Learn Hardcore Russian: Когда кто‑то говорит громко по телефону, я надеваю наушники и уменьшаю звук сериала. - When someone talks loudly on the phone, I put on headphones and lower the sound of the series.

Когда in this sentence introduces a time clause describing a situation that actually happens and is understood as a real, repeating condition:
- Когда кто‑то говорит громко по телефону, я надеваю наушники…
- “When someone speaks loudly on the phone, I put on headphones…”
This is about a regular, real‑life pattern: whenever this situation occurs, I do X.
Если would present it more as a condition (“if it happens at all”), not as a known, usual pattern:
- Если кто‑то говорит громко по телефону… – “If someone speaks loudly on the phone…”

Here the speaker is describing a habitual reaction to a typical situation, so когда is more natural than если.

Why is it кто‑то and not just кто or кто‑нибудь?

All three exist, but they have different uses:

кто = “who” (interrogative or relative pronoun)
- Кто говорит громко по телефону? – Who is talking loudly on the phone?
- You would not use bare кто here because we don’t have a question.
кто‑то = “someone,” “somebody” (neutral, indefinite person)
- Suggests some person, I don’t specify who, but it’s a real, actual person in the situation.
- Fits perfectly: some random person is talking loudly.
кто‑нибудь = also “someone / anyone,” often used:
- in questions: Здесь есть кто‑нибудь? – Is anybody here?
- in requests: Позовите кого‑нибудь. – Call someone.
- in contexts like “anyone at all / whoever”: Если кто‑нибудь позвонит… – If anyone calls…

In a simple factual statement about a typical situation, кто‑то is the default natural choice: when someone (or other) speaks loudly…

Why is the word order кто‑то говорит громко, and could it be кто‑то громко говорит?

Both orders are grammatically correct:

кто‑то говорит громко по телефону
кто‑то громко говорит по телефону

The difference is about information focus and natural rhythm:

кто‑то говорит громко по телефону
The basic statement: someone is speaking, and the manner is loudly. This is the most neutral word order.
кто‑то громко говорит по телефону
Moves громко closer to говорит, slightly emphasizing the loudness: someone is speaking loudly on the phone.
In many real contexts this is also perfectly natural and can even sound more expressive.

In everyday speech, both will be understood the same way. The sentence as given is just a very neutral, textbook‑like order.

What does по телефону literally mean, and why по and not something like на телефоне?

По телефону is the standard Russian way to say “on the phone / by phone” when talking about speaking:

говорить по телефону – to talk on the phone
разговаривать по телефону – to have a conversation on the phone

Literally, по телефону is something like “via the telephone,” “by means of the telephone.”

Using на телефоне in this context would sound wrong or at least very strange for “talk on the phone.” You might see на телефоне in other meanings (e.g., “on the phone (device)” in a technical sense: an app on the phone), but not for the idiomatic “speaking on the phone.”

So, whenever you mean “speak on the phone,” Russian almost always uses по телефону.

Why is it я надеваю наушники and not я одеваю наушники?

This is a classic Russian pair that confuses many learners:

надевать / надеть – to put on (clothes, shoes, accessories) onto oneself or someone
одевать / одеть – to dress (someone)

Rules of thumb:

You надевать clothes, shoes, headphones, etc.:
- Я надеваю наушники. – I put on headphones.
- Она надела куртку. – She put on a jacket.
You одевать a person:
- Мать одевает ребёнка. – The mother is dressing the child.
- Он одел сына потеплее. – He dressed his son warmer.

So я надеваю наушники is correct because you are putting the headphones on (yourself).
я одеваю наушники sounds wrong to native speakers.

Why is the present tense (надеваю, уменьшаю) used here to describe a general habit?

Russian uses the present tense of imperfective verbs to talk about:

current actions: Я сейчас надеваю наушники. – I am putting on headphones now.
regular, habitual actions: Я часто надеваю наушники. – I often put on headphones.

Your sentence:

Когда кто‑то говорит громко по телефону, я надеваю наушники и уменьшаю звук сериала.

corresponds exactly to English present simple for habits:

“When someone talks loudly on the phone, I put on headphones and turn down the sound of the show.”

So the choice of present tense imperfective is natural Russian for a repeated pattern / routine reaction.

Could we use the perfective forms надену or уменьшу here instead?

