hooking up a sub

[gogofast]

first, let me ask you this:

is using a sub somewhat like using "loud" button on your receiver?
will it unnaturally modify the low frequency? will it ruin your perception of good dynamic sound once you get used to the sub?

second, when hooking up a sub,

lets say i have a powered sub with "line level in", "xo frequency control, and "high level in". also a preamp with second set of output. do i just connect the preamp second output to sub's line level in and adjust the xo level at the sub? what is the high level in for (speaker wire)?

will doing this effect the sound of main speaker in any way? (since two preamp outputs are used)

thanks for any input.

 

[Zilch]

No.

Yes.

No.

 

[gogofast]

t
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! z i l c h

 

[Inspiribomb]

I can pretty much echo Zilch's response.

However, regarding #1, the way many people implement subs, yes it can "ruin" the rest of the music.

 

[viggy]

I've also just begun with subwoofers, so I like your questions.

It's easy to ruin things with the wrong settings, for sure. If the xo setting overlaps the frequencies your mains produce, or if the sub volume is higher than the mains, that produces a sort of "loudness" effect.

I suppose that settings vary according to what you're listening to, the room and plain old personal preference. I like to think of it as extending the freq range while adding nothing that shouldn't be there.

 

[zenith2134]

Well, I think Zilch's opinion is a vast generalization. Then again, the OP's question is kind of broad.

Using a sub can dramatically IMPROVE a system's performance. Assuming the system needs bass reinforcement to begin with of course. If you simply toss a sub into the mix and turn it to '11', then yes it can ruin the whole shebang.

Also, I'd rather have a hole in my system's bass response instead of adding a crappy sub. Nothing I hate more than boomy/flabby bass. The room's resonances are an integral part of determining whether or not you would benefit from a subwoofer.

 

[gogofast]

lets say that my speakers are capable of going down to 40hz. by setting the xo for the sub at ....say 50hz, will my main speakers perform better more efficiently? and are usual recordings go down below 40hz a lot?

if i am missing the very low of the low frequencies by just using what speakers i have, i'd love to add a sub to hear what i've been missing. if all it will do is just amplify what's already there in my current speakers, i won't bother.

i guess that's what i wanna really ask.

 

[zenith2134]

Well, if you set the xover so you bypass the low frequencies (sub-80Hz) on the main speakers, then use the sub for those frequencies, it would be the best situation IMO.

By doing this, you're freeing up amplifier power on the mains allowing for extra headroom (improved dynamic response) and also to a lesser extent, reducing the speakers' distortion since there will be less demand put on them. Less cone excursion = less driver distortion with most speakers.

And, as a sidebar, not many recordings have sound below 40 or 50 Hz.....some do of course, but even so, it may be at -2 or 3 dB anyway. An active subwoofer may or may not be to your liking.

Maybe try a store or dealer with a nice return policy ? Many are understanding of our desire to test and audition gear in the interest of bettering our system.

 

[Zilch]

lets say that my speakers are capable of going down to 40hz. by setting the xo for the sub at ....say 50hz, will my main speakers perform better more efficiently? and are usual recordings go down below 40hz a lot?

if i am missing the very low of the low frequencies by just using what speakers i have, i'd love to add a sub to hear what i've been missing. if all it will do is just amplify what's already there in my current speakers, i won't bother.

It's not a brick wall. Speaker LF does not drop off precipitously below a given frequency. Vented alignments fall faster than closed ones. Bass response is typically specified at -6 dB, i.e., audible, but only marginally so, and generally regarded as the limit of usable response. Below -10 dB, there's effectively nobody home.

Generally speaking, therefore, unless you're augmenting with a sub, you're missing much of the audio spectrum's lowest octave, 20 - 40 Hz, and perhaps more in the next higher one, 40 - 80 Hz.

And yes, most contemporary recordings, and many remastered vintage ones, contain substantial program material in this range.... :yes:

 

[Clmrt]

"...will my main speakers perform better more efficiently?"

It sounds like you are thinking of active crossover / bi-amping. This does not occour when you simply add a sub with that second pair of preamp outputs. You need something that will remove the bass from the mains at the preamp level for that.

Examples would be Outlaw's ICBM, an HT receiver, typical outboard crossover, etc.

I've never seen it confirmed that the speaker-level inout on a sub is integrated with it's crossover control. Full range in, full range out, with the sub picking up it's signal in the meantime.

 

[Fred Sanford]

"...will my main speakers perform better more efficiently?"

It sounds like you are thinking of active crossover / bi-amping. This does not occour when you simply add a sub with that second pair of preamp outputs. You need something that will remove the bass from the mains at the preamp level for that.

Examples would be Outlaw's ICBM, an HT receiver, typical outboard crossover, etc.

I've never seen it confirmed that the speaker-level inout on a sub is integrated with it's crossover control. Full range in, full range out, with the sub picking up it's signal in the meantime.

It's often full range in, high-pass out from a fixed frequency maybe 80-100Hz on the speaker-level inputs/outputs. Problem is many manuals don't give you that specific info.

je

 

[Clmrt]

Plus then, aren't you still wasting the main amp by generating the sub-80hz bass and just pushing it into a cap?

