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After a few DIY kit builds, a few more advanced builds based off of forum plans and a few homebrew tweaks, I'm at the point in my speaker life where I am now ready to begin the journey into the open baffle speaker world. Looking around for an easier starter project Paul's Sunflower Redux caught my eye, being both by a designer I am familiar with, cheaper, and fun-looking.
But I have a few questions about them. First off, i can't tell from any of the literature on them if he built these with the 4 ohm or 8 ohm version of the RS225. Paul's own site: Paul Carmody's DIY Speaker Pages - Sunflower [Redux] (google.com) doesn't mention AT ALL, with the sole clue being that the picture he chose for the woofers is the 4 ohm version. HOWEVER in his HT Guide forum post, announcing the build, he lists a BOM that calls for the 8 ohm version: Sunflower Redux (htguide.com) . HOWEVER HOWEVER that BOM had many self-admitted mistakes first flush, is not widely published and is suspect therefore. I looked at his modeled impedance graphs to see if i could glean it from that, but the low-point in his graphs is 5 ohms, which is 2 more than the driver-low of 3 ohms for the 4ohm nominal one and 2 less than the 7 ohms for the "-8" version. Once again inconclusive.
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Second: I know these are not truly full open baffle, at a minimum because the woofer section is monopole. I am pretty OK with this though because of the wide-directivity nature of lower frequencies, the design simplicity and performance making this trade-off sensible and sacrificing little (unless there is something about open baffle bass that i don't get, I just figure a good monopole at lower frequencies will still pressurize the room just fine, and the room reflections that make dipoles so good are not really relevant at low frequencies - feel free to correct me). So then the design does into true dipole alignment for the mids, starting at the first XO centered at ~250 Hz. The power radiation match between the monopole configuration of the bass and the dipole configuration of the mids should be well matched, for the reasons i gave above. Most full BSC bass systems radiate too much power at the lower frequencies any way and the dipole mids should help match that power. But then i see the tweeter and I get worried: not only is he crossing over from a dipole mid into a mono-pole tweeter, he chose a tweeter known for its high directivity. This tweeter already has notable off-axis drop-off starting around 2500 Hz, which also happens to be the chosen cross-over point for this system. I would be afraid that with a flat on-axis response, the jump from a dipole mid config to a highly directive monopole tweeter would be a jarring one for power radiation. Linkwit'z LX521 and Orion both have rear tweeters, for example (Though the LXMini does not, but the full-range driver that operates in the tweeter frequency range IS dipole, most of the higher frequency content will be blocked from traveling fully in the negative Z axis direction by the driver motor/installation tube.) . TL;DR: is the use of a single(monopole) highly directive tweeter a substantial shortcoming of this design?
Anyway - thanks for reading my book, and any help you can provide, even tangential to my questions, would be of great use!
After a few DIY kit builds, a few more advanced builds based off of forum plans and a few homebrew tweaks, I'm at the point in my speaker life where I am now ready to begin the journey into the open baffle speaker world. Looking around for an easier starter project Paul's Sunflower Redux caught my eye, being both by a designer I am familiar with, cheaper, and fun-looking.
But I have a few questions about them. First off, i can't tell from any of the literature on them if he built these with the 4 ohm or 8 ohm version of the RS225. Paul's own site: Paul Carmody's DIY Speaker Pages - Sunflower [Redux] (google.com) doesn't mention AT ALL, with the sole clue being that the picture he chose for the woofers is the 4 ohm version. HOWEVER in his HT Guide forum post, announcing the build, he lists a BOM that calls for the 8 ohm version: Sunflower Redux (htguide.com) . HOWEVER HOWEVER that BOM had many self-admitted mistakes first flush, is not widely published and is suspect therefore. I looked at his modeled impedance graphs to see if i could glean it from that, but the low-point in his graphs is 5 ohms, which is 2 more than the driver-low of 3 ohms for the 4ohm nominal one and 2 less than the 7 ohms for the "-8" version. Once again inconclusive.
​
Second: I know these are not truly full open baffle, at a minimum because the woofer section is monopole. I am pretty OK with this though because of the wide-directivity nature of lower frequencies, the design simplicity and performance making this trade-off sensible and sacrificing little (unless there is something about open baffle bass that i don't get, I just figure a good monopole at lower frequencies will still pressurize the room just fine, and the room reflections that make dipoles so good are not really relevant at low frequencies - feel free to correct me). So then the design does into true dipole alignment for the mids, starting at the first XO centered at ~250 Hz. The power radiation match between the monopole configuration of the bass and the dipole configuration of the mids should be well matched, for the reasons i gave above. Most full BSC bass systems radiate too much power at the lower frequencies any way and the dipole mids should help match that power. But then i see the tweeter and I get worried: not only is he crossing over from a dipole mid into a mono-pole tweeter, he chose a tweeter known for its high directivity. This tweeter already has notable off-axis drop-off starting around 2500 Hz, which also happens to be the chosen cross-over point for this system. I would be afraid that with a flat on-axis response, the jump from a dipole mid config to a highly directive monopole tweeter would be a jarring one for power radiation. Linkwit'z LX521 and Orion both have rear tweeters, for example (Though the LXMini does not, but the full-range driver that operates in the tweeter frequency range IS dipole, most of the higher frequency content will be blocked from traveling fully in the negative Z axis direction by the driver motor/installation tube.) . TL;DR: is the use of a single(monopole) highly directive tweeter a substantial shortcoming of this design?
Anyway - thanks for reading my book, and any help you can provide, even tangential to my questions, would be of great use!
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