When is it right to reverse phase/polarity?

[pathfindermwd]

I have heard that sometimes manufacturers will reverse polarity to some drivers in a speakers design.

This is also recommended as a tweak sometimes, due to room response??

Does my L100S's invert any phase in it's crossover design (I can't read a schematic) ?

http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/technicalsheet/L100t3 ts.pdf

In passive Bi-amp mode, could anyone make a guess of what would happen to the sound if I invert the woofer only?

Since I play most of my music through the computer, are there any free Windows software programs I could use with a mic to perform phase tests?

[Tim Rinkerman]

OK, this is coming from an old time seat of the pants response, but...listen to your system and pay very close attention to the sound AT the crossover point,..and reverse it,..and listen again. The position with the greater apparent volume at the crossover frequency is usually correct..
I'm sure I've really let my shields down, but...I've been right 99% of the time on this one. The focus being..you will only really notice the difference around the crossover frequency.

[pathfindermwd]

The position with the greater apparent volume at the crossover frequency is usually correct..


That seems to be consistent with what I am hearing....

[DavidF]

I have heard that sometimes manufacturers will reverse polarity to some drivers in a speakers design.

This is also recommended as a tweak sometimes, due to room response??

Does my L100S's invert any phase in it's crossover design (I can't read a schematic) ?

http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/technicalsheet/L100t3 ts.pdf

In passive Bi-amp mode, could anyone make a guess of what would happen to the sound if I invert the woofer only?

Since I play most of my music through the computer, are there any free Windows software programs I could use with a mic to perform phase tests?

Two drivers of different size and construction will have differing phase and frequency magnitude responses. A crossover filter diminishes the response of each driver around the xover point. So there is always some overlap of driver response. Different phase and timing of the drivers in the overlap zone can sum to increase response or cancel to reduce response, or create a nulls, around the xover point. To make it more complicated the actual sum or null will vary depending upon the angle you sit above or below, side to side, around the listening axis.

Changing the polarity of one driver against the other is a means to even out the phase differences in the most positive way in a good system design. Reversing the polarity on one or more drivers in a properly designed system should adversely affect the system response. If someone is reversing polarity as a tweak and calling that an improvement indicates the design was not so good to begin with, something was wired incorrectly at some point, or the person lacks experience in determining what constitutes an improvement.

Personally, I wouldn't mess around with the polarlity as orignally spec'd for the L100t.

[SoundOfSound]

The reason that polarity is reversed by the manufacturer is to compensate for the affects that the crossover has on the phase of the signal. They try the best they can to keep all components in phase with each other or a null will result. For example in noise cancelling headphones. They take the input from a small mic from the outside of the headphones and mix it back in 180 degrees out of phase with what you actually want to listen to. The result is you get the music you want but all the noise in the room is cancelled out. The same sort of thing happens if speaker components are wired 180 degrees out of phase.

The Engineers at JBL certainly understood this problem so the wiring of the speakers is fine if nobody got inside and mucked about with it.

With those speakers room placement is critical as they are probably too big for most small rooms, plus don't forget they have a port in the back that needs to be away from the wall a bit. If you are having problems with the sound try better speaker placement. If you put up a pic of your listening room people can give you some hints of how get better sound with them.

Here is a link with some tips on speaker placement for the grandfather of the L100t. JBL also has others like it if you dig around on the web.

http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/OwnersManual/L100%20om.pdf

p.s. keep in mind the port in the L100 is on the front and the port in the L100T is on the back.

[pathfindermwd]

Personally, I wouldn't mess around with the polarlity as orignally spec'd for the L100t.

You don't say!!??



If you are having problems with the sound try better speaker placement.

p.s. keep in mind the port in the L100 is on the front and the port in the L100T is on the back.

NO FREAKING DUH SoundOfSound!!!! I've only owned the damn things for a couple of years now,,,

Let me take this opportunity to welcome you and your lame replies to the forum!:thnkfast:

You guys bring new meaning to the term Zero Sum Game. Nothing can change because nothing is wrong, and even if it were, nothing can change because it wouldn't be stock.:blink:

Do you guys have anything intelligent to add? This is a serious discussion! :wtf:


What I want to know is, now that my XO is broken out into a mid/high and LF, is there any advantage or change in the way the mid and low frequency are interacting? Cmon you guys, I mean I'm ignorant, but not totally STOOPID, at least not to the extent your posts are!

