I have a 1999 Eclipse Spyder (convertible) and have recently installed a pair of 690's in the rear. The OEM speakers were smaller in the depth; but still 6 x 9. Installing the 690's required some modifications. After installing them, I noticed the low mids (400 hz to about 900hz) had no real definition but the low end (below 200 seemed to be there, but somewhat "echoie". So, armed with a function generator and SPL meter, I went to plot a graph of the speaker. What I found in the graph is exactly what I was hearing. The response was much like a Blows (Bose) system. The highs and the lows were pretty much to spec, but the mids just weren't there.
Mitsubishi's design of the speaker enclosure is quite pathetic IMHO. The back of the speaker is wide open and just resonates in an empty wall behind it. I'm sure the hollow mids were caused by that. So, I proceeded to make a fibreglass shell to make a psudo "box" inside the wall of the car. The result is an airtight seal around the speaker.
What I notice now is that the low mids are nice and crunchy and the highs are pretty much the same. However, the lows (below 130 hz) are pretty much gone. Of course, I assume it's because the fibreglass box I built the enclosure with is too small and it's not ported.
I am running 2 10" Rockford Fosgate HE2 subs. Each powered with 250W RMS.
Now with all that said, here are my questions:
1) Does anyone know the Q or the minimum box size of this speaker?
2) If I plan to cross these over at 120hz anyway, does the box size really matter? I mean, can the speaker even physically fit in a box small enough to drive the Q point up past 120Hz?
3) Should I install a port in that newly constructed fibreglass box? If so, lets say the box is about .175 cubic feet; if a port is needed to tune to lets say 80hz, what size port would I need.