Is One Subwoofer Really Not Appropriate For 2-Chnl

Ryder, I have a two channel system with one sub. I agree with Byron that it is important to blend the sub with the mains with respect to frequency cut-off, phase and loudness. My sub is a Paradigm Signature Servo, which is self powered and has separate controls for frequency cut-off, phase and loudness.

I don't know how to optimize time delay (phase) as close as Byron (within one miilisecond) other than just by using my ears to minimize phase cancellation at the cross over point. As regards FR, my mains start to roll-off at 40-50Hz, so I set my sub cut-off frequency at 34-40Hz. So . . . after phase response/time delay and frequency cut-off is adjusted as best as I can, the only adjustment remaining is loudness. I generally don't fool with loudness very often, but may based on source material.

FWIW, using one sub in a two channel system presents two issues in my rig. The first issue relates to summing the stereo signal from the pre into mono for the sub. That topic has generated a lot of discussion is several threads that I participated in, e.g., impedance matching and asymetrical loading of the pre's balanced and SE outputs.

The other issue relates to the placement of the sub. I don't have a lot of placement options in my basement. However, I am able to place the sub in line with the fronts of the Mains and I aim the sub at my left ear. As a result, it's not to difficult to adjust phase. Even though it's hard to hear the directionality and stereo effect of very low frequency sound, I can actually feel (though not hear) high SPL in my left ear. A cheap SPL meter I bought from Radio Shack confirms this. There is another thread on A'gon which discusses the concerns of listening to music at sustained high SPLs.

Anyway that's my experience with a single sub in a two channel system. Hope it helps. Good luck.

Hi Bryon, great post! I have a practical question. As I mentioned above, I don't have a lot of placement options for my sub. So, my sub is aimed directly at my seating position and sits about 4-5 inches behind the mains.

In addition, I summed the channels into mono for the sub, so I don't think I can reverse polarity as you suggested, or perhaps I still don't understand how the method works. Having said that, my sub has a built in phase adjustment capability which I adjust to achieve the loudest bass when playing music that puts out a lot of bass. The thought is that I am trying to reduce phase cancellation at the crossover point.

Anything else I can do to improve the bass with my sub?? Thanks.

To All --reporting back on results of using impedance buffer. Ok, I hooked up Tom Tutay's buffer. As a threshold matter, let me say a couple of things about Tom. He is very professional and knowledgeable -- a real gentleman. He turned around my order in lightening time. The shell of the buffer device is made wholly of metal, and is about 9" x 5" x 2". By all appearances from the outside, the device seems to be very sturdy and well made.

Now . . . as to how it works. As you can see from the posts above, the device was designed to: (a) load my Ref 3 symetrically (i.e., Main 1 and Main 2 in balanced mode), (b) sum the left and right channels without shorting the Mains since I am using only one sub, and (c) raise the impedance level of the two Mains to a level that better matches ARC's design specs.

As to tube life, I take it on faith based on conversations with ARC that by reducing the load on my Ref 3's outputs, tube life will be extended. I will have to wait and see.

As to sound quality, I can say with 100% certainty, my rig does NOT sound worse. Does it sound better?? Yeah, I think so. I think the imaging, detail and sound stage are a little bit improved. The highs seem a little smoother and better refined. But quite honestly, I don't think the change, if any, is day and nighgt. It's just subtle, kinda like a tweek, maybe two or three tweeks.

Now the impact on bass is more noticeable. Although I removed one active artifact from the system and added another, I think the X-30 crossover/controller did more than the buffer because the X-30 could adjust loudness, phase, cut-off and summed the channels. By contrast, the buffer has an active unitary op amp that raises the input impedance and just sums the channels. That's it.

When I first inserted the buffer, I initially thought something happened to the bass output from the sub. On Tom's suggestion, I tried using the old hook-up again by running an SE I/C from one of the SE Mains off the Ref 3 directly to the sub (sans X-30). I then ran the Ref 3 in mono mode to sum the channels. Interestingly, the bass seemed equally lame this way too.

Then I realized what was going on. I had set the cutoff frequency on the sub at 35 Hz to blend into my fronts. What I realized is that there simply wasn't very much going on below 35Hz in my source material. By contrast, when I raised the cutoff frequency -- bass galore.

So realizing what was going on, I then critically listened to some bass heavy source material, e.g., Norah Jones CD and Solti conducting Chicago Symph Orchest., Beethoven 9th 1st and 4th movements LP. Tons of bass in these source materials. But when I raised my sub's cutoff to about 50 Hz I had more than enough tight and smooth bass -- NOT boomy.

In summary, Tom Tutay of Transition Audio Design is a great resource for audiophiles. He is not limited to just buffer devices, but can custom design many different types of devices. Keep him in mind. Tom's phone number is: (850) 244-3041.