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Head scratching

Paul's Posts — 01 November 2012

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Head scratching

In our continuing story about trying to figure out why isolation bases mattered, how they worked and what we could do to perhaps make our products less needy of their services, I endeavored to build my own.  It’s been my experience that the best way for me to learn is to jump in, roll my sleeves up and get dirty with the work.  In this way I make a lot of failures and failures are the most important aspect of design.  When we fail we learn.  When we succeed we stop trying and stop learning as we move on to the next project.  I had a lot to learn and that meant a lot of failures.

I can see a few of my engineering readers rolling their eyes at me.  ”You should do this by measuring the vibrations levels and minimizing them”.  The problem is/was we didn’t really understand what it was we were trying to eliminate and why – so measuring for some elusive parameter that may or may not have the desired effect would have been pointless – at least for me, the consumate tinkerer.

My first attempt showed promise.  I used a 1/4″ steel plate mounted on some rubber feet as a test base and that worked well.  The next step was to test the steel plate as a given – I swapped it out for a 1″ piece of MDF (medium density particle board) – worse.  I swapped it out for a 1″ thick piece of HDF (high density particle board) – even worse.  Wait a minute, I was going backwards.

I took one of the particle boards and added a ring around the outside and filled the inside with sand – a trick my friend Barry at Bright Star had shown me.  Interesting indeed.  Better than just the particle board but worse than my original idea of the steel plate.  I went back to the steel plate and after all that decided it was clearly head and shoulders better than anything else I had tried.

So the obvious next step was the feet.  I scrapped the rubber feet for cones.  Yuck.  I swapped the cones for Sorbothane feet (a branded polyurethane product) that I had around and instead of going backwards, went forward.  Better for sure.  Sorbothane is available in many different durometers and sizes (durometer refers to hardness) and I got a kit from the distributor and went to town.

I soon discovered something interesting and counterintuitive: the larger the diameter of foot the better the sound.  I would have thought the opposite because it seemed to me that by limiting the contact area (as we would with a cone) the amount of vibrations would be reduced.  Yet the opposite was happening which made me quite happy I wasn’t on a mission of measurement and tuning to an unknown goal.  By simply listening and observing the results with an open mind I discovered this interesting twist.

So, if bigger and broader was best, how big and how broad?  Might a Sorbothane pad covering the entire area of the plate be the key?  Turns out no – it was worse.  The sound more open between instruments but the muddled effect worse.

I discovered that a Sorbothane foot close to a couple of inches in diameter and at a specific durometer, coupled to the heavy steel plate, worked best.

And interestingly enough my results now matched the original wooden base!  I was on to something but wanted more.

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About Author

Paul McGowan

Paul McGowan is the CEO and co-founder of PS Audio Inc. a Boulder Colorado design and manufacturing company of high-end audio products and services. McGowan has been designing and building high-end products for nearly 40 years. Hobbies include skiing, music, hiking, artisan bread baking, kick boxing and cooking. He lives in Boulder Colorado with his wife Terri and his 4 sons.

(6) Readers Comments

  1. paulsquirrel

    November 1, 2012 at 4:33 am

    Most interesting, Paul!

    In 1995 Alfred Rudolph from Acapella Audio Arts (famous for it’s ion- (plasma-)tweeter and spherical horn-speakers) had already done this empirical experimentations with different materials for base and footers and launched his “Fondato Silenzio” base. The empirical work was accompanied by two physicists who made laser-interferometry measurements to document the reduction in vibration even in the most expensive high-end gear from Burmester (see:http://www.acapella.de/de/testberichte/physikalische_analyse.php).
    I can confirm your finding that the design of the footers (the coupling elements between the absorbing base and the electronic gear) is most crucial here!!!

    I am most keen seeing/ hearing your new design to have it implemented for my Premiers and Quintessence!

  2. hahax

    November 1, 2012 at 6:53 am

    Audio got an order of degree harder when we discovered that wires are significant. And now there is another order of difficulty added by the mechanical relationships of our gear to what it’s on and what connects these.

    I recall when by accident I discovered that my speakers(on pointed feet) sounded better when a concrete rectangle(also) on pointed feet. And then thinking wood might dampen more nicely than concrete I found I was wrong and went back to the harder material.

    I have friends who over years have tried many different materials, mostly plastics under gear and found each material ‘sounds’ different. And the ‘sound’ depends on what kind of gear is being used what material is better. And unfortunately most of the time the most costly plastics are the best. And I’m talking about hundreds of dollars a square foot ouch!

    One friend makes a living making awfully good wires and inexpensive support gear. He is mainly concerned about the vibration loop between source, electronics and speakers and breaking the loop. He puts speakers on hard feet so they move as little as possible and uses isolation on every other piece of a system to break the loop. He is aware that isolating speakers sometimes improves the sound but that this is only true when the the sources and electronics are not isolated from the speakers.

    This is another tale that is still in its infancy and wikk go on for a long time.

    • November 1, 2012 at 7:02 am

      I remember the first UK show I went to and watched (I think it was Naim) tout these cable isolators that mechanically decoupled the stiff cable from the kit so as to reduce vibrations. All fascinating stuff that matters.

  3. Ian Blacker

    November 1, 2012 at 9:59 am

    Have you checked into MapleShade’s solid wooden plinths for speakers and equipment? They are pretty brilliant at reducing vibrations/improving details etc. many types/sizes available, and I have not found any better no matter what price. Ian Blacker.

  4. Soundminded

    November 4, 2012 at 5:43 am

    Welcome to the world of Newton’s second law of motion as applied to forced oscillation. You can find this in any college text on physics or mechanics dynamics. It’s one of the reasons Newton invented calculus. So we see an exact model of the phenomenon of resonance, the role of mass, dashpot, and spring. It is applied to many areas and problems. They way your car’s suspension is designed and tuned for example. It wasn’t untill I put 1 and 1 together and got 2 by applying this law that I really understood how woofer/enclosure systems actually work. (Thiel and Small canned the calculations to turn it into a cookbook recipe for design so you don’t have to learn the hard part, just plug in the numbers.) How phonograph cartridges behave is another. And so the value of visco-elastic materials originally developed by NASA for the space shuttle including sorbothane and memory foam are very useful for damping vibrations….at some frequencies. There’s the catch. Materials that are very useful at some frequencies are not so good at others, worthless at still others. That memory foam mattress on a platform will do nothing to damp an oscillation at say 0.1 hz with an amplitude of two feet. You’ll still feel like you’re going up and down in an elevator so it won’t help on a ship rocking at sea. This is why understanding the problem by measuring it and then measuring the results of your shock absorber design is important.

    So if you want a better understanding, read the chapter, tackle some of the easier mass spring dashpot problems at the end of it, and then go on to some of the harder ones where the mass whose motion you want to solve for is isolated by multiple intermediary masses, springs, and dashpots in series and in parallel. The good news is that today you don’t need a slide rule. Probably not even a calculator. There are bound to be many canned programs cheap or free on the internet that will crunch the numbers for you, even show you a graph of the resulting frequency response (that’s also predicted by the equation.) Does it work? Well we’ve only got a few hundred years of experimental evidence which so far has proven excellent correlation between theory and practice so the jury is still out. :-)

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