Question about Speaker db’s and math …?

[R.D.]

I’ve got a 4 x 12 cabinet that’s loaded with a special switching system that allows me to switch the individual speakers on & off, or replace each of them with an individual 16 ohm power soak.

My question is:

If I’m running all four ( 4 ) speakers and the cabinet is LOUD ( say 106 to 108 db measured at approx. 6 ft away from the cabinet ) and I start switching speakers to soak ( in essence turning them off one at a time ). How can I figure out what each individual speaker means to the total db level ?

I’m probably explaining this like crap ! Sorry ….

But if 4 speakers = 106 to 108 db

Approximately what db would 3 speakers equal ?

What would 2 speakers equal ?

What would 1 speaker equal ?

The caveat being: “IF” I didn’t change any of my Amplifier controls ( ie: lower master volume ).

Thanks for your help !

 

[blackba]

Every time you double the source you get 3dB to a point. I wish I could remember the equation, but basically all things equal 2 speakers should be 3dB louder than 1 speaker, and 4 speakers should be 6dB louder than 1 speaker. This is in the ideal world, so please keep that in mind.

 

[Capulin Overdrive]

this is a question for the live sound guys over at Harmony Central.


more speakers may be louder way far off, but up close it's not really gonna change much?


a person may hear or percieve a deference up close, but really think DB deference is negligible.


the sound guys do have some kind of math for figuring out speakers for the room size etc.

 

[GuitarGuyLP]

I have heard this discussion over at harmony central quite a few times. Basically if you run less speakers with the same input power you will get very little difference in overall output. But since you would be effectively be reducing the total power going to the speakers by 1/4 you will get a reduction in overall SPL. So if you replace two speakers with power soaks then you will have 1/2 of the power going to speakers. You should see about -3db if memory serves me right.

 

[sled]

you will not be able to figure much if anything and here's why...

if speaker outputs (including coupling to air) were linear, then there would be no increase adding a speaker because the power would be distributed between the two equally and each would then received 1/2 as much power as one by itself would receive. the total power output would still be the same.

but, speakers are anything but linear including the response when a power soak is added, so trying to calculate the response is no trivial matter.

but, for sure, reducing the output by one speaker (coupling to air) will reduce the total db level output (heard)... assuming the other speakers receive less power for any given frequency. it's actually possible for certain frequencies to be louder due to the resonant peaks that a speaker exhibits and the complex interactions of the varying impedances.

 

[Meathead]

My estimates (guesses) based on what I know and have heard...(2x the power = 3dB)

If 4 speakers = 106 to 108 db

Approximately what db would 3 speakers equal ? 104.5 to 107.5
What would 2 speakers equal ? 103 to 105
What would 1 speaker equal ? 100 to 103