Kinda sounds like a weak AM radio station to me.
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How a cartridge works
- Thread starter TG1
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I think tape would be more of a noise increase coupled with a frequency roll off with each generation.
Try applying a low-pass filter, Ray. Just select say 15k in Filter1 bank and select LP @start next to it. Then try a match to see if it looks any better. Of course, some noise shaping may also be necessary
...and what this amounts to is that pure horizontal motion of the stylus creates an equal, in phase, signal to both outputs while pure vertical motion creates an equal, out of phase, signal to both outputs. These signals are more colloquially known as sum and difference or Main & Side. The fact that mono records have only horizontal groove motion causes those mono records to play correctly on stereo gramophones and stereo records to play correctly on mono gramophones provided that the cartridge accommodates any vertical motion (i.e. the additional information required to create a stereophonic image) without damaging the groove.
So far I have mainly only seen very simplified, quasi-static, explanations of how cartridges, and the whole record player and its environment, produce an output.
In fact the system is a dynamic one which is compromised to make it convenient.
In actual fact the record playing system relies on resonance to work, ie to both track the record and produce a musical output.
In order for the cartridge to produce output the cartridge body has to be stationary relative to the groove.
In a simple dynamic system like this where the mass of the arm and cartridge are suspended over the record by the stylus and cantilever with its suspension spring, usually a bit of thin wire with a polymeric damper. At very low frequencies the whole arm and cartridge body are moved by the stylus, the suspension behaving as if it is more or less rigid. This is just as well since the arm has to be able to move over warps and disc eccentricity as well as track the spiral from its outermost to innermost locked groove.In order to understand what happens imagine holding a soft spring with a weight on the end. Your hand is the stylus and motor, the weight is the stator/cartridge body and arm. If you imagine raising and lowering your hand slowly the weight moves with you, that is the warps, for example, if you start moving your hand faster the weight no longer follows your movement but moves towards resonance, where the weight moves massively more than you are doing then, as the frequency increases its movement gets less and less until the weight is stationary and only your hand is moving. It becomes stationary at approximately twice the resonant frequency.
In a real system there has to be damping (movement at resonance is infinite with zero damping) which I will ignore because it is needed but bad.
I hope I have explained it simply enough.
The fact that the weight, headshell, is moving up to resonance and back means the low frequency output of the cartridge is wrong and exaggerated, to an extent depending on the damping. This doesn't matter much if the cartridge and arm are compatible and have a resonance of around 10 Hz, since by the time the cartridge output reaches musically relevant frequency the cartridge body is remaining substantially stationary relative to the stylus.
Sadly if damping is high whilst the resonant peak is then smaller the damper "short circuits" the suspension and the cartridge body is moved at higher frequency, so the point at which the cartridge starts being accurate is higher than 2 times resonant frequency and it is not perfectly stationary relative to the stylus at any frequency.
There is a lot of quasi-static semi-folklore rubbish written about record player systems. I am not sure why, either it is thought too difficult for lay people to understand, but over simplified hence misleading explanations abound.
Anyway the whole assembly is a complex distributed mass dynamic system and so anything which causes relative movement between cartridge body and stylus assembly will give an unwanted output added to the music.
A very rigid pickup arm may seem like a good idea from a static perspective but it will transfer more plinth vibration allong the arm to the cartridge body. Exactly what does and doesn't give an output requires a proper distributed mass dynamic analysis of the whole turntable (including its support and the floor) whilst outputting the movement between stator (cartridge body) and motor (the bit supposedly moved by the stylus which it is somewhat remote from)...
It may be that a mode where the finger lift is resonating will give output - maybe not. Without such an analysis one can not know.
I was working on this sort of thing in 1975/6 and I have never seen an analysis such as we were doing then published since.
Maybe manufacturers don't do it any more, after all it seems to me most of it is a boutique fashion business these days with buzz words pervading from makers rather than proper engineering explanations.
On top of this we have the compromises made to make record players cheap and easy to make and the stylus shaped to reduce wear.
Pivoted arms are not like the record cutting lathe, so the cartridge body, which needs to be perpendicular to the groove to read the cutter's wave shape accurately isn't except for 2 instants during replay. The distortion this adds is the reason I use a tangential tracking arm myself.
In addition, the cutter producing the groove of the master is sharp, obviously. The stylus needs to be sufficiently rounded to not wear the plastic of the record much. A simple conical stylus is easier and cheaper to make but is by far the least accurate at replicating the movement of the cutter.
