You've got to take into account cabin gain which in larger cars like Falcons and commos is usualy mid-high 50's. Build a box to match that, and you can get some impressive - if short lived results.

I got *cough* had a pair of 6x9's pushing 138dB - once. Problem being when cabin gain and box porting match, you unload the drivers, and they tend to tear themselves apart (unless they've got a really stiff suspension).

No worries sam. Reckon if you got a 2nd mono and 2 nice big slot port boxs(gotta love falcon boot space) plus the battery you should pull 140+.

Did you Realy pull 138 with those 6X9s?
Run off a amp I presume.

Yep, and Yep (~800W worth)

As said though they didn't survive.

Box design plays a HUGE part in getting loud if that's what you want. Also important for good sound quality.

How was that 2 6x9 box made?

???

Like any other box, six sides, some holes, glue and screw.

Yea I was thinking there would be some internal panels or something.

Ah, box design.

That one, no just a ported box.

I made another one, 6th order band pass* with the speakers internally in an isobaric config. simulation showed they'd get 2dB louder or so, but speakers died so never tested.

*effectively two ported boxes joined in the middle, speakers on the middle baffle, each side tuned for a different frequency, the speakers play their loudest between those two freqs. I'd had it tuned for 54Hz one side and 56Hz the other - completely useless for music, but loud at 55Hz.

That's the one.
How did you manage 138 with that setup as just a ported box.

I started by carefully measuring the TS parameters of each speaker (not relying on the 'on the box' specs, not the DD publish specs anyway - bad DD).

Again carefully measured the frequency of most cabin gain in the car. Stepping through a custom made CD of individual Hz tones, with a dB meter (wasn't a termlab as I don't have access to one normally).

Then design the box to suit the speakers and the tuning freq I wanted. Fed it bulk power, @ 2ohm's the amp specs say it'll do 800WRMS, so two 4 ohm speakers in parallel = 800W. No wonder they didn't last - they're rated for 50W each, and the port tune meant they'd be largely unloaded.

Starting at very low volume (power), ran through the tone CD again, to confirm the cabin and port gain were working together. Then figuring I'd only get one go at it, hooked up the termlab, cranked up the volume and played the one burp.

Additionally, being a "ghetto 6x9 comp" (an little for fun comp a few of us ran as part of a MEASQ and dBDrag event) the only rules were a control set of speakers the DD 6x9's and any box had to be below the window line and behind the B pillar. So it got sat on the rear seat, so didn't have to work from a boot.