Hi! A simple question: Two identical amplifiers with identical speakers. The only difference is that one amp is 300 Watts, the other 600 Watts. Theoretically this would give a 3 dB increase in volume, which is about barely noticeable (from what I have read..) Is there any difference between these two amps worth considering, (except for price and weight)? /Anders

Yes, doubling the power would result in a 3 dB increase in maximum sound pressure level (as long as you're not at the point of loudspeaker compression). However, 3 dB is certainly audible. It is generally thought that 1 dB is about the minimum perceptible difference in loudness. 3 dB is quite perceptible, but it takes about a 10 dB increase for us to regard the sound as twice as loud. - Mike

It might help if we knew what amps. Different manufactures rate amps in different ways. For instance. An amp that is marketed at 600 watts might be rated at 2ohms and peak level instead of RMS or program. Plugging this into an 8ohm cab will gives you a fraction of what the thing is sold as. What are you looking at? jc

"Peak" and "program" power are used in speaker specs. Amp power is normally measured and stated only as continuous power, although there are a few misleading exceptions.

So do you think talking about an 'amp' or a combo amp? BTW Bob, is it possible to upgrade an PLX 1602 to 2402? jc

Let´s say an Ashdown ABM 300 versus ABM 500 (305 Watts RMS versus 576 Watts RMS @ 4 Ohms) The same speaker, capable of all that power.

So I gather the answer is there is a clearly noticeable difference... At least that´s what I would like it to be..

Yes - noticeable, but not huge. In other words, while 600 watts seems like a lot more than 300, we are disappointed by the reality of the unimpressive increase in loudness. - Mike

There are various methods of specifying the output capability of an amp. IMHO there are a few to be avoided when comparing amplifiers: Music Power, Peak Music Power being the most two most notoriously used by SOME amp makers. Again IMHO the only correct method of evaluation amp outputs is the RMS rating. But beware. RMS output IS NOT THE SAME THING AS Continuous Output. And if you can find RMS Continuous then all the better. I'm with MickeyD [ I always try not to contradict the experts ]. The jump from 300 Watts to 600 Watts is a big number but is not that large an increase from the listerers point of view. To make your rig twice sound as loud you have to up the output to about 3k watts!!! John

After many years, I've developed this rule of thumb: if you feel your current amp is underpowered, go for at least FOUR times the wattage (6 dB increase). As far as buying an amp from the same maker and wondering about saving $$$ vs. having double the wattage, it does depend on your music. Playing loud rock? Get the higher wattage, you won't be sorry.

Actually, RMS is a way to measure AC voltage or current, but not power. When you multiply RMS current and RMS voltage terms to calculate power, you get average power. RMS is not synonymous with continuous. You can get an RMS measurement from part of a waveform cycle, a full cycle, multiple cycles, etc., but with a continuous wave signal, if you measure more cycles you get better accuracy. I know of at least one very minor "pro" amp manufacturer that specs "RMS power" measured using the old IHF method, with a repeating 1 kHz sine-wave tone burst for 20 ms at just the onset of clipping (at full power, IOW) followed by 480 ms at 1% power. It may be RMS, but it sure isn't continuous. Continuous average is really the best way to specify power. There are also two predominant techniques for measuring and specifying continuous average power: EIA and FTC.

If you have a 50 watt bassman and a 1-15 speaker enclosure and then run a 100 watt bassman head through the same speaker. you get 3db increase, right? Now add another 15 speaker enclosure, does the db increase, or is it the same with more headroom? Now, take two bassman 50s and two 15 enclosures. The is a total of 100 watts, but won't you double the SPL of the single stack? This has always confused me. I seems if you have double everything, you have double the volume. Please clarify this if you can. Thanks

Yes, Bob, a potential of 3 dB higher sound pressure level (SPL) is possible because you double the maximum power. It depends. If it's an identical enclosure, with the same impedance, then the amp might deliver more power to the pair if they are wired in parallel. Assuming electrically they can draw more power (there are conditions on this, depending on the amp, etc.), then yes, the SPL can increase - particularly if the speakers are near each other. Even if they still draw the same total power from the amp (100 watts to one cabinet vs. 100 watts to two cabinets), two will tend to be louder than one if they are placed close together. No. Doubling the SPL, which is measured in dB (decibels) is not the way it works - SPL is developed as a logarithmic quantity. However, the total power output is certainly doubled, so you gain 3 dB from that if the speakers are reasonably close to the listener; and then you might gain up to another 3 dB because of acoustic phenomena (e.g., mutual coupling) at certain frequencies. Yes, but here's where intuition doesn't work in acoustics! We perceive double the source intensity (it's actually a 3 dB increase when you do the logarithmic math) as only a modest increase in volume. For some reason, the psychoacousticians have determined that our ears need to hear about a 10 dB increase for a sound to seem twice as loud. I'm not sure where this came from. It is not well covered in the literature that I have seen so far. Anyway, it's sensible to me. The upshot is that it takes a tremendous increase in acoustic power to make a noticeable difference in perceived loudness. Dig this: the range of human hearing (before the pain threshold) is about 120 dB. If you study the math, this represents a factor of 1 trillion (not a typo!) difference in power level. That is fantastically huge. It might be something like the difference in power output of a race car vs. an ant (as a guess). The ears are truly amazing things to be able to detect that absurd range of air vibration. We should be awed by this fact. - Mike

Thanks, I'm a little closer to understanding it. Just to clarify, is this right? One 100 watt head and 2 identical cabs equals 2 50 watt heads with the same cabs? But two whole setups is NOT twice the volume as one setup, Right? I wish there was a visual aid to get a better perspective. The reason that I am so interested is I am buying an SVT head.The old vintage one. It is 300 watts. (Old Ampeg watts). I want to use it as a stage amp in place of my 1000watt Eden amp. I am afraid it won't have the headroom of the tranny amp. But everyone says that it is the mother of all bass amps. In spite of my understanding of the watts/db thing, I'm still inclined that 300 watts is not enough. But I have more effecient cabs now (D-210xlt, D410xlt & 1-18 EV) Any input here is appreciated. Thanks, Bob