Sub Question

A properly selected and integrated powered sub will reduce distortion in the mains in 2 ways:
1. You can cross-over to the mains at a frequency that will keep the main woofer from working at its extreme lower limit;
2. If you cross over to the sub BEFORE the main amp, you can reduce the power demand on the main amp, which will most likely allow it to operate more in its linear region.

I also have a sub-woofer (JM Labs SW900) and mains (Acoustic Zen Adagios), but my sub does not have crossover outputs to the main amp. My pre has 2 sets of main outs, I use one to the sub and one to the main amp. Therefore, the full frequency range goes to the main amp/speakers. What is the best way to roll-off the lows to the mains in this situation ?

There is a widespread school of thought that I subscribe to that it is better to run the main speakers full range rather than use a crossover. If you do use one it is better to insert a passive attenuation one in the signal going to the main speaker amp. While rolling off the main speakers will allow you to play them louder the crossover will degrade the sound. This does not bother the HT fans who value dynamic range and think special effects are more critical than music. I would look on the DIY audio sites for advice on constructing a passive attenuation network. They will also have info on who could build one for you.

It's funny but all the responders are correct in their approach. My approach to solve the problem was to have a pair of passive devices made with a (RCA input and RCA output)plugged into the input of the power amp and my interconnect pluged into the device(s). One for R and L channel. This device rolled the speakers off in a controlled manner and you choose the frequency you want it to roll your speakers off. All that is needed is the input impeadance of your amp and what frequency you want your main speakers to roll off. When one of the responders spoke of distortion with the rolling off of the bass from your main speakers it frees the speaker up to produce clearer midrange, mid bass and top end frequencies with better dynamics too.

This can be done on solid state and tube amps but the device is custom to the amp you have it made for. Tom Tutay made mine for my Spica TC 50's and It works well for my TC60's too because they are rolling off around the same frequency. By it rolling off the bottom end of the satellite at say 40Hz the subwoofer takes over from there. Understand that rear ported speakers are harder to blend with a sub than front ported speakers. My subs are acoustic suspension and my TC60's are rear ported. After tinkering and placing them in various positions I have them blending pretty darn good. You have to play with the phasing. Oh, I have two Dali Suite 1.2 12" subs. They are not boomy and are pretty articulate. My TC 50's blend even better than my 60's and they are acoustic suspension. I still prefer the TC60's. This actually gives you more clairty, soundstaging, and depth of sound stage too from your main speakers thus allowing the sub to take over in the bottom range. This is one way to tackle the problem and it is effective. You can call Tom @ 850-244-3041 10am to 8pm CT.

I would never give up my pair of Vandersteen 2Wqs. These subwoofers blend seemlessly with my mains (now Ohms, but previously they blended equally well with my Vandersteen mains). Check my review of these in the review section. Properly executed and set up, a dedicated, powered subwoofer can do things that most full range speakers simply cannot. I suggest you read about them at the Vandersteen web site. Their design is somewhat unique and addresses two major issues of subwoofers: crossover and placement. I got mine used here on Audiogon, but even new, they are a fantastic value for a music-oriented sub (as opposed to home theater), IMHO.

Rythmik Audio in Austin Texas.....Gread

Thanks for the responses so far, but I don't think we have adressed my original question. Does a sub indirectly help or improve the sound or frequencies by taking pressure off of the speakers?

Indirectly, yes. The sub by itself does not relieve the burden of reproducing the last one to two octaves. The passive attenuation circuit does that by filtering these low frequencies so that they never reach the main speakers. That way, the mains can concentrate on the easier-to-reproduce signals above 80Hz or so.

If you use high-pass in sub, it will take take pressure off your mains.

Best if you do this with stereo subs.

Kclone,

To repeat and restate:

If you put a crossover unit ahead of the main speakers it will reduce the burden on the main speakers' woofers by attenuating the bass signal they receive.

If you put an (active) crossover unit ahead of the amp feeding the main speakers, it will reduce the burden on both the main amp and the main speakers.

If you use no crossover on the main speakers - there will be no reduction in the work they do at low frequencies.

Subs can be wired in any of these ways, so the direct answer to your question is:

"It depends upon how you choose to wire the subs".

Marty

FWIW, I personally use an active x-over ahead of the main amp. Not only does this minimize the "work" of the main amp and the main speakers' woofers, it allows me to use digital room correction for the bass signal that is sent to the subwoofers. IMHO, this is a great solution. Other posters to these threads sometimes prefer a different approach. Different strokes....

Zanon, would a Rel be a high pass sub? I tried to google but came up empty. thanks.

Kclone: RELS are unusual in that they recommend binding the sub inputs to the binding post of the speakers.

Therefore, I don't think they introduce any crossover into the circuit.

It may be possible to wire them in different ways. Look at picture of backpanel and see if there is crossover.

Personally, I would get two subs and highpass them in series to my mains, then set up the room carefully. I would get sealed subs if I could afford them.

Well, IMHO, I have found my subs. to not only provide
a solid foundation, indeed taking the pressure off the
main speakers.

My personal Biggest surprise, is how the vocals are

much more full, and life like.

Never expected that. Huge +!

All instruments, become much more distinct and dynamic.

Given the right subs. in the right set-up, adjusted

just right, they (the subs) will disappear.

Most folks, NEVER imagined I use 3 subwoofers.

Because, I am not out for the "one note bass"

like the people get with the 18" sub. in a Civic.

But only YOU can decide, what is BEST for You!

I can assure you, that music, and movies, will

NEVER be the same, with the likes of a couple

of Velodynes best subs. an 18" an 2 each 15"'s

they are just idling, and they smooth each other out.

Flat at about 11 hz. which is plenty deep IMHO,

especially playing organ music.

Careful! Crockery, and dishes, have been destroyed.

"Seismic", becomes a word that your friends will,

start using, when say a 44 magnum is fired in a movie,

you HEAR what it REALLY sounds like.

Automatic weapons, are frighting, as they sound so real.

Check out some subs. in your listening room, listen,

your ears will let you know, when you are in the

"Butter Zone", where it is ALL Good!

Not exaggerated low frequency response, but just

"Life-like" reproduction.

I Love Music

OP - I agree with your friend. When you properly set up a sub (preferrably two) it will not be noticeable until you turn it off. That is how things should, and can work out for you. I'd get one (or two) and an SPL meter and sub freq. tracks to place and dial it in so it does not overpower/ interfere with your mains, but enhances them. Once this is achieved (not difficult, just a little time consuming), you will likely never want to not have a sub again, almost regardless of how low your mains can go.