Hooking up TWO subs

I know there are some out there that use more than one sub in their systems. I have two subs and was wondering how do I hook up two subs to my system. My receiver
(Denon AVR-2803) has one sub out on the back panel that I use to hook a sub cable to one sub and thats it. So how does one implement the second sub? Could I use a "Y" adapter on the sub out on the receiver and plug in two sub cables, one to each of the two subs? If not, why not and how is this done and how do I tell the receiver that there are now two subs instead of one?

Am I making any sense???

Thanks guys and gals.
Randy

 

Unless your receiver supports two subs, you will have to use a Y adapter. Some receivers support dual subs. I know that some of the Adcom recievers have dual sub jacks, but unfortunately they are in mono. This kind of defeats the point if you ask me. Obviously if you're only running home theater there is only one sub output. Running two subs out of this output still makes some sense, but it is for listening to music where the dual subs really helps. Some make the claim that the bass frequencies that come out of subs are onmidirectional and there is no point to having stereo subs. I totally reject this. I have stereo subs on my main system and I couldn't imagine having only one. In my case the subs are fed off the main output feeds and are basically a way to extend the lower frequency response of the speakers. You could also do this with home theater and tell the receiver that there is no sub installed. This would allow you to route the LFE channel to both subs and would allow for stereo subs for straight music.

Of course you'd have to tell the receiver to route the LFE to the main 'large' speakers. I can't say for sure how this would compare to a single sub system for home theater but it would certainly do better for music if your main speakers were bass shy.

 

My Marantz receiver does support 2 subs but I only decided to use 1 sub on it.

 

Is it really that easy? I guess I am trying to make this more difficult than I have to. Thanks, I will try the "Y" adapter route and see what happens.

 

Be careful when hooking up two subs--you can actually REDUCE your bass output this way if you don't pay careful attention to where you place the subs in the room. This is because the bass frequencies emanating from the subs interact with the room and can create standing waves. This standing wave effect can cause dips in frequency response and even cancel out the bass frequencies! Some speaker manufacturers claim that using more than one sub decreases the standing wave effect, but this is not always true.

 

Of course this is true. Be sure to make sure that the subs are in phase with each other and in phase with the larger speakers. That said, what Billy suggests is very true. Wave propagation at low frequencies in a small room can cause all kinds of combining issues with standing waves that can't be easily dealt with by flipping phase switches. Some subs have variable phase controls which can help in some cases. But you really can't easily correct standing wave problems with electronics. Speaker placement is by far the best way to accomplish this. It's also somewhat important to keep the sub drivers in the same plane as the main speakers. If they are farther away than the mains, there will be a lag between the main signal and the sub signal. That can cause problems as well.

 

The best answer to your question really depends on knowing more about the subwoofers you have, and whether they came with their own crossover network(s). And then, do the subwoofers allow the user to select frequencies, adjust volume levels and so on.

Using a Y adaptor defeats the purpose of using two subwoofers. Since the subwoofer output on your receiver sums the frequencies to mono, you would be, in effect, defeating one of the several important reasons for having more than one: retaining as much of the stereo information to as far down as the recording engineer allowed the bass to reach in stereo (the good ones will allow bass information to reach below 40 Hz before they sum it). A great example of this is Kodo's Mondo Head SACD which allows individual channels to reach well below this arbitrary point. Listeners with only one subwoofer don't know what they're missing.

The best approach to using multiple subwoofers would be to set your receiver to output all frequencies (20 - 20K) to the main speaker outs, then connect the woofers to these. If your woofers come with their own crossovers, then you won't have any problem filtering the lowest frequencies to them.

 

The original reason why I didn't bring home 2 Pioneer subs from my work is because I didn't want to carry them, and based on my situation, I learned from this thread that 2 subs isn't feasible for me either.

 

I agree with this for the most part. I can see one potential advantage to using two subs with a mono output. IMO, a mono sub should be right in the center of the sound stage. Assuming we're talking home theater, that is where the video monitor would be located. By using two subs, and putting them equidistant from the center, one can create a phantom sub image that is indeed located in the center.

 

My room measures out at 17 x 25 x 9

 

Using 2 subs will "load" the room much better than one. I used one Rel sub for about 3 years, then last year bought another one and run them in Stereo. I would recommend buying an SPL meter if you are going to use any sub with your system because as was said before, there is cancellation and support of frequencies far outside the actual range you have the sub set at.
With the SPL meter, you can run test tones to get an idea where cancellation takes place and find the optimum crossover point and phase for your sub(s).
If you are using a Home Theater receiver and have your sub connected to the LFE channel, you probably have a fairly limited selection where to blend your sub(s) and it becomes more challenging to implement.

 

Try running one sub out of your sub out and the other one in line with left and right

Scott

 

The main advantage to having two subwoofers is that you will gain 3 to 6 dB of headroom in the bass. At concert- or movie-level listening, this can be a huge advantage - the bottom two octaves require much more power to play clean than higher octaves, and you will notice much more accuracy with more headroom. Accurate LF reproduction can mean a more spacious representation of a good stereo recording, for example of an acapella singer in a great concert hall; Helmholtz tells us that reverberation increases below 200 Hz linearly, so natural reverberation can not be accurately presented without speakers that have good LF response, and a properly integrated subwoofer is one great way to achieve this.

