Well, I could make some assumptions based on what I think I know about box designer programming plus if you search enough you'll find where much more math/physics savvy folks than me have been somewhat critical of BBP’s accuracy, but the bottom line for me is that excepting AkAbak and possibly the LspCad 6 series, MJK's is the most accurate IME of the programs available to the general public, though I haven’t used them all, so for the alignments they are programmed to do, I see no reason to look elsewhere or wonder if I'll hear what I simmed.
That said, like any computer program it’s obviously only as good as the input data and theoretically only accurate enough up to the driver's mass corner [2*Fs/Qts] where it no longer is a point source plus it’s based on a 2 pi [half space] boundary loading, i.e. the speaker is buried flush in the ground of an acoustically large, flat space with the measurement microphone suspended above the driver's centerline and perpendicular to it. If an OB/IB, then with the baffle suspended in an infinitely large space, so there can be no acoustic compression or boundary reflections to alter its response.
Also, a basic program assumes that the cab’s air mass will have a uniform particle density, ergo no internal reflections, and that the driver and vent’s output radiates from the same centered point on the baffle to keep the math simple.
Then there’s the complex issue of comparing its damping assumptions………………
Once you move from a simple half space sim to one with more boundaries, then complexity increases exponentially? with increasing data points, though accuracy is typically limited to the lowest octaves where the room can be treated as a ~ empty box with just speakers and a measuring position in it and furniture, etc. can all be lumped together as a simple acoustic resistance/absorber.
Specific to MJK’s more recently revised software, you’ll have to ask him if I’ve ‘short changed’ him WRT accuracy, but IME it applies to the pre LspCad 6 series.
HornResp can sim in 0.5-4pi [corner/free] space, but each is a mathematically ideal one
AFAIK, so accuracy degrades as it shifts from free to corner space unless the ‘room’ is shrinking with it, i.e. the latter is probably only accurate if it’s an acoustically tiny one such as a tightly sealed car’s interior and why for corner sims it’s best to assume a 1pi loading and if you wind up with more gain BW in reality, then lucky you.
Plus, it has no ability to add damping to any alignment other than sealed, so as a general rule it takes some experience to interpret some of the more esoteric alignments such as TLs, horns, etc.. That, or use its Wizard designer to fairly rapidly ‘slide’ your way to a ~optimized alignment, then sim it with MJK’s to fine tune it with damping, basic room interaction.
Even after all that, you may still need to alter the amount of damping and/or vent tuning to get the best overall tonal balance in room, especially if relocating the speaker[s] and/or listening position [Lp] isn’t an option.
GM
27th July 2012, 05:42 AM
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