Why do you guys pursue a flat frequency response when you buy a subwoofer?

Interesting question because:  When we insist on a flat frequency response, then mess with it with the cheap crossovers most subs have, we are at least starting with a sub that does not add or subtract info from a poor design.  Personally, I use a pair of subs powered by a dual mono stereo amp, allowing manipulation of the volume without changing the frequancy response.  

A lot of people - just about all car audio guys, and a dismaying number of fairly serious audiophiles, are impressed with the slam of big bass and aren't really being honest if they say they want accuracy (although the ones on the audiophile end won't usually put up with too much boom that wasn't in the music).

Problem is that we are supposed to be trying to replicate a live performance in our listening room. Most people have zero idea what it would sound like if you put a guy playing an upright bass (much less a bass drum) in the corner of your listening room, nor how that would change if you moved him/her a couple of feet out or closer to the corner.

I am not sure that the average stereo fan IS looking for a flat response, although they might say they are.  Given that you don't get a flat response from the orchestra unless they are playing in a field, any structures within the sound field will affect what reaches your ears. All you can do is try and get a sub that is clean and doesn't start out by giving you artificial bumps.

A friend creates home theatres and sets in room response flat with pretty darned accurate instrumentation and tells me that he has NEVER - not once, had a client that didn't crank the gain on the sub channel.

Best we can do as home audio fans is to try and start with something that gives reasonably flat response and then try and modify that to eliminate variations introduced by the room. That takes good instrumentation, not guessing. I've been involved with that sort of set up, which can take several hours and a lot of speaker shifting about.

The speakers are a big factor - the main speakers in my main system are about the only ones I have heard that added no 'over-hang' in the low bass - a low note didn't fuzz and hang about, it simply stopped when the note stopped.   I had never noticed that over-hang until it wasn't there any more (on music that I was very familiar with). But I also think that it was more to do with driver design than having any sort of flat response.

Problem is that we are supposed to be trying to replicate a live performance in our listening room.

Not me, I’m definitely not doing this.

A friend creates home theatres and sets in room response flat with pretty darned accurate instrumentation and tells me that he has NEVER - not once, had a client that didn’t crank the gain on the sub channel.

So, to throw cold water on this whole conversation, you don’t want a flat in-room gated response. You want a smooth descending response. You want a flat power response, which is not the same.  This further challenges the main position of the OP that audiophiles want a flat subwoofer. I do not, nor do any experts I know of. A truly flat response is shrill. No one does this. The quasi-anechoic measurements of Stereophile are not what you set your listening position targets to.

Taming bass modes, a smooth integration with the speakers and a descending frequency response are my main priorities.

Best,

E