Need advice on building a 4th order bandpass

[cashmonkey38]

Alright thanks for all that, ok I've got new speakers I just put in the rear deck on the far sides, I don't mind cutting a big hole in the center of the deck though, do you think it would be better to still do 2 8" or just do one large port? One of the calculators I used said the min port area would be 250" or so but I don't know that I can fit that

[CortezDTV]

Your port should be around 150~170" square inches

You won't want a port as big as mine

If you cut a whole in the middle you will need to weld a piece in to reinforce what you took out

[CortezDTV]

2 cubes sealed 4-6 ported IMO bigger better

Tune to 48 ish

[cashmonkey38]

Alright here's what I've got at the moment - the box specs will change slightly when I add port displacement, but based on how my trunk is laid out I'm pretty much limited to one design due to the size of the box, couldn't change it much other than taking a few inches off width and adding it to height, etc.

35.5 x 21.5 x 18.75 (wdh) external, so internal I've got 2 cu sealed, subs firing into sealed so magnets are in the ported area, net volume of ported is 4 cu. I really can't make the box much bigger than this due to the trunk dimensions, attached what I'm thinking for the port, please excuse the crude ms paint drawing.

I also attached the gain plot that I got on WinISD using specs for the subs, does this look ok? It shows 16db of gain at the tuning frequency is that safe for the subs? Lol and the group delay is almost 100m/s at tuning frequency. And needless to say it's not very flat, I played around with the numbers and pretty much anything I did turned out more or less like that. I don't necessarily know what I'm looking at so just wondering

[Joe X]

This is for a single RF T212, red is BP 1 cuft sealed 3 ported @48Hz, orange is ported 2 cuft @34Hz generic cabin gain accounted for:

With BP you get your high group delay where you can hear it better (around tuning), no doubt you need to have a taste for these things.

[cashmonkey38]

Alright thanks for that, well I'm doing bandpass since all the noise right now (or a lot of it) is stuck in the trunk. Based on that other info do you think this design would be ok for the bandpass that I'm planning on doing?

[bassman619]

In a 4th order all of the out put comes from the port..as long as you have the port porting into the cabin unobstructed you will feel amd hear all the the bass that was previously trapped in the trunk..what they have suggested as far as cutting the rear deck seems like the best option. But you should do some research and find out what the optimal sealed volume for you subs are..if it says sealed 1 cubic foot.. then you do 1 cubic foot for each sub and double the size on the ported side...any shape will work as long as the air volume is right.but you also need bracing because without bracing the box you will get box flex and box flex = lost output ..you may want to look at fiber glassing the interior of the box .tune the ported side high around 45 htz because the sealed side will produce the low end output..

[DylanBunch]

If the subwoofer manufacture says that a speaker has an f3 of 46 hz in a sealed enclosure will a 4th order bandpass enclosure play lower that that??? sorry if this is a dumb question

If rockford says your sub has a sealed resonance of 46 in 1cbft, for 2 subs do 2cbft sealed and whatever ported size is, tune it to 46.