All right here it is. Your subs are designed a little differently than most. Consequently the best box design for your subs is some what unusual, so please bare with me because I am going to explain. At the end of my explanation I will give you strait forward instructions on how to build this box so don’t worry if some of this info is a little intense.
Here are the specs on your sub
Note that the spec labeled QTS is .593
In speaker design a QTS of more than .5 is usually considered undesirable because it makes the box size huge and the sub sound sloppy. After modeling this sub on BASSBOX PRO several times it became apparent What the engineers at MTX are trying to accomplish and it became apparent to me how we can use this design abnormality to our advantage.
I believe that MTX came up with this design because it allows you to build almost any size sealed box between 1cu. Ft and 6 cubic feet and you will get almost the same effect.
Also this design is cost effective because it is not very demanding of the speakers magnet structure.
Vented boxes for this sub are another story. In the box that MTX recommends (once again props to MTXs engineers) This sub is LOUD and will sound ok in some cars (SUVs for example) but will not sound to hot in a car with a trunk of a Mercedes 300e.
How do I know this? Because every time I build a box for a car I first test, plot, and record the effect that that car has on a test sub that I have. This enables me to apply the sound that that car has on a sub to my new design before I build it. Also when a new customer (or someone that I help on the net) comes to me with the same car, I can just look it up in my database and apply that info to my next design.
In your last post you did not give me a third dimension of your current box so I have to guess at what size it is. But like I said due to the design of this sub it really makes little difference. Here is my best guess at what your subs are producing now.
This is what it sounds like out side of your car (blue line).
The pink line represents what it sounds like in your car after I have added my acoustic file of the last 300E that I built a box for (this is what your box sounds like now, not what the box I built sounds like. I don’t show that here)
Note that the out put is louder across the entire bass spectrum. This is what happens when you put a sub in any car. The two important pieces of information that we get out of this graph is that the low bass is week and the large peeks of output happen at to high of a frequency (50-80hz is to high).
Here is what I suggest for you.
“Isobaric loading”
This means that you are going to take both of your subs and mount them face to face, then you will wire the outside sub out of phase( + and – reversed) so that they both move in the same direction while playing.
Internal net volume (volume of box – port, sub structure, wood thickness that the box is made of, and any bracing) 4.0 cu. Ft
Port: 5”x5”x14.59”long rectangular (inside dimensions) and made from ¾” MDF
Here is your cut list
Out side dimensions of this box are: 14”x36”x21.25”
You can rearrange the dimensions of this box in a number of different ways and get the same volume. If you need to do that so that the box will fit in your trunk and look a certain way, that’s ok. As long as you know how to recalculate volume.
If you need some help doing that, I am here to help. Pm me and I will give you contact info so that I can give you the run down by phone if you need me to.
You can place the port any where on the box as long as it has no obstructions and it is not butted right up next to the sub. The port is constructed out of 3/4”MDF
By the way
Here is the response that you will get from your new box. The yellow line is the box that I have designed for you
The red line is the box that MTX recommends (remember that they don’t know what kind of car you have)
This graph shows how much the speaker cone will have to move using any of these boxes. The darker area on the top is where the speaker can no longer handle the excursion.
This is important information to me because I can make the box look really good on paper, but if in reality the speaker cone wants to jump out of the basket it doesn’t really do you any good.
The graph shows very good cone excursion for all of these boxes.
And last but not least. This graph shows phase response vs. frequency. What we are looking for here is a smooth transition from left to right. The yellow line is the box that I designed for you and the red line is the MTX recommended box. Notice the ripples in the red line. This is what people hear and complain about when they say that a sub sounds sloppy and dose not hit hard. I have avoided this.
Conclusion
This box will be louder
Hit harder
Hit deeper
And sound great in your specific car
Int vol 4.0 cu. Ft
Port 5x5x14.59
No fill
Isobaric mounting
Anyone feel free to pm me on this