1 speaker vs 2 speakers

[mooreamps]

'PDF was also off the mark with the numbers. 3dB is not 'equivalent to doubling the power', nor is the number 3dB.'

Please explain why you think that, and then I'll try to help you see where you are getting mixed up.

http://en.wikipedia.org/wiki/Half_power_point



-regards
-g

[Regis]

It is generally accepted that with two really good 12" speakers (high SPL per watt).... you can expect that combo will be quite a bit louder than the same amp using a single 12".
What that infers is that a 20-30 watt amp driving a 2x12 bottom will sound as loud as a 50-60 watt driving a single 12" cab.
I would always go with the lower wattage and two better speakers.

I'm going to agree with Bruce. From my experieance, a 2x12 is usually a helluva lot louder than a 1x12. Lately I've been using a 2x12 open back and it is loud as hell, fills the room, and sounds really good. I don't think you need a particular speaker brand but right now I'm using Warehouse guitars Vintage 30's.

[Glass Snuff]

It also takes 10 times the power for twice the volume, not achievable by adding one speaker.

This is also not true, no matter how many times it's repeated on the internet. For hundreds of years, it's been accepted that if you want a violin part to be twice as loud, you hire three more violinists. That's four times the power, which is +6 dB.

[Tom Phillips]

This is also not true, no matter how many times it's repeated on the internet. For hundreds of years, it's been accepted that if you want a violin part to be twice as loud, you hire three more violinists. That's four times the power, which is +6 dB.

I've never heard that before. Since loudness has a lot to do with perception by the listener, maybe what you say is true for violins. However, it's not internet gossip that it takes 10 times the power to make a sound seem twice as loud. This knowledge has been around much longer than the internet. However, it's not that simple since the frequency range and the absolute original SPL affect how the power increase affects the perceived loudness increase.

Cheers,
Tom

[ZeroCool]

This is also not true, no matter how many times it's repeated on the internet. For hundreds of years, it's been accepted that if you want a violin part to be twice as loud, you hire three more violinists. That's four times the power, which is +6 dB.

You're confusing Sound Pressure with Sound Power and with Sound Perception, they are NOT the same.

Doubling the Sound Pressure yields a 6db increase (your violin example)
Doubling the Sound Power yields a 3db increase (what some people are talking about on this thread, amplifier power)
Doubling the "loudness" or Sound Perception in the mind of a human being (according to Psychoacoustical researchers) is approximately around the 10db mark.

[Glass Snuff]

However, it's not internet gossip that it takes 10 times the power to make a sound seem twice as loud. This knowledge has been around much longer than the internet.

Can you provide a cite?

[Glass Snuff]

You're confusing Sound Pressure with Sound Power and with Sound Perception, they are NOT the same.

No, I'm not. You are confused - sound power and sound pressure are the same, it's simply one is expressed in watts, the other as a referenced SPL.

Doubling the "loudness" or Sound Perception in the mind of a human being (according to Psychoacoustical researchers) is approximately around the 10db mark.

Again, do you have a cite for this research? Remember, we're talking about music in a venue, not jet engines on an aircraft carrier. And since the days of Fletcher and Munson it's been obvious that such a generalization is problematic for rock and roll.

Trust me, if you put ten Champs onstage, and play through one, then play through all ten, no one in the audience is going to think it's merely "twice as loud".

[Tom Phillips]

Can you provide a cite?

If you want to challenge accepted theory then you should provide a cite(s) to support your position

[ZeroCool]

Trust me, if you put ten Champs onstage, and play through one, then play through all ten, no one in the audience is going to think it's merely "twice as loud".

Strawman argument on your part, it's not the argument we're making, 10db increase it's not 10 Champs, it's 1 single Champ with 10 times the power, very different scenarios. 10 Champs increase cone area by 10.

No, I'm not. You are confused - sound power and sound pressure are the same, it's simply one is expressed in watts, the other as a referenced SPL.

On this matter of SPL and Power:

Loudness volume sound level change factor of loudness formula calculate power level noise levels volume logarithm dependence three four fold loudness sound - by what factor does level decrease dependence comparison decibel levels 3 dBSPL 6 dB 10 db d
This guy Eberhard Sengpiel, a multiple Grammy award-winning sound engineer (who studied electrical engineering) thinks that "Double the sound pressure is a SPL of +6 dB" Who does he think he is to say such a thing??

FAQ in music acoustics
In this article the Professors at this University say that "doubling the sound pressure gives an increase of four in the intensity, so an increase in the sound level of 6 dB, whereas doubling the power increases the intensity by a factor of two, so an increase of 3 dB."----those idiots!

http://www.kraftpower.com/pdfs/KPCInfo03_Sound.pdf
According to this team of foolish engineers "Sound power value is higher than given for sound pressure, because they are not affected by the ambient. For example a 60kW generator set measured has a sound power of 94.4dBA and sound pressure 66.9dBA" Maybe you should give them a call tell them that's ridiculous since both sound power and sound pressure are the same.

http://www.energymaine.com/brwind/br...ort_091206.pdf
According to this engineer from Wind Energy Consulting and Engineering, if you look at the graph on Page 4 (to which he refers on Page 3), the addition of two sound sources each producing the same db will yield a 3db gain, but again, maybe you should contact and educate this engineer as well.

