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PM DIY Baffle Step
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<blockquote data-quote="Andre Vergison" data-source="post: 213267" data-attributes="member: 13374"><p>True. I tried this out using two 6" drivers close to each other and an SPL meter somewhere in the room, and feeding the drivers with 400 Hz. In parallel I get 6 dB gain when adding the second driver, and power has doubled. When wired in series then shunting one of the drivers (half impedance -> double power on a single driver) yields about equal SPL.</p><p></p><p>So replacing one driver by two will buy me +3 dB for the same amount of power.</p><p></p><p>Now, if I replace a single 6" by four drivers in a tight square (let's not consider lobing effects etc.) and connect them in series and parallel to get a same input impedance then I would get +6 dB with the same input power, right?</p><p></p><p>Via <a href="http://techtalk.parts-express.com/forum/tech-talk-forum/44566-added-spl-by-doubling-drivers?p=628587#post628587" target="_blank">http://techtalk.parts-express.com/forum/tech-talk-forum/44566-added-spl-by-doubling-drivers?p=628587#post628587</a> and going to the said book, I read on page 78 that the frequency below which mutual coupling (causing an increase of radiation impedance) becomes effective is given by</p><p></p><p> F = sqrt(N) * c / d</p><p></p><p>N is the number of coupled drivers</p><p>c is the speed of sound (m/s)</p><p>d is the nominal spacing between drivers (m)</p><p></p><p>A figure on the same page confirms that 4 units may add up to 6 dB given a same input power.</p><p></p><p>So my four squared 6" drivers would then be 6 dB more efficient up to some 2500 Hz.</p><p></p><p>A more impressive example is two rows of four adjacent subwoofers (8 in total) which would gain 9 dB efficiency in their typical subwoofer range. If one subwoofer gets 1,000 watts then the equivalent power for the whole group would become 8 * 1,000 * 8 = 64,000 watts. I.o.w. if there were no coupling then you'd need 64 subwoofers to get the same SPL.</p><p></p><p>Crazy.</p><p></p><p></p><p></p><p>Of course. But do you have an idea of the directivity of the DIY mid horn both horizontally and vertically? Did you also mean that at lower frequencies (say 100 Hz) the box is not omnidirectional at all?</p></blockquote><p></p>
[QUOTE="Andre Vergison, post: 213267, member: 13374"] True. I tried this out using two 6" drivers close to each other and an SPL meter somewhere in the room, and feeding the drivers with 400 Hz. In parallel I get 6 dB gain when adding the second driver, and power has doubled. When wired in series then shunting one of the drivers (half impedance -> double power on a single driver) yields about equal SPL. So replacing one driver by two will buy me +3 dB for the same amount of power. Now, if I replace a single 6" by four drivers in a tight square (let's not consider lobing effects etc.) and connect them in series and parallel to get a same input impedance then I would get +6 dB with the same input power, right? Via [URL]http://techtalk.parts-express.com/forum/tech-talk-forum/44566-added-spl-by-doubling-drivers?p=628587#post628587[/URL] and going to the said book, I read on page 78 that the frequency below which mutual coupling (causing an increase of radiation impedance) becomes effective is given by F = sqrt(N) * c / d N is the number of coupled drivers c is the speed of sound (m/s) d is the nominal spacing between drivers (m) A figure on the same page confirms that 4 units may add up to 6 dB given a same input power. So my four squared 6" drivers would then be 6 dB more efficient up to some 2500 Hz. A more impressive example is two rows of four adjacent subwoofers (8 in total) which would gain 9 dB efficiency in their typical subwoofer range. If one subwoofer gets 1,000 watts then the equivalent power for the whole group would become 8 * 1,000 * 8 = 64,000 watts. I.o.w. if there were no coupling then you'd need 64 subwoofers to get the same SPL. Crazy. Of course. But do you have an idea of the directivity of the DIY mid horn both horizontally and vertically? Did you also mean that at lower frequencies (say 100 Hz) the box is not omnidirectional at all? [/QUOTE]
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