Free 4th order calculator/questions
 

http://www.colomar.com/Shavano/4thorder_info.html

Can subs be firing into a port with 8 subs in a 4*2 so half of them are pointing at the port (which is 15-30" away)? What if the sealed portion is oversized for the size of sub and doesn't have them loading well, would the two stacks load differently enough to matter?

I'm trying to get this 4th order with sub (QTC .5-FS 23Hz-VAS 8.26cf) to be playable from 20-50 Hz and it roll off completely (like -24db) by 10 & 60 Hz (components low passed at 60 hz), a flat response from 20-50. What's the best numbers to plug in? I'm thinking .7 & 20 Hz... it says:

lower 3db roll off 20 hz
higher 3db roll of 53.15 hz
sealed box 8.18 cubes
ported box 4.05 cubes
tuning frequency 32.6 hz

User definable port size:

Port Diameter: 2.00 inches ( 50.80 mm)
Port Length: 0.50 inches ( 12.72 mm)

Suggested: (.3 X Speaker Diameter)

Port Diameter: 4.50 inches (114.30 mm)
Port Length: 6.65 inches (168.99 mm)

Does that sound right?

How would cabin gain affect the calculated to be flat from 20ish to 50ish? How would you compensate? like a dip at 30-40 hz... ?

Does the minimum box size for ported still apply? Example - if the recommended minimum space for a ported box for a 15" is 3 cubes, does that mean with the 1:2 ratio of ported:sealed it has to be 3 cubes ported and 6 cubes sealed or would it not be choked with 1.5 cubes ported and 3 cubes sealed? When is the sub choked?

With Isobaric loading how much space should be left between the subs, just enough or leave up to like 1"?

I'm trying to design a 4th order for a Silverado reg. cab long box with a bed cover with a back window blow-through for 8 Dayton Classic 15's (250W RMS) or 16 isobaric, all facing forewards in a 4*2 or 8*4 stack and taking up the entire bed... just to see if it can be done! In roughly 8.25 cubes sealed it is QTC .707 @ FC 32.5 Hz which is pretty sweet... for HT lol.

What about a 1:1 ratio like this (the only one its giving when changing response & -3db because of .1 & 5 hz incriments)? If the bed cover is right it can fit around 96 cubes NET or for each sub 3 ported & 3 sealed.

Lower 3db Rolloff: 30.00 Hz (F3 Provided by user)
High 3db Rolloff: 73.98 Hz (Calculated)

Sealed Box: 2.59 cubic feet
= 4467.05 cubic inches
= 73.21 liters

Ported Box: 2.97 cubic feet
= 5138.38 cubic inches
= 84.21 liters

Tuning Frequency: 47.11 Hz

User definable port size:

Port Diameter: 2.00 inches ( 50.80 mm)
Port Length: -0.18 inches ( -4.65 mm)
++ Bad Choice ++

Suggested: (.3 X Speaker Diameter)

Port Diameter: 4.50 inches (114.30 mm)
Port Length: 3.19 inches ( 81.04 mm)

Unless you are designing some sort of grapefruit cannon, you had better rethink your port diameters.

Yeah that was for 1 15" (.7 from 20-50) so the port would obviously be bigger with 8 subs. I like the idea of 8 15's in 64 sealed/32 ported, the calc says 20-50 Hz response. 96 cubes should fit in a long bed with a cover. Cheap build.

4th orders are usually a 3:1 ratio ported chamber : sealed chamber