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Author Topic: Why Are Low Frequencies Non Directional And High Frequencies Are ?  (Read 9824 times)

Offline neilep

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Dearest Bass-ologists and All those Interested In Low Frequency Joyness !

As a sheepy I of course like bass....oh yes !...I'm there ' aving-it-large' and 'giving-it-some' every Friday night down the club enjoying some muzak with lots of bass !


Out of all the frequencies that are available to be enjoyed........ the low end ' kwality' depth just razzles my wool...

look...here I is enjoying some bass !!


Me Enjoying Bass Earlier Today



Thing is...I need not be standing right beside the subs to be able to enjoy them...in fact...they can be almost anywhere in the room and I would still enjoy bassgasms where ever I stand !

why's that then ?

Cos, the medium to high frequencies are very directional and quite fussy about where ewe are situated...but bass ?...well bass is the bad boy...he don't care where ewe be...he just rocks yours world and lets ewe know it !


As firm believer in empirical study I stacked twenty subs up outside my neighbours bedroom door at 3am this morning.....I had some Slipknot on endless repeat followed by some Drum 'n Bass and then three hours of ' Grandma we luff ewe  ' by St Winifreds School Choir (the ' we've-all-grown-up-and-shake-our-butts-Mix) .......I instructed him to carefully move from one part of the room to the other whilst keeping detailed notes and communicating it to me via the medium of dance...unfortunately....with the subs in the way and the door closed and locked..I could not see or hear him...so..no luck there then. However, he must have been enjoying himself because spying through the keyhole I could occasionally see him banging his head on the wall....

So, can ewe help me understand why bass is non directional and why higher frequencies are  ?




Hugs & shmishes



mwah mwah mwah




Neil
Totally Addicted To Bass
xxxxxxxxxxxxxxxxxxxxx










« Last Edit: 18/02/2010 20:12:34 by neilep »


 

Offline BenV

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I'll hazard a guess at this...

Our brains detect direction of sound from the time difference between reaching each ear.  If the frequency is higher, the time difference would mean the sounds are more out of phase (as in, with a short wavelength, the time difference will amount to a greater proportion of each wave). The longer the wavelength, the less phase difference there will be for the same time delay.

Does that make sense?
 

Offline Geezer

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I think it's more to do with air mass and energy.

Higher frequency sounds will be reflected off hard surfaces and absorbed by soft surfaces (like fleece for example). When they are absorbed, the energy is dissipated.

Low frequency sounds require a substantial mass of air movement. The oscillating air pressure wave tends to go right through things like walls by causing the wall to oscillate, and soft objects don't absorb the sound energy because of the longer wavelengths.

Or something like that!
 

Offline Geezer

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Come to think of it, low frequency sound can travel for great distances, whereas higher frequency sounds dissipate much more rapidly.

I seem to remember a device that was used during WW1 to locate the position of enemy guns by detecting the LF sound. If I remember correctly, the distances involved could be as great as 20 miles.

Also, elephants seem to be able to communicate over great distances by using infrasound.

EDIT:

Apparently the directionality of a loudspeaker is a function of the size of the speaker and the wavelength of the sound. At high frequencies, the wavelengths are quite short relative to the speaker dimensions, so high frequencies are quite directional. Even with large woofers, the wavelengths of low frequencies are still large in relation to the speakers, so the low frequencies tend to radiate in all directions.

So, I suppose if you use really big woofers, the low frequencies will be much more directional. You can also achieve a similar effect with an array of smaller speakers operating in phase.

« Last Edit: 19/02/2010 03:19:19 by Geezer »
 

Offline RD

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Diffraction is frequency dependent ...

Quote
lower-frequency sounds typically have a wide dispersion and sounds with small wavelenths have a narrow dispersion.
http://library.thinkquest.org/19537/Physics6.html

"lower-frequency" = long wavelength
 Higher frequency = "small wavelenths".

Low frequency sound travels further than high because the high frequency sound energy is more rapidly converted into heat: if the transfer of sound energy to heating the medium (e.g. air) is x% per cycle the more cycles per second means more rapid loss of sound energy. This is why when a boyracer approaches you can hear the banging bass of his stereo first.
« Last Edit: 19/02/2010 21:33:39 by RD »
 

Offline LeeE

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Yes, diffraction has a lot to do with it.  I calculate the wavelength of a 20Hz signal at sea level to be about 17 metres: this will generally be larger than the typical room that you'll be listening in and considerably bigger than your lugholes.
 

Offline neilep

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GOSH !!..Thank ewe Ben,Geezer,DDave, LeeE and RD for your very helpful answers.

I do recall now something being mentioned about wavelengths in one of the many courses I did when I was selling Hi Fi, specifically to do with Sub Woofers. It was always mentioned that Subs can really (with some exceptions) be placed anywhere in a room because of the non-directionality of the bass....but I never recall why so. There was also a way to find the ' sweet spot' by placing the sub in various locations in the room...I can't remember why..it may have been part of the setting up procedure....sheesh !.....My brain's a sieve !
 

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