This page is intended as a mini glossary of the words that I came across that had me baffled in my gramophone collecting and restoration. They will be added to as I come across them and whilst fuller explanations are available this is an attempt at a simple explanation of sometimes very baffling scientific terms.
Plano Reflex: A simpler one to start with. Plano Reflex refers to the design of a tonearm by Columbia in the late 1920's that used flattened sections in the tonearm to hopefully give a better reflection of soundwaves as they passed down the tonarm. Examples can be seen on all the Columbia models on the site with a graphic illustration shown in the image gallery oppsite.
Orthophonic: The first of the mesmerising terms! In it's simplest terms from the Greek for "correct sound" which I think gives the rest away. It was a term coined by Victrola in the USA for their attempts to recreate the true sound of the performance that was recorded. It's been the goal of every system of sound recording before or since. Sometimes soundboxes are referred to as orthophonic soundbox. (see opposite image).
Exponential Horn: Again this relates to the goal of having an "orthophonic" reproduction system. An accurate reproduction of the original performance is achieved when the sound waves that reach our ears from the recording match those from the original performance. Obviously many things prevent this but horn design can help. It was found that by applying certain mathematical calculations to horn design a more accurate end sound could be achieved. The result of applying these principles was horn of flared design like, (ironically) the crapophone horn shape shown on the Edison phonograph pages, though this no doubt was never the result of applying anything in the way of mathematical principles. (see opposite image).
Matched Impedance. Like orthophonic there is a give away in the words. Starting with impedance, it simply means blocking or something that gets in the way. Matching the impedance therefore has to do with even distribution of any obstacles that interrupt the natural flow and expansion of sound waves travelling through the tonearm and horn.
Re-entrant Horn: This refers what is considered by many to be the ultimate in acoustic gramophone horn design and was used on the HMV models 163 ( See my example here and opposite images) the 193, the 194, the 202 and finally the 203 of 1927. It uses the principle of matched impedance. Using scientific principles in the creation of folds and divisions a larger tone chamber was fitted into the cabinet space than used previously. Curves were flattened to overcome the problem of the outer part of the wave lagging behind on outer curves (think of the old playground game of a line of children holding hands and spinning in a line....the one in the centre hardly moves but the one on the outside has to run quickly to maintain the line. Not quite the same with sound waves as the speed is constant thus a sound wave going round a curve in a tone arm/horn the outer part lags behind.) In the re-entrant horn any sound wave lagging is avoided. By the way, why re-entrant? Re-entrant is a rarely used word nowadays probably mostly used by geographers when referring to re-entrant landforms which are contours that fold back on themselves. In the re-entrant horn I therefore imagine it refers to the way the horn is created in folds. The only other use of the term in a musical senseI know of is the tuning of certain string instruments like the ukulele and the banjo where it refers to a tuning in which there is a break in the sequence of low note strings to high note ones. e.g. the bottom string on a ukulele is a high note of G. The next string drops to a lower note of C and then a progression of increasing notes in sequence, each string highr than the previous one.