Needle length

[Daithi]

Just thinking out loud......
What are the parameters governing needle length given that the needle is at the short end of a lever which terminates at the diaphragm and whose pivot is the needle holder pivot.
1 Short needles are louder because they are less flexible than long needles and therefore dissipate less of the vibration generated at the needle point.
2 Short needles are also louder, not just because they are less flexible than long needles but also because they move the other end of the lever(IE the diaphragm) more than a long needle.
3 As with most things there are reciprocity failures associated with needle length at either end of the scale.

Question: How short is too short?
Question: How long is too long?
Question: What is the optimum needle length, as a percentage of overall lever length?

[JerryVan]

Or, maybe a longer needle produces more volume as it has a greater mechanical advantage over the resistance of the diaphragm. Might also equate to less groove wear.

[Daithi]

That is a very good point Jerry. There is no doubt the longer needle is more compliant which results in less record wear. My observations based on sharpened toothpicks of varying length are that long needles tend to be quieter.

[epigramophone]

The position in which the needle is held in the chuck affects the volume. It is loudest and stiffest when pushed in as far as it will go, and progressively quieter and more compliant when it is only part way in.

[Orchorsol]

The position in which the needle is held in the chuck affects the volume. It is loudest and stiffest when pushed in as far as it will go, and progressively quieter and more compliant when it is only part way in.

Exactly. It relates to pivot geometry rather than force/moment. The longer the needle, the less the excursion of the centre of the diaphragm.

This is only intuitive but personally, I think that flexing of the needle isn't really significant except perhaps with soft and extra soft needles. I can see the logic regarding less groove wear as a result - but - any flexing of the needle is undamped, so it would act as a spring, which would surely cause the opposite, i.e. higher groove wear. Maybe the two effects more or less cancel out. And above all, a highly compliant soundbox is by far the most important aspect.

[Marco Gilardetti]

My observations agree in full with those reported by Orchorsol.

Also, loudness considerations aside, there is no "ideal length" per se as it depends on the geometry of the tonearm. The goal is to "minimize the tracking error all over the record" (quotes because there are multiple theories/solutions to address this issue, each one with strong points and drawbacks) and while some arms may be helped by a longer needle, others may be helped by shorter needles.

As most tonearms were designed to be used with "standard needles", and by "standard needles" I mostly think about HMV or Columbia full tone needles, it is probably a good idea not to move too much away from their length.

[Inigo]

I've also noticed that certain generous lengths on small bore needles produce an undesirable dynamic effect. If the bore and length of the needle part protruding out of the set screw are in this curious match, part of the needle vibration, at certain frequencies, resonates within this outer portion of the needle, not even entering the diaphragm, and bounces back against the grooves, producing, at that fatidic combination of factors, a resonant sound and a terrible wear on the grooves carrying that particular frequency, and black residue at the point after playing. That needle point resonance must be avoided, keeping it out of the recorded frequencies, better if it is kept higher. Thin needles must be kept short, while thicker needles can be placed with a longer point. This is contrary to the desired effect, namely low volume with thin needles or higher with thick ones. But the mechanics and dynamics of our beloved acoustic sound system are full of these unavoidable compromises...

[Marco Gilardetti]

That's true as well. I, also, have observed that soft tone needles kept artificially longer than they should, tend to emphasize hissing sounds at the top of the audible spectrum. It is very likely that their resonance is lowered enough as to spread into the hearable frequencies.

[anchorman]

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.

[anchorman]

One thing known to cause groove wear in more modern record players is the mass of the stylus assembly, especially at the stylus itself. As u/orchorsol points out, undamped vibrations in the system are a bad thing. Too thin and flexible on the needle side of the pivots is a recipe for harmful resonances.

Ideal system has a diaphragm and needle bar assembly that weigh nothing and move completely freely, but are adequately damped so as to only move in response to the undulations in the grove, and not have any ringing effect that accompanies an undamped or under-damped system.

The one thing we have working in our favor is that an imperfect system tends to destroy the high frequency information in the grooves first. Playing a “modern” vinyl LP record with a less than ideal playback system will progressively loose high frequency sounds with each playing of the record. From what I understand, over time the maximum frequency that can be recovered from the grooves gets lower and lower with use, and it’s replaced by noise. 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.

Weight of the soundbox is the enemy when it comes to preventing record wear, but all things being equal, more weight compensates for a less compliant system. It would be interesting to see where the benefits of lighter weight begin to conflict with the ideal weight for a given compliance needed in order to reduce unwanted undamped resonances in the system.