JBL Monitor Users: You might want to read this! (SRX712m content)

Gamedojo

Gamedojo

Power User
My experience with vintage JBLs made me think today. And I'm glad I checked.

Vintage JBLs are wired backwards. Black is positive and red/white is negative.

I got a Crown XLS402 to run into my new JBL SRX 712m monitor today, and have to run banana clips to bridge the output of the power amp. On a whim, I quickly took a 9v battery to the end of the banana clip to check the polarity of my JBL monitor. Sure enough, I was rather surprised to see that the monitor is wired backwards.

how you tell is to line up the pos and neg of the battery to the pos and neg of the cable and check the woofer. if it pushes OUT then its the right polarity. If it pushes IN, then its reversed.

the Woofer in my 712m went INWARDS when I lined up the battery and cable the stock way. So I was able to reverse the banana leads into the amp and it does sound better. Some may claim it doesn't matter, but for guitar a woofer pushing inwards sounds congested IMO.

Give it a shot.
 
Man....now you really have me thinking.
I have older JBL SR-X dual 18" drivers....which I know are backwards, so I wired my cabs that way.
But I also have SRX722's (same series as yours), SR-X4702's, SR-X4722's......which I have never tested.

Oh boy....it's off to the garage with a battery.

Thanks for the post Gamedojo!
 
It doesn't matter.

but first answer this: are your pickups wired the right way round??, ie which way should the cone move when the string moves upwards ... in or out? If absolute phase of the system is important, then you have to be able to answer this. If you can't answer this, then how do you know your guitar pickups are not wired the wrong way round ;) ;) ... you get my point?

Or put another way, it only matters if your guitar plays down to DC :)

For every "push" of the cone out, there is another "pull" of the cone in ... the system is AC and always reutrns on avergae to zero, so for every push there is a pull .. sure you made the cone move outwards for applying a +ve voltage to the red pin, but, in reallity, when the signal comes out of the amplifier, equal positive and negative voltages will be applied ... pushing the cone in and out equally ... if you think the cone moves out for example on the "kick" of the bass drum, you are wrong. It doesnt. It moves in and out, pulled and pushed .. at the lowest system frequency, usually there is a cut-off LPF at around 25Hz, I know some guys on here are using 100Hz filters, so no frequency below that gets through ... when you hear that "kick" on the pass drum, its actually starting with a sine wave, 25Hz .. in and out. So saying the cones moves out is wrong ... its AC, in and out sine wave ...



if you think you can hear a difference, you are fooling yourself.
 
Of course this doesn't matter at all unless you're using it physically right next to other speakers wired correctly.

oops - this was to OP
(simultaneous post with CrazyTrainer)
 
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GM Arts said:
Of course this doesn't matter at all unless you're using it physically right next to other speakers wired correctly.
Click to expand...
Absolutely it doesn't matter, even if they are next to each other - and wired the same.
The problem arises when one is wired correctly and the other is reversed. They are out of phase with each other, can cancel each other out and cause all sorts of weird artifacts. :(
 
Actually, the correct fix for this problem is to change you're picking style to upstrokes on the beat :lol
 
Would it matter if they were being used as PA tops?
Assuming they really 'should' be wired the same phase as the Subs?
 
^ yes, it would mess with frequencies in the crossover region (given that having speakers in different locations does this to some extent anyway)
 
FWIW, it does matter. My best arguement will be to use Jay Mitchell's own words (keep in mind hes been designing and working in the field of loudspeaker technology for 30+ years):


Quote:
"For one speaker, it shouldn't matter."
Uhh, it does matter when you're playing guitar through that one speaker. Potentially a lot.

Quote:
"At 1000Hz, you're not going to be able to tell whether those 1000 cycles in that one second began with a push or a pull."
If all you ever played through your speaker were sine waves, that might be relevant.

Quote:
"I can understand how opposite phase would displace feedback/sustain frequencies at levels loud enough for the speaker to influence string vibration,"
That's it. Those levels are a lot lower than you think. Any interaction at all between the guitar body and the sound from the amp is enough to noticeably affect sustain and feel. Polarity has an effect on this.

Quote:
"but it seems you're implying some waveform dependency".
The audibility of reversing polarity in recorded signals has been established in blind testing. It's a subtle effect, and certain types of signals make it easier to detect.

