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  1. Member
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    Is it possible to connect two sources to a set of speakers having only one input and hear sound simultaneously? I tried a cable (a female to two female) to connect the cable (male) coming from the speakers and two cables (male to male) from the two sources, but even though I could hear the sound from the two sources simultaneously, for some reason the volume of the one of the two speakers was very low. Any ideas what is the problem?
    Last edited by kyrcy; 17th Dec 2018 at 11:18.
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  2. The correct way of doing this is with an audio mixer. One inexpensive example:

    https://www.amazon.com/Behringer-Micromix-MX400-Low-Noise-4-Channel/dp/B000KGYAYQ/
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  3. Member
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    I am aware of audio mixers, but I am looking to find what is wrong with with the cable connections above.
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    I wouldn't do it - potentially harmful to the equipment. Perhaps you should consult an electrician
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  5. Member
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    Would it be possible to direct sound from one source through line in to the speakers?
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  6. aBigMeanie aedipuss's Avatar
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    you'd potentially ruin the second amplifier connected to the speaker by feeding current backwards into it.
    --
    "a lot of people are better dead" - prisoner KSC2-303
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  7. Originally Posted by kyrcy View Post
    I tried a cable (a female to two female) to connect the cable (male) coming from the speakers and two cables (male to male) from the two sources
    So your basic idea is:

    Code:
    device 1 --------\
                      +--------> speaker
    device 2 --------/
    And you have two of those for a stereo pair.

    You need to be clearer about what your are doing. Are you combining line level outputs with a simple Y adapter and sending that to an amp or self powered speaker? Or are you combining the speaker outputs of two amplifiers to send to one unpowered speaker? The former is fairly safe but the latter is likely to fry one of the amps.

    Originally Posted by kyrcy View Post
    even though I could hear the sound from the two sources simultaneously, for some reason the volume of the one of the two speakers was very low
    Do you mean the sound from one of the sources was much louder than the other? Or literally that the sound coming out of one speaker was much louder than the sound coming out of the other speaker? If the latter you may have already fried one of the amps.
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    I am trying to connect device 1 and device 2, each with a male to male cable, to a twin female to single female cable, to a single male cable from Speakers.

    I am combining line level outputs (I think) with a Y adapter and sending that to self-powered (USB) speakers.

    The sound coming out of one speaker was much louder than the sound coming out of the other speaker (when performing left right speaker setup test in windows).

    Both sound the same when only one source is connected, so there shouldn't be any permanent damage.
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  9. Member
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    I tried this decades ago and the results were the same. I don't fully understand the Wiki quote below, but my basic understanding is that the load isn't (and won't ever be) split/balanced evenly between the two in/outputs. Also it can fry your speakers and (in your case sound card/sound chip). Just because you got away with it once or twice doesn't mean it wont fry something the next time.

    From Wikipedia (my emphasis):

    "Line out

    Line out symbol.svg Line waves03-0-out.png Line waves03-1-out.png Line circle out.png Line-out symbol. PC Guide color lime green.

    Line outputs usually present a source impedance of from 100 to 600 ohms. The voltage can reach 2 volts peak-to-peak with levels referenced to −10 dBV (300 mV) at 10 kΩ. The frequency response of most modern equipment is advertised as at least 20 Hz to 20 kHz, which corresponds to the range of human hearing. Line outputs are intended to drive a load impedance of 10,000 ohms; with only a few volts, this requires only minimal current.

    Connecting other devices

    Connecting a low-impedance load such as a loudspeaker (usually 4 to 8 Ω) to a line out will essentially short circuit the output circuit. Such loads are around 1/1000 the impedance a line out is designed to drive, so the line out is usually not designed to source the current that would be drawn by a 4 to 8 ohm load at normal line out signal voltages. The result will be very weak sound from the speaker and possibly a damaged line out circuit.

    Headphone outputs and line outputs are sometimes confused. Different make and model headphones have widely varying impedances, from as little as 20 Ω to a few hundred ohms; the lowest of these will have results similar to a speaker, while the highest may work acceptably if the line out impedance is low enough and the headphones are sensitive enough.

    Conversely, a headphone output generally has a source impedance of only a few ohms (to provide a bridging connection with 32 ohm headphones) and will easily drive a line input.