What would make me think such a thing about the XO being out of phase?

How about this article:

http://sound.westhost.com/bi-amp.htm

Here it states:

PHASE RESPONSE:
"This one is nearly as big a "killer" as the power gain - and from a musical point of view it may well be seen as even more important (I happen to think it is). The phase response of any crossover is quite predictable, as long as the source and load impedances are well defined and stable. In a passive crossover, this is rarely the case, and the results can be quite nasty. There is a phase transition around the crossover frequency, and with even-order crossovers (i.e. 12 and 24 dB/octave), there is actually a phase reversal between the low frequency and the mid+high frequency outputs. This can be seen if one examines the wiring of a speaker using an even-order crossover network, and it will be observed that the midrange driver is wired out-of-phase with the woofer. The same thing happens with the mid to high crossover, except that the tweeter is now back in phase with the low frequency driver.

It must be noted that the phase reversal is required only to ensure that the drivers are in phase at the crossover frequency. A couple of octaves each side, and with the inductive and capacitive load presented by a loudspeaker, the signals are out of phase to a greater or lesser degree. This can only be considered a completely unacceptable situation when you look at it, but there it is - alive and well in a great many speaker systems from the very beginnings of high fidelity right up to the present day.

A conventional crossover by way of comparison has a 3dB peak at the crossover frequency when the two outputs are summed."

3db summed people! That's what I want to talk about!

I'm interested in learning whether or not this is the case with my speakers, and whether or not this bi-ampable XO changes the electrical situation, or allows me to change the summing due to it's different configuration. I'm not interested today in proper speaker placement (see Cardas:http://www.cardas.com/room_setup_main.php), or your opinion about whether you would change the polarity or not, which by the way amounts to swapping the banana jacks!!:rolleyes:

Did you guys no notice that I had the XO's built to be Biampable???? They didn't come that way you know??? If you don't have anything more intelligent to add to the topic, don't bother! :banghead:

If on the other hand you do, welcome. :yes: :skeptical:


:)

[SoundOfSound]

You don't say!!??



NO FREAKING DUH SoundOfSound!!!! I've only owned the damn things for a couple of years now,,,

Let me take this opportunity to welcome you and your lame replies to the forum!:thnkfast:

You guys bring new meaning to the term Zero Sum Game. Nothing can change because nothing is wrong, and even if it were, nothing can change because it wouldn't be stock.:blink:

Do you guys have anything intelligent to add? This is a serious discussion! :wtf:


What I want to know is, now that my XO is broken out into a mid/high and LF, is there any advantage or change in the way the mid and low frequency are interacting? Cmon you guys, I mean I'm ignorant, but not totally STOOPID, at least not to the extent your posts are!

What would make me think such a thing about the XO being out of phase?

How about this article:

http://sound.westhost.com/bi-amp.htm

Here it states:

PHASE RESPONSE:
"This one is nearly as big a "killer" as the power gain - and from a musical point of view it may well be seen as even more important (I happen to think it is). The phase response of any crossover is quite predictable, as long as the source and load impedances are well defined and stable. In a passive crossover, this is rarely the case, and the results can be quite nasty. There is a phase transition around the crossover frequency, and with even-order crossovers (i.e. 12 and 24 dB/octave), there is actually a phase reversal between the low frequency and the mid+high frequency outputs. This can be seen if one examines the wiring of a speaker using an even-order crossover network, and it will be observed that the midrange driver is wired out-of-phase with the woofer. The same thing happens with the mid to high crossover, except that the tweeter is now back in phase with the low frequency driver.

It must be noted that the phase reversal is required only to ensure that the drivers are in phase at the crossover frequency. A couple of octaves each side, and with the inductive and capacitive load presented by a loudspeaker, the signals are out of phase to a greater or lesser degree. This can only be considered a completely unacceptable situation when you look at it, but there it is - alive and well in a great many speaker systems from the very beginnings of high fidelity right up to the present day.

A conventional crossover by way of comparison has a 3dB peak at the crossover frequency when the two outputs are summed."

