Sub placement is important, but not because low frequencies are directional. They truly are not, and it's because of the long wavelengths relative to the space between your ears. 

It's phase differences from one ear to the other that we subconsciously process to derive directional information. Consequently, frequencies with a quarter-wavelength less than the distance between your ears are difficult or impossible to identify where they're coming from. That's why the conventional cutoff between directional and non-directional frequencies is usually given as 500Hz - that's about a 24-inch wavelength, or a quarter-wavelength of 6 inches, a little less than the approximate distance from ear to ear.

At 100Hz, the wavelength is about ten feet, making it impossible to detect either a phase or amplitude difference from one ear to the other. You'd have to have a head 2 1/2 feet wide to have any hope of determining what direction the sound is coming from.

What makes sub placement critical is the dispersion of resonant peaks and nulls. This is also why mastering rooms typically have two (sometimes even 3 or 4!) subwoofers, so that they can partially cancel out each others' constructive and destructive interference. (See Floyd Toole's superb book "Sound Reproduction" for the full story.)

If you place your sub in such a way that there is a large peak at the listening position, ARC will have a hard time compensating for it. If you place your sub so that there is a large null at the listening position, ARC will be unable to do anything about it at all. You can't compensate for something that isn't there. 

What you could do is experiment with different sub locations and let ARC show you which one is the least problematic. Of course, you don't need ARC for that. You can do it by ear. And you don't even have to move the subwoofer to do it.

Rather than drag a heavy speaker around the room, set your subwoofer on a tall stool at the listening position and play music or noise while you move yourself around to different locations. When you find the spot that has the fewest noticeable peaks and nulls, that's where you want to set your sub.

"Sub placement is important, but not because low frequencies are directional. They truly are not"

Low frequency is directional... I'll never understand how people can say it's not.

"it's because of the long wavelengths relative to the space between your ears."

This is a description of our limitation as listeners... not an explanation of why something that actually is directional is not.



Elephants know exactly where the girls in rut are by listening to low frequency and subsonic* mating calls that travel for miles. The elephants have been observed to acknowledge the sound and then walk straight through the forest to the source of the sound.

Of course they do have bigger heads to better appreciate the directionality of the low frequencies.





*subsonic: Our understanding of "subsonic" hearing limitations has been modified by improvements in sound play back technology. 

http://en.wikipedia.org/wiki/Rotary_woofer

This woofer goes down to 1Hz with enough efficiency that it can easily reproduce what used to be considered subsonic with enough SPL that humans realize they can hear well below what has traditionally been described as a practical limit.

Turns out we just didn't have good enough test equipment... and now we do.



all the best,
mike

Do you get many Elephants listening to your stuff Mike?

I'm trying to penetrate that demographic, your input here may be vital to my success.

Thanks for the input.

btw the guy that designed these before radar existed knew that low frequencies were directional 80 or so years ago.  They worked out where the next enemy plane was coming from miles out in the English Channel.  But that application needed to work better than human hearing.  Music production doesn't generally have a requirement to identify a Heinkel's position from 20 miles out, unless I'm really old-fashioned.

Here's an article about Elephants.

http://www.pbs.org/wnet/n...ble/communication.html


I am familiar with those structures you posted a photo of.

http://en.wikipedia.org/wiki/Acoustic_mirror

"Spherical mirrors may be used for direction finding by moving the sensor rather than the mirror;"

"The acoustic mirror programme, led by Dr William Sansome Tucker, had given Britain the methodology to use interconnected stations to pin point the position of an enemy in the sky. The system they developed for linking the ranging stations and plotting aircraft movements was given to the early radar team and contributed to their success in World War II; although the British radar was less sophisticated than the German system, the British system was used more successfully."

I find them, and the imaginative people who formalized the procedure to make use of them fascinating.

Here's how the French were listening:

I don't know about you guys but I regularly enlist the help of an elephant when I'm having trouble tightening up the low end. A most useful mammal and, they work for peanuts. ;-)

FWIW ---  from the Audyssey web page:

ARC uses Audyssey MultEQ® XT32 

http://www.audyssey.com/audio-technology/multeq


MultEQ XT32 
Our newest and most accurate room correction solution with more than ten thousand individual control points allowing finer details of the room’s problems to be captured and corrected. The ultra high resolution filters are applied to all channels including the subwoofers, with the most obvious benefit being heard in the low frequency range where correction is needed the most.

Yes, that is a description of a system that is built in to a hardware appliance, usually a "receiver", that is designed around a surround sound matrix.

The surround "Matrix" is a crossover of sorts (only as a analogy... the technology is very different) in that the appliance has discreet control over the actual send to each speaker box.

What it doesn't do is work on individual drivers AFTER the actual cross overs in the speaker.

With stereo playback we only have 2 sends, left and right, and any sub woofer is split out AFTER a crossover and so unlike _.1 systems that have discrete subwoofer sends (2.1, 5.1, 7.1, 10.1 etc) a stereo send such as facilitated by Audyssy's little cousin ARC has no practical way to control the sub woofer discretely.

So you just incorporate it into the testing for both the left and the right and make the best of it.


best regards,
mike

Never thought I would learn this much with the question ! Now I am thinking I may need to plan on a few I beams in the floor and the pick up an elephant or two to put in the corners. If I can train them to trumpet when they hear too much low end, I will be able to really tune the room nicely! I guess I just need to make sure they are not male and female or I may really be in trouble LOL. Thanks again all! gs

Mix set up and playback really are important and can intricate fast. Especially when adding a sub. I've learned a bit here as well.