The horizontal effective mass for a linear air bearing arm is the sum of the mass of the bits that move sideways.
The ET2 reduces this mass by decoupling the counterweight. We all clearly understand this design feature. The benefit of this approach is to reduce the amplitude of Fr
The bearing design makes no difference to the effective mass or the resultant Fr. There is nothing particularly unique about the ET2 bearing. The cartridge still has to push this mass sideways. Either a relatively low mass with the ET2 or heavier with a Rockport , Kuzma, Walker or Krebs arms. In an undamped system with a fixed counterweight we see a large rise in amplitude at resonance. This is easy to control with damping. For a good discussion on this see CT0517's post on 01-12-12
Open the attachment and read pages 18-19 and 24-26.
The graph on page 25 shows how this peak is completely removed by adding an oil through. The subsonic peak has gone and provided Fr is low enough, so has its effect on the audio spectrum. In this paper Bruce talks about the effect being noticeable at 3x Fr. Way back in this thread I talked about the effect of resonance being present at up to 6x Fr. We use this safety factor in our designs in my business.
It is this effect that led me to fix the counterweight. With a stiff cartridge; the only way to get Fr low enough to avoid interaction with audio frequencies was to make the arm heavier. The Fr of my arm/cart is 5.2 Hz. Thekong's setup is a little under 5hz. In Fremer's review of the Kuzma he set it up with a Fr of 5 hz. This is no coincidence , we all set up our systems with effectively the same Fr, safely 4x below the audio spectrum. My point is that the Fr needs to be around 5-6 hz. To avoid this interaction. With a high compliance cart this target is achievable with a standard ET2, it cannot be achieved with a low compliance cart. At least 3 respected designers agree with me.
In past I have damped the resonant peak by adjusting the air pressure and deliberately dressing the lead out wires to damp horizontal movement. This method is fussy and not particularly robust. Adding the oil trough has solved these problems and allowed me to push the pressure back up. 17 psi seems optimum in my rig.
There have been concerns raised about the extra weight I have added pushing the bearing outside it's design spec.
I am using the original wand less its heat shrink wrap plus a lead headshell insert. Say the same weight. I am using an aluminum goose neck which eliminates one cap screw and the short lifter arm. I have also eliminated the male wiring plug and used a lighter grub screw instead of a cap screw for the gooseneck wand clamp. Say same weight.
I have fixed the counterweight and eliminated the I beam the brass threaded weight, several cap screws and the locking slider assembly. Say same weight.
My counterweight is 32 grams.
I have added 30 grams of lead inside the spindle in the center of working travel, such that it does not leave the bearing sleeve when tracking modulated grooves.
The ET2 can be optioned with the heavier magnesium wand. 8 gms heavier.
It comes with up to 40 gms of counterweight. 8 gms heavier.
In terms of bearing load carrying capability I have added 30 gm to a lightly configured ET2. If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams.
I use a Shelter Harmony at 9 grams. There are cartridges in the 16-17 gm range. If one of these was used the my weight adder shrinks to around 6 gms. It would be inconceivable that Bruce would design a bearing that could not take this small additional weight.
The ET2 reduces this mass by decoupling the counterweight. We all clearly understand this design feature. The benefit of this approach is to reduce the amplitude of Fr
The bearing design makes no difference to the effective mass or the resultant Fr. There is nothing particularly unique about the ET2 bearing. The cartridge still has to push this mass sideways. Either a relatively low mass with the ET2 or heavier with a Rockport , Kuzma, Walker or Krebs arms. In an undamped system with a fixed counterweight we see a large rise in amplitude at resonance. This is easy to control with damping. For a good discussion on this see CT0517's post on 01-12-12
Open the attachment and read pages 18-19 and 24-26.
The graph on page 25 shows how this peak is completely removed by adding an oil through. The subsonic peak has gone and provided Fr is low enough, so has its effect on the audio spectrum. In this paper Bruce talks about the effect being noticeable at 3x Fr. Way back in this thread I talked about the effect of resonance being present at up to 6x Fr. We use this safety factor in our designs in my business.
It is this effect that led me to fix the counterweight. With a stiff cartridge; the only way to get Fr low enough to avoid interaction with audio frequencies was to make the arm heavier. The Fr of my arm/cart is 5.2 Hz. Thekong's setup is a little under 5hz. In Fremer's review of the Kuzma he set it up with a Fr of 5 hz. This is no coincidence , we all set up our systems with effectively the same Fr, safely 4x below the audio spectrum. My point is that the Fr needs to be around 5-6 hz. To avoid this interaction. With a high compliance cart this target is achievable with a standard ET2, it cannot be achieved with a low compliance cart. At least 3 respected designers agree with me.
In past I have damped the resonant peak by adjusting the air pressure and deliberately dressing the lead out wires to damp horizontal movement. This method is fussy and not particularly robust. Adding the oil trough has solved these problems and allowed me to push the pressure back up. 17 psi seems optimum in my rig.
There have been concerns raised about the extra weight I have added pushing the bearing outside it's design spec.
I am using the original wand less its heat shrink wrap plus a lead headshell insert. Say the same weight. I am using an aluminum goose neck which eliminates one cap screw and the short lifter arm. I have also eliminated the male wiring plug and used a lighter grub screw instead of a cap screw for the gooseneck wand clamp. Say same weight.
I have fixed the counterweight and eliminated the I beam the brass threaded weight, several cap screws and the locking slider assembly. Say same weight.
My counterweight is 32 grams.
I have added 30 grams of lead inside the spindle in the center of working travel, such that it does not leave the bearing sleeve when tracking modulated grooves.
The ET2 can be optioned with the heavier magnesium wand. 8 gms heavier.
It comes with up to 40 gms of counterweight. 8 gms heavier.
In terms of bearing load carrying capability I have added 30 gm to a lightly configured ET2. If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams.
I use a Shelter Harmony at 9 grams. There are cartridges in the 16-17 gm range. If one of these was used the my weight adder shrinks to around 6 gms. It would be inconceivable that Bruce would design a bearing that could not take this small additional weight.