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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Chris Carpenter on April 04, 2011, 06:13:21 PM
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I snagged a pair of used jrx115s super cheap and am starting to play with them. The speaker I am testing now looks to have had a tweeter diaphragm replacement (the horn was mounted upside down). The magnatude graph seems to loose coherence and amplitude around 2k (right where the passive crossover is set). I flipped the polarity on the tweeter and got the second graph, which is much more even. Note that I bypassed all crossovers and EQs to get those graphs. Does this imply the tweeter is out of polarity? The leads are properly connected, could this be an after-market diaphragm that was wound the wrong way? Will reversing the polarity on the tweeters solve my problem, or is there something bigger I should worry about?
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Heres the phase graph... :(
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Looks like a classic polarity inversion to me. Of course, either the tweeter OR the LF could have been reversed...
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Looks like a classic polarity inversion to me. Of course, either the tweeter OR the LF could have been reversed...
And that absolute driver polarity does not necessarily reflect the phase response at acoustic crossover....
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Looks like a classic polarity inversion to me. Of course, either the tweeter OR the LF could have been reversed...
Ah, I didnt know this was normal. It's strange, I thought the graph with the components in polarity looked nicer.
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I snagged a pair of used jrx115s super cheap and am starting to play with them. The speaker I am testing now looks to have had a tweeter diaphragm replacement (the horn was mounted upside down). The magnatude graph seems to loose coherence and amplitude around 2k (right where the passive crossover is set). I flipped the polarity on the tweeter and got the second graph, which is much more even. Note that I bypassed all crossovers and EQs to get those graphs. Does this imply the tweeter is out of polarity? The leads are properly connected, could this be an after-market diaphragm that was wound the wrong way? Will reversing the polarity on the tweeters solve my problem, or is there something bigger I should worry about?
Bennett could be right...it could be an after market LF 15 or even a recone kit. For years, JBL has wound their voicecoils opposite of everyone else in the industry. DC voltage to the red post drives their cones rearward instead of forward. Either the LF or HF driver could be off.
If you use subs, the jrx115s should be in phase with those as well.
As you have already learned, it is simple enough to fix with wiring.
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Bennett could be right...it could be an after market LF 15 or even a recone kit. For years, JBL has wound their voicecoils opposite of everyone else in the industry. DC voltage to the red post drives their cones rearward instead of forward. Either the LF or HF driver could be off.
If you use subs, the jrx115s should be in phase with those as well.
As you have already learned, it is simple enough to fix with wiring.
Oh, i was under the impression this was normal? So I should flip the polarity on the tweets, right?
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Oh, i was under the impression this was normal? So I should flip the polarity on the tweets, right?
You should make them both be like the one without the big notch at the crossover frequency, and the loss of Smaart coherence. Sometimes it is part of the design for the absolute polarity of the tweeter to be different than the woofer, but that would be to smooth out the response through the crossover, not put a hole there.
The woofer should be in the correct absolute polarity.
Mac
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Oh, i was under the impression this was normal? So I should flip the polarity on the tweets, right?
It doesn't matter which speaker you flip to make the correction. And it doesn't matter which direction the cones move with positive current. As long as all drivers in the stack begin moving in the same direction, then they will be in phase with one another. This will avoid cancellation at the crossover points.
All speaker stacks in the system need to be in-phase with one another as well.
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It doesn't matter which speaker you flip to make the correction. And it doesn't matter which direction the cones move with positive current. As long as all drivers in the stack begin moving in the same direction, then they will be in phase with one another. This will avoid cancellation at the crossover points.
No. See my earlier post. Sometimes the various drivers in a given speaker will not all be in polarity with each other. Sometimes one of them will be intentionally out of polarity with respect to the others to smooth out the phase and amplitude response through the crossover region. It also does matter which drivers you correct if you ever want to use your speakers together with the same model that is unmodified.
All speaker stacks in the system need to be in-phase with one another as well.
All the speaker systems need to be the same, with all the low frequency drivers in polarity with each other, all the mids, and all the high frequency drivers.