Quote:
"How would opposite speaker phase be different than picking a guitar string up as opposed to down,"
The pickup responds to string movement at right anges to the guitar top (IOW, to motion towards and away from the pickup). Therefore, since the release of the string (the movement that initiates sound) is always away from the guitar top, the polarity of the pickup's response does not reverse between downstrokes and upstrokes. This is easily demonstrated.

Quote:
"or to the arbitrary phase when playing through various effect pedals and amplifiers?"
If devices in the signal chain reverse polarity, then that effect is detectable.

Polarity always matters. Even if it only matters a little, it costs no more to get it right than to reverse it.
CrazyTrainer said:
It doesn't matter.

but first answer this: are your pickups wired the right way round??, ie which way should the cone move when the string moves upwards ... in or out? If absolute phase of the system is important, then you have to be able to answer this. If you can't answer this, then how do you know your guitar pickups are not wired the wrong way round ;) ;) ... you get my point?

Or put another way, it only matters if your guitar plays down to DC :)

For every "push" of the cone out, there is another "pull" of the cone in ... the system is AC and always reutrns on avergae to zero, so for every push there is a pull .. sure you made the cone move outwards for applying a +ve voltage to the red pin, but, in reallity, when the signal comes out of the amplifier, equal positive and negative voltages will be applied ... pushing the cone in and out equally ... if you think the cone moves out for example on the "kick" of the bass drum, you are wrong. It doesnt. It moves in and out, pulled and pushed .. at the lowest system frequency, usually there is a cut-off LPF at around 25Hz, I know some guys on here are using 100Hz filters, so no frequency below that gets through ... when you hear that "kick" on the pass drum, its actually starting with a sine wave, 25Hz .. in and out. So saying the cones moves out is wrong ... its AC, in and out sine wave ...



if you think you can hear a difference, you are fooling yourself.
Click to expand...
 
Gamedojo said:
FWIW, it does matter. My best arguement will be to use Jay Mitchell's own words (keep in mind hes been designing and working in the field of loudspeaker technology for 30+ years):.
Click to expand...

Well, then you (and he) are wrong, or you have mis-interpreted what he said.

Polarity does not matter, and I ask you again: If I pull the string up, and then release ... should the cone move initially in or out? Personally, I think it doesnt matter ... if you insist on an answer I will say "inwards".

Your argument fails to take into account some pretty fundamental facts ... you have stated that when a positive voltage is applied to the positive pin, the speaker cone should move outwards. Why? please explain using the laws of physics rather than relying on convention why this must be the case. What if the convention (and thats all it is, a convention) had been that the cone moves inwards for a positve voltage applied to the red terminal, what then?? ... infact, are you sure that its is the JBLs that have it wrong and not everyone else??

What *exactly* makes you think the initial movement of the cone should be outwards, I would have thought it doesnt matter, but I am happy to argue the initial cycle should move the cone inwards if that helps?

You might also like to consider what "initially" means in a bandwidth limited system ...

Put simply, yes it does matter in a multi-speaker system that they all respond the same way. In a single speaker system it does not.

However ... I do have some good news for you, firstly, you may be able to get some free money! There has been as I understand it an offer from the AES for anyone to submit a recording where it is possible to detect the absolute phase ... should be easy for you, just record your signal, send a copy of your posting (full disclosure) to Audio Engineering Society (AES) for replication. They have been looking I understand for an example since 1987, so they will be very pleased you managed it.

In the meantime you can take this test:

Absolute Polarity Blind Listening Test

Over the years many people have made the same arguments as you do, but in double blind tests ... its another story.
 
AES?

Here is the AES paper referenced in which blind tests clearly establish its audibility:
AES E-library Observation

I'm not sure why you're even arguing the recording aspect of this. We're talking about an FRFR speaker system you use with your guitar. In this scenario, polarity matters.

Its easy to test. Stand in the same location, get a note to sustain. Reverse the speaker polarity and try again. its actually the reason I noticed the JBL was wrong in the first place because I couldn't quite get my guitar to sustain/feedback very easily or at all until I reversed the speaker.

CrazyTrainer said:
Well, then you (and he) are wrong, or you have mis-interpreted what he said.

Polarity does not matter, and I ask you again: If I pull the string up, and then release ... should the cone move initially in or out? Personally, I think it doesnt matter ... if you insist on an answer I will say "inwards".

