Custom box for 1 12

[Nightshade]

That port is awfully long. Typically for a port it really is not supposed to be longer than 22 or so inches or you have to figure in for port correction. Next time you do a design try to keep your port length under or around 22".

[dsw422]

That port is awfully long. Typically for a port it really is not supposed to be longer than 22 or so inches or you have to figure in for port correction. Next time you do a design try to keep your port length under or around 22".

Hmmmm.. I modeled the box in both WinISD and Torres... both had the same port length... what kind of port correction is needed?

[Triticum Agricolam]

That port is awfully long. Typically for a port it really is not supposed to be longer than 22 or so inches or you have to figure in for port correction. Next time you do a design try to keep your port length under or around 22".

What? Where is the 22" number coming from? In many cases its impossible to get enough port area while keeping tuning below 35 hz if the port is limited to 22" long or less, especially with smaller boxes. While you can run into pipe resonance issues if the port gets much over 45", that's a long way from 22".

[Nightshade]

Once your port exceeds 22" the efficiency of the output of the sub is decreased drastically. While it is possible to make a port longer and still get output it is not going to be optimum and should be avoided to get the maximum out of the setup. This is the main reason that the company that makes aeroports, PSP-INC, does not make any of their ports longer than 18".

As far as the correction goes there are ways to "trick" the port into thinking that it's longer than it actually is. One way to do this is to place the port close to a wall in the enclosure so it sees this as sort of an extension of itself. Another is when firing the enclosure the port can be fired directly into a wall inside the vehicle, like trunk lid, rear deck, or something similar and will effectively lower the tuning by reducing the amount of space directly in front of the port.

Edit:

I wanted to add this information that I found from a page that has quite a bit of information about box construction. "Putting a bend in a port tends to introduce unpredictable losses which reduce the port output and also lower the power level at which air noises due to turbulence (chuffing) will be heard." While this doesn't give 22" as the max length as most enclosures aren't 22" deep or better it is a good rule of thumb to keep when designing a ported enclosure for maximum output.

[Triticum Agricolam]

Thanks for responding back Nightshade.

I'm familiar with how port end correction works and I agree with you that excessively long ports can be detrimental to performance, but I really disagree with you that 22" is where ports become excessively long. While maximizing airflow through the port should always be a design priority and a longer port will create more air resistance than a shorter port, all else being equal, limiting yourself to a 22" long port is going to require significantly design compromises in other areas that will have a much greater detrimental impact on performance.

I'll use Sundown subs for example. Lets take a Zv4-12 in a 2.5 cube box on 2000 watts. Sundown recommends 40 sq in of port area. With that amount of port area and a 22 long port you aren't going to be able to tune below 40 hz, which I don't think is what most people are going to want to do. If you leave the port at 22" long and decrease port area to bring tuning down to Sundown's recommended 32 Hz then you are only left with 25 sq in of port area. On 2000 watts the port velocity is going to be above 50 m/sec. I've done my own testing and at much over 30 m/sec you are already losing around 3 db of output to port compression, so that's like throwing half your power away. I can only imagine out much output you will lose at over 50 m/sec.

If you look at the recommended designs Sundowns makes available for their subs ALL of them with the exception of one have ports longer than 22", most significantly so (30"+).

[Nightshade]

This is when I would suggest using a round port over a slot port. The reason for this is because a round port will now require much less port area than a slot port does to achieve the same amount of output.

If it were me though, I would adjust the size of the enclosure to compensate as I feel that the Sundown recommendations on their woofer is a bit on the large side anyway and I am sure you will agree with me. Take the SA or E series for example and you will not run into these issues. The woofer that is being used in this post is the E series so it does not require this uncommonly large 2.5 cube enclosure size, more so in the 1.5 cube size up to 2 cube max. The majority of other manufacturers do not require such a large amount of airspace for their subs as the Sundown Z and X series woofers, so I find them as an exception to the rule to be honest.

[Triticum Agricolam]

Yeah you are right, I do agree Sundown's box volume recommendations are on the large side, pretty much across the board. As a matter of fact, I have an E-12 myself in a 1.5 cube box and I think that's a pretty good size for it. It also has about a 42" long port :-)

The problem with smaller boxes though is if you keep tuning and port area the same the port has to be even longer. With a smaller box you can get away with a bit less port area as I'm sure you know, but overall the port still usually ends up being longer.

[dsw422]

Wow.. lots of info.. lol.. thanks for your replies guys.. I forget the length of this port (not currently at home) but I do believe it is close to 40" at 2in wide. Box size is 1.75 cuft.

15"d x 15"t x 30"w

[dsw422]

Paint...

[dsw422]

Almost done..