I've always wondered that.

 

[Fred Sanford]

Plus then, aren't you still wasting the main amp by generating the sub-80hz bass and just pushing it into a cap?

I've always wondered that.

Yep, I'd guess that you are. Helps the main speakers, but doesn't help with main amp's headroom.

je

 

[Zilch]

Simple sub:

Here's an easy and inexpensive approach to a passive sub:

http://manuals.harman.com/JBL/HOM/Technical Sheet/S1 ts.pdf

Not the cab, particularly, the elements -- DVC woofer and six passive components.

The balance is not adjustable, but there are ways to work with that, for starters, the woofer sensitivity.... :thmbsp:

More generally, Geddes teaches to simply use a closed-box alignment in the mid/high boxes (close the port(s) with ZilchPlugz) in lieu of highpass and use multiple subs with low-order lowpass filters. Gotta be sure your mid/high speakers can handle having the ports closed, though.... :yes:

 

[Markw]

I think you're headed in the right direction here.

lets say that my speakers are capable of going down to 40hz. by setting the xo for the sub at ....say 50hz, will my main speakers perform better more efficiently? and are usual recordings go down below 40hz a lot?

if i am missing the very low of the low frequencies by just using what speakers i have, i'd love to add a sub to hear what i've been missing. if all it will do is just amplify what's already there in my current speakers, i won't bother.

i guess that's what i wanna really ask.

First off, I'm talking about music here, not HT. Different rules apply there.

When I ran a sub with my maggies, which certainly needed a bit of help in the basement, I split the preamp output and ran one leg (full range) to the mains power amp and the other leg to the subwoofers crossover/amp input. I had nothing connected to the sub's output.

The speakers rolled off politely, starting around 70 hz or so. They were only rated dpwn to 40 hz or so to begin with.

I would up setting the sub's crossover (which was now acting as a low-pass filter) to around 50 hz. This way, the main's rolloff at the bottom intersected ths sub's rolloff at the top. It takes a bit of time and patience kerfutzing with the Xover frequency and level but it's worth it when you get it dialed in.

This way, the sub only took over where the mains started to run out of steam, thereby simply extending the system's response down to around 25 hz or so.

There should be no "reinforcement" of what the mains handle. That's not what a sub is supposed to to. It should simply fill in the low end where the mains stop.

Most times the sub is un-noticed. In fact, the only way to really notice it (and in any properly set up system) should be when it's switched out and music with a low end is playing.

 

[gogofast]

thanks markw.
i've heard a few set up with subs and i thought it was a totally different experience.

so, what's the rule of thumb when setting the sub xo point?

 

[Markw]

thanks markw.
i've heard a few set up with subs and i thought it was a totally different experience.

so, what's the rule of thumb when setting the sub xo point?

Trial and error.

My favorite trick is to put on the title track of Bela Fleck's "Flight of the Cosmic Hippo" and use it's fretless bass runs for a general guide for a rough initial setup. When it'sset properly the run should be the same level down to the bottom. After that, just play around with other recordings to fine tune it, if you think it needs it.

Oh, another variable to contend with is the sub's location. It may be better over here than there, or vice versa.

It took me afew days of on-and-off kerfutzing with the three variables (Xover, Level, and location) before I finally zeroed it in, but it was worth it.

Remember, the sub should not call attention to itself. It should simply invisibly take over when the mains fall off. You should only be aware of it's contribution when you turn it off and there's some deep content, if you know what I mean.

Remember, you only want it to fill in where the mains drop off.

 

[Clmrt]

If you have an SPL meter, it would help get the phase correct as well.

If your main's measured -3db is 40hz, I'd find a 63hz tone and find the phase where the sub adds. Switching the phase 180 degrees should show where it cancels or adds. Find the correct alignment then dial back the XO to remove the additional SPL.

If there's not enough bass, add some level and reduce the xo slightly.

If there's too much bass, reduce the level and perhaps add a touch of XO.

Listen, repeat.

Or buy a Velodyne with autocalibration and push a button...*dream*

 

[MikeCh]

It's often full range in, high-pass out from a fixed frequency maybe 80-100Hz on the speaker-level inputs/outputs. Problem is many manuals don't give you that specific info.

je

This has been my experience as well, that there's a high pass filter built into some powered subwoofers when utilizing the speaker level inputs. If you're wanting to truly add power amp headroom then you need to add a seperate high-pass filter between the preamp outs and main ins.

I use a little M&K HP-80 for this purpose and it works very well.

 

[gogofast]

If you have an SPL meter, it would help get the phase correct as well.

If your main's measured -3db is 40hz, I'd find a 63hz tone and find the phase where the sub adds. Switching the phase 180 degrees should show where it cancels or adds. Find the correct alignment then dial back the XO to remove the additional SPL.

If there's not enough bass, add some level and reduce the xo slightly.

If there's too much bass, reduce the level and perhaps add a touch of XO.

Listen, repeat.

Or buy a Velodyne with autocalibration and push a button...*dream*

you mean one of those $1200 sub?
it'll be probably cheaper to pay for a audio tech class and learn how to do it manually. i'm not ready to spend more than a few hundred. i was looking at partsexpress.