Originally Posted by Nick****achi
that's good to know, although is it relevant to compare 1w spl behavior when most instances at those frequencies the power will be at the thermal rating of the driver? what does the horn do at 12hz 250w and no high pass? where do the lines cross on that comparison? Wouldn't it be making all kinds of bad sounds by then?
All the above are posed as questions, and based on possible misconceptions
In real life use - the sub might see 100W transients, most of the time the power applied will be under a watt.
In a nutshell, the numbers all get bigger, but the relationships do not change.
Here are the same comparisons as presented above, except done at 250 watts.
The SPL lines still cross at 12 Hz. The horn is 10 dB louder at 20 Hz.
At 12 Hz, the model suggests that the driver in the horn will be moving +/-17 mm, which is over xmax, but still within the driver's xmech. Same power into the sealed box has the cone moving +/-27 mm. While the driver in the horn would certainly be distorting, the driver in the sealed box would be complaining audibly, possibly even experiencing mechanical contact (coil into backplate), because that is 7 mm over the 20 mm xmech on this driver. Clanking is FAR worse than a bit of harmonic distortion.
Clearly - I made the sealed box too large. Oopsies....
Let's try again, with a smaller sealed box, just to be fair.
250 watt comparison, 118 L sealed box vs. the F-20.
OK, now when we feed it 250 watts, we can't clank the driver above 10 Hz in the sealed box. As before, we can clank the driver in the horn at a few select frequencies..... Still, the horn's excursion for the great majority of frequencies below 80 Hz is still equal to or lower than the sealed box, even when we get below the horn's corner. The horn excursion is lower than the sealed box below 14 Hz, and continues to decrease as frequencies get lower, while the sealed box excursion rises slightly as frequencies decrease.
But....look what has happened to the SPL....
The lines don't cross at 12 Hz anymore. In fact - they don't cross at all on this plot. The spread at 20 Hz is now 12 dB. It takes a single driver in a sealed box over 10X the power (over 2500 W!!!) to equal the horn's SPL at 20 Hz, or it would take 4 drivers in sealed cabinets, each at 250 W. 4X the drivers, 4X the power.
Sealed boxes have a resonance and roll-off too. When you make the sealed box smaller to control the driver's excursion, you also raise the resonance of the enclosure, which reduces the low frequency SPL.
Sure - there is still the out of band distortion issue as I discussed earlier. I just wanted to show a comparison of the two to try and clarify things. Sealed boxes may go "low" but they do not do "low" and "loud" all by themselves.
Clearly, there are lots of ways to get to reference level at 20 Hz. This time, I chose to get there with a single 15" driver and 2.25 4X8 sheets of plywood.