Your argument fails to take into account some pretty fundamental facts ... you have stated that when a positive voltage is applied to the positive pin, the speaker cone should move outwards. Why? please explain using the laws of physics rather than relying on convention why this must be the case. What if the convention (and thats all it is, a convention) had been that the cone moves inwards for a positve voltage applied to the red terminal, what then?? ... infact, are you sure that its is the JBLs that have it wrong and not everyone else??

What *exactly* makes you think the initial movement of the cone should be outwards, I would have thought it doesnt matter, but I am happy to argue the initial cycle should move the cone inwards if that helps?

You might also like to consider what "initially" means in a bandwidth limited system ...

Put simply, yes it does matter in a multi-speaker system that they all respond the same way. In a single speaker system it does not.

However ... I do have some good news for you, firstly, you may be able to get some free money! There has been as I understand it an offer from the AES for anyone to submit a recording where it is possible to detect the absolute phase ... should be easy for you, just record your signal, send a copy of your posting (full disclosure) to Audio Engineering Society (AES) for replication. They have been looking I understand for an example since 1987, so they will be very pleased you managed it.

In the meantime you can take this test:

Absolute Polarity Blind Listening Test

Over the years many people have made the same arguments as you do, but in double blind tests ... its another story.
Click to expand...
 
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Gamedojo said:
Its easy to test. Stand in the same location, get a note to sustain. Reverse the speaker polarity and try again. its actually the reason I noticed the JBL was wrong in the first place because I couldn't quite get my guitar to sustain/feedback very easily or at all until I reversed the speaker.
Click to expand...

Absolutely true.

And stand 2 feet further forward or back and exactly the opposite set of circumstnaces will exist, the "non feeding back" polarity will become the feedbacky one, and vice versa ... now, which one is correct?

Infact, you do realise that in order to get feedback, you need a gain in excess of 1 with a phase angle of 180 degrees? .. ie you have to have a polarity reversal throughout the entire feedback loop (thats coming out of the speaker, through the air, into the gutar strings and back into the pickups and round the amplifier again) the gain has to be in excess of one when the phase shift is 180 degrees ... if that condition is not satisfied, it wont feedback. Given that info, that woudl tend to suggest you actually need a phase reversal in order to get feedback in when close to the cab ...
 
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CrazyTrainer said:
It doesn't matter.

but first answer this: are your pickups wired the right way round??, ie which way should the cone move when the string moves upwards ... in or out? If absolute phase of the system is important, then you have to be able to answer this. If you can't answer this, then how do you know your guitar pickups are not wired the wrong way round ;) ;) ... you get my point?

Or put another way, it only matters if your guitar plays down to DC :)

For every "push" of the cone out, there is another "pull" of the cone in ... the system is AC and always reutrns on avergae to zero, so for every push there is a pull .. sure you made the cone move outwards for applying a +ve voltage to the red pin, but, in reallity, when the signal comes out of the amplifier, equal positive and negative voltages will be applied ... pushing the cone in and out equally ... if you think the cone moves out for example on the "kick" of the bass drum, you are wrong. It doesnt. It moves in and out, pulled and pushed .. at the lowest system frequency, usually there is a cut-off LPF at around 25Hz, I know some guys on here are using 100Hz filters, so no frequency below that gets through ... when you hear that "kick" on the pass drum, its actually starting with a sine wave, 25Hz .. in and out. So saying the cones moves out is wrong ... its AC, in and out sine wave ...



if you think you can hear a difference, you are fooling yourself.
Click to expand...



I'm not sure that this is correct tho....as far as I know, guitar speakers are typically connected in DC. The reason that the speakers don't remain pushed out or pulled in is NOT because it's AC (it's NOT btw), but because the frequency of a note also has similar sinusoidal oscillations - so the speaker WILL move in and out as it vibrates as it's set in motion by a frequency of the note you played.

I'm no Jay Mitchell on the subject, but it's simple physics at play as far as I know......could be wrong, but that's how I understand it....

Another thing - the guitar is also ALL DC (unless you are pushing actives, the output of which is STILL DC), so not sure I understand......it's all to do with the right hand rule.....current, field and motion, all at right angles to each other. But AGAIN, the signal you get is due to the FREQUENCY of the notes, and NOT the oscillation of any AC wave in the chain.....
 
