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PM DIY Baffle Step
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<blockquote data-quote="Peter Morris" data-source="post: 213255" data-attributes="member: 652"><p>Firstly the PM DIY was designed to be relatively small and pole mount. This meant there were compromises made, especially in the low frequency area.</p><p></p><p>The trick was using a horn and compression driver that could go low enough to be used a 12” bent horn and a box design that had no wasted space to keep the size and weight down.</p><p></p><p>While I expect there would be an increase in SPL at the low frequencies by adding a baffle, I think you would be much better off increasing the size of the horn – longer path and bigger mouth, but then the concept has changed <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p><p></p><p>The gain from the baffle occurs because you are effectively radiating into ½ space instead of whole space, but where the directivity is already controlled by the horn there is nothing to be gained.</p><p></p><p>When you talk about getting 6 dB of additional output by putting 2 speakers together - you get 3 dB more output because you have doubled the power input, and 3 dB because of the increase in efficiency. The area of 2 cones provides a better impedance match (coupling) to the air and the efficiency goes up. There are limits to this, and when the array size becomes large compared to the wavelength of what its producing other problems occur ...</p><p></p><p>Put two compression drivers on more or less the same horn you will only get 3 dB increase in output. There will not be an increase in efficiency as the horn has already increased the efficiency of the system by matching the acoustical impedance of diaphragm to the air.</p></blockquote><p></p>
[QUOTE="Peter Morris, post: 213255, member: 652"] Firstly the PM DIY was designed to be relatively small and pole mount. This meant there were compromises made, especially in the low frequency area. The trick was using a horn and compression driver that could go low enough to be used a 12” bent horn and a box design that had no wasted space to keep the size and weight down. While I expect there would be an increase in SPL at the low frequencies by adding a baffle, I think you would be much better off increasing the size of the horn – longer path and bigger mouth, but then the concept has changed :) The gain from the baffle occurs because you are effectively radiating into ½ space instead of whole space, but where the directivity is already controlled by the horn there is nothing to be gained. When you talk about getting 6 dB of additional output by putting 2 speakers together - you get 3 dB more output because you have doubled the power input, and 3 dB because of the increase in efficiency. The area of 2 cones provides a better impedance match (coupling) to the air and the efficiency goes up. There are limits to this, and when the array size becomes large compared to the wavelength of what its producing other problems occur ... Put two compression drivers on more or less the same horn you will only get 3 dB increase in output. There will not be an increase in efficiency as the horn has already increased the efficiency of the system by matching the acoustical impedance of diaphragm to the air. [/QUOTE]
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