Comparison of lateral forces on Kuzma/Terminator/ET2/ET2krebs
For those who are interested in understanding the side forces on the cantilever :
Force = mass x Acceleration, where acceleration = mass/(velocity squared)
If the record is 12mm out of true, the arm travels 24mm in and out with each revolution, which takes 1.8 seconds.
On an eccentric record the acceleration will be the same for each arm –
0.0024metres / (1.8 sec x 1.8sec) = 0.00074 metres per second squared
The horizontal effective masses of the 3 arms mentioned in this thread are:
Kuzma has been quoted as 100g
Terminator 80g
ET2 25g
The force on the cantilever is as follows:
Kuzma = 0.1kg x 0.00074m/s2 = 0.000074 Newtons
Terminator = 0.08kg x 0.00074 m/s2 = 0.000059 Newtons
ET2 = 0.025kg x 0.00074 m/s2 = 0.000018 Newtons
Summarising then you can see that the increased mass of the Terminator and Kuzma arms increase the lateral forces on the cantilever by 300-400% over the ET2.
Now Krebs has modified his ET2 by adding 30gm of lead to the spindle. This adds 30g to the effective mass of the ET2. Krebs also couples the counterweight ( no spring ) which adds another 30g to the horizontal effective mass.
So Krebs has increased the horizontal mass of the original ET2 from 0.025kg to 0.085kg.
The Krebs modifications have increased the lateral forces on the cantilever by over 300%.
Furthermore he employs no dampening to control this mass and runs his ET2 at a lower pressure of only 12psi.
The arm moves in and out every 1.8 seconds.
This equates to a frequency of 100/1.8 = 55hz
The resonant frequency of the unmodified ET2 is roughly 3.5 – 5hz.
Krebs argument is and I quote:
Below this resonant frequency the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection.
He is wrong. This statement defies basic physics.
Below 0.55hz the cantilever WILL deflect on an eccentric record.
I assume he has misunderstood the explanation given to him by Frank Kuzma, and seems unable to comprehend this.