Jump to content
Second Skin Audio

Aero ports: port area, displacement, and thickness?


Met

Recommended Posts

Big thanks to Joe X for designing a box for me. Using his design, I've been tweaking it around as I'm a little worried about it not fitting.

I've been using Torres calculator, but the more research I've done, I've read it doesn't calculate multiple ports well. I've also tried Boxnotes which gives me different results than Torres.

Do they subtract the correct amount of air space from the ports, and port thickness? I'm not sure if thickness matters with the 4" PSPs I'm using, since it's not real PVC, like you'd get from Lowes or Home Depot. .125?

Then comes the PSP calculator, it completely confused me. When it says net airspace, do they mean before the ports? Or after? Does it subtract the correct airspace if it means before port displacement? And then theirs the flanges, which I believe subtracts 1" from the total length of usable airspace?

All three of them give me different results, so I'm completely confused.

Build: 2 DC level 3 15"s, 5x4" aero ports, 17" usable, 18" total according to PSP. I may need more tubes/couplers to get 34hz in a 6cu - 6.2cu enclosure.

I've googled for days for an explanation, they all I could find was conflicting threads.

Any help? :)

Link to comment
Share on other sites

  • Replies 21
  • Created
  • Last Reply

The PSP asks for net volume which is after all displacements. you can get that from Torres - 6.23 net it will say, then you plug that into PSP, I just noticed PSP no longer gives you the effective length but the total length with their custom flares so it has become useless for general purpose applications. Still you can find out the port lengths reading the following, towards the end it explains how to deal with multiple ports:

http://www.jlaudio.com/header/Support/Tutorials/Enclosure+Ports/Tutorial%3A+Enclosure+Ports/287541

I am aware that PSP port kits can only have 17" effective length so raw PVC would need to be used instead, small flares can be implemented through a roundover to the mounting holes.

Lastly there are many variants to the JL Audio equation (shown in the link) which will deliver slightly different results, almost every other software you use will give you slightly different results but you are not likely to notice a clear audible difference. Hope this covers most of your questions.

Link to comment
Share on other sites

The PSP asks for net volume which is after all displacements. you can get that from Torres - 6.23 net it will say, then you plug that into PSP, I just noticed PSP no longer gives you the effective length but the total length with their custom flares so it has become useless for general purpose applications. Still you can find out the port lengths reading the following, towards the end it explains how to deal with multiple ports:

http://www.jlaudio.com/header/Support/Tutorials/Enclosure+Ports/Tutorial%3A+Enclosure+Ports/287541

I am aware that PSP port kits can only have 17" effective length so raw PVC would need to be used instead, small flares can be implemented through a roundover to the mounting holes.

Lastly there are many variants to the JL Audio equation (shown in the link) which will deliver slightly different results, almost every other software you use will give you slightly different results but you are not likely to notice a clear audible difference. Hope this covers most of your questions.

So, 16x38x26 = 7.5cuft. (just an example) Subs displace .38, so 7.12cuft total. How do I know how much the ports will displace if I don't have the port length yet?

Also, I believe the PSP ports have couplers and extension tubes I can use to make them longer. Or do they not work this way?

Thanks again man, you're a huge help!

Link to comment
Share on other sites

If you are doing this on paper you set a net vol, tuning you want, find the length of the ports with the formula above then you have the displacement of the ports, so you add the displacement of the port and subs (and bracing) to arrive to the gross volume, then you find a set of external dimensions that satisfies that gross volume you found, that's it.

The PSP flares are 7 1/4" external diameter for a 4" so it would be difficult (if possible) to fit on the back wall all 5 ports, and also the clearance to the internal end of the ports to the opposite wall would need to be checked, if it does work out you would still need buy all that stuff and put together (all good if you don't mind).

Link to comment
Share on other sites

If you are doing this on paper you set a net vol, tuning you want, find the length of the ports with the formula above then you have the displacement of the ports, so you add the displacement of the port and subs (and bracing) to arrive to the gross volume, then you find a set of external dimensions that satisfies that gross volume you found, that's it.