I give you the benefit of the doubt in that maybe you thought I meant Sound Intensity when I said Sound Power, Sound Intensity is the one that is practically (but not theoretically) the same as Sound Pressure since both are trying to measure a unit of energy or force per unit of area. Sound Power is independent of space, however, Sound Intensity IS dependent on space and so it's basically Sound Power per unit of area (W/m^2). Sound Pressure is also dependent on space, hence the similarity to Sound Intensity.

I hope this helps.

[Steve Conner]

Sound pressure level (SPL) and sound power level (SWL) are related the same way as voltage and electrical power, when those are measured in dB.

So, a doubling of the sound pressure means that both SPL and SWL increase by 6dB.

A doubling of acoustic power means that both SPL and SWL increase by 3dB.

This seems non-intuitive, but it stems from the fact that dB are always power units, even when you use them to measure quantities that don't have dimensions of power. I don't have a problem with this, but when I worked with fiber optics I always struggled with "electrical" vs. "optical" dB. Optical ones are twice as big, so to make a laser power meter with a range of 60 optical dB, the electronics need a dynamic range of 120dB.

SPL and SWL have different definitions, so they can have different values as in the case of the generator set. For instance, SPL is whatever a SPL meter measures 1 meter away, and SWL is an estimate of the total acoustic power emitted by the device, which you calculate from a number of SPL readings taken in a sphere around it. If the source has directivity, then SPL and SWL can be very different.

But assuming the same source, changes in sound level always obey the above rules. Ganging up more amps or speakers, it isn't the same source any more: in particular the directivity is increased, so if you stand in a lobe of your new ghetto line array, you get more SPL for the same SWL.

[ZeroCool]

So, a doubling of the sound pressure means that both SPL and SWL increase by 6dB.

A doubling of acoustic power means that both SPL and SWL increase by 3dB.

I said that earlier too, but to no avail, maybe he'll listen to you.

Ganging up more amps or speakers, it isn't the same source any more: in particular the directivity is increased, so if you stand in a lobe of your new ghetto line array, you get more SPL for the same SWL.

Hopefully he understands how bad his Champ example was.

[Steve Conner]

Well, I wouldn't say it was "bad", just different.

If you gang a bunch of Champs together, then each has its own power amp built in, so the SWL will increase for each amp you add. And the directivity gain will give a SPL increase on top of that.

If you connect a bunch of speakers to the same amp, then the SWL will stay the same. The speakers all have the same efficiency, and the electrical power is the same as it was, so conservation of energy demands it. But you can find some point in the room where the SPL will increase because of the directivity gain.

Many people like to think of this directivity gain as an "increase in efficiency" of the speakers caused by ganging them up. And I think there are also coupling effects in the bass region that really do make the efficiency of a woofer array better than a single woofer, similar to directivity gain but not quite, because the SWL actually goes up too.

[ZeroCool]

Well, I wouldn't say it was "bad", just different.

I said "bad" specifically because his example was for the purpose of refuting previous statements made on this thread, when in reality his example was, if anything, refuting some other argument that was never made here, thereby making it a straw man argument. It was argued that as a guideline a 10db increase appears to be "twice-as-loud" to the human mind (emphasis on "guideline" since it's greatly influenced by frequency and absolute sound level) , and his example was in refutation of this statement, an example that was "bad" at illustrating that statement. A more correct example of illustrating the statement, using his same analogy, should've been that of 1 single amp (1 speaker) producing the effect of a 10db increase, but he went off to adding 10 amps (and 10 speakers), probably thinking that 10 amplifiers with 10 speakers = 10db increase. So specifically and exclusively in the context of what was being discussed, his example was bad.

[tedmich]

so an amp with one 8ohm speaker will be 3db quieter than the same amp (at the same gain) driving two parallel 8 ohm speakers (4 ohm total load)...right?

And a 4 speaker cab wired to 16ohms will be 3db louder than a single 8 ohm speaker at the same gain setting?

On a related issue, the majority of large touring acts have a huge amount of dummy speaker cabs (Brad Paisley's wall o' fake Dr. Zs come to mind) so the PA can handle all the volume, they don't blow out their ears with the backline and they're still COOL looking.

[Glass Snuff]

If you want to challenge accepted theory then you should provide a cite(s) to support your position

On the contrary, it is you who is questioning accepted practice. You claimed the "knowledge has been around much longer than the internet" and if your claim was to be taken as true, then you should have been be able to cite a reference to a study done. Apparently, it's just gossip.