# NEW BUILD IDEA, need help with port dimensions :)

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• 08-25-2011
XORstatus
Re: NEW BUILD IDEA, need help with port dimensions :)

http://i.imgur.com/sAKtt.png
• 08-25-2011
Moble Enclosurs
Re: NEW BUILD IDEA, need help with port dimensions :)
Quote:

Originally Posted by XORstatus

http://i.imgur.com/sAKtt.png

That would definitely be much easier for you to calculate. :) Just make sure you account for the bend area in those dimensions.
• 08-25-2011
XORstatus
Re: NEW BUILD IDEA, need help with port dimensions :)
HMMM

Ive always calculated the length of the separating port wall as the summation of the port length.

For example:

http://i.imgur.com/a2uBU.png
• 08-25-2011
XORstatus
Re: NEW BUILD IDEA, need help with port dimensions :)
IS THE TUNING OF THIS BOX CORRECT?

I told the memphis tech guy that I wanted it tuned to ~ 32 Hz, he came up with this design.

Total 4 cubes including port and driver displacement.
Port 31 sq. inch (14.5 x 2.15) by 25 in long which he claims to be 31 Hz tuning.

Also is the port width small? I have built a few boxes and the port width seems small to me.

I WANT TO BUILD THIS TONIGHT / TOMORROW, as soon as you guys OK it ill start and POST PICS.

:)
• 08-25-2011
XORstatus
Re: NEW BUILD IDEA, need help with port dimensions :)
ALSO when is a dual baffle necessary?
SOULD I USE ONE ON THIS BUILD?
• 08-25-2011
Moble Enclosurs
Re: NEW BUILD IDEA, need help with port dimensions :)
Quote:

Originally Posted by XORstatus
HMMM

Ive always calculated the length of the separating port wall as the summation of the port length.

For example:

http://i.imgur.com/a2uBU.png

it should be calculated as (19-0.75)+(8.25+0.75), which will give you 27.25", and can be even tuned more accurately with the bend accounted for if a 45 is used. But not a big deal for a simple design.

Now regarding tuning, that......I cannot tell you unless I figure for the driver specs along with the box information together, as the driver will affect the tuning depending on the mechanical parameters of the driver and displacement volume as well. Now, with double baffle, considering dampening factors of 0.75" wood against 1.5" wood, then doubling is ALWAYS going to be a recommended idea, but for simplicity, again, usually is more of a concern with excursion and power levels beyond average. The average can be said to be the mm distance equal to the drivers sd diameter. So, if a driver has an sd of say 500 square cm, then the sd diameter is 8.8" respectively(obviously as an average, as this is just an example). So, the xmax average for that driver would be 8.8mm(just replace inches with mm).
This is a good way to figure if the driver has better than average excursion, and why some companies consider 10mm "high excursion capability" even though we may not. So, if the driver exceeds this average, it may be recommended to double baffle.

Now, for those who want to rip apart what I just mentioned, this is ONLY used as an averaged example of what I came up with for the question of double baffling. This does not mean that a driver WILL be 8.8" diameter if the area is 500 square cm, as some drivers are unique, like square drivers, or the TB 8X12. And this does not relate to the drivers sd. The sd of a driver can be calculated by measuring the ACTUAL diameter of the cone and using a formula to figure for sd from that measurement.

So, in general, if the xmax exceeds this simple little example I put together as an average, then a double baffle will be recommended...and should always be used regardless, for added support and resonance control.
• 08-25-2011
XORstatus
Re: NEW BUILD IDEA, need help with port dimensions :)
Here are the specs of my woofer: I have the 15-M3MOJO15

http://i.imgur.com/VaRh1.jpg

Yeah its X max definately surpasses the 8.8mm mark.

I also used the RE box calculator With the same demensions of the box that MEMPHIS designed. RE calculator stated that the memphis design was ~ 27 Hz.

THE RE calculator however did NOT account for my driver. So how ACCURATE can this information be?

Further it is saying that my design is NOT 4 CUBES, its saying that my 30 x 19 x 16 design is 3.73 cubes?
Im assuming its discounting a portion of my cubic volume for the port?

I dont knwo whats CORRECT?

I dont want to build a MISTUNED box, that would make me REALLY REALLY SAD!!!! :(
• 08-25-2011
Moble Enclosurs
Re: NEW BUILD IDEA, need help with port dimensions :)
Yea, for the 12 on that list, for instance, the maximum excursion for single baffle use is 9.06mm. It has just over 15mm. SO, double baffle would be recommended, yes. It's not 8.8mm for every driver, lol, it depends on the drivers sd and power levels. But the example I gave was for 500 square cm-as an example, not a constant.

