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What is the difference between 1 speaker of 400 watt and 2 speakers of 200 watt? All the speakers are 12 inch.

Of course, I know the difference is mono/stereo. But I want to play in a little band including two guitars and an electrical drumset (which has to be monitored). For the guitars, we won't notice the difference. But I guess that the drumset will be bad monitored.

I own the speaker of 400 watt, and my opinion is that the 400 watt speaker is not enough and that I need an extra SubWoofer Speaker.

What would you advice? The 2 of 200 watt or the single of 400 watt?

Thanks in advance.

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  • \$\begingroup\$ Are the speakers the same physical size? Bigger speakers have lower frequency response. \$\endgroup\$ – endolith Sep 18 '11 at 18:42
  • \$\begingroup\$ @endolith: They are all 12 inch. Or do you mean something else? \$\endgroup\$ – Martijn Courteaux Sep 18 '11 at 18:58
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There are a lot of things to consider with this, especially if the two speakers are not identical. But let's assume that they are...

Theoretically, if you double the wattage then you'll get +6dB more sound level out. This is true (theoretically) regardless of if you take a single speaker from 200 to 400 watts, or go from one to two 200 watt speakers. In both cases the wattage doubles, so the sound level will rise +6dB.

In theory, theory matches practice. In practice, it doesn't.

Things are rarely so simple, and this is doubly so when it comes to sound. When you go from 1 to 2 speakers, you can get strange effects from the two speakers interfering with each other. Placement and orientation of the speakers can have a huge impact of this. In some cases, certain frequencies can completely cancel out while other frequencies will rise as much as +6dB. This is called "comb filtering". There are other related effects that could be a good thing (like a line array) or a bad thing, creating lots of really bad sound.

There is too much here to go into, but suffice it to say that if you want (effectively) a single speaker at 400 watts then that's what you should go with and not two 200 watt speakers. If you don't have that as an option, then I suggest that you place the speakers in such a way as the speaker coverage patterns don't overlap.

There is one thing that you didn't ask about, but I suspect you need to know, is how to calculate the apparent sound level given the wattage and speaker. Knowing this will greatly improve your chances of getting the right speaker/amp setup. Here are some rules/guidelines to know:

  • A 3dB change in sound level is considered "barely perceptible" to the human ear. A 6dB change in sound level is a doubling (or halving) of the power (watts), but is still considered a small change in perceived sound level.

  • If you double the distance from the speaker to the listener then the sound level will drop to 1/4th, or -12 dB.

  • Typical speech over a PA system should be somewhere in the 65 to 85 dB range. A loud rock concert might be as high as 115 dB. Movies are in the 100-105 dB range.

  • Speakers have "sensitivity ratings". A typical rating would be something like 85 dB/Watt/Meter. Meaning that if you put 1 watt into it, and measure it at 1 meter, you'll get 85 dB.

So here's what this means... Let's say that your speaker has a sensitivity of 85 dB/watt/meter, and you are 2 meters away and feeding it 1 watt. The sound you hear will be 73 dB. If you go to 2 watts then you get 79 dB. 4 watts = 85 dB. 8 watts = 91 dB. 16 watts = 97 dB. 32 watts = 103 dB. 64 watts = 109 dB. 128 watts = 115 dB.

Now if you move the speaker to 4 meters away you drop down to 103 dB. To get back up to 115 dB you need a 4x in power, or 512 watts. The point is, very quickly you get into some serious power levels for just a modest increase in sound level.

All of this is irrelevant to the topic of needing a sub woofer. If you need more low frequencies, then get a sub. If you don't, then don't.

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    \$\begingroup\$ Good on-topic answer to an off-topic question! \$\endgroup\$ – Kevin Vermeer Sep 19 '11 at 19:31
  • \$\begingroup\$ physics.stackexchange.com/a/9018/8577 says doubling the power only gives +3dB. \$\endgroup\$ – Cees Timmerman Dec 12 '13 at 11:24
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    \$\begingroup\$ Right, the 1/4 power = -12dB equation is wrong. 1/4 signal = -12dB, but 1/4 power = -6dB because there's a square relationship between signal and power and the equations are chosen to provide the same change in dB's on both sides of the aisle for the same change of the volume control. 2x signal = 4x power. \$\endgroup\$ – AaronD Jan 22 '15 at 19:48

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