So to a less knowledgeable person like myself, this all means that my srx718 subs will draw more power from the amp than my srx715's will even though the speaker power ratings are the same because of the lower frequencies?
Speakers don't "draw" power. They just present a load (that is NOT the rated impedance) It may be at some freq-but as a general rule-the ACTUAL load is both higher and lower than the speced load-depending on what freq you look at.
The lower freq response of the driver usually has nothing to do with the power it "draws". The only way to tell is to look at the IMPEDANCE CURVE of the loudspeaker. They are not the same. You will see all kinds of peaks and valleys in the curve. This is an indication of the tuning of the cabinet. So it is very freq specific as to what the impedance is.
As a "general rule", given 2 bass reflex cabinets and one goes lower than the other-at the "lower freq" (you have to decide what is "lower"), the cabinet with the lower tuning will have a higher impedance. This is a function of the tuning. But at a higher freq-the one with the lower tuning will have a lower impedance than the one with the higher tuning-because the one with the higher tuning will have one of its peaks at a higher freq.
The amp does not "deliver" wattage. It delivers VOLTAGE. The actual wattage is a combination of the voltage applied and the complex impedance (NOT RESISTANCE) of the loudspeaker.
How much the loudspeaker can "handle" is a combination of the voltage that can be applied and the impedance of the loudspeaker.
NOTE: This impedance changes with input voltage-once the loudspeaker gets hot. This is called power compression-and the actual impedance rises as the voice coil gets hot.
The "wattage" as presented on the spec sheet (from all manufacturers I suspect) is also wrong. It is NOT the point of maximum input in terms of watts-even though it says so.
It is the VOLTAGE that can be applied to the driver without damage-and the rated impedance. Since the impedance rises when the driver gets hot-the wattage can actually go DOWN.
But the thing to consider is-what is the number trying to tell you? It is a suggestion of the size of the amplifier than can be used with a particular loudspeaker.
I know to some people it doesn't matter-but it is important to understand what is really going on.
Take a look at the following example-it is a single 12"sub (bottom) and a single 18" sub (top). The 18" sub is tuned much lower. So let's look at just 2 freq 11Hz and 26Hz.
At 11Hz the 18 sub has a much higher impedance than the 12", and at 26Hz, the 12" has a much higher impedance than the 18". So if you say that the one that goes lower "draws more"- what is low?
The question that HAS to be asked when anybody presents a "spec" is AT WHAT FREQ? This involves all sorts of topics-coverage pattern-power capacity input and output)-impedance-SPL-noise.
A simple answer is GOING to be wrong-at at best-incomplete.
You cannot use simple numbers to describe something in a dynamic environment-such as audio. With a light bulb on a standard line it is MUCH easier-the voltage remains the same-the freq remains the same-the heating remains pretty constant and so forth. So it is real easy to come up with simple numbers that describe it.
But when all sorts of variables are "moving around" (as in audio) it becomes much harder. And if you want to "pinpoint" a specific number-you HAVE to put a lot of variables around it to qualify the answer.
Even something as what would seem simple SPL. How loud is it? What scale is the meter using? (that can account for a 20-30 dB difference. What is the speed of the measurement-slow-fast-impulse etc? that can account for possibly another 10-20dB.
So you could use the same meter-at the same distance-measuring the same source and get a 30-40dB difference in level. So how loud was it? It depends-on the parameters you set up in the measurement.
Sorry to rant-but "simple numbers" get me going.