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Old 30th March 2004, 04:47 PM   #1
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Default To decouple or not.Counter weights

Hi any opinions on decoupling counter weights?
I belive its dependant on whether you deck is springy or not and whether the counter wieght is truly decoupled.
Those arms that use rubber to decouple are not doing it at the right frequency , the weight is to low and the rubber too hard so they end up muddying the sound(and smoothing out some harshness in the process.
the only truly decouple arm i can think of af the top of my head are those from roksan(there must be others)
They use a point to rest the counteweight so its free to move and is decopled at a very low frequency.
But if you had a suspended deck this would undo the good of the counterweight as any movment wouls sway the deck slighly and start oscillation as good suspentions are also at low freqencies.

My wilson benesch arm uses a compressesd spring to decouple the weight but I use it on a wobbly linn and have found it sounds better with the spring compressed so it out of action , and the screw done up tight, also when decoupled the azimuth slips out of alignment every few days.
I would like to find a counter weight that bolts on tight to try on this arm, I wonder if any of the rega mod weights would fit and be the right weight range?

Any thoughts experiences or experiments on this issue?
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Old 6th April 2004, 02:03 PM   #2
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Lightbulb Re: To decouple or not.Counter weights

Quote:
Originally posted by sleepy
Hi any opinions on decoupling counter weights?
I belive its dependant on whether you deck is springy or not and whether the counter wieght is truly decoupled.
Those arms that use rubber to decouple are not doing it at the right frequency , the weight is to low and the rubber too hard so they end up muddying the sound(and smoothing out some harshness in the process.
the only truly decouple arm i can think of af the top of my head are those from roksan(there must be others)
They use a point to rest the counteweight so its free to move and is decopled at a very low frequency.
But if you had a suspended deck this would undo the good of the counterweight as any movment wouls sway the deck slighly and start oscillation as good suspentions are also at low freqencies.

My wilson benesch arm uses a compressesd spring to decouple the weight but I use it on a wobbly linn and have found it sounds better with the spring compressed so it out of action , and the screw done up tight, also when decoupled the azimuth slips out of alignment every few days.
I would like to find a counter weight that bolts on tight to try on this arm, I wonder if any of the rega mod weights would fit and be the right weight range?

Any thoughts experiences or experiments on this issue?
Hi sleepy,
My Dual 701 had a VERY decoupled counterweight leading to excessive bass. I bolted the counterweight with added rubber damping and the bass is more tight. Owners of a Technics SP-10 can adjust the counterweight to hard or soft.
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Old 9th April 2004, 11:38 AM   #3
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In theory, an undecoupled arm weight exacerbates structural resonances down the arm tube. The pivot is one fixed point, and when you add the inertia of the counterweight, that is another, so the tube has been clamped at one end - just like holding a ruler on a desk and twanging the free end. Decoupling the counterweight means that when you twang the free end of the arm (by applying energy at the headshell), the arm's stub going into the counterweight is free to move, so the resonance is damped.

In practice, the materials used to decouple the counterweight from the arm stub are not completely free to move at the frequencies of typical arm tube resonances, so the dcoupling doesn't work very well. I don't understand why decoupling the counterweight should make the arm sound worse, but the popularity of modifications to remove the decoupling on the Rega arms seems to be proof that it does.
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Old 9th April 2004, 02:24 PM   #4
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Quote:
I don't understand why decoupling the counterweight should make the arm sound worse, but the popularity of modifications to remove the decoupling on the Rega arms seems to be proof that it does.
<speculation>It's possible that the decoupling means prevents higher frequency arm modes from being sunk efficiently by the counterweight mass by reflection at the boundary.</speculation>
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Old 9th April 2004, 02:48 PM   #5
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That's possible, but what I was getting at is that you would have thought that even an imperfect solution (practical decoupling) would be better than no solution at all (no decoupling). I wonder if hysterisis in the rubber is the problem?
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Old 9th April 2004, 03:28 PM   #6
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But reflections work both ways.If the cartridge end sends vibrations down to the counterweight then counter weight end if 'wobbling" as well will send them back.
worse still at a different time causeing intermodulation distortions.

"The pivot is one fixed point, and when you add the inertia of the counterweight, that is another, so the tube has been clamped at one end - just like holding a ruler on a desk and twanging the free end."

There fore the closer you can get the counter weight to the pivot the better.
wouldn't it make sense to sell arms with variable counter weight options for different cartridge weights?
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Old 9th April 2004, 03:33 PM   #7
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Hi,

Quote:
wouldn't it make sense to sell arms with variable counter weight options for different cartridge weights?
Of course.
Any half decent arm should come with a series of counterweights.
If not standard then at least as an option.

Cheers,
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Old 9th April 2004, 04:06 PM   #8
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Quote:
Originally posted by sleepy
Therefore the closer you can get the counter weight to the pivot the better.
That's a very good point - I hadn't thought of that. As Frank says, most arms offer a choice of counterweights, although the usual reason for this is that a heavy weight close to the pivot has less inertia than a lighter weight further from the pivot.
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Old 13th April 2004, 02:47 PM   #9
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Default Re: To decouple or not.Counter weights

Quote:
Originally posted by sleepy
Hi any opinions on decoupling counter weights?
Hi Sleepy,

I had the Roksan Tabriz with original counterweight as well as with the so-called intelligent counterweight (called -Zi). I tried it out. With original counterweight the tonearm sounds more or less like a Rega tonearm. With the -Zi-weight, it gets more highs and detail, but in my high resolution setup that was clearly shown as additional resonances not been there before.

The Roksan Artemiz is not my cup of tea, either !

When talking about old SME tonearms, those with their counterweight coupled rigidly have deeper and clearer bass.

kind regards,
Hartmut
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