Ljudet i videon är dåligt, eftersom högtalaren på mobilen är trasig.

Because Swedish usually puts the definite article on the end of the noun instead of using a separate word like English the.

• ett ljud → ljudet = the sound
• en video → videon = the video
• en högtalare → högtalaren = the speaker
• en mobil → mobilen = the phone

So the sentence is talking about specific things: the sound, the video, the speaker, the phone.

Because adjectives in Swedish agree with the noun they describe, even after är.

• ljud is an ett word: ett ljud → ljudet är dåligt
• högtalare is an en word: en högtalare → högtalaren är trasig

So:

• dålig → dåligt with an ett noun
• trasig stays trasig with an en noun

If the nouns were plural, both adjectives would become dåliga and trasiga.

Here i videon is the natural choice because the sentence is talking about the sound contained within the video. In other words, it means the audio that is part of the video.

Using på videon is much less natural in this context. A learner can usually safely think of ljudet i videon as the sound in the video.

Eftersom means because or since, and it introduces a subordinate clause.

So this part:

eftersom högtalaren på mobilen är trasig

explains the reason for the first part of the sentence.

A useful grammar point: in a subordinate clause, Swedish keeps normal subject-before-verb order. If you add inte, it goes before the verb:

• eftersom högtalaren på mobilen inte är trasig

That is typical subordinate-clause word order in Swedish.

Yes, in many cases you can.

• eftersom = because / since
• därför att = because
• för att can also mean because in everyday Swedish, but it can also mean in order to, so sometimes it is less clear for learners

In this sentence, eftersom is a very clear and natural choice.

Yes, you could.

• högtalaren på mobilen = the speaker on the phone
• mobilens högtalare = the phone’s speaker

Both are possible. The version with på mobilen sounds very natural in everyday speech when talking about parts or features of a device. Mobilens högtalare is also correct and a bit more directly possessive.

You may also hear högtalaren i mobilen, especially if the speaker is thought of as physically inside the phone.

Yes. Trasig is a very common adjective for something that is damaged or not working.

So:

• högtalaren är trasig = the speaker is broken

In spoken Swedish, people also often say är sönder, for example högtalaren är sönder. But är trasig is standard, clear, and very useful for learners.

Then the main clause that follows uses inversion: the verb comes before the subject.

So you get:

Eftersom högtalaren på mobilen är trasig, är ljudet i videon dåligt.

Notice är ljudet, not ljudet är, after the opening subordinate clause. That is normal Swedish main-clause word order after something has been placed first.

Not necessarily. In modern Swedish, commas before subordinate clauses are often optional.

So both of these are possible:

• Ljudet i videon är dåligt, eftersom högtalaren på mobilen är trasig.
• Ljudet i videon är dåligt eftersom högtalaren på mobilen är trasig.

The version with the comma gives a slightly clearer pause. The version without it is also very common.

In most modern Swedish, the l is not pronounced clearly in this combination. At the start of a word, lj usually sounds roughly like English y in yes.

So ljudet starts approximately like yoo- rather than a full l-yoo- sound.

The stress is on the first syllable: LJU-det.