Only driver that is small enough, available and me thinks suitable is
4NDF34.
FS 110Hz x 2 / QES 0.28 =785. Thats a bit highish, but could work? How can one guesstimate the f3 frequencies from this center freq? Does this mean that, in theory at least, one could cross to the CD over 1KHz? And would that mean a cheaper CD could be used vs coax CD.s? Im guessing 4 4NDF34 would get me to desired spl? Has anyone played around with these in a MEH?
I've played around with the 4NDF34 in a MEH using it as low as 125Hz.
The 4NDF34 works great. Located at the throat apex not a lot of gain from a conical 90x50, but an easy 130dB from four drivers at 400 Hz. At 1kHz four 4NDF34 could exceed 145dB.
Crossover at 1000 Hz is good, so a decent 3" diaphragm driver could be used, though 130 dB may be optimistic. If you don't want the HF to be the weak link, 4" diaphragm or coax will still be required.
Mark100 has lots of good info:
https://www.diyaudio.com/community/threads/syn-10.383607/
What about woofers? could I get away by using 2 12"?
TS-12W350/8A would have availability, and would not break the bank. I have no clue what to look for in the woofer section.
High Bl and Xmax in the 6mm+ range would be required for 130dB from a pair, relatively small VAS so cabinet volume does not need to be huge.
The TS-12W350/8A would work, but a pair won't reach much over 120-125 dB in the 100Hz-125Hz range even using bass reflex due to the limited excursion it's Xmax is only 3.8mm.
About the horn itself. Does the flare from S1 to S2 determine the horn geometry, or what ever its called? So lets say I'm going for 90°x50°, is that the rate of the first conical section and the second flare is then wider?
A conical horn's flare rate depends on the driver entry position down it's axis.
Bwaslo's spreadsheet helps:
http://www.libinst.com/SynergyCalc/
The first portion of the conical horn determines it's flare rate.
Standard practice is doubling the angle for the second flare.
In practice, the horn break makes the two conical sections behave somewhat like an exponential horn approximating the curve between the two parts at lower frequencies.
The square root of the HxV angle of a conical horn is the equivalent of a symmetrical flare.
A 90x50 conical is the equivalent of a 67x67, a 90x40 a 60x60.
Going narrower increases output, the second flare holds pattern control to a lower frequency.
130dB cabinets should be elevated way above head height, usually requiring front fill for clarity- 80x35 would probably be enough coverage, output like a 53 x 53.
Found the plans for the Skhorn. Does anyone have an idea what kind of spl these are capable with some nice 21"s?
Skhorn should be around 140dB at 1m with under 10% THD, depending on drivers used.
Josh says:
"The second harmonic accounts for nearly all the THD 100-120Hz but it doesn't break 10% until it is producing 134-135dB at 2m outdoor ground-plane which is extremely loud."
https://data-bass.ipbhost.com/topic/613-riccis-skhorn-subwoofer-files/page/17/
If you want a good proven 130dB+ top design, Peter Morris PM90 or PM60 would be good choices:
https://soundforums.net/community/threads/new-diy-mid-high-90deg-aka-pm90.11601/
https://soundforums.net/community/threads/60-degree-diy-mid-hi-aka-pm60.12390/
That's what I suggest for those that want more than the 125dB the SynTripP will do.
Art
