Nie spodziewałam się, że ten mały flet będzie tak głośny w całej sali.

Because spodziewałam się is the past tense, feminine singular form.

• spodziewałam się = I expected / I was expecting (said by a woman)
• spodziewałem się = the same thing, but said by a man

So the sentence tells you that the speaker is female.

Się is part of the verb spodziewać się, which means to expect.

In Polish, some verbs regularly appear with się, and you usually have to learn them as a whole unit:

• spodziewać się = to expect
• bać się = to be afraid
• uczyć się = to learn

So here, się is not optional. You should think of spodziewać się as the full dictionary form of the verb.

The dictionary form is spodziewać się.

This is an imperfective verb. In this sentence, the past form spodziewałam się means something like:

• I didn’t expect
• I wasn’t expecting

It is very natural in Polish to use this form for a general past expectation.

Że means that and introduces a subordinate clause.

So the sentence structure is:

• Nie spodziewałam się = I didn’t expect
• że... = that...
• ten mały flet będzie tak głośny... = this small flute would be so loud...

This is very similar to English I didn’t expect that...

Because flet is a masculine singular noun, and both the demonstrative ten and the adjective mały have to agree with it.

• ten = this (masculine singular)
• mały = small (masculine singular)
• flet = flute (masculine singular)

So they all match:

• ten mały flet = this small flute

If the noun were feminine or neuter, the forms would change.

Będzie is the future tense of być (to be).

Here the speaker is talking about what they did not expect before hearing the flute. From that earlier point of view, the loudness was still in the future:

• Nie spodziewałam się, że... będzie...
• I didn’t expect that... it would be...

In natural English, we often translate this as would be, even though Polish uses the future form będzie.

If you said jest, it would sound more like I didn’t expect that it is so loud, which does not fit as well here.

Tak means so, and głośny means loud.

So:

• tak głośny = so loud

Głośny agrees with flet, so it is in the masculine singular form.

Polish often uses tak + adjective just like English uses so + adjective:

• tak duży = so big
• tak trudny = so difficult
• tak głośny = so loud

Yes, it can. In Polish, just as in English, an instrument can be described as loud if it produces a loud sound.

So ten mały flet będzie tak głośny naturally means:

• this small flute would be so loud

It refers to the sound the flute makes, not to the object making noise on its own in some strange way.

W całej sali means in the whole hall / throughout the whole hall.

After w in the meaning in, Polish usually takes the locative case.

So:

• sala = hall, room
• w sali = in the hall
• w całej sali = in the whole hall

Both words change:

• cała sala → w całej sali

This is locative singular feminine.

No. Here it means that the flute’s sound carries throughout the whole hall.

So the idea is not that the flute itself is everywhere, but that it sounds loud in the entire hall.

A natural interpretation is:

• its sound was loud enough to be heard strongly across the whole room

Yes, Polish word order is flexible, and this sentence has a neutral, natural order.

Current version:

• Nie spodziewałam się, że ten mały flet będzie tak głośny w całej sali.

This sounds smooth and ordinary.

You could move parts around for emphasis, for example:

• Nie spodziewałam się, że w całej sali ten mały flet będzie tak głośny.
• Nie spodziewałam się, że tak głośny będzie ten mały flet.

These are possible, but they shift emphasis and may sound more marked or literary. The original sentence is the safest, most natural version for everyday use.

Yes. Depending on context, Nie spodziewałam się can be translated as:

• I didn’t expect
• I wasn’t expecting

Both work well here.

That is common with Polish past tense verbs: English may choose either a simple past or a past continuous-style translation, depending on what sounds most natural.