הי, אני מבינה שהמילה נשמע מתורגמת לאנגלית ל- sound. זאת אומרת שזה צורת הפסיב של הפועל להשמיע.
That is not a valid conclusion.

In Hebrew, נשמע is formally a passive form, but the verb להישמע has two distinct meanings, one of which ("to sound") does not have a passive meaning. In English, the verb "to sound," when used to mean להישמע, is an intransitive linking verb, so it has no voice (it cannot be active or passive).
The other meaning of להישמע is not "to sound," but, as Nun-Translator indicated, "to be heard."
השאלה שלי היא האם יכול להיות משפט שבו מופיע הצירוף was sounded. אם כן, מה המשמעות של הצירוף הזה.
Yes, "was sounded" exists, but it has nothing to do with "to sound" meaning להישמע. "To sound" can also be a transitive verb, meaning "to cause to make a sound," so you can "sound the alarm," for example. Consequently, you could say "The alarm was sounded."
1. קולה הצומרני נשמע למרחקים (2 משפטים: בלשון הווה ובלשון עבר)
2. ההצעה שלך נשמעת אטרקטיבית מאוד
1. "is heard," "was heard" (transitive verb, passive voice)
2. "sounds" (intransitive linking verb)
(בלשון הווה) sound לדעתי יותר מתאים ל-משמיע מאשר ל-נשמע.
I'm somewhat perplexed by this statement. Are you saying that משמיע is always a better translation of "sound" than נשמע?
What about sentences like "Your idea sounds good" or "The piano sounds beautiful"?
1. The alarm / alert / whistle / shofar / buzzer / chord / siren / call / signal (etc) was sounded.
2. "Aleph" is sounded as "a".
1. That is the definition I mentioned above, but "was sounded" is not used with all of those nouns.
2. I would not use "is sounded" in that context. I would say "is pronounced."