Originally Posted by Tommy457
So I have a nob question. What is a flat response and how do achieve it?
Disclaimer: I only started reading up on this stuff a few weeks ago. Wait for somebody to verify or contradict what I say, but I am going to attempt to answer this off the top of my head as a knowledge test of sorts for myself:
This is referring to frequency response (FR), usually seem in graph form. If you click on the "Tech Specs" tab when viewing a sub on SVS's site, the graph you see is FR. SPL (sound pressure level) is on the vertical axis, frequency is on the horizontal axis. In a perfect world you would get a perfectly flat line indicating that the speaker/sub produces the same SPL (think of it as volume) at every frequency in its range. This would give the 'smoothest' most accurate performance as it would reproduce every frequency equally, IOW, it would not alter the way the source material was intended to sound.
However, it isn't a perfect world. Due to physics and stuff I only slightly pretend to remember from college, FR is not flat. And when you put the sub in a room, things can change drastically. Bass frequencies have such long wavelengths that they interact with the room, walls, ceiling, floor, all that good stuff. The waves bounce around and interact with one another. Based on the sub's base output, the location of the sub within the room, the room boundaries' (ceiling/floor/walls) locations and lengths, etc, different frequency's wavelengths will be higher or lower at different points in the room.
When two wavelengths (say, coming from the sub, and coming off of a wall back at the sub) meet, they can reinforce one another...this can be a positive gain (peak, that frequency will be louder/stronger at that location) or a negative gain (valley/null) due to cancelling each other out. You also get peaks/nulls simply as a result of "room gain", which is, depending on the dimension of the walls (especially the longest one I think) some frequency or frequencies will be elevated more than others.
When you only have one sub in a room, there are going to be peaks and valleys or nulls at different places in the room. That's just the way it is. Finding your best sub placement generally means minimizing the peaks/valleys for the listening position(s).
With multiple subs, properly places, you can get a smoother in room response, that is, you can have a flatter FR across more of the room, including the MLP (main listening position). So even if you are only concerned with how it sounds in one spot (where you sit), multiple done right will improve it.