Eminent Technology ET-2 Tonearm Owners

Dover.
No confusion at all. In Engineering, the term absolute is.....absolute.
By way of example, over on the TT drive thread, a fellow poster said that " there is no stretch in the silk thread I use to drive my platter." or words to that effect. Within the loading the thread sees, this statement is almost certainly true. However if he had said that "there is absolutely no stretch..." he would be making an indefensible statement.
One would also be very unwise to say that "tracing an eccentric record with a standard ET2 causes absolutely no cantilever deflection"

Hasn't this discussion run its course.
Like the light weight ET2, there are many heavy weight linear arms in use, performing well, producing beautiful music.

Richardkrebs -

You have now conceded after 4-5 weeks of obfuscation that there is cantilever deflection on eccentric records below the resonant frequency.

It follows that adding mass increases deflection as I asserted back in February. On 02-16-13:

By increasing the horizontal mass of the arm significantly, when you play an eccentric record the increased resistance to motion from the additional mass will result in increased cantilever flex.

Your latest comparison of the deflection of a sprung cantilever with the elasticity of a silk thread is at odds with the application of scientific principles.

Do we need to spend another 5 weeks going through the difference between the modulus of elasticity of a woven silk thread and the bending motion of a cantilevered suspension.

Hasn't this discussion run its course.

This is the third time that I'm aware of over the past weeks that you have requested a discussion be terminated. It is not obligatory for anyone to participate. Whilst you are keen to champion your Technics modifications and your own homebrew tonearm, this is not your personal thread.

No confusion at all. In Engineering, the term absolute is.....absolute.

This not correct. The discussion we are having is on the cantilever flex generated by an eccentric record. This is not absolute as there are variables involved, to wit - the mass and inertia of the arm, the compliance of the cartridge and the level of eccentricity in the record.

The laws of physics are absolute. Correctly applied they enable us to develop mathematical models for scenarios that are not absolute.

Some impressions –

First

Some text from Richards very interesting post of 03/14/13

http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1325551242&openflup&527&4#527

For input frequencies that are 300% of the resonant frequency we get transmissibility of around 15%, unless the structure is highly damped and we all agree, I think, that lots of damping doesn't sound good.

So at 3x the resonant frequency we are loosing around 15% of the groove modulation, as the arm is still at this point moving back and forth sideways slightly.

This is not a problem provided this 3 x resonant frequency is not a valid audio signal. Actually you would need to extend the graph out to around 6x resonant frequency before the transmissibility was approaching 0. Until we reach that point, part of the low frequency goove modulation goes into moving the cartridge and arm sideways and not into generating an output voltage.

Now Page 9 of the ET2 manual.

Adjustable Effective Mass

The effective mass of the tonearm is adjustable, both vertically and horizontally. The arm has low-medium mass vertically and medium to high mass horizontally.

Four counterweights allow the vertical / horizontal mass to be changed. For example; if the user decreases the amount of counterweights used, and moved the this position back (higher scale number) the horizontal inertia of the tonearm would go down and the vertical inertia would go up.

Decoupled Counterweights.

The effective mass of the arm horizontally is equal to the sum of its component parts. (It does not pivot) it needs to be as light as possible for low mass, however, making the arm too light sacrifices rigidity. By decoupling the counterweight system horizontally, but not vertically, the mass of the counterweight is not seen by the cartridge above a certain frequency and is lowered. This allows the use of heavier (more rigid) components in tonearm design without increasing effective mass.
The decoupling mechanism is damped at its natural frequency (2hz – 5hz). THIS DECREASES THE RISE IN FREQUENCY RESPONSE AT RESONANCE IMPROVING LOW FREQUENCY PERFORMANCE

Well it looks like Bruce studies this and note the text in upper case.

------------------------------------------------------

MY IMPRESSIONS

ET 2.5 at 19 PSI. Use of a Time Aridyne Medical Pump which produces very little resonance at the source. (I don't dare say "never" on this thread :^) ....just joking....not

http://www.alliedhpi.com/images/zs168-263-002.pdf

It dumps moisture at the pump down a tube just like a cars AC unit. Have never seen a drop in the second regulator in my room – except for that incident where the pump outlet clogged (minerals in moisture) and sent moisture down the line. My room water trap bulb was half full before I noticed it !

Test Cartridge
Benz Micro MC3 Soundsmith Ruby Retip.
15 x 10 – 6cm/dyne (1.6 - 2.2 vtf) (weight 7.2 gms)
Used at 1.8 gms wide open at 47 k and loaded at 100.

My wiring is unshielded

http://cgim.audiogon.com/i/vs/i/f/1332259084.jpg

With the preamp inputs about two feet away from the ET2.5.
I have been listening to this cartridge for a few months now with a double leaf spring. Very enjoyable.

I inserted the triple leaf spring which effectively for any anyone that has tried this, turns the counterweight into a rigid one – imo. No movement at all. Defeats the decoupling.

Bass performance changed with the triple leaf spring in my room with the 801 monitors. Lets understand this is relatively speaking as the 801 have prodigious bass. But the effect of the leaf spring versus no leaf spring was noticeable in the ears with the sound compression in the room and this (15 x 10 (– 6)cm/dyne) cartridge. Bass performance was not as good with the triple leaf spring with this specific cartridge in MY room.

So I believe what I heard supports what is in the ET2 manual.

Maybe I will have different results with the even lower compliance XV1 soon ? It may sound better with the triple leaf spring. This will have to wait as I have amps arriving this week. Its easy to swap out Leaf springs. I am not going to hurry with the XV1 - for those aware of its history with me.

Guys - I have made a promise to myself not to email or contact Bruce anymore with questions until first reading the manual. It really is like having his knowledge in your back pocket.

Hi Thekong – do not know what speakers you are using but the above impressions, further support the reason I recommended the double leaf spring with your test cartridges based solely on their specs.

Cheers

Chris,
Thanks.

The results concur with both my own testing and the correct application of the laws of physics and sound engineering practice when setting up the ET2. The use of decoupling is an essential element to optimize the performance. To remove the decoupling and add mass is an ill conceived notion not supported by the laws of physics and cannot be recommended.

The removal of the decoupling mechanism and adding mass will result in an unnatural hump in the low bass as explained in the ET2 manual.

Chris.

I also thank you for your insightful testing of the ET2.5.
It confirms that adding too much mass, by way of locking the counterweight is not a good idea, if it takes the arm out of the appropriate resonant frequency range. I did say earlier that in my testing of the ET2, I added too much weight and had to backtrack. The key point being where does the arm in standard form sit relative to the optimum.

Adding additional weight to an ET2.5 would be inadvisable since it is already in the Goldilocks zone I mentioned. Namely its horizontal resonant frequency is in the range of 2-3hz, when using a decoupled counterweight and a low to med compliance cart.
Now bringing the ET2 down to this optimal range, that would be interesting. Are you able to fit 3 leaf springs to an ET2 carrying a low to med compliance cartridge?
Another question please. How stiff is the beam with the 3 leaf springs? As I mentioned earlier, the arm is very sensitive to any resonance at this point. I would urge caution if the resultant assembly rings in the audio band.