L300 phasing issue

[DougK]

After purchasing some vintage L300’s I discovered the tweeter on the "right" speaker was not working. The problem was fixed by OC Speaker repair, and traced back to the crossover connections which were not connected properly by the prior owner who had undertaken some questionable repairs. Fortunately , the tweeter was in working order.

When I got the crossover back, I noticed the "right" speaker does not plainly label which is the "positive" lead, and which is the "negative " lead to the respective drivers, and I am not sure I hooked them up in phase.

When comparing the cabinet wiring from "left" and "right" to trace the colors to the same drivers for phasing/polarity purposes, I noted that the crossover wiring was a different gauge and color from speaker to speaker. Both speakers had the N333 crossover inside. The "left" speaker has a solid green positive woofer connection, a solid red tweeter positive connection, and a solid white mid connection. All negative driver connections were black. This is in complete agreement with the schematic you can find online for the N333 crossover.

However, the "right" speaker has a solid green wire for the woofer positive?, a green with black stripe for woofer negative?, a yellow wire for mid positive?, with yellew w/black stripe for mid negative?, and white for tweeter positive?, with white w/black stripe for tweeter negative? I cannot find anything online to determine why there was a change in wiring color, and to confirm which one is truly supposed to be the positive (solid?) and which one is truly supposed to be the negative (solid w/stripe?).
How can I know absolutely that I have the polarity correct and the speakers in phase. They sound really great, but I want it perfect. My electrical knowledge is very limited. I read some detailed posts on reversed polarity and other issues with vintage JBL’s and find it very confusing yet intriguing.
Thanks, Doug

P.S. I was the guy who recently sold the NOS Camel grill covers on Ebay for $503!!

[boputnam]

Hey, Doug...

Since both crossovers are the same model (lucky with the prior owner having mucked around in there... :scold: ), my grab is the two are marginally different in date. No problem...

Your supposition is correct. Solid leads go to Red terminals on the transducers; black-striped wires go to the Black terminals. Good to go...

:wave:

[DougK]

Thanks Bo for the reply.

[Steve K]

Hope you don't mind my jumping in here with my own little question.:)

I'm okay with Doug's internal wiring scheme for the L300, solid to red and striped to black. But, recently I was told by a guy who runs a speaker repair/tune shop that, for old JBLs (including the L300) the speaker wires have to be connected in reverse, that is amp's red (positive) to the black terminal, etc. Can anyone tell me if this guys really knows what he's talking about? That's kind of strange because I figure if the internal wiring from the N333 crossover to the binding posts was designed ex-factory for reverse polarity from the beginning, JBL would have reversed the wires inside the box to the speaker input terminals, and then the customer (me) will just have to connect the amp's speaker outputs the normal way, which is red to red and black to black. This makes much more sense to me. Appreciate your expert comments!

Steve K

[mech986]

Not so sure about the expert part but here is JBL Pro's official document on at the polarity questions for JBL Professional speakers and drivers.

IMO, one should also be assuming that the consumer counterparts may have similar polarity issues? Haven't had a chance to look it up here at LH.

http://www.jblpro.com/tech-library/JBL_TechNoteN1V12C_v5.pdf

Note for the 4300 series (except the 4311 and 4312), they are negative systems, positive voltage to red terminal will have an inward or negative pressure at the woofer.

Same holds true for some of the 4400 series including the 4425, 4430, 4435. Geez, I've been hooking them up with the wrong polarity forever.

Also negative is the 4660A (Everest horn) that I'm using in the same church with MR series floor monitors which are positive. Wow, I wonder IF that suggest I'm not getting the right polarities and bass response....

Also note that many legacy drivers - 2235H, 2245H woofers and many compression drivers we commonly talk about - 2402H, 2404H, 2405H, 2450H,J are also negative.

Wow, we could really have a lot of drivers incorrectly wired out there if any speaker system has been opened or DIY'ed.

Regards,

Bart

[DougK]

Mech986, after reading the JBL bulletin...that is the exact stuff I am worried/confused about!!!...am I properly in phase or not? After correcting my "right" speaker last night (black stripe to negative terminal), I listened to my speakers and the midrange really opened up, and became much warmer and less intense. The sound was fabulous. When they were wired out of polarity, the midrange was so powerfull, I had trouble listeneing at higher sound levels. Well, at least they sound better right now, and they are both hooked up "identically", although I guess I will never know/appreciate/understand if they are truly "in phase/polarity" or not. Thanks to this forum for the information.

Doug

[Steve K]

Thanks, Bart, for the JBL reference material! I had owned a couple of the systems mentioned there (4343, 4425, etc) and now know that I had them wired the wrong way all that time. :(

Steve K

[Thom]

There is no right or wrong polarity for "a" speaker. Phasing is relative. The only time it is a problem is if you are listening to more than one speaker in the same place at the same time. Then you want all the cones coming out at the same time and going in at the same time and even that isn't 100% true in some speaker placement setups. Your speakers won't sound better hooked up one polarity or the other unless you are listening to another set in the same room as them. It would be just as true to call the other set marked backwards except that that way became standard. When it comes to technical info a very little bit can cause a lot of worry and lost time and bad info. Better in slightly larger bites or not at all sometimes. Everybody awake? Usually if you put your system in mono and go slowly from one side to the other if they're you will find a center speaker even though there isn't one and if they are out of phase all of a sudden you will switch from one speaker to the other with no center channel. Another test, again in mono, play something with some bass and switch leads back and forth on one speaker. The position with the most bass will be right.

[toddalin]

Simple way to tell the correct phase of the horn/tweeters. Play a tone at the crossover frequency and listen with a sound level meter. Reverse the horn (or tweeter) leads and do it again. The louder hookup will typically be the correct setting.

