Haven't learned the tap /r/
, yet? Do that first ...
The Spanish /rr/ sound is sometimes written with double 'rr' and sometimes single 'r'. As with the Spanish tap /r/, /rr/ has nothing to do with the English /r/ sound. Spanish /rr/ is a trill, closely related to the Spanish tap /r/. Because English has no trilled sounds, many people find the trill intimidating; but with a little practice, it is readily learned.
1. How to trill
Once you're comfortable making the tap /r/, say ara a few times, using the tap. Now freeze just at the moment when the tip of your tongue touches the roof of your mouth. That's the position for /rr/. The trill is made not by moving your tongue, but by focusing the air stream on the tongue so that it vibrates forcefully and rattles against the roof of your mouth. In order for that to happen, it should be relaxed but with enough tension to keep it close to the roof.
Take a deep breath, then breathe out, focusing the air stream on the tip of your tongue. The tongue is relaxed, it's the breath that does the work. Don't be shy—it's easier with a lot of breath.
2. My tongue isn't vibrating
If you're having trouble getting your tongue to vibrate, it's either because your air stream is not focused correctly or your tongue is too tense.
Practice focusing the air stream: With your tongue in the tap position, keep your tongue rigid and make a sharp /s/ or /sh/ sound. That is the feeling of focusing your air stream right down the center of your tongue.
Experiment with making an /s/ or /sh/ sound and gradually relaxing the tongue until it vibrates. Don't feel it has to stay up right next to the roof of your mouth; let it drop down, if it needs to. The main thing is that it vibrates.
Practice relaxing the tongue: Start by relaxing your whole mouth. Relax your lips and let them vibrate as you breathe forcefully out. Make sure you have plenty of breath—that's your engine.
Then, let your tongue hang loosely out of your mouth and make a "raspberry" sound (both tense and relaxed).
Then, bring your tongue inside your teeth and let it sit loosely on the floor of your mouth. Again, use that air stream to make everything vibrate.
All these vibrations use the same basic idea: you're focusing the breath in different places to cause different mouth parts to vibrate. Once you've gotten your lips and tongue vibrating in all these ways, bring your tongue back up to the tap position and focus the air stream on it. It will vibrate.
3. Incorporating the trill into words
Once you're comfortable making the vibration, practice incorporating it into Spanish words. Some words (eg., arroz, carro) will be much easier than others. With practice they'll all feel natural.
4. When to trill
A. The trill is obligatory whenever you see the double "rr". That occurs only in the middle of words such as perro and carro; the trill is essential so that the word is not confused with its tap counterpart (eg., pero, caro).
B. The trill is obligatory whenever a word begins with "r" (eg., rojo, reina)
C. The trill is obligatory when a single "r" follows "n", "l" or "s", as in alrededor or Enrique.
D. The trill is optional at the ends of syllables and words (eg., puerta, mar).
The other 23 sounds of Spanish ...
This lesson on the Spanish trill is included in the SuperCoco app, which also covers the other twenty-three sounds of Spanish—nineteen of which are different from English. The pronunciation course is part of SuperCoco's overall approach teaching Spanish through conversations
—with training wheels
on. Read more about it here...