Wanted: Little Known Secrets To Increase SPL

You covered sound proofing, but more importantly sound deadening. ie. make the panels rock solid so no energy is used in flexing them. thats roof, door skins, boot, etc. remove soft seats which can absorb some energy too.

do you really have the optimum box design? ported to the right frequency for that subwoofer and car combination?  the maths behind setting up a box for max SPL is pretty major. work out the frequency the car is loudest at, calculate the wavelength, set the box so the speaker is the right distance from the mic. every speaker will be different.

here's a few rules-of-thumb you probably don't know.

double the power gives +3dB

add extra sub gives +6dB

a good box gives +6dB

the car itself can add a few.

I think the implied assumption here is that you're adding a second sub AND providing it with the same amount of power as the first sub.  You're right, just doubling the cone area alone would only give you +3dB, but doubling the cone area *and* the power is probably where Eargasm is getting the +6db.

Scott Gardner

yeah, the sensitivity is an important one. for the same final dB reading, a sub rated at 88dB sensitivity needs twice the power of a sub rated 91dB sensitivity.

this can take some time, but theory goes you put a sub in a basic box and measure its spl performance over a range of frequencies while running in open air. then measure over the same frequencies in the car. you will notice that in the car there will be higher readings, usually with a bit of a peak. thats the cars resonant frequency and if you can find a sub that has a similar tuning frequency, and tune your box and port to that frequency, it gets you a long way towards a high SPL figure coz everything is working together.

had a guy near here win an SPL shootout with 2 8inch subs. just gotta put it all together right.