More complex stylus shapes are much better but also orders of magnitude more expensive to manufacture. Fortunately these distortions tend to be at higher frequencies where they are less noticeable.
So in the end record players work amazingly well considering how many compromises were accepted to make the discs cheap and the record player easy to make!
I laugh out loud over some of the technically naive bollox I seen written about record players in magazines and the internet by the "audiophile cognoscenti".
In fact the system is a dynamic one which is compromised to make it convenient.
In actual fact the record playing system relies on resonance to work, ie to both track the record and produce a musical output.
In order for the cartridge to produce output the cartridge body has to be stationary relative to the groove.
In a simple dynamic system like this where the mass of the arm and cartridge are suspended over the record by the stylus and cantilever with its suspension spring, usually a bit of thin wire with a polymeric damper. At very low frequencies the whole arm and cartridge body are moved by the stylus, the suspension behaving as if it is more or less rigid. This is just as well since the arm has to be able to move over warps and disc eccentricity as well as track the spiral from its outermost to innermost locked groove.In order to understand what happens imagine holding a soft spring with a weight on the end. Your hand is the stylus and motor, the weight is the stator/cartridge body and arm. If you imagine raising and lowering your hand slowly the weight moves with you, that is the warps, for example, if you start moving your hand faster the weight no longer follows your movement but moves towards resonance, where the weight moves massively more than you are doing then, as the frequency increases its movement gets less and less until the weight is stationary and only your hand is moving. It becomes stationary at approximately twice the resonant frequency.
In a real system there has to be damping (movement at resonance is infinite with zero damping) which I will ignore because it is needed but bad.
I hope I have explained it simply enough.
The fact that the weight, headshell, is moving up to resonance and back means the low frequency output of the cartridge is wrong and exaggerated, to an extent depending on the damping. This doesn't matter much if the cartridge and arm are compatible and have a resonance of around 10 Hz, since by the time the cartridge output reaches musically relevant frequency the cartridge body is remaining substantially stationary relative to the stylus.
Sadly if damping is high whilst the resonant peak is then smaller the damper "short circuits" the suspension and the cartridge body is moved at higher frequency, so the point at which the cartridge starts being accurate is higher than 2 times resonant frequency and it is not perfectly stationary relative to the stylus at any frequency.
There is a lot of quasi-static semi-folklore rubbish written about record player systems. I am not sure why, either it is thought too difficult for lay people to understand, but over simplified hence misleading explanations abound.
Anyway the whole assembly is a complex distributed mass dynamic system and so anything which causes relative movement between cartridge body and stylus assembly will give an unwanted output added to the music.
A very rigid pickup arm may seem like a good idea from a static perspective but it will transfer more plinth vibration allong the arm to the cartridge body. Exactly what does and doesn't give an output requires a proper distributed mass dynamic analysis of the whole turntable (including its support and the floor) whilst outputting the movement between stator (cartridge body) and motor (the bit supposedly moved by the stylus which it is somewhat remote from)...
It may be that a mode where the finger lift is resonating will give output - maybe not. Without such an analysis one can not know.
I was working on this sort of thing in 1975/6 and I have never seen an analysis such as we were doing then published since.
Maybe manufacturers don't do it any more, after all it seems to me most of it is a boutique fashion business these days with buzz words pervading from makers rather than proper engineering explanations.
On top of this we have the compromises made to make record players cheap and easy to make and the stylus shaped to reduce wear.
Pivoted arms are not like the record cutting lathe, so the cartridge body, which needs to be perpendicular to the groove to read the cutter's wave shape accurately isn't except for 2 instants during replay. The distortion this adds is the reason I use a tangential tracking arm myself.
In addition, the cutter producing the groove of the master is sharp, obviously. The stylus needs to be sufficiently rounded to not wear the plastic of the record much. A simple conical stylus is easier and cheaper to make but is by far the least accurate at replicating the movement of the cutter.
More complex stylus shapes are much better but also orders of magnitude more expensive to manufacture. Fortunately these distortions tend to be at higher frequencies where they are less noticeable.
So in the end record players work amazingly well considering how many compromises were accepted to make the discs cheap and the record player easy to make!
I laugh out loud over some of the technically naive bollox I seen written about record players in magazines and the internet by the "audiophile cognoscenti".
