Is doubling speakers +3dB or +6dB? What's parallel and series wiring?

Devin demonstrates the differences between parallel and series wiring and answers the age-old question about whether doubling speakers adds 3dB or 6dB, with a close look at what happens in real-time with the voltage and current output from the amp as the frequency and speaker impedance changes.

Special thanks to all those who fact checked me on this. I am amazed at how many incredibly brilliant people follow my videos and are willing to help iron things out. Sorry to the crowd who thinks voltage should always be represented by V (including ChatGPT), you lost this one. Also, for those wondering, the NXampmkii was on the "FLAT" setting. The test mic was a DBX RTA-M going into a Rio1608-D. Softwares included Logic Pro X, Signal Scope X, DATS, and Dante Via.

[SilentShadow-ssxp]

This is the kind of audio content we need on YouTube. Very informative.

[gibbytravis]

Eskimos have been hooking their woofers up in series parallel configurations for hundreds of years.

[SimonJones_zx]

Great video was taught this on a Rockford Fosgate amplifier and system design course 30yrs ago, first time seen such good explination of it :)

[stefanmplayer]

Easily one of the best video’s regarding this subject I’ce ever seen, keep the good stuff coming 👌🏼

[JSmith-lktq]

What determines whether two signals of equal amplitude combine to produce a 6dB gain or a 3dB gain in signal level (voltage or SPL, but not power), is the “correlation” of the signals at the point of combining.

FULL CORRELATION CASE:
If the correlation is 100% between the two source signals at the location where the combined signal is being measured (the two source signals are received with identical amplitude and with identical phase) then a 6dB gain in level (SPL or voltage, but not power) is achieved.

Example 1: Two side by side subwoofers which are both fed the same signal (with the same amplitude and same phase) and which are both equal distant from the measuring device. In this case, the measurement device will measure a “combined” signal which is 6dB higher in SPL than that measure by either subwoofer alone.

For a sine wave signal source, the two source signals would always have their sine wave peaks “synchronized” and always providing a doubling of peak level. And we know that a doubling of level (voltage or SPL) results in a level gain of 6dB. However, it is important to note that the “power” delivered to the room is only 3 dB higher than that delivered by either subwoofer alone (a doubling of power results in a gain of 3 dB).

NO CORRELATION CASE:
If there is no correlation between two non-identical, but equal amplitude, signals at the location where the combined signal is being measure, then a 3dB gain in level (SPL or voltage) is achieved.

Example 2: Two side by side subwoofers are fed pink noise signals generated from two different noise generators (the pink noise signals are not correlated). In this case, the measurement device will measure a “combined” signal which is 3dB higher in SPL than that measure by either subwoofer alone.

The two signal’s peaks and valleys will only be in alignment part of the time. And over time, the signal alignment of the peaks will vary between in phase (0 degrees) and out of phase (180 degrees). And the average increase in SPL or Voltage signal level achieved will be 3db higher than that delivered by either subwoofer alone.

MAINTAINING 100% CORRELATION ISNT ALWAYS EASY
Even in example 1 above, if the SPL meter where to move around the room, the path length from each subwoofer to the measurement device would change differently for each subwoofer, and the correlation between the two signals being combined would not stay at 100%. The axis of the room where the measurement device is equidistant from the two subwoofer will always receive the 6db gain in SPL. But there will be some locations in the room where the path length from each subwoofer would result in a 180 degree phase shift at the measurement device, and the signal would be cancelled. But most people, who are not equidistant from both subwoofers would experience a 3 dB gain in SPL.

Another interesting example is the case where two signals of varying phase are combined.
Example 3: Two side by side subwoofers are fed sine wave signals from two different signal generators (one at 60 Hz and one at 61 Hz). In this case, the measurement device will measure a “combined” signal which varies in SPL reading over each one second period. For one instant in each one second period, the measurement device will measure a “combined” signal which is 6dB higher in SPL than that measure by either subwoofer alone. But AVERAGED over the full second period, the measurement device will measure a “combined” signal which is 3dB higher in SPL than that measure by either subwoofer alone.

