OT: 12" or a 15" for a 6732 cubic inch bass reflex ?

[Audio_by_Goodwill]

Actually, I'm working with the blocked off tweeter horn cutout rather than dink around with the oversize vent with its half round ends, which of course will need to be sealed off. FWIW, I knocked off a 1/2 ft^3 in my calculations to allow for the driver, etc.. Anyway, what's a +/- ~1 Hz tuning variance among friends?

GM

Oh, I see.

[Altec Best]

Anyway, what's a +/- ~1 Hz tuning variance among friends?

GM

Right on Brother !

[johnobub]

Let me see, so, in knocking off 1/2 ft^3 for the driver, duct, and bracing the inside area becomes 3.3 ft^3.

A tuning frequency of 42hz is the same as a 612 or 614 but for deeper bass response a lower tuning frequency should be built into the duct. A 42 hz tuning frequency would produce bass response similar to what a 612 or 614 would but it maybe possible to produce a deeper bass response by increasing the port length longer than 5 1/2 inches. Tuning the boxes to 39hz would produce deeper bass but not as loud as at 42hz. Tuning to 39hz would require a port length of 7 inches.

The tuning frequency would be 47.5hz using a 3 1/2" duct. For a 42hz tuning frequency
a duct 2 1/2 inchs high and 8 inches wide with a 5 1/2" vent length should be made.

Port Length Calculator

[johnobub]

Let me see, so, in knocking off 1/2 ft^3 for the driver, duct, and bracing the inside area becomes 3.3 ft^3.

A tuning frequency of 42hz is the same as a 612 or 614 but for deeper bass response a lower tuning frequency should be built into the duct. A 42 hz tuning frequency would produce bass response similar to what a 612 or 614 would but it maybe possible to produce a deeper bass response by increasing the port length longer than 5 1/2 inches. Tuning the boxes to 39hz would produce deeper bass but not as loud as at 42hz. Tuning to 39hz would require a port length of 7 inches.

The tuning frequency would be 47.5hz using a 3 1/2" duct. For a 42hz tuning frequency
a duct 2 1/2 inchs high and 8 inches wide with a 5 1/2" vent length should be made.

Port Length Calculator

can I get any feedback?

[Altec Best]

Let me see, so, in knocking off 1/2 ft^3 for the driver, duct, and bracing the inside area becomes 3.3 ft^3.

A tuning frequency of 42hz is the same as a 612 or 614 but for deeper bass response a lower tuning frequency should be built into the duct. A 42 hz tuning frequency would produce bass response similar to what a 612 or 614 would but it maybe possible to produce a deeper bass response by increasing the port length longer than 5 1/2 inches. Tuning the boxes to 39hz would produce deeper bass but not as loud as at 42hz. Tuning to 39hz would require a port length of 7 inches.

The tuning frequency would be 47.5hz using a 3 1/2" duct. For a 42hz tuning frequency
a duct 2 1/2 inchs high and 8 inches wide with a 5 1/2" vent length should be made.

Port Length Calculator

Correct..By lengthening the vent/port tube you lower the tuning.Or raise it by shortening vent/port tube.

[johnobub]

Thanks, and I'll be updating my progress on the cabinets, they are an amazing find. I was just thinking to make some new boxes and now I have these to use for experimenting. What an amazing day it was and I'm looking forward to the final results of my garbage find. Anyway I believe I will build some A9's in the long run after I get up some extra cash.

[GM]

Hmm, closer to 3.396 ft^3 based on your i.d. dims minus a 1/2 ft^3.........

Most vent calculators assume a perfect Helmholtz resonator, so will tune a cab lower then predicted, which may, may not be acceptable. A more real world calculation for an un-damped cab puts the 3.5" long duct at ~44.5 Hz and the fact that there's some cab damping with a big pad of it right next to the vent will lower it some more, hence my more or less [~] 42 Hz somewhat educated guess. At 5.5", ~37 Hz.

Regardless, human hearing isn't very acute down this low plus the room's modes will dominate, so in room, most folks can't tell the difference between this small fractional [~0.18] octave spread tunings even when the vents are driven to audible distortion. Actually, you may find that moving this damping pad to the bottom of the cab will sound subjectively better even though it will raise tuning a little.

Bottom line, nobody's figured out how to shrink the LF BW, so if you want deep bass at high SPL [< this cab's ~60 Hz], think big cabs tuned at least at/below the lowest frequency you want to reproduce and/or be in a smaller, better sealed room to increase 'cabin gain' and why some vehicles can do true infrasonic bass at high SPL with a small sealed cab loaded with a high power handling driver.

GM