Double Bass phase reverse

[Swinging Beef]

So, after playing upright for over 20 years, and struggling with feedback for about half of them, I come across this place.

Now I hear about "phase reverse" and have:

1. No idea what it means
2. No idea if my amp has this facility
3. No idea of how to get it in to my signal chain if it doesnt

Im using the K&K Bassmaster Plus setup with an Eden Nemesis 2x10

 

[Jack Clark]

K&K Sound provides a one-paragraph discussion of phase reversal at [Invalid or Expired Link Removed].

As I understand it, it's somewhat like phasing considerations between two speakers in a stereo system, except that in this case the phasing is between your cab's speaker(s) and the vibrations put out by your acoustic instrument itself. You simply A-B the phase reversal switch on your pre-amp and listen for an improvement in sound. Theoretically, at least, if the speaker is out of phase with your instrument, some of the sound of each will be swallowed up by the competing vibrations. Supposedly, proper phasing from the switch will make the sound seem more full to your ears.

(In my particular case, I'm not entirely sure I can hear it. Perhaps, but it seems slight to me. It certainly does not sound as dramatic to me as reversing the phase of two stereo speakers.)

 

[Jaromir]

It depends on a particular situation (room acoustic, volume of the music, placement of your amp etc.). Sometimes (not very often though) the phase reverse saves your gig, sometimes it almost doesn't matter, it's very variable...

 

[William Hoffman]

3. No idea of how to get it in to my signal chain if it doesnt

two words: F-Deck

Invalid Link Removed

 

[boylebass]

Fishman Pro Platinum offers this feature as well.

 

[drurb]

The utility of polarity inversion in cutting feedback is that, when you get lucky, you can place the offending frequencies "out-of-phase" between the cabinet and the instrument. In such situations, when they are in-phase, the reinforcement of vibration from the cabinet is what contributes to feedback. I say "when you get lucky" because it's not really that simple. Given different cabinet placements, room reflections, room resonances, etc., inverting all frequency components by 180 degrees is really a hit-or-miss solution. It can often produce a benefit and it's an uncomplicated, inexpensive solution. If you want to try it out, fashion yourself a speaker cable with the signal leads reversed at one end. This would be your "inversion cable." Then again, I wholeheartedly endorse fdeck's gem of a device. Biggest bang for the buck going!

 

[Mike Dimin]

The utility of polarity inversion in cutting feedback is that, when you get lucky, you can place the offending frequencies "out-of-phase" between the cabinet and the instrument. In such situations, when they are in-phase, the reinforcement of vibration from the cabinet is what contributes to feedback. I say "when you get lucky" because it's not really that simple. Given different cabinet placements, room reflections, room resonances, etc., inverting all frequency components by 180 degrees is really a hit-or-miss solution. It can often produce a benefit and it's an uncomplicated, inexpensive solution. If you want to try it out, fashion yourself a speaker cable with the signal leads reversed at one end. This would be your "inversion cable." Then again, I wholeheartedly endorse fdeck's gem of a device. Biggest bang for the buck going!

That is why EA but a sweepable phase (0 to 180) on it's Doubler

 

[drurb]

That is why EA but a sweepable phase (0 to 180) on it's Doubler

For sure, that's a better option. Often, feedback is caused by a narrow band of frequencies and being able to adjust the phase, rather than simply invert polarity, offers a greater likelihood of success. It's still hit-or-miss, however, with a somewhat greater probability of "hit." Depending on the bandwidth (range of frequencies) affected by the control, one can solve (or nearly solve) one problem but create another. The greater the bandwidth affected, the more likely that is to occur. If the bandwidth affected is too narrow, you may miss being able to affect the offending frequency region. The truth is that phase-shifting doesn't always work.

There are many fancy algorithms for eliminating feedback and, let's face it, few of us are likely to use, much less pay for high-level processors to accomplish it. Phase-shifting is a useful and relatively inexpensive tool in the arsenal and EA's approach, in principle, is definitely superior to simple polarity inversion.

