Help understanding 4TH order tuning

[Jroo 10+ year member]

I have basically been told this statement and want to make sure it is close to true?

A 40 hz tune in a 4th order is like tuning a ported box to 25 hz. If I tune my 4th to 45 hz, I should play well at 20-60hz depending on the woofer. My woofers have a low fs or around 28, so they should also play pretty low in a 4th order.

Does that sound about right? I assume this is why I very rarely see a 4th order tuned past 50 hz?

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[n8skow 10+ year member]

Without knowing/plotting the woofer and volume sizes of your planned enclosure, your question can't be answered...

The sealed side of a 4th order influences the tuning frequency, the ported side influences the bandwidth.

The woofer FS is somewhat irrelevant (unless your planning to run it freeair).

 

[galacticmonkey 5,000+ posts]

The sealed and ported chamber sizes are going to be the main things affecting your frequency response and the steepness of your rolloffs.

If youre going for loud above 30hz, go with a big ported chamber and big port tuned anywhere from 45-50hz.

If you want something to play super low (below 30hz easily), go with a ported chamber roughly the same size as the sealed, maybe a little bigger, and do a relatively small port tuned low, like 38-40hz.

To give you an idea of what sort of sound the tuning has, I had 4 CVR 12s in my Avalanche in a blowthrough. Was 4 cubic feet sealed, and 7 cubic feet ported. I had an 80in^ port that was tuned at 30hz. My truck peaked at 25hz with both doors open and killed every note from about 15hz-30hz. Anything above 35hz had very little output.

 

[Buck 5,000+ posts]

Wider bandwidth, use a close ratio of sealed to ported.

You want to be really loud in a small bandwidth, do a big ported section (compared to sealed).