Turntable isolation platforms

brotw69
I look at vibration control through an RF impedance matching background. Spiking heavy speakers or platforms improves sound by rejecting high energy bass frequency vibrations in a suspended wood floor moving up into the component or speaker.

Varying pressures in the floor and around supporting beams due to concentrated weight on spikes causes diffraction or reflection of sound, stopping travelling waves in the wood medium moving up the speaker or component. An abrupt change in density is a fraction of bass frequency wavelengths, rejecting sonic conductance which minimizes cross talk between woofers from left to right speaker or speaker to component. Bass frequencies have the most energy and can morph into higher frequency resonance in cabinets and audio racks.

That is just the start of treatment as I understand it. Performance improves if the fraction of vibration that finds it way up the feet or leaving the feet is attenuated as loss or sound absorption through the use of rubber, sand, isolation feet or platforms - whatever provides wideband absorption of vibration energy.

>>>>I’m not sure I agree with your detective work. What seems clear is that spikes and cones minimize contact area and reduce the contact with compliant or springy materials like carpets/pads. There are several variables just for cones and spikes, e.g. material, shape.

For traditional mass-on-spring isolation devices we know they function as 🔜 mechanical low pass filters 🔙, 6 dB per octave, preventing or at least reducing the transmission of vibration from the floor to the component. The vibration of concern is both the seismic type - traffic, Earth crust motion, etc. - and speaker mechanical feedback and footfall.

We're all talking about the same thing here. I've just provided a alternate, general way to understand what's going on, not just with turntables but speakers and components with noisy transformers as well. Mass on spring works well at low frequencies because of bass energy loss in the spring. Sand is likely needed for the high frequency isolation through absorption.

If you place a lightweight platform on spikes on a suspended wood floor without carpet, I doubt your going to get low frequency isolation.

That gets to my point, the floor is acting like a diaphram which has to have relatively even movement of soundwaves to be an effective transducer. Place a heavy weight in one spot and you have a node or lower energy zone. Sound waves traveling through the floor are reflecting off the perimeter of that weighted floor spot and travel around it or through supporting beams to other sections of the floor that allow vibration. It's like a large scale piezo-electric buzzer for bass.

Cones or vibrapods work on components because weight is concentrated under the metal chassis effectively conducting or draining vibration out of the component. Unlike the floor, the metal in the chassis doesn't change density near the cones. Cones work best with lossy plinths that dissipate energy.

The effective channeling, isolating and dissipation of vibration energy can be achieved by knowing when to minimize boundary reflections and when to incorporate loss. It's all wave energy, highly similar to RF.

brotw70

brotw70
We’re all talking about the same thing here. I’ve just provided a alternate, general way to understand what’s going on, not just with turntables but speakers and components with noisy transformers as well. Mass on spring works well at low frequencies because of bass energy loss in the spring. Sand is likely needed for the high frequency isolation through absorption.

>>>>At the risk of you thinking I’m picking on you, we’re not talking about the same thing here. In fact, mass-on-spring isolation is better (more effective) as you go up 🔝 in frequency. By the time you get to 25 Hz on the way up 🔝in frequency - even for a modest iso system - the effectiveness of isolation is more than 95%. By the time you get to 30 Hz it’s 99.5%. So, it’s more effective for high frequencies than for very low frequencies. Hel-loo! Not to rub it in too much but mass-on-spring isolation is not due to losses in the spring. It’s more complicated. That’s why it’s called mass-on-spring. It functions as a mechanical low pass filter with a 6 dB per octave characteristic.

Ok, had to look that up. Mass on spring looks effective for isolating turntables through other means. I'm more interested speaker and component vibration solutions that drain sources of vibration to the floor. Haven't seen many spring solutions for those. I think springs just solve the floor moving up and down problem rather than lateral.

I would go to your local granite countertop site and ask them to cut you a 1.5 to 2 inch thick piece large enough to place your table on. all the imaging greatly improves and feedback becomes a non issue.