Morino built instruments with resonance chambers in the 1910s, long before his Hohner tenure.I'd say cassotto wasn't even dreamt of when these maestros were in their prime!
Double tone chamber
- Thread starter Elizabeth
- Start date
Class B gets a bad rap because of old unregulated class B amplification. In practice, the driver stage in solid-state amps has large negative feedback and travels across that gap faster than the speaker membrane can follow. My ancient Solton Turbojet from the seventies is class B (with a driver transitioning gap of about 2V) and you don't hear it in use. The idling noise does have a certain somewhat rustling character instead of only a constant hiss. And this is a transistor driver stage, with a single-stage differential amplifier, nowhere near the amplification factors of modern (or even old) opamps.
I also think your description is likely to create confusion about the main sound source in an accordion: the lion's share of the sound energy is not created by the vibrating reed (which has lots smaller vibrating mass than a violin string, say) but by the compressed air stream chopped into bits by the vibrating reed. A significant contributor to a helicon bass reed's loudness is the trapezoid reed plate that prolongs the time that the reed blocks the air flow. Good reeds don't have all that much more vibration of their own than low-quality reeds, but they have minimal air gaps and thus cut off the air stream more completely.
That makes their tone more overtone-rich, meaning that reed chambers and cassotto and the grille and other acoustic factors get more material to work with. It also means that the direct tone quality is quite harsh, so there is actually more of a need to mitigate it with cassotto and other measures. Cassotto instruments with machine reeds are more of a marketing gag than an asset, and the overtone structure does not have the strength where the cassotto imprint on it would make for a well-recognizable formant signature.
By the way: human voice also operates on the interrupted-air-stream principle with good closure (in lower vocal ranges, typically complete) and using mouth shapes on the overtone-rich material to convey vowels. Our ears are trained to recognize formant structures (and tell speakers apart by their voices), so a cassotto instrument stands out. That is more of an asset for small ensembles than large orchestras, and it doesn't help if identically built instruments are scattered across the voice groups. The Russian "Timbre" ensemble utilizes this effect to the max.
My description must have been confusing because what it tried to convay is indeed that the sound is the air stream being interrupted and stopping almost completely while the reed moves from one side of the reed plate to the other side... I still do not know how the trapezoid reed plate contributes to the reed's loudness. In pure amplitude it should not help. The time the air is blocked is longer, so a longer "flatline" in the sine wave, but I think the fact that an L and M reed share the same reed plate may also play a role. I just don't know enough about the physics.
I can see the waves in my sound editor and see the differences in amplitude between reeds deeper inside a cassotto and those less deep, but just listening to the accordion I don't hear a difference in volume, just in timbre (because overtones are eliminated more as you go deeper inside).
Here is your mistake. The sine wave is irrelevantly small. It is what you hear as sound after stopping the bellows but not releasing the key/button. Pretty much nothing, even if some bass reeds don't stop vibration on the spot. It is the blockage of the air stream that you hear almost exclusively. A soundwave conveys sound energy by changes in pressure and velocity. An interrupted air stream is an almost pure form of velocity change. That's the working principle of hand-cranked air sirens (rotating disk with holes in an air stream) and of reed and brass instruments and of the human voice. The tiny bit of primary vibration does not deliver significant sound. But the interruption of the air stream controlled by that vibration does.
