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Watts and volume

#4
+1... 3db... which is quite meaningful. However, as with most things, its not as simple as that. If you go from 800 watts to 1600 watts, and you rarely push the 800 watts to full power, you mightl notice very little difference. If you go from 100 watts to 200 watts, and are constantly driving the 100 watt amp into clip, it might be a life changing experience, all other things being equal:)
 
#5
to double the volume, you need to multiply your source by 10.

100W x 10 = 1000W (double the volume)

If you are worried about sound generated by Guitarists and or Keyboard players, I use the following rule:

Guitar amp wattage x 4 = my bass amp wattage.

I use a 300W Trace Elliot at my local rehearsal room. The guitar amp is a 50W Marshall. It all sounds good. I can get a good undistorted sound to sit under 'that' marshall sound.
 
#7
KJung said:
If you go from 100 watts to 200 watts, and are constantly driving the 100 watt amp into clip, it might be a life changing experience, all other things being equal:)
Click to expand...

+1 :D



I have always heard/read that 10xwatts=twice the volume. However I am not sure as to the exactness of that, or if you'd hear it twice as loud, I would assume that that means ohns, woofers etc are all exactly the same. Hearing volume can be an odd thing, if the EQ is different something could "sound" louder w/out being db louder.

But, I will let the experts answer that, Bill F or Bob Lee should be able to give very educated answers.
 
#8
stedtale said:
+1 :D



I have always heard/read that 10xwatts=twice the volume. .
Click to expand...

10dB is twice as loud, though not necessarily 10x the power, as power and output aren't linear. For the most part if your rig isn't loud enough just doubling the power is a waste of $, you need to make increases by a factor of at least four to be worthwhile.
 
#9
billfitzmaurice said:
10dB is twice as loud, though not necessarily 10x the power, as power and output aren't linear. For the most part if your rig isn't loud enough just doubling the power is a waste of $, you need to make increases by a factor of at least four to be worthwhile.
Click to expand...

Ahhh...I see now, 10dB in the dB scale (is it an exponential scale?) is not necessarily the same as 10 x wattage. Makes perfect sense.
 
#10
You also need to get speaker efficiency and power handling into your thinking... To get louder, you can increase power or use the same power and go more efficient - as long as the more efficient speaks have the capacity to hold the power on tap.

Trusting mfgr's efficiency ratings - talk about a can o' works ...
 
#11
A lot of the R&D for neo drivers has been beneficial regarding power compression as well, since heat is an issue for either. I'd guess that a lot of lead-sled drivers may exhibit as much as 6 dB of compression when really being hit, where a lot of neos probably come in at 3.
 
#12
stedtale said:
Ahhh...I see now, 10dB in the dB scale (is it an exponential scale?) is not necessarily the same as 10 x wattage. Makes perfect sense.
Click to expand...

A 10 dB boost is a 10× power boost. A 10 dB boost in sound pressure level (SPL) is an approximate doubling of apparent loudness, on average across the audio spectrum. (The unit of perceived loudness is the phon, and like the decibel, it is logarithmic--a 10 phon increase is a doubling of perceived loudness.) It actually varies with frequency, though. At very low frequencies, where we bass players often dwell, it takes much more SPL than at high mids just to be heard at all by normal human hearing systems. Above the threshold of hearing, though, at these same bass frequencies the human hearing system does catch up a little bit with its sensitivity at mid frequencies: while a 10 dB increase in SPL at the mids generally causes a 10-phon increase in loudness, it may take only a 7 or 8 dB increase in the low bass to cause a 10-phon increase in loudness.

For a more detailed explanation, with charts, see these articles on Fletcher-Munson contours, Robinson-Dadson curves, and Equal-loudness contours.

Then it gets a little complicated. Sometimes putting X dB more power into a loudspeaker doesn't produce X dB more SPL. This is due to a phenomenon called power compression. Typically, over 90% of the power going into a loudspeaker driver turns into heat instead of acoustic energy. That heat causes a driver's voice coil to heat up. And being made of metal, its resistance increases with temperature. When the voice coil's resistance increases, less current flows through it for a given amount of voltage applied across it (and consequently, less power). And current (i.e., electron flow) is what creates the magnetic field that moves the coil and cone in and out to produce sound.

