Questions about Dual Subwoofers

Discussion in 'DIY Speakers and Subwoofers' started by mdheller, Apr 20, 2014.

  1. I just finished building all the main speakers for my HT (Tempest F/L and Volt Coaxials for the surrounds/center). I love them! I'm now thinking of building a sub, and much of what I've read says that 2 subs are much better than 1. I've never run more than one sub before, so I have a couple noob questions, and I'm hoping I can get some advice. I'm more interested in SQ than volume, so I'm leaning toward a pair of 3 cu ft or 2 cu ft sealed subs (based on the flat packs available here).
    • Do you agree that 2 subs are better than 1?
    • Do the two subs run in stereo, or does the same signal go to both?
    • How do I set this up? I'm also thinking of replacing my amp with an Emotiva setup (UMC-200 and UPA-700). The UMC-200 has 1 balanced and 1 unbalanced sub output. Do I use one for each sub? Is there a special amp I should buy that powers two subs from one signal?
    Any advice is much appreciated!

  2. Yes, two is better than one (and four is better than two!).

    You have a few choices with wiring and amplification. Depending on the amp and the driver you choose, you could run both subs from a single amp channel - but two channels would not mean stereo; it's generally one signal, but may have separate EQ, delay, or phase adjustment. For most processors, there is only one subwoofer signal - so all you need is to split it (like with a simple "y" splitter cable) if you want or need separate amplification channels. Some processors can EQ multiple subs (usually two) and will have two outputs - so two cables works fine without a splitter in that case.

    Choosing the way you want to do it will be a combination of practical considerations. For instance, will you be setting them up symmetrically? If one is near your primary seat and one is far, you may benefit from separate EQ and therefore need separate amplification. If you only have space for one amp, then you'll need to pick two drivers that can be configured into a single load that the amp can drive, and then of course you'll be stick with only one set of EQ adjustments. Then if you pick 2 ohm drivers, you'll need to make sure you have an amp that's stable with that load.

    For specific advice (which I may not be capable of providing), how about some details of your space and your expectations?

  3. Thanks Fred. The room is roughly 16' x 19' with a vaulted ceiling (10' center, 8' sides). It's on the second floor, so it's all framing around it (no concrete). As far as expectations go, I'm looking for clean, tight, accurate sound as far down as I can reasonably go. I'm sure that whatever option I choose, I'll get plenty of shake for me, so I'm more about sound quality. That's why I wasn't sure if 2 subs was really necessary. Does it just add volume? Or can it improve SQ?

    As far as amping, I was thinking of getting plate amps to power each sub individually. So if I read your post correctly, in that instance I would run the balanced sub output from the UMC-200 to one sub and the unbalanced output to the other, yes?

    Does it matter that one's balanced and the other unbalanced?
  4. You'd have to know the details of how the UMC-200 works. One would imagine that identical signals at same level were output on both connections, but that may not be true. The circuitry may only allow one to be active at a time, or they may not be at the same level (but this could be corrected in calibration through the amp gain settings). That may take some investigation, and a splitter may be simpler or required.

    The primary advantage, IMO, of running more than one sub is the smoothing of the response when one seat is compared to another. The smaller the variation between seats, the easier it will be to get satisfactory results at more than one seat (through EQ). For that goal, four subs tends to be the optimum, but good results can be had with two or three. In theory, a second sub adds something like 3dB output (or is it 6?), which is not inconsequential. But the in-room response of any sub is totally dominated by position. The response will vary by 10-20dB from place to place and frequency to frequency - so these variations are much more important than 3dB total output. Additional subs can produce smaller seat to seat variation as well as overall smoothing of the frequency response at any single listening position, so adding subs is a win-win and IMO one of the simplest ways to improve the overall experience.
  5. Having multiple subs is (usually) far more about smoothing out your overall response - which would fall into the "sound quality" category - than it is about simply getting more volume. When you go from one sub at a given power level to two subs each at that same given power level, you only gain 6 db of output capbility... which isn't all that much.

    As for how you'd wire that, even if your processor has both outputs active at the same time (it may or may not, i'm not familiar with the umc-200), you'll be pretty hard pressed to find a plate amp with either xlr or trs input. Sure, you could buy a cable that goes xlr or trs to rca, but at that point I'd just use a y-splitter from the rca out.

    EDIT: looks like great minds think alike... but fred's thinks a little faster than mine
  6. I could take the balanced SW output and send it to a pro amp like this:

    Then hook up both subs to that amp (so the subs would be passive in this option--no plate amps). Would that be preferred to running individual plate amps for each sub? The advantage of the plate amps is that they can be adjusted independently. Not so with the pro amp, but there's no need for a Y splitter.

    For someone who's electronically, um, stupid... what happens if you split the RCA output from a pre-amp? Does the signal get weak? Does it degrade the quality? Will it harm the pre-amp?
  7. The pro amp (that one and most) is stereo, with independent gain adjustments but no phase or delay (on that particular model). So that's a drawback compared to plate amps. They tend to be a little loud with fan noise as well as having bright lights on the face, so if the amp is going to be in your line of sight or near your listening position, those are drawbacks too. Also, I think you're mistaken about not needing a splitter with the pro amps - generally they need one input signal for each amp channel - but I could be wrong about that.

    On the other hand, you get more power for your dollar. The only cable to run to the sub is signal, which may make setup easier and potentially improve WAF (since you don't have to locate an outlet and hide the power cord). If you were to go with an amp with DSP built in, like some of the Behringer iNuke series, you could get EQ built in and actually have more versatility than the plate amps. The 3000DSP model is very popular, combining a good amount of power with easy-to-use DSP (it comes with software so that you can use your PC to configure the filters). You'd ideally want something like REW to help you design the filters, but it can be done crudely with an SPL meter and test tones.

    When you split the signal cable out of the processor, the voltage is unchanged - so you don't loose any signal per se. If the connection is poor you can have signal quality problems, but in most cases this is a moot point, IMO. The pre-amp won't be damaged.
  8. Sounds like individual plate amps are the way to go. Where the pro amp would go is right in the line of sight, and I really would rather have no fans.

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