Would dragons be able to purr?

Question

My dragons have a... "difficult" personality.

They're very catlike. Sure, they're more like KrimsonRogue's cat (somewhere around chaotic good). But, if I want to make my dragons smug, blue-blood a-holes that you still want to cuddle, then I might as well give them the ability to purr very loudly.

Well, that actually would have one tangible advantage, if the dragon could use it to transmit data and instructions to the nanomachines in their body.

Problem is, dragons here are about as large as a draft horse, are filled with spongy and hollow structures on top of having air sacs to assist breathing, and I'm afraid that would ruin the acoustics.

Basically, there are two unique features to my dragons:

1. Air blubbers, a special type of aerogel, made out of fibrous, CNT-reinforced organic matter with densities around 200 kg/m^3.
   These air blubbers are primarily located under the dragon's skin, serving as protection against blunt force trauma (like crash-landing).
2. Air sacs and hollow bones are present throughout the body, as dragons have a respiratory system similar to birds'.

There's also that large cats (lions, tigers, etc...) can't purr.

So, how would dragons be able to purr very loudly?

Answer 1

How Cat Purrs Work:

Cats purr based on a set of muscles in their larynx:

How Big Cats Roar:

As to how we can let a dragon roar loudly, we can look at how big cats roar:

"What's peculiar about the lion and tiger vocal folds is that they have a very flat surface on the front," Titze said. "It's almost like two parallel plates."

When just a small puff of air is blown between these two plates, vibrations start, Titze said. That's one key to the roar of a lion or tiger: They need very little lung pressure to make large vibrations, which translate to a big sound.

The second secret to a big cat's roar is a layer of fat within the vocal folds, where other animals have a ligament. Fat is squishy, offering more leeway for the vocal cords to vibrate, Titze said.

Dragon Rawrs:

Generally speaking, big cats that can roar cannot purr, while small cats that can purr cannot roar. However, seeing as dragons are biologically engineered, perhaps one way to achieve this is to use two sets of vocal cords in series.

One set, deepest in the throat, would generate the purring sound, using something similar to the cat's larynx. The other set, higher up, would be like a big cat's vocal cords, with two parallel folds and a layer of fat, allowing sounds to be amplified into roars.

Like this, the two sets of vocal cords would allow three modes of operation: dragon roar, dragon purr, dragon purr roar.

This would allow the dragon to intimidate foes using its roars, purr when it is enticed by dragon-nip, or purr-roar as a vibrational sound attack.

Cute but deadly!