-And thats why i asked what (commercial) sound emmiter components can you suggest to me?

Digikey lists 2944 Piezo sound products. I do not know why you will use one or why you want it to be small with a very high frequency.

 

...why you want it to be small with a very high frequency.

- I dont want anything special except to work normal. I didnt look for any special characteristics. As i said, it was some time ago when i bought them, and i didnt knew i could look in their specifications on ebay. And most data i dont completly understand to be honest. I do understand some of it, but not in full 100%.
- I only look for the cheapest price and to be a piezo. This is my criteria of searching (when im not searching for specific item). I imagined before i buy it, that will be larger and work normally, like other 2-3 buzzers i have. But imagine my surprise when they arrive, so little and not working with my standard testing. And I left them there.
I know there are some piezo larger than what i bought, about 4cm in diameter , and they work loud enough with my standard testing (wire touching at 3-5V making click sounds) and quite loud.
I did not look (ever) for the frequency of it's resonance as I learned here about it from you ! To be clear.
I didnt put this problem. But now, i got wiser because of your help.
Being said that, what are the normal audible frequencies i should look for? In any buzzer or piezo or speaker?
As a rule of the thumb.
Again, im not a electronist, i do this for hobby. And also i didnt work in the audio branch. It's not attracting me that much. I like the automatization of things, that's what is attractive to me in electronics.
So, from all this educational discussion, i resume: 1-That i should look in the future for larger diameters of piezo or buzzers or speaker. 2-To pay more attention to its frequencies of operation ; i usually do look at freq but i assume it will work normal, so even if i look at it, i dont think about it very much. Probably because i dont have a good experience in this particular sector.
My intended question to you was, not to enumerate every thing you can find (2944 products), but point to me 1 or 2 most used, easy to test and work with, from the top of your head and experience, even if you didnt use it, but looking at its characteristics, you can be sure it will be good and normal (not special like i got). In these lines. Its very trivial subject for you I assume, and I am sorry for bringing it up, but when i have problems i ask around. You are helping me greatly with your very good answers so far. And if this post will remain, it will help others as well.

 

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I just tried your circuit. And nothing on the piezo, and nothing on the buzzer either.
I tested pin3 with a led and it stays lit. So the circuit is working.
I am also thinking that these little piezo are for headphones, those little ones that you insert in your ear. But still, it should make a perceptible sound as they are.
I glue the piezo to a glass too, and no effect either.
I just measure it on capacitor mode and it has 4 nF. (4.3nF)

 

A piezo beeper has a built-in transistor oscillator and in enclosure tuned to its resonant frequency. Most beepers produce 2kHz to 4kHz, the 4kHz ones are smaller.
Digikey in the US has many more piezo beepers than in Canada but they do not have them with an oscillator anymore. Canada has a few remaining is stock.

A piezo is not used in headphones because it produces only a few peak frequencies which sounds awful.
A good sounding audio frequency response graph shows a flat line with no peaks and no nulls.
Here is a good sounding transducer and here is an awful sounding piezo:

 

I discovered today that there are 2 types of piezo transducers, with OR without (fv) generator (while looking on a website).
I was not aware of this little detail. Again, I work very little with these things.
My piezo version is without generator ! But my buzzer(in black case) is with generator.
But we built one generator and didn't work. Maybe the range is too wide and i must be super precise in finding the right fv ? like +- 100hz and is off? I imagine it could be the case. Hmmm.

I also discovered today that you are very right. 8.5khz is very high fv.
The buzzer (in black case) have only 2khz ! And is working normally, as volume i mean(but is not buzzing while on voltage, it only clicks, so im not sure if that is normal or not). So, 8khz is very high. I've also find 4khz are normal buzzers too, on the website.

 

A transducer (speaker) is passive. It must be driven by an external AC signal. It is the loudest at its resonant frequency which needs manually setting the frequency of the AC signal.
A Beeper or buzzer has a built-on oscillator that needs to be powered from DC. The oscillator automatically adjusts its frequency to the loudest resonant frequency.

A piezo generator is a horrible sounding microphone that produces a signal when a sound vibrates it.
I think piezo generator is a bad translation of "piezo oscillator".

 

to Audioguru again
I completely agree with you and VERY good explanation. Thank you !
This is the website (if interested) i find it: https://www.tme.com/us/en-us/katalog/piezo-transducers-with-generator_112500/
In the left is a tree panel that unfolds and give you the products categories.
Also i noticed in this website, at least for what i searched for, my piezo, they have pdf for their products. Very helpful. I really look for the frequencies of some and are from 2khz to 4khz.
A friend recommend it to me for quality products - he said, not me. Because he does not love (like me) the ebay products. I like ebay because is very cheap. My opinion to be super sincere, is that ebay have the same items as every other dealer, but you really have to know what to search for. Maybe not ALL, but a large majority. Its my impression, not a fact. Its my thought that i still use in searching on ebay. I might be wrong but so far, i got good products and some were not what i wanted because my lack of technical knowledge,negligence and sometime stupidity by rushing without thinking.
My friend also like you, told me that these high frequency piezo are low volume because are high freq. The higher the freq the lower the audible sound. And I should know these things also, but i really forget a lot if i don't use them in decades. A very good lesson for me even if i didnt get a good result. I will have to play with other oscillators to get (hopefully) closer to that piezo work range.
I can not thank you enough for the competent answers you give me so far. Thank you so much to everyone in this discussion.