Sound level

R

RyanEmerson

New member
I don't know crap about sound (or about proper diction either...), and was wondering if, with an 800-watt PA head, you're pumping 400-watts into two speakers, if that results in the same volume level as one 800-watt speaker.

In other words, if I were mowing my lawn, to my ears, would it make a difference if my neighbor's house blew up, if the lawnmower was louder, or do they "add" onto each other, and therefore, my ears start to hurt?
 
same volume level....no its all about perception listen to a 50 watt 1x12 guitar amp..then listen to a 50 2x12, then listen to a 50 watt head on a 4x12 cab......it sounds different each time around and though one may be louder....another may sound more full and almost as loud.
 
It may sound lounder because there are multiple sound sources and so the number of reflections are increased. I suspect if you were in an anechoic chamber there may be very little difference if you stood behind the cabs.

In actual fact, if you receive two identical sounds at the same time you perceive an increase in loudness of +6db but you need an increase of +10db to perceive a 'doubling' in volume. So if you were to have one 800W powered cab and then two 800W cabs totalling 1.6kW you would not nearly double the volume.

As for adding to each other ... only at identical frequencies at identical points in their periodic wave ... i.e. when a wave 'peaks' and another identical one does at the same time, they add together (to make an increase of +6db). This is called being 'in phase' .... this will become a familiar term to you eventually in its many settings.
 
You can push more air with more speakers and get a higher volume. I'm not sure if halving the power negates that or not but I would think it would still be louder. All things being equal more speakers means more volume.
 
I think that's right but as I say the amount of difference depends on your setting. Outdoors it will make much less difference than in your tiled bathroom.

And double speakers will not = double volume even if you double the power.
 
Spl is a compound mathmatical formula. And loudness is all just a perception of the listener. And if a tree fell in a forest, and there was an audio engineer there to record it...................
 
Yeah sorry, I was only talking about perceptions of loudness, obviously decibels being a logarithmic scale means we 'should' hear way more difference than we do.
 
...obviously decibels being a logarithmic scale means we 'should' hear way more difference than we do.
Click to expand...

Huh?

I thought it just meant that the range of values we hear from low to high is too large to display coherently via a linear scale.
 
my understanding of logarithms and decibel scales weighted to a reference point is this:

in a logarithmic scale, +1 actually equals *10. so one 'extra' dB compared to the original point should equal ten times the amplitude. but our ears (specifically the basilar membrane) don't respond anywhere as near as sensitively as this, so you actually need an increase of +10dB to perceive that the source is twice as 'loud'.

feel free to correct!
 
Actually, it's an increase of one "bel" that equals 10 times the physical intensity. Bels were relatively impractical, so we tend to use decibels (one-tenth of a bel). So every additional TEN decibels equals 10 times the intensity.

The reason for using a logarithmic unit is because all human perception is logarithmic by nature. Whenever you say, "this is a little bit heavier than that", or brighter, louder, higher in pitch, a faster tempo, more forceful of a punch, and so on down the line -- the difference you perceive is the *ratio* of the two values.

For example, a 50-pound box feels "a little heavier than" a 40-pound box, but a 15-pound box feels much heavier than a 5-pound box. Even though the difference is the same in both cases. What you're really perceiving is that in the first case, one box is 25% heavier than the other, and in the second case one box is 200% heavier.

The logarithmic nature of human sensory perception is described by the "Weber-Fechner Law".
http://en.wikipedia.org/wiki/Weber-Fechner_Law
 
Fascinating stuff. The bit I can't get my head round with my basic understanding of maths is:

+10dB = 10*intensity

but:

+5dB does NOT = 5*intensity!

So there really is no way of fitting it in your head (other than trying to picture a graph, but that's impossible for increases of more than 10dB/1B anyway!) - you just have to learn to 'hear' the differences!

And the weirdest bit is, 10*the intensity (+10dB) only yields a perceived increase of the volume *2!:confused:
 
Technically they would be the same, but in real terms, the two speakers might well sound louder. As others have said, the dual speakers have more surface area to push air, and result in a wider sound source.

Suppose one speaker at 400W produced 100 decibels (db). Then going to 800W would be double or +3db. However two sources at 100 db each would produce a total of 103, which is the same.

Ed
 
Why +3? I understood that if they were perfectly in phase (talking sine wave theory rather than practical use here!) that doubling up two identical sources would increase by +6dB. And, as we've said, a perceived doubling in volume would be +10.
 
True. However in this example the 800W, which is where the max power is referenced, is for a single speaker. That's why it is +3db.

Again assuming (for simplicity only) that one of these speakers produces 100 db with 400W in, you would have:

1 Speaker

400W = 100db
800W = 103db

2 Speakers

400W = 103db
800W = 106db

Since the comparison was for 800W and one speaker and 400W for two speakers, both combos yield 103db.

Ed
 
Hang on, I'm getting there gradually. I'd got confused between Bels and tenths thereof again.

So if I was to draw a logarithmic graph of one Bel's increase (i.e. 10dB), the point at which the y-axis value would be twice what you started with would be 3 tenths of 1B across the x-axis?

Am I starting to understand?

EDIT - Thanks for the links, I'll look at them shortly! But if I already understand it ... I won't need to - nerr!
 
I don't think of in graph form, but rather than in common standards.

Doubling the output power results in a +3 db change. Most audio folks beileve that +2db is about the smallest change that can be detected by most folks ears.

Doubling the output by +10db is usually perceived by the ears as about twice as loud.

Thus 10W produces a sound level. It takes about 100W to be twice as loud, and 1000W to be 4 times as loud.

Ed
 
Ok, I'm getting you. Thanks a lot, this thread has been very helpful in helping me understand this a bit more!

My main mistake was in mis-remembering my physics class on adding adding identical sources together. In my head, if you doubled the number of sound sources, you would get a +6dB increase but clearly it was actually +3dB. Now that I understand the theory, it doesn't mattert whether I remember or not because I can work it out!
 
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