Two L1 Systems
- This discussion pertains to using two L1 systems with the same sound source (Dual Mono). For a discussion about stereo see Stereo / Mono / Distributed Systems
- What is the benefit of using two L1 systems over one?
- You will get more coverage (based on the distance between the L1 systems) and an increase in loudness (but not double the loudness) .
- How much more coverage will I get?
- The increased coverage will be the result of the distance between the two systems. For example, if you place them twenty feet apart in the horizontal plane, you will get twenty feet more coverage from side to side. You will also increase the overall sound level by +3 dB. Your projection straight ahead may improve but that is harder to predict as the distances increases.
- How much gain do you get when you run two L1 systems with the same source?
- Short answer: +3 dB in practice
- +6 dB in theory
The most you can ever get from putting two sources fed by the same signal together is +6 dB. The reason?
- Sound waves add in space through the principle of superposition. If the waves from two sources perfectly add, you get twice the amplitude, which is +6 dB.
- To get the full +6 dB the two sources have to be spaced very closely together relative to a wavelength of sound. at 50 Hz, where the wavelength of sound is about 20' (about 7 meters) that's pretty easy to do. Massing your bass modules is done for this reason -- to get the 6 dB per doubling of bass module systems. But at 1,000 Hz, where the wavelengths are 12 inches (about 30 cm) you just can't do get L1 speakers close enough. As a result, you get something less than 6 dB because at some angles instead of the sound waves constructively adding they will destructively cancel (one will be partly or completely out of phase with the other).
- +3 dB in practice
Once you separate the sources by several or more wavelengths, the summations and cancellations are so numerous and so complex that we say the two sources are essentially uncorrelated (not strictly true, but for the purposes of this argument, a very close approximation.) When two sources are uncorrelated the only thing you can count on is that the total amount of acoustic power going into the room will be doubled. Doubling the power is +3 dB.
- Is +3 dB twice as loud?
- Doubling the power (+3 dB)is not twice as loud.
- A non-exact rule-of-thumb is that every 10 dB increase is a doubling of perceived loudness. 
- Put bass modules together if you can because they'll give you an honest 6 dB per doubling of bass modules/
- If you are sending a mono or stereo signal to spaced L1 systems, try to space them 20 feet (7 meters) or more if you can because this will minimize any audible cancellations.