1 speaker vs 2 speakers

[mooreamps]

Originally Posted by LeoZeppelin

What I can't justify yet is, why would I need 2x12 instead of 1x12 (I used 12" there as generally I find that as standard size). What extra kick a second speaker will give when it comes to basement practice with band or a regular gig? In your opinion guys, will there be any difference amongst 2, going by the usage I mentioned above?

Thank you all in advance.
Best Regards.

OK, how about this....... The big difference when you are gigging ; you place one speaker stage left, and another speaker on stage right. Try it with only a 5 watt amp, and see how much volume it makes.....


-g

[ZeroCool]

Originally Posted by pdf64

In the real world, all else being equal, my experience is that a 2x12 is appreciably louder than a 1x12.It actually sounds like more than the theoretical 3dB gain that doubling up the number of drivers provides.

True, but from my experience, friends of mine that have gone from a 1x12 to a 2x12 or 4x12 have, after the switch, kept their volume knobs at either the same position as before or at less than what it was before, and it's important to mention that this position was nowhere near the max volume. In other words, they could've 'kept up' with the new speaker configuration if they just turned the volume up with their 1x12. In other words, everytime I had a friend switch, especially from a 1x12 to a 4x12, the main factor they always raved about was not the gain in OVERALL loudness, but the new tone-related attributes, like they'll say "I love the way the bass sounds now, it's awesome." But, I'm just speaking of my experiences, everyone has different experiences. I also have to admit that these experiences I'm talking about were always with amps 30W and above; that may be an important factor for why my friends did not have their volume knobs too high, in essence giving them enough headroom to still turn their volume up considerably, so maybe my experiences might not hold true for owners of lower wattage amps (like those SE Class A you see all the time) who may be riding their volume knobs close to max.

This is just my experience, I'm not going to hold that it should be true for everyone, but once the switch is made I would encourage the OP to do an A/B comparison and see if they could've kept up with the gain in apparent loudness of the 2x12 by turning the volume up higher with the 1x12 (assuming there's no considerable loss of headroom), and after that, to examine carefully the reasons of why they might like the 2x12 more, that being, if it has to do more with tone-related attributes than with merely overall loudness.

[Glass Snuff]

Quasi on topic, I found myself thinking about this:

If you have, say, a 30 watt amp, and you play though a 1x12 and a 4x12, set to the same SPL with a meter (1 metre on axis, etc), which will be louder?


Out in the room, in the middle of the crowd or at the back, the 4x12 will be louder. More focus, coupling of the bass, less square of the distance, etc. However, on stage, the 1x12 will sound louder. It will require greater excursion to match the level, and this will induce greater distortion. To our ears, it will sound like it's working harder... sort of making a guitar face.

[raiken]

Originally Posted by mooreamps

perhaps one of the most simple concepts for power transformers inside a guitar amp, but it eludes so many. Think of it this way ; for a given input, the 8 ohm tap produces "twice" the output voltage as the 4 ohm tap....


It's just that simple ......


-g

Apparently, it has eluded you, too.

The 8 ohm tap does not produce "twice" the output voltage of the 4 ohm tap, it produces sqrt(2), or 1.4 times the output voltage of the 4 ohm tap. the 16 ohm tap produces twice the output voltage of the 4 ohm tap.

Randall Aiken

[mooreamps]

No, perhaps I was not clear ; measured as when terminated to a loud speaker, not open, and not terminated to a resistor ; as measured on a true rms meter. But "for u", I'll look at that again.

-g

[raiken]

Originally Posted by mooreamps

No, perhaps I was not clear ; measured as when terminated to a loud speaker, not open, and not terminated to a resistor ; as measured on a true rms meter. But "for u", I'll look at that again.

-g

It will be the same measured as terminated to anything, as long as it is the correct impedance for the tap. It also doesn't matter whether you measure RMS, peak, or peak-to-peak, the relationship holds, as it is a function of how transformers work.

Randall Aiken

[teemuk]

Someone once said wisely about the speaker cluster theory: If it worked, we could rock stadiums with 1W amplifiers and enough of speakers.

I still haven't witnessed that happening.

Each time you add a speaker to the cluster it will rob it's own share of total power the amplifer produces to drive the speakers and consequently make the other speakers in the cluster behave less efficiently.

---

As for doubling up the perceived loudness: General consensus is that it requires a 10 dB or tenfold increase in output power or sound pressure level. 6 dB increase indeed doubles up the sound pressure but that, however, is not the same thing as doubling up loudness we humans perceive.

[Steve Conner]

Originally Posted by teemuk

Someone once said wisely about the speaker cluster theory: If it worked, we could rock stadiums with 1W amplifiers and enough of speakers.