In a room smaller than 12,000 cf, you will gain about 3 dB of general gain by placing the second subwoofer just about anywhere in the room, and about 6 dB if the second sub is near or on top of the first (from coupling).

You can't accurately predict that asymmetrical placement will fill in some of the dips in frequency response caused by room modes excited by the first subwoofer, although I have found a few rooms where this is possible. You also can't predict that the second sub will create less overall output, but some dips in FR can be exacerbated by adding a second sub.

There is no such thing as stereo bass. The directional cues that contribute to a solid 3-dimensional sonic image are all above the subwoofer range (unless you are using a small sub/sat system like B*** that crosses over way, way too high). Don't make the wrong assumption that since you have two speakers you need two subwoofers (any more than if you have five speakers you need five subwoofers).

I will disagree that you need to put the subwoofer on the same plane as your front speakers - room acoustics don't work like that (necessarily). You do need to time-align the subwoofer with the mains, either physically or with digital delays, since the speed of sound is, well, the speed of sound. And, anytime you let your main speakers run full-range and just add a subwoofer, you are likely to have great phase problems since the mains and the subwoofer are playing common notes, and this is not always an easy problem to fix (the variable phase controls found on some subwoofers generally add group delay and cause more problems that they fix). Always integrate a subwoofer with main speakers using an appropriate crossover.

The great advantage to using a subwoofer as opposed to true full-range speakers is that to play full-range sounds, you can embrace the room instead of fighting it.

 

I've been running two subs for about two years now to great effect with movies. Their is a slight tonal difference between my two subs which I feel helps with most soundtracks. My SVS sub goes low and deep for those action movies while my Velodyne is just above the SVS giving a nice balanced sound even with music.

I also split the mono signal from the reciever to the two subs. Haven't tried it any other way.

 

Don't forget that using a Y-adapter will result in 3dB signal drop in each of the branches compared to the trunk.

 

How many pro sound mixers place the same sounds in the sub and the other speakers? Isn't that defeating the purpose of having a separate subwoofer channel? At least with surround music, for the last two years I've read that many 5.1 mixers recommend running satellites full range (if they can handle that), with no bass management, plus a subwoofer. That's what I've been doing with my own system and it sounds fine.

 

Why would this be?

Assuming the output impedances of the preamp sub output is fairly low compared to the input impedance of the subwoofer amps the loading of the second unit wouldn't seem to be that much. Also I assume that most powered subwoofers have gain controls with more than enough range to make up for a 3db loss.

Losing 3db of gain is not nearly as big a deal as losing 3db of output power.

 

Vinyl addict


i also have a Rel Sub (Storm 111) and was thinking about getting another. what was the effect of having a pair (ie is it worth the upgrade) and how did you conect it to your amp. do you just connect both to the same jacks??

when i first put the Sub into my system i thought it was perhaps the biggest improvement to my system in several years of trying. the soundstage just increased and everything had more body throughout the frequency range. i've often heard that supertweeters can do the same.

 

Hi, Taurus!

I don't think this is the point.

If a bass guitar is mixed to any main channel or combination of channels, whether 2.0 or 5.1, this sound goes from around 40 Hz (or lower) on up. A speaker that plays well down to 50 or 60 Hz (as many speakers assumed to be full-range do) can't do this job. Add a subwoofer that plays summed bass from all main channels and this sound most likely will be greatly affected by the frequency, time, and room-mode characteristic of the mains and subwoofer; integrate this subwoofer using an appropriate crossover and these problems either go away or can be addressed since they are limited to a small range of frequencies.

If this bass guitar is mixed to the mains and to the LFE channel in a 5.1 mix (as has been done far too often, by mixing engineers who should know better), all bets are off and problems will occur.

I'm sure your system sounds fine. The industry standard is to mix on a full-range monitor system. There are two ways to make a full-range monitor system: five true full-range (20-20 Hz) speakers with a subwoofer (or another speaker...) just to reproduce the LFE channel, or five limited-range (bass response that doesn't play the full range the channel is capable of delivering i.e. down to 20 Hz) speakers properly integrated with a subwoofer. When this isn't done, inconsistency from one mix to the next is inevitable.

At the recent Surround Conference www.surroundexpo.com in Beverly Hills, Tomlinson Holman gave the keynote address. He gave a written test to attendees at his speech about the basics of Bass Management. Over half of the respondents got a failing grade on the test. Many of us at the conference agreed that this lack of understanding is fundamental to the current failure of surround music. This lack of understanding also has great impact on the consumer playback side, so it is fundamental to this discussion.

 

The standard crossover is a Linkwitz-Reilly characteristic crossover: fourth order 24 dB/octave. Most consumer-audio receiver bass management systems assume that the main speaker has a 12 dB/octave roll-off. Most sealed-cabinet speakers have this - ported and passive-radiator systems have a sharper rolloff with a bump near the rolloff; maybe this is a poor assumption but it usually works.

