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Phase Reverse Switch Questions

Discussion in 'Amps, Mics & Pickups [DB]' started by rickwolff, Jan 24, 2017.


  1. rickwolff

    rickwolff Certified Gear Junkie, Amateur Adjunct Professor Supporting Member

    I use a Headway EDB-2 which has a phase reverse switch which allows me to reverse Channel 1 or Channel 2 or neither (off position).

    The manual talks about getting two inputs to be 'in phase' with each other and that makes sense to me.

    What I don't understand is why, when I'm running only 1 channel, reversing the phase makes a significant change in the tone.

    For example, I'm running my Ischell mic into channel 2 using the phantom power. Having the phase switch 'off' results in a 'fuller or fatter' tone which I think is often what you might want.

    However, when I reverse the phase switch on channel 2 the sound I get is actually much more 'natural and acoustic'. It's not at all thin sounding. It's still very full and rich but it just has more clarity.

    I don't think this is explained by putting the speaker 'in phase' with the acoustic instrument. It just seems that the sound coming out of the speaker sounds significantly better to me when the phase is reversed.

    Can someone explain this to me? (Curious Gear Junkie would really like to know).
     
  2. rickwolff

    rickwolff Certified Gear Junkie, Amateur Adjunct Professor Supporting Member

    I go t an explanation from Drurb which I quote below:

    "Rick...

    What you are experiencing results from the different constructive and destructive acoustic interference that occurs between the loudspeaker and the bass when you flip the polarity inversion switch. If you were to separate the bass from the amp, what you would hear from the speaker would be the same, regardless of the position of the switch. That is, unless the circuit is faulty.

    Keep in mind that the acoustic interaction affects what reaches your ear. Someone standing elsewhere in the same room may not experience what you do. Humans are insensitive to the absolute phase of waveforms in all but some very special circumstances that involve asymmetric waveforms. That does not apply to your situation. If you reliably hear a difference in terms of what comes out of the speaker with the bass acoustically isolated from the rig, then that would indicate that the spectral balance is actually changing when you change the polarity. That's not what should happen."

    Thanks, Drurb. Bottom line for me: I'm going to set everything so the sound I get is most pleasing to ME. That may or may not translate to the audience, but it has to sound good to me first in order for me to get in 'the groove' and play well.

    If FOH needs something different I'll leave that to the sound person running the PA (when there is one).
     
  3. Same for me. I know not everyone will agree, but if I'm not digging my own sound, how am I supposed to enjoy myself and hopefully play well? Just my 2 cents...
     
  4. rickwolff

    rickwolff Certified Gear Junkie, Amateur Adjunct Professor Supporting Member

    +1. Glad to see someone else is drinking the same Kool-aid.
     
    bassmanbrent likes this.
  5. Ortsom

    Ortsom Banned

    Mar 23, 2016
    Achieving effective acoustic isolation between instrument & speaker, while you play the bass and hear the speaker, may be difficult. If you want to test if it is in the amp, it may be easier to connect a non-microphonic source (like MP3 player, or EBG) to the amp, and try same.

    Aligned w/ drurb's reply, I suspect it is because not only do you hear the bass from 2 spatially separated sources (instrument & loudspeaker), but also the signal coming from the instrument is influenced by the sound from the speaker.
     
    sevenyearsdown likes this.
  6. rickwolff

    rickwolff Certified Gear Junkie, Amateur Adjunct Professor Supporting Member

    Yes, that would take some extraordinarily LONG ARMS (Go Go Gadget Man???).

    I was thinking of putting a mic in front of the speaker and recording it with and without the phase reverse.
     
  7. Tom Lane

    Tom Lane Gold Supporting Member

    Put your amp facing away from you in another room and close the door? Could be 10 feet away. Then mic that. Let us know!
     
  8. Ortsom is right, as long as you can hear your bass acoustically too, the acoustic sound and the amplified sound, which you obviously hear too, interact. Since the sound is not exactly the same, an inverted phase partially cancels some frequencies which results in a different sound.

    Some of the amplified signal might get back into the bass, but this would rather influence the sound when it gets loud, whereas the mix of amplified and acoustic sound influences the sound color more if the volume level is low to medium.
     
  9. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri

    Rick,
    I hear what you're talking about. My Walter Woods MI-400-8 has a phase reverse switch that I often prefer in the reverse position. The thing that's I think important to remember
    is that Phase Reverse is most often used to tame feedback. In those instance reversing the phase either works or it doesn't.

    Ric
     
  10. rickwolff

    rickwolff Certified Gear Junkie, Amateur Adjunct Professor Supporting Member

    Hi Ric,

    I rarely have any issues with feedback. All of the 3 mics/pickups I currently choose from are extremely feedback resistant (The Ischell, The Lifeline, and the AKG C411).

    What I DID notice was that there was a significant difference in tone (or timbre, if you like) when the phase reverese switch is on or off. I can accept that this is either a) inherently a bit mysterious, or b) well beyond my knowledge and understanding.

    Regardless, this is one more little thing in the toolkit that I had not taken advantage of previously, but I certainly intend to from now on.

    PS I should add that in those very RARE instances where I have any feedback, the adjustable notch filter on the EDB-2 is 'brilliant'. (in case any Brits are reading this).
     
    Last edited: Jan 24, 2017
  11. Ortsom

    Ortsom Banned

    Mar 23, 2016
    No, you'll need a neck extension, and stick your head in the room with the amp, while your bass is elsewhere. Toggle the switch with your nose.

    Anyway, on the mic in front of the speaker: best not. That way the sound from the speaker still interacts with the bass.
    If you want to test the phase-reverse circuit, use a line-out (which should be after the phase-reverse switch). Record that line-out (or send it to over-the-ear closed headphones), with the power stage of your amp turned-down completely (so no sound coming from the speaker). If you want to test while listening to the speaker, plug in an EBG or MP3 player.
    BUT: a 180° phase reversal is rather trivial, and not likely to be frequency dependent or faulty.
     
    Ric Vice likes this.
  12. Hi Rick,
    the 'manual' for the Schertler Dyn-B has a little diagram which might throw some light on this concept for you. The dyn-B has a phase/polarity reversal switch built into the xlr jack that sits in the afterlengths, where it is very easy to trial both 0 and 180 degrees. As you suggest, I would always check which setting sounded better - whenever I remembered to :rolleyes:.
    Steve
     
    Ric Vice likes this.
  13. sevenyearsdown

    sevenyearsdown Supporting Member

    Jan 29, 2008
    Sanborn, NY
    Technical explanations aside, I find the best method for setting up gear is - turns knobs and flip switches until it sounds cool!
     
    Ric Vice, Ortsom and rickwolff like this.
  14. 9Thumbs

    9Thumbs

    Jul 3, 2013
    Near Boston
    I play in a rather loud blues/roots band, so achieving a big sound is important to me. I have found that by flipping the phase switch on my FDeck 2, I can get a lot more volume without feedback with the switch one way than I can with it the other. I don't know whether I use it in or out of phase, doesn't really matter to me.
     
    Ric Vice likes this.
  15. And i always use the phase buttomn mere it renders the most full sound, to me indicating it is mainly in phase with the bass acoustic outout. I might then have to take more bass out in the eq, but to me that is stil the most "natural sound... And "feels" that way.
     

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