Turntable Isolation Journey

Good post and I see that many of you are astute and have a good understanding of vibrations and their effects on our stereo gear.  I want to add a few remarks to help everyone understand how best to isolate their gear.

Springs isolate and rubbers dampen.  A spring/mass system has a dynamic response curve that can be expressed as a ratio of input vs output across a frequency range.  Beyond the natural frequency of the spring/mass system the response ratio becomes less than one.  That means the vibrations going into the spring/mass system are reduced coming out.  I isolate my gear with spring rates that achieve a Natural Frequency of 3 Hz, or there abouts in order to isolate my gear at all higher frequencies.  It is easy enough knowing the mass of a stereo component to calculate the spring rate required to achieve a system natural frequency of 3 Hz.  I have never seen a Townsend speaker platform in person but I'm sure that is what it does.

Rubbers dampen.  I know, we often see the term "rubber isolators" but that is not entirely accurate.  Dampers reduce vibrations- especially important around the natural frequency of spring mass systems since the system can go out of control at its resonance point.  But dampers also cause phase shift.  This phase shift property of rubber is why we hear tonal variations or colorations.  Sometimes these colorations are helpful and sometimes they are undesired.  Nevertheless, all of the spring/mass systems of our stereo gear need dampening.  The problem for me is I am not smart enough to determine the best dampening materials or amounts to use beforehand with calculations.  I have to use the trial and error method or what we call experimentation.  In most cases I found that isolating each of my stereo components with springs and then utilizing the factory supplied feet for dampening is sufficient.  So I have each component on a wooden or delrin board supported by springs.  In the case of my Sota turntable, I have it standing on a carbon fiber board supported by Isoacoustics Orea feet.  After much experimentation with various materials I found this was the best solution.  Yes, I was surprised by how much even my Sota is affected by the base it stands on.  It has never been susceptible to footfalls or woofer pumping, but the tone changes based on the stand it is placed on.  Since the Sota turntable suspension has a natural frequency of 3 Hz it cannot be placed on a spring isolation platform.  A double spring/mass system would be a total disaster.

I built my own speaker isolation platforms a few years ago using springs and butcher blocks.  I got 48 lb/in springs from McMaster Carr and four per speaker got me a natural frequency of 3.1 Hz for the speakers I had back then.  I was amazed at the difference in the sound on my suspended floor that isolating the speakers made.  Eventually, I bought the Isoacoustic Gaia footers to try on my speakers.  The speakers sounded better with the Gaia footers although they did not isolate the speakers from the floor as perfectly as my spring platforms.  Why?  The Gaia footers add dampening and this made the tonal balance of my speakers more pleasant.  I moved my spring platforms to my home theater subwoofers.  They make the bass deep, clear and crisp.  

To sum up, it takes a combination of isolation and dampening to find the optimum sound.  I do it by putting each of my components on a spring loaded platform for the isolation part and then dampen the component at the base- in my case typically the feet supplied by the manufacturer.  But experimentation with other dampening materials for each component may yield a better solution.

PS.  I'm amazed at the number of expensive high end turntables that lack any sort of isolation, or just a minimal amount of isolation requiring the consumer to spend yet even more money on a highly engineered isolation platform.  If your turntable lacks a spring isolation system then build platform yourself and save yourself some money.  You can find natural frequency calculators online for spring/mass systems.

Just like in life- too much of a good thing can be a bad thing. Too much dampening can deaden the sound. That is especially true when working on room reflections. Too many reflections muddy the sound but too few makes the sound dead/dull.

If you look at a chart of a spring mass system, the response ratio is about one below the natural frequency, then wants to shoot to infinity (constrained by physical limitations and dampening) at the resonance point (the natural frequency) and then falls below one and lower as the frequency input goes well above the natural frequency. So the spring mass system is absorbing the energy that is being put into it via airborne or mechanical vibrations through the floor.

Think of a car. A car’s suspension system is simply springs. The shock absorbers are pistonic dampeners that keep the car from bouncing at its natural frequency while driving down the road. If you have ever driven over an old bouncy suspension bridge at just the right speed the spring action of the bridge can interact with the car’s suspension and make for quite an exciting ride because the car’s suspension will interact with the bridge.

You might wonder why then if speakers are sitting on springs for isolation from the floor shouldn’t they start bouncing around and dancing across the floor like an out of balanced washing machine on spin cycle? They don’t because the spring suspension system is tuned for a natural frequency around 3 Hz and speakers are not typically able to go that low. Also, the mechanical energy output of the speakers is still way below that crazy washing machine on spin cycle.

One more thing before you I start to annoy you all. A turntable tonearm is also a damped spring/mass system. The stylus in mounted to a cantilever which is mounted to a spring in the phono cartridge. The cartridge also has a dampener- typically a tiny o-ring. Phono cartridges have a compliance figure- that is the spring rate. The tonearm has an effective mass. It is not the same as the total mass of the tonearm and counter weight because the tonearm is mounted on a pivot. Knowing the compliance of the phono cartridge and the effective mass of the tonearm (always provided in the manufacturers specifications) one can calculate the natural frequency of a phone cartridge and tonearm system. Why is that so important? The goal here is to have a system natural frequency around 10 Hz. That’s because if the record has a warp- that is at 0.5 Hz (33.33 rpm) or 0.75 Hz (45 RPM) we don’t want the tonearm to have a resonance response near that frequency. And on the other side- the music frequency response starts at 20 Hz so we do not want the tonearm to respond at that frequency either. With the wrong set-up the tonearm will fly right off the record. Been there, done that.

My Sota Nova VI has the magnetic bearing.  Much quieter than my previous Sota Star V.  I thought the Star was quiet and what I was hearing was groove noise because the noise seem to vary from record to record but that noise is gone with the Nova.  Further, I have the Eclipse Motor and Roadrunner speed control system.  It works really well but I wasn’t too sure until I figured out how to use it.  One button turns the motor on/off and also toggles the speed between 33 and 45 rpm.  I had to learn to hold the button down for a count of 2 when starting the motor.  Otherwise, the speed wants to toggle to 45 rpm.  The button has to be held down for the count of 2 when turning the motor off.  I knew that and once I realized the same holds true for turning the motor on everything was fine.

I have a set of Sota cones as well as the Sota rubber feet for the turntable.  I experimented with both.  For me the sound is better with the rubber feet.