Port conversion

[Alex2507]

I'm redoing the cabinet for an RBH SEN 1010.

I was considering ditching their round port and making something just a tad bigger to get a minimal reduction in air speed at the port ... just a thought.

It has a 3" diameter port that is 6" long total and the ends are flared (flares are within the 6" number)

The box it came from is 5500^3" minus the port and a couple of window braces or ~ 3' cubed

If I wanted to turn that into a slot port ... would 2"x5" for a length of 6.35" or so keep the same tuning?

Using this calculator the length for 2 ports of the 2x5" size would need to be 17.81".

Is any of this making sense?

EDIT:

I'm probably gonna reuse the round flared port due to the path of least resistance but wondering ...

 

[ryanosaur]

Round ports generally perform better than slot ports. With flared ends, better still. If particle velocity and chuffing are a concern, then a larger diameter is necessary… of course with that, greater length is too.
Thus the age old question: “will it all fit?”

Are you actually getting chuffing from the speaker as it stands?

 

[highfigh]

I'm redoing the cabinet for an RBH SEN 1010.

I was considering ditching their round port and making something just a tad bigger to get a minimal reduction in air speed at the port ... just a thought.

It has a 3" diameter port that is 6" long total and the ends are flared (flares are within the 6" number)

The box it came from is 5500^3" minus the port and a couple of window braces or ~ 3' cubed

If I wanted to turn that into a slot port ... would 2"x5" for a length of 6.35" or so keep the same tuning?

Using this calculator the length for 2 ports of the 2x5" size would need to be 17.81".

Is any of this making sense?

EDIT:

I'm probably gonna reuse the round flared port due to the path of least resistance but wondering ...

The existing radiused port produces less turbulence and less noise than any other, but the dimensions determine whether it will be audible.

Why are you trying to change things they spent a lot of time & money developing? I think they may have tested area/slot ports in the past, although it would be ignorant to assume cosmetics didn't enter the picture WRT the radiused round port.

 

[Steve81]

Path of least resistance would be to just turn the sub around so the chuffing is less noticeable.

 

[Verdinut]

Round ports generally perform better than slot ports. With flared ends, better still. If particle velocity and chuffing are a concern, then a larger diameter is necessary… of course with that, greater length is too.
Thus the age old question: “will it all fit?”

Are you actually getting chuffing from the speaker as it stands?

With a larger diameter port and a longer duct length, that would reduce the internal volume and increase the box tuning frequency. It's definitely better not to change anything to avoid a poorer performance.

 

[Alex2507]

I'm making a new cabinet. Size isn't a factor. There isn't currently any chuffing.

Round ports generally perform better than slot ports.

How? I thought it was all about getting under like 17 m/s or something for vent velocity.

better not to change anything

That ship already sailed. Actually my new cabinet is too big. That's why I mentioned going w/ dual ports. I need to eat up the space.

 

[Alex2507]

Path of least resistance would be to just turn the sub around so the chuffing is less noticeable.

Real helpful ...

 

[ryanosaur]

With a larger diameter port and a longer duct length, that would reduce the internal volume and increase the box tuning frequency. It's definitely better not to change anything to avoid a poorer performance.

Hold it… are you… talking about…
Trade offs?

(Not gonna lie, Verdi, I was just trying to gaslight Alex by talking about length and girth. *blushes)
You are absolutely correct. Given the finite volume of the existing cabinet, changing the dimensions and resulting volume displacement of the ports will have an impact on cabinet performance. The resulting change of adding a 100uF poly cap in place of an NPE likely won’t cause much change, but changing a 3” port to a 4” port would likely introduce some issues, if it would even fit in the first place. Of course, building a new cabinet to accommodate new ports is a viable option… but then you have a whole different can of worms.

 

[highfigh]

(Not gonna lie, Verdi, I was just trying to gaslight Alex by talking about length and girth. *blushes)
You are absolutely correct. Given the finite volume of the existing cabinet, changing the dimensions and resulting volume displacement of the ports will have an impact on cabinet performance. The resulting change of adding a 100uF poly cap in place of an NPE likely won’t cause much change, but changing a 3” port to a 4” port would likely introduce some issues, if it would even fit in the first place. Of course, building a new cabinet to accommodate new ports is a viable option… but then you have a whole different can of worms.

WRT the bold sentence- are you forgetting about the phase shift?

If the port wouldn't be seen, making it longer could involve extending it outside of the box, which might be doable. Outdoor subwoofers have this and it works as well as if it were in the box.

 

[highfigh]

Real helpful ...

You should be chuffed by the number of responses to your question.

 

[Steve81]

Real helpful ...

It’s not entirely a joke. Flipping it around may well reduce that problem, the audibility of any associated pipe resonances, and the Allison effect. It was good enough for Josh Ricci after all, and it’s easier to try / reverse than what you have in mind.

 

[ryanosaur]

WRT the bold sentence- are you forgetting about the phase shift?

You guys are so anti-fun.
I was only talking in terms of volumetric impact on cabinet performance, not getting into electrical behavior. Hyperbole be d@mned.

