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Author Topic: 1 + 1=7?  (Read 9955 times)

Ivan Beaver

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1 + 1=7?
« on: July 17, 2011, 12:27:50 pm »

Just a little thought make your brain hurt.

Everybody agrees that if you take 2 identical loudspeakers and place them close enough together (within 1/4wl) that they will sum together well.

So if you have 1 of those producing 100dB, and then simply add another one producing 100dB you will get 106dB.  Of course at the freq at which the spacing is small as compared to the wavelength.

If you have 2 loudspeakers-each producing 90dB and put them together you get 96dB.

But here is part that just seems "odd".  If each loudspeaker is producing 1dB, then when you add another one producing 1dB, you get 7dB.

Somehow that just doesn't seem possible-but the "math" says so.  How can such a small level of sound, result in a much larger output than either one?  Damn log scale

Just something to think about.
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Ivan Beaver
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John Moore

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Re: 1 + 1=7?
« Reply #1 on: July 17, 2011, 01:08:03 pm »

I thought doubling power was a 3dB increase and doubling distance was a 6dB decrease
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Ivan Beaver

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Re: 1 + 1=7?
« Reply #2 on: July 17, 2011, 01:41:10 pm »

I thought doubling power was a 3dB increase and doubling distance was a 6dB decrease

You are correct.  But when you add 2 cabients together you get a 6 dB increase.  3dB from doubling the power and 3dB from the mutual coupling of the drivers (assuming they are close enough for the wavelengths involved) or do you?

Yes you will MEASURE a 6dB increase-but exactly where is that coming from?-That will be another post in a little bit.
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Ivan Beaver
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Frederik RosenkjŠr

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Re: 1 + 1=7?
« Reply #3 on: July 17, 2011, 01:58:24 pm »


But here is part that just seems "odd".  If each loudspeaker is producing 1dB, then when you add another one producing 1dB, you get 7dB.

Somehow that just doesn't seem possible-but the "math" says so.  How can such a small level of sound, result in a much larger output than either one?  Damn log scale

Just something to think about.

And you have one producing -10dB and add another producing -10dB you'll get -4dB :)
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Mac Kerr

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Re: 1 + 1=7?
« Reply #4 on: July 17, 2011, 02:10:59 pm »

Just a little thought make your brain hurt.

Everybody agrees that if you take 2 identical loudspeakers and place them close enough together (within 1/4wl) that they will sum together well.

So if you have 1 of those producing 100dB, and then simply add another one producing 100dB you will get 106dB.  Of course at the freq at which the spacing is small as compared to the wavelength.

If you have 2 loudspeakers-each producing 90dB and put them together you get 96dB.

But here is part that just seems "odd".  If each loudspeaker is producing 1dB, then when you add another one producing 1dB, you get 7dB.

Somehow that just doesn't seem possible-but the "math" says so.  How can such a small level of sound, result in a much larger output than either one?  Damn log scale

Just something to think about.

What is 1dBSPL? it is 1dB higher than 0dBSPL, which is an arbitrary level related to human hearing. Just like 0║F isn't the lack of all heat, neither is 0dBSPL the lack of all sound.

Mac
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paul bell

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Re: 1 + 1=7?
« Reply #5 on: July 17, 2011, 02:12:57 pm »

Yes, doubling your speakers will result in a +6db in level.

The key here is "doubling" of your speakers. The formula also needs a doubling of power. If the original first speaker is at say 500 watts, the second speaker also needs to be at 500 watts to achieve the +6db in level.

I doubt you'll be able to measure a speaker producing just one db, unless you were in a anechoic chamber.
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Ales Dravinec

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Re: 1 + 1=7?
« Reply #6 on: July 17, 2011, 02:31:10 pm »

Here's another :

If speaker produces 100dB @ 1m, does it produce 112dB @ 10" ???
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Just sayin'
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Paul Dershem

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Re: 1 + 1=7?
« Reply #7 on: July 17, 2011, 02:50:17 pm »

If adding a second, identical, speaker provides a 3dB increase through cabinet coupling, and another 3dB is attributable to halving the impedance, will the increase be limited to only 3dB if the speakers are driven by separate amplifiers?
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Mac Kerr

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Re: 1 + 1=7?
« Reply #8 on: July 17, 2011, 02:54:02 pm »

If adding a second, identical, speaker provides a 3dB increase through cabinet coupling, and another 3dB is attributable to halving the impedance, will the increase be limited to only 3dB if the speakers are driven by separate amplifiers?

No, because each one will still be driven by the same power as the original single speaker. It will be a doubling of power whether it is one amp or two.

Mac
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John Roberts {JR}

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Re: 1 + 1=7?
« Reply #9 on: July 17, 2011, 02:58:05 pm »

If you take two identical amplifiers and add them together does that make two amps?
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Re: 1 + 1=7?
┬ź Reply #9 on: July 17, 2011, 02:58:05 pm ┬╗


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