It's as much HOW and WHERE you strike it as it is WHAT you strike: THE TRIANGLE

 Everyone has an opinion for their 'go to' or 'default' triangle and many hours can be spent arguing about them. When the Alan Abel triangle was first introduced it was considered one of the best on the market. Over the years companies started to focus on making different sizes, designs and metals. This has raised the standard for the quality of sound while increasing the confusion over what a 'good sound' is. This has caused the Abel triangle to be shunned by many people, the most common reason is it's purity of sound.  

The triangle sound should not produce a specific pitch, it's shimmering quality is what makes it stand out from the rest of the instruments. This 'shimmering' is caused by the many different overtones as it vibrates. So for this discussion I'm using a standard 6" Alan Abel triangle keeping in mind that no 2 triangles regardless of make or model will sound exactly the same.

The first 'default' position that band directors teach their students is to strike the closed side opposite the open end. The beater strikes at a 90° angle creating a clear almost pure pitch.

  

Playing near the top produces a softer/lighter sound with a few overtones.

The bottom leg with the beater perpendicular to the floor produces a big sound with some added low overtones. This is the second 'default' position that most students are taught.

Striking the bottom leg at a 45° angle causes a rotational torque bringing out even more low overtones.

Other positions and angles create various combinations of pitches and overtones.

Using different beaters (tubular, solid, steel, brass, heavy, light, etc.) even at the same positions and angles creates even more variations of sound.

One triangle, many sounds. Adding only 1 more triangle to this mix gives the percussionist an almost limitless number of sounds to use. Or putting it another way, a good quality triangle is bound only by the ability of the percussionist.