Mac
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No. See my earlier post. Sometimes the various drivers in a given speaker will not all be in polarity with each other. Sometimes one of them will be intentionally out of polarity with respect to the others to smooth out the phase and amplitude response through the crossover region. It also does matter which drivers you correct if you ever want to use your speakers together with the same model that is unmodified
According to the jrx115 spec sheet, the tip (1+) pin goes to the + terminal on both HF and LF components. However, we don't know if the components are factory. The only way to go now is to get the crossover point between horn and LF (15) to be coherent. (as he has already done.) Then check the phase between 15 and subs.
What other choice does he have since the boxes have been hacked?
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No. See my earlier post. Sometimes the various drivers in a given speaker will not all be in polarity with each other. Sometimes one of them will be intentionally out of polarity with respect to the others to smooth out the phase and amplitude response through the crossover region. It also does matter which drivers you correct if you ever want to use your speakers together with the same model that is unmodified.
All the speaker systems need to be the same, with all the low frequency drivers in polarity with each other, all the mids, and all the high frequency drivers.
Mac
All of the leads are connected correctly in the cabinets, both woofers in the 115s push out when positive voltage is applied to the positive side of the speaker. Now knowing jbl winds their voice coil opposite of the norm, looking at the difference in charts, and that the tweeter diaphragm has been replaced, can I conclude that I should flip the polarity of the tweet?
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No. See my earlier post. Sometimes the various drivers in a given speaker will not all be in polarity with each other. Sometimes one of them will be intentionally out of polarity with respect to the others to smooth out the phase and amplitude response through the crossover region. It also does matter which drivers you correct if you ever want to use your speakers together with the same model that is unmodified
According to the jrx115 spec sheet, the tip (1+) pin goes to the + terminal on both HF and LF components. However, we don't know if the components are factory. The only way to go now is to get the crossover point between horn and LF (15) to be coherent. (as he has already done.) Then check the phase between 15 and subs.
What other choice does he have since the boxes have been hacked?
Maybe if you read the quote of you that I was referring to, you would know that I was not talking about the OP's speakers, but about your incorrect statement. Not every response in a thread on an Internet forum is going to be about the original post.
Mac
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@Mac - I was just speaking in general about how to achieve component phase. I don't dispute that some boxes may differ. Sorry for the misunderstanding.
@Chris - Do you know that the 15's are original JBL drivers? If so, then they (the 15's) are probably correct as is. However, if the horn diaphragm has been replaced with a generic brand, that happens to be wound opposite of the original, then reversing it may be necessary. I can't tell you that. I don't know.
The reason I brought up the polarity of the 15's was due to the possibility of those being generic replacements as well.
Many JBL drivers, but not all, move rearward when positive DC current is applied to the positive pole. Perhaps an owner of original jrx115's can tell us which way the cone moves.
Hope this helps.
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I checked the crossover, it definitely flips the polarity of the tweeter.
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I snagged a pair of used jrx115s super cheap and am starting to play with them. The speaker I am testing now looks to have had a tweeter diaphragm replacement (the horn was mounted upside down). The magnatude graph seems to loose coherence and amplitude around 2k (right where the passive crossover is set). I flipped the polarity on the tweeter and got the second graph, which is much more even. Note that I bypassed all crossovers and EQs to get those graphs. Does this imply the tweeter is out of polarity? The leads are properly connected, could this be an after-market diaphragm that was wound the wrong way? Will reversing the polarity on the tweeters solve my problem, or is there something bigger I should worry about?
Bennett could be right...it could be an after market LF 15 or even a recone kit. For years, JBL has wound their voicecoils opposite of everyone else in the industry. DC voltage to the red post drives their cones rearward instead of forward. Either the LF or HF driver could be off.
If you use subs, the jrx115s should be in phase with those as well.
As you have already learned, it is simple enough to fix with wiring.
Incorrect. Starting in the '50s JBL had standardized on a polarity convention specific to their drivers. As time went on and "MI - musical instrument" drivers became a large part of their inventory JBL began to fall in line with the rest of the industry and newer speakers were wired to the spec we accept as standard today. That is, positive voltage = voice coil moves out.
