NEW BUILD IDEA, need help with port dimensions :)

[XORstatus 10+ year member]

Hello all I am designing a box for a SINGLE memphis MOJO 15.

I am putting 1.2k watts to it daily.

The OVERALL dimensions that I have worked out are 4cubic feet total.

And the port tuned to 31 Hz is 14.5 x 2.15 x 25, I have to "U" turn the port which is giving me problems, I've never done that before and I want to double check my dimensions.

PLEASE give my your two cents!!!!

THANK YOU!!!

This is the FRONT VIEW, sorry about the quality I made these on paint.

This view is ON TOP of the BOX looking down.

 

---------- Post added at 07:08 PM ---------- Previous post was at 07:07 PM ----------

 

Will there be a problem in the back corner behind the port wall?

Click to read more...

 

[XORstatus 10+ year member]

ALSO where does one buy auto audio carpet?

 

[akheathen Premium Member]

there will be a problem, you have to ballance your net volume [internal, not counting the port(and 1/2 width beyond) or the speaker displacement] with a good port area ratio of 12-16"^2 per cu. net. right now, you are somewhere between 7.5, and 9" per, not knowing the net. that makes for allot lower output. it does help to put 45's on the radius of the bend to make it more round, just as long as it does not constrict the port width. keep it square, like you did, do not slope with the back of the box, and you should be good. i buy my carpet/vinyl at a local autosound shop, but i've bought it at walmart in a pinch.

 

[Moble Enclosurs 10+ year member]

If the mounting depth does not interfere with the port being ran along the rear wall, you could benefit more acoustically from that, accounting for the obvious characteristics of the internal volume requirements. This will be easier to design as well as more acoustically efficient.

 

[akheathen Premium Member]

are you saying that the 1:5 angle on the back wall is not going to have a negative effect on the port as it makes the bend?

 

[XORstatus 10+ year member]

there will be a problem, you have to ballance your net volume [internal, not counting the port(and 1/2 width beyond) or the speaker displacement] with a good port area ratio of 12-16"^2 per cu. net. right now, you are somewhere between 7.5, and 9" per, not knowing the net. that makes for allot lower output. it does help to put 45's on the radius of the bend to make it more round, just as long as it does not constrict the port width. keep it square, like you did, do not slope with the back of the box, and you should be good. i buy my carpet/vinyl at a local autosound shop, but i've bought it at walmart in a pinch.

I am not exactly sure what you're saying?

Would you please clarify as I am a noob.

I talked to memphis tech support and thats where I got the 4 cubes net internal (including port and sub displacement)

They told me to keep the port 31 square by 25 long, which should tune it to 31 Hz they said.

Do you see problems with this design?

 

[Moble Enclosurs 10+ year member]

are you saying that the 1:5 angle on the back wall is not going to have a negative effect on the port as it makes the bend?

Regardless of the shape of the port, the path the sound travels is constant as long as the port is constant. So, yes there will be effects at the bend, but nothing that cannot be controlled. Here is an example of where the pressure will affect the output.



The darker red is the most pressure in the port. This area needs to be controlled for optimum output, but since the output is based on pressure in this type of design, there will be minimal effects anyhow, but no one can say they will not be audible yet. I bet they will be with a trained ear, but for general music, not so much different. it will however affect the tuning when calculated, unless this area is accounted for as well.

If you want to get technical, then controlling these red areas is the best option.

 

[XORstatus 10+ year member]

Should I just block them off?

THe port is designed to be 16 inches long on one side, then wrap wround and an additional 9 inches so the entrance of the port wont be near the "red zone"

But is causes too much problem I can just remove it.

Keep the prot the same and just use extra mdf to completely encase that portion of the box.

Is that a good idea?

OR IS THIS WHOLE IDEA STUPID?

SHOUD I START OVER?

AGAIN I KNOW HOW TO ASSEMBLE THEM, don't know too much about designing them.

And as always thanks guys //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[Linkz 10+ year member]

Perhaps you could use some aero ports instead of a slot port.

Otherwise, I would just block off the angle, or get rid of it all together.

 

[Moble Enclosurs 10+ year member]

Should I just block them off?
THe port is designed to be 16 inches long on one side, then wrap wround and an additional 9 inches so the entrance of the port wont be near the "red zone"

But is causes too much problem I can just remove it.

Keep the prot the same and just use extra mdf to completely encase that portion of the box.

Is that a good idea?

OR IS THIS WHOLE IDEA STUPID?

SHOUD I START OVER?

AGAIN I KNOW HOW TO ASSEMBLE THEM, don't know too much about designing them.

And as always thanks guys //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Good idea. As the angle is really only needed for flushing the exterior of the design to the seats or wherever you have it. It really does not do much for acoustics, so sealing it off on the inside will be easier for you.

 

[on1wheel01 10+ year member]

Go with aero ports. I did on my newest box 2 6" and man I love them. U could always just have someone design u a box, pro rabbit designed mine for my mojos

 

[XORstatus 10+ year member]

How would one go about using or designing aero ports?

How does one tune those?

 

[akheathen Premium Member]

to me, comes out to 26.5hz that way.....i would go with 14.5x3.5 and it would need 29.5" length to get you to 31hz....... ok, i just run some #'s..... going off what you said, i calculated an appropriate port for a 4^3 net, and it's displacement came to just over 1^3..... then i looked at your box, and that 21.5" back wall stood out (should have been 16.5") and, anyways, your gross internal, subtracting the wall thickness, is only ~4.2.... so, that would knock you town to the range of 3'^3 ported or less..... as your net, guessing on sub displacement, and what the new port would need to be...36-43"^2, imho at that point, and that may be under-estimating sub displacement...... the t/s parameters of the sub would be nice to have....

mobile- i'm all ears, it just has never seemed right to run a port like that in my book, but you are the pro builder, so i will take what you have to say. i just see the high pressure area and un-even port pressure causing a bit of turbulance and break-up as the un-even volume tries to blend with the even slot. what if the bottom half of the port allong the back wall mirrored the top, making it even from top to bottom?think that would work well?

 

[Moble Enclosurs 10+ year member]

How would one go about using or designing aero ports?
How does one tune those?

Far too much to explain in a thread without ample time and energy to explain it. I recommend getting the loudspeaker cookbooks for that information. For me, I do it a little different than most, so my explanation may not be recognized, and too many questions would evolve from it, which I do not have time right now to keep up on answering. But you should be fine if you read the recommended literature I mentioned.....if you can get your hands on it.

 

[XORstatus 10+ year member]

I think Im gonna scrap the angled back, and run the port along the out side wall.

After talking to memphis they say 4 cubes @ 31 Hx, which includes port displacement and diver displacement.

Are their calculations wrong?