PDA

View Full Version : Echo Location



Rorrik
2012-03-17, 12:03 PM
So my group and I do almost pure homebrew, because we like making things as much as playing them, and one of my players is looking at making a character race with echo location as opposed to dark or low light vision. So I figure this trait would allow him to see around walls to a certain degree, and thus have a non line-of-sight view of the terrain or enemies. How detailed should this be able to see?

Winds
2012-03-17, 02:33 PM
Several humans have learned echolocation, so we actually have a real-life baseline. Those people can do even things like dirtbiking by echolocation, so 30 or 40 feet of blindsight should cover it. You'll want to include the listed limitations for hearing-based blindsight and make sure any player using it knows that that means they're making noise. If that's a dealbreaker, I would think that you could cue of of the subsonics feat in Complete Adventurer and have a racial feat that reduces or removes the ability of most creatures to detect it.

Mystify
2012-03-17, 03:30 PM
Blindsense is the standard way to give echolocation. Look at a dire bat, for example.

Rorrik
2012-03-17, 08:37 PM
Wow, I had no idea. We were thinking that the race would make a high pitched noise, not recognizable by most hearing ranges.

Cirrylius
2012-03-18, 10:36 AM
Wow, I had no idea. We were thinking that the race would make a high pitched noise, not recognizable by most hearing ranges.

Since it's homebrew, that's up to you. IRL, I believe, echolocation is audible to the human hearing range when used by roughly human-sized creatures 'cause they're unable to make higher or lower pitched sounds.

hamishspence
2012-03-18, 11:12 AM
Dolphins tend to be human-sized or larger, and echolocate in the 80-220 kHz range- doesn't human hearing stop at 20 kHz and above?

Mystify
2012-03-18, 01:10 PM
Dolphins tend to be human-sized or larger, and echolocate in the 80-220 kHz range- doesn't human hearing stop at 20 kHz and above?
They are also underwater, not sure the precise effect that would have on it, and I don't feel like trying to figure it out right now.

MesiDoomstalker
2012-03-18, 07:41 PM
They are also underwater, not sure the precise effect that would have on it, and I don't feel like trying to figure it out right now.

Sounds travel faster (denser media makes the vibrations easier) and further (less decrease in energy as molecules bump into each other). So ya, theres that.

Circle of Life
2012-03-18, 07:43 PM
Blindsense or the Syntheste power ('hear' light) both work just fine for this already. If you want to 'brew something up, I'd use one of those for the basics.

Rorrik
2012-03-19, 09:48 AM
I'll definitely take a look at those, but our whole rule set is basically homebrewed, so they'll need to be adapted.

Jay R
2012-03-19, 10:32 AM
Don't forget that this will not include color sense, which means that (among other things) they cannot read, or tell dragons apart. They also probably cannot see through a window or gauzy cloth.

Rorrik
2012-03-19, 11:26 AM
Right, I hadn't thought about windows. On further thought, we decided a low frequency(low pitch) would actually fit the race better, but we figured this would give a blurrier/lower definition image. Does that sound right?

Bagelson
2012-03-19, 12:27 PM
Right, I hadn't thought about windows. On further thought, we decided a low frequency(low pitch) would actually fit the race better, but we figured this would give a blurrier/lower definition image. Does that sound right?
Just about. Low frequency sound would make it harder/impossible to notice small/medium objects but enable echolocation at greater distances.

Also keep in mind that being able to use infra- or ultrasound for echolocation would allow the user to perceive sounds in that frequency range. Infrasound can include such things as earthquakes, weather and loud bangs or explosions; Infrasound also travels very far (since it bypasses objects that would stop higher frequency sounds), whale song can travel hundreds of miles under water, elephants can communicate when up to six miles away and infrasonic monitoring is used to detect nuclear weapons anywhere in the world. All this means that a character using infrasonic echolocation may hear an army marching in the next time over, a mine collapse in the nearby mountains, a thunder storm half a day in advance and a dragon roar in the next nation over.

High frequency sounds are more useful in that they allow for a far better resolution at close range and you only have to worry about ambient noise interference in your immediate vicinity.

Mystify
2012-03-19, 06:54 PM
you cannot perceive something with echolocation if its smaller than your wavelength.
And since the bottom of human hearing is 20hz, thats a wavelength of 17 meters, and its not even subsonic yet. You would detect a building in front of you, put will walk into trees. Its not really a functional sound for echolocation.
Of course, you can ignore all of that if you want, but thats the science.

Look at this chart, for instance:
http://www.soest.hawaii.edu/GG/HCV/NEWSV2N1/mary1_full.jpg
The sonar frequencies are on the right. 50hz is only good for long-range sonar. You are looking at something with a significantly lower resolution than that. And that is long range for a submarine. A Submarine generally doesn't deal with things 5ft in front of them.

Thomar_of_Uointer
2012-03-19, 08:06 PM
Why not let them switch between different frequencies for different levels of detail? Human vision allows for focusing on near or far objects, so there's precedent for that.

Rorrik
2012-03-20, 12:01 PM
Right, then scientifically, low frequency is probably out both to make the resolution at all reasonable and to limit seeing through walls, not to mention the information overload.