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BruceyQ

Port proximity - big deal?

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I know the rule of thumb is to keep the end of the port (inside the box) away from any walls by a distance equal to the diameter of the port.

However, although great in theory, how big of a deal is this in real life in terms of chuffing or other negative effects? Let's say I build a sub similar to this SVS one, having a flared 8" port that runs straight towards the rear without any bends, where the distance from the edge of the end flare is very close to the bottom of the sub (e.g. half an inch) inside the box:

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This one would have the port end close to both the botton and side wall:

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Perhaps far from ideal but so many commerical designs seem to be built like this:

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Also on the outside, these ports are very close to the floor - certainly no diameter away from this "obstruction".

As long as you tune the length of the port to account for any resulting boundary effects (compared to sim), why should I just not go ahead and do it this way? Especially if the only other option available is to mount the port on top facing up?

If I do it, is it better to keep any fill away from the critical distance or would it be better to strategically add some around there to mitigate any turbulence?

Speaking of which, does nobody stuff their boxes any longer, say for 15-80Hz? A friend of mine said that's old school and to go ahead if I like wooly and loose bass....🙄

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You're meant to keep the port end away from the wall it is facing, which would be the rear wall in the cases you listed. Proximity to the side walls doesn't really matter.

Stuffing your box reduces distortion and mechanical noise at the cost of output. Both seem to be rather small, so it's up to taste. If you have resonance issues in large back chambers, the filling can mitigate that, but you'll need a lot of it. That means in bandwidth resonances, so any dimension above 1/4 of the wavelength. That's 85cm or 2.8' at 100Hz.

Keep the filling away from the port so that it can 'breathe'. Wave your fingers close to your mouth and blow. What you hear is what objects to do airflow, noise wise.

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39 minutes ago, peniku8 said:

You're meant to keep the port end away from the wall it is facing, which would be the rear wall in the cases you listed. Proximity to the side walls doesn't really matter.

Stuffing your box reduces distortion and mechanical noise at the cost of output. Both seem to be rather small, so it's up to taste. If you have resonance issues in large back chambers, the filling can mitigate that, but you'll need a lot of it. That means in bandwidth resonances, so any dimension above 1/4 of the wavelength. That's 85cm or 2.8' at 100Hz.

Keep the filling away from the port so that it can 'breathe'. Wave your fingers close to your mouth and blow. What you hear is what objects to do airflow, noise wise.

Gotcha on the proximity to the side walls being a non-issue - that's great to hear!

Should I be expecting any boundary effects though due to being close to the wall, effectively making the port longer. I will obviosuly tune the box properly by measurement but would like to know what to expect.

This will be a pretty large box (net 500 liters for 2 x 21") which will have inner dimensions of 135x 90 x 75 cm so there could be some quarter of a wavelength resonances  to deal with... hhmmm.... If stuffing is too inefficient, I may have to come up with something else, like staggering panels inside to break up distances.... bummer!

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2 minutes ago, BruceyQ said:

Should I be expecting any boundary effects though due to being close to the wall, effectively making the port longer. I will obviosuly tune the box properly by measurement but would like to know what to expect.

If your ports run along a side wall you can add anywhere from half to a full port width to the length. I've even had a case where I had to add 1.5x the port width to its length, but that was a spline shaped port. One of my designs has the port opening about twice its width from the rear wall. I had to add 80% of the width to get to the actual tuning in hornresp.

Stuffing isn't too popular in PA subs as you might lose 1-2db. The l.acoustics KS28 for example isn't even lined with foam or anything. They have good limiters in their system amps which prevent the subs from being overdriven, so they don't really need to mask distortion near or even above Xmax, which you might reach without a properly matched dsp.

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I don't have any stuffing in my ported subs as I figured it was pointless with one driver operating magnet out.  I only get noise out of them if pushed beyond xmax or if they are pushed at the tune frequency with sine waves (air noise).

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