Building a BIB for a tricky room

[GM]

A slot vent the width of the new internal dimension of 8.28” would need to be 1.52” tall to equal the area of a 4” circle (but still 3” deep).

Note that if you make a full width slot, then the additional side, floor wall loading creates a huge pipe end correction, so to maintain the same tuning will require a much shorter vent top plate: https://www.diyaudio.com/forums/att...-dayton-port-length-effective-port-length-jpg

GM

 

[CraigSu]

Thank you, GM! Any day I learn something new I consider it to be a good day.

 

[Etaoin314]

I think aesthetically I prefer a round port and if I can fit it I would go that route

 

[chrisb]

To be frank, for me slot ports were as much a matter of convenience and sloth as any putative advantage.

 

[GM]

For vents that don't have to be large, long, to get a low vent mach, but a boon for these apps, so yeah, for all these little driver, low power cabs on most forums it's strictly cost saving, cosmetic.

GM

 

[CraigSu]

Doing the (late at night) math it seemed that a slot port the full width of the cabinet was the best way to shorten the overall cabinet height while still retaining the desired distance between driver and port centers. It looked like a 4" diameter circular vent, even if moved to the bottom front edge of the cabinet wouldn't be far enough away (not to mention the other boundary issues noted by GM). Math will tell, however.

 

[GM]

Hmm, we want the vent at an odd harmonic, so at the very bottom is one and while moving the vent closer does change the response, placing a tube at L*0.848 will be inaudible except possibly if there's no damping in the cab.

Heck, even if the vent is next to the driver like the pioneers concluded was the best compromise regardless of cab configuration until RCA introduced its tower bass reflex [aka MLTL] circa 1950 as a viable alternative, once damped the dip isn't noticeable, just its corresponding mid-bass peak, so one can argue that this location is best for 'foot tapping' Altec/JBL 'west coast sound' type alignment.

In short, by far the most critical dimensions in TL assisted alignments is total length, driver offset.

GM

 

[Etaoin314]

Let me make sure I understand, are you saying that with l*848 port placement Mltl physics will not be in play and it will just expect bass reflex style bass reinforcement? If that is so, why? is that not an odd harmonic? Thanks for helping me understand this. While I can’t wait to start building the speaker, I am even more excited about finally getting a grasp on the theory!