Dynamic Drivers vs. Balanced Armature Drivers

As we discussed in our blog post on noise cancellation technology, all of the sounds that reach your ear—from your favorite tunes to the UPS truck driving down your street and the incessant barking that follows—exist as waves.

Waves of what, though? For the most part, the sounds that reach your air exist as waves of pressurized air, and those pressure waves are almost always caused by something else out there in the world vibrating. Maybe it’s the surface of a drum, or all the moving bits in a diesel engine.

HOW DYNAMIC DRIVERS WORK

When it comes to recorded music, the vibrations typically come from what’s known as a driver. If you have a speaker sitting near you, pull off its grill and you can see this in action. The cones and domes that line the face of your speakers push and pull the air around them, and although the smallest drivers in your speakers may be vibrating so slightly and so rapidly that you can’t see their movement, if you cue up some Muse or A Tribe Called Quest, you’ll surely see the largest cones in your speakers huffing and puffing in time with the beat.

What causes those drivers to vibrate is generally a magnet that moves a coil of wire (called the voice coil) attached to the cone itself. Also known as dynamic (or moving-coil) drivers, these are pretty much the same sorts of drivers you’ll find in most headphones. Those are much smaller, of course—the drivers in a headphone that fits over your ear might be as large as the top of a soda can, whereas in-ear earphones might have drivers as small as the end of a AAA battery, or even tinier—but in most headphones and earphones there’s only room for one of them for each ear.

Of course, that’s not the only way to create sound. Just as some in-room speakers rely on exotic designs like electrostatic panels, there’s more than one way for earphones to translate an electrical signal into physical motion and vibrate the air headed in the direction of your eardrums. One of the most popular driver technologies amongst high-end earphone enthusiasts is called the balanced armature, and although—as with a dynamic driver—it relies on coils, magnets, and a moving diaphragm, the way those pieces are put together and engineered is radically different.

HOW BALANCED ARMATURE DRIVERS WORK

In balanced armature drivers like the ones found in Phiaton’s new BOLT BT 700 true wireless earphones with charging speaker case, an armature (which is basically electrical-engineering jargon for “the moving bits of a motor”) is surrounded by a stationary coil and suspended (or balanced) between two magnets. As electrical current is passed through the coil, it changes the magnetism of the armature, which causes it to wiggle in the direction of one magnet or the other. This wiggling motion is used to drive a diaphragm, which creates sound in much the same way as the reed in a woodwind instrument. Not exactly, but close enough for our explanatory purposes.

If you read all of the above and thought, “Hey, that sounds complicated,” you are correct. Balanced armature drivers are complicated, which makes them more expensive than dynamic (or moving-coil) drivers. So, why use them?

• For one thing, they’re smaller. Much smaller. Which is why they’ve been employed in hearing aids since before color TV was a thing.

• Secondly, they are much more efficient, meaning they can generate louder sounds using less electricity than dynamic drivers. Again, that makes them perfect for hearing aids, but it’s also particularly useful in true wireless earphones like the BOLT BT 700. Less power used means longer playtime between battery charges.

• Thirdly, the small size of balanced armatures means that there’s often room for multiple drivers within a single earphone case.

Packing more drivers into each earpiece isn’t about making the sound louder, mind you, but if you’ll think back to our earlier discussion about in-room speakers, you’ll remember that those usually rely on separate drivers for high-frequency and low-frequency sounds, and sometimes midrange as well. Multiple balanced armatures can be employed in the same way within earphones, with individual drivers that are custom-tuned to handle one small slice of the audible frequency range. The result? Clearer, more accurate sound with sparkling detail that you must hear to believe.

By Dennis Burger

October 11, 2018