Stereo Sub woofers

[malsackj]

I found this article on sub woofers and think it is a good article on the problems encountered when working with multiple subs.

http://www.prosoundweb.com/article/opti ... echniques/


What do you all think about the article?

 

[Batman]

I will definitely read it, I am currently toying while multiple subs (as you know) and will give you my feedback on how the article pertains to me...

 

[Flint]

The article is about PA applications where the subs could be great distances apart with no reinforcing barriers near them. Basically, it is all about lobing from two drivers, directionality from multiple drivers, and line array patterns over very large areas.

In a real room, where the longest distance between subs is under 16 feet, I don't think any of this stuff will apply if the crossover is below 80Hz.

 

[malsackj]

That may be well true to the facts but look at the math and consider your second harmonic from the 70 hz or 80 hz. How much second or third harmonic resonance is produced and at what distance between subs? 16 feet would be half of 32 feet for 20 hz or 180 out from 0. This has been to show the effects in stereo subs and a strong position for single sub. Unless one has the time to test with a meter for problems in the room and based on size of the room adding to the room modes.

If a larger system outside with no room acoustics has these problems. Than bringing the stereo subs into the room will have these problems plus the room issues to help cloud the problems that need to be addressed.

 

[Flint]

That may be well true to the facts but look at the math and consider your second harmonic from the 70 hz or 80 hz. How much second or third harmonic resonance is produced and at what distance between subs? 16 feet would be half of 32 feet for 20 hz or 180 out from 0. This has been to show the effects in stereo subs and a strong position for single sub. Unless one has the time to test with a meter for problems in the room and based on size of the room adding to the room modes.

If a larger system outside with no room acoustics has these problems. Than bringing the stereo subs into the room will have these problems plus the room issues to help cloud the problems that need to be addressed.

The 1/4 wave rule doesn't work the same in a room with tons of hard reflective barriers (walls, floor, & ceiling), so one has to reach nearly full wave distance between two sources in that environment to really experience the comb filtering effect discussed in the article. The article assumes there is no nearby reinforcing surface to derive the math.

So, in order for the effects discussed in the article to apply to a room, the subs would need to be 28 feet apart for a 40hz comb filter, and the listener would have to be seated outside of the 28ft distance between the subs.

Also, the entire article was based on all of the subs reproducing exactly the same signal - in parallel. With good stereo recordings you won't see this effect much. For HT LFE signals you could if all the criteria are met.

 

[malsackj]

Thank you our man Flint.

I look forward to further educating facts.