OK, here's the 'deal'..........😉
To the 1st approximation, worst case: 74.5 L, 48 L Vas, 50 Hz Fs, 0.843 Qts'
(a) = 48/74.5 = 0.644
Qtc = sqrt(0.644+1)*0.843 = 1.08
Fc = (1.08*50)/0.843 = ~64.1 Hz sealed
BR Fc ratio = 1.08/0.5 = 2.16
50/2.16 = 23 Hz Fb
Tuned > an octave below Fs = a very long TL that needs a hi-pass filter to protect the driver, so best we can do is design based on its published Qts and you'll have to use some form of EQ to flatten any amp output impedance frequency shaping (historically done with variable DF bass, treble tone controls).
Best case: 74.5 L, 48 L Vas, 50 Hz Fs, 0.52 Qts
(a) = 48/74.5 = 0.644
Qtc = sqrt(0.644+1)*0.52 = 0.667
Fc = (0.667*50)/0.52 = ~64.14 Hz sealed
BR Fc ratio = 0.52/0.5 = 1.04
50/1.04 = 48 Hz Fb and assuming a ~ matching impedance amp, best to tune to exactly Fs, i.e. equal amplitude impedance peaks, so need to start with an oversize baffle thickness reflex vent (typically Av = Sd) and reduce as required via actual measurement.
34400/4/50 = 171 cm pathlength same as your sim, though ideally would want the driver offset to be ~171*0.349 = ~59.68 cm for smoothest response or 171*0.21 = ~14.14 cm for max TL vent loading.
As previously noted these are guessed and maybe have a 10% or less chance of being optimum.
dave
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Ok, this is Hornresp simulation with dimensions from your post #16:
1.Input window
2.Schematics showing stuffing
3.Response
4.Cone displacement
When using HR, please Export/attach, so 'we' can Import if desired. 😉
edit: Also, for now we're assuming a matching impedance amp, so need to add 8 ohms (Rg) to the sim.
edit: Also, for now we're assuming a matching impedance amp, so need to add 8 ohms (Rg) to the sim.
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I agree, mh-audio calculator only takes Fs and Sd into account.
But what is optimum?
Lowest F3?
Most flat response?
Smallest box?
Best cone movement control?
Smallest group delay?
Depends on the users needs.
But the by guess method rarely is.
Your sim has an issue with whatever harmonc is causing the 100+Hz peak. Less of an issue the slow roll-off brfore plunging is perhaps a bit to dramatic.
dave
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OK, all I did was change the flair to 'par', added 'chamber/path' difference.
Ideally need a Fs tuning when high output impedance tube coupled to get the max bass efficiency required for such low Xmax drivers.
Ideally need a Fs tuning when high output impedance tube coupled to get the max bass efficiency required for such low Xmax drivers.
What Dave said. 😉
That said, I started to do a better sim based on the way I did them pre T/S knowing what to expect, but the long and short of it is that high Qt drivers in general and especially if SE, etc., tube driven is that it needs significant damping for best overall performance to the point where a tall or folded in half damped MLTL performs just as well with less damping, woodworking, footprint if tall, so once the driver/floor height is chosen, set pipe length based on the driver being at L * 0.349 i.d. and tune to Fs with as large a vent as will fit and doesn't exceed Av = Sd.