Example Cabinet for the Great Plains Audio 604-8H-III unit

[GM]

Quite a few MLTLs around the net that I've done the design basics and there's been some others too such as a few corner cab systems. Unfortunately, I don't have access to my 'links' library.

Google will get you started though: mltl altec 64 - Google Search

That said, mine have been either calculated based on the individual's system's [high] output impedance and their average seated ear height or just made them large Vb = Vas] with a ~38" ear height, tuned to Fs [Fb = Fs] and let them use some form of EQ to flatten them out in room. Vent location varies depending on the app, though is always down near the bottom to take advantage of the MLTL's superior vent damping whereas Altec/GPA's is up near the driver where it causes a fairly deep notch in the mid-bass and other just a reflex vent that ideally needs some damping if not covered with a tightly stretched grill cloth.

Damping is always Altec's recommended top, one side and back with 1" acoustic fiberglass insulation [OC 703 'duct board'] or loose polyfil stuffing at 0.2 lbs/ft^3 concentrated along its length, though some folks prefer more or less, so a good plan to make a removable access cover with good [re]sealing properties just in case rather than going through the driver cutout, increasing the risk of damage and/or poor seal.

GM

[VolvoHeretic]

Didn't I read somewhere that the driver should be something like 1/3 down from the top? and if so with a known front baffle width and 38" speaker placement, it should be easy to figure out height and depth?

[GM]

Didn't I read somewhere that the driver should be something like 1/3 down from the top? and if so with a known front baffle width and 38" speaker placement, it should be easy to figure out height and depth?

Correct, the two specific offset driver dims are L*0.21 for 1/4 WL and L*0.349 for 1/3 WL, but in general for smoothest overall performance, both it and the vent should be at an odd harmonic, though as shown for the 1/3, the vent shifts it down some, but once damped, there's no audible difference between them and frankly, I always recommend L*0.4 when appropriate as it makes the cab taller, ergo more vent damping. When I do certain designs, I use a proprietary formula that takes all three dims into account to reduce the amount of damping to a minimum, to the point where so many folks were removing most of it that I quit recommending any, just 'damp to taste'.

GM

[VolvoHeretic]

Assuming the height of the Stonehenge III is 44" from post #4, and scaling this photo of the Stonehenge I, III, and V from this website: GPA 64-8H-II - Audio verleden - High-End Forums I come up with a height of 49" for the Stonehenge V, and it would appear that the front baffle is the same width as the III.