Needle length

[Marco Gilardetti]

Part of what makes the hissing is that the sound of the record surface noise is not being covered up by the overall louder volume of all the other tones, since the surface noise exists to some extent outside of the tone arm and horn. Some is the higher frequency sound coming off of the diaphragm surface on the outside of the soundbox.

The characteristic extra hiss is distinctly audible even in the first grooves with no musical content, and in my educated opinion is not due to a rebalancing of the frequency response, but to the increase of the soundbox compliance while the mass of the tonearm stays steady, which drags the resonance of the soundbox-tonearm system into the audible frequencies.

The part that works in our favor is we can’t reproduce extremely high frequencies in the first place, so any damage that would quickly occur to sounds as high as 20khz can’t be reproduced in the first place due to limitations of diaphragm and needle bar mass.

The theoretical upper frequency limit of 78 RPM records can be calculated considering the size of the groove, and is 12 KHz. In most records of the golden era there is nothing above 4 KHz. So there's not much to damage, to begin with.

all things being equal, more weight compensates for a less compliant system.

I won't say so, or at least it depends on where the resonance of the soundbox-tonearm system is initially located. Which is why sometimes people here replace the original soundbox with one that is theoretically "better", but happen to be unhappy with the change.

[anchorman]

That hiss is surface noise from the blank groove. There’s a certain amount of roughness on most shellac pressings due to various things: embedded dirt, poorly integrated filler material, or simply the surface of the shellac itself.

All of that roughness is moving the stylus side to side just like recorded sounds would, but in a relatively random fashion.

[anchorman]

Marco,

What do you mean with the term compliance? My understanding of it is that it is a measure of the force needed to overcome the gaskets and pivot bearings impeding the needle’s (and diaphragm’s) movement. More compliant is more easily able to move. I would not include undamped resonances forming in the needle or the needle bar as relating to the ease of movement of the diaphragm and needle bar that are supposed to be able to move freely. The detrimental resonances are a factor of the various rigid/moving parts not being ideal in nature.

[Marco Gilardetti]

More compliant is more easily able to move.

Correct. Compliance is the reciprocal of stiffness.

I would not include undamped resonances forming in the needle or the needle bar as relating to the ease of movement of the diaphragm and needle bar that are supposed to be able to move freely. The detrimental resonances are a factor of the various rigid/moving parts not being ideal in nature.

There is no reason to devise an ideal model, the relation between compliance, mass and resonance is well known and well assessed. Whichever object that has a mass and an elasticity (read: compliance) will have a specific resonance frequency. Change the mass and/or the compliance, and the resonance frequency will change.

[Orchorsol]

Excellent thoughts!

[anchorman]

There is no reason to devise an ideal model, the relation between compliance, mass and resonance is well known and well assessed. Whichever object that has a mass and an elasticity (read: compliance) will have a specific resonance frequency. Change the mass and/or the compliance, and the resonance frequency will change.

I find it helpful for both myself and it seems also helpful for others when we break down how a complex system like this works into its component parts. Much easier to grasp how the individual bits and pieces contribute to the system's function as a whole, and from there easier to analyze how changing some aspect *ought* to affect overall function. And if it doesn't seem to affect function in a meaningful way, give us reason to study further what we are not seeing.

Regarding compliance: in my limited experience, it is usually reserved to talk about the stiffness of the suspension... when the needle itself becomes resonant enough that it is acting in a meaningful way as part of the suspension, and not primarily acting as the part being moved precisely by the recorded audio in the groove, we have a problem!

[anchorman]

Marco,

I was thinking about this some more today, and remembering that one must balance the compliance with the entire moving mass of the diaphragm, needle bar, and needle itself. Too much compliance and you get undamped response from motion of the needle and diaphragm that continues to ring past the point when it was given an impulse by the record groove. Too little compliance, and it can’t move fast enough. The resistance of the column of air in the reproducer, tone arm, and horn will all affect how much compliance is perfect for a given reproducer. And this will all affect the maximum frequency at which the reproducer can vibrate and reproduce tones with any clarity.

Depending on the modulation of the record groove both amplitude of the sound and the frequency, will surely also affect how well the system responds to impulses generated by the information in the record groove.

[Inigo]

There's still another factor in the equation, the mass of the whole soundbox, which dampens the vibration trying to escape to the tonearm as a body. A massive soundbox makes more vibration of the needle come into the diaphragm... Even if you add a counterweight, to reduce the weight acting on the needle, it also adds to the mass of soundbox and tonearm, making the system yet more effective to compel the energy into the diaphragm! Don't forget that part of the needle vibration passes to the soundbox body through the needlebar supports, so a heavy mass behind the pivot always helps.

