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In Reply to: RE: bearing and/or motor noise can't be dissipated or eliminated by the armboard ... posted by Lew on March 14, 2012 at 16:36:36
>>Most of the energy was dissipated as heat or reflected back into the plinth at the armboard/plinth interface, on its way to the armboard. However, that fraction can vary depending upon the material composition of both the armboard and the plinth.<<
(assuming that the armboard is directly coupled to the plinth, and that no compliant material is used)
Although material composition can and does effect transmission, since motor noise remains a constant, no material I've heard has changed or dissipate it to nearly the degree in which I considered it "isolated" or "dissipated". Even the amplitude remains relatively consistent, in other words, if you put the steth near the motor, then away at the armboard, you're basically going to hear identical motor noise.
I've heard this behavior - consistently - with a variety of 'tables ... many using different materials. In fact, the hardest lightest materials types (which I use and think sounds best for any armboard) tend to transmit noise without any hesitation. Even 'tables that use outboard motor pods (claiming motor noise isolation), if the motor is noisy, that noise will STILL travel and be heard within the turntable.
And yes, you can hear amplitude differences, frequency changes, resonance effects, dissipation, isolation, and a host of "noise" issues ... using a good steth.
Without one, my table wouldn't be nearly as refined.
tb1
Follow Ups:
Your experiences are inconsistent with wave mechanics as we understand them to operate. You should probably get them written up in Physics Journal. Really, I think you are just splitting hairs for no purpose whatsoever. Nobody is claiming an armboard will fix a noisy motor or bearing, or that a stethoscope isn't a useful tool. But you can't possibly believe that literally, absolutely zero vibrational energy from the motor or bearing is absorbed or reflected on its way to the tonearm mount. That's just not physically possible.
> > Your experiences are inconsistent with wave mechanics as we understand them to operate. < <
Not at all.
> > You should probably get them written up in Physics Journal. < <
And they say "I'm" condescending?
> > But you can't possibly believe that literally, absolutely zero vibrational energy from the motor or bearing is absorbed or reflected on its way to the tonearm mount. That's just not physically possible. < <
Didn't say that, I'm stating that an armboard, when directly coupled to the plinth, will not (and should not) "isolate" a CONSTANT source of noise to nearly the degree you, and others here, are suggesting.
In other words, your claim that "vibrational energy from the motor or bearing is absorbed or reflected on its way to the tonearm mount" is true, but it is so minimal in practice, as to make this point ... moot.
tb1
Sorry, I wasn't trying to be condescending, just making a little joke.
To be clear, I did not say, nor do I believe, that an armboard can provide sufficient isolation from an excessively noisy motor or bearing. In fact, I explicitly said just the opposite: that an armboard should never be considered a "band-aid" for a noisy motor or bearing, which I think is the point you are trying to make. I can't speak for what others here believe.
But the mechanics of the materials used for armboards are not exactly irrelevant either. The kind of material used for an armboard (or plinth) will determine the degree to which vibrational energy is absorbed or reflected, and can also change the frequency of vibration due to the impedance difference between different types of materials. That is in part why a stainless steel armboard or plinth will have a different sound than one constructed of maple or carbon fiber, and acrylic will sound different still. This is true even in cases where the motor and bearing are extremely quiet.
we are actually arguing (i prefer debating) the same argument.
> > That is in part why a stainless steel armboard or plinth will have a different sound than one constructed of maple or carbon fiber, and acrylic will sound different still. This is true even in cases where the motor and bearing are extremely quiet. < <
Yes, it will, but IMO this has more to do with the armboard ability to quickly dissipate tonearm induced energy, rather than dissipate motor or bearing noise.
In my travels, I've found that bearing noise is nearly impossible to isolate from the arm/platter. Motor noise can be isolated to degrees, depending on the amount of vibration and the quality of it's mount, and a well tuned suspension will very much isolate a large degree of motor noise. There are ways to do it, but simply placing a noisy motor in an outside mount/pod (which many current tables do) does near nothing, the noise will still migrate towards the stylus.
That said, and we both agree, it's best to eliminate (or minimize) bearing and motor noise at the source. One of the very reasons my turntable sounds as good as it does, is based on the above principles.
It took me years to refine.
tb1
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