Tonearm Resonance (FFT)

Doctorcilantro · 1st September 2010, 07:47 PM

I was doing some reading about alterniative theory for tonearm resonance here. Stated that vertical should actually be between 15-20hz, and horizontal at really low freq. like 3-6hz. Would love to hear some comments on that as I may add a new cart and be right around 8 using a 28cu high compliance moving iron with 1g VTF.

This is a needledrop of the Ultimate Test Record. Grado Ref. on MG1 airbearing, and I'm curious if the 20-30hz rise in amplitude is by nature of a resonance or not. It is cut at -20db so I'm guessing this is a resonance. At 10hz, where I had calculated the vertical resonance to be, is an expected hump where I can see the cart. shake visibly. I will add fluid damping to test the same track soon. I have an air ballast tank but I also notice that some air is actually impacting the vinyl itself on edge and making noise which I had not noticed in my last setup. Just curious as I use a digital rumble filter and hopefully the damping will help.

jlsem · 2nd September 2010, 07:06 PM

Did you try sliding a damper up and down the arm to see if you could damp or tune the resonance? There are some engineered polymers in sheet form that could be cut and rolled into a tube.

This is a very interesting measurement, for I have found that controlling resonances and isolating external vibration from a moving-coil analogue playback source (read: record player) has the greatest influence on the sound of a system.

John

Doctorcilantro · 2nd September 2010, 07:08 PM

I will try some fluid damping and do a new needledrop.

In the meantime, until it gets here, I will try something else like you describe.

thanks

pcb121055 · 3rd March 2011, 05:40 PM

i'm surprised that this thread didn't get more notice. way back when i was in audio retail, the chatter was that the vertical resonance needed to be between record warp frequencies(4-5) and program material frequency ranges(20+). as i understood it, the target used to be 8-15 hz to keep the cartridge/arm combination from being excited during playback. is this outdated thinking ?

SY · 3rd March 2011, 06:06 PM

2-3 Hz could be a problem in the horizontal plane, since it would be excited by even slightly off center hole or stamping. I'd still follow the conventional wisdom and aim for 10Hz or thereabouts.

kevinkr · 3rd March 2011, 06:21 PM

Quote:

Originally Posted by SY

2-3 Hz could be a problem in the horizontal plane, since it would be excited by even slightly off center hole or stamping. I'd still follow the conventional wisdom and aim for 10Hz or thereabouts.

What SY says.. Have been dealing with similar issues in my set up. The old wisdom seems to be on the spot IMLE.

rowuk · 3rd March 2011, 10:53 PM

I am not sure that resonance is desirable. It seems to me the lower amplitude and frequency the better. Then the cartridge has a "solid" mechanical ground instead of a fuzzy one.

SY · 3rd March 2011, 11:58 PM

Well, the resonance is inevitable. If you remove the spring from the system, the cartridge can't track and it just shaves off the modulation. If you go the other direction and make the compliance ultra-high, the cantilever will just collapse. Ultra-high damping requires records that are perfectly flat and perfectly centered- that's not many in this universe!

So you have to site the mass-spring resonance

Quote:

somewhere

. And tucked between the lowest recorded frequencies and the subsonic stuff from warps and off-center causes the least harm.

This is one more reason why the quality of bass in digital recordings is so startlingly better.

DF96 · 4th March 2011, 10:11 AM

Perhaps to avoid future confusion, it ought to be pointed out that this thread is (I think) about arm-cartridge resonance (LF, sub-audio - hopefully!), not tonearm resonance (typically mid or HF).

I agree that the arm-cartridge resonance should sit somewhere between record warps and wanted LF, and that it is more or less unavoidable. It would be difficult to arrange sufficient damping to eliminate it without damaging bass too.

pcb121055 · 4th March 2011, 11:06 PM

hey ! thanks for validating my old notions. so if i read Doctorcilantro's graphs correctly, his resonant frequency needs to come down. we used to add mass to the headshell or find a cartridge with a lower compliance cartridge and retest to see if the resonant frequency was satisfactory. is there another way ?

1st September 2010, 07:47 PM	#1
Doctorcilantro diyAudio Member Join Date: Apr 2004 Location: Maine	Tonearm Resonance (FFT) I was doing some reading about alterniative theory for tonearm resonance here. Stated that vertical should actually be between 15-20hz, and horizontal at really low freq. like 3-6hz. Would love to hear some comments on that as I may add a new cart and be right around 8 using a 28cu high compliance moving iron with 1g VTF. This is a needledrop of the Ultimate Test Record. Grado Ref. on MG1 airbearing, and I'm curious if the 20-30hz rise in amplitude is by nature of a resonance or not. It is cut at -20db so I'm guessing this is a resonance. At 10hz, where I had calculated the vertical resonance to be, is an expected hump where I can see the cart. shake visibly. I will add fluid damping to test the same track soon. I have an air ballast tank but I also notice that some air is actually impacting the vinyl itself on edge and making noise which I had not noticed in my last setup. Just curious as I use a digital rumble filter and hopefully the damping will help.

3rd March 2011, 06:06 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	2-3 Hz could be a problem in the horizontal plane, since it would be excited by even slightly off center hole or stamping. I'd still follow the conventional wisdom and aim for 10Hz or thereabouts. __________________ “There are no greater liars in the world than quacks, except for their patients.” - Benjamin Franklin

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2nd September 2010, 07:06 PM	#2
jlsem diyAudio Member Join Date: Jun 2003 Location: Dallas,TX	Did you try sliding a damper up and down the arm to see if you could damp or tune the resonance? There are some engineered polymers in sheet form that could be cut and rolled into a tube. This is a very interesting measurement, for I have found that controlling resonances and isolating external vibration from a moving-coil analogue playback source (read: record player) has the greatest influence on the sound of a system. John

2nd September 2010, 07:08 PM	#3
Doctorcilantro diyAudio Member Join Date: Apr 2004 Location: Maine	I will try some fluid damping and do a new needledrop. In the meantime, until it gets here, I will try something else like you describe. thanks

3rd March 2011, 05:40 PM	#4
pcb121055 diyAudio Member Join Date: Sep 2008	i'm surprised that this thread didn't get more notice. way back when i was in audio retail, the chatter was that the vertical resonance needed to be between record warp frequencies(4-5) and program material frequency ranges(20+). as i understood it, the target used to be 8-15 hz to keep the cartridge/arm combination from being excited during playback. is this outdated thinking ?

3rd March 2011, 10:53 PM	#7
rowuk diyAudio Member Join Date: Mar 2007	I am not sure that resonance is desirable. It seems to me the lower amplitude and frequency the better. Then the cartridge has a "solid" mechanical ground instead of a fuzzy one.

4th March 2011, 10:11 AM	#9
DF96 diyAudio Member Join Date: May 2007	Perhaps to avoid future confusion, it ought to be pointed out that this thread is (I think) about arm-cartridge resonance (LF, sub-audio - hopefully!), not tonearm resonance (typically mid or HF). I agree that the arm-cartridge resonance should sit somewhere between record warps and wanted LF, and that it is more or less unavoidable. It would be difficult to arrange sufficient damping to eliminate it without damaging bass too.

4th March 2011, 11:06 PM	#10
pcb121055 diyAudio Member Join Date: Sep 2008	hey ! thanks for validating my old notions. so if i read Doctorcilantro's graphs correctly, his resonant frequency needs to come down. we used to add mass to the headshell or find a cartridge with a lower compliance cartridge and retest to see if the resonant frequency was satisfactory. is there another way ?

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