Are the JL Fathom subs really that good....

Interesting. Since your post, Bizango1, I've more carefully listened to see if I could tell where the subwoofer is in my room. I have to admit the results inconclusive, for two reasons. First, my sub is positioned about midway between my main speakers (though not exactly midway), making the sub more likely to appear blended. Second, a lot of recordings are mixed with mono bass. Perhaps most recordings. This, of course, means that a centrally placed sub will blend even better. So it possible that the only reason I can't tell where my sub sits is because that's how the bass would sound even if the sub weren't present.

NVP: All very good points. I was thinking more in terms of getting the easiest in-phase blend wherever your listening position. With a sub in a different place than the the mains, the phase relationship changes as you change listening positions. But as you say, the subs may need a different position for smoother response and better room coupling.

In my own setup I have a compromise between the two. I run a stereo pair of subs, but they need back wall reinforcement for any meaningful low bass, so I position them as stereo pairs against the wall and directly behind the R-L mains. That way I get the room reinforcement and only have to adjust the phase control a little bit, and the frequency range stays pretty uniform throughout the listening area.

Another advantage of separate subs is that the mains and the subs can be built and optimized to their frequency ranges, and it keeps the internal vibrations produced by very low notes (and contained within the sub) from smearing the cabinet vibrations handling the midrange and treble.

Irv, I have a large aquarium in between my speakers so I have never been able to locate the sub near the middle. Who knows, if I had I might never have been driven to try stereo subs. I guess the plot thickens as our system details come out. In my setup with the tank in the middle two subs to my ears are conclusively better. I suppose the bass blend across the soundstage could be inhibited by the half-ton body of water in the middle!

Jb8312
To be honest, I cannot "fathom" a sub integrating into 2 channel so well it is seamless, completely cohesive and disappears into the music…

It can be done, but it is very difficult. IME, seamless integration is only achieved when BOTH frequency response AND transient response are optimized. The problem is that it is very difficult to optimize both, and optimizing only one results in an audible "disconnect" between the sub(s) and the mains. To quote myself from another thread...

Much of the time and effort that goes into subwoofer setup is spent optimizing frequency response. That is typically done in one of two non-mutually-exclusive ways: Sub placement or digital EQ. Either of these approaches can result in a much flatter frequency response, making the bass sound less bloated. But both of these approaches can result in a sub-optimal transient response, due to the time misalignment between the sub and the mains. That makes the bass sound slow. To elaborate…

If placement is used to optimize the sub’s frequency response, then the sub often winds up closer to or farther from the listener than the mains, thereby misaligning the sub relative to the mains. Alternatively, if digital EQ is used to optimize the sub’s frequency response, then a processing latency is introduced into the sub’s the signal path, but not into the main’s signal path, thereby misaligning the sub relative to the mains. Hence either approach to optimizing frequency response can disturb the system's transient response, making the bass sound slow (or “out of sync”). On the other hand…

If you set out to optimize transient response, you will usually place the subs on a plane very close to that of the mains. Now the bass no longer sounds slow. But, due to room modes, this kind of placement often results in a highly uneven frequency response. Now the bass sounds bloated again...and so on.

The result of all this is that, when trying to optimize both frequency response and transient response, you often have the experience of chasing your tail. That is what I mean when I say that, under many circumstances, optimizing frequency response and optimizing transient response is a zero sum game.

IMO, the way to defeat the zero sum nature of this game is to:

1. Place the sub(s) to get the best frequency response (varies from room to room) and fix transient response problems with DELAY. This assumes you can independently delay the sub(s) and the mains, which doesn't seem to be a common capability in audiophile systems.

-OR-

2. Place the sub(s) to get the best transient response (i.e. roughly coplanar with the mains) and fix frequency response problems with EQ. But to the extent that the EQ introduces processing latency, you will have to move the sub(s) CLOSER to the listener than the mains. Again, this doesn't seem to be a common arrangement in audiophile systems.

-OR-

3. In light of (1) and (2), the most effective way to optimize both frequency response and transient response is to be able to INDEPENDENTLY CONTROL BOTH THE EQ AND THE DELAY OF BOTH THE SUB(S) AND THE MAINS. That allows you to correct for room modes (better frequency response) and time align the various speakers (better transient response). Very few systems have this capability, and for this reason, very few systems seamlessly integrate subs.

You said don't hold back.

Bryon

P.S. I use a Fathom F113 for 2 channel.

Bryon, it might be helpful to explain what you mean by transient response.

Lyngdorf systems (most probably also TACT ones) that have the room correction module do exactly what you have described under point 3 in your post. Thus, what follows is based on my experience with Lyngdorf systems.

When set up right the Lyngdorf room correction system can indeed work wonders, i.e. significantly improvs in the bass response, imaging and coherency (which is related to the transient response you were talking about) of a system. However, unless one goes for the top of the line Steinway Lyngdorf system this often comes at a price, i.e. dynamics (which on one hand is what most system lack anyways, and one the other hand is the main requirement for having system that sounds life-like).

On the other hand, if set up wrong (which often happens in untreated rooms) the Lyngdorf room correction system will literally such out all life from the music. One will be left with a good bass response, a good transient response, good stereo image but crappy lifeless sound...

I would rather opt for speaker designs that attempt to time align the drivers and use a subwoofer that is cross-overed as low as possible, e.g. a REL. Of course, I am just a hobbyist and my opinion is based on my experiences so far :).