[Marco Gilardetti]

a heavy mass behind the pivot always helps.

If you think twice about it, you will understand that it is not so. In a massive tonearm, the resonance frequency can be dragged down to the point of resonating with the wows and flutters of the record itself. Massive tonearms are awful trackers and tend to jump across grooves.

Mass and compliance have to be matched (not at an exact figure, but mostly within an acceptable range). Adding mass unthoughtfully, or increasing the compliance randomly, will not generally improve the sound, but will most likely lead to unwanted resonances, sound colorations or poor tracking.

[Inigo]

I see your point, Marco. But in the well known Wilson's electrical circuit equivalent to the soundbox, the soundbox and tonearm are not represented. It has been my long time idea to try to fit these elements in the circuit, to understand their role. No success yet, but some thoughts about it are clear to me. And one is this: whatever the link in the circuit, the soundbox mass is the second reaction the needle vibration finds in its path to the diaphragm, the first being the resistance to bending as felt from the short end of the needlebar. But the needlebar is supported on the soundbox, and some vibration will escape to the soundbox mass through the fulcrum supports. Here, the first reaction it finds is the inertia of the soundbox to vibration, and this is precisely its mass, as felt from the needle point. Further in that signal escape path, we have the compliance of the soundbox rubber neck, the mass of the tonearm, the compliance of the tonearm bearing, and the mass of the machine. Do you see this circuit branch? It has to be connected to the main circuit at some point, don't know where... But they're clear all these points:
1) the lower the soundbox mass, it comes into vibration and some energy escapes through this. 2) the higher the compliance of the rubber neck, makes easier to the soundbox body to vibrate, and this vibration remains in the soundbox body, not passing to the tonearm. If this compliance is low, 3) some of this vibration passes to the tonearm body, and here, the tonearm mass will react against it. If the tonearm is very light, then 4) some energy will be used to vibrate also the tonearm, and if 5) the base bearing is too stiff, some vibration will come into the machine body. Here I consider that the vibration is reflected, because of the enormous mass of the machine. This hurts the grooves...
Reverting all this escape path, it is clearly desirable: 1) a massive soundbox, 2) a compliant rubber neck, 3) a massive tonearm, and 4) a compliant tonearm bearing. These will make the vibration at the needle being spent in vibrating the needlebar instead of going through this escape path. And the first stop in this route is the mass of the soundbox. Carefully considered, it's the reactance of the soundbox mass when compared to the compliance of the diaphragm! Also a stiff diaphragm will make more energy to escape trying to vibrate the soundbox body! So we need a massive soundbox, a stiff and light needlebar, and a compliant diaphragm edge, so more energy goes this path. Of course, the diaphragm must be edge-compliant but stiff-center, to convey the energy ultimately to the air column behind it.
We usually don't see that, because our soundboxes (in the orthophonic machines) are comparatively massive (150-250 grams) against the masses and compliances in the main path (diaphragm, needlebar, etc). But low frequencies have more chances to escape through this alternate path. The case is obvious when you use a handmade light soundbox, as those of our colleague mgrrstuff, for instance. The bass freqs don't enter the diaphragm because of its comparative stiffness, and because of the low mass of the soundbox body, escaping through this alternate path. Of course, all masses and compliances must be matched, but my point is that for this escape route, a massive soundbox as seen from the needle, is beneficial to convey more energy into the needlebar+diaphragm path, stopping the soundbox body from vibratinh with the needle.
This escape route is something not represented in the main circuit because a comparative great mass of the soundbox is assumed, so the energy escaping there is very small. But think of experiments made with lighter soundboxes, as the mysterious Thomas E. Kimble soundbox owned by Joe Busam, of which I'd love to know more details: https://youtu.be/3MOLfhk5icI
And this has happened to me when studying the Exhibition soundbox, a clear example of the alternate escape route being favoured: a light soundbox, a stiff diaphragm and needlebar fulcrum, and a stiff rubber neck. All these factors play together to let the vibrating energy escape through the vibration of soundbox and tonearm. For me it's a clear case of unmatched impedances, completely opposite to the orthophonic design. Even those dreadful ringing tones of the Exhibition, and the clear reaction against the grooves in medium-high sustained notes, which break the groove walls... You know...
So read this as wholly a great question, that worries me and I try to get deeper knowledge...
Of course, the orthophonic system is well designed and for our 78s, it's almost perfect. But in trying to analyze this in the aim of improving the performance of the Exhibition soundbox... A long eagerly caressed desire of mine... Or at least, being able to adjust it properly!
This escape route, of course, if properly misadjusted, produces a resonance and harmful reaction on the groove walls, which get worn in the resonance places.