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Post subject: Polarity
Posted: Sat Jun 15, 2019 3:46 pm
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Hi guys....bought this....... Image He said it was around a '66 or so.

I'm about to do the swap out with the OEM Eminence.....but before I do I will attempt a somewhat scientific A/B comparison and see if it pans out. I'll record both speakers into Pro Tools and will try to be critical about positions, distances....all measurements and levels. No effects on the recorded audio as well....what went in is what we hear.

My question though is this.......the guy told me that "what a lot of people don't know is........" going on to say that with the JBL D130F......you do not wire it up normally. He told me to reverse the polarity of the speaker wires......( + goes on - and vise versa). He went on to explain that, if I wire it normally....then instead of the cone pushing forward as a signal is applied....the cone will pull back.

I've heard of tone suck.....LOL!!! Certainly don't want my tone to suck......forwards or backwards for that matter. :lol:

How accurate is this....do I need to follow his instructions?


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Post subject: Re: Polarity
Posted: Sat Jun 15, 2019 8:45 pm
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I tore my hair out over JBL polarity.
It was a floor monitor with 2 12s in a wedge.
I had rebuilt the crossover and the house soundman swore it wasn't hitting as hard as its mate.
I visually checked it, but the 9volt battery test didn't move the cones enough to see them move.
I never did figure it out. A guy from a band passing through knew about the JBL difference and they fixed it on the spot.
Now, I don't know if your old speaker is the same reverse setup
But, phase matching is not the same as polarity.

Different amps may have different polarity outputs.

I think that right polarity is obtained when you push on the diaphragm of a microphone and the speaker cone moves outward


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Post subject: Re: Polarity
Posted: Sun Jun 16, 2019 12:17 pm
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This is actually a phase thing, and is important in multiple-speaker cabinets or multiple cabinets.
You will hear no difference with a single driver in your studio.

The signal is an AC waveform. The cone moves both forward and backwards with respect to its center "resting" state.

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-- Rich


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Post subject: Re: Polarity
Posted: Mon Jun 17, 2019 12:24 pm
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Let's summarize:
When you do "the battery test", you hook up a 9 volt battery to the speaker terminals. All this does is tell you if the voice coil is fried. If the coil is bad, nothing happens. If the voice coil is good the cone moves in (or out). As the battery is direct current, the cone will move in only one direction (in or out - makes no difference) and stay there as long as the 9 volts is applied.
If you have two speakers, and one cone moves "in" while the other speaker moves "out", the speakers are out-of-phase. Now is when you switch the connections on *ONE* of the speakers. Again, makes no difference which one. This is why speaker terminals are labeled plus and minus, so we know how to hook up two or more speakers and keep them in phase.
As we all know, the signal coming from the amp and going to the speaker is A/C, so IRL the speaker cone moves alternatingly, in-and-out, both directions.
If you only have one speaker, you can't be out-of-phase.


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Post subject: Re: Polarity
Posted: Tue Jun 18, 2019 2:09 pm
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You know Rich......my brain was telling me this but I just kinda defaulted to what that guy said....since he seemed more knowledgeable than I, about speakers. But yes......that makes total sense.

Thanks all.


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Post subject: Re: Polarity
Posted: Wed Jun 19, 2019 9:48 am
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"Absolute phase" -- pushing the mic diaphragm inward makes the cone move outward -- is proven to sometimes be audible.

Vocals particularly. Words that start with "p" or "b" -- sounds that are formed by your mouth/lips modulating a blast of air leaving your lungs. (As opposed to the sounds created by your vocal chords.)

Trumpets and other non-reed wind instruments also sound a little different when the initial movement of the cone is inward instead of outward.

In the hifi world there have been several research studies that show it's clearly audible with some sounds -- in A/B tests through headphones or high-end rigs tailored to the particular listening room. And a lot of high-end audiophile gear have phase switches for that reason (because recordings aren't always phase-correct).
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But most systems mask absolute phase. EQ circuits, crossovers, room reflections all throw in phase discrepancies. Reportedly, if you've heard the difference through headphones it's a little more noticeable when listening to more chaotic systems, but it's generally insignificant for most listeners most of the time.

