Calculate port length w/ bend

[jinjuku]

How is a port tube's length calculated if you need to put a 90 degree bend in it to keep it all in the box?

 

[Energize]

I'm 99% sure that its calculated the same as if there was no bend. However, there are those who know alot more than I do on the subject, and im sure they will post here shortly!

 

[annunaki]

One must measure from the center of the port. Don't forget your end correction factor

Check out this link:

http://mobile.jlaudio.com/support_pages.php?page_id=165

Scroll down part way and it explains how to measure length.

 

[Warpdrv]

Thanks annunaki for the link, that will help me...

I hope its ok with jinjuku, but

I have a question then, would the design of the slot port in my build be wrong to do and I should go with a square at the bend instead of a 45 that is shown in this pic...? Any help and thoughts are more then welcome, and hopefully be part of this thread as its relevant...


I can easily change it and it would be easier to do a 90 instead of the 45, using corner molding and filler to a nice rounded transition of the bend...

 

[Alex2507]

Warp,

I've read that link and don't see why the 45 would be an issue. Just measure the length down the center. I want to point out that the end of your port has another bend at the end where it will use the top of the cabinet for length, plus that end correction factor thing.

Alex

 

[jinjuku]

One must measure from the center of the port. Don't forget your end correction factor

Check out this link:

http://mobile.jlaudio.com/support_pages.php?page_id=165

Scroll down part way and it explains how to measure length.

Annunaki that was the single most succinct, single page read of port design mechanics.

AND I learned about port friction. Very cool. I will now have to mess with slot design. I was looking at using this driver for a "doing it for the hell of it" design. Let me know what you think:

Dayton DCS450-4 Classic 18"

For $115 for the driver, and another $228 for a 300 watt BASH plate amp, not to bad for a sub woofer. Maybe another $50 in materials. That would be a hoot.

 

[Warpdrv]

Warp,

I've read that link and don't see why the 45 would be an issue. Just measure the length down the center. I want to point out that the end of your port has another bend at the end where it will use the top of the cabinet for length, plus that end correction factor thing.

Alex

Thank you Alex... appreciate the forethought...

 

[annunaki]

Thanks annunaki for the link, that will help me...

I hope its ok with jinjuku, but

I have a question then, would the design of the slot port in my build be wrong to do and I should go with a square at the bend instead of a 45 that is shown in this pic...? Any help and thoughts are more then welcome, and hopefully be part of this thread as its relevant...


I can easily change it and it would be easier to do a 90 instead of the 45, using corner molding and filler to a nice rounded transition of the bend...

Warp the 45 is fine, and is actually a really good idea. One could also do the molding & filler like you suggested as it would work quite well. A 45 with rounded edges will be less restrictive than a 90 with rounded edges.

 

[annunaki]

Annunaki that was the single most succinct, single page read of port design mechanics.

AND I learned about port friction. Very cool. I will now have to mess with slot design. I was looking at using this driver for a "doing it for the hell of it" design. Let me know what you think:

Dayton DCS450-4 Classic 18"

For $115 for the driver, and another $228 for a 300 watt BASH plate amp, not to bad for a sub woofer. Maybe another $50 in materials. That would be a hoot.

Have you modeled that beast yet? Some of Dayton's subwoofers do not model well whatsover. For instance the Dayton Reference High Fidelity15" needs an 11 cu.ft. vented enclosure to yield quality response.

Don't overpay for the amp. Here is one for $149.00 http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=300-750

 

[jinjuku]

Have you modeled that beast yet? Some of Dayton's subwoofers do not model well whatsover. For instance the Dayton Reference High Fidelity15" needs an 11 cu.ft. vented enclosure to yield quality response.

Don't overpay for the amp. Here is one for $149.00 http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=300-750

That's funny, PartsExpress has the same amp @ wildly different pricing.

Here is the WinISD plot:


Looks like one note wonder if I am reading the plot correctly...

 

[Warpdrv]

I am not familiar with your driver, but
If you lower your tune and go for a slope like this, the room gain will account for the drop in the low end should provide you with a smoother response.

[/IMG]

 

[annunaki]

I am totally with Warp on this one. You do not want that peak at the tuning frequency. You will want to lower you tuning frequency a bit to smooth the response. Make sure you check the excursion plot with the driver (with rated power inputted for signal) to make sure you are not bottoming it out at that frequency. With an Xmax of only 8.5 mm or so it won't take much. Granted it is an 18" driver .

