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Subwoofer: XLR vs RCA?

Discussion in 'Sound Science' started by rebel975, Oct 5, 2012.
  1. Rebel975
    A little while ago I bought a UMC-1, and hooked up my subwoofer using a single RCA cable. Not the Red+White RCA- just the red one. The UMC-1 only has a single RCA or a 3 pin XLR for the subwoofer output.
    I don't know if it makes any difference, but I power my sub via a NU3000DSP. It has combo 1/4" TRS/XLR jacks. Originally, I was hooking the UMC-1 up to the NU3000DSP via RCA > 1/8" TRS adapter > 1/4" TRS adapter. 
    Yesterday, I replaced the RCA with a XLR cable, and immediately noticed that the subwoofer seemed to have better transient response. The subwoofer didn't seem to be any louder, but it did seem to be snappier, etc. 
    Does XLR provide a higher voltage, therefore making my subwoofer play louder (even though I didn't perceive it at being louder)? Or does XLR simply cancel out some noise, and the problem may have been that my previous unbalanced subwoofer hookup was slightly noisy (even though I never noticed any noise)?
    Perhaps going from RCA to 1/8" to 1/4" was lowering the input voltage on the NU3000DSP?
    I'm wondering if my feelings that the sub sounds better would go away in a DBT? 
  2. joeyjojo
    Tough one. Usually XLR provides the same voltage as unbalanced for each phase, which results in 2x the voltage down the chain. If that's maintained then it's 4 times the power (6 dB) which should be audible.
    So this is a passive sub? How are you connecting it to the amp?
    If it's not in your head (good work for acknowledging this possibility) then it's to do with the inner workings of the amp, which I know nothing about. Perhaps it's faster with a balanced input.
  3. Rebel975
    Yes, it's a passive sub. I have a TC Sounds Epic 12" hooked up to the NU3000DSP via a 4 pin speakon connector (although the sub only uses 2 of the pins- the other 2 are there so you can bridge the 2 outputs if you want).
  4. joeyjojo
    Get a friend/partner/spouse/neighbour to swap the cables at random and listen to some music. If you can tell when it's swapped (throw in some fake swaps too) keep the one you prefer. I think it's likely that there's too small a difference to hear. Without seeing the amp schematic I can't predict it.
  5. Rebel975
    I expect to hear the XLR click in to place or something while the cables are being swapped, and therefore skew the test. I don't think I could pull it off carefully enough to believe the results.
  6. dvw
    The transient of a pulse is the high frequency component of the wave form. It is not intuitive how the XLR can "speed up" the subwoofer because in theory the transient is bot even in the same path. My guess would be maybe the balanced frequency splitter has less attenuation.
  7. Rebel975
    Could you dumb that down for me a little bit? [​IMG]
  8. dvw
    All signals are composed of a series of different sine wave. This is what differentiates say a bass drum vs a bass guitar. The bass drum even though it is low frequency it also has high frequency components. This high frequency component is create the impression the transient is fast of slow.
    In amplification, the signal is divided into two paths; the high frequency and mid frequency go to the main speaker and the low frequency go the the sub-woofer. So in theory,the sub-woofer is not responsible for the transient.
    However, the difference might be caused by the frequency divider part of the amplification. The balanced circuit might allow more high frequency portion of the signal to pass through and thus, the perception of a faster transient. This is of course, pure speculation as I don't know what the circuit looks like.
  9. Rebel975
    I see...interesting. Thanks.
  10. JerryLove
    As mentioned: XLR puts out a louder signal (+6db). This is part of why XLR cables can be run much longer distances than RCA. In theory, some portion of the gear should account for that (presumably the sub should -6db on amplification on XLR relative to RCA); but I would not be surprised if this is not happening and your Sub is indeed playing louder (I am assuming that the source is +6db on its XLR output).
    It's worth mentioning that this is entirely dependent upon the equipment. You can adapt an RCA cable to XLR without making any changes to the signal (it will be -6db and the inverted-phase line will be neutral); and so to what extent either piece of equipment actually provides an XLR-compliant signal is, sadly, independent of the presence of the plug.
  11. firev1
    Might also be a case of poorly built RCA, XLR cables are usually very well built(or at least better than most RCA). There are a bunch of RCA cables whose insulation is pretty terrible which may degrade signal performance. The hum or degrading may be inaudible during playback which may be why you did not notice it.
  12. proton007
    I think you should explain what difference did you hear, in order to find out if the transient was really responsible for the change in sound.
    Its possible as dvw says.
    I'm also speculating that the damping factor might have to do something with this.
  13. Rebel975
    I don't know if I'm the best at describing things, but it was like going from one-note "boom-boom" bass to a more complex tune.
    I'm leaning towards it being all in my head, tbh. I just did a very uncontrolled test between the RCA and the XLR (switching the cables myself, etc.) and found that the XLR is indeed slightly (but noticeably) louder than the RCA.
    I don't know if I could DBT the difference, but I'm pretty sure the XLR is slightly louder than the RCA.
  14. Rebel975
    Okay, yeah- XLR being +6dB was right. I just downloaded a sound meter app on my phone and placed it on top of the sub while running a tone generator. The XLR measured exactly 6dB louder than the RCA.
    Louder = perceived as better turns out to be true.
    Thanks everyone.
  15. mikeaj
    Thanks for following through with the mystery and letting us know the final result in the end.
    Weird how louder doesn't even necessarily sound louder, just different, huh?  [​IMG]

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