nondirectionality

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sakhavi

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Hi all - something I've always wondered about; no doubt one of the many geniuses in this community can elucidate me.

I've always heard that low bass and sub-bass sound waves are nondirectional, as opposed to higher frequency waves, which are more or less highly directional. This is counterintuitive to me; as far as I know there's no qualitative difference between a long-wavelength compressive wave and a short-wavelength one (at least, no difference in the way they propagate through space). Why should the spatial origin of one the former matter less than that of the latter? I'm wondering if there's a neurological threshold past which the human brain can't process a bass signal's direction, or if wavelengths that long just exceed typical room dimensions, or....
 

Jeff Zaret

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I know I can not give you the techincal answer here but others may be able. I know that bass frequencies are very long and at times double due to room size and frequency. I personally believe there is some directionality to lower frequencies but not as defined as the mids and highs. If you listen to live music, small combo, jazz or rock and you definetly localize the lower frequencies. If this is all amplified it is much harder. We can feel lower frequencies at times where we actually can not hear them.

I think I need Roberto here to help as well as others :confused:

Jeff :cool:
 

MarkNewbie

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Jeff Zaret said:
We can feel lower frequencies at times where we actually can not hear them.


Jeff :cool:
I felt a low frequency in the car tonight. I could not hear it but I could smell it. I think the technical abbreviation is SBD. LOL

Actually this could be a perfect example of the "Post Hoc" falacy.
 

Peter Hogan

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Hi,
As I understand it, your ears get direction information by the timing or phase difference between the two ears. A sound off to your right will reach your right ear slightly before the left one, and lead it slightly in phase. As the frequency goes down, the wavelengths become longer, and the phase difference becomes a smaller percentage (it's basically the relationship of how widely spaced your ears are in comparison to the length of the sound wave.)

Personally, I have found that under about 50 Hz sound really is non-directional, between about 50-100 Hz, you have a general idea of direction, and by the time it is much above 120 Hz or so, you can do a pretty good job of pinpointing the location.

Peter
 

aliveatfive

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I believe the overtones of very low frequencies provide clues as to their location. Listen to an electric bass at a live band concert and you can usually tell where it is.
 

roberto

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Jeff Zaret said:
I know I can not give you the techincal answer here but others may be able. I know that bass frequencies are very long and at times double due to room size and frequency. I personally believe there is some directionality to lower frequencies but not as defined as the mids and highs. If you listen to live music, small combo, jazz or rock and you definetly localize the lower frequencies. If this is all amplified it is much harder. We can feel lower frequencies at times where we actually can not hear them.

I think I need Roberto here to help as well as others :confused:

Jeff :cool:
Hola Jeff, you are too much...our ears have a difference in timimg, .3 milisegs and these difference in time make us to, like the bats, triangule the sound and know from where it is coming...but we need the frequency to be above 100Hz, so lower notes, because of this timing, we can´t triangule right, and it is very difficult to our ears to know from where the sound is produced (lower notes)...you are right too...regarding the wave lenghs...happy listening
and always trust you ears!
Roberto. :D
 
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sakhavi

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thanks

Cool - thanks for the response, guys. As a great man once said, "I can see clearly now, the brain has gone."
 

Muad'Dib

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Peter Hogan said:
Hi,
As I understand it, your ears get direction information by the timing or phase difference between the two ears. A sound off to your right will reach your right ear slightly before the left one, and lead it slightly in phase. As the frequency goes down, the wavelengths become longer, and the phase difference becomes a smaller percentage (it's basically the relationship of how widely spaced your ears are in comparison to the length of the sound wave.)

Peter
Interaural timing differences are also influenced by head related transfer functions which lead to differences in intensity between ears. Obviously as you drop in frequency, HRTF's are decreased (unless you have an enormous head :)). HRTF's can lead to interaural intensity differences of over 20 dB at extremely high frequencies.

Typically you can assume that anything under 90Hz will be relatively non-directional. Oddly enough, if I remember correctly humans are least able to localize either 1200 or 700Hz and best at localizing the opposite. Sorry, totally blanking on which one goes where. But in my case, I'm least able to localize whichever tone is emitted by an elevator arriving at your floor - especially the elevators in the ACVAC at Rush Joey. lol

-D
 
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