How could a biological loudspeaker work and naturally evolve?

Question

In this Answer I suggested that an animal could have a tampani acting as a loudspeaker, as in Vernor Vinge’s The Blabber, later featured as the race called Tines in A Fire Upon the Deep. In the original Blabber it was shown that the animal could reproduce any sounds it had collected, like a mockingbird or lyrebird. The use of a structure that’s essentially a loudspeaker allows playback of any waveform within the bandwidth of the speaker. (In the referenced post, separate woofer/tweeter and resonance cavities extend the total bandwidth. That’s not important to this question.)

This begs the question: how can such a natural loudspeaker work? The membrane is no problem, nor is a stiff ring to set it in. But how does the driver work? It is doubtful that they could evolve an electromagnetic voice coil though I'm certainly interested in answers that would explain the biology and evolutionary pathway of that.

More generally, how could it work (e.g. using muscles) and be able to playback an arbitrary waveform? Note that the Tines in particular used ultrasonic sound for their group mind, so let’s say it handles up to 30 kHz.

Normally vocal cords and the like will simply use muscles to tension a string and then it vibrates at the natural frequency. That can give a repeating wave train of a fundamental and harmonics, but the muscles don’t have to respond on the speed of the sound’s frequency! To simply use muscles to actuate a voice coil would require speed beyond any muscle tissue we understand.

I would also be interested in biological adaptations of “alternative” speaker designs such as electrostatic and magnepan — it doesn't have to be exactly analogous to a compact central voice coil driver.

Answer 1

We know how a normal loudspeaker works, you typically have a rigid cone typically surrounded by a flexible rim, that is further surrounded by a rigid framework. at the center and behind the cone is a coil and a fixed magnet. Electrical impulses create small magnetic fields that move the coil, and thus the cone. This moves the air, and moving air is the basis of sound.

You have already resolved the rigid ring and membrane (cone) parts, you now need a driver to replace the coil and magnet arrangement.

I can see a small but strong muscle arrangement to act as the driver. The muscle arrangement could work on the principle of alternating cells contracting and relaxing. Say 15000 muscle cells each contract in sequence like cell 1 contracts, cell 2 contracts 1/10000 of a second later while cell one relaxes....and so on. In addition, the membrane should be able to alter it's tension, giving it a different natural frequency, much like tightening a drum head.

Loudspeakers will often include multiple, distinct driver/Cone arrangements in order to faithfully reproduce a broader variety of sound. Your critter to do the same thing by utilizing 6 driver and cone arrangements, in pairs. 3 different sizes. That way each size only has to produce a specific range of sound. The pairing arrangement allows for increased volume and the ability to create a 3 dimensional reproduction of the sound.

Your critter is going to need a substantial brainpower in order to control this arrangement.

Edit: I think I see a pathway for the critter to need a biological loudspeaker. Think of an environment that has very low levels of light and lots of slow moving water, like a swamp, but underground. This creature is not an herbivore, but a heavily armored scavenger/predator/omnivore. Call him Bobby the Boom-Turtle.

Very low light means that sight based survival traits take a back seat to sound and smell. Bobby's far distance ancestors became successful because they had good hearing and also learned to mimic. At first, the mimicry was to draw food toward them, either by duplicating mating calls or sounds of other prey animals in distress. Later, in a more sound sensitive environment, a good scream was discovered as a good method of driving away other predators. That's how you get a variety of speakers and larger sizes so that accuracy and volume are both possible.

The Bilateral arrangement comes from the following. The ability to produce directional sound means that the potential prey not only gets drawn to the animal in general, but to the head of the animal for a quick strike and kill, like a snapping turtle. In addition, being able to tune the sound in an enclosed environment like a cave, Bobby may be able to "project" sounds to fool competing predators to other areas, leaving Bobby to eat in peace. The directionality comes from the ability to generate the same frequency on a slight delay from two different spots. That's a kind of crude description of how stereo works.

This particular guy would end up looking like a tortoise with the "speakers" arranged on the underside with the smaller speakers closer to the head and the larger ones to the rear.

Bring Bobby back to earth and he could hire himself out as a self contained mobile DJ.

Answer 2

In Earth biology, birds have perhaps the widest range of sound production capability. Moreover it's small, can be stabilized during movement, and offers excellent control over volume and pitch.

