Lyden er lav i stuen.

In Danish, the definite article (the) is usually added as a suffix to the noun, not as a separate word.

• en lyd = a sound
• lyden = the sound

So Lyden er lav i stuen literally means The sound is low in the living room.
If you said Lyd er lav i stuen, it would sound wrong to a Dane; you need the definite form lyden here.

Lyd is a common gender noun (n-Word).

Key forms:

• Indefinite singular: en lyd (a sound)
• Definite singular: lyden (the sound)
• Indefinite plural: lyde (sounds)
• Definite plural: lydene (the sounds)

Examples:

• Jeg hører en mærkelig lyd. – I hear a strange sound.
• Lydene udenfor er meget høje. – The sounds outside are very loud.

Yes, lav means low, and that includes:

1. Physical height:
   
   • Et lavt bord – a low table
2. Level/intensity, including sound volume:
   
   • Lyden er lav. – The sound is low (quiet)
   • Tal lidt lavere. – Speak a bit more quietly / at a lower volume.

So in this sentence, lav refers to the volume level of the sound, not its physical position.

Not in the same way.

• lav with lyd is about volume level (quiet vs loud).
• stille means quiet/silent as a general atmosphere, not as a technical “low volume”.

Natural uses:

• Lyden er lav i stuen. – The sound volume is low in the living room.
• Der er stille i stuen. – It is quiet in the living room (overall, not much noise).

Lyden er stille is not idiomatic Danish; you would normally say lyden er lav or lyden er svag for a weak/quiet sound.

• lyd = sound (neutral word; any sound)
• støj = noise (usually unpleasant or unwanted sound)

Compare:

• Lyden er lav i stuen. – The sound is low in the living room.
• Der er meget støj i stuen. – There is a lot of noise in the living room.

You wouldn’t normally use støj with lav in this way; you’d say something like Der er ikke så meget støj (there isn’t so much noise) instead.

For rooms inside a house or building, Danish normally uses i (in):

• i stuen – in the living room
• i køkkenet – in the kitchen
• i soveværelset – in the bedroom

på is used with some specific places (e.g. på arbejde, på skolen, på hospitalet), but not with normal rooms in a home. So på stuen would be wrong in standard Danish in this context.

Same reason as with lyd: you need the definite form for a specific room.

• en stue – a living room
• stuen – the living room

You’re talking about a particular living room (probably the one in the house you’re in), so you say i stuen.

i stue would sound incomplete/incorrect, just like in living room is wrong in English.

Yes, I stuen er lyden lav is also correct.

• Lyden er lav i stuen. – neutral word order, subject first.
• I stuen er lyden lav. – puts extra emphasis on the location i stuen (“In the living room, the sound is low”).

Both are grammatical; the difference is a matter of emphasis and style.

With the verb at være (to be), the basic pattern is:

[subject] + er + [adjective] + [place]

So:

• Lyden er lav i stuen.

Putting lav after i stuen – Lyden er i stuen lav – is not natural in Danish. The normal position for the adjective is directly after the form of “er” and before the place expression.

You change both the noun and possibly the place phrase, depending on what you mean.

1. Several sounds in one living room:

   • Lydene er lave i stuen.
     – The sounds are low in the living room.

2. The sound in several living rooms:

   • Lyden er lav i stuerne.
     – The sound is low in the living rooms.

3. Several sounds in several living rooms:

   • Lydene er lave i stuerne.
     – The sounds are low in the living rooms.

Notice the plural forms: lydene, lave, stuerne.

Approximate pronunciations (in simple English terms):

• lyden – roughly “LEW-then”
  
  • Danish y is like the French u in lune or German ü in müde.
• lav – often like “laow” (a bit between lahv and English loud but shorter)
• stuen – roughly “STOO-en” (with a short, unstressed -en)

Real Danish pronunciation has some subtleties (vowel length, soft d in lyden, etc.), but these approximations are close enough to be understood.

Yes. That’s perfectly natural.

• Lyden er lav i stuen. – The sound is low in the living room.
• Lyden er meget lav i stuen. – The sound is very low in the living room.

You can also use other degree words:

• Lyden er lidt lav i stuen. – The sound is a bit low in the living room.
• Lyden er for lav i stuen. – The sound is too low in the living room.