Thekong, hi there,
Hi Dover,
You have mentioned that too high a horizontal effective mass would result in a raised bass response by 6-12db. So, in what frequency range are we talking about (the Fr at below 12Hz?)?
I just wonder if the high horizontal effective mass is the only consideration here, and whether other factors, such as the design of the air-bearing, would make a considerable difference in the outcome. In short, does that only apply to the ET design, or also to the Rockport and Kuzma etc?
I asked because my Rockport 6000, already has a high horizontal effective mass of 80g (with the lightest counterweight, and excluding the cartridge), but yet MF found it lacking in the bass! The upgraded 7000 and Sirius III arms added even more mass to “cure” this problem!
Just to clarify there are 2 separate issues with the Krebs set up -
1. Removing the decoupling of the counterweight
This is where Bruce has tested extensively and posted his results on his website. The removal of the decoupling increases the amplitude of the fundamental resonance by 6-12db.
Now if you read the Audio review posted by John47, bottom of page 5, you will see that with the Talisman they measured 2 resonances at 4hz & 9hz. This illustrates how the decoupling system works, by splitting the resonance it actually reduces the peak of the fundamental resonance and results in a flat response in the bottom end.
Now Richard is saying that doesn't matter because the resonance is outside the audio band. That statement is not correct because a large resonance at the fundamental frequency will generate signal out of phase that imposes itself on the audible range, negatively impacting timing accuracy, imaging etc. A bass note for example will have harmonics that carry right through to the high frequencies. The preservation of phase at all frequencies is critical to presenting an accurate soundstage, harmonics etc. This is precisely why Frogman, Ct0517, Slaw and myself hear better timing with the counterweight decoupling tuned properly. Frogman has described hearing more bass notes.
The other problem generated by the resonance is tracking and tracking distortion - if you have instability at very low frequencies there will be a negative impact on tracking, whether you hear it or not.
2. The other issue is adding significant mass. Now Richard is partially correct when he says that damping with oil, wire, air hoses etc will also help to control resonant peaks at FR. But the real issue is that there are 2 downsides to this approach of high mass -
Firstly by carrying this additional mass the cantilever is now pushing a much higher weight. This means that on eccentric records the cantilever deflection will be much higher, and there is increased distortion from the coils moving into a non linear phase. This is one of the primary design considerations Bruce has endeavoured to address by keeping the mass as low as possible.
It is wrong to think of this particular issue as a bass problem. The biggest negative is the phase distortion and tracking distortion which impacts the whole range.
Secondly in my experience damping tends to slug the sound, as you heard at your friends place.
There is a logical explanation for this - by loading up the cantilever it becomes less responsive, less nimble. By loading up the horizontal mass, you are increasing the inertia of the arm, it resists movement, the cartridge cant follow the groove, the cantilever flexes more, more distortion.
In a nutshell you might get a more solid bottom end with more mass, but in my experience it comes at a cost - loss of speed and the preservation of accurate phase and time throughout the whole frequency range is compromised.
Sometimes in audio less is more. Bottom end extension is not much good if it is muddy and out of phase. High frequency extension can tell you more about how hard a drum is hit than the actual fundamental. From this you can see that having the fundamental in phase with the upper harmonics is critical. In my early days of audio I reckon my Proac Tablettes, which rolled of from 70hz could tell you more about whats happening at 30hz simply because they were very quick compared to many full range speakers - and before the naysayers here get in - I had Proac Studio 3 EBS monitors at the same time.
Bearings of course play a role, not just the pressure but the design and airflow etc. An air bearing can be stiffer than one at much higher pressure due to bearing surface area, etc. In the TAS review of the Kuzma/Walker clearly to the arms have different strengths and weaknesses. The Kuzma supposedly is very strong in the bottom end, the Walker appears to be more nimble presents timing better. Pretty hard to work out why these differences occur, because we dont have enough information.
In my view given that you have both the Rockport and ET you should enjoy the benefits of both approaches - why anyone would try and convert the ET2 into something that it was never intended to be - a high mass arm - is beyond comprehension.
I know at least one reviewer who considers the Kuzma is not as good as the ET2. With regard to Fremers comments on bass response, I dont take much notice. The chances of him getting the ET2 set up correctly are pretty remote, simply because he is time constricted. About the only reviewer that I would trust to ensure that the ET2 is set up correctly would be Martin Colloms due to his technical knowledge and insght, and in the early days of audio reviewers spent many months with gear, not days/weeks.
