multiple speakers and SPL

[ultra-gain]

Hello,

All things being equal, sens., impedance, power, and speakers, stacked so wave front is close to one and distance is all held constant, will the SPL change when adding or subtracting speakers. Say 1x12 vs 4x12 vs 8x12, all the same speakers, all being used at the same impedance, all being powered by the same amp.

Thanks!

[Chuck H]

Each time the number of speakers is doubled you gain 3dB...

And acquire more of a taste for ibuprofen

[Helmholtz]

Each time the number of speakers is doubled you gain 3dB...

And acquire more of a taste for ibuprofen

To my understanding only on-axis SPL level of middle and high frequencies will increase caused by beaming - while off-center SPL should decrease accordingly. Otherwise efficiency would increase infinitely with higher speaker number.

This assumes constant amp power input for all speaker arrangements.

[ultra-gain]

That is not what I expected to hear. I assumed since the power stayed the same the speakers would all share that power and the SPL would not increase. So 1 speaker at 100 watts. 2 speakers at 50 watts each, 4 speakers at 25 watts and 8 speakers at 12.5 watts each. The power stays the same. I have no idea though.

[nickb]

It's real. Not often you get something for nothing. Paper with analysis: Loudspeakers, Mutual Coupling.pdf

[Helmholtz]

Bass response may be improved also. But that would be mainly due to a larger cabinet.

[Justin Thomas]

All I know is that I prefer a lower-powered amp with lots of speakers over high-powered amps with a single speaker...

Justin

[g1]

As a practical example, run a 5W guitar amp flat out into a single small speaker (like a Champ for example), then do the same into a 4x12 of the same impedance. The power delivery in watts stays the same, the SPL is much greater.

[HaroldBrooks]

There is mutual coupling and that is real, and then also the relative efficiency of each speaker running in a certain range of operation. I don't have data to back this up, but most speakers seem to run very efficiently at low wattage. More watts into the voice coil seem to eventually create more waste as heat, as a percentage of the total

Again, I believe the process of losing increasing wattage to heat is probably not linear, and may be flat for a while, but at the brink of what the speaker can handle it becomes obvious the speaker has become less efficient, and is wasting more power to heating the voice coil.

I vote for the more speakers, the bigger and louder the sound at the same wattage (all else equal).

[nickb]

There is mutual coupling and that is real, and then also the relative efficiency of each speaker running in a certain range of operation. I don't have data to back this up, but most speakers seem to run very efficiently at low wattage. More watts into the voice coil seem to eventually create more waste as heat, as a percentage of the total

Again, I believe the process of losing increasing wattage to heat is probably not linear, and may be flat for a while, but at the brink of what the speaker can handle it becomes obvious the speaker has become less efficient, and is wasting more power to heating the voice coil.

I vote for the more speakers, the bigger and louder the sound at the same wattage (all else equal).

+1 thanks for being that up. Great point.

Speaker compression due to voice coil heating is well known but clearly makes multiple speakers even more effective when the source power remains unchanged.

[Leo_Gnardo]

Another excuse to post a picture of the Wall of Sound, in circulation some 45 years ago. It may have been "wretched excess" BUT there was a sound principle behind the design, pun INTENDED. Nothing new about it either, sound engineers 90 years ago had it all worked out, way better than you would expect.

Time was, a band would pay me a couple hun to haul my van full of gear to a venue, where they sounded terrific. Compare that to the sound you get today, a couple overdriven cheapo speakers-on-sticks that sounds like a fly fart. That's progress ... NOT. You get what you pay for, you get what you work for. The only "progress" is today's audiences are trained to accept crap audio because they listen to their plastic pocket pals with a ten buck pair of ear buds, and think that's good. IOW the "broken AM radio" sound is now the law of the land. Phooey.

[ultra-gain]

...Otherwise efficiency would increase infinitely with higher speaker number....

So can one just infinitely add speakers and gain volume? Why add power when one just needs speakers? Double the speakers and effectively double the power? Doubling of power gains 3dB. Therefore doubling speakers adds 3dB, infinitely?

[g1]

The speaker motor is still a physical object that must be moved. I think there is a point where you are delivering too little power to the speaker to move it properly. So the power to spl curve for a speaker would not be linear, but fall off at low power levels.

[ultra-gain]

I guess besides my appetite for "knowing" I'm trying to validate myself for playing a full stack...lol. I've been on a Peavey kick and bought a Triple XXX head, triple XXX 412A cab and a 5150 412B cab.

I was a profeasional soundman for 14 years in small venues and had a great disdain for local musicians when they walked into my club with more speakers in their rigs than my entire PA. But now that I have my adolescent dream Marty McFly Gigawatt full stack it seems like the amp is able to be cranked up more with less SPL. It sounds bigger but I can crank the amp up higher without it sounding louder.

I have no idea. I would love to know how this works. Either way I'm rocking the full stack. You only live once and if I can do it with grace....

[Chuck H]

Well I can say (from experience today and historically as a matter of fact) that sitting in front of a single twelve can get rather "beamy". I think spreading the power among eight speakers has to resolve that to some degree even if SPL is improved.