Haha hey how’s it goin man, I remember you from the last time I posted, iv thought about gettin 4 12s in this poor accord for a while now, I just don’t know how to build custom boxes and I’m not sure how it would fit in the trunk, but iv gotten to far into subs man, just got these runnin right and I already wanna upgrade again, maybe move to more high quality subs, but why would having diffrent size subs confuse the sound?
Even the same make of a different size will have different sound signatures, volumes and mechanical properties and this alone would make is difficult to tune it correctly. If you had separate amplification for each size and could tune them using individually calibrated DSP channels, you "might" get them to play well together.
Let's assume their the same brand and model, just different sizes. two 15s of the same efficiency ratings will be quite a bit louder than the two 12s. How would you equalize this without separate amplification?
Say you can amplify both separately. Then two things occur. You make one less productive to try and keep up while you subdue the other to tone it down, that is an impossible order as there will be differences in rise, gain, volume, air movement regardless of how you try to manipulate it. While it is possible to install different sized subs in the same box (individually chambered/tuned), it is not recommended and will not help the sound of your system. Instead, it will likely lead to an unbalanced sound in your car.
The beauty of forums like this one is there is a plethora of individuals with experience in designing and building enclosures that are here to help should you decide on a a build that has specific goal in mind.
I would start with posting some information on what you currently are using (equipment, car year make and model, HU, subs mids, tweeters, in general and what is it that you don't like about your current setup or what is it that you desire to change or gain from changing what you have. This way the forum can chime in on what the best solution might be.
Just seems like a lot of hurdles to overcome just to say you "did"it, when there isn't any guarantees you will accomplish your objective/goal. Novel idea, been down this road with others too, never heard it (no pun intended) workout before.
My $0.02