 

[jinjuku]

I am not familiar with your driver, but
If you lower your tune and go for a slope like this, the room gain will account for the drop in the low end should provide you with a smoother response.

I adjusted for 3.0 Ft cubed enclosure and a 16Hz tuning. With a 16 Hz tuning I am not worried about sub-sonic filter since I doubt there is material out there mastered that low. I can use a PEQ to play with the curve.

WinISD beta I don't believe can plot excursion. Even 8.5 MM that is a lot of cone to get going.

Correct me if I am wrong.

 

[Warpdrv]

I adjusted for 3.0 Ft cubed enclosure and a 16Hz tuning. With a 16 Hz tuning I am not worried about sub-sonic filter since I doubt there is material out there mastered that low. I can use a PEQ to play with the curve.

WinISD beta I don't believe can plot excursion. Even 8.5 MM that is a lot of cone to get going.

Correct me if I am wrong.

Don't place bets on no material below tuning point.... Its out there big time...

You still have a huge bump there, that with room gain, will be over whelming.
Do you have a strict budget for your driver, Size limitations?

The Elemental Designs 190v.2 models really well.. but its $100. more...
http://www.edesignaudio.com/product_info.php?cPath=1_21&products_id=37

 

[jinjuku]

Don't place bets on no material below tuning point.... Its out there big time...

You still have a huge bump there, that with room gain, will be over whelming.
Do you have a strict budget for your driver, Size limitations?

The Elemental Designs 190v.2 models really well.. but its $100. more...
http://www.edesignaudio.com/product_info.php?cPath=1_21&products_id=37

I was just pondering a ' what if ' in-expensive big sub. I could always put in a subsonic filter also... I will play around with the edesign woofer to see what the differences are. Definitely learning which is the point.

Just wanted so see what ~$300-400 could do...

 

[avaserfi]

I was just pondering a ' what if ' in-expensive big sub. I could always put in a subsonic filter also... I will play around with the edesign woofer to see what the differences are. Definitely learning which is the point.

Just wanted so see what ~$300-400 could do...

Hows about 120dB at 20Hz sound?

First pick up a 12" Infinity Kappa VQ . This is the same place I bought both of mine.

Put it in a 4 cubic foot box with a 12.5" wide x 3" tall x 55.5" long port (or a variation of this size) with 3/4" round overs/coves in all corners that could impede airflow. See my build here. I should also note I used total volume in creating my port rather than measuring down the middle due to its folded nature. This method will result in a port of approximately the same length as the method described in the JL article and I found it to be easier.

Get the amp annunaki linked and that will put the total at around $350. Use ply for the cabinet and bracing and that will be a little more than another $50. If you do this I strongly suggest you put the amp in a separate area from the box itself as you will want to eventually upgrade to an EP2500 and build yourself another subwoofer .

Such a design will provide optimum sound quality as shown by the measurements on the Kappa Perfect on HTS. Lets also not forget about the massive SPL that can be produced.

 

[Warpdrv]

I think you may have to also take in mind his room size before saying 120db at 20hz, but nothing wrong with two like that in a big room...

You have a nice build there andrew... I like the large radius sweeping corners... for the outside... Made a very pretty box.

 

[avaserfi]

I think you may have to also take in mind his room size before saying 120db at 20hz, but nothing wrong with two like that in a big room...

I said about for a reason . In a mid sized room this unit will achieve 118dB corner loaded with proper power. In a fairly large room I would speculate at minimum 112dB corner loaded. To be honest, I have never been able to fully test SPL abilities of my build due to the apartment I am living in being so old. The last time I tried I cracked the ceiling and a window finally giving up before the whole placefell apart...

You have a nice build there andrew... I like the large radius sweeping corners... for the outside... Made a very pretty box

Thanks. This was originally planned to be the 'stand' for an upper module and the corners were designed for continuity as they would have been used to minimize high frequency diffraction. I believe plans might have changed though...

 

[jinjuku]

Such a design will provide optimum sound quality as shown by the measurements on the Kappa Perfect on HTS. Lets also not forget about the massive SPL that can be produced.

What advantages did the slot porting provide over tubes? Less compression around the port?

 

[avaserfi]

What advantages did the slot porting provide over tubes? Less compression around the port?

If the port does not provide sufficient surface area for the air flowing through it there is the possibility of port noise as well as port compression. If a driver is moving enough air that port compression becomes an issue SPL limitations can occur as is evident in many commercial designs. Basically, typical tube ports just doesn't have a large enough cross section for most subwoofers with large excursion.