O eco continua por causa da acústica.

Eco is normally masculine in standard Portuguese, so the usual form is o eco.

Examples:

• o eco
• um eco
• esse eco

You may occasionally run into less common variation in older or regional usage, but for a learner, o eco is the safe and natural choice.

Continua is the 3rd person singular present indicative of continuar.

So in this sentence:

• o eco = the subject
• continua = continues / keeps going / persists

It agrees with o eco, which is singular.

Portuguese often uses the simple present where English might prefer either:

• continues
• is continuing

So O eco continua can sound natural in contexts where English might say:

• The echo continues
• The echo is still going on
• The echo keeps going

You could say está continuando, but in this sentence it sounds less natural and heavier than continua.

Por causa de is a very common expression meaning:

• because of
• due to
• as a result of

It is followed by a noun phrase, not a full clause.

So:

• por causa da acústica = because of the acoustics

Because da is a contraction of:

• de + a = da

The expression is por causa de, and the noun acústica here takes the feminine singular article a.

So:

• por causa de + a acústica
• becomes por causa da acústica

Other common contractions:

• de + o = do
• de + os = dos
• de + as = das

Portuguese uses definite articles more often than English does.

Here, a acústica refers to the acoustics of the place being discussed, so the article sounds natural:

• da acústica = of the acoustics / because of the acoustics

Leaving the article out, as in por causa de acústica, would sound unusual here.

Here, acústica is a noun.

It means acoustics.

Compare:

• a acústica da sala = the acoustics of the room → noun
• guitarra acústica = acoustic guitar → adjective

So in this sentence, it is not describing another noun. It is itself the noun.

Because por causa de is followed by a noun phrase, while porque introduces a clause with a verb.

Compare:

• O eco continua por causa da acústica.

  • followed by the noun phrase da acústica

• O eco continua porque a sala tem uma acústica ruim.

  • followed by the clause a sala tem...

So both can express cause, but they are used with different structures.

Yes. That is completely natural.

Both are correct:

• O eco continua por causa da acústica.
• Por causa da acústica, o eco continua.

The difference is mainly emphasis:

• starting with Por causa da acústica emphasizes the cause
• starting with O eco continua emphasizes the echo first

Yes. A few common alternatives are:

• O eco continua devido à acústica.
  • a bit more formal
• O eco continua por conta da acústica.
  • common in Brazilian Portuguese, a little more conversational

Notice:

• devido à uses crasis: a + a = à

All of these are possible, but por causa da acústica is very common and neutral.

A rough pronunciation is:

u EH-ku kon-tchi-NU-a por KAU-za da a-KUS-tchi-ka

A more IPA-style version is approximately:

/u ˈɛ.ku kõ.tʃiˈnu.ɐ poʁ ˈkaw.zɐ dɐ aˈkus.tʃi.kɐ/

A few useful pronunciation notes:

• eco stresses the first syllable: EH-co
• continua has four syllables: con-ti-nu-a
• acústica stresses kús: a-KUS-ti-ca
• in Brazilian Portuguese, unstressed final o often sounds like u, so o may sound like u in speech

No. Here continuar works intransitively, meaning it does not need a direct object.

So O eco continua is a complete sentence by itself:

• The echo continues
• The echo persists

Then por causa da acústica simply adds the reason.