3db summed people! That's what I want to talk about!

I'm interested in learning whether or not this is the case with my speakers, and whether or not this bi-ampable XO changes the electrical situation, or allows me to change the summing due to it's different configuration. I'm not interested today in proper speaker placement (see Cardas:http://www.cardas.com/room_setup_main.php), or your opinion about whether you would change the polarity or not, which by the way amounts to swapping the banana jacks!!:rolleyes:

Did you guys no notice that I had the XO's built to be Biampable???? They didn't come that way you know??? If you don't have anything more intelligent to add to the topic, don't bother! :banghead:

If on the other hand you do, welcome. :yes: :skeptical:


:)


Have You Taken Your Meds Today??? ...You Talk a Lot Of Crap For Somebody That Can't Read A Schematic.

[speakerdave]

Woah! That's a lot of wormwood to throw at someone just trying to be helpful.



You don't say!!??



NO FREAKING DUH SoundOfSound!!!! I've only owned the damn things for a couple of years now,,,

Let me take this opportunity to welcome you and your lame replies to the forum!:thnkfast:

You guys bring new meaning to the term Zero Sum Game. Nothing can change because nothing is wrong, and even if it were, nothing can change because it wouldn't be stock.:blink:

Do you guys have anything intelligent to add? This is a serious discussion! :wtf:


What I want to know is, now that my XO is broken out into a mid/high and LF, is there any advantage or change in the way the mid and low frequency are interacting? Cmon you guys, I mean I'm ignorant, but not totally STOOPID, at least not to the extent your posts are!

What would make me think such a thing about the XO being out of phase?

How about this article:

http://sound.westhost.com/bi-amp.htm

Here it states:

PHASE RESPONSE:
"This one is nearly as big a "killer" as the power gain - and from a musical point of view it may well be seen as even more important (I happen to think it is). The phase response of any crossover is quite predictable, as long as the source and load impedances are well defined and stable. In a passive crossover, this is rarely the case, and the results can be quite nasty. There is a phase transition around the crossover frequency, and with even-order crossovers (i.e. 12 and 24 dB/octave), there is actually a phase reversal between the low frequency and the mid+high frequency outputs. This can be seen if one examines the wiring of a speaker using an even-order crossover network, and it will be observed that the midrange driver is wired out-of-phase with the woofer. The same thing happens with the mid to high crossover, except that the tweeter is now back in phase with the low frequency driver.

It must be noted that the phase reversal is required only to ensure that the drivers are in phase at the crossover frequency. A couple of octaves each side, and with the inductive and capacitive load presented by a loudspeaker, the signals are out of phase to a greater or lesser degree. This can only be considered a completely unacceptable situation when you look at it, but there it is - alive and well in a great many speaker systems from the very beginnings of high fidelity right up to the present day.

A conventional crossover by way of comparison has a 3dB peak at the crossover frequency when the two outputs are summed."

3db summed people! That's what I want to talk about!

I'm interested in learning whether or not this is the case with my speakers, and whether or not this bi-ampable XO changes the electrical situation, or allows me to change the summing due to it's different configuration. I'm not interested today in proper speaker placement (see Cardas:http://www.cardas.com/room_setup_main.php), or your opinion about whether you would change the polarity or not, which by the way amounts to swapping the banana jacks!!:rolleyes:

Did you guys no notice that I had the XO's built to be Biampable???? They didn't come that way you know??? If you don't have anything more intelligent to add to the topic, don't bother! :banghead:

If on the other hand you do, welcome. :yes: :skeptical:


:)

[BMWCCA]

58141

[pathfindermwd]

Have You Taken Your Meds Today??? ...You Talk a Lot Of Crap For Somebody That Can't Read A Schematic.

For someone who knows how to read a schematic, you seem more comfortable discussing speaker placement...

While my reply to your post might have been scathing, I did not make any personal attacks towards you as you have done. Ad Hominem, this is clearly forbidden in the forum rules. You might want to read up on them.

My ranting post was in fact very intentional, it's not my usual style. While I generally appreciate the reply's, I couldn't help being frustrated that they completely side-stepped the most important part of the question: Polarity and Phase as it relates to the L100S.

