Calibramos el audífono antes de que empiece la audiometría.

Because antes de que normally triggers the subjunctive in Spanish when you are talking about an action that has not happened yet.

So:

• antes de que empiece la audiometría = before the audiometry starts
• not antes de que empieza...

Here, the start of the audiometry is seen as a future or pending event relative to the calibration, so Spanish uses the subjunctive.

A very common pattern to remember is:

• antes de que + subjunctive

Examples:

• Te llamo antes de que salgas.
• Cerramos la puerta antes de que entren.

Empiece is the present subjunctive form of empezar.

Its forms are:

• yo empiece
• tú empieces
• él/ella/usted empiece
• nosotros empecemos
• vosotros empecéis
• ellos/ellas/ustedes empiecen

Notice the stem change e → ie, just like in the present indicative:

• empiezo
• empiezas
• empieza

Calibramos is the present indicative. In Spanish, the present tense is often used to talk about:

• a habitual action: We calibrate the hearing aid before the audiometry starts
• a procedure/instructional style: We calibrate the hearing aid before the audiometry begins
• something happening in the current routine or context

Without more context, the sentence sounds like a general procedure or standard practice.

Also, calibramos could technically also be the preterite form (we calibrated), but here the rest of the sentence strongly suggests a present/habitual reading.

Yes. That is a very common alternative.

Compare:

• antes de que empiece la audiometría
• antes de empezar la audiometría

Both are correct, but the structure is slightly different:

1. antes de que + subjunctive

   • used when there is a new subject or when you want a full clause
   • antes de que empiece la audiometría

2. antes de + infinitive

   • used when no new finite verb is needed
   • antes de empezar la audiometría

In this sentence, both sound natural. The original version is a bit more explicit because it gives the event as a full clause.

Because antes de que is a fixed conjunction meaning before when it introduces a clause with a conjugated verb.

Compare:

• antes de la audiometría = before the audiometry
• antes de empezar la audiometría = before starting the audiometry
• antes de que empiece la audiometría = before the audiometry starts

So:

• antes de + noun
• antes de + infinitive
• antes de que + conjugated verb

That que is required in the third structure.

Because Spanish usually omits subject pronouns when they are not needed.

The verb ending -amos already tells you the subject is we.

So:

• Calibramos el audífono... = We calibrate the hearing aid...

Adding nosotros is possible, but it usually adds emphasis or contrast:

• Nosotros calibramos el audífono, pero ellos hacen la prueba.

In normal neutral Spanish, leaving the pronoun out is more natural.

Spanish uses definite articles more often than English does.

So:

• el audífono
• la audiometría

In English, you might sometimes say we calibrate hearing aids before audiometry or before the test starts, but Spanish often prefers the article when referring to a specific item or a procedure understood in context.

Here, the articles make the sentence sound natural and complete.

Most likely, yes.

In medical context, audífono usually means hearing aid.

A learner may be confused because related audio words can overlap depending on region and context. In Spain:

• audífono commonly means hearing aid
• for headphone/earphone, people often say auricular, auriculares, or sometimes other device-specific terms

Since the sentence also contains audiometría, a clinical term, audífono here strongly sounds like hearing aid rather than headphone.

Audiometría is the medical term for audiometry, meaning a hearing test/measurement of hearing ability.

It is a technical noun, not an everyday casual word for most people.

So the sentence has a fairly professional or clinical tone:

• calibramos
• audífono
• audiometría

Together they sound like something said in an audiology or medical setting.

This is just how the present subjunctive of empezar works.

Start with the yo form of the present indicative:

• yo empiezo

Remove -o:

• empiez-

Then add the present subjunctive ending for -ar verbs:

• -e

So you get:

• empiece

That is why the stem change remains:

• empezar → empiezo → empiece

This pattern is very common:

• pensar → piense
• cerrar → cierre
• comenzar → comience

Yes. That is very normal in Spanish.

Spanish often uses the present indicative in the main clause and the present subjunctive in the subordinate clause to refer to a future sequence.

So:

• Calibramos el audífono antes de que empiece la audiometría

can mean something like:

• We calibrate the hearing aid before the audiometry starts
• We’ll calibrate the hearing aid before the audiometry starts, depending on context
• We normally calibrate the hearing aid before the audiometry starts

Spanish relies heavily on context for this kind of time reference.

Yes, absolutely.

• empiece comes from empezar
• comience comes from comenzar

Both mean to begin/start, and both are natural here:

• antes de que empiece la audiometría
• antes de que comience la audiometría

Comenzar can sound slightly more formal in some contexts, but both fit well in medical or professional Spanish.