Because it was not possible to change entire lines or products already in production simply to meet the "MI standard" JBL began a gradual phase in of their products. They did not change existing products. Regardless of that fact mutli driver boxes, those with crossovers, should be considered "in phase", and they will be until re-wired or the crossover modified. That also includes bi-amped products where the internal wiring has taken this into account. The only time phase is an issue will be when a raw driver is used by another manufacture or home brew specialist, and then, maybe. "Fixing the wiring" is only an option if the wiring is incorrect to begin with, and I suggest some education on a subject prior to making blanket and misleading statements covering entire product lines.
It is best to check polarity in those cases, or any case where you may feel there is a polarity problem. You can do this by referencing JBLs white paper on the subject, the final word on JBL polarity. See below;
http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3 (http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3)
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I checked the crossover, it definitely flips the polarity of the tweeter.
Not all that uncommon. I have seen and measured this on various other boxes in the past. In fact, when paired up with Bob's response I think you have a good reason to verify all your drivers are correct.
In addition, as a sanity check, I would also compare the crossovers from all suspect boxes with a "known good" crossover to see if the polarities are correct.
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I checked the crossover, it definitely flips the polarity of the tweeter.
Not all that uncommon. I have seen and measured this on various other boxes in the past. In fact, when paired up with Bob's response I think you have a good reason to verify all your drivers are correct.
In addition, as a sanity check, I would also compare the crossovers from all suspect boxes with a "known good" crossover to see if the polarities are correct.
So all you need now is the schematic below and a volt meter. Let us know how you make out.
http://www.jblproservice.com/pdf/JRX%20Series/JRX115.pdf (http://www.jblproservice.com/pdf/JRX%20Series/JRX115.pdf)
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Incorrect. Starting in the '50s JBL had standardized on a polarity convention specific to their drivers. As time went on and "MI - musical instrument" drivers became a large part of their inventory JBL began to fall in line with the rest of the industry and newer speakers were wired to the spec we accept as standard today. That is, positive voltage = voice coil moves out.
Because it was not possible to change entire lines or products already in production simply to meet the "MI standard" JBL began a gradual phase in of their products. They did not change existing products. Regardless of that fact mutli driver boxes, those with crossovers, should be considered "in phase", and they will be until re-wired or the crossover modified. That also includes bi-amped products where the internal wiring has taken this into account. The only time phase is an issue will be when a raw driver is used by another manufacture or home brew specialist, and then, maybe. "Fixing the wiring" is only an option if the wiring is incorrect to begin with, and I suggest some education on a subject prior to making blanket and misleading statements covering entire product lines.
It is best to check polarity in those cases, or any case where you may feel there is a polarity problem. You can do this by referencing JBLs white paper on the subject, the final word on JBL polarity. See below;
http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3 (http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3)
Wow! I must say, I stand corrected. In fact, I've learned something new today. Thanks, Bob.
All of my hands-on experience with JBL cone drivers was with 2202, 2220, 2226, 2240, and 2241. They are all negative transducers, so naturally I thought all JBL systems were negative up until their most recent product lines. I never owned any of their MI speaker cabs, so I guess I couldn't see out past the rut I was in. The MPro boxes I now use for monitors are not mine, they are my bosses. They have never been opened or modified, so I never had a reason to check their polarity.
I will definitely bookmark that white paper. It may come in real handy some day. And I will watch what I say about JBL polarity from now on. Thanks again.
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Wow! I must say, I stand corrected. In fact, I've learned something new today. Thanks, Bob.
All of my hands-on experience with JBL cone drivers was with 2202, 2220, 2226, 2240, and 2241. They are all negative transducers, so naturally I thought all JBL systems were negative up until their most recent product lines. I never owned any of their MI speaker cabs, so I guess I couldn't see out past the rut I was in. The MPro boxes I now use for monitors are not mine, they are my bosses. They have never been opened or modified, so I never had a reason to check their polarity.
I will definitely bookmark that white paper. It may come in real handy some day. And I will watch what I say about JBL polarity from now on. Thanks again.
