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| ==== Two {{L1}}s in Mono ==== | | ==== Two {{L1}}s in Mono ==== |
| How much gain do you get when you run two L1® with the same source.
| | {{Two L1 Systems}} |
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| <!--This is an excerpt from a recent post from Ken-at-Bose. He will be updating this soon. -->
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| :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. Now, I've been proven wrong on a number of occasions, but if that happens on this occasion, Alan, the sound engineer you've been talking to is going to get a Nobel Prize.
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| :The problem is that 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 B1 bass modules is done for this reason -- to get the 6 dB per doubling of B1 systems. But at 1,000 Hz, where the wavelengths are 1' (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.
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| :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.
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| :So what we've said is
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| # put B1s together if you can because they'll give you an honest 6 dB per doubling of B1 systems;
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| # if you are sending a mono or stereo signal to spaced L1 systems, try to space them 20' (7m) or more if you can because this will minimize any audible cancellations.
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| :Alan, you've got enough spacing of your L1 systems and so I really don't see any problem with destructive interference. On the other hand, given the maximum benefit in level is only 3 dB, and you are somewhat reducing the clarity and accuracy of localization, I question the benefit. Your willingness to experiment is a good ingredient.
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| :I'm going to work next week on a Wiki article on this subject, someplace where I can try to put these thoughts together where they can be found time and time a again.
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| [http://bose.infopop.cc/eve/forums/a/tpc/f/778102955/m/108102942?r=879106073#879106073 Source: Ken-at-Bose]
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| === Distributed Systems for Covering a Large Area === | | === Distributed Systems for Covering a Large Area === |