Gain when using nore speakers

[hedalfa]

Does anyone know the actual db gain when you add more drivers
close together. Ie one speaker with 95db and you add another of the same type you get plus 6 db. What happens when you add a third driver and a forth. Is it 1-2db and 1 ldb or less.

Thanks!!!!

[sreten]

The log of the number of drivers x 10
is how much more efficient they are are.

2 drivers +3dB , 3 drivers +4.7dB, 4 +6dB, 5 +7dB, 6 +7.8dB etc.

You also need to consider any change in impedance
to arrive at the change in voltage sensistivity (dB/2.83V)

For 2 drivers :
- 2 in parallel gives +6dB (current is+3dB, Z is half).
- 2 in series gives 0dB (current is -3dB, Z is double).

For 3 drivers :
parallel = +9.5dB, series = 0dB.

For 4 drivers :
parallel = +12dB, series/parallel = +6dB, series = 0dB.

For six drivers:
+15.5 (6||), +9.5 (3||-3||), +6.0 (2||-2||-2||), 0 (1-1-1-1-1-1).

etc....

sreten.

[spd]

Hi

Does this mean that if I put 100 speakers in series I
would get +20dB and a total impedance of 800ohms
which would result in only 10mW required from the
amplifier at 2.83v

[sreten]

Originally posted by spd
Hi

Does this mean that if I put 100 speakers in series I
would get +20dB and a total impedance of 800ohms
which would result in only 10mW required from the
amplifier at 2.83v

Yes, and sensitivity dB/2.83V is the same as one driver.

sreten.

[spd]

Wow

So if I use an infinite number of drivers in series then I get the
same sensitivity as 1 driver and zero power required.

[Svante]

Originally posted by spd
Wow

So if I use an infinite number of drivers in series then I get the
same sensitivity as 1 driver and zero power required.

No, but Sreten is right anyway. His description assumes that the efficiency of the speaker is low. Speakers have poor efficiency. But when you add more and more speakers the efficiency increases, and on the way towards infinity, somewhere, the efficiency is no longer low, and the model does not work anymore.

Another way of looking at it: The description assumes that the radiation resistance is small compared to the mechanical impedance from the mass of the loudspeaker cone. As you increase the number of drivers, the radiation resistance will increase faster then the total mass of the cones. The model does not work anymore.

But for most sensible number of drivers, the efficiency (in %) is proportional to the number of drivers.

All the above assumes that the drivers are monted close to each other compared to the wavelength.

[sreten]

Well Svante's comphrehensively answered one question
before I got a chance to, the model only works assuming
acoustic coupling is poor, i.e. low efficiency.

Also note the 100 drivers do not have to be wired in series.

For 100 drivers any combination where all driver currents
are equal will require 10mW of drive, i.e. 0.1mW per driver,
for the same level as one driver driven by 1W.

For the same bass response as a single driver,
the box volume could be a minor problem..........

sreten.

[hedalfa]

2 drivers +3dB , 3 drivers +4.7dB, 4 +6dB, 5 +7dB, 6 +7.8dB etc.

If you have four drivers to they need be placed in a row or in a square to get the best acoustic coupling for efficiency or doesnt it matter?

Paul



2 drivers +3dB , 3 drivers +4.7dB, 4 +6dB, 5 +7dB, 6 +7.8dB etc.

You also need to consider any change in impedance
to arrive at the change in voltage sensistivity (dB/2.83V)

For 2 drivers :
- 2 in parallel gives +6dB (current is+3dB, Z is half).
- 2 in series gives 0dB (current is -3dB, Z is double).

For 3 drivers :
parallel = +9.5dB, series = 0dB.

For 4 drivers :
parallel = +12dB, series/parallel = +6dB, series = 0dB.

For six drivers:
+15.5 (6||), +9.5 (3||-3||), +6.0 (2||-2||-2||), 0 (1-1-1-1-1-1).

etc....

sreten. [/B][/QUOTE]

[sreten]

Originally posted by hedalfa
If you have four drivers to they need be placed in a row or in a square to get the best acoustic coupling for efficiency or doesnt it matter?

At low frequencies it doesn't matter.

Higher up you get different off-axis responses and other issues
also enter the equation, e.g. baffle width for a vertical array.

sreten.

[michael]

Me and a friend had an extensive discussion about this just a few days ago, we never came to an agreement.
Ill use a practical situation so that we have a base.

1 Shiva in 100L 24hz box reaches xmax with ~270w
We use a 300w amplifier to drive it (4ohm)
now we connect 3 more shivas, keeping the impedance at 4ohms, we should now need 1/4 power to reach the same SPL as the single shiva. Does this now mean that by using 4 shivas with a 300w amp they can all reach max excurtion with 270w.

The reason for this discussion was on whether to go big drivers with big amps, or an affordable amp, and several drivers, another example.... lets use my situation a 200w plate amp, and i want a shiva to replace my peerless 10" CSX, i will get a shiva, then later one get another shiva, then another, then another.
I would then have 4 shivas that reach the equivelant SPL as 4 shivas all with a separate 200w amplifier, yes?