# Resonant frequency of piezo elements, and generating multiple tones

In another question I posed, there were couple of "piezo sounder" parts suggested for the purpose of a compact but reasonably loud, alternative to electro-mechanical hooters.

Was trying to understand the various device characteristics that these "pieze sounders" have, and how I could use them to generate a sound-pattern (involving at-least 2 different frequencies), without sacrificing too much on the "loudness" aspect.

This is where I ran into "resonant frequency" of piezo elements, which is mentioned in all the data-sheets. So my question is, is this the frequency at which the device is loudest but it is still possible to generate tones at other frequencies, possibly with reduced loudness ? None of these data-sheets provide a graph of the loudness-vs-frequency characteristics for the device. So I am wondering if the piezo sounders with "resonant frequency" mentioned (but missing the graph), can produce sound at only one frequency ?

The two SE QnA's referred to:

You can use the piezo to produce sound at a wide frequency range, but indeed it will be the loudest at the resonance frequency. If you look at a few more datasheets you'll find that some manufacturers do publish SPL versus frequency data, like Murata, for instance.

As you can see the spectrum can be very different between two piezo buzzers (the graphs are for types from the same PKM series), so it's worthwhile to compare many different types.