1. Register NOW and become part of this fantastic knowledge base forum! This message will go away once you have registered.

Multiple Monitor Inputs?

Discussion in 'Pro Audio Equipment' started by Doublehelix, Mar 18, 2003.

  1. Doublehelix

    Doublehelix Well-Known Member

    OK, this is a weird one folks!!!

    I am considering a possible studio setup where I would plug 2 separate line feeds into my monitor speakers (one TRS and one XLR). These are bi-amped monitors with both sets of connectors on the back, so they would both be line-level signals.

    In a nutshell, I want to feed the monitors from one source while tracking, and then from another source while mixing.

    Is this possible, or could I potentially screw up my speakers? Or alternatively, is there an A/B switch box out there that can do this?

    I only plan on feeding one signal at a time, but "stuff happens", so just in case, what would happen if I screwed up and sent both sources at the same time? :d:

    Thanks!
     
  2. Kurt Foster

    Kurt Foster Distinguished Member

    DH,
    It wouldn't "hurt" your speakers but it could cause impedance loading and affect the frequency response. In addition, this would not be good for the two source devices. Signal can literally, back up the line and burn out output stages. Get an A/B switchbox... Kurt
     
  3. Doublehelix

    Doublehelix Well-Known Member

    Ouch! OK...is there such a thing as an A/B box for TRS or XLR sources?
     
  4. knightfly

    knightfly Active Member

    James, first of all just in case I never mentioned it, I've worked as an engineering tech in the SF Bay area for several years before moving north to raise my kids in a less congested situation, so what I'm going to tell you is not coming from a "hobby" standpoint -

    What Kurt told you is correct - now here's the "why", just in case you remember things better when the reasons are part of the answer.

    The rules for connecting inputs to outputs of electronic circuits are:

    NEVER, repeat NEVER, hook two OUTPUTS together.
    Reason: One of the two outputs is going to be stronger (in terms of drive capability, or source impedance) and will KILL the other one.

    You CAN hook two INPUTS together, as in sending one output to two inputs, IF the output has enough drive (low enough source impedance) so that the signal is minimally attenuated. This usually means that you want the combined input impedance of both destinations to be at least 10 times as high as the source impedance. In fact, if you follow the 10:1 rule you can connect a single output to several inputs.

    For what you want to do, I'm going to assume (yechhh) that the TRS inputs on your monitors do NOT disconnect the XLR connectors when a plug is inserted. Correct me if this isn't true.

    Under those conditions, if you hook the output of a mixer bus to the XLR's, then hook the output of another device to the TRS connectors, you have effectively connected the two outputs to EACH OTHER.

    Even if one of those devices has its volume turned down, or if there is a mute switch of some kind, the probability still exists that the two devices STILL have their OUTPUT stages directly connected to each other, through the two connections on your monitors. NOT GOOD.

    So, as I said earlier, Kurt's advice still stands.

    As to a switch box with both XLR and TRS connectors, I've not seen one (doesn't mean they don't exist, obviously) - in fact, most A/B boxes I've seen are just guitar stomp types, usually only T/S phone connectors. Add to that the fact that they're only one channel, and it's not a good way to go.

    In fact, if you have TRS patch bays in your setup you would be better off running the monitor inputs from the pair of TRS connectors thru the patch bay, and plugging whatever source you want to monitor into those points.

    Doing that, however, is most likely going to cause thumps and pops in your monitors whenever you switch. So would any passive switch such as a stomp box type.

    Maybe we could come up with a workable solution better if you mentioned WHY you need to do this, and what the two different sources are - there may be simpler solutions available for what you need to do.

    Your turn... Steve
     
  5. Kurt Foster

    Kurt Foster Distinguished Member

    Steve,
    I too was a SF dude until I too moved "north"... Where "north" are you? I'm in the "commie ratt bastard" Eugene area in Orgon... Kurt
     
  6. Doublehelix

    Doublehelix Well-Known Member

    NEVER What??? :)
     
  7. knightfly

    knightfly Active Member

    Sorry James, my stupid laptop has a glitch somewhere in the mouse department and sometimes posts for me before I'm ready - read it again...

    Kurt, you're closer than I thought - I'm in the countryside about 14 miles east of Albany - we definitely need to meet for coffee or something... Steve
     
  8. Kurt Foster

    Kurt Foster Distinguished Member

    Steve,
    What, like Sweethome? I used to gig out there back before dirt... Kurt
     
  9. knightfly

    knightfly Active Member

    Not quite - let's take this part PM, I get a little nervous about privacy considering just how open this forum is... Steve
     
  10. Doublehelix

    Doublehelix Well-Known Member

    Thanks for your help guys, I think I am going to pursue another route, it sounds like somewhere I don't want to go...I was concerned with my monitors, but it sounds like I should be more concerned with my source devices! It was just a wild idea I had, but I think it complicates everything too much anyway...if I tried to explain it in a forum message, it would take too long and be too complicated anyway...
     
  11. Kurt Foster

    Kurt Foster Distinguished Member

    DH,
    I get the idea. I do the same thing. I have an old Nakamichi 450 preamp that I use to monitor switch. I can switch to the CDR, mains on the monitor board, a SR 24, C/R out on the Monitor board and the C/R out on a 1604 I was going to use for inputs until I decided it sounded like a steaming pile.The outs of the computer go into the CDR on the SPDIF inputs so I can hear that by monitoring the CDR... Monitor switching is a very handy thing to have... Kurt
     
  12. knightfly

    knightfly Active Member

    Same here - I use an older SAE audiophile-type preamp, has several in's, switchable (thankfully) EQ, mute, multiple tape ins, etc - works well and doesn't seem to color the sound at all (unless I switch in the EQ)

    It's not balanced, but I use all Tascam low-cap RCA cables and can't complain (but I do anyway)

    Maybe you could find something like that James - like on Ebay or??? Just a thought... Steve
     

Share This Page