Thekong –
The answer to your question regarding frequencies impacted by horizontal Fr from Richardkrebs are mostly wrong. It is important that they are addressed.
Impact of Fundamental Resonance:
05-20-13: Richardkrebs
Thekong.
The answer to your question regarding frequencies impacted by horizontal Fr is shown in the attached graph. From memory your Horiziontal Fr was around 5hz with the A-90. So substitute 5 for 1 on the x axis and scale up from there. At 15 Hz (3) the rise in response is almost zero. This is what BT was talking about when he mentions 3xFr.
This statement is not correct. I quote from Richardkrebs earlier post
05-15-13: Richardkrebs
In Bruce's paper on the oil trough he talks about the effect of Fr being apparent at 3x its frequency. Targeting say the 12 hz you mentioned would mean that it is causing phase and amplitude problems at 36 hz. This is not good. .
As you can see Richardkrebs appears to be confused. On the 15/3 he cites Bruce Thigpen as saying that there are phase and amplitude problems at 3 times Fundamental Resonance, then on 20/5 he cites Bruce Thigpen as saying the rise in response is almost zero.
Neither of these statements are correct.
What Bruce Thigpen actually says on his website is that on an undamped standard ET with decoupled counterweight there is a resonant peak at 3 times the fundamental resonant frequency, and that this is reduced with fluid damping on a standard ET with decoupled counterweight.
The other mistake that Richardkrebs continues to make is to use as a reference a graph for a single harmonic oscillator that plucked from Wikipedia.
Wikipedia -
http://en.wikipedia.org/wiki/Harmonic_oscillatorRichardkrebs -
http://s1173.photobucket.com/user/CT-993/media/ResonanceGraph_zpsdd78e0f4.png.html?sort=2&o=7This graph does not represent the forces on the cantilever because the cantilever and cartridge is not a single harmonic oscillator. A cartridge tracking a record groove has a fulcrum point at both ends – the stylus in the groove, about which the cantilever pivots, and the cartridge end of the cantilever which has a suspension. Forces are exerted on BOTH ends of the cantilever. The graph represents a pendulum with only one fulcrum point at one end only. The mathematics that Richardkrebs uses does not apply.
05-20-13: Richardkrebs
Now look at frequencies below Fr. At say 0.25 Fr we get transmissibility of 1. What this means is that, with the compliance of the cartridge used, the whole arm moves sideways. The cantilever does not deflect. This is important for eccentric record issues. .
This assertion is wrong on several fronts. The cantilever deflects.
Firstly – the record grooves are cut at 45 degrees. The cantilever deflects. For a moving coil cartridge the cantilever deflection moves the moving coils within a magnetic field. That is how sound is reproduced from a record player. This video shows how RCA Living Stereo stereo playback is achieved.
http://www.youtube.com/watch?v=Jq2sjGFvNnM If there is no deflection of the cantilever then Richardkrebs system cannot be producing any sound that resembles music.
Secondly, the statement defies physics. I quote Bruce Thigpen directly:
Bruce Thigpen
“the cartridge will "see" .55Hz mounted in any tonearm, more so in one with higher horizontal inertia. I don't think Kuzma means the stylus does not deflect at all at .55Hz, that would defy physics.”
Furthermore, Richardkrebs assumption with regard to Bruce Thigpens views on eccentric records are not supported by what Bruce Thigpen actually says in the ET2 manual.
05-20-13: Richardkrebs
BT uses at 30cu cartridge in his manual to calculate horizontal Fr. The arm weight he uses is 30gm plus 7gm for the cartridge. We have to assume that he is ok with this combination and that he is not worried about cantilever deflection on eccentric records.
This assumption again is just plain wrong. I quote from Bruce Thigpen’s ET website:
ET2 Manual page 47 :
“if you like to play severely eccentric records, ones with run out greater than 1/8th of an inch, then we suggest you use a low mass pivoted arm.”
In summary, Bruce Thigpen is very much of the view that the horizontal effective mass should be kept as low as possible, and the decoupling employed to minimsie fundamental resonant peaks at FR and 3xFR.
He has also expressed his view that increasing mass increases distortion, and I quote Bruce Thigpen -
Bruce Thigpen:
If the weight is coupled the system resonant frequency would be extremely low, a resonant frequency at 3Hz with a significant rise in response (6-12dB) results, which would affect tracking slightly because of the asymmetric position of the cantilever, we opt for splitting the horizontal resonance frequency into two points and lowering the "Q" which improves tracking.
More important than tracking, the intent was to reduce the modulation effects of low frequency energy (FM and AM) that increase distortion in the cartridge,
Thekong , I trust this clarifies the queries you raised.
