Hi Kirkus,
Many thanks for your thoughtful Post (as usual).....and it has made me realise how wrong I am about the importance (or lack thereof) of the Arm/Cartridge Resonance…..😲❗️
I’m really kicking myself now because I’ve done a great deal of thought and study on the subject of Structure-Borne Feedback as it relates to Audio and yet…..because I fortunately don’t suffer from it myself…..I completely ignored its possible relationship to the Arm/Cartridge Resonance…😅❓
As I have written many times previously….EVERY suspended floor structure….be it timber, steel or concrete…..is under stress.
At points of maximum bending and deflection…this stress induces low subsonic frequencies which can be so severe in certain cases…that vibrations may even be felt....🔊
Contrary to popular belief…..a suspended reinforced concrete slab can often be worse than a suspended timber floor, especially in modern high-rise apartment buildings which commonly use thin prestressed, post-tensioned slabs with little standard steel reinforcing…😱
The subsonic frequencies in most suspended floor systems are commonly in the order of 2-5Hz and vary in location and intensity on an individual basis. In other words….no two audiophiles are experiencing exactly the same conditions….but ALL audiophiles with a turntable located on a suspended floor are living with a vibrating ‘singing’ demon under their feet….👿
Normal equipment racks are of little use against these types of subsonic frequencies and ‘cures’ like rubber, sorbothane and air-bladders may ameliorate some aspects to the detriment of others…😕
Only the expensive ‘active’ acoustic stands developed for electron microscopes (like Minus K) which utilise ‘tuned’ springs along with mass plates designed to handle exactly those frequencies 2-5Hz, will be effective on a suspended floor system…..😃
The best floor of all….❓
A reinforced concrete slab on the ground….which is what I have…👀😍
If you don’t have this luxury…mount your turntable on a shelf fixed to a wall which sits on its own footing. A masonry wall is preferable to a timber-framed wall, as a masonry wall will not support ‘tension’ whilst a framed wall will. Remember…’tension’ equals ‘stress’ equals ‘noise’.
If you can’t use a wall-mounted shelf…then try to locate your turntable as close to an external wall as possible. The middle of any floor span has the most stress and deflection….😖
As anyone with ‘feedback’ problems knows…..with the stylus stationary on the record, as you turn up the volume you will suddenly hear a deep and progressively louder continuous ‘drone’ emanating from your speakers…🔊
This (I suspect) is the Resonant Frequency of your tonearm/cartridge combination being excited by the harmonics of the structure-borne floor.
If your floor is producing 2Hz…then 4Hz, 8Hz and 16Hz are the harmonics.
If your floor is producing 3Hz…then 6Hz, 12Hz and 24Hz are the harmonics.
If your floor is producing 4Hz…then 8Hz and 16Hz are the harmonics….and so on..
The common silent woofer-pumping many complain of, seems again indicative of the Resonant Frequency activating the woofers...🔊
This is why I suspect, changing cartridges or headshells or adding mass or damping to the tonearm often ‘solve’ the problem….❓
You are simply shifting your resonant frequency ‘out’ of the feedback harmonics…..👀
You are not ELIMINATING the problem….😞
You are DODGING the problem….😜
If you have this problem.….you could never have 2 turntables, 6 tonearms and 40 headshells and cartridges (as I have) without experiencing a single feedback problem…❓
One thing puzzles me and perhaps Kirkus or Al can help here……😃
The ‘feedback’ on the stationary stylus increases when the volume is turned up….but I thought this is amplified AFTER the cartridge in the preamp stage….❓
