decibel scale and amount of speakers

[Flyer 10+ year member]

I understand how the decibel scale works but in actual practice I have no idea what would realistically happen.

My hypothetical question is this (and this may help out others thinking of the same situation)

If you have one subwoofer in a sealed box at a given power and hit 120db, what approx. decibel level would be obtained by adding another of the same subwoofer with the same power that you had to the first.

For example a 130 db system is 10 times more intense than a 120 db system.

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[SBLAZER]

i believe usually when u double the cone area and double the power u get around 3dbs. but it varies so much, from wha i have tested, ive known people who have gain'd 2.5 and some who gain 5. it varies. but usually they say its 3 IIRC

 

[trow100 10+ year member]

Wait for squeak, he just posted this the other day if i remember correctly. but as a rule of thumb hes right about 3 dbs. depends on install and a whole bunch of other stuff.

 

[helotaxi 5,000+ posts]

Doubling cone area is +3 dB. Doubling total system power is +3 dB. In the original poster's question if you were to go from 1 sub getting x watts and you go to 2 subs getting a total of 2x watts, you would theoretically get a 6 dB increase.

 

[Flyer 10+ year member]

The other day I was inquiring about switching to vented boxes, now I am just going to double everything based off of all the responses I have recieved. Thank you for your help guys.

Flyer

 

[squeak9798 5,000+ posts]

Doubling cone area is +3 dB. Doubling total system power is +3 dB. In the original poster's question if you were to go from 1 sub getting x watts and you go to 2 subs getting a total of 2x watts, you would theoretically get a 6 dB increase.

Helotaxi is correct.

Double cone area or double power (one or the other, not both), and the theoretical increase is 3db.

Double both cone area and power and the theoretical increase is 6db.

Remember though, that it's only theoretical. Numerous factors will determine your actual output increase and are nearly impossible for us to try to predict.

 

[Pyro_By_Nature 5,000+ posts]

And 130 vs 120, it'd be 2x as loud or 2x as 'intense'.Not 10x

 

[Flyer 10+ year member]

This is an exerpt from the

http://www.howstuffworks.com/question124.htm

On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB.

Thats why I figured that 130 was 10 times more intense than 120, (I have been wrong in the past though)

Flyer

 

[helotaxi 5,000+ posts]

It would be 10 times more powerful, because it is a logrithmic scale, but because of the way the ear works it would only sound twice as loud.

 

[CBFryman2 5,000+ posts]

Remember that when you double motors you cut efficency in half. But how much you gain is 100% dependant on the space it is working in. When you begin to get to extreme dB levels it takesm ore motor force to fight the pressure changes and once the panels reach their resonance point you being to loose energy so you need more acoustical energy to get louder to the mic. remember loud to the ear isnt always loud to the mic.

 

[CBFryman2 5,000+ posts]

And to furhter ilistarte this point, large cones, if not properly stiffened by a dust cap, begin to distort at high SPL levels. this is why 2 12's can burp over 170dB if they have alot of Motor force, 12" cones have less potential for flex and when you reach thoes levels displacement is alot less important than linear force and tuning //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[helotaxi 5,000+ posts]

remember loud to the ear isnt always loud to the mic.

And the opposite is true as well. Loudness as percieved by the human ear is psychologically and well as physically driven. The frequency is just as important as the dB in perceived loudness.

The halving of the efficiency that you mention is why you only get 3dB from doubling cone area and have to add the extra power to get the next 3dB.