Turntable Isolation Journey
Nearing the end of my journey to solve footfall & feedback issues in my small-room "home office" system with very bouncy floor and flexible walls. Turntable is the only source here -- and it’s a Clearaudio Innovation Compact with no suspension or special isolation feet. This system always sounded good, but was rendered nearly unusable at higher volumes due to turntable isolation that was inadequate relative to this room’s challenges. The worst artifact was when structure-borne feedback from the speakers would cause amp clipping on bass-heavy tracks. This clipping would manifest as an extremely loud singular POP sound, especially hitting the tweeters. It only occurred during the loudest parts of track with bass-heavy elements, and was so loud it was still significantly above the level of the music -- much louder than a POP you would hear from vinyl surface defects. The POP sound was startling, and clearly very bad for tweeters (fortunately my Tannoys seem to have survived several of these incidents). For a time I thought these POPs were from static electricity discharge, but they were NOT. In my quest I tried many solutions and tweaks over a few months, and I’d like to share a rundown of what worked versus what didn’t.
What Helped (MVP products & tweaks):
What Underperformed:
What Was Worthless (Don’t waste your money like I did):
I’m not going to bother expanding upon these; suffice to say they had no discernible positive effect.
@tonywinga Another great post. Thank you. Regarding your statement, "A double spring/mass system would be a total disaster.". Since products like Oreos are damped isolation devices as you stated, would a set of those beneath a good platform which supports a spring type suspension turntable be detrimental? |
I’ll defer to @tonywinga for better explanation since he knows far more about this topic. But yes, I was aware one should never stack springs -- since their resonant frequencies can interact in very detrimental ways (huge displacement amplitudes when excited) -- I believe this has to do with the constructive & destructive interference nature of waves. My old dealer actually warned me of this when I first got into vinyl. So you should never, for example, put a SOTA turntable atop Townshend springs. I don’t believe stacking "squishy" damping interfaces like Orea feet suffers the same problem. Or at least, not severely enough to be of concern in typical use cases. I also don’t believe combining springs with damping devices is a problem -- in fact that’s a great approach! The main issue would be loss of stability when over-stacking -- don’t risk that expensive turntable toppling over! Technically, my turntable's full vertical support stack is: @tonywinga I would like to better understand the actual differences between damping devices and mass-on-spring systems. Doesn’t a spring system act "kind of" like damping above its resonant frequency? Or is there something else going on? And don’t damping interfaces also have resonant frequency? Thanks!! |
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. |
@mulveling One very important material that is being overlooked in your list of Materials, is the B25 Panzerholz (Densified Wood), it is the most upper layer of the Tiers produced and is the one used to support all of the critical mechanical components required for the TT to function. It is for the best, to not overlook the magic that this material brings, when used for the role to connect all the critical mechanical operating parts together. I would even encourage as an investigation that Densified Wood to be used as a exchange material for the Base of the Sota TT. The Link will give an indicator as to the values offered from a Phenolic Impregnated Densified Wood. https://www.lessloss.com/page.html?id=80
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The 1.5" thick brown wood layer in these Clearaudio Innovation and Ovation tables is panzerholz :) I’ve been admiring the Taiko audio panzerholz platforms. And I’ve definitely wondered if a nice slab of panzerholz atop the Townshend platform might be a good idea. @tonywinga Yes, I was aware the tonearm mass + cartridge compliance forms its own spring system, which can be difficult to deal with. Even when you’re right in the "ideal" 8 - 12Hz range, what they don’t tell you is that footfalls (etc) can very easily excite this resonance until you’ve properly addressed structural issues and isolation in a setup. I could observe this excitation very plainly -- by both sight and sound. Finally now with rack bracing, the Townshend, and (to a lesser degree) hockey pucks, this excitation no longer occurs :) Probably the worst case of feedback I’ve ever observed, even worse than this small room setup (before current solution), was with one of those Clearaudio full-magnetic bearing tonearms ("Concept", "Clarify", and "Verify") on a Clearaudio table, on a suspended wood floor, near the speakers. The magnetic arms act like their own spring system, and good god their interaction with other non-ideal system factors is just pure nightmare fuel! The hybrid-bearing "Magnify" arm (rigid in one direction, magnetic in the other) was a LOT better in this regard, at least. It looks like Clearaudio has either discontinued or de-emphasized these models in their line -- no surprise to me!! |