The anatomical mechanism is known as a Syrinx, and has been the subject of a fair bit of study recently, including some 3D modeling efforts.

Answer 3

How about you allow your creature some form of Bioelectrogenesis?

If the animal has some kind of appendage similar to the body of an electric eel, then it could give off electric discharges with strong voltage and amperage in around the millisecond range.

The eel like appendage might evolve as a defensive measure, then over time, the creature might gain the ability to curl the appendage, creating coils or loops along its length. The electric eel already does a rudimentary version of this behaviour

Moving two of these loops close to each other could attenuate a signal, and a natural selection for that ability would possibly give rise to offspring with the ability for more and more windings (possibly by extending the length of the appendage?), which would eventually give you your natural voice coil I think.

An amphibious or semi aquatic environment would seem to have a higher likelihood of bringing about this kind of an appendage given the electric eel's evolution. Or maybe some incredibly moisture rich atmosphere would allow it's evolution ?

Answer 4

For animals on earth, the simplest and most common method of achieving extreme loudness is a resonance chamber - basically a large vibrating air pocket. You don't need any special exotic mechanism to make sounds as loud as an electronic loudspeaker - just a big enough resonance chamber and regular old vibrating muscles. A rock concert reaches 120 decibels (right at the edge of the human threshold for pain). The loudest land animal on earth, the howler monkey, goes up to 128 decibels. Keep in mind that decibels are a logarithmic scale; 128 decibels is much louder than 120.

The sound produced by a resonance chamber is mainly limited by the resonance chamber's size. Because of this, larger animals will find an easier time producing loud sounds (not too surprising) but smaller animals can pull off big noises by making extra space for big resonance chambers. Usually this resonance chamber is in the throat, but it doesn't have to be; the proboscis monkey has one in its big honking nose, and the hadrosaurid dinosaur Parasaurolophous had one in its crest (which was technically an elongated nasal cavity). Frogs can create temporary resonance chambers by inflating their throat pouches, so they don't have to carry them around all the time. Human singers and orators learn to use parts of their mouth, throat and chest as resonance chambers, though of course our ability to do so is limited by our relatively non-inflatable physiology it does demonstrate the principle in action.

Sound amplification mechanisms commonly evolve in animals that require large territories and prefer to avoid physical confrontations whenever possible. Birds, who can move quickly, require large territories due to their high energy requirement, and risk life-threatening injury whenever they fight (flight requires extremely precise mechanisms to work, and a bird that can't fly is as good as dead), are well known for staking out their territory through sound.

Mimicry is often related to sexual selection, as being able to memorize complex and varied sounds is an advertisement of intelligence; this form of competition is also commonly found in birds, possibly because, as stated previously, birds are taking a huge risk whenever they get into a physical fight so non-physical methods of competition tend to flourish instead.

So, I would expect such a creature that is both loud and capable of mimicry to have a bird-like lifestyle. Like a frog, it could have an inflatable throat pouch that enables it to amplify its calls. It may resemble a Great Frigatebird in appearance, although frigatebirds do not use their throat sacs for sound amplification. A howler monkey's resonating throat chamber is only a few inches across and can create sounds that can be heard up to 2 kilometers away; the Great Frogatebird's main limitation is going to be its ability to avoid deafening itself with its calls! To avoid this, it may be able to "lock" its ear bones in place when it makes loud noises. There are some species of bats that do this to avoid deafening themselves with their own echolocation sounds (they lock their bones when making the sound, so they only actually hear the echo).

Answer 5

A living speaker can be made out of organic matter, it's possible; as stated by @PaulTIKI.

For this kind of Organism to "Naturally" evolve though, it would really depend on the environment it's living in, an environment that favors an organism that can reproduce sounds it had heard (or new ones), and loudly too..

it could be as a means of communication, to repel predators, or just a byproduct of something else that they do.

being able to produce large sounds means they make easy prey, so i suggest a symbiotic relationship with another organism is in place.

an example : a cold planet, where days are mostly dark; most organisms are blind and rely on only sounds as a means of interacting with the environment; the living speakers could vibrate as a means of heating itself. they produce loud sounds to deter predators, and mimic sounds of other organisms to lure prey (they might have to be stationary, these speakers).