This is the JBL forum, this is where such a question belongs, if anywhere. The reply's I got were so basic the information could of been found on any site. Hardly worthy of what I was really getting at, and where I was.

I'm not looking to make the forum a rude place, but trying to evoke a level of awareness. If you reply to someone's post you ought to answer the question, or logically explain why the question is flawed. The internet is full of posts that pose good questions but in the end don't answer the question. They get derailed for pages and after hundreds of posts, are nowhere, hijacked by well intentioned people who have little useful to add.

It was right of me to criticize you guys on the irrelevant answers you posted and state unequivocally that it didn't meet the standard, it didn't answer the question. Your reply's disregarded the question, and suggested an irrelevant solution without any reasoned argument. My reply was fashioned to to be as ridiculous as the dog and pony show I felt was being handed to me.

I believe that my reply, though possibly rude, meets the criteria set forth in the forum rules, and the spirit of healthy debate as defined in those rules.

I'm sorry if you didn't find any humor in my reply, I didn't think it could be taken very seriously, I did use emoticons :)

[pathfindermwd]

Woah! That's a lot of wormwood to throw at someone just trying to be helpful.

Just trying to be helpful how? If they don't answer the question or propose a better question, how is it helpful?

So far, there is not one thing mentioned in this thread that is useful to the forum. It's a bunch of hot air, wasted space, wasted time. Should I be appreciative for that?

My post is directed at their replies, not them. It's directed at useless information, at all the posts out there where someone asks for a fish, and is instead offered a song and dance.

[DavidF]

"....
Did you guys no notice that I had the XO's built to be Biampable???? They didn't come that way you know??? If you don't have anything more intelligent to add to the topic, don't bother! :banghead:

If on the other hand you do, welcome. :yes: :skeptical:


:)

You are right. I shouldn't have bothered.

[Robh3606]

Why can't we be friends, Why can't we be freinds, sang to Why can't we be friends.



In passive Bi-amp mode, could anyone make a guess of what would happen to the sound if I invert the woofer only?


If you are in passive bi-amp mode why would you reverse the polarity on the woofer? You have not changed the woofers phase relationship with the other drivers. You most likely end up with a hole through the crossover region between the 2214 and the 104.

If you look at the L100T3 schematic they have all the drivers with the acoustic phase with a + Positive voltage to the red terminal all drivers move forward. If you look closely at the wiring the woofer is wired with the polarity reversed relative the mid and tweeter.



Rob:)

[grumpy]

I have heard that sometimes manufacturers will reverse polarity to some drivers in a speakers design.

Yes, this is by design, and as previous posts indicated, this often depends on the slope of the crossover between two drivers.


This is also recommended as a tweak sometimes, due to room response??

I don't know why someone would do this, but it they think it sounds better, who am I to complain.


Does my L100S's invert any phase in it's crossover design (I can't read a schematic) ?

The L100t3 schematic both shows electrical 12db/oct type crossovers, as well as non-inversion of any drivers... which may be just
wrong, there may be an acoustic slope involved as well (rotating the phase at crossover even further), or it may just have measured
and sounded better that way. Normally, the mid would have been inverted in this arrangement.

http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/technicalsheet/L100t3 ts.pdf


In passive Bi-amp mode, could anyone make a guess of what would happen to the sound if I invert the woofer only?

Normally, you would end up with a cancellation and a "hole" in the frequency response, but as this design might depend
on more than the electronic (passive) crossover to achieve the desired crossover function, the "cancellation" may not be as noticeable.
You may end up just hearing a change in timbre in the crossover area.


Since I play most of my music through the computer, are there any free Windows software programs I could use with a mic to perform phase tests?

I believe there are several (arta, holmimpulse,... but measurement type mics usually also require a power source and a preamp.
I think parts-express has a fairly cheap measurement package.

(a simple, "thanks but let me clarify what I was looking for", could have saved a lot of grief)

... again, I type too slowly :P



If you look at the L100T3 schematic they have all the drivers with the acoustic phase with a + Positive voltage to the red terminal all drivers move forward.

yep


If you look closely at the wiring the woofer is wired with the polarity reversed relative the mid and tweeter.