(Mike, maybe you can get me details/specs/measures on the operation of that control.)

 

[MrSidecar]

(Mike, maybe you can get me details/specs/measures on the operation of that control.)

Hi all,

I'd really appreciate that as well- since both the 0-180 bit and another piece of info I remember from somewhere hint to the sweep actually occuring somehow measured in degrees (of an angle, 180 being halfway round a circle, thus, perfectly opposing). ANd that is something that I with my layman idiot understandings of "phase reversion" fail to grasp- how can you take a signal (the pu signal at the amp input) and move its phase around by degrees? Flipping i understand perfectly, and use regularily, but you can't gradually change polarity.

As one can easily see, info bits and remebered things swirl around in my brain and I can't make sense of them. (Maybe I'm being incredibly stupid and just have to read a manual...) So any enlightenment in this regard is appreciated.

Best
Sidecar

 

[Mike Dimin]

(Mike, maybe you can get me details/specs/measures on the operation of that control.)

I can try. As you know I no longer work for EA

 

[Mike Dimin]

For sure, that's a better option. Often, feedback is caused by a narrow band of frequencies and being able to adjust the phase, rather than simply invert polarity, offers a greater likelihood of success. It's still hit-or-miss, however, with a somewhat greater probability of "hit." Depending on the bandwidth (range of frequencies) affected by the control, one can solve (or nearly solve) one problem but create another. The greater the bandwidth affected, the more likely that is to occur. If the bandwidth affected is too narrow, you may miss being able to affect the offending frequency region. The truth is that phase-shifting doesn't always work.

There are many fancy algorithms for eliminating feedback and, let's face it, few of us are likely to use, much less pay for high-level processors to accomplish it. Phase-shifting is a useful and relatively inexpensive tool in the arsenal and EA's approach, in principle, is definitely superior to simple polarity inversion.

(Mike, maybe you can get me details/specs/measures on the operation of that control.)

I agree that sweepable phase is a better solution than a 180 switch, but it is not and never will be the end all solution. Phase is also frequency dependent - so what works at certain frequencies will not necessarily work at all frequencies. It is and always will be a bit of a compromise

Mike

 

[drurb]

Hi all,

I'd really appreciate that as well- since both the 0-180 bit and another piece of info I remember from somewhere hint to the sweep actually occuring somehow measured in degrees (of an angle, 180 being halfway round a circle, thus, perfectly opposing). ANd that is something that I with my layman idiot understandings of "phase reversion" fail to grasp- how can you take a signal (the pu signal at the amp input) and move its phase around by degrees? Flipping i understand perfectly, and use regularily, but you can't gradually change polarity.

As one can easily see, info bits and remebered things swirl around in my brain and I can't make sense of them. (Maybe I'm being incredibly stupid and just have to read a manual...) So any enlightenment in this regard is appreciated.

Best
Sidecar

Actually, I wanted the specs, etc. to see how well it is implemented and over what bandwidth. Indeed, you can shift the phase of all component frequencies of a signal by a constant number of degrees. It's rather easy to do via digital signal processing. What's not so easy is to build an analog continuously adjustable broadband phase shifter so that one can rotate the phase of all components by an arbitrary number of degrees.

Although I suspect many here won't care about this history, back in the '60s, 70s, and even into the 80s, one of the most coveted pieces of laboratory equipment for auditory research was the Grason-Stadler E3520B phase-shifter (Google it). This was a large vacuum-tube-based unit. The heart of the unit was a big adjustable capacitor that the manufacturer eventually stopped making. There really was no substitute except for a circuit someone designed using resolvers but it meant building your own. I still have three or four E3520Bs but it's been ages since I fired one up. They were marvels.

I agree that sweepable phase is a better solution than a 180 switch, but it is not and never will be the end all solution. Phase is also frequency dependent - so what works at certain frequencies will not necessarily work at all frequencies. It is and always will be a bit of a compromise
Mike

Yup, indeed, exactly.