    For similar reasons, "wye"-cables (or "Y-splitters") should not be used to combine two line out signals into a single line in. Each line output would be driving the other line output as well as the intended input, again resulting in a much heavier load than designed for. This will result in signal loss and possibly even damage. An active mixer, using for example op-amps, should be used instead.[6] A large resistor in series with each output can be used to safely mix them together, but must be appropriately designed for the load impedance and cable length.

    https://en.wikipedia.org/wiki/Line_level
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    I was thinking about getting a pair of speakers with two line inputs so I can connect simultaneously two sources, but I came across with the EDIFIER R19U 2.0 speakers that have USB/AUX connections. They seem to have good reviews, but I am not sure if the USB connection will cause any issues. Does anyone have experience with these?
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    Originally Posted by kyrcy View Post
    I am combining line level outputs (I think) with a Y adapter and sending that to self-powered (USB) speakers.
    Each line of the stereo pair needs its own resistor network in order to combine signals. If it doesn't contain the right electronics, then your Y-adapter is just physically bridging the conductors and you get a big loss in level.
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    What about the solution above and the specific speakers?

    https://www.edifier.com/int/en/speakers/r19u-compact-2.0-usb-speakers
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  13. Member Cornucopia's Avatar
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    USB does NOT support more than one source (host) at a time.

    The answer is NO.
    Get a switch, or a mixer, or 2 separate sets of speakers, or live with only 1 set connected. Those are your options.

    Scott
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    Originally Posted by kyrcy View Post
    I am aware of audio mixers, but I am looking to find what is wrong with with the cable connections above.
    What is wrong is simple. It's a dumb idea to fit 2 cables simultaneously as you did. The reason for the difference in volume is almost certainly impedance differences. Just do the intelligent thing and get a mixer or input switcher.
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    Originally Posted by Cornucopia View Post
    USB does NOT support more than one source (host) at a time.

    The answer is NO.
    Get a switch, or a mixer, or 2 separate sets of speakers, or live with only 1 set connected. Those are your options.

    Scott
    The above speakers have USB and AUX (3.5mm) connectors. The USB connector is for a PC and the 3.5mm connector for a second source. Are you saying that these would not work?

    Originally Posted by Hoser Rob View Post
    What is wrong is simple. It's a dumb idea to fit 2 cables simultaneously as you did. The reason for the difference in volume is almost certainly impedance differences. Just do the intelligent thing and get a mixer or input switcher.
    I do not want a mixer or input switcher. It will be either one or two sets of speakers.
    Last edited by kyrcy; 15th Jan 2019 at 12:42.
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  16. Originally Posted by kyrcy View Post
    Originally Posted by Cornucopia View Post
    USB does NOT support more than one source (host) at a time.

    The answer is NO.
    Get a switch, or a mixer, or 2 separate sets of speakers, or live with only 1 set connected. Those are your options.

    Scott
    The above speakers have USB and AUX (3.5mm) connectors. The USB connector is for a PC and the 3.5mm connector for a second source. Are you saying that these would not work?
    That should be safe if you plan on using USB for one device and the 3.5mm connector for the other. You may still have the problem of different levels from the two devices.
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  17. Member Cornucopia's Avatar
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    Most "USB" connections on budget range desktop speaker models do NOT provide audio output via the USB interface, it is merely there for control & status feedback (which you could ignore). In those instances, the audio is ONLY coming through the 1/8" mini phone plug.
    However, if your model truly has 2 separate inputs, as jagabo said, you could have 2 different sources (caveats still in effect). In essence, your input button on the speaker is/can be the SWITCH I referred to.

    Here's an easy way to tell: does your speaker set have an [Input] button?

    Scott
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  18. Originally Posted by Cornucopia View Post
    However, if your model truly has 2 separate inputs, as jagabo said
    In the description it says:

    It can be connected to your laptop or desktop computer with a single USB cable for both power and sound.
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    As I suspected, plugging the mini-plug into the Aux input disables the USB audio:

    "Design-8: Here is a closer inspection of the front speaker. The red L.E.D light indicates its connected only with USB for audio streaming and power input, whereas the yellow L.E.D. means its connected with USB for power input and AUX for audio streaming. The yellow L.E.D. only activates when a 3.5mm audio jack is connected at the rear of the active speaker." https://tech.ayumilove.net/edifier-r19u-speaker-review/ Same idea as when you plug in a headphone into the front jack of most portable speakers and portable devices. It cuts off the speaker sound.

