Impious

While I can't agree with your subjective analysis of "big difference", let's just look at the numbers. You went from 500w to 750w and gained 1db. You should have gained 10*log(750/500) = 1.76db, so you had .76db of power compression. With double the power, you only gained 1.5db, you should have gained 10*log(1500/750) = 3db. So you had 1.5db of power compression. How much power compression do you think is going to be occurring with 9000 watts on a pair of subwoofers? Oh, and I don't care about your personal subjective analysis of the "audible differences". If you want to prove anything at all with regards to your ability to discern audible differences, go have a properly conducted, scientifically valid test conducted in a controlled environment by someone with the proper training in administering such a test.

And you would be wrong. 1.1db is the maximum difference. This is a fact of acoustics. It's been tested. It's been verified. It can be reliably predicted. You might not like this. You might think it's bullshit. You would be wrong. Real world, the increase will be significantly less than predicted because of the real world issue of power compression. I don't need to test anything myself to know this. This has been tested and verified by people far more intelligent than myself for decades. So realistically we are looking at an increase that is much less than 1db. And based on even a cursory understanding of the human auditory system, it can reliably be predicted that this small of an increase will not be perceptible by human ears. Again, you might not like this. You might think it's bullshit. You would be wrong. It's been tested. It's been verified. It can be reliably predicted. That's because there are also a lot of idiots in this hobby. If you chose to follow those idiots, more power to you. Hopefully they won't lead you into jumping off a cliff, because you would apparently follow them right over the edge. The alternative is that you are a watching a bunch of SPL'ers who are chasing every last tenth of a decibel. I have and always will concede that in SPL formats the more the better as a tenth of a decibel can make the difference in competitions. However, for "daily driving" setups not primarily concerned with numbers on a meter, this is completely unnecessary and a complete waste of resources, time and space. But because many people have a monkey-see monkey-do personality, they see everyone else running the largest amps they can support (and a lot of times, larger than they can support) and think it's the way to do things. They are full of ignorance and don't have the understanding to know why that route is completely unnecessary for someone who doesn't intend on focusing heavily on the competition circuit.

I meant in your setup... People throw all these formulas and such to determind spl, and it doesn't work. Way to many variables. You're right. It doesn't work.....because the formula is the MAXIMUM increase under perfect conditions, which don't exist. So the results will almost always be worse than the formula predicts. (I say almost because at very low power levels before power compression/etc kicks in, it will hold pretty close to true). Don't know what you're review talking about. But certain things in this discussion are not from "people on this forum" but rather, the people on this forum are stating the simple acoustic and auditory system facts. You would be better off to start by learning some on the subject. Scientists and individuals with advanced acoustics/physics degrees have engaged in this research for decades. For your purposes, you would learn far more by picking up a few good books than you could learn in your driveway as results in your driveway are subject to your own ignorant error. And I don't use ignorant in the derogatory sense, but rather in the sense that you likely do not have enough knowledge to maintain the proper constraints to make any results valid.

In this case: Audibly, No. Measurably, on a meter...Maybe. How much is hard to predict, but it won't be a large increase by any stretch of the imagination. It's not about the absolute value of the wattage increase. It's about the amount of the increase relative to the starting point, and relative to the behavior of the subwoofers both thermally and mechanically. As Bangin' pointed out above, a 2kw increase from 500w is much different than a 2kw increase from 7kw.

Fun Fact: Does everyone know why the THD+N curve takes the shape it does, not only increasing in percentage as power increases but also as power decreases? First, what is THD+N? It is the total harmonic distortion (THD) of the amplifier plus the amplifier's noise (N), and in the graph it is expressed as a percentage of the signal. Now, THD is strongly correlated to the signal.....as the level of the signal increases (i.e. as power output goes up), THD increases. As the level of the signal goes down, so does THD. The right hand portion of the graph makes sense then.....we see the % of THD+N increasing as power increases. But if we look at the left hand side of the graph, in the lower power output levels, we see that the % of THD+N increases as power decreases? Well, that's because the "N" portion of the THD+N, or the noise, is uncorrelated to the signal. The level of the noise is going to be relatively the same at low power levels as it is at high power levels. Because of this, as the level of the signal decreases, the noise becomes a larger percentage relative to the signal ! So the percentage of THD+N is going increase as power decreases because, even though "THD" is decreasing, "N" is increasing as a percentage of the signal. So the THD+N starts out high because N is a larger percentage of the signal at low power levels, then the graph slopes downward because "N", as a percentage of the signal, is decreasing while THD is increasing (although not at as rapid a rate as "N" decreases, so the overall slope of the graph is still downward) until it reaches a point where THD begins to become more significant as power increases and the graph swings back upward again. This is why the SNR (signal-to-noise ratio) of an amplifier is completely dependent on the level of the signal. As the power output of the amplifier increases, it's SNR improves. So if we measure the SNR of an amplifier at 1w, it will be worse than the same amplifier measured at 100w. This is a typical marketing trick by amplifier manufacturers.....some of the less scrupulous manufacturers will list the SNR of their amplifiers at full power output, while others will list it as a 1w measurement. Which is why it's important to know the test conditions of a SNR measurement before trying to compare them between amps. The SNR measurements of two amplifiers can not be directly compared unless they were taken at the same power level, or you adjust one of their SNR measurement numbers to account for a difference in the power level the measurement was taken at. So, there's my attempt at posting something educational today.

