding]

This is my tap test along the grain for a spruce soundboard 560mm x 210mm and 4mm thick,still trying to get my head around this stuff, does this look right,and is it showing 90Hz ?

[woodrat]

This is a bit hard Tod....It is not 90 hz....I seemed to always have this crazy high spike at 90 Hz and I dont know what it is so I discount it...For the long freq you are looking for somewhere between 50 and 75 Hz. I keep going until I get a definite peak somewhere in that zone.
Reference Table 6-1 on page 6-8

John

[Tod Gilding]

I did the test several times again this time holding the board with a small spring clamp and I consistently get this, It is 50Hz, Correct ?.is this what you would expect ?

[woodrat]

That sounds about right Tod. Refer table I mentioned above. The 90hz spike is a strange one I dont know what it is....

John

[Tod Gilding]

Thanks John, I get that 90Hz spike when I hold the board between thumb and finger, but not when held with a small spring clamp, strange

[woodrat]

OK Tod, I will have to try the small clamp on the node...interesting....

Seems like your away now though:)

John

[simso]

Mmm, I read it differently

A sharp spike at any location is an indication of a distinct singular frequency, a flowing waveform is simply soft / large overtones. The problem with your display is you have no reject turned on, there is always unnneccasary back ground noise and you need to filter this out, also you are running a combination display of frequency and volume, you really should only use one for testing

What program are you running

[Tod Gilding]

Thanks Steve, all input appreciated.

I am using Visual Analyser 9.0.6 and have it setup according to Trevor Gores instructions as given on his website.

I also have a Shure SM58 dynamic microphone connected with XLR to USB cable.

After posting last I have been getting a very similar wave form as the second one that I posted regardless of how I hold the board and regardless of where I hold it, so I thought all was good,but obviously not,and I havn't had time today to try a few tests.

[woodrat]

Tod, on that first long grain frequency tap you are looking for something in the 50-75 Hz range anyway for typical guitar half plate....Refer to the references I gave you above.

[Tod Gilding]

Yeah John, I'm aware of Reference Table 6-1 on page 6-8, these frequencies are what I'm looking for, and it seems good for fL being at 50Hz but then I am getting an almost identical response for fc and fLc
and that can't be right fc should be 100-140Hz and fLc should be around 35-60 Hz but what I am getting is all the same or similar to my second posted wave form, I am obviously doing something wrong or reading it wrong. I will continue to test when I get time and see what I can come up with.

[Trevor Gore]

Tod, this:

Attachments:
4freq spec.jpg

(i.e. your last chart posted)
looks like no signal to me. Check your connections and that you have the sound input turned up. You might need to apply microphone boost, too (via the loudspeaker icon in the tray, bottom right of your screen)

[Tod Gilding]

Thanks Trevor, You may have hit the nail on the head. it looks like I have purchased a faulty XLR to USB , moving the cable at the XLR end gives an intermittent signal .

I havn't got time to repair and set up the test again at the moment but that would be the likely problem.

Doing this test for the first time, it is hard to know what I'm looking for exactly, maybe someone might post a typical result for fL, fC and fLC for comparison purposes

[kiwigeo]

Tod,

Maybe your hammer isnt big enough. Try an 18lb sledgehammer and see how ya' go

[Tod Gilding]

Been head butting it martin, my heads harder than any sledgehammer