The bass management applies a 12 dB/octave rolloff to the mains (making it 24 dB/octave when it adds to the speaker's 12 dB/octave), and a 24 dB/octave filter to the subwoofer. This fourth order filter tends to produce pleasing in-phase response in a wide and usable physical space in a small room (different characteristic filters tend to be used in larger spaces).

The best frequency to pick is the main speaker's -3 dB point, measured at the listening position (or an average of positions), per speaker. Most often, the subwoofer crossover (not the same as the LFE filter present in encoders and decoders) gets set to the same point as the mains, and rarely higher or lower than the mains to work creatively with room frequency response issues. In most small rooms, five identical main speakers will have five different -3 dB points, so with most consumer bass management a compromise common crossover point will need to be chosen. Also, too high of a crossover point makes the subwoofer call attention to itself making positioning difficult, and too low of a crossover point is bound to run into room mode issues for the main speakers making their low frequency response even more different from each other.

Since sound, whether low or high, travels at the same speed (the front of the waveform travels through air at the same speed), all individual tweeters, woofers, etc., in your system should be exactly the same distance from the listener - even a few inches can make a difference. This physical time-alignment is difficult to achieve, especially if the subwoofer is positioned in the room to present flat frequency response to the listener. Digital delay (in the processor, performed at the same point in the signal flow as the bass management) can be used to delay the speakers that are closer to you so their sound does not reach you before the more distant speakers.

 

You're splitting the signal in half. This results in a 3dB loss. If you split it four ways it's a 6dB loss.

This is probably true, depending on how much head room is left in the amp. My point was only that the loss will have to be accounted for by recalibrating the setup.

3dB is 3dB. If you loss 3dB of "gain" you also lose 3dB of "output power" unless you correct for it in the preamp or the sub amp.

 

Thanks Doug.

This may sound like a weird thing to say on a forum dedicated to quality sound, but if a disc does have less-than-optimum bass reproduction, whether because of the playback system or the choices made in the studio, it doesn't bother me that much because bass is only part of the music experience. What I am mostly enjoying as far as surround music is concerned is the directional portion, i.e. everything above the lower bass. It seems that if the bass portion is negatively affected, mostly what I hear is the amount of bass (too much/too little), something that for all I know the musician wanted me to hear. In other words, ignorance is bliss!

All the years we've all listened in stereo,with speakers NOT in their optimum positions for best bass reproduction, didn't stop most people from still enjoying their music. While I don't want to be stagnant technologically-speaking, I also don't want to get bogged down in it. Hence me buying two large-ish speakers for my rear channels that make it down to 45Hz (fronts get to 42Hz), switching everything to "large" and not worrying about this issue anymore.

For me, surround music is too cool to let it pass by because it isn't reproduced *perfectly*.

 

You can easily correct for a 3db loss of gain in many places, but if you're at maximum power at the sub amp output there is no way to increase the power. Of course if you are not near maximum power you can easily add 3db. My point was if there was a 3db loss of gain prior to the amp that is usually not a problem at all.

I'm still not in agreement about splitting the signal and losing 3db. This is true in RF splitters because the impedances on the input and output are constant. But a 10k or higher input impedance on an amplifier is not much of a load on a low impedance preamp output. I've seen a preamp drive a dozen amps without noticeable loss of any gain on any of the amps. We used to use 'bridging' inputs all the time in PA. One low impedance signal goes into a bridging input and there is a bridging output for the next amp. This is pretty much like a Y cable. You can do this quite a few times. The higher the impedance of the load (compared to the lower impedance of the source) the less it drains the source. Of course if the input and output impedances are both 10k than I think you might get your 3db loss.

The same thing happens in video. For example, a video signal feeds a video cctv monitor and there is a termination switch on that monitor. Many cctv monitors have a second connector for hooking up to a second monitor. If you do this the picture will be weaker on both monitors because of the termination on the both monitors. There is your 3db loss. If you take the termination off the first monitor, both monitors are fine again. It is the parallel load of the dual terminator resistors that causes the loss. Without the added termination the load of the monitor is at a significantly higher impedance than the source. As a result you can usually hook many monitors up in series as long as the termination is only on the last one. The video connections are essentially in series, but the terminations are in parallel.

Think of this as a car. If you try to tow another equal sized car your first car will not be able to go as fast. If you tow a skateboard your car will not know the difference. In this case the second car is a low impedance load and the skateboard is very high impedance load. You can in fact tow many skateboards without being much of a load on the car. Each additional skateboard will not slow the car noticeably. Hook up many cars to tow and you won't even move. That could be like a dead short and would probably destroy the source car just as hooking a dead short up to an amplifier will probably destroy it.

 

Anybody know why most subs are equipped with 2 RCA inputs, i.e. left and right? But more and more subs also come with a jack labeled LFE, which usually means it bypasses the internal crossover, but this time it's a *single* RCA input.