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building enclosure, port location?

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=83104
Printed Date: May 27, 2022 at 12:51 AM


Topic: building enclosure, port location?

Posted By: hemanjoyman
Subject: building enclosure, port location?
Date Posted: September 19, 2006 at 4:09 PM

I want to build an enclosure with two slot ports with no dividers to separate the two subs.

I was wondering, is it better to put both ports in the middle, with one single vent opening in the front of the enclosure for the exit point of both(I hope this is clear), in which case they would share the back wall. Or, should I put one port on each side, along the side walls???

Any suggestions???



Replies:

Posted By: killer sonata
Date Posted: September 19, 2006 at 4:47 PM
I would think that would pay a huge number on the sound. There would be 2 different phases coming out of that box that could cause cancellation. Keep both ports on the same side of the box.




Posted By: hemanjoyman
Date Posted: September 19, 2006 at 5:35 PM
Can't put both ports on the same side of the box, since they will be slot ports and they will be L-shaped. They either have to both go in the middle of the box, or one on each side.




Posted By: stevdart
Date Posted: September 19, 2006 at 5:54 PM

If there's only one shared chamber, why are you not considering using only one slotted port?  If your reasoning is that you are concerned that the L shape will favor one sub over the other, then throw that concern out.  The airspace is shared by both subs.

Place the port on either side, whatever design you like best and fits your installation.

If you want a center slot design, refigure you box so that each sub has its own chamber.  The middle divider will separate the ports (two side by side in the center).  Calculate port for each individual sub / airspace.

If you want a slotted port on each side of the box, there again, use a middle divider to separate the subs.  Calculate port for each individual sub.



-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: hemanjoyman
Date Posted: September 19, 2006 at 6:21 PM
I was thinking about doing only one slot port, and yes, I was worried that it would effect each sub a bit differently and not give a desirable sound. I also thought about giving each sub a separate chamber, and each sub it's own port, but that would make the enclosure even bigger and I don't have much space in my trunk as it is.

Thanks for the info. stevdart




Posted By: killer sonata
Date Posted: September 19, 2006 at 7:59 PM

why not design a box with a sub on either side of the port in the middle with the port splitting in 2? kinda like the picture below.

posted_image




Posted By: hemanjoyman
Date Posted: September 19, 2006 at 8:34 PM
Hey killersonata.......that was actually part of my original question, that is what I meant by both ports exiting in the front and sharing the back wall.

I guess my question was just not clear enough, and that's what I was afraid of. Would that design work better than having only one port on the side? The design picture you posted is basically 2 ports.




Posted By: killer sonata
Date Posted: September 19, 2006 at 10:35 PM
ewll it is 2 ports and it isnt. They merge into 1 so it is still considered a single port. The main port has to be twice as wide as the port chambers on the back wall. In this case i used 2" for the main port and it broke into 2 1" chambers. I used this same box for my last setup and it sounded great. Whether or not it actually sounds better than a true single ort I have no idea. This would be your safest bet though.




Posted By: stevdart
Date Posted: September 19, 2006 at 10:35 PM

killer sonata:  lay it out for me.  How are you going to calculate tuning frequency with that design?

Make me a believer.  posted_image

...and an edit because we happened to post at the same time....how is that the "safest bet"?



-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: hemanjoyman
Date Posted: September 19, 2006 at 11:48 PM
Well, I am assuming it should be the same as calculating for two 1" ports, except if I do it like that, I would probably make them 1.5" inch ports.




Posted By: bellsracer
Date Posted: September 20, 2006 at 1:08 AM

Put the port on the same side as the subs in the middle. Computer programs (well most of them) won't tell you how the soundwaves will travel specifically but putting the port in the middle will achieve the best results on the reflecting waves in the enclosure. If you want to put the port on the side of the box, keep it as close to the side of the box as the subs to keep the imaging stable.

Then your next issue would be to control the reflected waves within the box. Sound absorbing materials (not sound dampening) lining the walls and the port (not on the inside of the port) will allow the side port to function at its best.

But for maximum effect, stick with the port in the middle. It's a known, proven system for big hits.

Good Luck!



-------------
Never send your ducks to eagle school.
The difference between ordinary and extraordinary is that little extra.
The 3Ls of life: Learn from the Past, Live for the Present, Look to the Future.