The PSP flares are 7 1/4" external diameter for a 4" so it would be difficult (if possible) to fit on the back wall all 5 ports, and also the clearance to the internal end of the ports to the opposite wall would need to be checked, if it does work out you would still need buy all that stuff and put together (all good if you don't mind).

Finally, an explanation that made sense to me! Thank you!

Tell me if I'm heading in the right direction:

I really didn't want to extend the ports, as it would be really simple to just drop in their 17" kit. So using the PSP calc, I played with tuning and airspace to attempt to get the length as close to 18" as possible:

KEBGxcK.png

I was able to get 17.99 total length, with 6.56cuft net @ 36hz. I figured I could go a couple hz higher as this is an SPL build.

Here is the dimensions I came up with to match:

2Ep4F0f.png

3.14(2^2)(16.99) x 5 = 1066.972in3

Converted that into ft3 = 0.617461ft3

So the ports will displace 0.617461ft3

Then I added the driver displacement (.36): 0.617461 + .36 = .977ft3

So, total displacements is .977ft3. I just added it all up and put it in the driver displacement box.

Using .75 MDF and using the dimensions above (15.5 x 39.5 x 26), I was able to obtain the exact net space needed for 36hz.

I will add another baffle, but on top, so the subs are recessed.

I'd be awesome if you, or anyone could look this over to make sure I didn't fuck up any of my math.

6.55cuft @ 36hz, 2 DC level 3 15's running 2k RMS, all Knu non-CCA 0 gauge, Shuriken BT120 (battery), 180amp alt.

Considering what I've got, do these level 3's perform well at 6.5cuft@36hz? I may have to keep an eye on power and I'm over powering them already by 100w each, and the box is bigger than I originally planned .. and tuned higher.

I just want to make sure it doesn't should like shit! haha

Thanks again for all your help.

Link to comment
Share on other sites

It's close to what you state but adding a layer on top of the external dims you give will make the box taller.

Yeah, total dimensions would be the same besides the height would be 16.25" total, which will fit easily. I didn't put a 1 in the baffle box, that's just the cursor. I'm just going to add a later on top, cut it wider so the subs are flush.

I'm a little worried about width .. does there need to be a certain amount of room between each port? or does it matter?

Since I'm adding .5cuft more than recommended and tuning 36hz instead of 35hz, while overpowering them by about 100w each, do you think this will still sound alright? I'm aiming for SPL>SQ. I listen to mainly rap .. like trap shit that gets low. That's why I'm slightly worried about the higher tuning. I'm used to 32hz .. I've never heard 36hz.

Also, just for clarification, why when I put those exact specs into Torres does it give me completely different tuning/airspace? What does his calculator screw up?

I just REALLY want to cover all my bases before I start this haha.

1MlbZ0r.jpg

Link to comment
Share on other sites

No problem on the extra airspace, 36Hz is a little high if playing low tuned music, it comes down to preference, for rap I would look for lower tuning.

You did some slight mistakes and Torres does some others but mainly Torres fails to calculate tuning correctly when using multiple round ports.

Link to comment
Share on other sites

  • 3 weeks later...

No problem on the extra airspace, 36Hz is a little high if playing low tuned music, it comes down to preference, for rap I would look for lower tuning.

You did some slight mistakes and Torres does some others but mainly Torres fails to calculate tuning correctly when using multiple round ports.

I've had a pretty busy month, so I had to put this on the back burner. I'm going to have some free time this weekend and all the parts finally came in.

I was set on 34hz originally, so I will tweak it a little. The only enclosures I've gotten to hear personally are the few I've built, all tuned to 32hz. But it seems everyone likes higher tuning for these specific subs, so I shot higher. I really like the way my previous builds (type R 12's, SA-12's) sounded at 32hz, but my friend I'm building this for listens to rap like I do, but also listens to some EDM (heavy kicks) and a little metal. So I figured 34hz-35hz would work for him.

I'm going to stay away from Torres then. What other calcs do this correctly if any? I may just have to do all the math again .. although, I thought I was pretty accurate .. but my math skills are pretty damn rusty. So I'll run the final designs by you once I figure it out.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Who's Online   0 Members, 0 Anonymous, 377 Guests (See full list)

    • There are no registered users currently online



×
×
  • Create New...