How do holograms produce audio?

[Trekky0623]

In the holodeck, this could be easily explained with a complicated array of speakers that produce audio to mimic the visual illusion. However, if two character wander off far from each other in the simulation, the holodeck would have to be able to mask audio as well. Like in the Voyager episode "Fair Haven," we see some characters hang out at the bar while others can wander off to do their own thing. If they were all in the confined space of the holodeck with their own visual illusions to recreate environments, the recreated audio would have to be masked from others in the same room.

This is further complicated by the existence of the Doctor. If he was confined to sickbay or the holodeck, speakers could also explain his speech. But he isn't confined to those areas. He can use the mobile emitter to wander around 20th century Los Angeles, still with the ability to speak and produce audio. So somehow, the use of forcefields would have to be utilized to vibrate air, mimicking something akin to vocal cords. Either that, or I guess the mobile emitter could have its own small speaker, though surely this would be a dead giveaway for the Doctor in 20th century Los Angeles, with a voice originating from his arm rather than his mouth. Or in "Renaissance Man," where the Doctor is able to effectively disguise himself as members of the crew.

 

[B.J.]

So somehow, the use of forcefields would have to be utilized to vibrate air, mimicking something akin to vocal cords.

I believe you've answered your own question in the last sentence here.

 

[T'Girl]

Or, holographic lungs, windpipe, vocal cords, tounge, teeth and mouth.

 

[bbjeg]

^That.

 

[Mytran]

That sounds complex. What about a simple holographic speaker inside the head?

 

[Timo]

I gather that a vibrating forcefield could be generated at any arbitrary spot - and that for the perfect audio experience, there would be thousands of sound-emitting points to create the best possible illusion of the sound coming from spot X, even if users A, B and C had different illusions about where exactly this spot X was in relation to them.

Sound is nicely additive like that. And you can also kill it with perfect counternoise, or by erecting a sound-impermeable forcefield wall between the source and the user. It's probably among the easiest of holodeck illusions to produce, and yet one of the most convincing because the user doesn't realize how simple a trick it is.

Timo Saloniemi

 

[137th Gebirg]

I hate to use Voyager as a precedent, but if the EMH could give Neelix a holographic set of lungs after being stolen by the Vidiians (it was them I think, harvesting organs to replace ones destroyed by the Phage), that process and distrubte oxygen into the bloodstream, it stands to reason that holographic people would have similarly-designed artificial organic constructs to precisely simulate other body parts and their functionality, such as vocal chords.

 

[Forbin]

That sounds complex. What about a simple holographic speaker inside the head?

How would a holographic mecahnical speaker be any simpler than a holographic voice box?

 

[Mytran]

One requires air pumped through it to operate - the other just needs electrical impulses.

We saw in "Basics" that the Doctor is not dependent on air to speak.

 

[Crazy Eddie]

I just assumed the holodeck has a speaker system built into it that is capable of projecting sounds from specific locations within the room. The idea of a vibrating forcefield makes sense too, considering that objects that are in the process of vanishing seem to audibly "fade out" in a way consistent with their appearance (like what happens to Cyrus Redblock in "The Big Goodbye").

I hate to use Voyager as a precedent

Please refrain from doing so in the future.

but if the EMH could give Neelix a holographic set of lungs...

Then he's a fucking idiot for not first considering a simple heart-lung machine. A 21st century CPB can keep a patient alive for up to twelve hours at a time; by the 24th century, that kind of device would be the size of a fist and would probably keep Neelix alive for a solid month.

"Temporary supplement to the medical team" indeed.

 

[Timo]

That's a rather probable downside to relying on holograms for emergencies... A jack-of-all-trades tool for saving lives has its limitations, including the inability to create mobile prosthetics. But I can see Starfleet still doing it, as a holographic sickbay can save lives in a lot of different situations with minimal resources (that is, the one and the same resource), while a diverse set of cures and aids and prosthetics would be more resource- and labor-intensive.

Of course, a heart-lung machine could have been produced even by this starship-stranded-with-few-resources - if not for the unfortunate fact that the replicators were down! Apparently, they weren't fully repaired until after "Basics" and access to civilized ports outside Kazon space (although Janeway still kept the replicator ration system for disciplinary purposes); making such a machine out of actual physical materials (rather than forcefields) might plausibly have been impossible at the time of "Phage".

A ship equipped with replicators is very likely to be launched without the sort of spares or tooling that any replicator-less ship would obviously be carrying...

Timo Saloniemi

 

[JarodRussell]

I don't know what it's called, but it's already possible to emit audio waves from a speaker in a way that they appear to come from a completely different point in space.
A guy at work got it for a project a couple of years ago, but we only used it to pull pranks, like letting people search for their ringing cellphone.



Something similar appeared in Mission Impossible: Ghost Protocol

 

[Timo]

That's the great thing about sound: it's a very crude form of physical wave motion, so it's eminently "additive". You can intensify sound by having two wavefronts from two speakers interfere constructively (that is, the tops of the waves hit the same spot in space and time, and you get a double-high wave), or silence it by having two wavefronts interfere destructively (that is, a top and a bottom of a wave coincide, and the sum is zero). So two or more loudspeakers can "project" loud sound at a spot in space while the space around it is more or less silent - and you think the sound is coming from that spot. (Well, yeah, it is, in every physical sense, but its energies are being projected from a distance.)

You can do that with light, too, but it's much more delicate work, due to the immensely shorter wavelength and the more complex physical nature of the wave. So it takes effort to create an optical hologram, and the brain doesn't easily accept it, but it's almost trivial to create an auditory hologram, and the brain doesn't bother to scrutinize it much because our directional hearing is frankly piss-poor anyway.

But a holodeck wouldn't need to rely on interference from multiple sources, because it can generate forcefields at an arbitrary spot in space and time already. If a fly needs to make a buzz, say, it can be accompanied through its flight by an invisible speaker made of forcefields. No need for its wings to be actual flapping forcefields - they can be mere images, while the speaker creates the sound by directly vibrating the air at the spot.

OTOH, the holodeck could create a small directional loudspeaker right next to the user's ear and have that create the illusion of a buzzing, flying insect. Neither of these options is available today.

Timo Saloniemi

 

[Crazy Eddie]

Of course, a heart-lung machine could have been produced even by this starship-stranded-with-few-resources - if not for the unfortunate fact that the replicators were down!

No they weren't. The EMH asks tom for a "cytoplasmic stimulator." Tom says "We don't have one" at which point EMH tells him in a huff of annoyance, "Then replicate one." Which Tom does.

I don't know what it's called, but it's already possible to emit audio waves from a speaker in a way that they appear to come from a completely different point in space.
A guy at work got it for a project a couple of years ago, but we only used it to pull pranks, like letting people search for their ringing cellphone.



Something similar appeared in Mission Impossible: Ghost Protocol

That's about what I figured. Basic ventriloquism: get the computer to throw the sound waves where they're supposed to be coming from.

 

[Timo]

No they weren't. The EMH asks tom for a "cytoplasmic stimulator." Tom says "We don't have one" at which point EMH tells him in a huff of annoyance, "Then replicate one." Which Tom does.

Damn, there goes that rationalization...

Plus a hundred more waiting in the line, as machinery replication capabilities would preempt most of their early woes. Or did the EMH blow a year's replication rations for the entire crew by having the stimulator made?

Timo Saloniemi