Eminent Technology ET-2 Tonearm Owners

Richard - I don’t pretend to understand the math. I will ask Bruce again when I can for clarification.

Dover - Lets face it – the manual contains great information but is in a really bad need of a re-write with some pretty fonts that audiophiles will actually like to read. A summary two pager to get up and running is also needed to hit the top 10 points.

Hell 643 posts on modifying a bloody tone arm!
It's so great seeing people I have known for over 25 years write such stimulating posts.
It's time we all met for a coffee. Mark.

Welcome to the thread Mark.

It's time we all met for a coffee.

For some reason I assumed you were from downunder, but when you said “coffee” you confused me. I expected to see flat white ?

Good things come from Downunder I have learned. We already discussed the wine.

But I was a little surprised at the Australian recommendation and not a NZ one.

Well sometimes the goose lays a golden egg in NZ.

But in this case its silver colored. And it’s not an actual egg but part of the Goose herself – the neck in this case.

We affectionately call it an ET Gooseneck here.

Just received

Sorry Mark – another ET2 mod :^(

Thank you Richard Krebs for coordinating.

Hell 643 posts on modifying a bloody tone arm!

At least we know what “this” thread is about ?

Cheers

Maths and Physics.

A few days back I wrote that the res freq of the arm was proportional to the square root of the inverse of the mass and stated that there was a discrepency in the ET2/2.5 comparitive figures that Chris had posted. This because the figures showed a halving of resonant frequency for the ET2.5. I speculated that this meant that the two sets of figures must have been taken under different circumstances. Chris followed up my post up with a question to BT where Bruce appeared to say that no, the measurement conditions were the same.
This did not make sense and was contrary to resonance theory. Since I did not know the actual question Chris asked Bruce, I decided to contact Bruce myself for clarification. Below is my question and Bruce's answer.
Note Bruce uses the phrase "everything else is the same". This could be where the confusion came from.



On 4/18/2013 10:22 PM, Richard Krebs wrote:
> Bruce.
> Good day to you..
>
> My question concerns the horizontal resonant frequencies of the ET2
> and ET2.5 Chris spoke to you about this some time ago and you gave him
> a range of frequencies 5-6 hz for the 2 and 2-3 hz for the 2.5. Chris posted your info on the ET2 audiogon thread. The range of frequencies for the ET2 was approx double the ET2.5 This is confusing if the same wand, cartridge weight and compliance was used for both arms, as it implies the the ET2.5 is around 4 times heavier in the horizontal plane.
>
>
> For a 8 gm cartridge of 30 cu I get horizontal resonance figures of around 4.7 hz and 4.2 hz for the ET2 and ET 2.5 respectively.
> Are my figures correct? If not where am I going wrong?
>
>
> Many thanks .
>
> Richard.
>
>

Richard,

Your figures are correct and closer to reality. The only difference in mass is in the spindle, everything else is the same. The spindle adds about 10 grams to the horizontal inertia figure and almost nothing to the vertical inertia. I hope this helps.

brucet

As you can see Bruce has confirmed my figures are correct and the resonant frequency of the ET2.5, for the same cartridge, is not half that of the ET2, but only slightly less, exactly as I calculated.
If any one wants to confirm this for themselves, they need only go to the horizontal frequency formula in the ET2 manual. Choose a total mass (Mc plus Ma) of say 40 gm.(simulating an ET2). Insert the compliance figure for your chosen cartridge and calculate the res freq. Now recalculate with Mc plus Ma equal to 160 gm. You will get 1/2 the original number. Recalculate again with Mc plus Ma equal to 50 gm (simulating an ET2.5) you will now get a figure only slightly lower than the original.

So what can we conclude from this.

Someone who understands the math and physics around the ET2/2.5 would know that......
a)....it would be obvious, from a mile away, that the resonant frequency of the ET2.5 with the same cartridge would not be 1/2 that of the ET2.
b)....a heavy arm, when and only when, connected to a low compliance cartridge is a high performance, viable alternative
c)....the air bearing employed on these arms is effectively rigid at audio frequencies. So they should look elsewhere when looking for the cause of compromised note leading edge performance.

Richard Krebs
For a 8 gm cartridge of 30 cu I get horizontal resonance figures of around 4.7 hz and 4.2 hz for the ET2 and ET 2.5 respectively.

Thanks for this info Richard. We have always discussed just the spindle HZ resonant numbers before (5-6hz for ET2), and (2-3 for ET 2.5). As you point out this is just part of the equation. Understanding how they interact with the other “parts” in coming to an overall horizontal 4.7 and 4.2 for ET 2 and 2.5 is interesting using a 30 cu cartridge.

But we need to remember even if we all use the same 30cu cartridge, the numbers will be slightly different for each of us. We use different cartridge screws, #’s of lead weights, different positioning of the counterweight cap; a little higher, middle or a little lower; and finally the single double and triple leaf spring. Each one of these changes the parameters a little. So like the saying goes trust your ears.

The big consideration here for me is how the I Beam is affected. Dover mentioned the 2 – 6 hz variance in the I Beam from Bruce.

As soon as you change any variables in the I Beam Hz changes.

I also use a larger bolt to hold the lead weights.

So for tuning the ET2, ET2.5
Based on my observations/hearing. The tonearm has been designed for the first time user to let the weights fall at their natural location on the I Beam. This is what the manual says. This is how it is setup with most users and those that don’t like to tinker with it; and the sound achieved is very good and musical when setup properly. All the past reviews of the arm are probably based on this setup. The manual does also say to get the lead out to the end of the I beam if possible. For those that like to tune it even more – that is the one of the objectives of this thread.

Single, double and triple leaf springs that are not discussed in the manual but Bruce supports as we are still using a decoupled counterweight system.

Chris,

The thicker spring results in a higher resonance frequency. Thanks
Brucet

The thicker spring works better for lower compliance cartridges for me. But it raised the resonance frequency – not good. This is countered by getting the lead to the end.

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

If the sound is still not right with a double spring in your setup – drop down to the single leaf spring.