Now, if you are worried a lot about tuning and such, I have not recommended this yet, because I usually do not throw myself out there as a sign of need, but if you want one of us designers on this forum to do the enclosure for you, by all means, it will be worth the cost of a design if your concern it great for accuracy. i would NEVER consider using any port calculator, or program that does the math for you, other than checking your work. As, quite a few of them do not consider the most important parts of the acoustical aspects of the design.

So, myself, pro-rabbit, surreal, Ram, and a few others (forgive me if I left you out), can definitely make sure this happens the RIGHT way for you. Just ask. :)
• 08-25-2011
XORstatus
Re: NEW BUILD IDEA, need help with port dimensions :)
How much does this usually cost?
• 08-25-2011
Moble Enclosurs
Re: NEW BUILD IDEA, need help with port dimensions :)
Quote:

Originally Posted by XORstatus
How much does this usually cost?

From myself, a design is \$45. From others, they might have to chime in for that. I cannot answer for that. Others may be less expensive than myself, so it's worth asking around. And by all means, this is no advertising thing for me right now.....it is clear that you need someone experienced to help you with this more than pure advice, so again, recommended.
Now, if you would like those of us who build them as well, to do a build design, this will vary upon different design approaches, so that will need to be discussed through PM, or during a request form for a more accurate quote. I will say this, that I am reverting to a new way of purchasing for customers. The initial price will only include the base price, and the shipping can be paid after the item is built and ready to ship. This allows for accurate shipping/handling costs rather than overcharging you for what the company calculates for. I have had a LOT of people request this, as it is more accurate for costs to you, and can be split up in case you do not have the costs of the total amount up front.

Just an idea, if you choose to have a build done as well.
• 08-25-2011
XORstatus
Re: NEW BUILD IDEA, need help with port dimensions :)
Thank you for you input, I appriciate you going above and beyond.

I like the feeling of doing it my self tho. it makes the outcome better to me. BUT I WILL KEEP IT IN MIND.

I have redesigned the box and calculated the tuning.

New box is:
30 x 16 x 21
Gross vol: 4.66 cubes

Port:
14.5 x 2 x 14 tuned to 32.99 Hz
NET vol: 3.9 cubes

Im building this baby TONIGHT!!!!
• 08-25-2011
Moble Enclosurs
Re: NEW BUILD IDEA, need help with port dimensions :)
Quote:

Originally Posted by XORstatus
Thank you for you input, I appriciate you going above and beyond.

I like the feeling of doing it my self tho. it makes the outcome better to me. BUT I WILL KEEP IT IN MIND.

I have redesigned the box and calculated the tuning.

New box is:
30 x 16 x 21
Gross vol: 4.66 cubes

Port:
14.5 x 2 x 14 tuned to 32.99 Hz
NET vol: 3.9 cubes

Im building this baby TONIGHT!!!!

SWEET! Post a pic or two! And obviously, you have to let us know how it sounds, lol.
• 08-25-2011
akheathen
Re: NEW BUILD IDEA, need help with port dimensions :)
ah, they just give it to you in the wrong format. it is actually about 3cu, maybe less ant then their port dimensions would be 31hz, but i'm telling you that you do loose some effectiveness of the port once you get below 12"^2 per cu. generally, we go off net displacement, not displacement before the port and driver. i do not know about how people are calculating aero-ports, but i remember reading on their site, and i don't 100% know if it's correct, that you tune them like normal round ports, just calculate them as bigger ports. only used them a couple times, but generally, i prefer to stick to slots, but that is my own preference.
• 08-26-2011
XORstatus
Re: NEW BUILD IDEA, need help with port dimensions :)
Here are some pictures of the build!

http://www.caraudio.com/forums/gener...ml#post7723870

Tell me what you guys think.
• 08-26-2011
akheathen
Re: NEW BUILD IDEA, need help with port dimensions :)
oh, tripple wowee..... first, i need to start making sure there is not another page before posting, lol, 2nd, i can't belive i read that right. mobile measured the port from the outside, not the centerline?!?!?!?, and 3rd, you went way backwards on that port area. that is only 7.3"^2 per cu, which is absolutely tiny.... like those truck boxes that had the tiny 1.5" round ports in them or even bigger prefabs back inthe day, the ports really did nothing.......... and yours will be highly inefficient and barely effective. at lower power levels, say 300watts, the port will have an effect, but with some ral power, not so much. if you hadn't already glassed it, i would suggest putting it in raw, with just sealant and seeing how you like it. then, when it doesn't reall have the output you expected, then add 1.5-2" width to the port and it will be more than you hoped for.... your tuning and volume #'s were just about spot on, so you are doing good there, just remember lenght of the port is measured down the centerrline of the port, and port displacement also includes 1/2 width of the port beyond.....
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