Moderators: pompeiisneaks, Colossal
Amp splitter, that sounds like a neato torpedo project!paulster wrote: I gave a similar thing a quick try on my Express the other day when I finished building a transformer-coupled amp splitter which I'd put phase reverse switches on (like a Lehle P-Split).
You need to find that sweet spot . There are a lot of other things that come into play like harmonics and room acoustics but this may give you something to think about. When you run into problems in phasing is when you have say two 4x12 cabs on stage and they are out of phase with each other. This will cause cancelation and they won't sound as full. If you don't believe me ask your sound man 
If you will notice, Steve Vai will change his position on stage to get different feedback harmonicsUR12 wrote: If you play a 440 note and you move around with your guitar you will find a place where it feeds back better...
Glen, what GT tube rating are these? (1-10)geetarpicker wrote:Try some of the new Groove Tubes EL34M tubes. I'm not kidding, they are some of the best tubes I've ever run in my original Express.
GK
Very well explained.
Glen, what GT tube rating are these? (1-10)geetarpicker wrote:Try some of the new Groove Tubes EL34M tubes. I'm not kidding, they are some of the best tubes I've ever run in my original Express.
GK
For speaker phase reversal then yes. My project was a transformer-isolated splitter so you could use an ABC or ABY box with more than one amp with no ground loops. I just put phase switches after the transformers because some amps are inverting and others aren't. I did exactly the same thing with a DPDT switch, just at signal level.gearhead wrote:Amp splitter, that sounds like a neato torpedo project!
For dedicated, simple, phase reversal, couldn't you do it in a little box with a hefty DPDT switch and two jacks?
What I didn't expand upon when I said I'd noticed a distinct difference was that was in one specific position. I didn't try moving to see whether the reverse scenario was applicable in a different position, which I think is highly likely. I was more concerned about the neighbours at that point!dartanion wrote:Thanks for the explanation. I was pretty sure it had to do with wavelength and distance from the amp as I have done this for years to get feedback, but wasn't sure how to break this all down as I am no EE
So, my next questions is why exactly would reversing the polarity improve the ability to get feedback? Would this just reverse the scenario that you described? Using the 40Hz test tone, would it sound softer 9ft back, then louder another 9ft back as the phase of the wave starts 180 degrees out of phase and thus altering the sweetspot location?
I’m no EE either. Even if the wave is 180 degrees out of phase as you described above you will still have 2 spots that will be loud and that is at 90 degrees and 270 degrees so to answer your question no, the sweet spot won’t be altered by a 180degree phase shift. . Like I said there is a lot more involved that we could go on for days about, Reflected waves, waves coming from the back of an open cab mixing with waves from the front of the cab. Does your speaker move out when you strike down on a string and move in when you stroke the string in an upward motion? What would happen if you miked the back and the front of an open cab and mixed the two signals together? What if you had a rhythm player with an amp who’s output was out of phase with the lead players amp and you wanted to do some harmony parts. Even harmonics will still have the same “Sweet spots” as the fundamental only a whole lot more of them. When you mix 2 signals that are in phase they sum together and the resultant wave is larger (Louder) than the individual waves. When you mix 2 waves out of phase they cancel each other out and the resultant wave is smaller than the 2 individual waves.dartanion wrote:Thanks for the explanation. I was pretty sure it had to do with wavelength and distance from the amp as I have done this for years to get feedback, but wasn't sure how to break this all down as I am no EE
So, my next questions is why exactly would reversing the polarity improve the ability to get feedback? Would this just reverse the scenario that you described? Using the 40Hz test tone, would it sound softer 9ft back, then louder another 9ft back as the phase of the wave starts 180 degrees out of phase and thus altering the sweetspot location?
Yes, Guitar techs will sometimes put these tape spots on the stage or it could be the light guy said ”Stand on the cross so I can get this blue light on you while you are getting all of that feedback”paulster wrote: What I didn't expand upon when I said I'd noticed a distinct difference was that was in one specific position. I didn't try moving to see whether the reverse scenario was applicable in a different position, which I think is highly likely. I was more concerned about the neighbours at that point!
As a vaguely-related aside I noticed that the taped white cross on the stage when Gary Moore last played London was so that in Parisienne Walkways he could hold that note on feedback for 30seconds without using a Fernandes Sustainer like he used to, by standing on the cross.
Dana, I'm no EE either and can't explain it. But your question above was addressed in that TGP thread by someone much more knowledgable than I and they indicated that if you strike the same string, same note, same pick, same motion, same everything...that sometimes the speaker will move forward first and sometimes move backward first. And they indicated that the attack of the note is just basically 'noise' followed by an actual pitch/frequency (i.e. the note).Does your speaker move out when you strike down on a string and move in when you stroke the string in an upward motion?
I am not sure which thread you are talking about at TGP. I was trying to be rhetorical with the questions. I don't know of any guitar players that worry about which way their speakers are moving when you pluck the string. (Well maybe a couple)Fischerman wrote:Dana, I'm no EE either and can't explain it. But your question above was addressed in that TGP thread by someone much more knowledgable than I and they indicated that if you strike the same string, same note, same pick, same motion, same everything...that sometimes the speaker will move forward first and sometimes move backward first. And they indicated that the attack of the note is just basically 'noise' followed by an actual pitch/frequency (i.e. the note).Does your speaker move out when you strike down on a string and move in when you stroke the string in an upward motion?
Also, if the person that mentioned Vai moving to get feedback was referring to the first G3 DVD (the one with EJ)...Satch does a similar thing in his set...and in at least some cases they don't 'move'...they just rotate their body/guitar ~90 degrees and the pitch/harmonic of the feedback would change.
To be honest, I don't spend that much thought trying to explain it from a theory standpoint. I just collected empirical data and went with that.
You couldn't do anything about it anyway. They usually just hook up their amp and cab , find a spot on stage that sounds good to them and where they can get the tactile response they need and go at it. There has been volumes written about the physics of sound and there is a lot of it that you just can't do anything about except to abide by the lays of physics. I think it is cool to think about making sure that all you speakers are in phase with each other and stuff you have some control over, but what I am really getting at is that the sound changes every time you move a few feet one way or the other. Too much depends on the room, the equipment and the miking, air temperatures, humidity, etc,etc. I think everyone who has played in a band has had one of those moments when it all seems like everything is clicking together, when everyone is in the groove and you have never sounded so good and then ask yourself what did we do different this time. The answer is usually "nothing " or "I don't know"What I have been trying to say is one polarity feedsback better than the other and it doesn't matter where you stand. Well...it matters in that you'll get better feedback in one spot than another (like we've all seen before) but the polarity will affect it regardless of where you stand. Better one way than the other regardless of where you stand. I didn't believe it until I tried it either. Once I tried it though...believer. If you haven't tried it you really owe it yourself to do so. I can't even be sure it applies to all amps...but it sure does to the ODS. And if you read that thread...it appears that both HAD and Andy were aware of it too.I think it is cool to think about making sure that all you speakers are in phase with each other and stuff you have some control over, but what I am really getting at is that the sound changes every time you move a few feet one way or the other.
