Resonance Frequency Am I Pushing The Limit

I am about ready to pull the trigger on a LO MC cartridge. AT33EV or AT33Sa

My tonearm effective mass is 12g, matching a 6.9g cart with a compliance of 10
will give a resonance frequency of 11.56Hz

Is the 7 gram weight of the headshell included in the tonearm effective mass of 12 grams on the Technics SL1200MKII?

If I add a four gram weight the resonance frequency drops down to 10.50Hz. My dilemma is that I don't think there is enough room outward for the counterweight to balance the tonearm prior to setting the VTF. I'm afraid that if I add a heavier counterweight that it will throw the whole thing off. How is he counterweight factored into the tonearms effective mass?

Technics SL1200MKII

Your thoughts please.

Cheers,

Don't forget Audio Technica, as most Japanese manufacturers, provide dynamic compliance specs at 100Hz whereas resonance calculators / equations want the value at 10Hz. Conversion is to multiply by a factor of 1.5 to 2.

If Dynamic compliance at 100Hz is 10×10-6cm/dyne (= 10 cu = 10 'compliance units') then at 10Hz we'd probably be about 18 cu.

12g effective mass for the Technics arm is quoted in the manual as 'without cartridge'. So that would include the stock headshell. The cart is 6.9g and you include an allowance of about 1g for mounting hardware, your total is 7.9g (say 8g)

Using vinylengine's tool, http://www.vinylengine.com/cartridge_resonance_evaluator.php?eff_mass=12&submit=Submit with a tonearm effective mass of 12g, gives you a resonance frequency of 8 to 9 Hz.

Using this tool: http://www.resfreq.com/resonancecalculator.html wants you to enter total mass = 20g ... gives you a resonance frequency of 8.4Hz.

Rule of thumb is to keep it between 8 - 12 Hz. So you should be ok.

So no need to add any mass to the headshell. IF you did have a heavier cartridge or headshell you could use the Technics auxiliary weight to help balance, which (if it is missing) is available at kabusa.com.

Michael,

I am using the AT33EV on a 1200MKII. I measured the resonance freq. at around 8 - 8.5 Hz, with the HFNR. The HFNR is not the best for that. I ordered the 'Shure Audio Obstacle Course test record for the Shure V15 Type V'. Which is supposed to be better. I will post the data here when I have the record.

Best,
Rudy

Meloski said:

How is he counterweight factored into the tonearms effective mass?



Cheers,

Click to expand...

it's half of the equation. Not only mass, but the distance of the mass from the vertical pivots. The further that given mass is from the pivots,(in setting tracking weight) the higher the effective mass of the arm becomes.

Meloski said:

I am about ready to pull the trigger on a LO MC cartridge. AT33EV or AT33Sa

My tonearm effective mass is 12g, matching a 6.9g cart with a compliance of 10
will give a resonance frequency of 11.56Hz

Is the 7 gram weight of the headshell included in the tonearm effective mass of 12 grams on the Technics SL1200MKII?

If I add a four gram weight the resonance frequency drops down to 10.50Hz. My dilemma is that I don't think there is enough room outward for the counterweight to balance the tonearm prior to setting the VTF. I'm afraid that if I add a heavier counterweight that it will throw the whole thing off. How is he counterweight factored into the tonearms effective mass?

Technics SL1200MKII

Your thoughts please.

Cheers,

Click to expand...

The bad news is it´s difficult to calculate the resonances by any precision. We seldom know exactly the present figures we should use.

The good thing is that for most arm/cartridge combinations the resonances will be between 8-10Hz, when measured.

For a heavy cartridge there is an extra CW to be screwed into the CW-stub.

The CW´s influence on eff mass is calculated by calculating the Mass Moment of Inertia (MOI) around the pivot, and than tranferred as a mass at needle.

All good info for the OP. But the key thing in my discussion that I want to make sure doesn't get lost is the 100 Hz vs. 10 Hz issue. That seems to muck up a lot of people. Even some of the 'guides' on the internet seem to be vague or not accounting for it.

