Sub on a 2 channel amp

[Marks57]

I have a Musical Fidelity A3.5 Int Amp which has L&R PreOuts on it. I know they are intended to drive another amp, but couldn't I run line level into a subwoofer? I know it's not the same as on an A/V receiver that has a dedicated SW preout and that the line level signal will be the full sound spectrum instead of a SW preout that has internal crossover settings in the receiver.....but if the sub has crossover settings, wouldn't this "bleed off" everything I didn't want....say above 80-100hz?

Thanks for any input.

Mark

[Otto]

Hi Mark,

That will work fine, and that's exactly how most of us ran sub/sat systems before there were 5.1/7.1 receivers. You won't have remote control of the level feeding your sub, but that's OK. If you find you have too much bass (or too little) on some program material, you might have to get up and adjust your sub's output level knob. A minor hassle.

Also, there's a remote control thing that Wayne A. Pflughaupt uses. That would come in handy if you did indeed want control over the level feeding the sub. Sorry I can't think of the name of it right now... EDIT: it's called the Chase Technologies RLC-1 remote line controller (check Google/eBay if you're interested).


So, yeah, use your sub's crossover to filter out the highs that your mains are handling and go for it.

[Marks57]

Thanks Otto,

I actually brought home a Sunfire 10" sub from where I work last night to test it out. It does work and it does sound good.

The question I have for all of you 2 channel guys with a sub is....where do you place your sub? I connected the sub with 2 line levels from the preout on the amp to the line level in on the sub. The cables were only long enough to place the sub to the immediate left of the audio rack. I could tell the sound was a little off, meaning my towers have such good imaging, but I could tell that the low frequencies were slightly off the center axis.

Should I use 2 subs or place the sub on a side wall firing across the room? Also, I am planning on building a custom cabinet with 3 vertical sections. I could leave the bottom center section open to the floor and put the sub in the direct center of the 2 towers (front firing of course). What do you think about that idea?

What do you do?

Thanks, Mark

[Otto]

Hi Mark,

What's your crossover point? If it's low enough you shouldn't be able to place the sub's location that easily. 80 Hz is a well-accepted upper limit for this, but I like to go lower. I have my mains crossed at 40 Hz using an IB sub, and I can't tell where the bass is coming from (the IB is outside the right main).

Placement is something that you can play around with, and there are no hard and fast rules. A lot of people place the sub in the corner to take advantage of some room gain. Some stereo-only guys actually run two subs in stereo. I would consider that if I had a dedicated stereo-only room that used subs. The center position you described would also help your imaging.

I'd say that for now, just buy a long cable and play around with placement until you find something that really works for you. Play around with that output level knob as well, and the phase knob if you have one. What mains are you using?

Good luck.

[brucek]

Since your mains are fed full range and are not crossed with a HP filter, then the manual crossover on your sub will have to be quite low to ensure the common frequencies aren't additive creating a peak. This is likely what you heard.

If the sub is crossed low (i.e. < 60hz), then its location with respect to sound-stage is irrelevant, since it won't be localizable. Place it where it integrates best with the room and the mains. Use REW and do a response check to set it up properly.

brucek

[norpus]

brucek wrote:

Since your mains are fed full range and are not crossed with a HP filter, then the manual crossover on your sub will have to be quite low to ensure the common frequencies aren't additive creating a peak. This is likely what you heard.

If the sub is crossed low (i.e. < 60hz), then its location with respect to sound-stage is irrelevant, since it won't be localizable. Place it where it integrates best with the room and the mains. Use REW and do a response check to set it up properly.

brucek

Agreed. Have a look at the -3dB spec of your mains, that might be a starting point for the sub crossover
If you don't use REW, then a couple of warble test tones an octave above and below might be useful for level checking?

[audiobomber]

Marks57 wrote:

Thanks Otto,

I actually brought home a Sunfire 10" sub from where I work last night to test it out. It does work and it does sound good.

The question I have for all of you 2 channel guys with a sub is....where do you place your sub? I connected the sub with 2 line levels from the preout on the amp to the line level in on the sub. The cables were only long enough to place the sub to the immediate left of the audio rack. I could tell the sound was a little off, meaning my towers have such good imaging, but I could tell that the low frequencies were slightly off the center axis.

Should I use 2 subs or place the sub on a side wall firing across the room? Also, I am planning on building a custom cabinet with 3 vertical sections. I could leave the bottom center section open to the floor and put the sub in the direct center of the 2 towers (front firing of course). What do you think about that idea?

What do you do?

Thanks, Mark

What main speakers are you using? As others have said, it sounds like you're crossing the sub at too high a frequency. Like most of us when starting out, you probably also have the sub level set too high. Did you try adjusting phase? I recommend a Radio Shack SPL meter so you can see what's happening. Well worth the investment.

[audiobomber]

Otto wrote:

Hi Mark,

That will work fine, and that's exactly how most of us ran sub/sat systems before there were 5.1/7.1 receivers. You won't have remote control of the level feeding your sub, but that's OK. If you find you have too much bass (or too little) on some program material, you might have to get up and adjust your sub's output level knob. A minor hassle.

Also, there's a remote control thing that Wayne A. Pflughaupt uses. That would come in handy if you did indeed want control over the level feeding the sub. Sorry I can't think of the name of it right now... EDIT: it's called the Chase Technologies RLC-1 remote line controller (check Google/eBay if you're interested).

What you said would be true if he were using the tape outs, but since he's using pre-outs, the sub level is controlled by the volume setting on the preamp.

[Otto]

audiobomber wrote:

What you said would be true if he were using the tape outs, but since he's using pre-outs, the sub level is controlled by the volume setting on the preamp.

Well, yeah. I meant that he wouldn't have independent control of the signal going to the sub, as when using a sub out or an LFE out on a multichannel processor.

[audiobomber]

Otto wrote:

Well, yeah. I meant that he wouldn't have independent control of the signal going to the sub, as when using a sub out or an LFE out on a multichannel processor.

So you meant he'd have to get up to adjust the levels during the setup stage only. OK, now I get it.

[Chrisbee]

I like the use of a stereo amp + sub and I am still using stereo with my 4 x 15" IB using an active stereo crossover on the main speaker channels.

Adding a 3.1 processor for center and rear channels for films makes me a bit of an HT dinosaur.

The obvious advantage (to me at least) is higher sound quality.

Place your sub between your main speakers and don't take anything for granted.

With my SVS cylinder I used a 60Hz crossover despite my 40Hz floorstanders playing fullrange.

Try REW to see what is really happening to your frequency response at the listening position.