a Power vs Volume Question


I just replaced my old 200w power amplifier with a new 300w amp. by my surprise, with all things left the same, including the volume setting, the output read by my spl meter was the same between the two amps. isn't the 300w amp supposed to be louder at the same volume setting?

please post your thoughts.
thank you
Not necessarily. Depends on the senstivity/gain of the amp. All the rating tells you is what it will put out IF you drive it enough.
Just as a point of reference:

All other variables being exactly the same; to have something play twice as loud as a 200 watt amplifier, you would need 2000 watts (not 400). Just for you to note that 100 more watts from 200 is not a lot.

You might notice more refinement, dynamics, and less distortion, because the 300 watt amp does not have to work as hard to drive the speakers. You probably would not really notice more volume.
Actually, if your speakers' sensitivity are 85db/1W/1M, then, of course with 1 watt of power at 1meter, you'r SPL will be 85db. Since you'd need to double your power to increase your SPL by 3db, you'd need 536,870,912 watts to double your volume to 172db. So, if your SPL was X at your listening distance with 200w,and you now raised your power by 50% you're only raising your SPL by 1.5db. Not very much.
thanks for your enlightening responses.

Ohhhhhh, THAT'S where I miscalculated! I thought I needed 536,870,913 watts.

Sheesh, and yet another 37.062017-foot Marshall stack!
172dB??? Wouldn't that cause incontinence, impotence, deafness, blindness, and sudden death? WOW, now that's really something to shoot for!
You think 172dB is double the volume of 85dB? You are kidding, right?

Maab, the ampunt of power delivered is determined by the input to the amp and the gain of the amp. The gain is basically how many times the amp multiplies the strength of the input signal. A 10W amp can have the same gain as a 1,000W amp, but the 10W amp will reach it's maximum limit and clip before the 1,000W one will.

If both amps have the same gain then they will produce the same volume with the same input. The differences are as Suarbrie pointed out and the headroom.
... very intersting. thank you.

just for info, the speakers in use have a sensitivity of 90db. I don't know if that says anything at all.
A lot depends on the speakers. There was a thread explaining all this about one week ago but it got nuked.

If your speakers are heavily compressing (like most do) at 200 watts then you gain very little if anything by going to 300 watts...you need the kind of speakers that can use that kind of power and actually turn it into clean sound.

Volume is often constrained by the speakers and not the amp. An extremely well built 85 db SPL sensitivity speaker may actually play louder and more cleanly than a 90 db spl sensitivity speaker with the same 200 watt amp. It doesn't seemv logical but it is true. Driver construction is crucial. Lightweight cheap northern european mass produced drivers with small motors very soon run out of gas!
Herman, why isn't 170db twice the loudness of 85db?
This is a simplified response:

Sound pressure levels are expressed in dB and the softest sound a normal person can hear is around 4dB. The threshold of pain is somewhere around 130dB, but this isn't 32.5 times the pressure level of 4dB. It is closer to 4,000,000,000,000 times the pressure level since the scale is logarithmic.

130db – 4dB = 126dB
126dB = 10 times log (pressure at 130dB divided by pressure at 4dB)
12.6 = log (pressure at 130dB divided by pressure at 4dB)
Inverse log 12.6 = about 4,000,000,000,000

This isn't exactly the same thing as loudness since it takes about 10 times the pressure level (10db) to be perceived as twice as loud and the ear's sensitivity changes with frequency and pressure level, but they are correlated.

check this out


Pawlowski, the decibel is a logarithmic function, not a linear one. Each doubling of power increases loudness by 6 db. The ear perceives a 10 db increase in sound level as a doubling of volume.

A jet plane taking off is around 130 db. A rocket launch close hand is around 180 db.
Each doubling of power increases loudness by 6 db. The ear perceives a 10 db increase in sound level as a doubling of volume.

Actually a doubling of power is 3dB, a doubling of voltage is 6dB.