Also note that the list will specify a model as well as individual drivers. In that case regardless of how the components are wired internally the cabinet is wired as listed. The OP's cabinets are an example of this.
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I snagged a pair of used jrx115s super cheap and am starting to play with them. The speaker I am testing now looks to have had a tweeter diaphragm replacement (the horn was mounted upside down). The magnatude graph seems to loose coherence and amplitude around 2k (right where the passive crossover is set). I flipped the polarity on the tweeter and got the second graph, which is much more even. Note that I bypassed all crossovers and EQs to get those graphs. Does this imply the tweeter is out of polarity? The leads are properly connected, could this be an after-market diaphragm that was wound the wrong way? Will reversing the polarity on the tweeters solve my problem, or is there something bigger I should worry about?
Bennett could be right...it could be an after market LF 15 or even a recone kit. For years, JBL has wound their voicecoils opposite of everyone else in the industry. DC voltage to the red post drives their cones rearward instead of forward. Either the LF or HF driver could be off.
If you use subs, the jrx115s should be in phase with those as well.
As you have already learned, it is simple enough to fix with wiring.
Incorrect. Starting in the '50s JBL had standardized on a polarity convention specific to their drivers. As time went on and "MI - musical instrument" drivers became a large part of their inventory JBL began to fall in line with the rest of the industry and newer speakers were wired to the spec we accept as standard today. That is, positive voltage = voice coil moves out.
Because it was not possible to change entire lines or products already in production simply to meet the "MI standard" JBL began a gradual phase in of their products. They did not change existing products. Regardless of that fact mutli driver boxes, those with crossovers, should be considered "in phase", and they will be until re-wired or the crossover modified. That also includes bi-amped products where the internal wiring has taken this into account. The only time phase is an issue will be when a raw driver is used by another manufacture or home brew specialist, and then, maybe. "Fixing the wiring" is only an option if the wiring is incorrect to begin with, and I suggest some education on a subject prior to making blanket and misleading statements covering entire product lines.
It is best to check polarity in those cases, or any case where you may feel there is a polarity problem. You can do this by referencing JBLs white paper on the subject, the final word on JBL polarity. See below;
http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3 (http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3)
By looking at this white paper and looking at my "new" SR4732A boxes I just got, It looks like I'll have to reverse the polarity of either my subs or the jbls to get them in phase with each other, correct? My subs are positive equals outward movement.
http://www.jblproservice.com/pdf/SR-Series/SR4732A.pdf
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You need a "Cricket" tester from Galaxy. Magical little box.
http://www.galaxyaudio.com/CRICKET.jsp
As a side note, I know from experience (and JBL tech info) that many of their boxes show "reversed" polarity in the HF driver when compared to the LF. It's normal. Most of their products use spade connector of different sizes so it's impossible to hook up backwards.
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My subs are positive equals outward movement.
So is your SR4732A, as long as it is original wiring in the cab.
From the JBL link that Bob supplied:
"SR Series (Prefix SR): all models are positive"
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Bennett could be right...it could be an after market LF 15 or even a recone kit. For years, JBL has wound their voicecoils opposite of everyone else in the industry. DC voltage to the red post drives their cones rearward instead of forward. Either the LF or HF driver could be off.
If you use subs, the jrx115s should be in phase with those as well.
As you have already learned, it is simple enough to fix with wiring.
Incorrect. Starting in the '50s JBL had standardized on a polarity convention specific to their drivers. As time went on and "MI - musical instrument" drivers became a large part of their inventory JBL began to fall in line with the rest of the industry and newer speakers were wired to the spec we accept as standard today. That is, positive voltage = voice coil moves out.
Because it was not possible to change entire lines or products already in production simply to meet the "MI standard" JBL began a gradual phase in of their products. They did not change existing products. Regardless of that fact mutli driver boxes, those with crossovers, should be considered "in phase", and they will be until re-wired or the crossover modified. That also includes bi-amped products where the internal wiring has taken this into account. The only time phase is an issue will be when a raw driver is used by another manufacture or home brew specialist, and then, maybe. "Fixing the wiring" is only an option if the wiring is incorrect to begin with, and I suggest some education on a subject prior to making blanket and misleading statements covering entire product lines.