How? I thought it was all about getting under like 17 m/s or something for vent velocity.

You are effectively now getting into fluid mechanics and the ideal method of moving air with minimal turbulence. The best way to do this is with flared (asymmetrical) ports and gentle sweeps. Slot ports and 90º angles introduce turbulence, thus affecting their efficacy.
Is a slot port a deal breaker? No. Or at least, I've never heard a designer say you can't employ a slot port in a design without some drastic penalty: they are easier to build into the cabinet, as well.
From a pure performance aspect, regular cylindrical pathways are better than rectangular pathways. This becomes more important, I would think, if pushing the performance extremes of high SPL and low frequency/infrasonic extension.
This leads back to the circular issue of tradeoffs in determining your design goals: how low and how loud you want to push the drivers against their physical limitations (Xmax, Xmech, Bl and power handling); how large a box you want to build.
Rephrasing what was said earlier, why reinvent the wheel when RBH most likely designed the best system they could from the parts in question?

 

[Alex2507]

it’s easier to try / reverse than what you have in mind.

We're past that. The new box is on the railing of my balcony being assembled.

This leads back to the circular issue of tradeoffs in determining your design goals:

I was just looking for the slot port equivalent of the tube that I have. There's no designing here, just copying.

If the port wouldn't be seen, making it longer could involve extending it outside of the box

It's gonna bee seen and I have room in the new box.

Why are you trying to change things they spent a lot of time & money developing?

I want it to be a different shape. I'm not looking to change anything regarding Vb and port tuning. The original was 5500 cubic inches and the new box is 7000 cubic inches. I have room in the box for a slot port or two if my little heart desires. The new box will be 5500 after it's done and I thought the slot could help me eat up some of that extra volume.

 

[Pogre]

You tell 'em, Alex!

 

[highfigh]

We're past that. The new box is on the railing of my balcony being assembled.

I was just looking for the slot port equivalent of the tube that I have. There's no designing here, just copying.

It's gonna bee seen and I have room in the new box.

I want it to be a different shape. I'm not looking to change anything regarding Vb and port tuning. The original was 5500 cubic inches and the new box is 7000 cubic inches. I have room in the box for a slot port or two if my little heart desires. The new box will be 5500 after it's done and I thought the slot could help me eat up some of that extra volume.

You can't change the box volume and not need to change the port- is the 7000 in³ for a larger volume port?

 

[highfigh]

You guys are so anti-fun.
I was only talking in terms of volumetric impact on cabinet performance, not getting into electrical behavior. Hyperbole be d@mned.

You are effectively now getting into fluid mechanics and the ideal method of moving air with minimal turbulence. The best way to do this is with flared (asymmetrical) ports and gentle sweeps. Slot ports and 90º angles introduce turbulence, thus affecting their efficacy.
Is a slot port a deal breaker? No. Or at least, I've never heard a designer say you can't employ a slot port in a design without some drastic penalty: they are easier to build into the cabinet, as well.
From a pure performance aspect, regular cylindrical pathways are better than rectangular pathways. This becomes more important, I would think, if pushing the performance extremes of high SPL and low frequency/infrasonic extension.
This leads back to the circular issue of tradeoffs in determining your design goals: how low and how loud you want to push the drivers against their physical limitations (Xmax, Xmech, Bl and power handling); how large a box you want to build.
Rephrasing what was said earlier, why reinvent the wheel when RBH most likely designed the best system they could from the parts in question?

Pro tip- If you make a flat spot on a wheel, you can stand it up without needing a corner.

NOW, tell me I'm anti-fun!

 

[ryanosaur]

Pro tip- If you make a flat spot on a wheel, you can stand it up without needing a corner.

NOW, tell me I'm anti-fun!

Fair enough…

but it would seem you are anti-fun-ctional if you want to leave a flat spot on a wheel!

 

[Verdinut]

Hold it… are you… talking about…
Trade offs?

(Not gonna lie, Verdi, I was just trying to gaslight Alex by talking about length and girth. *blushes)
You are absolutely correct. Given the finite volume of the existing cabinet, changing the dimensions and resulting volume displacement of the ports will have an impact on cabinet performance. The resulting change of adding a 100uF poly cap in place of an NPE likely won’t cause much change, but changing a 3” port to a 4” port would likely introduce some issues, if it would even fit in the first place. Of course, building a new cabinet to accommodate new ports is a viable option… but then you have a whole different can of worms.

But there's another solution which not everyone would like. The duct or part of the duct could be outside the cabinet, at the back with the use of an elbow.
For instance, Alex could use a bigger diameter pipe and let the excess volume, as compared to the existing one, outside the enclosure. That would work without changing the box tuning, provided that a proper calculation of the pipe length is done with the use of a software such as BassBox.

 

[Alex2507]

You can't change the box volume and not need to change the port- is the 7000 in³ for a larger volume port?

The new box will be 5500 after it's done

 

[Trell]

19 posts and still no mention of lube in a thread named "Port conversion"