- Thread Starter
- #47
Thank you for taking the trouble to communicate the above so clearly. It does make sense (if I have understood) - the cartridge has to be stationary so the signal generated by the stylus in the record groove does not pick up any contamination as it passes through the head.
So all the DIY attempts at isolation I made were - though I didn't know it- attempts to keep the cartridge perfectly still.
As I mentioned before these are really much more generous explanations than I deserve, since I have nothing to offer in return, and the whole experience I find to be rather humbling. Thanks again.
Frank has forgotten more about how record players work than I've ever known, in spite of years in the audio industry. Frank's contributions to various forums have been most welcome by me, less so by those purveyors of bullshit, aka audiophile cognoscenti.
S
S
somebodyelse
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I would imagine such analysis would be much easier today than in 1975/76. The software tools and computing power to model this are now readily available even to a hobbyist. Having said that, modelling the dynamic properties of an elastomer accurately might be a bit of a challenge at the hobby level. I hope at least some manufacturers are doing this and simply not telling people about it, but you may be right that the money's in fashion not technical superiority.
Tom C
Major Contributor
Strain gauge is similar.
somebodyelse
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As in similar to Condenser as capacitance and strain gauge resistance both vary with displacement. Does anyone make a strain gauge mic or cartridge?
Tom C
Major Contributor
Sound Smith makes a stain gauge system. Pretty pricey though.
Tom C
Major Contributor
I heard it at RMAF 2018. It did not stand out from the pack, in my mind.
A crystal / ceramic cartridge or microphone are both forms of 'strain gauge', and these have been around for a very long time. They're not very good compared with magnetic transducers. There have been attempts at capacitor cartridges, one famous one was the Weathers FM cartridge. This used the capacitance to FM modulate a carrier. There have also been ribbon cartridges, Ferranti for example.
Every now and then, somebody reckons they can make a product by being different, like SoundSmith but really no better than MM or MC cartridges.
S
The "zeroes" --- was comparing L+R, comparing only one channel gets rid of them. sum of the channels = 0 sometimes
Yes, massively easier today than back then. It was a mainframe computer with tiny memory and a set of matrices defining the mechanical properties of each of a limited number of large lumped elements. The early laser doppler interferometer (I think that is what it was) which a colleague was using on a massive concrete block in the basement to measure plinth and arm vibration was pretty ground breaking too. He found he could change the mode of a resonance which caused a high level of headshell vibration to a harmless one by punching a slot in the plinth - production cost - almost nowt.
I have never seen this sort of analysis being done today. Maybe it is but I would have thought one of the marketing people would have used it by now if it was.
It would not be trivial to do even now, building a good enough dynamic model of even just the arm would be a lot of work and, as you write, elastomer models ha-ha-ha, but the computer power and software is easily available and relatively cheap.
I suspect that the analysis would kill so many sacred cows that it would be suppressed or simply not believed like so much fact in the hifi business.
- Thread Starter
- #57
So does something as simple as a mat made of a different material offer an opportunity to reduce vibration? I'm going to be trying to think all this through for some time but so far it occurs to me the motor in my turntable must be producing vibration which will be picked up and cause a spike at a particular frequency, and that this is likely to be in the audible range. At least that gives a clue why as to why a glass platter sounds different to an acrylic platter on the same deck. Presumably each of those two materials is allowing more or less free passage of the distorting frequency.
It would help if I had paid any attention in science class at school and hadn't played cards instead. Payback is a bitch.
It would help if I had paid any attention in science class at school and hadn't played cards instead. Payback is a bitch.
DKT88
Active Member
What tangential tracking arm do you use?
Goldmund T3f.
It is one of the few with a low lateral effective mass as well as being parallel.
Nothing I know of is "rigid" over the whole range of audible frequencies.
A "rigid" arm may have its first resonance at 2 to 3kHz rather than 200 Hz, so different, not better. Also the normal arm will be decoupled from the plinth at around 2x its natural frequency 400Hz or so whereas the "rigid" one will still be coupling the plinth vibrations to the cartridge body at 4 to 6 kHz, so probably worse in terms of colouration.
Mats do change resonance but are likely to move it a bit or damp it a bit.
In the end record players are full of resonances and it is so complex that predicting the effect requires complex analysis.
It is yet another case of "they that say don't know and those that know don't say". I am very used to this from my line of work.
Sounds like you are not scientifically minded anyway, otherwise you would have been riveted during class not playing cards...
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