Axiom Home Page Forums General Discussion Home Theater Phase setting when using 2 subs ?

I will be receiving my EP500 in a few days and adding it to my current setup which contains an Energy 10" sub. I will place the EP500 where my current sub is, being my listening position, and the 10" sub in the front, diagonally accross from the other sub. Question is: do I have to adjust the phase setting on the EP500 to 180 ? because I have 2 subs ?

For those with 2 subs, how did you set the phase, or other settings on the EP500 ?

Riker,

If both of your subs are about the same distance from your seat, then you should definitely keep the phases set the same. The phase setting on your sub is not dependent on the number of subs but rather on the distance the sub is from the main speakers. The phase comes into play in the crossover slope area where the sound waves from the sub mix with the sound waves from your mains. You want the peaks from the speakers to line up with the peaks from the sub (more or less). If, instead, the troughs from the sub line up with the peaks from the speaker, you'll have a canceling out effect. The phase switch is there to compensate for this situation.

I made some images a while back to try to illustrate this.



In the above picture, notice that 360° for a sound wave is the distance of one Hertz, or one cycle of the wave.



This second picture shows the same sound wave, but it is exactly 180° out of phase with the first wave. Keep in mind that your ear absolutely cannot tell the difference between one phase or the other -- unless there's more than one wave source reaching it at the same time.



This image shows the two waves overlaid. When you have two or more sound waves interacting, the energies sum up. Your ears hear the wave that results from this "wave addition." As you know, adding a negative number (sound below the horizontal axis) to a positive number (sound above the horizontal axis) results in subtraction. The end result of this example would be complete silence.

The basis for white noise, Yes?

I know in Ian's multiple subwoofer video, he said in most cases, leaving at 0 on all subs should be fine. Most of the time when I've done testing it is hard to tell the difference.

I think white noise works by filling in the gaps between sounds and making everything sound like a normalized droning. A steady sound is much easier for your brain to tune out.

Stephane, another reason for keeping the same phase setting on your two subs is to maximize the smoothing of room modes. When two subs are in diagonally opposite corners they both excite the room modes for length and width to the maximum, but the positioning results in a partial cancellation of those modes because each sub's output is of opposite phase when it reaches the other corner. So, to allow this effect to operate, the subs should start out with the same phase setting.

Ok.. Thanks John.. I am going to start with the EP500 as the only sub and make sure all is well ie: levels etc.. then add the second sub (my current energy) . I will start with both subs at the Zero position for Phase and go from there.

Thanks Peter for the graphs.. I actualy understand what you are describing, well 90% of it at least

I will experiment with both settings on both subs until I find what sounds best in my room .. which I guess is always the real answer to most questions.. just play with it until you find what sounds best in your specific room