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Possible stereo sub setup?

826 Views 9 Replies 4 Participants Last post by  Tom Rosback
Hi, great forum! I've been lurking about for quite a while, and I've learned quite a bit from you guys.

I have an Onkyo DS989, and I'm very happy with it. One drawback though is the lack of stereo sub pre-outs (Maybe some see this as an advantage, I'm no expert). I've read here and elsewhere that stereo subwoofers can add significantly to the soundstage, so I've been trying to conceive of a way to do it with this receiver. I'd like to find out if my ideas make any sense, before I purchase a pair of subs.

Again, I'm no expert, so I may be unaware of a serious flaw in my plan. That's why I'm here. http://www.avsforum.com/ubb/smile.gif

The 989 uses jumper plugs in the L, R, and C pre-outs. I don't know how common this is, so please excuse me if I'm stating the obvious. I was thinking of using a couple of Y-cables to replace the jumper plugs on the L and R pre-outs. That is, I would plug the double end of each Y into where the plugs would go. So, in essence, the Y-cable would act the same as the jumper plug, only now there would be an output on the single end of the Y. The single ends would go to the left and right subs respectively, using the subs' internal crossovers. Under setup, Subwoofer would be set to None and the mains set to Large. I'd be using subwoofer Y-cables from bettercables.com.

One advantage I see would be complete control of the crossover frequency as opposed to depending on the 989's sub-out. And basically I just think it would cool if the subs were acting as pure extensions of the mains which fall off around 60Hz.

Is there anything stupid or foolish about this idea? Go ahead and tell me, I can take it. Will I end up frying something? Even if it would work, is there some reason why you still wouldn't do it? Do you think there would be serious signal degradation to the mains? Any thoughts are appreciated.


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You are right on target. Nothing stupid or foolish. There are a couple of things you should consider.....(aren't there always?)

1.) You'll also need to make sure your receiver has an option to route the LFE signal to the left and right mains when no SUB is selected in the speaker setup menu.

2.) Some subs have built in high pass crossovers for the main speakers. Do yours? The advantage with this setup is that very low frequency info won't appear on your mains. Wiring is easier because you run speaker level into the subs, then into your mains via the sub's crossover. If your mains have small woofers (<8" dia), you should strongly consider this option. Bass in some movies is really loud. Small woofers will overload and sound muddy. If your sub(s) don't have a high pass crossover, you can put a passive high pass crossover in the pre-outs of your receiver, in line (series) with the Y-cables. Audio Concepts, Inc in Wisconsin sells a passive high pass crossover for about $75.

Finally, borrow or buy a sound level meter and use it to set initial levels, crossover freq's, and phase on the subs. Then fine tune and experiment. I think you'll like stereo subs. I sure do.

Best regards,



Tom Rosback
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It sounds like a good plan....the only snag I can think of is that the 989 may sense the L&R preouts are being used and assume that you are using an external amp and shut down the L&R internal amps. My suggestion is to go to Radio Shack and buy some real cheap y-connectors and try it out before investing in more expensive "Better Cables".


Thanks for the replies,

OK I plugged in some cheap Y adapters and the internal amps stay on, so I think it'll be alright.


Thanks so much for your help. Yes, the 989 routes the LFE to the mains when no sub is selected. My mains are LARGE, so I definitely want to run them as such.

I just had another idea. What if, in addition to the Y-cable setup I described, I were to enable the Sub in Speaker Config and then connect the sub pre-outs to each subwoofer as well. This would direct the LFE only to the subs, while the Y-cable setup lets the subs handle what the mains don't do so well (<60hz) in stereo. Follow me?

I'm wondering though if it would be bad thing to be using the internal sub crossovers while connected to the sub outputs on the 989. If the crossovers are set to 60hz for the Y-cables, would it be sonically unwise to plug in the 989's sub outputs as well? Is that one too many crossovers? Would I need an external low-pass crossover in line with the Y-cables, so I could disable the sub's crossover?

I'd start testing this stuff but I don't have a sub yet. My head hurts. http://www.avsforum.com/ubb/confused.gif

Thanks again,

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Your plan to run the receiver sub outs to the subs, in addition to the y connector main setup, will have the advantage that the mains won't see any LFE. That's a good thing. It'd be easy to try. LFE stops dead at 80 Hz, little to no info above that frequency. So you could leave the sub crossovers set at 60 Hz and not lose any bass. You won't need to disable the sub's crossovers, so you won't need an external low pass.

The only caveat would be that, if your center and surrounds are SMALL, their bass will be re-directed to the subs, which are crossed over at 60 Hz. So you'll need a center and surrounds that go down to 60 Hz.




