Hi,
Let's say I have a braodband speaker with a sensitivity of 90dB/W/m.
If I apply some EQ, for instance a room curve or any other bass boost (like +10dB at 40Hz descendint to 0dB at 20kHz):
- does it "change" the speaker sensitivity?
- how much SPL will I have at 1 meter with 1 Watt?
- do I need a more powerful amp?
Cheers.
The music signal is complex, and the effect of EQ is spread out in time and blended with the music signal in a way that makes the impact less intuitive. And a lot of folks give an intuitive answer to these questions.
I ran some simulations a few years ago, with fullrange FIR filter that cut all tops and boosted depressions with max 6 dB. The simulation was done with a random signal (noise). The result:
Overall sensitivity (in the digital domain) dropped by around 6 dB in the case I was using. The sensitivity will drop by the max boosting you apply. You can put it back by digital amplification, but then you will experience digital clipping from time to time - at least on compressed music.
Output SPL per watt input was the same for pure frequency correction, but dropped 1 dB for frequency plus time domain correction. In other words: The system will be practically as efficient as before correction.
To answer your questions:
1) No, but the gain in (the digital part of) your system will be reduced accordingly.
2) As much as before if you have sufficient gain headroom. If you don't have 10dB to spare on your volume control, you will not be able to play as loud as you wish.
3) No, it will basically be the same load, except for the very rare situation where you play a pieceof music that has very high spl content on the exact frequency you have boosted.
The only thing you need to consider when you EQ boost a frequency region is how much the subject speaker drivers can handle. There will be more driver excursion on the amplified frequency - 6dB boost doubles the excursion. If this happens in the low end of the speaker it will reduce how loud you can play before the speakers start to sound distorted. A midrange driver can sometimes be a bottleneck too, but usually this will only be an issue for the low frequency driver. In other words: Be mindful about how much you extend the low frequency range if you intend to play loud.