# Estimate SPL by adding more speakers.

Discussion in 'Amps and Cabs [BG]' started by jsa0100, Mar 17, 2008.

1. ### jsa0100

Apr 6, 2005
Norway
Is there a way to calculate how added cone area, will
increase power ?

I know that lets say 200w in to 4x15" gives a higher SPL
than 200w in to a single 15".
But what is the increase in db ?
Is the room size a factor (more air) ?

2. ### KJung

I don't think 'cone area' is the right way to look at it.

The simple 'rule of thumb' is that adding another similar cabinet will result in a +3db increase (which is quite a bit). If you have a solid state amp, then the associated decrease in nominal impedance will give you another +3db or so (from the increase in power from your amp.

Since db is a log scale, +6db is HUGE.

Also, what these figures don't take into account is the 'not quite loud enough' versus 'loud enough' factor. If you feel a little buried with a single cab, and adding another results in your volume level being 'enough' for the mix you are playing in, then the impact can be life changing, even though you aren't 'doubling your volume', etc.

3. ### bgavin

May 3, 2001
Orangevale, CA 95662
For a reference point, we will use the Eminence Kappalite 3015LF 8 ohm drivers. To simplify the math, assume an artificially low power limit for this driver at 100 watts, which is 28.3 volts into 8 ohms. At 100w input power, this driver produces 107 SPL at 50 Hz, at 1 meter.

You gain +6dB from a 2nd driver wired in parallel. You get +3dB from the doubled cone area and another +3dB from the increased sensitivity of driving a 4 ohm load at 28.3v. Daisy chaining two 3015LF jumps the SPL up from 107 to 113. The impedance drops from 8 to 4 ohms. Power consumption increases from 100w to 200w, so your amp must be capable of handling 200 watts into a 4 ohm load.

You gain zero dB from a 2nd driver wired in series at the same input voltage. The +3dB doubled cone area is negated by the -3dB sensitivity drop because each driver runs at half voltage (25w) in a series circuit. The 2nd series driver provides additional power handling and each cone is only moving half as far.

You gain +6dB with 4x15 wired in series-parallel. The doubling of cone area from the 2x15 gain is negated by wiring the two parallel groups in series. The 2x15 parallel has the same sensitivity as the 4x15, but the 4x15 has higher power handling ability, and will make more noise at higher power.

You gain +12dB with 4x15 wired entirely in parallel. Cone area is doubled twice to give +6dB, and power handling is doubled twice for another +6dB. This produces a 2 ohm load, which is a problem for most amps.

Summary at 100 watts:
107 SPL, single driver
107 SPL, two drivers in series
113 SPL, two drivers in parallel
113 SPL, four drivers in series-parallel
119 SPL, four drivers in parallel

The ideal solution for any 4x configuration is a two-channel power amp. No series wiring is used at all, so the full benefits of increased cone area and parallel wiring are realized. The amp is not subjected to very low impedance loads. For the 3015LF, the amp must be capable of 900 watts per channel (60v into 4 ohms). 3015LF will accept 450 watts without hitting Xmax limitations.