How to add db

Do db add up? If you have a sub producing a sound pressure of 140db, how much will two of these subs produce? 143db or more? Assuming that they are in phase.

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Poly Dollies

Doubling of surface area adds 3db.
Doubling of power adds 3db.


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New Project: 2003 Pathfinder

what if I paste a 34in cone ontop of my 12in subs (producing 90db's), doubling the surface area ^4power .  Will it produce a 102bd sound pressure momentarally before the cone or coil rips or burns?

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Poly Dollies

Well ... by increasing the moving mass of the cone you increase the work the motor has to do. So I'm not sure where you'd end up.

If, somehow, you could add the 34" cone w/o increasing the moving mass then it would follow the 3db rule.

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New Project: 2003 Pathfinder

typically adding a sub will add 3 db in a perfect enviroment, some vehicles I have seen more then 3 db due to cabin gain.   Others and this is a very select few, It has been less then 3 db gain.   But you have to remember just by adding a sub will not give you 3 db, You also need to have that sub powered with just as much power as the first, You cant just run them both on the same amp as before,

I have had so many people come in and say I added a sub and now it sounds quieter or the same.    Well your 2 channel that was able to run at 4 ohm mono produced 500watts to one sub.   Now when you have 2 subs wired to the same amp with a 4 ohm load you are only give each sub 250!

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2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR
2007 USACI World Champion
2007 World Record
2006 USACI Finals 2nd Place

Actually Jeff, that is wrong. Double the surface area driving with the same amount of power to the system will still yield a 3db increase in efficiency. The people coming in and saying 2 subs are quieter are saying so for different reasons (like not enough air / cancelation).

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New Project: 2003 Pathfinder