Loudness and volume are the same thing.

It should read "Each doubling of power increases sound pressure levels (SPL) by 3 db. The ear perceives a 10 db increase in SPL as a doubling of volume."
Twice the power is a 3db increase.
10db is twice the volume or loudness.
Further to Herman above, each doubling of SOUND PRESSURE level (i.e. spl), i.e. what we "listen to", is 6dB. You need four times the "power" to achieve double sound pressure -- in fact twice "as loud". Yr mic should record +6 dB when your power rises 4times.
In other words... on paper, going from 200W to 300W gives you an extra 1,4dB. That's assuming, of course, that the speakers can take 300W continuous -- which they usually can't.
Both loudnes and volume are perceptual terms correlated with acoustic level. The knob you twirl is a level adjuster.

Not all amps have the same gain. For example, McIntosh, IIRC, rated their MC 60 at 60 watts RMS 20- 20 kHz with a .5 volt input, whereas the Dynaco 60 watt amp required a 1.5 volt imput to reach that level, so its gain was much lower. (I think the days of the MC 60 were before the JASA style sheet required capping the H in hz for Hertz or the B in db for Bell.) Two other things to look for in amp specs is power bandwidth and distortion rating. Those two numbers can make two different 200 watt amps quite different.

As to the OP, for most practical levels and with equal quality amps, there shouldn't be a difference in SPL whether the amp is 200 or 300 watts, unless the speaker represents a very difficult load.

each doubling of SOUND PRESSURE level (i.e. spl), i.e. what we "listen to", is 6dB. You need four times the "power" to achieve double sound pressure -- in fact twice "as loud". Yr mic should record +6 dB when your power rises 4times.
In other words... on paper, going from 200W to 300W gives you an extra 1,4dB.

Greg, I believe you are a bit off in your analysis.

Incorrect: Doubling SPL is not 6dB, it is 3 dB,

Correct: Double it again for 4 times and that is 6dB as you stated.

Incorrect: Going from 200 to 300W is not 1.4dB, it is 1.76dB.
dB = 10 log (300/200)
dB = 10 log 1.5
dB = 1.76dB
Thanks Herman, I knew there was a log function involved somewhere here...It would be interesting to hear something as loud as 180 db...Isn't the atmospheric pressure something like the equivalent of 164 db? I have heard that the human ear can even become more sensitive if isolated. If you were put into a room with no sound you would quickly be able to hear blood flowing through your body, and air particles brushing your ear-drum. If you were left there for a period of time, you may even be able to tell the changes in atmospheric pressure...

Food for thought,
db growth chart:
85db @ 1 watt
88db @ 2 watts
91db @ 4 watts
94db @ 8 watts
97db @ 16 watts
100db @ 32 watts
103db @ 64 watts
106db @ 128 watts
109db @ 256 watts
112db @ 512 watts

You need to double wattage to gain 3 db
To get a perceived doubling in volume, you need a 10db gain
THX = 110db
THX ultra = 112db
Jet planes, rock concerts and jack hammers usually don't break 130db to 140db or so.
170db could cause a lot more than deafness (brain damage?)
NONE of us own stereos capable of 140db, let alone 170db!
If I understand correctly:
For acoustic SPL and electric voltage, 20dB is a tenfold rise. For (electric or acoustic) power, 20dB is a hundredfold rise; 10dB is tenfold.
appx. 6dB SPL is a doubling of spl and a fourfold of power, and appx. 3dB is a doubling of power.
The human ear is quoted as having a 120dB range. This spans a millionfold spl (10E6 = 6 20dB steps) and a trillionfold (US convention, 10E12 is 12 10dB steps) power range.
You guys made me look it up. (grin)
cheers ww
Nope, Herman, tsk, tsk:)
I referred to dB spl: 20log(delta L). Remember, the relation W = V2/R. It's 20 log, so 6.
See elevick's chart above. Cheers.
Does the above volume/db chart hold for speakers that are 4 ohm, or would the value have to be doubled?
Greg, you are confused, do some research and you will see you are wrong on all counts except that 6dB is 4x power.

