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Thread: How to connect to a powered sub via compressor & mixer?

  1. #1
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    Unhappy How to connect to a powered sub via compressor & mixer?

    Hello all.. I have been scratching my head on this one for a while now and figured i would finally ask for help with connecting my powered subwoofer to my mixer via a compressor.
    Here is my setup:

    My mixer is a Berhringer Xenyx 802 --> https://www.bhphotovideo.com/lit_files/61870.pdf
    My compressor is a Berhringer Multicom xl-pro 4600 4 channel compressor --> https://media.americanmusical.com/It...600_manual.pdf
    My sub's input amp is a BASH 300s sub amp --> https://www.parts-express.com/bash-3...w-rms--300-750

    I currently use 2 channels on the compressor for left and right main speakers, i use another channel for a microphone and want to use the last channel for subwoofer.

    I am trying to get an stereo output from my mixer to go into that ONE channel of my compressor and then from compressor into the bash 300S

    I have tried using only one channel of the "control out" on my mixer, via a 1/4" balanced jack to 1/4" input of compressor, then output of compressor into bash 300s via a 1/4" to rca cable, it works but i am missing half the sound as i am only getting one channel, so sub is not as loud.

    I want to go through the compressor so help smooth out and protect the sub
    If i go out from mixer via rca tape out directly to rca in on sub it works fine but i am bypassing the compressor, which i don't want to do.

    Any help is appreciated!

    Thanks very much

  2. #2
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    Quote Originally Posted by robmorin View Post
    I want to go through the compressor so help smooth out and protect the sub
    Compressing recorded audio more than it already is which these days is excessive to start with.... will NOT protect your sub it will actually put more stress on it. A limiter on the other hand could help and the unit you have can be setup to act as a sort of limiter but it has to be setup such that it is only occasionally active otherwise it is just adds another layer of excessive compression. The way you do this is set the limiter ratio to maximum and the threshold to a level that activates just below amp clipping.. assuming the subs can handle full output from the amp. And the idea is this device is there to protest against accidents which means it should rarely be activated, if you drive the system so this limiter is always active you WILL cook the subs and this also means you simply don't have enough sub for the task at hand.
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  3. #3
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    To do the above with only 1 channel of the compressor you first have to combine the stereo signal into a single channel and to do that correctly requires another piece of equipment. But now you have to ask yourself is all this going to be worth it? Powered subs usually have quite a bit of protection built in, I do 50-60 events a year with powered speakers where there is no additional protection between the DJ console or mixer and don't have any problems.
    Paul O'Brien
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  4. #4
    Quote Originally Posted by robmorin View Post
    I have tried using only one channel of the "control out" on my mixer, via a 1/4" balanced jack to 1/4" input of compressor, then output of compressor into bash 300s via a 1/4" to rca cable, it works but i am missing half the sound as i am only getting one channel, so sub is not as loud.
    I think you need a summing cable like conanski said.

    Some would recommend using resistors for summing but they aren't necessary, I'd start carefully at 1kOhm (there's a formulae for calculating the "correct" value too, do keep in mind though that resistors are known to cause hiss in the signal)

    I want to go through the compressor so help smooth out and protect the sub
    If i go out from mixer via rca tape out directly to rca in on sub it works fine but i am bypassing the compressor, which i don't want to do.
    Most mixers have tape out with fixed volume (usually +4dB), ie. the master fader doesn't affect the tape output. I believe this engineering practice comes from the era of 2-track tape recorders where you would calibrate the recorder input to desired level and gain stage from the mixer, leaving the master fader for setting monitor levels.

    I've used a compressor in a sub out as well but I'd proceed with caution too like stated earlier because in the worst case you may blow the voice coils in doing so.

  5. #5
    That kind of sub amp is just not suitable for PA use, applying too much compression will just result in you melting your sub's voice coil and the whole thing is just a bad idea, I'm sorry to say.

  6. #6
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    As the others have said, limiting, which is a type of compression, does not prevent increases in average volume or "loudness", rather only limits the peaks. Peaks rarely kill PA woofers. Loudness that's the result of crushing into a limiter will still cook a voice coil the same, just sound less unpleasant in the moments before you do it since it will round what would have otherwise been square waves. Therefore, limiters tend to increase the chances of cooking coils since they are more likely to be abused. Compressors should be left to studio environments and maybe for certain mic feeds (like drum kits) in live multi-microphone setups for rock bands, not DJ stuff. The only place for a limiter universally in live environments is on the in-built output section of amplifiers to prevent 4X clip harmonics way beyond its rated power. Everywhere else live is usually a bad idea done by clueless sound guys who go through drivers pretty frequently.
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    The other issue with cheap compressors.... The attack time isn't fast enough. Try it. Apply some compression and record the output into something that will show you a wave display. Set the fastest attack time. Add a lot of compression to make it stand out more. You will get very narrow transients that are let through. These transients are often inaudible but will result in clip light activity. Imagine running only 3db of compression, that's 3db sooner your clip light will be warning you about max volume. The transient can often be too small for the speaker to even react to, more problematic for tweeters due to the higher frequency content to make such a sharp audio curve/waveform/oscillation what ever!.


    Compressors are only good for mics and pre 90's music, music that's more dynamic, the peaks in this music is a lot higher than the body and varied over time, uncompressed, this can lose you a lot of volume (perceived loudness) before clipping, unless running the old 3x amp power to speaker power ratio (which is very expensive)... Anything naughties+ has already been squished to death.
    Last edited by mitchiemasha; 09-18-2019 at 07:38 AM.

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