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What Frequencies are Omnidirectional?

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#1
I searched and found a lot of answers. So, now to the scientists...

What frequencies are omidirectional?

Just askin' ;)

Thanks!

Aaron
 

Cbdb2

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#4
Short answer. The ones with 1/4 wave lengths much larger than the transducer.

"Bass frequencies have very long wavelengths which make it difficult to control the direction they travel. For a loudspeaker to have moderate control of directivity at 40Hz would require a physical size greater than 18 feet (6m) square. To maintain any directional control at 100Hz requires a size in excess of 6 feet (2m) square. Even at 500Hz, a loudspeaker has to be over 3 feet (1m) square. Up in the rarified atmosphere of higher frequencies, say 2,000Hz+, the speaker can be as small as 1 foot (30cm) square. At ultra-high frequencies, above 8,000Hz, a super tweeter is difficult to build without it having too much directional control, because at any physical size you can build the device it tends to become very directional through its operating band."

From http://www.mcsquared.com/speakers1.htm

There are some tricks to get around this (like using the walls as a LF horn), but this is the basic rule.
 
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A
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Thread Starter #5
Hmm, good. This explains why I didn't find one answer. Maybe a different question would be better:

What frequencies work for flexible subwoofer placement(s) around a room? In other words, at what frequency does it become difficult to discern where the sound is coming from?
 

sq225917

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#6
You're falling into the gap between directivity and direction. After 200hz it's pretty easy to tell where the sound is coming from, ie left, right, front, back etc, below 100hz it barely matters.

Being able to control directivity and sound having an identifiable source and direction aren't quite the same thing.


Ime if your sub outputs much over 150hz placement becomes much more important in terms of sound field, obviously placement is important for room effects at any frequency, but over 150hz other things increasingly come into play
 

Cbdb2

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#7
Another trick question. But an important one. If you can point to the sub with your eyes closed it will steer the image at LFs. (unless its between the mains). Some of the factors. The steepness of the filter. The amount of distortion (the third harmonic of 40hz sounds 15db "louder"). The level of the sub compared to the mains, the position of the sub and the room. Mostly thou its the LPF.

The upside, you can use your ears. Turn of everything but the sub and try to locate it. If you can, steepen the filter and or decrease the freq. You may be surprised how low/steep you have to go. Thank Fletcher and Munson for that. Mine is set to below 40hz.
 
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Wes

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#8
The fun thing is that while higher frequencies "beam" they can also bounce off of things, making it hard to echolocate a source.
 

Cbdb2

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#9
Our brains are great at using the ears for location. Evolution to survive. We can locate even in a highly reflective room, maybe not as acurately but we still do it. The direct sound always reaches the ears first, unless theres an obstacle inbetween, and the brain sorts it out. Some experiments show some humans can hear a 1 degree change in location. This is equal to a time difference of 10 usec! ( look up intra aural time delay).
 

noname

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#10
sound_radiation.png


I'm not sure if this is what you're looking for. I got it from Genelec Monitor Setup Guide.
 
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