my new 604 cabinets I'm building.

[GM]

I just don't know how he calculated the 41 hz box tuning frequency? I just used this online one and came up with 29.4836? Not sure If I'm doing it right, but it looks right. Did you read the link I posted in post #32 by
John L. Murphy Physicist/Audio Engineer?

Easy, I used well-proven math for vented alignments, not the formula for a heavily stuffed sealed alignment as this calculator does.

Yes, I?m familiar with it; the basslist threads I was usually a part of prompted many of his tech topics. For the record though, his generalizations are just that, a ?vents for dummies? tutorial since at the time few of us on the forums that understood most/all of the ramifications didn?t want to part with our hard won knowledge just so folks could go off and use it for profit.

Anyway, if anyone is serious about DIY speaker design as a hobby or business, I strongly recommend you use MJK?s MathCad software [please pay the business fee if applicable] as it?s the most accurate I?ve ever used and not nearly as hard to learn in depth as AkAbak.

FWIW, the math I?ve used for decades to calculate vents match right up with his calculations when a lightly damped golden or acoustic ratio cab is simmed and his MLTL vent calculations line up with the measured results of some of my old designs I still had final details of, so confident enough that any other alignments would be too, though if I needed it to be tuned to Fs I would cut the vent[s] too long and do the measurements to fine tune it.

GM

[GM]

I'm still quite confused on this, especially after reading my Radio Shack "Advanced Speaker Design" book three times and doing all of the math long hand. Isn't the only frequency coming out of the port the box/port resonance and at Fb the speaker is motionless and all of the air motion is in the port and in faze with the woofer? Doesn't aiming the port out the rear, bouncing off of the wall make it out of faze with the woofer?

It?s a narrow pass-band of frequencies with its width [Q] being determined by the vent and system Q which in turn determines how ?locked up? the driver is at Fb. Consequently, it?s only in acoustic phase at Fb, rotating increasingly out of phase on either side as shown on an impedance or transfer function phase plot. This animation does an excellent job IMO of visualizing driver/vent interaction: Essay

This is addressed in JM?s tech note. Still, I?ve used rear and bottom firing to good effect and in many cases preferred bottom firing for MLTLs, using adjustable feet to fine tune vent loading.

GM

[voice of the theater]

Wow--lots of great info for all of us to absorb here--thanks GM! I was about to put an SOS message on this thread (Save Our Speakers)! Much of this goes over my head but I'm going to do some reading and see if I can make (more) sense of at least some of it. Greg, I know this stuff is not always completely black and white, but do you think Cradeldorf is "better off" putting the port on the front or the back of his cabinets? Also, 65 square inches seems awfully big to me for a port size if he wants to get a "modern hi-fi" tuning for his cabs (as you alluded to)--any suggestions (even a ballpark suggestion?) as to what port dimensions may get him a nice low tuning--say closer to the tuning of the Model 19 cabinets?

I'm mulling over filling all the voids between the braces with 2" egg crate foam. I hope the 2" is the total height of the foam plus the eggs and not just the foam itself.

I'm not sure foam is a good dampening material internally in the cabs.Good old Fiberglass insulation performs better IMO.YMMV

Maybe someone else could help out with this decision and chime in.I only ever use insulation.

Anyone have any preferences/ideas that they'd like to share as far as this "egg crate" foam vs. more conventional insulation?

[cradeldorf]

Easy, I used well-proven math for vented alignments, not the formula for a heavily stuffed sealed alignment as this calculator does.

Yes, I’m familiar with it; the basslist threads I was usually a part of prompted many of his tech topics. For the record though, his generalizations are just that, a ‘vents for dummies’ tutorial since at the time few of us on the forums that understood most/all of the ramifications didn’t want to part with our hard won knowledge just so folks could go off and use it for profit.

Anyway, if anyone is serious about DIY speaker design as a hobby or business, I strongly recommend you use MJK’s MathCad software [please pay the business fee if applicable] as it’s the most accurate I’ve ever used and not nearly as hard to learn in depth as AkAbak.

FWIW, the math I’ve used for decades to calculate vents match right up with his calculations when a lightly damped golden or acoustic ratio cab is simmed and his MLTL vent calculations line up with the measured results of some of my old designs I still had final details of, so confident enough that any other alignments would be too, though if I needed it to be tuned to Fs I would cut the vent[s] too long and do the measurements to fine tune it.

GM

I love how you force us to learn, it kinda feels like your a professor and were your pupils. It truly is a good feeling and as my dad used to say nothing worth earning is free. I have the winIsd at home on my puter so I'll fire it up and see if I can remember from the last time I tried using it. As always Thanks Greg.