I still haven't witnessed that happening.

Each time you add a speaker to the cluster it will rob it's own share of total power the amplifer produces to drive the speakers and consequently make the other speakers in the cluster behave less efficiently.

Well, we discussed that. If you're using a tube amp, it's assumed that you adjust the impedance switch to suit the new load, so it delivers the same total power as it did before. Under these conditions the SPL increase is 3dB because of the directivity gain.

A solid-state amp delivers more power as the load gets heavier, so it's more or less delivering constant power per speaker as you add more, and the gain of doubling the speakers is nearer 6dB than 3. Until the amp can't take any more and blows up.

These figures are per doubling of speakers. So going from 1 speaker to 2 gets you 3dB. To get the next 3dB you have to go to 4 speakers, then 8, 16, 32 and so on. You can see that you'll need a lot of speakers to rock the stadium with 1W.

It reminds me of the proverb about the guy who asked the King for one grain of rice on the first square of the chessboard, two on the second, four on the third and so on, and he never did get his (2^64)-1 grains of rice, because there isn't that much rice in the world.

And, you can't do it anyway, because you have to fill the stadium with sound so the whole crowd can hear. Directivity gain can't help you because you need to spread the sound around.

[pdf64]

Something that I'm struggling with, is, why there's the same potential 3dB SPL increase when the noise source is doubled up (ie 2 champs) as when the speakers are doubled with just the same power input (ie 1 champ with 2 speakers connected).
Ok we have to imagine that these Champs have got a 4ohm tap available on their OT.
Assuming 5 watts power, surely 2 speakers with 5 watts inputs each (2 champs) have to be able to generate a higher SPL than the same 2 speakers with only 2.5 watts each (1 champ with 2 speakers)?
But acoustics theory has it that 2 singers/fiddles/champs are 3dB louder than 1.
As per the thrust of teemuk's post, why bother with the other champ amp, when just adding a speaker would get us the same SPL?

[Steve Conner]

Well, you're struggling with the concept because it's wrong.

If you're playing with a wall of combo amps, the SPL goes up 6dB per doubling, not 3.

That's 3dB per doubling of speakers, because of directivity/coupling gain, and 3dB per doubling of electrical input power, because each combo has its own power amp inside.

You only get the directivity gain if the two signals are correlated, so you can get constructive interference between them. Two different guitarists, each playing through his own Champ, are just 3dB louder than either guy on his own, not 6. And same with two singers or fiddles.

And say one amp had a Vintage 30 and the other a Greenback (well assuming those came in 8" ) then even if they were fed with the same guitar, the difference in speaker frequency responses might well be enough to uncorrelate the signals.

[pdf64]

'Two different guitarists, each playing through his own Champ, are just 3dB louder than either guy on his own, not 6'

Would that hold true if the guitarists were replaced with white or pink noise sources - could the constructive interference take place?
I'd guess not, as even though all frequencies might be present in the same amount, their phase relationship wouldn't be locked together.
But it seems counter-intuitive that with 2 champs and 2 noise sources, the SPL would increase 3dB if 1 of the noise source was switched out such that both amps were fed the same input.
Perhaps not though - it could be the same effect that makes stereo centre mix tracks become louder when mixed to mono.
Apologies for documenting the mental cog's slow rotation.

[Steve Conner]

Originally Posted by pdf64

Would that hold true if the guitarists were replaced with white or pink noise sources - could the constructive interference take place?
I'd guess not, as even though all frequencies might be present in the same amount, their phase relationship wouldn't be locked together.
Perhaps not though - it could be the same effect that makes stereo centre mix tracks become louder when mixed to mono.

You're exactly right (well as far as I know! )

If you replaced the two guitarists with two different noise sources, those are uncorrelated because of the phases, as you said, so you only get 3dB.

If you routed the SAME noise source into both amps, boom, another 3dB as their outputs are now correlated.

And yes, instruments panned to the centre of a stereo mix are correlated in the left and right channels, by definition. If they weren't, your ears wouldn't hear them in the centre. So I guess they get 3dB louder than uncorrelated information in the mix, when mixed to mono.

What's the difference between a guitarist and a white noise source?
The guitarist drinks more.

[Glass Snuff]

Originally Posted by Steve Conner

And yes, instruments panned to the centre of a stereo mix are correlated in the left and right channels, by definition. If they weren't, your ears wouldn't hear them in the centre. So I guess they get 3dB louder than uncorrelated information in the mix, when mixed to mono.

Which is why stereo balance controls and pan pots are -3dB in the center.

BTW, there's a lot of good stuff here:

FAQ in Music Acoustics