And guitar strings are similar to vocal chords. They produce lots of harmonics that are phase shifted versus the fundamental -- not the clear phase of an air impulse.

Plus, guitar signal chains often have phase inversals. Many pedals invert phase. Some guitars have phase switches that invert the signal of one pickup -- if you select that pickup by itself, one way it'll be correct absolute phase, the other way will be an inverted signal. In amps like a Twin Reverb or Deluxe Reverb, the two channels are out of phase. If you turn on your boost pedal, or flip your guitar's phase switch, or plug into a DR's "normal" channel instead of the "reverb" channel, you'd need to reverse the speaker connections to maintain absolute phase.

So most guitarists under most conditions don't notice absolute phase.
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But some do. Steve Kimock is a big advocate of correct absolute phase. Says it makes guitars sound "livelier", and makes feedback easier but also more controllable. Says that when the phase is reversed, the guitar sounds like it's fighting against you.

And in the tweed Bassman community, there are people who say they sound better with the speaker connections reversed. Like many other amps, the Bassman inverts the signal, but unlike most other amps it has a thin floating baffle that vibrates and contributes a lot to the sound at high volume -- and supposedly phase affects that.
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Of course when mixing speakers it's important that they're all in-phase with each other. So as others have said, JBL's reversed markings matter a lot if you're running them alongside other speakers.

But the seller wasn't completely wrong that it matters even when you run one speaker by itself. There is a tiny minority of guitarists who swear they can hear it. (As a subtle thing, the icing on the cake -- not a huge thing that slaps you in the face, but just a nuance.) Maybe the seller hears it, or has read that others hear it.
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A conversation with Mr. Kimock inspired me to experiment. Maybe absolute phase was the difference between good rigs and great rigs, and I had experienced it without knowing what was causing the difference?

But no, I personally don't notice absolute phase. Just like 99% of guitarists.
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But JBL's spring clamp connectors make experimenting super easy in an open-back cab. You can't hurt anything by reversing them.

Give it a try both ways, under a variety of conditions. The proponents say it's a subtle "feel" thing. It may be more noticable with some amps, pedals, or playing styles.

(This isn't just a JBL thing. In the Bassman example, because it's an inverting amp you have to connect "properly marked" speakers backwards to have correct absolute phase. And you can try it with any amp/speaker combination. Whatever floats yer boat.)


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Post subject: Re: Polarity
Posted: Wed Jun 19, 2019 6:56 pm
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I can't speak to the music, because I don't have "ears". But I can see the difference clearly on an oscilloscope.
While most of a guitar note ia an equal AC waveform, the initial string drop creates an asymmetrical positive peak. So it is probably important to have absolute phase to get lead guitar to cut through the band.
The odd thing is when you pick the string above the halfway point on the neck, the asymmetric peak at string drop is negative on the scope.
If you pluck low then high on the neck, you can discern a slight hollowness from the string pluck near the top of the neck compared to near the bridge.


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Post subject: Re: Polarity
Posted: Wed Jun 19, 2019 10:20 pm
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Yes, visible on a scope...

But if it was clearly audible, we'd all be counting gain stages so we could connect the speaker correctly depending on whether there's an odd or even number. We'd be bothered by the inverted channel on TRs and DRs. There'd be pedals designed expressly to correct phase. Phase switches on guitars would be tone suckers.

Some people hear it under some circumstances. It's another geeky thing to experiment with if you enjoy that sort of thing.

But most of us don't notice it most of the time. Some of us never notice it.

I just brought it up because the seller may not have been crazy, making stuff up. There aren't a lot of people who ever consider absolute phase, and for me I've found it to be a non-issue. But there are some people who think it's another little piece of the magic that separates good tone from great tone.


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Post subject: Re: Polarity
Posted: Thu Jun 20, 2019 10:17 am
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I agree that it is a nebulous factor for most musicians.
But I remember a cover from an old Chet Atkins album. It was a studio photo and prominent among the gear shown was an oscilloscope. So I know musicians can make use of them. Was it for phasing or mic placement???


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Post subject: Re: Polarity
Posted: Sat Jun 22, 2019 6:19 pm
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Thanks for the interesting info folks. I’ll wire it the way the guy said.....if I can only mount it in the cabinet. :0(


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