Maximum theoretical difference: 10*log(Power1/Power2) 10*log(9000/7000) = 1.1db A 1.1db difference wouldn't really be audible to begin with, so we can scratch "noticeably louder" off of the list of possibilities as the audible difference would amount to pretty much zero even under idealized, unrealistic conditions. Also, that formula doesn't account for power compression, which your subwoofers will be experiencing. At a level of 9kw, they will be experiencing a significant amount of power compression. How much power compression you'll experience depends on the thermal capabilities of your drivers and their mechanical behavior in the enclosure.....but realistically it will be significantly less than 1.1db on a meter, possibly even zero if the amount of power compression is high enough.

AP2 is pretty much industry standard for amplifier testing AFAIK. I'd say the piece itself is more than likely relatively accurate. Never used one myself obviously so I'm not sure if there are setting within the software/hardware that will affect accuracy, although my assumption would be that there is. As far as that Arc goes......definitely a stout amplifier output that much power with low THD, although the low THD is of no aubible benefit.....other than the fact you'd get a lot more power than 4kw out of it before distortion becomes audible. That RF amp is just shy of 80% efficiency, which is pretty impressive for that large of an amp running at 1ohm.

LOL....I like the little table on top of the sub in that last pic. Though I can't imagine that stays in place with the sub going full tilt.

Those results are misleading. Don't pay any attention to them.

Yes, it's a 50% increase in power. Sounds substantial, doesn't it? Until you realize that an increase of 50% power yields a maximum increase in SPL of 1.76db, without considering the effects of power compression. If you don't understand power compression, look up Neil's article in the Tech Section here on the site. How much power compression is a subwoofer going to be experiencing at a level of 3kw? Substantial. Substantial enough that it would easily bring that 1.76db maximum theoretical gain well below the 1db mark. It would be entirely possible for there to be a 50% increase in power and zero gain in SPL, depending on the thermal capacity of the subwoofer and how the subwoofer behaves mechanically in the enclosure. So he would be increasing his power by 50% and have an increase in output of less than 1db in return. Are you or anyone else going to hear an increase of less than 1db in subbass with a BTL playing with 2-3kw of input power? No, they are not. The only thing the increased power would do for the OP is take more money out of his wallet, cause him to tax his electrical system even more, cause the sub additional stress with no audible benefit. You can state your view all you want....that doesn't make it accurate. What does any of this have to do with the amplifier?

As M5 said, the entire reason amplifiers have a gain knob is to allow the amplifier to provide full power output with a wide range of input voltages. If you properly readjust the gain, there would be zero difference in output levels between a 2V headunit and an 8V headunit. What happens most of the time is that someone switches from a lower preamp voltage headunit to a headunit with a higher preamp voltage output, and then don't readjust the gain on the amplifier to compensate for the increase in input voltage the amplifier receives. In those cases the output increases because of the higher preamp voltage, but only because the installer did it wrong and didn't properly readjust the amplifier's gain setting.

Yes, they would get less than 600w. We can use basic ohms law to approximate the power they would receive. sqrt(600*2) = 34.64v 34.64^2/2.67 = ~450 So, at 2.67ohm you'd receive roughly 450w from the amplifier, or about 150w/sub. But, I'm confused because of this: If you only ordered two of the Fi X's, what three subs were you planning to use?

The difference in efficiency between full power output & lower power output levels for a given Class D amplifier is generally not very much. Obviously the "heat" would be less than at full power simply because the output is lower, but it would be the same as a lower rated power output amplifier of equivalent efficiency. But efficiency wise, there won't be a whole lot of difference. One thing that would more significantly improve efficiency would be to run the amplifier(s) at a higher impedance......i.e. a 2ohm load on two 2500w amplifiers would be more efficient than a 1ohm load on a 5kw amplifier (assuming the amplifiers are relatively similar in efficiency levels at similar impedances to begin with). The distortion difference would be 100% inaudible. The one benefit you would have in using an amplifier with higher rated power than you intend to use would be higher available headroom, which reduces the risk of clipping on dynamic peaks. How much of a benefit that may or may not be depends on different factors. I wouldn't worry too much about the birthsheet or bench test. The differences involved at these power levels are going to be inaudible anyways.....unless you plan on hitting the comp circuit. Then it's a little more important.

