34 replies to this topic

[Blackrazor]

ferdie said:

1; work out box volume for the specific sub tuned low in a big box(75-120 lts for a 12"approx)

Most of the posts i've read about it mention perhaps aiming to make the box 2x as large as the recommended enclosure for a normal ported box for the sub

[VL Commy]

ferdie said:

1; work out box volume for the specific sub tuned low in a big box(75-120 lts for a 12"approx)

typically you would go for the largest size ported box you can that would still sound musical.

ferdie said:

6;put them in and play, tuning by shortening/lengthening the exposed ports 2 suit (or is it all three ports that need 2 be played with?)

if you change one port, you must change them all.

[Scott Neill]

ferdie said:

ok, so i dont do this wrong and get crap results, lets re-cap

1; work out box volume for the specific sub tuned low in a big box(75-120 lts for a 12"approx)
2; divide this total volume in the ratios 1/3 and 2/3
3; use 3 identical ports as calculated for the single chamber big box (port size from step 1)
4; one in each chamber and one connecting them,
5;drop the sub in 2 the face of the bigger chamber, having exposed ports and sub all on the one face of the box.
6;put them in and play, tuning by shortening/lengthening the exposed ports 2 suit (or is it all three ports that need 2 be played with?)

Guys just a quick note, in Step 1 you need to calculate this tuning with TWO ports not one.

Both ports in the final design will be in use therefore you need to calculate the starting value for both ports!

I've built quite a few and had REALLY good results with them. The tuning ends up being exactly 1 octave apart if the ratios are maintained. The roll-off on the bottom end is quite steep so I usually tune to 30 or 35Hz (therefore the top end becomes tuned at 60 - 70Hz respectively). The top end roll-off has not been an issue with any of the boxes I've built so far, in fact the peak gain typically ends up being approx 5Hz above the tuned freq. The 12" design will quite easily play up to 110Hz!

On the downside these enclosures are not the most accurate and can require some EQ adjustments to smooth out the response. In addition there is a fair bit of group delay as well.

Bang for buck though these things rock and LOVE the low notes while not loosing the upper end punch!!

Hope this helps...

[shiny_car]

crazy canadian! :roll:

[Blackrazor]

OK this is going to sound weird, but...

Can i build an ABC box with a removable cover over the ports which bolt down via wing nuts, so that i can use the box as either a large sealed box for SQ comps or an ABC box for daily driving?

And if so, how hard is it going to be to get a sealed box of 0.707 Qts alignment AND still be able to port to 28Hz/56Hz or so without port noise for when the blocking panels are removed?