3db increase by doubling driver count

[Bazukaz]

Hi,
Sorry for posting a thread about what was probably discussed many times , but i didn't find the explanation.
In many forums , i have read that doubling the driver count increses sensitivity by 3db. But i don't understand this.
For example , if you contiue doubling the driver count to infinity, the sensitivity is approaching infinity as well , right ? But it is impossible to get infinite sound power from , for example , 1W of electrical power ! It would be great if someone could include not too complex equations in the explanation , or a link to it.

Thanks a lot,
Lukas.

[richie00boy]

I see what you're saying, but infinity is a point that will never be reached, that's the whole idea. 'A bit' below infinity you will have passed the point where 1 watt electrical input produces more than 1 watt acoustic power, but that's not really like a magic perpetual motion machine or anything.

[Bazukaz]

So , the relationship (doubling driver count and gained sensitivity) is actually non-linear , i.e , i actually gain a bit less than 3 db by doubling speaker count ; even less by quadruppling , and so on.
So i end up with less than 1W of acoustic power for 1W electrical input , regardless how many drivers i add.Right ?

Regards,
Lukas.

[richie00boy]

No, that's not what I said. It's linear.

[Bazukaz]

So , i don't understand this...
For example , we have a driver with sensitivity of 90db/1W.
if we take a billion of drivers , and power them the same 1W(1W for all drivers, 1/(10^9) for one driver).
We get spl = 90+10Log(10^9) = 190db.
190 db SPL is more than 1watt of acoustical power for sure.
Please point where i am wrong.

Regards,
Lukas.

[darkfenriz]

If you double drivers and connect them in parallel, than voltage sensivity increases, but power sensivity remains the same.

[Bazukaz]

Hi,
Thanks for reply. I have read a lot of posts in another forum when people try to proove that increasing driver count increases power sensitivity as well, for example , connecting two drivers in series would not affect the SPL , even though 2 drivers are getting 0.5W due to increased impedance.

regards,
Lukas.

[richie00boy]

Electrical power input does not need to equate to acoustic power output, they are different things. Energy conversion is taking place.

[Bazukaz]

So , the acoustical power will always be less than electrical due to losses

[darkfenriz]

Of course, much less than electrical because of mechanic-acoustic impedance mismatch. Horn loudspeakers work as acoustic impedance transformers and may reach power efficiency of, say, 80%. Typical drivers have very low power efficiency.