1 dB is not nothin', though, and the difference between 500 watts and 400 watts is also not insignificant. There's something weird about the Acme cabs; they just sound better and better the more power you run into them. The maker once mentioned he thought it was absurd how much wattage people were dumping into them, but in my experience it makes a difference. My Eden WT400 sounded great with the Acme, but it would overheat every night when I was Rocking Down To Electric Avenue (and Then, some nights, Taking It Higher, depending on the mood). Maybe that's a question of headroom or current capability or whatever; my Neanderthal solution was to just get an iAMP 800, which could bring on the noise without breaking a sweat. (Said Neanderthal impulse is the same one that kept me away from the parametric EQ...that, and the fact that the stage was dark and there was beer being spilled everywhere on everything.) There was a noticeable improvement in tone with the iAMP, which of course could be the result of a thousand things; but from a psychoacoustic standpoint, it felt like the amplifier had more control over the speakers at ridiculous volumes, and when it was super loud it didn't feel out-of-control as well. (Kind of like the whole "arm strength" thing with NFL quarterbacks: it doesn't have to do with just being able to throw the ball 70 yards, but it means being able to control exactly where the ball lands when you do throw it that far.)
Sounds to me like you switched from a 400-watt to an 800-watt amp. That's a 3 dB difference-- still small but noticeable. I do not question for a minute your experience. I do not mean to be argumentative in the least-- but--
If one takes a 400-watt and a 500-watt amplifier that are otherwise identical, then the difference really is just about insignificant, from the point of view of physics and psychophysics. It's only 1 dB. Whatever the 400-watt amp could do, the 500-watt could do one decibel higher. It seems intuitive that if you've got 100 more watts, you've got more margin before severe distortion and clipping set in. In fact, you do-- but only 1 dB worth. Considering the waveforms we amplify and the way the ear works, it's a virtual spit in the ocean.
There are so many other factors involved. For example, one can take two amplifiers rated at 400-watts and get very different results driving a particular cabinet. The two amps may differ in their headroom, current capability, damping factor, etc. Let's take current capability. What is often overlooked is that the impedance ratings on cabinets are "nominal" values. This is, after all, impedance and not resistance. That means it is a function of frequency. The actual impedance changes with the frequency being amplified. If a particular cabinet's impedance drops within some frequency region, say from 4 ohms to 2 ohms, then the current required from the amp to maintain the same wattage into that cabinet must increase by a factor of 1.414 (square-root of 2). One amp may be able to handle that, another may not. Current capability is recognized in the audiophile world as being quite important.
All this is to say that if you find that a 500-watt amp works much better than a 400-watt amp into the Acme it doesn't mean it is because the latter delivers more continuous power. The "greater control" over the speaker you experienced with the iamp could very well be related to damping factor (I won't even start with that here) or better rejection of infrasonics.
A montra of mine (as you may know) is "Think SPL, not watts." That 's important when evaluating a rig. I could start another one, "Think about watts in terms of decibels." If people would do that, they'd save a bunch of money.
Salesman: "Oh Mr. Allen, we have a special today at BassCrazy Sound. I can offer you this 650-watt amp for just $200 more than our 500-watt model."
Jeremy: "Are you crazy? Why would I lay out $200 more for 1.1 dB?"
I use the parametric section of my iamp all the time. I find it to be an enormously useful and flexible tool. I admit, however, that many feel that it's just too many knobs and dials. They do take some time to learn to use but, IMO, the time is well spent. In my case, as a result of years of professional exposure, I can pretty much walk into a room, play my bass and identify the frequency bands that need cutting or boosting. With not too much training, many can become fairly good at this. It's a useful ability to have in your bag of tricks.