In summary, achieving a 6DB gain in SPL with two subwoofers only occurs where the resulting phase difference between the two identical subwoofer signals at the measurement position is near zero degrees.

[johnk]

Very good video! Reiterating old knowledge and this was perfect, thank you.

[freebeerecords]

Nice job, many thanks! Fascinating to see those frequency related impedance spikes. Great charts and hands on measurements.

[MichaelLaferriere]

Nice explanation of parallel vs series wiring with visual examples! I think anyone studying electronics or amateur radio should check out this video.

Nicely done!

[shazam]

Nice! This, along with many of your other lessons and demonstrations, should be mandatory study requirements for all "Audio People", especially live performance types!!! Most of them are clueless and believe myths of their predecessors, urban legends, hearsay and of course: "that's the way it is, everybody knows that!"

[lumpyfishgravy]

Depends if they're acoustically coupled (coherent). If so, pressure adds and you get 6dB. If not, power adds and you get 3dB.

[Petermaler]

Incredible clear explanation, thanks buddy !

[topimaurola]

There is no such thing as "3 dB more from the speaker".

The amount of available power is what voltage*current shows - period.

What you are demonstrating with "3 dB more from the speaker", is actually a coherent speaker array. Try moving your meas mic up and down and you see that the +6 dB isn't consistent.

Also if you switch the polarity of the second speaker, when in parallel configuration, you see that the measurement from the front drops dramatically, as the phase fronts from two speakers are cancelling each other.

[marshad]

On a side note: that hum coming from sub has an interesting effect of "robotizing" voice when speeding up or slowing down video's playback speed.

[TimpBizkit]

It's quite interesting to see how using more speakers saves energy. Although I'd expect this to gradually taper off as you add more and more speakers, so maybe you'd only get 5 dB from 2 more subwoofers.

[msanand]

Good effort and thanks a lot for the Video. I would like to experiment like you did, but hardly find opportunities with gears. To whatever I have learnt: Doubling the Voltage or current should result in 6 dB not 3 dB. Correct the video @3:24. Doubling Power results in 3dB change.

Please correct me if I am wrong.

[mrstyle]

I still don't get it. Doubling the power on one subwoofer results in a 3dB gain. But the same power split on two speakers suddenly should gain an additional 3dB so 6dB total? How can 3dB magically appear out of nowhere? Where is this "acoustic energy" supposed to come from?

[dcsheldon]

If you use powered subs to simplify the whole process, a lot more people will understand it. Basically doubling your speakers gives you +3db . If one sub max SPL is 135db, adding an extra sub would make it 138 db SPL Max, and to increase it another 3 DB you have to add two more subs, the four subs would produce 141db Max SPL and if you want to add another 3 db, you have to have eight subs to increase it to 144db SPL Max. Basically, you have to double the speakers for every 3 db increase you want in SPL.

[MrDuzra]

When you raise the amplifier by 6dB it makes output voltage doubled (20V to 40 V), and current flow also doubled as manner (1A to 2A).calculating the (P) power it show 4 times increment as this: 20V x 1A =20W and 40V x2A= 80W. Clearly 80W means 4times like 20W.

But when you attached additional speaker it only cost more current, but no voltage increases, resulting power = 20V x 2A = 40W.

My question is, why the measurement mic showing 6dB same increment at both testings above, while the amplifier produce completely different power output as, 40w vs 80W.

[papatronix]

6 db+ so is this why they say is better to double the speakers instead of the power first??? more cone area vs more power?

[UniformDelta]

What it is two separated active sub ?
+3db ?

I dont understand when you say +3dB acoustic power. Because the power produced by the added membrane, is the exact additional power transmitted by the amp. So why do you count it twice ? (+6dB)