norburybrook wrote: ↑Fri Mar 02, 2018 12:54 pm
Interestingly.....or not... I used my Express with my #102 and they were both in phase at the speaker.
Marcus
Isn't 'phase' in the recording sense more about how well you place the mic's though, so they don't end up colliding with one another in some slight phase variance? I thought basically if you do micing wrong even with two 'in phase' sources you can cause phase issues no? Basically implying that just because you got them 'in phase' at the speaker, it could be related to mic positioning etc.
Phase is phase Phil, it's basically how waveforms either go up and down together or not. Totally out of phase will cancel but there's everything in between, and it's frequency dependent as well,and obviously when recording it's very important to keep all microphones in the best phase possible from the source sound.
With amps and speakers though it's simple, they're either in phase or out of phase relative to each other.. It rears it's ugly head when you start using either multiple amps and or multiple microphones.
So my comments about the two amps were really to say that when plugging in to both amps at the same time they were both in phase..i.e. both sets of speakers were going in and out at the same time. If they'd been out of phase one would be going in at the same time the other was going out, cancelling a lot of the low frequencies. It would have still been possible to put microphones on the cabs though and be our of phase due to their positions.
so if you wanted to use a JTM 45 and a Trainwreck together you'd have to have a phase flip on one of the speakers otherwise they'd naturally be out of phase., or most decent ABY boxes have a phase switch for this reason. so the signal is flipped as it hits the amp input.
You were but that is also an interesting topic that admittedly I don't know much about! Does remind me of when I recorded my guitar in a band years ago using two mics and couldn't work out why it sounded so dull and lacked bass on the recording. This explains why!
So basically it seems that Ken was wrong, at least about the JTM45 anyway. I'm sure I read somewhere that the Express was in phase but can't find it now. I personally think it does make quite a different to the sustain and in theory it would make all notes sustain for longer.
Another thing to consider is phase shift, something else I don't know much about. I heard that every time the signal goes through a capacitor it phase shifts slightly. Is that true?
Littlewyan wrote: ↑Sun Mar 04, 2018 12:34 pmAnother thing to consider is phase shift, something else I don't know much about. I heard that every time the signal goes through a capacitor it phase shifts slightly. Is that true?
Yes and it's frequency dependent. Have a look here:https://www.electronics-tutorials.ws/fi ... ter_3.html and scroll down to the Bode and phase shift plots. You'll recognize that this network appears after each gain stage.
Littlewyan wrote: ↑Sun Mar 04, 2018 12:34 pmAnother thing to consider is phase shift, something else I don't know much about. I heard that every time the signal goes through a capacitor it phase shifts slightly. Is that true?
Yes and it's frequency dependent. Have a look here:https://www.electronics-tutorials.ws/fi ... ter_3.html and scroll down to the Bode and phase shift plots. You'll recognize that this network appears after each gain stage.
Yes I learned about this building my Vox AC30/4, it has a phase shift network that is part of the tremolo circuit. Very cool stuff.
Littlewyan wrote: ↑Sun Mar 04, 2018 12:34 pm
So basically it seems that Ken was wrong, at least about the JTM45 anyway. I'm sure I read somewhere that the Express was in phase but can't find it now. I personally think it does make quite a different to the sustain and in theory it would make all notes sustain for longer.
I doubt that the ouptput phase on a single amp and speaker will have any impact on sustain. Phase is only relevant in relation to another source, hence my first post saying that 'Phase is always relative'
you can easily test this by fitting a simple phase switch on your speaker. Just play your amp and then flip the phase switch, you'll hear immediately if there's a difference.
norburybrook wrote: ↑Sun Mar 04, 2018 8:16 pmI doubt that the ouptput phase on a single amp and speaker will have any impact on sustain.
In a combo amp there is significant opportunity for acoustic waves from the speaker and resonances in the cabinet to excite electronic components like capacitors and tubes. This could become either positive or negative feedback, so it's worth trying both speaker polarities to see if there is any noticeable difference.
But in phase the cones move out on the attack and they move back when the phase is flipped. Phase is king. If you record a band properly with blasting attack then flip the phase of the guitar.. wimper by comparison. It's a real thing.
AC30 will drive a newb mad. haha
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
norburybrook wrote: ↑Sun Mar 04, 2018 8:16 pmI doubt that the ouptput phase on a single amp and speaker will have any impact on sustain.
In a combo amp there is significant opportunity for acoustic waves from the speaker and resonances in the cabinet to excite electronic components like capacitors and tubes. This could become either positive or negative feedback, so it's worth trying both speaker polarities to see if there is any noticeable difference.
That's an interesting thought Martin and one I've never considered as I only tend to worry about 'amp/speaker phase' when using more than one amp/speaker together.
I'm going to give it a try though at some point to see if I can hear any difference.
Miles, I think a cranked amp through a sealed 4x12 would be an easy exaple to hear that positive/negative phase realtionship. You certainly get a lovely pressure wave on the back of your legs from a sealed cab when hitting a sharp transient power chord
Reeltarded wrote: ↑Sun Mar 04, 2018 9:56 pm
But in phase the cones move out on the attack and they move back when the phase is flipped. Phase is king. If you record a band properly with blasting attack then flip the phase of the guitar.. wimper by comparison. It's a real thing.
AC30 will drive a newb mad. haha
Yep; you want the bass players amp to have the same phase as the guitar and kick drum as well ideally so everybody is pushing air in the same phase.
With computer DAW's you can adjust after the fact if something is mic'd badly (out of phase) providing the tracks are isolated, but it's always better to get it right first if possible as it will sound better straight away. I think a lot of inexperienced engineers fall foul of poor technique when it comes to phase.
A little OT comment; the reason a lot of studio engineers/mixers liked using the classic 80's Yamaha NS10 speaker (the back speakers with white cones you would see n the meter bridge of large consoles) was mainly because they had really good phase characteristics due to their fully sealed cabinet design. The frequency response wasn't great but they had great phase so you could mix well on them once you knew their sound.
This ties in with my point about the 4x12 cabinet as that too is a sealed unit and the phase response is very obvious.
Really, when comparing 2 signals and their sources, their relative phase and polarity are completely different, separate characteristics.
That's why it may be better to use the terminology signal 'polarity' or 'inversion', rather than signal 'phase'.
As noted, phase applies to specific frequencies/distances/times, whereas polarity (theoretically) applies equally across the bandwidth.
Mixing truly 'equal but out of phase' real signals (ie not single frequency) will result in a comb filter response, whereas mixing equal signals of opposing polarity will result in silence.
Unfortunately we're stuck with the terminology, I think that Langford Smith et al just assumed that anyone who had to deal with these things would have had the education background to understand the difference when they used the words interchangeably in terminology such as 'phase inverters'.
Op amp terminology eliminates this confusion, eg inverting and non-inverting inputs.
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!
