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Ghostbusters

Paul's Posts — 26 October 2012

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Ghostbusters

We’ve been focusing on microphonics and how they affect the performance of our AV equipment.  Vibrations from the output of the loudspeakers in our room generate airborne as well as floor-borne movement that is coupled into the audio signal we listen to forming a type of insidious loop that smears the music we listen to by injecting a type of “ghost image” onto the pure music.

This ghost image is a distorted and time delayed copy of what’s coming out of our systems.  The sharper the focus or imprint of this image the more noticeable it is – so we work hard to decouple our equipment from these vibrations by putting spikes under our loudspeakers, installing heavy shelving to set our equipment on etc.

The problem is that unless you put your kit in one room and the speakers in another you’re going to have to deal with this problem as it will impact your system and its performance.

I like to imagine this problem like I imagine the issue we wrote about earlier, the actual room itself.  We know that our listening rooms contribute mightily to the sound we hear and mostly not for the better.  The same type of delayed and distorted image of the sound hits our ears after it bounces off the walls of the listening environment.  Again, the sharper the “focus” of the reflected sound the greater the problem we hear.  This is why diffusing the sound with wall mounted diffuser panels works.

Because we cannot eliminate the walls in our listening room we have to deal with the reflected sound – and the best way to do that is diffusion.  Diffusion works because it defocusses the sound into something the brain interprets more as noise to be ignored rather than interfering with the image.  If you can’t eliminate something at least make it less noticeable – and that’s what we need to do with our microphonic issue.

Realizing that we cannot eliminate floor-borne and airborne vibrations within the listening room we need to stop trying to eliminate the effects of the vibrations and figure out how, instead, we can diffuse them properly.  That’s the key we’ll discuss tomorrow.

Diffuse the vibrations and bust the ghosts.

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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.

(3) Readers Comments

  1. Soundminded

    October 26, 2012 at 6:50 am

    What is the single element most vulnerable to microphonics? IMO vacuum tubes (one of so many reasons to avoid them. I bought my last vacuum tube amplifier in 1962.) Why? Because the operation of a vacuum tube is dependent on the critical dimensional relationship between thin metal plates and wires. These generate a cloud of electrons that travel in a vacuum from the cathode to the plate and are controlled by the thin wire mesh, the grid. The cloud is called the space charge. Anything that disturbes the physical relationships between these elements will be superimposed on the modulation of the space charge and will be eventually heard as sound. What about transistors? Not the same. The atoms that form the the physical entity of the transistor, silicon, aluminum, phosphorous, arsenic among others are locked in a crystal. If enough energy were introduced to disturb their relationship to each other, the crystal would be destroyed. What’s more the connectoins to the pins of a transistor are soldered, a tube is a plug in unit where the pins and pin holders can oxidize over time. So can the contacts of switches although often just working them back and forth or an occasional squirt of contact cleaner can fix that. It’s also surprising that the power transformer, a constant source of physical vibration is mounted within inches of the tubes on the same chassis, often without any vibration absorbing bushings.

    What about other devices like capacitors, inductors, resistors? In theory there is some validity to it but again we get back to order of magnitude. For a capacitor or inductor, changing its properties would simply modulate the frequencies it filters at. For a resistor it could spell trouble if it is large enough.

    How would you test the effect of microphonics, in nature and degree. I’d start with two identical setups in close physical proximity. One connected to the loudspeakers and one not connected to anything at all, or at most a resistor load. An impulse or square wave with no sound outupt is the reference. Then the systems with the speaker is excited and the one without the speaker is measured again. Why two systems? Because the one with the speaker might be affected by reverse EMF coming from the speaker itself. So what would you expect to see? The degree of subjectivity to microphonics will show up as ringing added to the output of the system not terminated in the speaker. OK, what are the measured results? How many db down is the ringing? Is it enough to worry about?

  2. peterh

    October 26, 2012 at 7:41 am

    There is another method if dealing with vibration. Goldmund made cones that act as a diode. They have three different hardness of steel with the hardest at the tip that sits in the table/shelf.

    Vibration goes only in the direction from softest to hardest and is moved out of the system to the shelf…where it dissipates with less/no effect on the component. The technology comes from precision machining for industry. The lathes has these cones as feet so the vibration of the lathes is grounded into the shop floor and doesn’t effect the microscopic cutting of the item being machined.

    I was stunned by the result 20+ years ago when these cones were put under a Meridian PRO CD player. At the time they cost $180 and that was a LOT of $$$. The effect was not subtle.

    I brought them home and the next thing my wife ask was when I was getting some for under the T-Table!
    I had a MicroSeakie table with the motor mounted in the plinth. Not a good design. But when I put the cones under the table and turned on the motor you could clearly hear a faint hum/buzz near the T-table. The arm is not on the the record. Just the platter is turning.
    Putting my ear right at the table I could clearly hear the sound coming from the shelf the table sat on. The shelf was made of biology class room counter top….synthetic granite…heavy and hard. Records played on the T-table were much clearer, more dynamic, and the sound of the record playing compleatly overwhelmed the faint buzz/hum. Remove the cones the buzz is gone and the music is as before.

    Goldmund equipment is designed to move vibration from the units using different hardnesses of metal in the construction of the circuits and the “box” to the shelf the unit sits on. Even their Epi 1 speaker has a BIG spike, 30in. screwed into the bottom with a point going into the floor. The owner is instructed to place the spike/speaker colse or over where a joist goes under the suspended wood floor for the most complete connection to drain the vibration.

    Look at their web site. Goldmund prices have become insane. But the research behind their produces is different from other companies too. You can drink a little of the Cool Aid and still stand on your feet.

    Goldmund cones sometimes show up on Audiogon. Buy a set of three and try them. They are not like other cones.
    I find other manufactures start to make use of technology about 10-20 years after Goldmund.
    Magico is making speakers with aircraft grade aluminum boxes. Goldmund did this 15/20 years ago.

    I enjoy your postings. The diode idea works with the dissipation of vibration idea to create wonderful syncopation of the music from your system! Enjoy, Peterh

    • Soundminded

      October 26, 2012 at 8:31 am

      Over 40 years ago Edgar Villchur suspended the motor, arm, and platter assembly of his turntable on a sub chassis hung from the main “plinth” with springs to isolate vibrations from reaching the platter. At its introduction at an audio show, to demonstrate how effective it was, every few minuts a guy would take a good wack a the top of the plinth with a steel hammer. Not a sound from the speakers. It was such a good idea, Empire copied it in their 598 and 698 models and probably a lot of others did too. The problem with putting cones under the turntable to isolate it is that it does not eliminate the air coupling between the speaker and the turntable, only the vibrations transmitted through the floor and walls. As for the CD player, it sounds like there wasn’t nearly enough isolation in the player. 20 years ago was still early in the era of CDs but that problem should have been taken care of by then. My Denon 1520 cd player bought in 1989 could be jarred hard enough to get the laser knocked off track with powerful bass tones. A JVC player I still use bought in 1991 is not affected in the least.

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