Elvick's chart clearly shows a doubling of power for every 3dB. Robert Harley's book on high end audio states “each increase in SPL of 3 dB requires a doubling of amplifier power output.”

Yes, 6dB is 4 times the power but that is because it is 3dB plus 3dB which is double times double (2x2=4) however another 3db for a total of 9dB would be 8 times the power (2x2x2=8)

Your formula is for voltage, not power.

dB power is 10 log p1/p2

dB voltage is 20 log v1/v2

Why is one 10 and the other 20? Since power is proportional to the square of the voltage this keeps the dBs in step. An increase in voltage of 6dB will result in a 6dB increase of power. A few examples:

If I double the voltage I get 4 times the power (2 squared = 4)

Voltage dB = 20 log 2 = 6 dB
Power dB = 10 log 4 = 6 dB

If I produce 5 times the voltage I get 25 times the power (5 squared = 25)

Voltage dB = 20 log 5 = 14 dB
Power dB = 10 log 25 = 14 dB

and it isn't delta. Delta means the "amount of change" so the delta from 200 to 300W is 100W. The formulas use the ratio so you would take the log of 300 divided by 200.


Mbacinello, yes it holds true, a watt is a watt.

The confusion is caused by manufactures who state sensitivity in terms of voltage instead of power. It takes 2.83V to produce 1W into 8 ohms. This same voltage produces 2W into a 4 ohm speaker.

This means a 90dB/1W/1m 4 ohm speaker will be a 93dB/2.83V/1m 4 ohm speaker since the voltage spec is actually 93dB/2W/1m. This can can be misleading but the manufacturer will say that since most amplifiers are voltage amps and can produce twice as much power into 4 ohms as they can into 8 ohms they are justified in inflating their sensitivity by 3dB.
To add to the discussion;

1) Each additional speakers gives you 3 db SPL

2) Each time you double the distance you lose 6db SPL ( 2 meter is -6 db, 4 meters is -12db )

3) Line arrays drop at 3 db per meter when are very close to the speaker....as you get into farfield they behave just like other speakers

4) The room will help reduce the loss of the sound level with distance through reverberation.

5) Speaker close to a rear wall add up to 3 db SPL in the bass.

6) Speaker in a corner add up to 6 db SPL to the bass.

If you are serious about audio reproduction then consider this: a drum set can produce 115 db SPL and a symphony orchestra can produce 110 db SPL, marching bands and rock concerts can achieve more.

A drummer sits at the back of the stage. A conductor stands several feet back from the orchestra.

A system that can achieve 105 db spl continuous cleanly at the listening position (with 10 db of head room) is roughly what you need to cover all but the most extreme situations.
He Shadorne; I like that!!
I also read somewhere that you lose 3 dbs output going from a 8 ohm load to a 4 ohm load with the same wattage.
Does adding a powered sub to the mix free up the amp to play at louder volumes,ie: will the amp seem to play louder with the sub in line?

Yes of course - a tweeter never needs more than 50 watts....if you remove the ultra LF load from the amp then it will play cleaner louder...

If the "gain-sensitivity" on the amp has not changed with the addition of a sub, how than, can the amp play louder at any given volume? I understand, all things being equal, that the bass impact will be enhanced with the powered sub in line but how does that increase the "gain-sensitivity", and hence, the output of the main stereo amp? Thanks...

Was wondering if anyone could answer my question from above, it would be nice to know. Thank-you in advance...
Aolmrd, I don't think it is a matter of louder but cleaner. Think in terms of energy.

The capacitor bank in the amp can only store a finite amount of energy. Bass notes take a lot more energy to reproduce than treble notes. If you free the amp from having to provide energy to the bass notes it can loaf when providing energy to the spectrum above and can therefore play more cleanly.