4th Order Confusion

[Dr.BeatGood]

Okay, I'm debating on building my first 4th order setup with my IAD 15. I have read the the 4th Order Flat Response Sticky thoroughly, but I have some questions. For example, if I follow the sticky thread using the general cabin gain filter, I use 3 cubes on the sealed side and 1.5 cubes on the ported side tuned 60 hz, that gives me a flat response and rises around 50-60 hz. If I design a 4th in the program with 2.5 cubes sealed and 5 cubes ported tuned 60, it peaks at tuning. I've been researching and most people run double the volume on the ported side versus sealed/2:1 ratio. According to WinISD, that should peak at tuning of the vented side with the cabin gain filter applied, but everyone says they get nasty on the low frequencies. Any idea as to why WinISD shows a 2:1 (Ported to sealed) ratio 4th order peak at tuning?

[Dr.BeatGood]

My goal is head jarring low bass while with optimum output. White line represents slot ported box tuned 30hz. Yellow line represents 2:1 Ratio (Ported to Sealed) with ported side tuned 60hz. Blue Line represents 2:1 ratio (Sealed to Ported) tuned to 60hz.

[smfonic1]

You need to increase the sealed volume as much as you can while maintaining a minimum 1:2 sealed to ported ratio. When I say as much as you can, I'm saying as big as recommended for a sealed box or maybe a tad bigger. This will help with the lows.

[Dr.BeatGood]

Originally Posted by smfonic1

You need to increase the sealed volume as much as you can while maintaining a minimum 1:2 sealed to ported ratio. When I say as much as you can, I'm saying as big as recommended for a sealed box or maybe a tad bigger. This will help with the lows.

I've always built ported enclosures. This will be my first 4th. Would you choose a 4th over a conventional ported enclosure for my application and goals? Pros and cons?

[profundus-sanus]

if you're just looking for jarring lows i'd say go large low tuned ported. 4ths are very versatile but they need to be large to be loud.

4th's are nasty for lows due to the sealed section handling the hpf thus having a 2nd order(shallow) roll off. Where as bass reflex have a 4th order hpf causing them to have a steep roll off below port resonance. However you can simply tune a bass reflex lower.

something like 2.25 cubes sealed w/ 2 lbs of poly fill 4 cubes ported tuned to 55hz models pretty well in bbp for being well rounded.

you need adequate port area for the sub to breath as you play below port tuning, which is difficult to do with small ported chambers. if you were to do 2.25/2.25 at a 60hz tuning you'll need a 15.5x5 port area @ 20" where as if you did 2.5 sealed 4 ported that port would only have to be 8'' long

the 1:1 will play hella low and sound amazing. Just don't expect it to put up big numbers.

[Dr.BeatGood]

When you say tune the ported portion low, how low would you say. Would 55hz be considered low?

[profundus-sanus]

Originally Posted by Dr.BeatGood

When you say tune the ported portion low, how low would you say. Would 55hz be considered low?

sorry, i mixed up a few terms throughout my post.

i was actually referring to running a large, low tuned bass reflex enclosure. not tuning the 4th low.

[Dr.BeatGood]

Originally Posted by profundus-sanus

sorry, i mixed up a few terms throughout my post.

i was actually referring to running a large, low tuned bass reflex enclosure. not tuning the 4th low.

Ah, my mistake Pro. I have modeled the sub further. It seems to get the response I would like with a conventional vented enclosure, I would need 4 ft^3 with tuning 29-30hz. How would you feel this would fare in loudness against a 4th with a 3 ft^3 sealed chamber and 6 ft^3 ported chamber tuned to 50hz? I will say I'm not building it to be a meter machine. I will pick whichever one will yield more output on the lows. Thanks for all the words of wisdom as well guys. I really appreciate it as always.

[Dr.BeatGood]

I've noticed one thing about my truck as well. I don't have any software to model the cabin gain with a flat response sealed box, but the cabin gain is hard on the low end. My last setup was a Death Penalty 12 in 2.5 ft^3 tuned to 40hz and it still murdered the lows.

[southerntrendkill]

Just remember that someone like pro might think of something different when using the term murdering the lows just saying.

[Dr.BeatGood]

Murdered Lows = Was loud as hell on low notes lol!

[profundus-sanus]

Originally Posted by Dr.BeatGood

Ah, my mistake Pro. I have modeled the sub further. It seems to get the response I would like with a conventional vented enclosure, I would need 4 ft^3 with tuning 29-30hz. How would you feel this would fare in loudness against a 4th with a 3 ft^3 sealed chamber and 6 ft^3 ported chamber tuned to 50hz? I will say I'm not building it to be a meter machine. I will pick whichever one will yield more output on the lows. Thanks for all the words of wisdom as well guys. I really appreciate it as always.

i'd go ported man

Originally Posted by Dr.BeatGood

I've noticed one thing about my truck as well. I don't have any software to model the cabin gain with a flat response sealed box, but the cabin gain is hard on the low end. My last setup was a Death Penalty 12 in 2.5 ft^3 tuned to 40hz and it still murdered the lows.

ive seen this a lot with extended cab trucks. you don't have to tune them as low to dig really low.

stk is probably right. my murdering the lows is peaking around 25hz haha.

[Dr.BeatGood]

Originally Posted by profundus-sanus

i'd go ported man



ive seen this a lot with extended cab trucks. you don't have to tune them as low to dig really low.

stk is probably right. my murdering the lows is peaking around 25hz haha.

I believe I will go ported. I think I'll tune 30hz. I think my cabin resonance is around there. I'm ready to see what she'll do!