So if the voice coil is hot, you might find that putting in what would be, say, 3 dB more power (2× the power) results in 1 dB (or even less) of increased SPL. This may lead to a temptation to push the loudspeaker harder, with more applied voltage from the amp. You might see where this is going. The voice coil gets hotter and hotter, to the point where it burns out, the adhesives fail, etc.
 
#15
Bob Lee (QSC) said:
So if the voice coil is hot, you might find that putting in what would be, say, 3 dB more power (2× the power) results in 1 dB (or even less) of increased SPL. This may lead to a temptation to push the loudspeaker harder, with more applied voltage from the amp. You might see where this is going. The voice coil gets hotter and hotter, to the point where it burns out, the adhesives fail, etc.
Click to expand...
I asked a question regarding thermal compression some time ago, nobody answered; we used a similar principal in our explosive gass testers on British Telecom.

In the 70s we wondered why our PA system fed back when set at the previous nights settings.

Question is a 5db gain at 30dbs the same as a 5 db gain at 98 dbs
 
#16
Bassman62 said:
In the 70s we wondered why our PA system fed back when set at the previous nights settings.
Click to expand...

Not neccesarily related. Could have been AC supply differences, some slight change of monitors or mics position, even humidity or amount of people in room ; }

Question is a 5db gain at 30dbs the same as a 5 db gain at 98 dbs
Click to expand...

Yes and no. See the Fletcher-Munson graphing and it'll intimate that when doing this at a lower general volume that a 5 dB in the sub 125-Hz region will make less perceptible difference than say gaining 5 dB at 3-4K Hz. Since the ear is more sensitive at one frequency than the other, and you started at a low full-bandwidth volume, the general perceptible difference will not be as obvious as if you had started at a moderate level and then added 5 dB.

So: the dB itself is constant and linear; 5 dB change is the same always. But the EAR is not equally sensitive at all frequencies and that varies at different levels, so its PERCEPTION of the actual change in SPL may be different in different cases.
 
#18
thrashermatt said:
it also depends on how the company rates things.
My ampeg svt350h (350 watts at 4 ohms) was quieter than my peavey nitrobass (300 watts at 4 ohms) by a landslide
Click to expand...

Not necessarily on how the company rates things. Different loudspeaker cabinets will usually have different sensitivities, and of course of you use 100 watts of a 500-watt amp, it won't be as loud as using 200 watts of a 300-watt amp.
 
#19
Bob Lee (QSC) said:
Not necessarily on how the company rates things. Different loudspeaker cabinets will usually have different sensitivities, and of course of you use 100 watts of a 500-watt amp, it won't be as loud as using 200 watts of a 300-watt amp.
Click to expand...

Which is to say, User misconceptions enter the picture. Different heads have different gain structures; make assumptions about the input gain, etc. Then the user thinks his knob positions being the same on two different designs will have the same overall gain. Wrongo! You need to treat each one as a unique entity until proven otherwise.

And really. The difference between 350 and 300 watts is miniscule in terms of SPL. Even if one company fudged by quite a few percent by rating at a higher distortion figure the difference would not be that significant.

In either scenario, or when perhaps using them with different cabs in a different environment at a different time in a different mix, it usually comes down to subjective user [mis?]perceptions - or failure of User to understand and properly use gain structure.




; } Unless, of course each head has some cheesy default voicing that fools the user into thinking flat EQ on each actually means flat output - then there is another level of band-specific gain structure there to fool the user ; }
 
#20
I have read that the best way to add volume to a rig is to add speakers. For example you have 300 watt head and a 2x10 cab. You will get more volume by adding another 2x10 cab (or a 4x10 cab, 1x15, etc.) than upgrading the amp to say 500 or 750 watts and sticking with one 2x10. Is this correct?
 

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