You?re welcome!
Material stiffness increases at the cube of thickness, making ?? to 1? a ~2.37x increase in rigidity, so in theory well worth it, but all things considered, a vertically braced ?? thick panel is just as good, if not better, for a lot less $$$/effort and if you break the baffle up into sections with the driver and vent areas removable, then effective stiffness increases to the point of rendering the subject moot.
The trade-off of course is a lot more mounting hardware and potential for air leaks of which even a tiny amount will ruin a reflex?s tuning. If the driver is front mounted, then brace a one piece baffle the same and preferably all the panels due to their size.
OK, there?s at least four different ?optimal? driver locations depending on who you ask and/or what works best overall for the needs of the app:
At the extreme closed end [opposite where the vent is]. Typically for subs or when coupled to a horn or other driver on top.
Down 0.21. Some folks believe this is optimal based on simple ? WL closed pipe theory.
Down 0.349. MJK?s conclusion based on wave theory, so very popular.
Mine, which is based on mechanical resonance theory, varying based on length and cross sectional area [CSA] or down 0.4588 in your case.
The further down the pipe within the lower limit, the less damping material required to smooth out its harmonics, but the less pipe action [acoustic efficiency] as the trade-off, so in the scheme of things performance wise; lower is better for wide BW use, though never having compared my way to MJK?s, don?t know if there?s an audible difference or if it?s enough to matter. I?m guessing probably not in most cases unless it changes the fundamental ?tone? of a male voice.
In short, driver cutout centerline anywhere between ~15.71? ? 20.65? i.d. down from the top would be ?optimal? with as little as ~9.45? down if you think a higher stuffing density is OK.
Conventional wisdom dictates the vent system be near/at the bottom, though at least one designer uses MJK?s software to shift it up the pipe a bit whereas again, I calculate it a bit differently to get a specific type of alignment for when the speakers are well away from any wall boundaries. In your case it would be near/at the bottom front.
WRT vent size, for the kind of specs Altec or similar have; due to the pipe?s ? WL action impacting vent damping, it depends on the driver location, with it decreasing in area to keep vent length short with increasing driver distance from the closed end of the pipe.
Or, you could use the largest size as the pioneers of audio chose to maximize vent efficiency, but if you tune to actual Fs as you normally should when using a high output impedance amp, this just means that you?ll probably need to damp it more in your app to keep it from sounding ?boomy?. Only one way to know for sure though.
Anyway, vent area decreases from ~132.73?^2 - ~95?^2 as the driver ?slides? down the pipe with vent length shifting from 0.75? [baffle thickness] to 3? respectively. This assumes a ~22? wide slot vent down 39? i.d. with of course its height being variable.
I?ll post 2 pi [1/2 space] loading sims including aperiodically sealed [highly damped vent] as time permits, so with your near 1 pi [1/4 space] loading combined with no way to accurately sim a current [tube] amp?s impact on driver performance and with no room eigenmodes consideration that will cause peaks/nulls in the lower octaves, they will be strictly for driver/vent comparison purposes.
GM
Originally Posted by Encyclopediabsh
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