Expert Senior gramophone

[emgcr]

Many thanks Marco for your interesting post.

Just for confirmation, I have attached some photos of the component parts of the "Quincke" tube clearly showing the lack of complication. The adjustable end is merely a movable buffer and the connection to the tonearm a right-angled joint of hollow tubing. The goose-neck is threaded into the tubing and allowed to swing between positions controlled by the retaining grub-screw. All pretty basic.

[Marco Gilardetti]

Many thanks for these very interesting pictures!

At least according to me, this is by no means a quincke tube, as it lacks the typical two separate tubed paths that the sound should travel. As written previously, it looks preminently like an adjustable resonating chamber, which may also have *some* subtle effect on the acoustic loading of the diaphragm.

As a side note, what strikes me of EMG gramophones is that they have the famous godzilla-size horn (good) and also an unusually long arm (excellent for tracking error control), but at the same time they have this 90° join right after the soundbox, just like the Victor "goose neck" arm, which is basically the worst you can do to sound travelling inside a horn-loaded duct.

[ALVES]

They are very much like an improved goose neck HMV/Victor arm .
Used by EMG and Expert , But later EMG tonearms were more flowing like on my Xa .

[Marco Gilardetti]

Indeed this latter looks like an excellent arm.

[emgcr]

As promised on page 6 on 8th October, here are some four-spring soundbox measurements.

---------------Outside case-----Top to bottom----Approx' weight

Large-------------2.160"---------------2.692"------------7 Oz (200 G)

Small-------------2.043"---------------2.514"------------7 Oz (200 G)

It was interesting to discover that the "working" diameter of the diaphragm of each soundbox (ie. inside the gaskets) is identical even though the case sizing is different. Stylus bar lengths are similar. Weight is also comparable although my (cooking) scales are not very accurate !

Top to bottom refers to the measurement from the top of the case to the underside of the needle holder.

[emgcr]

For the sake of completeness, here are photos showing different numbers on the front of the case (normally hidden by the shield). To what they refer I am unable to say.

[emgcr]

As a side note, what strikes me of EMG gramophones is that they have the famous godzilla-size horn (good) and also an unusually long arm (excellent for tracking error control), but at the same time they have this 90° join right after the soundbox, just like the Victor "goose neck" arm, which is basically the worst you can do to sound travelling inside a horn-loaded duct.

I agree---it does seem crazy. However, what I think Percy Wilson might have said is that the importance of this seemingly illogical sharp bend is very small at that diameter---perhaps surprising to him too at the time ? I think I remember him saying this from what I have read about his empirical results. At larger diameters, the supreme importance of exponential trunking is well-known. Even regarding the Wilson-designed EMG swan-neck tonearm, the conduit is conical---not exponential. This too was found to be of minor relevance (even beneficial) to eventual sound output quality.

[Marco Gilardetti]

That's an interesting point, which I have considered many times. In turn, also the Victor "tapered" arm with goose neck - which is an engineering nightmare under many aspects - doesn't sound as bad as it should.

My educated speculation is that, while usually the volume of air inside the soundbox is considered to be the loading chamber and the goose neck the throat of the horn loaded duct, instead the whole soundbox + goose neck air column may act as a loading chamber, and the aperture of the tapered arm may act as the actual throat of the horn. There would then be no "sharp angle" in the sound path, but just a throat facing over a curved loading chamber. Incidentally, this is what I had in mind when I wrote that the "non-quincke tube" may instead act by changing the volume of the loading chamber.

In my opinion, the reason why an arm with a linear ("conical") envelope works remarkably well is because an exponential curve in that region is sufficiently well approximated by a straight line. This is well seen in formula, as the exponential function is asymptotic to the y = 0 axis for strongly negative values of x. In the mouth region of the horn, the exponential envelope flares up and it departs very significantly by a linear/conical behaviour.

What I would like to remark is that both these points, in my opinion, highlight a peculiarity of the horn loading: its (unusual) wide tolerance for approximations and mistakes. Although the theory is well assesed since many decades and the acoustical impedance adaptation principle is well understood, there are still some sides that suggest that the "real world" seems to behave better or more forgivingly than the strict theory would imply. For example, in general, it is always suggested that curves and bends are kept to a minimum and, if possible, sharp bends are avoided in a horn path. However, there are many examples of high quality loudspeaker cabinets with sharp bends as acute as 180° that sound amazingly well and show a very high efficiency figure. Also, there are examples of cabinets which resulting parameters, especially the bass frequency response, go significantly beyond the calculated figures.

[emgcr]

Although the theory is well assesed since many decades and the acoustical impedance adaptation principle is well understood, there are still some sides that suggest that the "real world" seems to behave better or more forgivingly than the strict theory would imply.

Thought provoking points.

EMG and Expert systems start with either goose-neck or swan-neck shapes (mainly parallel tubing) and continue along the tonearm in a gentle conical way. However, after that, their respective expansion rates are quite different. Both are referred to as “exponential” but have different curves which is interesting in relation to your reference to "forgiving" science.

[Marco Gilardetti]

Thought provoking indeed. The people who developed the gramophone were lucky enough that on this world almost everything that "flares" has the property of "amplifying" a sound (by impedance adaptment). But, for a while, imagine that the laws of Acoustics were so restrictive that an exponential envelope would amplify sound as usual, but that instead a conical envelope would do nothing or would even dampen the sound, so that an exact type of curve had to be used. Most probably the gramophone would have never be invented, and almost surely the electromagnetic pick-up/loudspeaker combo would have preceded it.

Coming to your observations, bear in mind that the exponential curve is not one specific curve, but it's a family of curves which shape (graph) depends on the parameters of the function. Thus, two horns that look pretty much different at eyesight may be indeed both exponential: they just have different parameters.

Moreover, although historically the exponential envelope has been firstly recognized to be a very efficient shape (which lead to the building of the family of orthophonic - that is scientifically engineered - gramophones), it is not the most efficient of all. Later, it was discovered that the tractrix curve is even more efficient, and also gives an extended frequency response (or, in turn, can give the same frequency response, but with a shorter horn). So even a curve that is not exponential isn't necessarily worse than the exponential, in rare cases it can actually be better (even though you never go wrong with an exponential profile...)

Looking at EMG horns, like the one on your profile, it looks to me that they're nor exponential nor tractrix-shaped, but a mix & match of various curves. The first part emerging from the cabinet looks vaguely exponential, but the final flare of the horn seems to have a much less complicated profile: it looks almost like a circular envelope. However, reading about the high reputation that these gramophones have, although their horn is perhaps not theoretically perfect, its shape is good enough to deliver an outstanding sound quality.