Car Audio Classifieds! banner

Do 4th orders move more air verse flat wall

6.7K views 8 replies 7 participants last post by  mitchell0715  
#1 ·
Howdy,

Just curious as I can't find any good information but would a 4th order move more air then a simple ported flat wall or should they be similar? I imagine it doesn't necessarily move more air but that leads me to the next question...

On that note would inverting your subs "push" more air on a flat wall? It seems having the motors inverted would seem like there's more air being pushed just because the air flow is that much closer and doesn't have to go through the box and out the port. However I don't fully understand the mechanics involved and was hoping someone much smarter than I could enlighten me.

Any information would be appreciated!
 
#2 ·
On that note would inverting your subs "push" more air on a flat wall? It seems having the motors inverted would seem like there's more air being pushed just because the air flow is that much closer and doesn't have to go through the box and out the port. However I don't fully understand the mechanics involved and was hoping someone much smarter than I could enlighten me.

Any information would be appreciated!
I'm going to address this first before getting to the main question.

The air in a port (and the speaker cone) doesn't blow out in one direction, it oscillates back and forth. The volume of air taken up by the port can be considered an "air plug" that moves back and forth just like a speaker cone. In addition, at the point where the most air is being moved back and forth in the port, the speakers themselves are not moving (relatively) much at all. This is because the port resonance moving in-phase with the speaker cone makes the pressure inside the enclosure high, which makes it harder for the speaker cones to move. There's a lot more to it than that, but that's the jist. So basically - no, inverting subs won't change the perceived air flow.

For the second question on what moves more air, I'd have to say a 4th would have an advantage, at least on lower notes. Below the tuning of the vent on a 4th the subs are playing just like they are in a sealed enclosure. There is no restriction on air flow from the port below tuning. Sealed subs have a much much higher excursion (and displacement of air) at lower frequencies than vented subs due the the port/air plug coupling I talked about above. Of course with a vented enclosure you will get a lot of displacement from the port, but I don't think it will be as much as from a direct radiator due to losses in the spring/mass system of the port.
 
#3 ·
Evan who won his SPL class with my Wardens swears that flat walls are louder than 4th orders. He knows what he's taking about, so I would give the same advice.

You see a lot of builds on youtube and there are a lot of loud 4th order builds out there. Masterofallbass would probably disagree, but he's got a lot more motor force in his build than most people, haha

Either way, I'd go with a flat wall unless you have an absurd amount of room for an enclosure
 
#5 ·
Flat walls unless you lack the flat baffle space to mount all the subs you intend to run
 
  • Like
Reactions: adulbrich
#7 ·
The only real variables are amplitude and frequency. Air molecules move further back and forth on lower notes compared to higher notes of similar 'loudness' and the louder and lower the system can play the more air it seems to move. Because 4th orders are more efficient over a certain bandwidth, doesn't mean they are necessarily better at 'moving air,' but a very low tuned 4th will be very loud over its bandwidth.

The overall volume in the enclosure relative to the Vas of the woofer has a direct influence on how the air in the port is excited. Since the port output is out-of-phase with the driver output the cone movement is minimal at the maximum output frequency of the port, and the cone movement has no direct effect on the 'air movement' other than affecting the amplitude of the sound wave being reproduced.

Summary: loud and low moves the most air. Depending how you build your system, you can optimize it to play this way. Whether it's a 2nd, 4th, or 6th (etc) alignment, if it's optimal for those frequencies it will 'push air.'