It is best to check polarity in those cases, or any case where you may feel there is a polarity problem. You can do this by referencing JBLs white paper on the subject, the final word on JBL polarity. See below;
http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3 (http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3)
By looking at this white paper and looking at my "new" SR4732A boxes I just got, It looks like I'll have to reverse the polarity of either my subs or the jbls to get them in phase with each other, correct? My subs are positive equals outward movement.
http://www.jblproservice.com/pdf/SR-Series/SR4732A.pdf
NO. The DC polarity of a transducer does NOT, by necessity, determine the phase behavior of 2 systems through the acoustic crossover. You will need to determine this with an FFT analyzer.
Tim Mc
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My subs are positive equals outward movement.
So is your SR4732A, as long as it is original wiring in the cab.
From the JBL link that Bob supplied:
"SR Series (Prefix SR): all models are positive"
Somehow I missed that on the first reading, Thanks!
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By looking at this white paper and looking at my "new" SR4732A boxes I just got, It looks like I'll have to reverse the polarity of either my subs or the jbls to get them in phase with each other, correct? My subs are positive equals outward movement.
http://www.jblproservice.com/pdf/SR-Series/SR4732A.pdf
Maybe or maybe not. What the POLARITY (NOT PHASE) is between different freq bands depends on quite a few different factors. In many cases you want them to be out of POLARITY. But always in PHASE. You can't test phase with a battery BTW.
It all has to do with the physical placements of drivers-crossover slopes and types, eq applied and so forth.
It is the end result of a smooth phase and amplitude response that you are interested in-and it doesn't matter whether one band is out or in POLARITY (NOT PHASE!) with the adjacent band.
I am just a proud member of the POLARITY police and try to correct people when they use the term phase incorrectly. There is a MAJOR difference.
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By looking at this white paper and looking at my "new" SR4732A boxes I just got, It looks like I'll have to reverse the polarity of either my subs or the jbls to get them in phase with each other, correct? My subs are positive equals outward movement.
http://www.jblproservice.com/pdf/SR-Series/SR4732A.pdf (http://www.jblproservice.com/pdf/SR-Series/SR4732A.pdf)
Maybe or maybe not. What the POLARITY (NOT PHASE) is between different freq bands depends on quite a few different factors. In many cases you want them to be out of POLARITY. But always in PHASE. You can't test phase with a battery BTW.
It all has to do with the physical placements of drivers-crossover slopes and types, eq applied and so forth.
It is the end result of a smooth phase and amplitude response that you are interested in-and it doesn't matter whether one band is out or in POLARITY (NOT PHASE!) with the adjacent band.
I am just a proud member of the POLARITY police and try to correct people when they use the term phase incorrectly. There is a MAJOR difference.
Ivan is of course correct. In this case if you refer to the schematic again you'll note two of the drivers using JBLs older standard show outward movement and the third inward movement with the cabinet connected properly to the amplifier, plus to plus, minus to minus at the input.
This is intentional by JBL and will confirm Ivans statement.
In all cases try not to over engineer the solution. Simply hook up the input cables to the speaker as stated in the owners manual. If from that point you have an issue you can always contact JBL and they will always gladly assist.
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I am just a proud member of the POLARITY police and try to correct people when they use the term phase incorrectly. There is a MAJOR difference.
It doesn't help that equipment manufacturers traditionally use the greek characters theta or phi to label the polarity button. In engineering and mathematics we use these characters to denote phase.
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I am just a proud member of the POLARITY police and try to correct people when they use the term phase incorrectly. There is a MAJOR difference.
It doesn't help that equipment manufacturers traditionally use the greek characters theta or phi to label the polarity button. In engineering and mathematics we use these characters to denote phase.
Very true... Well, at least that is probably why it originated the way it did...and since audio signals are AC in nature, there you have it. But, in this special case, you are not using AC mechanisms to manipulate "it". You are just flipping two wires, regardless of whatever "it" may be.