My eyes must be going... I'm seeing all + terminals on the drivers going to the "black" input terminal (?)
unless there was a goof and the mid really is reversed.

[Robh3606]

My eyes must be going... I'm seeing all + terminals on the drivers going to the "black" input terminal (?)
unless there was a goof and the mid really is reversed.

No it's mine that are going! Your right, sorry for the missinformation.

Rob:)

[grumpy]

:) I still wouldn't be terribly surprised if there was a goof in the documentation.

I don't have enough gumption to tear into my in-regular-use L100T pair which are very similar.

[pathfindermwd]

You are right. I shouldn't have bothered.

David, I humbly apologize for my rude behavior towards you.

[pathfindermwd]

Why can't we be friends, Why can't we be freinds, sang to Why can't we be friends.

What, no dance? :p



If you are in passive bi-amp mode why would you reverse the polarity on the woofer? You have not changed the woofers phase relationship with the other drivers. You most likely end up with a hole through the crossover region between the 2214 and the 104.

If you look at the L100T3 schematic they have all the drivers with the acoustic phase with a + Positive voltage to the red terminal all drivers move forward. If you look closely at the wiring the woofer is wired with the polarity reversed relative the mid and tweeter.

Rob:)

I noticed the polarity notation the other day.

My questions reveals several areas of weakness in my understanding...

Um, the initial reason for my query was brought about by a suggestion that I try reversing the polarity of the midrange. This was suggested as something I could try to contour the sound to my liking, not as an improvement as such. I tried it and didn't like it. This didn't really surprise me since these speakers came to me with their tweeters wired in backwards, they even went through all the trouble of soldering the posts in reverse. It was only because I had two sets (L100T/L100S) that I became aware of this while poking around inside. This inverted tweeter is actually how I got to buy the L100S since the owner said they didn't sound right, they did sound different..

I realized after trying to invert the mid that I could try to invert the woofer, and since I was in passive bi-amp, it was very simple. This actually didn't sound too horrible. It did seem to cause a "hole" in the midrange, but I can't be certain what the effect is since I read the the summing of the woofer and mid could cause a 3db increase at the XO.
Was I hearing a hole, or the lack of summation? I think it's a hole.

I wondered if the biamped XO offered any solution since it's network is divided. Apparently not.

I'm not too far away from actively bi-amping the speakers. This is all just about understanding better how my system works, and how to improve it. And addressing some long standing issues with the performance.

[DavidF]

David, I humbly apologize for my rude behavior towards you.

Acknowledged and accepted.

[pathfindermwd]

I don't know why someone would do this, but it they think it sounds better, who am I to complain.


To be fair it was suggested as an experiment with no claims for certain improvement. My understanding about it was that sometimes it's a simple design call and that there might be some room for interpretation. My initial question to the forum was posed to get a better understanding of the complexity of it, specific to this speaker design.



The L100t3 schematic both shows electrical 12db/oct type crossovers, as well as non-inversion of any drivers... which may be just
wrong, there may be an acoustic slope involved as well (rotating the phase at crossover even further), or it may just have measured
and sounded better that way. Normally, the mid would have been inverted in this arrangement.

So, you bring up a couple of points I didn't realize. 1. That the schematic doesn't definitively trace the polarity of the signal. 2. It doesn't show the acoustic slope you speak of. 3. The schematic could be wrong.



Normally, you would end up with a cancellation and a "hole" in the frequency response, but as this design might depend
on more than the electronic (passive) crossover to achieve the desired crossover function, the "cancellation" may not be as noticeable.
You may end up just hearing a change in timbre in the crossover area.

It doesn't sound as bad a reversing the mid, to my ears. It sounds attenuated, and the bass is different, sometimes heavier sounding. The sweetness of the sound goes away, so I can't call it an improvement.




I believe there are several (arta, holmimpulse,... but measurement type mics usually also require a power source and a preamp.
I think parts-express has a fairly cheap measurement package.

Thanks!


(a simple, "thanks but let me clarify what I was looking for", could have saved a lot of grief)

Duly noted.




Soon, I'll get the electronic XO hooked up. Would you hazard a opinion on how it would improve performance?
Would it offer me the ability to have a steeper XO, and would that improve phase at the XO between the mid/woofer?