# 4th order myth vs ported



## guimond47

Alright ive searched over and over and i cannot get a straight up answer. 

Heres what i am trying to find out, - 4th order benifit over ported.

I hear people say 4th orders have a very narrow bandwith. Makes no sence to me. Everyone i see graph the sound curve in winisd shows 25hz-55hz . How is that a narrow bandwith? How would i be able to get a 25-70hz bandwith from bandpass? I also hear the quality dosnt add up. 

How is that a fact? Theres a sealed enclosure in a 4th order.. Sealed is usually the best sounding all around for SQ.

I listen from rock, to country, hip hop, heavy asap ferg rap, oldies 80's and 90's .

I like it loud but i also like clean. I heard a 2:1 ratio 4th order is best compared to 3:1

So if i tune 50 hz on the port side im hoping to acheive the wideband of freq im looking for. 

Btw ive never done a 4th order, im jungling between the 4th and ported due to the fact im making a blowthrough on my truck. 

I like an enjoyable listening experience and loud when i want it to be!

Subs are AB xfl 15"s X2
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## thehatedguy

A blow through...I would do bandpass if I could get one to look good. I don't know too much about those subs you have to be able to point you in a good direction.

The first question- how is that a narrow bandwidth? That's not barely an octave there. You can get bandwidth at the expense of gain. Usually with bandpasses, if you get 2 octaves out of them, then you are doing good. Quality depends on the sub and the design of the enclosure.


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## guimond47

Im not saying its a narrow bandwith. Im saying thats what people been saying thay bandpass is only good for narrow...

Im trying to wrap my head around why they say that....


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## thehatedguy

Because if you want gain from the enclosure, you have to do it over a narrow pass band. The more extension and larger bandwidth comes with a loss in efficiency. 

A wideband width bandpass enclosure can be tough to do right.


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## guimond47

Is it still a benifit over a ported enclosure though? If i pay someone to sketch me one out. Anyone on here that does that stuff?


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## thehatedguy

I don't know about on here.

But a bandpass would get all of the output into the cabln, which is or could be a benefit depending on how much you are wanting to cut the back of your truck.


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## guimond47

Well i bought enough accordian seal to seal a ported box, huge opening. But if i go bandpass i wouldnt need such a masive opening. Anyone on smd forum or somewhere that has capabilities to do this?


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## SPLEclipse

It has to do with how a 4th order works. We know that in a regular vented enclosure a little below the port tuning the port just acts like a big hole of the speaker unloads. We also know that above the port tuning the port air mass becomes a stationary "block" and allows the enclosure to act like it's sealed. 

Taking those principles to a 4th: below the port tuning the port just acts like a hole and the natural response from the sub in the sealed enclosure comes through. Above the port tuning the port becomes less and less compliant - it want's to block all the sound. This is why you get a lot of gain around the tuning frequency with a shallow roll-off on the low end (because the sealed enclosure/rear chamber dictates the low end) and a sharper roll-off on the higher end (because the port air mass doesn't want to move).

You can spread the "ends" of the frequency response out by using a larger sealed enclosure and a higher-tuned front enclosure. The size of the vented chamber can adjust peak gain at the tuning frequency just like a larger regular vented enclosure will get louder at the tuning frequency vs. a smaller enclosure with the same tuning and power. The sacrifice is a reduction in the gain within the passband as winslow mentioned. Also, if you try to "stretch" things too far you'll get a really wacky frequency response.

That's all very simplified, but I hope you get the point.


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## SPLEclipse

Forgot to add: for those subs and your listening preferences a vented enclosure would almost certainly be more ideal. You could build a louder 4th order if you had around 20 cubit feet for the 4th, but you'd have to sacrifice basically everything over 50hz. If you listen to a lot of 80s/90s/hip-hop stuff with "higher" bass a 4th isn't going to work too well. unless you've got some killer midbass speakers to compliment the sub.


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## guimond47

Thanks for the suggestions guys, thinking of just sticking vented then. Even tho i tune at 34hz vented. 

I came across an re xxx 15" in my home town. 

They have 54mm of xmas. I thought of buying that and putting one of those in a bandpass... Due to the fact the 2 15 ab would take so much cuft for bandpass. But would the single xxx over come the two 15" AB? Cone area is greater with 2. So would 1xxx be louder with the greater xmas

And also i heard the newer xxx's dont like to be over powered. I know my rf t2500 will feed 2800rms anyday to anysub.(efficient electrical)

Going vented just confuses me alittle. How big will my blow through hole need to be? At least bandpass i thought it would be a resonable size.


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## Lyons238

Also, keep in mind not all subs are suited towards 4th order BP boxes. Typically subs that perform well in sealed or ported work good in 4th orders, for instance JL subs, Image Dynamics, among others. But if you get an SPL sub, sometimes they don't mesh well with 4th order BP boxes, especially if it's a smaller enclosure.


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## nineball76

Bandpass does what you design the enclosure to do. You see narrow bandwidths because of what's trendy, either spl or to "kill the low lowz". The sealed section controls the bottom end, so going towards the large side to lower the fb then using the ported side to raise the top, tuning to 55-65 hz and not a huge ratio. Bigger ratios tend to raise the peak gain, and so will a smaller sealed.


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## nineball76

Lyons238 said:


> Also, keep in mind not all subs are suited towards 4th order BP boxes. Typically subs that perform well in sealed or ported work good in 4th orders, for instance JL subs, Image Dynamics, among others. But if you get an SPL sub, sometimes they don't mesh well with 4th order BP boxes, especially if it's a smaller enclosure.


This is rubbish. Dd 9500 are huge ported performers and it's widely said they don't work well in 4ths which is ********. They do very well in 4th orders.


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## Hanatsu

Generally a sub suited for sealed boxes work good for 4th order, it's merely a rule of thumb though. The main advantage of 4th order over vented is the acoustic lowpass filter that kills a lot of non-linear distortion. A vented box have no damping from the enclosure below Fb, a 4th order acts like a sealed box.

Bandwidth is no problem if you get a suited driver. A sealed box generally got a flat response in-car with a rolloff around 50-60Hz. If you design a 4th order with a Fsc a tad higher up you might might even reach 3 octaves combined with the transfer function of the car. At some point you will have to choose between extended bandwith or better efficiency.


Sent from my iPhone 6 using Tapatalk.


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## Rob4607

I had a single reflex bandpass with 2 Orion xtr 12"s in a scirocco and everyone at every show or event was floored with the sound and output. I've always been a fan of the bandpass enclosures. It had a 8" port that was literally a hole in the MDF and that was it. It became an attraction to put stuffed animals in the port to see how fare we could shoot them. Yeah I know, dumb.


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## craiggus365

Scirocco was a 'loud' car from the hatch days. I remember them fondly!


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