# Has Anyone Tried a 2 Cu. Ft. Box for the Betsy K?

#### Karl71

The subject line says it all. It would be sealed. What would be the Q of such a box? I’d line it with 10mm thick felt. A planar tweeter would sit on top.

Last edited:

#### WhiteDragon

Never tried the Betsy K
(Misco?) I can give you volumes for Qtc = .707 / .8 /.9

By rule of thumb EBP = 91 so closer to wanting vented alignment

But Sealed does look good around 1.5 to 2 cubic feet
Im Familiar with Visaton BG20 8" about the same
1.8 to 2.3 Cu Ft doing the same thing adding a tweeter.
8" directionality leans around 1500 to 1800 Hz crossover.
So its interesting and looked at larger diameter tweeters to cross low.
What planar you looking At ?

Attached Transfer Functions for just about any alignment you would care to
use for the K

Sealed Qtc for .707 = 2.2 ft^3 yellow
Qtc .8 = 1.3 ft^3 pink
Qtc .9 = .95 ft^3 red

Vented Alignments = Gray line
Quasi Butterworth 3rd order ( QB3 )
4.8 ft^3 / 43 Hz Fb

Big Bass 4th order ( BB4) = Green line
2.8 ft^3 / 50 Hz Fb
( basically tuned to Fs, BB4 always tuned at Fs)

I like tuning below Fs if possibly looking at vented curves
I would take the BB4 volume 2.8 ft^3
then use lower tuning closer to Butterworth about 45 Hz Fb
and call it a day , or run sealed 1.2 to 2 ft^3
pretty forgiving even small box 1 cubic is less than 1 dB bump

posted thumbnail click to fullscreen

#### GM

Using this math, 0.596 Qtc, though HR always calcs higher with 0.66 Qtc for this driver. 2 ft^3 is ~ the correct net Vb for a classic BR with Fb = Fs tuning. Attached overlay.

#### Attachments

• Betsy K in 2 ft^3 0.596 Qtc_sealed_classic BR tuned to Fs.PNG
4.1 KB · Views: 53

#### Karl71

WhiteDragon -

Thanks for all of the leg work; I appreciate it very much. I used to have Bass Box Pro 6, but that was on another machine, and I misplaced the disc sometime ago. On top of that I run an iMac now.

I love the simplicity of a sealed box & the sound. However, the grey graph looks best to me. Of course, it’s the biggest box. It does go the lowest with a very, very slight bump. Vented spooks me a bit, but it’s now a strong contender. I don’t how much driver displacement to allow for in the final box dimensions. I understand that vented designs aren’t as forgiving as are sealed alignments.

Regarding a tweeter: I intend to run the Betsy Ks wide open at first & then experiment with surplus planar tweeters that I got from Madisound several years ago.

#### Karl71

GM -

I also appreciate your input. Thanks very much.

#### WhiteDragon

Yeah the grey line is going to stand out the most.
But agree always like sealed when possibly and it seems
to do well.

These drivers about 2mm linear travel.
Would probably keep the box around 2 to 2.8 cubic feet.
For decent power handling. The graph looks nice, but bass will be bass
and will work the guy pretty quick
If vented if you get around 43 to 47 Hz should be fine.
Even up to Fs around 49 Hz
Overall driver displacement isn't much. Could calculate.
Mainly the magnet likely .6 to 1 liter at most.
Hardly a smudge when playing with 56 to 130 liter cabinets.

Of course if you like towers/ floor standers a large box makes
such a tall design feasible. I personnel love 8" speakers
and like the old Altec Utility boxes 618 is about 1.8 to 2 cubic ft.
So have a unfinished project in the works. Plays well for many 8"
After the 618 is done moving to high Qts 8" in large box.
Same thing adding a tweeter. Idea I had for a tower wide ish baffle.

And then the 618 / 618c is always inspiring for me at least.

1 user