I posted this over on DIYMA but it never hurts to get more opinions before I screw something up.... and to make Eggy happy as well lol.

I modeled my current IB setup in WinISD but ported rather than large sealed. It actually came out really nice. A single 4" port needs a length of .5" for a 22hz tune lol. It would basically be cutting a 4" hole in the baffle. Obviously a single 4" port is not enough for a pair of 15s, I would need at least double that so two 4" ports would require about 4" of length which would be perfect, taking up very little space since half of that could be in front of the baffle.

It would give up to a 6db gain down low and fading out to match the current setup around 60hz. Response is extremely flat right now even before eq. So what this would mean is eq-ing it back to where it is now, cutting the low end to match what I currently have. The benefits would be even less power required, more potential output if desired, less distortion, less excursion, basically a win-win.

The problems are that even though I've gone to great lengths to seal the front from the rear, I'm sure it's not air tight. The trunk vents are wide open to atmosphere so those would have to be sealed. Even with the best sealing job, it's never going to be air tight but I hope it can be close enough.

I don't expect the model to be perfect due to the leaks. I don't know what's going to happen at tuning frequency. Will the subs actually load at resonance or will there be too many air leaks? I plan to do the single 4" hole first to see if it remotely behaves like a ported design. If that's successful I'll do the second hole and buy some PVC.

This setup seems to be capable of 125db+ at 22hz before cabin gain and only 250w per sub.

The best thing is if I tune it to 15hz (keep reading lol) I get a +3db gain EVERYWHERE with about +5db from 15hz to about 50hz. I lose a little peak output but the curves look very similar to what I have now, just with more output. A 15hz tune and a 5" port would require 10" in length. If it put it up top of the baffle I don't think I would be losing anything. I also don't see why I couldn't make the stock sub opening the port. The whole rear deck is filled with foam right now. I would have to cut through the foam but doing it that way would be stealth with no trunk space lost. Am I crazy? I'm seeing a ton of free output with very little work.

 

I have no idea, but it would be awesome if it works. If you decide to do it I think you should go with the 10" port through the stock sub hole. First, I'm sure you're not lacking in output right now so I would shoot for the flattest response possible. Second, if you screw up, it seems like it would be much easier to re-fill the hole through the deck with spray foam than patching a hole in your baffle.

 

Very good point on the hole. If this happens it will be through the stock sub hole.

 

I'll be following this closely. I'd like to add a port to my setup just to relieve some of the pressure on the trunk lid. Gaining some additional output would be a nice bonus.

 

In my experience, sealing the cabin completely from the trunk provides the best result.

No need to port.

 

Tell me what a 28hz & 30hz tune shows.

 

I might be wrong but isn't there a chance it can increase pressure in the trunk?

I will when I get home but I remember it giving something crazy like almost 8db near tuning.

 

I don't know. I just assumed that since the back wave would have somewhere to go (the cabin), there would be less pressure built up in the trunk and less flexing of the trunk lid.

 

I don't think the trunk is completely sealed from the outside.

 

I don't think so either, but I also don't think that the trunk vents and other points of leakage allow large amounts of displaced air to move freely to the outside. I think this is illustrated by the fact that when my trunk lid is closed it flexes like it's going to pop, but if I open the trunk just a little it goes away.

 

Yikes! That's nuts.

But wouldn't porting the rear waves into the cabin cancel out the front waves? Why not use a passive radiator like this in place of the OEM sub?

http://www.parts-express.com/pe/show...number=295-492

Sorry I'm not too inclined but just did a crap load of research when I did a IB setup in my Maxima.

 

I admit I don't know much about ported setups so I could be way off, but I would think that it wouldn't be any different than, for example, using a ported box in an SUV. I'm guessing that the phase of the rear wave has been sufficiently altered by the port that it would no longer be out of phase with the front wave and therefore would have an additive effect rather than causing cancelation.

 

Makes sense. I'm just basing my 2 cents off what I learned on DIYMA back then. I just kept reading that sealing the cabin from the rear waves would provide the best result.

After I linked the passive radiator up top, I think I might look into that idea myself after reading one of the reviews from that particular link.

 

You know that I think that WinISD is not terribly accurate in regards to output and the algorithms are too basic, but can be helpful in academia... so, since I might suppose that you have now idea what to really expect, the decision is to tinker, or not? What kind of a guy are you? Tinkerer, or not a tinkerer? I am a tinkerer and would do it if you can easily go back if it sucks - I don't like to forsake something good to tinker if I cannot roll the change back.

Tinkering > modeling any day, for me.

 

Passive radiators need to be the same size or larger than the sub. If it is possible to install all, why not just double up on 'real' subs Vs radiators?