How do we determine resonant frequency of objects for less than the cost of a Big Mac?

J!m

Veteran and General Yakker
Joined
Dec 24, 2019
Messages
9,253
Location
Connecticut
Tagline
BOT
#1
So, I'm designing a tone arm (again) and I would like to do some analysis to make sure I don't end up with a low resonant frequency somewhere that will open a time vortex and suck the earth into an inverted parallel universe. Or, maybe that's not such a bad thing afterall...

So, is there an "ap" for that? Do I have to get some special pickup, or would a $10 clip on piezo do it? Some freeware that goes on the computer? Has anyone doe these tests? Where's my beer?
 

nakdoc

Chief Journeyman
Joined
May 11, 2011
Messages
619
Location
Nashville, TN Music City
Tagline
highly biased
#3
I'm trying to remember how that was tested in the old days. You could play a sweep record and look for peaks, but I believe the method was to set the stylus on a piezo transducer and induce the sweep that way. The method I would think most effective is to thump on the turntable base while the needle is sitting in a silent groove, then look at a FFT for peaks. You would guess what was ringing, add dampening or whatever, then run the test again.
 

J!m

Veteran and General Yakker
Joined
Dec 24, 2019
Messages
9,253
Location
Connecticut
Tagline
BOT
#4
Well, since the arm exists only in my head (and a few drawings) now, I wanted to test sub-assemblies as I went, so I could make changes if needed.

For example, the inner gimbal is hollow and aluminum. I could make it a solid, which would help "pre-load" the gimbal bearings while adding almost nothing to overall effective mass. But, will that set up a resonance in the arm tube? I'm still leaning toward a solid, as I think I could then use less expensive bearings (which have less initial energy input to get moving) without them "rattling".

Just some thoughts...
 

AngrySailor

Veteran and General Yakker
Joined
Oct 15, 2014
Messages
3,419
Tagline
---not quite right
#5
You need a quantity of the stable isotope of element 155 to generate the anti-gravity field required for dimensional travel... of you do succeed in escaping the prison planet, take me with you!
 

J!m

Veteran and General Yakker
Joined
Dec 24, 2019
Messages
9,253
Location
Connecticut
Tagline
BOT
#6
Actually the plutonium in the microwave trick seems to work pretty well. You could try it on board even. (Don’t tell the cook)

“Tickling the dragon’s tail”
 
Top