Sub Alignment

So you've reviewed my resources on system design. You've seen the materials on system tuning and reading phase graphs. Now you realize you want to align your subs with your mains but you just want a simple method.

Well, this article by Merlijn van Veen with Meyer Sound is probably the best article on the topic.

Process is outlined here.

In this article, Veen discusses the process to aligning your subs and provides a useful calculator for doing so. Bob McCarthy and Merlijn van Veen are the leading experts on these topics of system design, tuning, and sub alignment. Veen's website is stocked full of articles on all kinds of audio engineering topics that are sure to make you excited if you like getting a little nerdy. I'd also highly recommend this book by McCarthy. I actually haven't read it myself, but at only $86, it's top of my reading list and has been highly recommended by other audio professionals I respect.

The quick and simple run down of sub alignment is... unless your subs are coplanar and at the same height with your mains, there is, by simple geometry, only going to be one place in the room that you will get exact alignment between your subs and mains. Every other location will have a different distance between the main speakers and the subs. Thus, if you plan to have a system flown, you want the subs flown too! If you have speakers close to the stage, you'll want your subs at the same level. Once you've determined the time difference between different speaker locations to a single reference point, you will then dive into phase alignment in your software to get the crossover frequency range to have matching phase graphs.

Contrary to popular belief, the best location for your subs is.. 95% of the time... NOT on the sides of the stage. This may be shocking, as it seems they are almost always located far L and R. But as you can see in my MAPP 3D tutorial, subs will cause valleys of cancelation through the middle of the venue if they are separated from each other. The distance of separation will determine the number of troughs in cancellation and the frequencies at which they occur. Your best location for subs is front and center. The exact positioning can be adjusted to achieve different response patterns in low end.

So, if you want a quick and simple way to align your subs and mains. Pick a location, take measurement data of your mains. Determine time offset, then work on time aligning your subs with your mains at that location. 

There are some sites you can pay for a sub alignment calculator, but I would highly recommend looking at this free calculator from Veen.

To better understand how phase shifts as you move back from reference point, I created the below Desmos simulation which shows phase at a given frequency given that subs and mains are coplanar but with subs on the floor and mains flown. The calculator uses an alignment to a reference location and then determines degree of phase shift if you move forward or backwards in the room. Veen recommends that you stay between 0 and 60 degrees of shift in crossover region.

Remember this very important truth when aligning subs, in time does not mean in phase. You can have signals which are arriving at the same time but out of phase. You must get comfortable with reading phase graphs and aligning them in order to get constructive summation between waves in the crossover region.

Additional videos on aligning subs and dealing with the phase graphs.

• At time 33 minutes, talks about phase of mains and subs

• At 9 minutes, talk on sub alignment

You can play with your own copy and adjust all the details here: Link to Desmos worksheet.