Subwoofer (for the organ) on an ultra-budget system?

[Deliriumbassist]

Not arguing with that, I am talking of 2 of the same subwoofers will only give +3db due to increased come area, amplification remains the same.

Bill

You say you're not arguing with that... and then you do. Which is it? When you double the number of powered subwoofers, you are doubling the amplification. If you double the drivers without doubling the system wattage, you are dividing the wattage between the additional units, which is why you only yield the extra 3dB through additional cone area and acoustic coupling. When you double the number of powered subwoofers, you are doubling the cone area and system wattage, yielding +6dB.

 

[abacus]

You say you're not arguing with that... and then you do. Which is it? When you double the number of powered subwoofers, you are doubling the amplification. If you double the drivers without doubling the system wattage, you are dividing the wattage between the additional units, which is why you only yield the extra 3dB through additional cone area and acoustic coupling. When you double the number of powered subwoofers, you are doubling the cone area and system wattage, yielding +6dB.

Matching subwoofers, both are 150w and with the same input produce 86db individually, play them both together and the only thing that has changed is the doubling of the surface area, hence the 3db increase.
You have a 7 channel Receiver that that puts out 50w per channel, which means a total of 350w, however the sound produced by the speakers is still only 50w each as they are individual with their own dedicated channel . (Just because you have more power doesn't mean more volume unless you increase the power on the channel)
If you connect to drivers to 1 amp then you should also get 3db (In reality it is less due to the way the drivers interact to each other), now if you double the output of the amp as well then you will get a theoretical 6db increase in output (Due to losses and interaction it will always be less)
To put it simply, adding an extra separate amp to drive another speaker, does not give you double the power output. (That's not how amplification works)

Bill