No help to your electrical system since each amp would still "see" a 1ohm load. One sub per amp and a strapped pair is identical as far as the amplifiers are concerned. I would still just run one amp per sub.

I don't have full details of your test methods, but I would that you could hear a .5db difference in subbass with a BTL playing at the level of 2-3kw. (or in most circumstances for that matter). In the more sensitive regions of the hearing (midrange, for example) at certain listening levels where your ears aren't being stressed I would agree it's possible for someone to notice a .5db difference, although they probably wouldn't describe it as a difference in volume but rather some other subjective term such as a change in "warmth" or "detail". But in the subbass, especially at high listening levels.....no, probably not. Chances are I could keep playing the same test tone over and over at the same SPL and you'd think you were hearing differences.....especially if you were expecting there to be differences. Unless there were extremely stringent testing conditions maintained, over a multitude of test sessions to verify results, and correct interpretation of the results (you could simply guess and average a right answer 50% of the time) then you probably didn't test anything at all. Sorry I didn't lay my test out for everybody else. This was personal. I'm sorry I can tell differences. That 3dbs to hear a noticeable is bullshit to me. My test was at 45hz and around 140-145dbs. Done right at 15 tests. And I guessed right every time. Now it could be different at 150dbs and so on. But I just stated I can hear the difference of a 1000watts I'm sure. But it could be different details I am hearing that makes it seems its louder or quieter. But regardless I could tell. Also this was a setup I've listened to quiet a lot, which could of effected the outcome. Now somebodies setup I hear today then again next week, I can't tell a difference. No one said anything about 3dbs, did they? The ability to discern an audible difference in .5db in the subbass where your ears are least sensitive at a level of 140db+ where your ears are under extreme stress themselves would put you well into the realm of superhuman hearing. You should try out for that Stan Lee show on the Discovery Channel. Or the alternative......is that you didn't test what you think you tested, results aren't valid, and you can't discern a .5db difference under the conditions you described. Which one sounds more reasonable?

Don't underestimate the power of stupidity. Stupidity will ultimately prevail.

Unnecessary to purchase an o-scope for the purposes of gain setting unless you plan on having some other future use for the device.

Isn't that what you just did?

Or you could just drill a small hole in the divider to wire the subwoofers together inside the enclosure, then just have a single run of wire to the amplifier. Saves having to stuff multiple wires into the terminal cups. Or if your amplifier has dual outputs as some mono amps do, you could just wire the subwoofers individually to the amplifier.

I don't have full details of your test methods, but I would that you could hear a .5db difference in subbass with a BTL playing at the level of 2-3kw. (or in most circumstances for that matter). In the more sensitive regions of the hearing (midrange, for example) at certain listening levels where your ears aren't being stressed I would agree it's possible for someone to notice a .5db difference, although they probably wouldn't describe it as a difference in volume but rather some other subjective term such as a change in "warmth" or "detail". But in the subbass, especially at high listening levels.....no, probably not. Chances are I could keep playing the same test tone over and over at the same SPL and you'd think you were hearing differences.....especially if you were expecting there to be differences. Unless there were extremely stringent testing conditions maintained, over a multitude of test sessions to verify results, and correct interpretation of the results (you could simply guess and average a right answer 50% of the time) then you probably didn't test anything at all.

Maximum you're looking at a difference of 1.76db. That's before accounting for power compression, which at 2-3kw is going to be significant. Easily significant enough to knock that 1.76db well below the 1db mark. Which means no difference to the ear. Worth it? Not in a setup designed primarily to listen to music with. Definitely not with the added cost of the amplifier and electrical upgrades. If you plan on hitting the comp circuit on the weekends then yes it might be a worthwhile upgrade.

In that case, yes.....just go for a single amp

Can't say without knowing if the subwoofer is D2 or D1.

Class GH is basically a class A/B output stage with a different type of power supply that switches rail voltages based on demand. It's more efficient during operation because it only switches to the higher voltage rails when demand requires it, otherwise it stays on the lower voltage rails......but I'm honestly not sure off hand if efficiency at full power output is improved.

two d2 rl-p 18s. the reason i ask is because i bought the twisted 8 gauge speaker wire not thinking about it, and would waste a bunch if you see what i mean. Then why bother strapping them? Run one amp per sub and call it a day. Matching them isn't difficult by any stretch of the imagination. It would take 15 minutes max with a DMM and some test tones.