tosyokan de ookina koe wo dasite ha ikemasen.

で marks the place where an action happens.

• 図書館で = in/at the library (where the action takes place)

Here, the action is 声を出す (to make/use a voice, in this context to speak loudly / make loud noise), so で is the natural particle.

Compare:

• 図書館で勉強します = I study at the library
• 図書館に行きます = I go to the library

So:

• に often marks destination
• で often marks location of an action

Both 大きな声 and 大きい声 are possible, but they are used a little differently.

• 大きい is a normal い-adjective
• 大きな is a special form that can only come before a noun

So:

• 大きい声 = a loud voice
• 大きな声 = a loud voice

In many cases, both sound natural. 大きな can sometimes feel a bit more descriptive or stylistic, but for learners, the important point is:

• 大きな + noun
• 大きい can be used both before a noun and at the end of a sentence:
  • 大きい声
  • 声が大きい

But 大きな cannot end the sentence by itself:

• natural: 大きいです
• not natural: 大きなです

Literally, 声を出す means to put out / produce a voice.

Breakdown:

• 声 = voice
• を = marks the direct object
• 出す = to put out, take out, produce

So 声を出す means:

• to speak
• to raise one’s voice
• to make a sound with one’s voice

In this sentence, because of 大きな, it means something like:

• to speak in a loud voice
• to make loud vocal noise

This is a very common Japanese expression.

Because 声 is the direct object of 出す.

In 声を出す, the thing being produced is the voice, so it takes を.

This is similar to other verb-object combinations:

• 音を出す = to make a sound
• 結果を出す = to produce results
• ゴミを出す = to put out the trash

So 声を出す is a set phrase where 声 naturally takes を.

This is a very common grammar pattern for prohibition:

• て-form + はいけません = must not ... / may not ...

So:

• 出して = the て-form of 出す
• はいけません = it is not allowed / it won’t do

Together:

• 出してはいけません = you must not produce/use...
• here: you must not speak in a loud voice

This pattern is very important:

• ここで食べてはいけません = You must not eat here.
• 入ってはいけません = You must not enter.
• 話してはいけません = You must not talk.

In てはいけません, the は is part of the fixed grammar pattern.

The full pattern is:

• verb-て + は + いけません

Examples:

• 食べてはいけません
• 見てはいけません
• 入ってはいけません

Historically and grammatically, the は adds contrast/emphasis, but for learners it is best to treat てはいけません as one set pattern meaning must not do.

In casual speech, ては is often pronounced:

• ちゃ after -te
• じゃ after -de

For example:

• 食べてはいけません → casual contraction: 食べちゃいけない
• 読んではいけません → 読んじゃいけない

Because the prohibition pattern requires the て-form:

• verb-てはいけません

So the dictionary form 出す changes to 出して.

Conjugation:

• 出す → 出して

Then add the pattern:

• 出してはいけません

You cannot say:

• 声を出すはいけません ❌

because はいけません does not attach directly to the dictionary form like that.

Yes, that is also natural.

Compare the two:

• 大きな声を出してはいけません
• 大きな声で話してはいけません

The second one is more explicitly do not speak in a loud voice because it uses 話す (to speak).

The original sentence, 声を出す, is slightly broader and can suggest making loud vocal noise in general, not just conversational speech.

So:

• 大きな声で話す = to speak loudly
• 大きな声を出す = to raise one’s voice / make loud vocal noise

Both are natural in the context of a library.

No. 大きな modifies 声.

Structure:

• 図書館で = in the library
• 大きな声を = a loud voice
• 出してはいけません = must not produce/use

So the noun phrase is:

• 大きな声 = loud voice

It does not describe the verb directly. Japanese often uses a noun phrase like this where English might use an adverb:

• Japanese: 大きな声を出す
• English: speak loudly

They are similar, but not exactly the same in tone.

• てはいけません = must not; not allowed
• てはだめです = you must not; don’t do that

Both can often be translated the same way.

Examples:

• 入ってはいけません
• 入ってはだめです

Differences:

• いけません can sound a bit more formal or rule-like
• だめです can sound a bit more conversational

In signs, instructions, schools, and polite rules, いけません is very common.

There is also:

• てはなりません

This sounds even more formal or stiff.

It is usually understood as a general rule or instruction, but in practice it applies to the listener/reader.

Japanese often leaves out the subject, especially in rules and signs.

So instead of saying:

• あなたは図書館で大きな声を出してはいけません

Japanese simply says:

• 図書館で大きな声を出してはいけません

This sounds more natural. It means something like:

• One must not speak loudly in the library
• You must not speak loudly in the library

depending on context.

The basic order is:

• place + で
• object + を
• verb
• grammar ending

So:

• 図書館で = in the library
• 大きな声を = a loud voice
• 出してはいけません = must not produce/use

Japanese usually puts the main verb at the end, so the sentence builds up to the prohibition.

A rough literal order in English would be:

• In the library, a loud voice, you must not produce

That sounds unnatural in English, but it shows the Japanese structure well.

Yes.

• 図書館 = としょかん = library

Full reading of the sentence:

• としょかん で おおきな こえ を だして は いけません。

A natural spoken flow would be:

• としょかんで おおきなこえを だしてはいけません。

In normal speech, the spaces are not actually present; they are just there to help learners read the sentence.