05-15-13: Richardkrebs
Dover.
My calculation of weight delta was based on how much weight the air bearing has to carry. Not the horizontal effective mass. You voiced concern that I had taken it outside its load carrying capability.
Optimum load capacity. You have added 30g of lead to the mass the bearing has to carry. This has 2 negative effects - it pushes to mass to the extreme and one would redesign the bearing if one were knowingly going to operate the arm at a higher mass level. Secondly the added mass will impact the shearing forces involved - the arm is not frictionless and the bearing is not absolutely rigid - these are some of the reasons why users are hearing different results with higher pressures.
As a point on your calculations on FR I led slide the error in your calculations - the bearing has a resonance, the bearing tube has a resonance and the total resonance will be a sum of the resonances inherent in the arm. One really needs to measure the resonances to see whats going on , thats why Bruce does extensive testing. The maths you are using for FR calculations is not the complete story.
05-15-13: Richardkrebs
Re heavy arms. I assume you are saying that ANY heavy arm, and this includes the Rockports, Walker and Kuzma have serious problems with distortion. Further, by implication, you are saying that the owners of these arms are deaf to these distortions.
I think you should use the word preferences, when making judgments on other folk, but certainly they may well be. Some folk like fat bottom ends others prefer speed and musical timing. For me music is about timing and nuance - I can certainly hear the slugging of the sound and loss of musical timing when adding too much horizontal effective mass to the ET2 as others in this thread have also found when they removed the decoupling from the I Beam.
You may also like to read the comparison of the Kuzma to the Walker in the Absolute Sound mag December 2006 where the reviewer articulates the differences - the Kuzma being dark and solid vs the Walker having more of "the "gestalt" of a live concert, more lifelike presence of instruments, their colors, their dynamics, and the space they play in" of the Walker "fuller, more realistic in tonal color, bigger, bloomier, wider, deeper, more layered in soundstaging, and a bit more authoritative dynamically".
05-15-13: Richardkrebs
Targeting say the 12 hz you mentioned would mean that it is causing phase and amplitude problems at 36 hz. This is not good.
Depends how big the amplitude problems are. Some of the heavy arms you have mentioned have additional measured resonances at 100hz & 200hz.
In your case you you have reduced the theoretical resonance from 8.08hz to 5.17hz. so yes you have a small residual at 24hz in a standard unmodified arm - but this is outweighed by the amplitude of the resonance being much higher when you added 62g of horizontal effective mass. Furthermore that small secondary resonant peak at 24hz with the standard arm can be dialled down with careful tuning of the counterweight spring. I very much doubt whether many systems are truly flat to 20hz in a real home environment.
In your case you have shifted the secondary resonance from 24hz to 15hz, but have increased the amplitude of the 15hz resonance substantially - probably 6-12db higher in amplitude compared to the smaller resonance at 24hz with the arm as standard.