Posted By: hemanjoyman
Date Posted: September 20, 2006 at 11:59 AM
killersonata

I, like stevdart, would like to know how to go about tuning a cabinet with that particular design you mentioned. It seems like that might be the way I go.

posted_image




Posted By: bellsracer
Date Posted: September 20, 2006 at 8:30 PM
nouseforaname wrote:

~snip~

bellsracer, why in the world would you line the inner walls with a sound absorbing material? i've never heard of that nor have i ever done it and my boxxes function just fine. and who proved the middle of the box is the best place for the port for "maximum effect"? the port can be on the top, bottom, either side, OR the middle, as long as the port fires in the same direction that the sub is facing, it doesn't matter.


It's an overkill thing. Pressure is the determining factor for getting sound out. but as much as 2 db can be gained by having the walls absorb the soundwaves instead of dampening them. When we analyzed various single chamber, dual sub, side port boxes this helps create a better munsen curve and gives the sound a cleaner exit to match the subs. It's a physics thing we played around with for one of our concept mini-cars.

-------------
Never send your ducks to eagle school.
The difference between ordinary and extraordinary is that little extra.
The 3Ls of life: Learn from the Past, Live for the Present, Look to the Future.




Posted By: stevdart
Date Posted: September 20, 2006 at 9:13 PM

bellsracer wrote:

this helps create a better munsen curve

bellsracer, let me get this straight:  you and your crew performed scientific testing on sub enclosures, at least one of which had the port on the front at the side, and at least one that had the port dead center between two subs.  And being a controlled test, both enclosures, bracing, drivers, power input, source material, etc. were identical.  Is this right so far?

So now, what is perplexing:

You said that you found a difference in Fletcher-Munsen curves between the two enclosures?



-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: bellsracer
Date Posted: September 21, 2006 at 11:50 AM
stevdart wrote:

bellsracer, let me get this straight:  you and your crew performed scientific testing on sub enclosures, at least one of which had the port on the front at the side, and at least one that had the port dead center between two subs.  And being a controlled test, both enclosures, bracing, drivers, power input, source material, etc. were identical.  Is this right so far?

So now, what is perplexing:

You said that you found a difference in Fletcher-Munsen curves between the two enclosures?


Pretty much... D is one of those guys who love to refine things to perfection. Tek is like his no. 2 for these concept things.

When it came to power draw versus SQ for flatline, we found that during our test between 80-125 Hz @ 100 db the curve lifted slightly in order to match target spl properly.

After absorbing the sound, we found a 2 db increase in spl and had to drop the power a bit in order to match target spl. This was consistant with the calculations that Tek and D did to figure out what was happening to the soundwaves reflecting in the box.

To be honest I'm not 100% sure what the equations are or anything but I do remember seeing their book they filled with all the calculations. It was about 120 pages of calculations and 15 pages-ish of written notes.

Tek made us crossovers that bandpass the targeted tone with 24db/octave cuts +-2Hz from target. It was kind of strange and I don't understand it all myself, but that is their results.

I didn't think that the overkill deal would get this attention... It was more of a chindogu (useful but not practical idea)

As for the technology in the shop, most of our testing equipment is the same equipment used in SPL and SQ competitions. A Gateway (top notch) computer controls our sound test equipment. TPI 440s help us double check what the equipment is doing while installing and fabricating. It's nothing wow worthy so much as it is just used a lot.



-------------
Never send your ducks to eagle school.
The difference between ordinary and extraordinary is that little extra.
The 3Ls of life: Learn from the Past, Live for the Present, Look to the Future.




Posted By: hemanjoyman
Date Posted: September 21, 2006 at 1:01 PM
Well, does anyone know how to go about tuning with this type of port? How to account for the end correction factor, how to properly apply the length calculated since It cannot be done like a regular L-shaped port, since this is more like a T-shaped port?

L-shaped calculated like this for L1 and L2: posted_image

I'm assuming the T-shaped port would be L1, L2, and L3, but how do you go about taking the actual measurements of it?




Posted By: stevdart
Date Posted: September 21, 2006 at 8:25 PM
The box is already divided into two chambers with that design.  Just put one thin piece of wood down the center to separate the ports and be done with it.  Each sub will have its own port and you'll be able to model without all the guessing.

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: hemanjoyman
Date Posted: September 22, 2006 at 11:51 AM
I figured out how to design that type of port. beerman over at deCaf: Car Audio Forums helped me out with it.

posted_image




Posted By: hemanjoyman
Date Posted: September 22, 2006 at 11:52 AM
This is the discussion we had about it:

https://www.subwoofertools.com/forum/topic.asp?TOPIC_ID=1003





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