Eminent Technology ET-2 Tonearm Owners

Dover - if I may say - you come across as a real hard ass sometimes in your posts; but you have a very direct sense of humor. lmfao.

btw - what I just said my kids say to me alot. they unfortunately both being only 18 have not yet seen alot of my humor. I try to save it for you guys as I my wife just doesn't appreciate it either. This thread is 11 pages long now. She will never be able to trace back to what i am saying here.

Richardkrebs

Astounding!
After 25 years of tinkering with your ET2 tone arm, you now reveal in your recent posts that you have only just worked out how the arm works.

Only now have you realized that the sprung I beam has a resonance and the tuning of the I beam and the number and position of lead weights used is critical to optimizing the performance of the ET2. This is clearly explained in the manual and was discussed at earlier on this thread..

Let me quote your recent posts:

03-19-13: Richardkrebs
I don't have any proof of this, it is just a recent thought. While higher or lower weight is obviously a factor, I think that the one leaf spring, two leaf spring plus number of weights thing, has probably a whole different set of cause and effect issues. So with reference to a rigid or sprung counterweight beam, it is probably an all or nothing event. In other words because we have the "potential" interaction of the swing frequency of the beam and the resonant frequency of the arm assembly, depending on the number of leaves and the number of lead weights used. It could be that tuning here with springs and weights (and their position) is at least partly to do with sorting this possible frequency interaction rather than just the weight or stiffness employed. Others may have already thought of this but, it is just an idea to put out there for comment.

03-20-13: Richardkrebs
The thought that there may be more going on with the decoupled counterweight was triggered by your post where you quoted BT where he said that the ibeam had a natural frequency of 2-5 hz.
This is close to the resonant frequency of the arm itself. This could have performance implications.

For the last 5 weeks I have been saying that you do not understand how this arm works. At the same time you have been promoting your modifications that include adding significant amounts of lead mass and removing the decoupling of the I beam which, I keep repeating, takes this arm out of its designed operating parameters.

Your latest revelations make it clear that you have not understood the set up procedures described in the ET2 manual, nor do you understand their purpose and what principles they are based on.

For this reason I would continue to caution readers that your advice on adding lead mass, M10 bolts and coupling the counterweight to the ET2 should be disregarded.

Dover.

....Sigh.....

My comment re "All or nothing" was designed to open useful dialog on the subject. I was trying to be subtle.

So now, not so subtle..
Do you really think that it is a good idea to have a spring driven mass, ( cartridge and arm ) attached to a spring suspended mass ( ibeam and counterweight). Both with resonant frequencies in the same neighbourhood?
If you refer to the math and resonance graph I posted, it shows that this can be problematic. The two resonances need to be far away from each other to avoid any interaction. At best a good compromise can be achieved with adjustment of the parameters. I don't like compromises. Better to eliminate one of the compliant joints in the system completely.

As I have said earlier. If fixed, the counterweight beam must be very strong. I note that Kuzma also know this as the counterweight beam is substantial indeed. Three springs don't cut it.

It is no accident that other arm manufacturers have a rigid joint there....it simply sounds better.

I don't understand why you are so set on trying to stop people experimenting on this area of the arm. It will do no harm and at the very least add to our collective pool of knowledge. A big hand will not come out of the sky and squash anyone who deviates from the original design parameters, it will be a bit of fun and it may just bring the owner closer to the absolute joy of listening to music, which is what this hobby is all about.

Put on your knitwear cardy so don't catch a cold, your thick lensed glasses so you don't fall, then pop out and replenish your Prozac.

Chris (such a lovely guy):

"You come across as a real hard ass .."

Acronym: PITA

BTW did Richardkrebs pick on you at preschool?

Well I am not sure what to say now. I gotta admit that the folks from down under and specifically NZ, are not a subtle group by any means. You all seem to be in close proximity to one another? Can you by chance hear each others stereos when you turn them up ?

BTW – Does Canadian Shania Twain still live in NZ ? I always had a crush on her.

Richardkrebs
Do you really think that it is a good idea to have a spring driven mass, ( cartridge and arm ) attached to a spring suspended mass ( ibeam and counterweight). Both with resonant frequencies in the same neighbourhood?

Chris,

You always want the horizontal natural frequency of the counterweight to be less than the cartridge/arm resonance, this is the case 98% of the time.
The natural frequency of the I-beam/leaf spring depends on the thickness of the spring, the amount of weight, and where the weight is on the beam. The natural frequency goes down as the weight moves further out on the beam which is where we want it to be.

brucet

************************************************************
Page 49 of the ET2 manual.

LOW FREQUENCY RESONANCE MEASUREMENTS

The curve below shows the typical response for the vertical resonance of the the tonearm. This was done with a medium-high compliance cartridge (30 x 10-6 cm/dyne) with a mass of 7 grams and two counterweights 15g + 15g. This counterweight combination gives a vertical effective mass for the tonearm of about 12 grams, which results in a resonant frequency of 6 hz (measured).

Horizontally the resonant frequency will be much lower because of the tonearms higher mass (30grams). The horizontal resonant frequency is damped by the decoupling spring and is very well controlled.

************************************************************

Actual measurements and graphs for the above are also shown on page 49.

Thoughts on the above ?

At this rate we will probably have the whole ET2 manual on the thread by Christmas?

My personal take on this as an amateur hobbyist.

Bruce makes a lot of sense and has done the analysis and measurements to back it up. The ultimate test is "hearing is believing". My reference point for sound in my room is 15 IPS master tape dub. Both the MM 420str and MC Benc Micro that I discussed earlier play beautifully on my ET 2.5 with the CF armtube. I have the MM 420str on the ET 2.0 right now with aluminum armtube / other room and it sounds great there too.

Each of us have different gear and rooms. We need to experiment with the different leaf springs to see what sounds best to us. But it is very obvious and clear to me that we should be trying to get

*** AS FAR OUT ON THE I BEAM AS POSSIBLE - THIS IMPLIES THE LEAST AMOUNT OF WEIGHT *******

I haven’t tried a rigid counterweight with damping. If anyone would like to volunteer up a DL103 or similar low compliance cartridge I can give it a longer term try on the ET 2.0. If a good cheap DL103 pops up on the classified I can try to snap it up. I don't have a problem experimenting.
Time permitting.

Cheers