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jon said:
I'm not sure that this is correct tho....as far as I know, guitar speakers are typically connected in DC. The reason that the speakers don't remain pushed out or pulled in is NOT because it's AC (it's NOT btw)
Click to expand...

Umm .. sorry, you are wrong. Most audio amplifiers have a low frequency cut-off around 25Hz ... It is extremely unlikey you have a audio amplifer that goes down to DC ... put simply, the reason it does not remain pushed out is precisely because it is being fed with an AC signal, ie the mean value of the signal is 0v, it has no DC content ... because it is high pass filtered at around 25Hz ... The speaker may well be wired directly to the amplier output ... but what it recieves is an AC signal. (in fact solid state amplifiers almost always have a DC protection circuit that assesses the mean value of the signal, and if it becomes non-zero, ie it has some DC content, opens a relay to protect the speaker.)

You may care to note that a valve amplifer has a transformer connected to the speaker which is a device which by its very nature, can only pass AC. You'll not find any DC there.

Maybe you are confused about what AC means? If the signal is varying in nature and has a mean value of zero, its is generally called an AC signal.

If the signal has a non zero mean value, it is said to have "DC content" ...

And if it has a significant amount of DC content with minimal AC content, it is said to be a "DC Signal"

A typical AC signal would be the output from your pickups, a typical DC signal would the output from a battery. and a typical signal with "DC content" woudl be the output from a bride rectifier, where you have a DC signal with an amoutn of AC ripple.
 
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I don't comprehend most of this....so I'm going to check all my JBL's...just so I know which way they are wired.

I think the only collective thing I can pull from this thread is that nobody is saying it's bad to have them wired 'in phase', with the battery causing the speaker to 'push'. So i'm just going to make sure they are all wired that way.
 
BBN said:
I don't comprehend most of this....so I'm going to check all my JBL's...just so I know which way they are wired.

I think the only collective thing I can pull from this thread is that nobody is saying it's bad to have them wired 'in phase', with the battery causing the speaker to 'push'. So i'm just going to make sure they are all wired that way.
Click to expand...

Yep, having them all your speakers wired the same way round is a very good idea, you never know when you will use them together.

Whether + to red makes them pull or push doesnt matter, but it is a good plan if all your speakers work the same way, you wont have phase problems when you use any of them together :)
 
Years ago, back in my conventional amplification days, I felt something just wasn't quite right with my amp-to-guitar interaction. So one day I took my speaker cable and reversed the wires on one end. Made a huge difference. From that day on I always reversed polarity when using that amp/cab combination. At the time I knew nothing of polarity studies and didn't know anyone who had experimented with polarity. All I knew was that it felt and sustained much differently with the polarity reversed.

In my recent studies I have found that the most guitar interaction occurs in the range of 100-300 Hertz. In air that corresponds to a wavelength of roughly 1-3 meters. Most guitar players are within 1-2 meters of the cabinet so it is not at all surprising that a polarity reversal would be make a difference.

Also, we tend to prefer the pick attack with positive pressure, for whatever reason. If the speaker is wired in reverse there will be negative pressure on the pick attack.
 
FractalAudio said:
In my recent studies I have found that the most guitar interaction occurs in the range of 100-300 Hertz. In air that corresponds to a wavelength of roughly 1-3 meters. Most guitar players are within 1-2 meters of the cabinet so it is not at all surprising that a polarity reversal would be make a difference.
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Yes, that makes perfect sense. As I said, for feedback to occur, you need a gain of more than 1, with a 180 phase shift (if you prefer to think of it in terms of poles and zeros, then thats an imaginary pole, with a radius grater than 1 in the transfer function).

Again, it is quite impossible to say whether that will be with +ve volts making a "pull" or a "push" on the speaker, it depends on how the air is interacting with the string, which is interacting with the pickups etc .. but a phase reversal will have an effect for sure, I guess youd need to try both and see which worked best. You may well find that different guitars require the opposite setting ... or stand + - half a wavelenght nearer/further the speaker :)
 
Yes that makes sense, Cliff.

What would also make sense is a phase reverse swicth on amps (like the AxeFX and common on acoustic amps as a possible feedback cure). That way we could manage the other sources of phase reversal such as pickup polarity, variable number of preamp stages, arbitrary o/p transformer connections, etc.
 
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