# How do I calculate how big to make a 4th order band pass box



## rdac33 (Feb 22, 2013)

I have two re audio xxx 15s how do I calculate the size of the box. The manual says the optimal sealed enclosure is 2.1 cubic ft and the optimal ported is 4.0 cubic ft. Since a 4th order is a sealed box and a ported box do I use those specs to build the box.


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## SPLEclipse (Aug 17, 2012)

4th order bandpasses can be made to sound great or made to be "one-note wonders". Both have their uses depending on what your goals are.

In general, for those who want a "ground pounder" type setup, the rear (sealed) chamber should be of a volume to bring Fb (sealed resonance) to 40-50hz. The front chamber (ported) should be tuned to the same frequency as Fb. The size of the front chamber will determine how "peaky" the response is, with a very large chamber (2x or more the volume of the sealed chamber) being higher in output around tuning but with less bandwidth. A 1 to 1 ratio (sealed to vented) will produce a wider bandwidth at the expense of peak SPL.

There's a massive thread on CACO that's been going on for years called "why's my 4th order so quiet?". You can search for it over there and read up, it answers just about every question you could have.


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## qwertydude (Dec 22, 2008)

Keep in mind that a bandpass subwoofer would ideally be a very low Qts subwoofer. In order to extract the most efficiency out of the bandpass alignment you need a lot of motor force. Usually these are subwoofers in the .30 Qts or less.


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## Jroo (May 24, 2006)

You cant really use the company spec, you really need to model it and then listen to it. The sealed specs can get you close but people really guess on the ratios. I have had a few 4th and heard a lot. Some sound really good and others sound like hot mess. Usually the ones that have the large ratios like 3:1 dont sound good to me. 

this is one of the better threads I have read on 4ths, but again you really need to model the subs you have first

Designing a 4th order bandpass with a flat response - Realm of Excursion


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## HiloDB1 (Feb 25, 2011)

I wouldnt pay much attention to ratios. Thats more important if all youre looking for is SPL. If you want a good flat response you will have to model those particular subs in some sort of modeling software.


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