And if it's a US-made cartridge that's being checked then the spec. is probably Static compliance, not dynamic, but usually at 10Hz. So in that case dynamic is taken as about 1/2 of static ... correct?

marcmorin said:

it's half of the equation. Not only mass, but the distance of the mass from the vertical pivots. The further that given mass is from the pivots,(in setting tracking weight) the higher the effective mass of the arm becomes.

Click to expand...

Yes, mass at the cartridge end changes "effective mass" WAY more than mass at the counterweight end, because of the cartridge's distance from the pivot.

sqlsavior said:

Yes, mass at the cartridge end changes "effective mass" WAY more than mass at the counterweight end, because of the cartridge's distance from the pivot.

Click to expand...

Mass at the cartridge end changes the eff mass with the mass that is actually at the cartridge end. It is just a mass.

Van_Isle said:

All good info for the OP. But the key thing in my discussion that I want to make sure doesn't get lost is the 100 Hz vs. 10 Hz issue. That seems to muck up a lot of people. Even some of the 'guides' on the internet seem to be vague or not accounting for it.

And if it's a US-made cartridge that's being checked then the spec. is probably Static compliance, not dynamic, but usually at 10Hz. So in that case dynamic is taken as about 1/2 of static ... correct?

Click to expand...

Yes the 100Hz and 10Hz are measured differently, besides the different frequences. The problem is there is no universal conversion between static, dynamic 10Hz and dynamic 100Hz, it´s a guess work.

So I,ve spent some time researching the internet and this is what I came up with.

AT33EV has a dynamic compliance of 10×10-6cm/dyne (100Hz)

Ok lets take that number and covert it to a US standard

10×10-6cm/dyne (100Hz) x 1.5 = 15µm/mN (15) (I found so many different standards I just split the difference of them all.)

factor in effective mass of the stock tonearm including the stock headshell 12g

the cart mass is 6.9g lets add a gram for the screws 7.9g

ok lets enter the numbers into this, Freek's Resonant Frequency Calculator
http://www.theanalogdept.com/cartridge___arm_matching.htm

Results = 9.20

Well thats a number I can live with, unfortunately my OCD can't allow me to keep punching in numbers till I get what I like. Irregardless I have to figure the accurate resonance frequency for this cart will fall in the range of 8.0 - 12.0Hz so this cart should be an appropriate match for my stock tonearm in the SL1200MKII

If it's any help many of the Technics cartridges compliance were 12x10-6cm and the weight was 6.5gr so you should be close in compliance matching using the factory Technics headshell for the SL-1200Mk2.

Meloski said:

So I,ve spent some time researching the internet and this is what I came up with.

AT33EV has a dynamic compliance of 10×10-6cm/dyne (100Hz)

Ok lets take that number and covert it to a US standard

10×10-6cm/dyne (100Hz) x 1.5 = 15µm/mN (15) (I found so many different standards I just split the difference of them all.)

factor in effective mass of the stock tonearm including the stock headshell 12g

the cart mass is 6.9g lets add a gram for the screws 7.9g

ok lets enter the numbers into this, Freek's Resonant Frequency Calculator
http://www.theanalogdept.com/cartridge___arm_matching.htm

Results = 9.20

Well thats a number I can live with, unfortunately my OCD can't allow me to keep punching in numbers till I get what I like. Irregardless I have to figure the accurate resonance frequency for this cart will fall in the range of 8.0 - 12.0Hz so this cart should be an appropriate match for my stock tonearm in the SL1200MKII

Click to expand...

If You are very concerned about the res freq You have to measure the res with actual cartridge in Your own arm. But they will be between 8-10Hz.

Van_Isle said:

(...) And if it's a US-made cartridge that's being checked then the spec. is probably Static compliance, not dynamic, but usually at 10Hz. (...)

Click to expand...

Uhm, no - because that would make no sense. Static compliance is static, i.e. simply excursion per constant/static (= 0 Hz) force - otherwise it would be dynamic.

Greetings from Munich!

Manfred / lini

Poor wording on my part. I was thinking of it in terms of the conversion between static and dynamic.

... so if a spec listed as static compliance and you need dynamic, the equivalent dynamic compliance at 10 Hz is roughly half (open to argument, I'm sure) of the static compliance.