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<blockquote data-quote="Nick Hickman" data-source="post: 51802" data-attributes="member: 556">Re: Single 18&quot;&nbsp; LF Box vs DoubleThe 3dB increase in efficiency is what people generally mean by &quot;coupling&quot;, but it does depend on the positions of the sources.&nbsp; If you add a second identical source separated from the first in open space and drive it identically, you&#039;re putting an extra 3dB into the system and you get an extra 3dB out.&nbsp; As you say, this isn&#039;t spread evenly over space but is +6dB at some places and -lots dB at others, and this varies with frequency.Now do nothing other than push the two sources together (relative to wavelength) and you get (ideally) +6dB everywhere.&nbsp; That&#039;s a net 3dB gain from the increase in radiation resistance caused by the sources being close together, aka &quot;coupling&quot;.&nbsp; A single source against a solid boundary does the same thing.&nbsp; It&#039;s thus not really about cone area (same cone area in the two cases) but about radiation resistance.This doesn&#039;t really affect the choice between single or double 18&quot; boxes, however, as the same phenomenon occurs with both.Nick</blockquote>

[QUOTE="Nick Hickman, post: 51802, member: 556"] Re: Single 18" LF Box vs Double The 3dB increase in efficiency [i]is[/i] what people generally mean by "coupling", but it does depend on the positions of the sources. If you add a second identical source separated from the first in open space and drive it identically, you're putting an extra 3dB into the system and you get an extra 3dB out. As you say, this isn't spread evenly over space but is +6dB at some places and -lots dB at others, and this varies with frequency. Now do nothing other than push the two sources together (relative to wavelength) and you get (ideally) +6dB everywhere. That's a net 3dB gain from the increase in radiation resistance caused by the sources being close together, aka "coupling". A single source against a solid boundary does the same thing. It's thus not really about cone area (same cone area in the two cases) but about radiation resistance. This doesn't really affect the choice between single or double 18" boxes, however, as the same phenomenon occurs with both. Nick [/QUOTE]

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