A lot of people seem to suspect that the Wheelock ES uses speaker hardware for its tone generation, but has this been confirmed? It looks like it might be, but the tones are all much higher pitched than what I would expect.
Also, how about the System Sensor MA and MAEH? These also sound like they might be speakers, but I haven’t seen this confirmed anywhere.
Finally, is there a term to specifically describe this type of device? “Sounder” seems to be commonly used, but it is also used to refer to other devices such as mini-horns and horn sounder bases (such as the B200S).
Piezoelectric buzzers (“piezos”) are essentially tiny speakers that are intended for high-pitched sounds. If you just hook up power, you get the “default” sound for that piezo, be it a high-pitched 3khz tone (like smoke detectors and mini horns) or a broadband tone (Advance, L-Series, TrueAlert), or even a buzz (like the Simplex 4100 Classic/+ or the famous “Dover buzz” generated by many of that company’s elevators).
However, a piezo can typically play much more than just its “default” sound. Many devices, such as the U-MMT, Wheelock MT, and Gentex Commander work in this fashion. An onboard tone generator sends the piezo a pattern of which tone it should play, and it plays that sound. If you took this tone generator circuit and connected it to a small, non-amplified speaker, instead of the piezo, it would likely be a higher quality and less raspy tone.
Piezos, however, cannot effectively generate lower frequency tones, such as those required for 520Hz coverage in sleeping spaces, at a sufficient volume. For this, a small speaker is actually required. If you were to take apart an HW-LF, you would find a speaker beneath the grille, attached to a tone generator which generates the LF sound. If you hooked this LF tone generator up to a piezo, it would be much too quiet to reach the decibel amount required.
Also, I assume that the Wheelock low frequency sounders are still speaker devices, despite having very poor quality sound output? Or were the LED2 sounders piezo-based and the LED3 sounders (which have a higher reverberant dBA with the same anechoic dBA) speaker-based?