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Low Earth Orbit
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New DIY Mid High (90deg) - AKA PM90
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<blockquote data-quote="Peter Morris" data-source="post: 138064" data-attributes="member: 652"><p>Re: New DIY Mid High</p><p></p><p></p><p></p><p>Hi Jeff,</p><p></p><p>That’s fantastic! </p><p></p><p>Some more information about the 12 inch driver selection: </p><p></p><p>The mid horn needed to go from 100 Hz to 700 Hz. Building the prototype was to test if the W design would work over that range … and it does.</p><p></p><p>This is also where the BMS 4594 has an advantage in this design when compared to a normal compression driver, it will operated down to 700 Hz at full power. This means that the 12", the HF and VHF are all operating in their piston range without cone or diaphragm breakup. </p><p></p><p>I looked at many many different 12 inch drivers and the RCF had the right combination of cone mass, BL product, Xmax and power handling. There were many other drivers that are just as good as the RCF but they didn't have parameters needed for this design.</p><p></p><p>One driver that would work OK is B&C 12NDL76, slightly less power handling than the RCF but it SIMs well. I think it’s also a little lighter and cheaper, but I don’t know how its distortion level compares. </p><p></p><p>As it turns out I just happen to have 4 of these lying around and when I get a chance I will do a comparison with the RCF. If they work in this design Bennett may be able to assist :?:</p><p></p><p>The B&C has a much more conservatively rated Xmax. That may translate to a performance advantage when pushed … however I don’t know. </p><p> </p><p> - 12NDL76 – Xmax = 6.5mm, coil length 19mm, top plate 10mm</p><p> - RCF MB12N351 – Xmax = 5.5mm, coil length 16.5mm, top plate 11mm</p><p></p><p>At the rated power the maximum Xmax needed is 5.5 mmm @ 100Hz. Below 100Hz the Xmax is less because of the porting. </p><p></p><p>Dynamic compression and distortion can increase when the amount of the VC in magnetic gap is less the the height of the top plate / magnetic gap. In this respect the B&C should do better as it maintains 100% VC in magnetic gap up to an Xmax of 4.5mm. The RCF can only do 2.75mm ... but its not quite that straight forward.</p><p></p><p>With respect to the 60 degree version using 18sound XT1464 it looks like it will provide 2 – 3 db more output. Some of this is due to the narrower pattern, and some because it a little larger and maintains it efficiency down to a lower frequency.</p><p></p><p>The horn is slightly deeper and will require the box to be 10 – 20 mm deeper. This will increase a little extra length to the horn which in this case will be a plus.</p><p></p><p>Given that a 60 degree box is likely to be used in pairs the plan to make the rear section of the box trapezoidal as far as possible (tricky). The SIMs indicates that a pair of boxes will run continuously at around 138 dB whole space in the low mids. I suspect because I have not included directivity in the model its probably 3 dB more in use.</p></blockquote><p></p>
[QUOTE="Peter Morris, post: 138064, member: 652"] Re: New DIY Mid High Hi Jeff, That’s fantastic! Some more information about the 12 inch driver selection: The mid horn needed to go from 100 Hz to 700 Hz. Building the prototype was to test if the W design would work over that range … and it does. This is also where the BMS 4594 has an advantage in this design when compared to a normal compression driver, it will operated down to 700 Hz at full power. This means that the 12", the HF and VHF are all operating in their piston range without cone or diaphragm breakup. I looked at many many different 12 inch drivers and the RCF had the right combination of cone mass, BL product, Xmax and power handling. There were many other drivers that are just as good as the RCF but they didn't have parameters needed for this design. One driver that would work OK is B&C 12NDL76, slightly less power handling than the RCF but it SIMs well. I think it’s also a little lighter and cheaper, but I don’t know how its distortion level compares. As it turns out I just happen to have 4 of these lying around and when I get a chance I will do a comparison with the RCF. If they work in this design Bennett may be able to assist :?: The B&C has a much more conservatively rated Xmax. That may translate to a performance advantage when pushed … however I don’t know. - 12NDL76 – Xmax = 6.5mm, coil length 19mm, top plate 10mm - RCF MB12N351 – Xmax = 5.5mm, coil length 16.5mm, top plate 11mm At the rated power the maximum Xmax needed is 5.5 mmm @ 100Hz. Below 100Hz the Xmax is less because of the porting. Dynamic compression and distortion can increase when the amount of the VC in magnetic gap is less the the height of the top plate / magnetic gap. In this respect the B&C should do better as it maintains 100% VC in magnetic gap up to an Xmax of 4.5mm. The RCF can only do 2.75mm ... but its not quite that straight forward. With respect to the 60 degree version using 18sound XT1464 it looks like it will provide 2 – 3 db more output. Some of this is due to the narrower pattern, and some because it a little larger and maintains it efficiency down to a lower frequency. The horn is slightly deeper and will require the box to be 10 – 20 mm deeper. This will increase a little extra length to the horn which in this case will be a plus. Given that a 60 degree box is likely to be used in pairs the plan to make the rear section of the box trapezoidal as far as possible (tricky). The SIMs indicates that a pair of boxes will run continuously at around 138 dB whole space in the low mids. I suspect because I have not included directivity in the model its probably 3 dB more in use. [/QUOTE]
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