    If you do find a speaker that will allow two simultaneous inputs, internally there has to be a mixer to achieve that.

    I just remembered, back in the early 70's, I was experimenting with my Dad's old reel to reel recorder and put potentiometers in line to vary and mix the audio signals. In essence a cheap DIY mixer.
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    Originally Posted by lingyi View Post
    As I suspected, plugging the mini-plug into the Aux input disables the USB audio:

    "Design-8: Here is a closer inspection of the front speaker. The red L.E.D light indicates its connected only with USB for audio streaming and power input, whereas the yellow L.E.D. means its connected with USB for power input and AUX for audio streaming. The yellow L.E.D. only activates when a 3.5mm audio jack is connected at the rear of the active speaker." https://tech.ayumilove.net/edifier-r19u-speaker-review/ Same idea as when you plug in a headphone into the front jack of most portable speakers and portable devices. It cuts off the speaker sound.

    If you do find a speaker that will allow two simultaneous inputs, internally there has to be a mixer to achieve that.

    I just remembered, back in the early 70's, I was experimenting with my Dad's old reel to reel recorder and put potentiometers in line to vary and mix the audio signals. In essence a cheap DIY mixer.
    If the above is true, then I will have to look for something else. For now I re-directed audio from the second source through the line-in of the sound card to the speakers and it works fine. But this requires the PC to be powered on, which is not always the case.
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  21. You can build some passive combiner - few resistors and capacitors will do the job. As you have no information about architecture of outputs then it should provide galvanic separation (so 6 capacitors with 4 .. 10 resistors in total). My advice is based on assumption that you wish to combine power (moderate like 0.5 - 2W) amplifier outputs and signal is feed to voltage input of other amplifier with relatively high impedance input (compared to source output impedance).
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  22. Member Cornucopia's Avatar
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    So...basically a mixer, whether active or passive.

    Scott
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  23. Originally Posted by Cornucopia View Post
    So...basically a mixer, whether active or passive.

    Scott
    Yes. Any form of combining two signals is mixing (even hooking wires directly). IMHO by mixer i understand device that allow to perform variable mixing, fixed ratio mixer i would prefer to call combiner.
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    Originally Posted by kyrcy View Post
    I am combining line level outputs (I think) with a Y adapter and sending that to self-powered (USB) speakers.
    It's not brain surgery to build a box or cable that will do this with proper impedances.



    In this case, "STEREO" means, say, the Left channel from Source 1 and from Source 2. "MONO" means the mixed output for that channel which goes to the speakers. Repeat for the Right channel.
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  25. My M-Audio powered speakers have two audio inputs and they play at the same time. There's no way to adjust the relative volume of the two inputs though.
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  26. Originally Posted by JVRaines View Post
    It's not brain surgery to build a box or cable that will do this with proper impedances.



    In this case, "STEREO" means, say, the Left channel from Source 1 and from Source 2. "MONO" means the mixed output for that channel which goes to the speakers. Repeat for the Right channel.
    True, but there is one missing thing - galvanic separation - power output may have non grounded "Ground" and it may misbehave - nowadays power amplifiers may use floating ground or balanced output. It is safe to separate ground and outputs galvanically. Additional capacitors are required (i would avoid transformers).
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  27. Member Cornucopia's Avatar
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    I would agree, pandy.

    Scott
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  28. Member
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    Originally Posted by pandy View Post
    Originally Posted by JVRaines View Post
    It's not brain surgery to build a box or cable that will do this with proper impedances.



    In this case, "STEREO" means, say, the Left channel from Source 1 and from Source 2. "MONO" means the mixed output for that channel which goes to the speakers. Repeat for the Right channel.
    True, but there is one missing thing - galvanic separation - power output may have non grounded "Ground" and it may misbehave - nowadays power amplifiers may use floating ground or balanced output. It is safe to separate ground and outputs galvanically. Additional capacitors are required (i would avoid transformers).
    This is for line-level signals, not amplifier output.
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  29. Originally Posted by JVRaines View Post
    This is for line-level signals, not amplifier output.
    Perhaps i didn't get OP however i've had impression that OP wiling to combine power outputs (headphone out) to line input of active speaker.
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