The Talking Machine Forum — For All Antique Phonographs & Recordings

Inigo wrote: Mon Oct 17, 2022 2:30 pm 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.

You basically compiled a list of second-order effects, which make you loose the sight of the first-order effect. The mass of the tonearm as a whole is not negligible when compared to the mass of the soundbox alone, to begin with. If you don't set - first of all - the resonance of the needle compliance / tonearm mass in an area in which such resonance won't give sound colorations / interference cancellations / tracking issues, all other lesser tweakings will be to no avail.

Changing a heavy soundbox with a much lighter one in which the compliance has not been changed accordingly, will unavoidably lead to disappointing results.

That's the point, yes.
Maybe all these questions of mine are out of place, because current masses and compliances of these elements make them fall out of the main equation, or play a mere small percentage in the whole thing. I agree on that.
My problem comes when trying to apply this knowledge to an old acoustic Victrola with exhibition soundbox. Here the comparatively low mass of the soundbox against the higher stiffness of the diaphragm and needlebar damping springs, make these elements much more conspicuous and not deniable. That's my point. I feel (or I wish) that the performance of the Exhibition could be improved by small changes.
This said, I've been doing such experiments, relaxing the gaskets pressing on the diaphragm, changing the springs for a more compliant system, etc. Trials to make the diaphragm and needlebar system more compliant. But this didn't clearly work, except with electrical recordings, and not very much.
I'm frustrated because I'm not capable of tuning the Exhibition soundbox properly. I find it very tricky... If I improve sound in soft recordings, then a high level Caruso or orchestral record makes it blast. If I tune it for high level recordings, then the soft ones sound muffled...
I've thrown out the towel! I simply don't play that machine anymore... I cannot bear it. Maybe it's the short horn (it's the HMV version of the Victrola VI). I don't know.... I have two extra Exhibition soundboxes for experiments, keeping the original one untouched. Even I installed glass diaphragms on them, and soft rubber gaskets. It slightly improved the definition and crispness of sound, but nothing more. My other machines are all orthophonic, small and huge, and the difference in sound, even with acoustic records, is so big when compared with the older one...

There is little one can do with a short horn of poor design. I'm always astounded by how much better the sound is on orthophonic portables compared to the older victrolas. I'm going to try a nice number 4 soundbox on a friend's VV XVI (i think that's the model at least!), in hopes of improved reproduction. The arm/horn taper is simply not ideal, though, and little can be done to make it better.

My british friends seem to obsess over the sound more than the americans do, to the point where they have different soundboxes tuned for different records, and change them out accordingly. or simply play certain records only on certain machines. Because as you have discovered, inigo, you can get some of these soundboxes tailored for louder music, and they won't play well on quieter passages, and then you can tailor them for quiet, and they are over-driven on the louder recordings. The design is limited, as there is not proper damping when the compliance is too high. It like a car suspension, where they use hydraulic dampers (shock absorbers) to impeded the undamped motion of the springs. Still allows for proper movement, but ideally keeps the motion from ringing after an impulse is applied. The only place I could see where such action happening on a soundbox is in the type of rubber used for the diaphragm gaskets. changing the resistance characteristic of that rubber may have a positive effect, and provide better damping of the system, while allowing freedom of movement needed.

That's a clever idea...

The problem with mica soundboxes, I feel, is that their resonant frequencies fall within the recorded range, much more accentuated in the stiff and small Exhibition than in the bigger and more compliant no4. The last resonates on certain strong low notes as a strong piano mid bass plunk, etc. The former resonates with those mid high Caruso notes...
The enormous difference with the corrugated aluminium diaphragms of the orthophonic is their completely different characteristics: this one is very light and very stiff, and damping too, it has no apparent resonance, and at the same time it's edge is compliant, so it acts as a dead light effective piston without problems.

anchorman wrote: Wed Oct 19, 2022 11:12 amThere is little one can do with a short horn of poor design.

Correct.

The tracking error of the gooseneck tonearm is horrible to begin with. It can be improved to some degree (but only to some degree) by the interposition of an adapter that would change the angle of the soundbox, however I've never seen such adapters for sale, it's mostly one-piece home made stuff.

Then they come the soundbox and the horn. Everything there is made "by ear" and trial and error: the chamber behind the diaphragm has a random volume, the horn is not calculated but is just made in order "to sound better than all other shapes that were tried". Indeed also the mica diaphragm has some unavoidable limitations, compared to the much thinner and much more elastic aluminium diaphragm.

I thus tend to agree that any trial to improve the Exhibition soundbox is very likely to be frustrated. It's quite impressive that it happens to sound "so good", all considered.

I’ve seen Victor goosenecks that hold the soundbox at an offset angle. In fact I have one in my collection of random parts. It looks like it would be interchangeable with a standard gooseneck without the angled offset. I’d have to see what exact angle it is and try to calculate how much better or worse it would make things one one of those machines.

Yes, I've seen both entire gooseneck replacement parts, as well as adapting bushings that will change the angle at the throath of the original gooseneck.

The original tracking error is so great that even crafting a replacement "by eye" will vastly improve it. However, as the tonearm has also a completely random length, which should be addressed in order to optimise the tracking error, I believe the replacement gooseneck to be a better solution, as the curve can be changed in order to compensate the length of the tonearm. If well engineered, it might deliver a nearly optimal tracking error.

You may test your replacement gooseneck by measuring the tracking error with a protractor specific for gramophones. Member Orchorsol once posted one that can be printed at home.

Users may find this ball joint tracking adapter of interest.

Where did you find that connector? It's off the shelf hardware?
I made one by eye, from a 18mm 135 degree copper elbow ( standard hardware herein) from which I cut enough to leave a 15 degree connector. It works fine!