No, not in this sentence. Here’s why:

надеваю (imperfective), уменьшаю (imperfective) – focus on the process / repeated action / habit.
надену (perfective), уменьшу (perfective) – focus on a single, completed action in the future.

Compare:

Когда кто‑то говорит громко по телефону, я надеваю наушники.
Whenever this happens, I (typically) put on headphones. → habit
Когда он придёт, я надену наушники.
When he comes, I will put on headphones (that one time). → one future event

In your sentence, the situation is general and habitual, so imperfective надеваю / уменьшаю is required. Perfective would sound like you’re describing a single future occasion, not a usual reaction.

Why is наушники in this form? What case is it, and how do we know?

Наушники here is in the accusative plural.

Key points:

The verb надевать “to put on” is transitive and takes a direct object in the accusative.
The noun наушники (headphones) is plural only in Russian (like “scissors” in English).
- Nominative plural: наушники – “headphones”
- Accusative plural: наушники – same form for inanimate nouns

So:

Я надеваю что? – наушники → accusative object of the verb.
The form happens to match the nominative plural because for inanimate masculine plural nouns, nominative and accusative are identical.

Why is it звук сериала and not something like звук сериал or звук сериалу?

This is a genitive construction meaning “the sound of the series/show.”

звук – “sound” (nominative singular)
сериал – “series / TV show”
сериала – genitive singular of сериал

In Russian, when you want to say “the sound of X”, X is normally put in the genitive case:

звук сериала – the sound of the series/show
звук телевизора – the sound of the TV
звук музыки – the sound of the music

So уменьшаю звук сериала = “I reduce / turn down the sound of the show.”

Forms like звук сериал or звук сериалу are grammatically wrong in this context.

Could I say делаю тише сериал or делаю тише звук сериала instead of уменьшаю звук сериала?

Yes, and they would be natural, but with slightly different wording:

делаю тише сериал
Literally “I make the series quieter.” Idiomatically: “I turn the series down (make its volume lower).”
Native speakers do say this.
делаю тише звук сериала
Literally “I make the sound of the series quieter.” Also correct and clear.
уменьшаю звук сериала
Slightly more neutral/formal sounding: “I reduce the sound of the series.”
Very natural in both speech and writing.

So уменьшаю звук сериала, делаю сериал тише, and делаю тише звук сериала are all acceptable. The given version emphasizes the “sound” explicitly.

Why is there a comma between the two parts of the sentence?

Russian punctuation rules require a comma between:

the subordinate clause introduced by когда, and
the main clause.

Structure:

Когда кто‑то говорит громко по телефону, – subordinate clause (time clause)
я надеваю наушники и уменьшаю звук сериала. – main clause

Rule:
Subordinate clause + main clause → comma between them.

If you reverse the order, you still keep a comma:

Я надеваю наушники и уменьшаю звук сериала, когда кто‑то говорит громко по телефону.

What is the little dash in кто‑то? Is it a hyphen, and is it always needed?

In кто‑то, ‑то is a suffix that attaches to the pronoun кто to form an indefinite pronoun: “someone.”

The dash is written in standard Russian orthography and is always required with this suffix.
It’s the same with other ‑то pronouns:
- что‑то – something
- где‑то – somewhere
- когда‑то – sometime / once
- кто‑то – someone

So yes, you must always write it with that dash: кто‑то, not ктото.

How do you correctly pronounce the whole sentence? Where are the main stresses?

Here are the main word stresses (stressed syllables in bold):

Когда́ кто‑то́ говори́т гра́мко по телефо́ну,
я надева́ю нау́шники и уменьша́ю звук сериа́ла.

More precisely, word by word:

когда́ – kog‑DA
кто‑то́ – KTO‑to
говори́т – go‑vo‑RIT
гра́мко (actually гро́мко) – GROM‑ko
по телефо́ну – po te‑le‑FO‑nu
я – ya
надева́ю – na‑de‑VA‑yu
нау́шники – na‑USH‑ni‑ki
и – i
уменьша́ю – u‑men‑SHA‑yu
звук – zvuk
сериа́ла – se‑ri‑A‑la

Natural speech stress pattern (with the correct гро́мко):

Когда́ кто‑то говори́т гро́мко по телефо́ну, я надева́ю нау́шники и уменьша́ю звук сериа́ла.