You?re welcome!Originally Posted by Encyclopediabsh
OK, this shrinks the cab to ~11.7 ft^3, so allowing ~0.75 ft^3 for the driver and bracing, in a sim this equates to a longer vent for each alignment [ditto if the bracing takes up more volume] and ideally shifts the ~20.65? driver location up a bit to ~20.49? [or higher if more loss due to bracing] to maintain the ?ideal? tuning where the impedance peaks are equal amplitude for a 33 Hz Fs, which in turn means a slightly higher F3.
Bottom line, since we don?t know the cab?s actual net Vb or each driver?s Fs or much of a clue as to what tuning will work best in-room to the audience?s ears, in the scheme of things then; these types of sims are mostly for making sure the cab, vent starts out big enough to allow said manual tuning to achieve the desired performance or at least give some idea how much it will likely be compromised.
My only concern then is how accurate GPA?s published Fs is. If it?s lower, then all?s well as this just means a longer vent, but if higher, then the shortest simmed vent[s] may need to be larger in area. This in turn requires the vent to be wider to maintain the simmed driver/vent acoustical loading that becomes more vintage sounding as it shortens, rendering the extra effort to optimize vent acoustical loading [damping] moot.
All this is of course just theoretical and the room?s impact on a speaker?s LF performance often swamps it plus can be ameliorated with additional vent damping [AKA ?critical? system damping]. Still, many folks can subjectively perceive such minor variances, so I leave it to the reader to decide at what point ?good enough? is.
For a simple reflex or ducted port, the math is strictly cab net Vb and vent length dependent, i.e. Helmholtz plus ? WL resonant pipe theory math is all that?s required, but this assumes a cab with a ~uniform particle density, i.e. no eigenmodes within its audibly perceived BW and the vent is acoustically occupying the same space as the driver when used for vented speaker design.
This is why the original reflex patent uses an acoustically small cab with the vents ringed around the driver as close as physically possible, hence the reason behind all the vintage simple reflex/ducted port cab designs until Harry Olson?s late ?40s MLTL designed for his new LC1 15? ?full-range? driver, though he referred to it as a reflex, missing a major patent/marketing opportunity to enhance its promotion:
Sound translating device - US 1869178 A - IP.com
Anyway, the math is in WP?s PiAlign doc:
http://www.google.com/url?sa=t&rct=j...N7Mt5w&cad=rja
I don?t know the math for calculating the ? WL TL?s impact on vent design nor ever found a simple pattern to scale it, just that as the distance between the driver/vent increases, vent area increases due to vent length decreasing, which only AkAbak and MJK?s MathCad software can accurately enough calculate it including any added damping AFAIK:
http://www.google.com/url?sa=t&rct=j...1p7wdQ&cad=rja
http://www.google.com/url?sa=t&rct=j...VuH8Kg&cad=rja
GM
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