Tom Rosback
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I also agree with stereo subwoofers. I know several OBJECTIVISTS, serious experts in the field who feel that a minimum of 2 point source subs is necessary. Timing differences are audible and do create a more spacious, realistic sound field. Summing any channel to mono as the LFE does, is inferior. In fact, I'm getting angry again. I have to stop myself from posting the LFE is lame thead again. DOH I can't help it now! The most superior audiophile format would be multichannel (0-20,000 Hz, no LFE)--

Basically, think of an Erich Kunzel Telrc disc in 5.0, 6.0, 7.0, 8.0 http://www.avsforum.com/ubb/smile.gif

It gets trickier for evey point source subwoofer one implements. You can make the room response better, in addition to achieving 'stereo' spaciousness. However, it is much more easy to make it worse. all that mens is that anything beyond two point source subs would require proper measurments and experimientation with placement. Depending on the distance between the front 2 subs, you will have a coupling of the frequencies from "x" frequency and down... Don't have the formula off hand for wavelegth and frequency.. In other words, you will still get the benefit of having increased SPL in the low similar to what you would from stacking in the same corner... but only for "x" frequency and below... again depending on the distsnce between the front Left sub and front right sub. I will be using (2) point source subs in front left and front right (2 Black hole subs in each corner vertically stacked).

[This message has been edited by Health Nut (edited 11-05-2000).]
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Thanks Tom, I forgot about my little surrounds. But it doesn't matter, because apparently, according to the Secrets review www.hometheaterhifi.com/volume_7_3/onkyo-tx-ds-989-receiver-8-2000.html , the 989 sends the LFE to BOTH the subs and the mains (if set to Large). This pretty much blows the advantage of using the sub outputs along with the Ys, since the LFE would be doubled in the subs. Of course setting the mains to Small would defeat the whole purpose to begin with.

The best plans are usually the simplest, so I'll stick to my original scheme with the Ys alone.

Health Nut, sorry I didn't mean to set you off in a frenzy. http://www.avsforum.com/ubb/eek.gif http://www.avsforum.com/ubb/wink.gif


"LFE stops dead at 80 Hz, little to no info above that frequency."

I don't believe that is true. It depends on the person doing the mix.

I'd like to see where it is specified that 80 Hz is the limt of the LFE.

Further, stopping dead implies a brick filter at 80 Hz. I've seen no evidence to indicate either. I've seen a bandwidth specification for 20-120 Hz, that's it. I've certainly heard a few DVD's with ample 100 Hz info in the LFE.

If there is a built in filter specification as you claim, please state the point, the slope, and the reference you obtained this information.



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Tom your point about the LFE channel stopping dead at 80 Hz is incorrect. The LFE stops dead at 120 Hz:

There are arguments as to when a subwoofer can become audible... I believe that point to be much closer to 50 Hz, not 80 Hz.. especially considering that a crossover is a slope, not a brick filter. Setting a crossover to 4th order 80 Hz still allows for a fair amount of upper frequencies to be produced via the subwoofer.. with 80 Hz 4th order,-24 dB down at 160 Hz.

The LFE as it stands allows for up to 120 Hz bandwidth... This is too high. At the very least EXTEND THE BANDWIDTH IN THE OTHER DIRECTION. The LFE, IMO, should be spec'd from 1-50 Hz fourth order, no subharmonic filtering period. Hey, going from 20 Hz to 10 Hz is a FULL OCTAVE. Going from 10 to 5 Hz is also anothe full octave... I'm not aware of any 'physical' (technical) limitation for the LFE channel to go as low as Red Book Cd (Can go to DC 0 Hz, a clipped recording )

I need to separate out the differences between LFE limitations and LFE poor implementations. These questions need to be answered:

1) Is there any subharmonic filtering built into the LFE spec? Can somebody place frequencies down to DC (0 Hz)?

2) The LFE is defined as having a bandwidth of 20-120 Hz.

What prevents an engineer from placing above 120 Hz information in the LFE channel? How is the LFE crossover actually provided? What slope is used for the LFE? How is the LFE handled in terms of the crossover in all regards: recording/encoding, and at the processor/playback level?

These are answers which need to be determined in order to understand how the LFE track can be improved.

ANSWER in article:

"For Dolby Digital, the LFE channel carries additional bass information from 120 Hz on down. This is not a roll-off but a digital brick wall (i.e., no 121 Hz info), so the content is usually rolled off by the sound engineer starting around 80 Hz for a smoother blend."

This tells me that the sound engineers are to blame.

Perhaps many of the poor LFE tracks used the LFE channel as a crossover, instead of starting an early rolloff. The rolloff (crossover point determined by the mixing artist) needs to be around 50 Hz fourth order, not 80 Hz.... this would yield a significant improvement.

Further, assuming ther are no limitations in the 'low end', Hollywood needs to strive to use effects that are more naturally recorded and capture the entire subsonic frequencies. Can someone verify that there is no 'filter' built in to the LFE track...
http://www.hometheaterhifi.com/volume_7_2/feature-article-misunderstood-lfe -channel-april-2000.html

[This message has been edited by Health Nut (edited 11-06-2000).]
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Chris, I stand corrected. I cannot find any info on LFE LPF turnover frequencies, slopes, shape, etc. I confused hope with reality!

Thanks for providing a more definitive response.

Shouldn't impact the original topic of this thread.


Tom Rosback

[This message has been edited by Tom Rosback (edited 11-08-2000).]
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