Subwoofers - crazy upgrade!

@lewinskih01

In my case, going from 2 Rythmiks F12 to 4 didn't make the bass louder (as I did adjust the power to a target) and I couldn't tell if they were distorting less (they weren't to start with), but the improvement came from a more homogeneous bass response across the room.

Going from 2 subs to 4 subs helps with better bass distribution but it's not he same as if you coupled/stacked them together.  When you couple them its a new subwoofer that has twice the power and twice the cone area. It will far outperform and move more air, with more force than any of the single subs. 2 double stacks will outperform 4 single units spread around the space.

This is the same reason why at pro concerts the subs are always stacked in a cluster rather than spread around when output is the goal. 

@lewinskih01    A good analogy is each of your subs are capalble of generating a certain size wave. All 4 of them are generating the same size wave in different locations evenly around the room.

If you stack them they now become 2 units instead of four but they each push double power and double cone area and can create 2 much LARGER waves. Almost double the size!!! Big powerful waves instead of 4 little waves.

It's physics. It's how it works.

@gdaddy1 

sorry, but it's not. At the same sound level in the room, the 4 subs/amps put out the same energy whether they are stacked one on top of the other or spread out. When stacked, acoustically both subs behave as one larger one, but still outputting the same energy as if they were spread out. The advantage of spreading out is the more even bass response in the room across different locations.

Stacked subs provide larger headroom, but that's rarely the issue with multiple good subs in a living/audio room. Stacked subs can push twice the power and surface, but that's headroom and not SPL at a given sound level in the room.

@lewinskih01  At the same sound level in the room, the 4 subs/amps put out the same energy whether they are stacked one on top of the other or spread out. 

That's just not true..it takes LESS energy to get the same sound level in the room. When you stack them, without changing any of the settings, you would get a 3db to 4db boost in your room just by making stacks of two instead of 4 seperated locations.

Acoustic coupling vs. amplifier power

People often confuse these.

Case 1

One sub.

100 watts.

Reference SPL.

---

Case 2

One sub.

200 watts.

Cone excursion increases by about √2.

Pressure increases by √2.

Result:

+3 dB

---

Case 3

Two identical subs.

100 watts each.

Total amplifier power = 200 watts.

Pressure doubles because both cones radiate together.

Result:

+6 dB

 

@ozzy I have 4 subs, placed in the corners of the room. But I wonder if stacking 2 in the front would be better?

In 2011 when I slightly asymmetrically corner positioned two Velodyne 12" Plus, one DD-18" and a 15" Earthquake Nova in a large vaulted living / dinning room.This eliminated ALL that rooms standing wave bass modes. The Velodyne Auto EQ and gain were changed substantially. This distributed bass array became my audible low frequency reference experience even today.

In 1967 a recording engineer sold his Octavium Subwoofer cabinet to me and demonstrated how to find any rooms bass modes for optimal sub positioning, now referred to as the subwoofer crawl. While the distributed bass array essentially eliminates the need for the crawl, it's still nice to know a rooms modes. 

Other than a brief time with a huge REL Studio III "Sub-Bass System" using its corner placement instructions I have found corner or front wall positions to be very problematic for -3dB rated subwoofers. The -6dB Studio III simply didn't play low enough to excite the rooms standing waves, as a result it could be located most anywhere in the room.  All the best.