[Thom]

Simple way to tell the correct phase of the horn/tweeters. Play a tone at the crossover frequency and listen with a sound level meter. Reverse the horn (or tweeter) leads and do it again. The louder hookup will typically be the correct setting.

Again, it's phase relative the other drivers.

[Ian Mackenzie]

I am note sure of the point Thom was making?

Doug,

I agree it is quite confusing and based on my own recent experience a new owner can be unwittingly listening to a system with asyametrically wired and hence phased drivers the whole time they own them. Little do they know the imaging is out of wack or there is midrange suckout in one channel. Often its an error passed on from the previous owner(s) who have changed out the drivers at one stage another. Its nearly improssible to sort out with odd wiring codes unless you are able to trace the signal path through the network in some cases.

Ian

[hjames]

Interesting thing ...
I checked the spec sheet/schematic in the Library for the L-300 as well as for the 4333.

136A woofer (for L-300) 136H for L300A (replace with 2235H)
LE-85 (with the 92 Long horn in the 300), 077 slot (2405 in the Pro Monitor)
Drivers don't seem to be the issue ...

But looking at the Crossover schematic for both, its apparent the slot (HF) is polarity reversed in relation to the other 2 drivers.

cropped images attached below.

[toddalin]

Again, it's phase relative the other drivers.

I think that you may be referring to the relative phase of the left and right speakers. I'm referring to the phase of the mid and tweeter relative to the woofer all within the same cabinet, which addresses the original question.

[Ian Mackenzie]

Without going too OT both the woofer and horn have 2 pole high pass filters and the tweeter is a 3 pole high filter. It depends on how they juggled the final values and what gave the smoothest response. The horn is in phase and that is odd by convention but if you consider the path length of the horn that could be why.

Ian

[Thom]

I believe we had a couple of people who were very concerned about which amp lead went to which colored post on the speaker (system). They felt (my impression that perhaps to make things sound just right the amp red must go to the jbl black etc. and I was saying only if you were mixing them with speakers which used red and black differently would that be an issue (I wanted to add something about the bottom of the earth but my jokes suck and I'd probably accidentally offend). I think many who still put those little plugs into unused receptacles to keep electricity from running out and pooling on the floor are needlessly confused by the JBL "backwards" polarity which is only backwards relative convention and means nothing unless mixed with other speakers. For that mater whether a driver should be wired in phase or out of phase with the one before or after it (internal 2 way or 3 way) depends on the crossover. I believe one wrote that he had reversed the polarity on all of his speakers and now the sound opened up. It's like moving all three wires on a three phase motor or reversing both the armature and the field on a dc motor. You have done nothing.


Quote
"Hope you don't mind my jumping in here with my own little question.

I'm okay with Doug's internal wiring scheme for the L300, solid to red and striped to black. But, recently I was told by a guy who runs a speaker repair/tune shop that, for old JBLs (including the L300) the speaker wires have to be connected in reverse, that is amp's red (positive) to the black terminal, etc. Can anyone tell me if this guys really knows what he's talking about? That's kind of strange because I figure if the internal wiring from the N333 crossover to the binding posts was designed ex-factory for reverse polarity from the beginning, JBL would have reversed the wires inside the box to the speaker input terminals, and then the customer (me) will just have to connect the amp's speaker outputs the normal way, which is red to red and black to black. This makes much more sense to me. Appreciate your expert comments!


Steve K"
End quote.

Obviously this poster believes it makes a difference which terminal goes to which amplifier lead. I was trying to explain that it does not.

[Russellc]

There is no right or wrong polarity for "a" speaker. Phasing is relative. The only time it is a problem is if you are listening to more than one speaker in the same place at the same time. Then you want all the cones coming out at the same time and going in at the same time and even that isn't 100% true in some speaker placement setups. Your speakers won't sound better hooked up one polarity or the other unless you are listening to another set in the same room as them. It would be just as true to call the other set marked backwards except that that way became standard. When it comes to technical info a very little bit can cause a lot of worry and lost time and bad info. Better in slightly larger bites or not at all sometimes. Everybody awake? Usually if you put your system in mono and go slowly from one side to the other if they're you will find a center speaker even though there isn't one and if they are out of phase all of a sudden you will switch from one speaker to the other with no center channel. Another test, again in mono, play something with some bass and switch leads back and forth on one speaker. The position with the most bass will be right.
Cant agree with this, maybe its my imagination, but I notice a difference in sound with different phasing. (Yes i mean with both speakers in the same phase) One way just seems a little more dead than the other. Again, I suppose it could be my imagination. Lord knows I have been wrong before!



Russellc

[toddalin]

Cant agree with this, maybe its my imagination, but I notice a difference in sound with different phasing. (Yes i mean with both speakers in the same phase) One way just seems a little more dead than the other. Again, I suppose it could be my imagination. Lord knows I have been wrong before!



Russellc

Maybe not your imagination. I can see where it would certainly make a difference if a transient slams you in the chest or sucks the air out of your lungs. ;)

[Steve K]

I have one comment and one question on internal wiring.

1) On the external speaker binding posts , whether one should actually reverse the polarity from the amplifier (amp's red to black post & vice versa) on older models, it seems irrational as it would raise the question of why would JBL confuse us, the end-users, by taking such a convention breaking route, unless the company just wanted to be 'different' from all the world's speaker manufacturers. Besides, all they have to do is to reverse the internal connection, from the crossover to the backside of the binding posts. Also, as JBL's standard inside-the-cabinet standard wiring scheme is black or black-striped to the negative/black connector of each speaker unit, again it doesn't make sense that the user would have to reverse that standard for the amp-to-speaker connection.

I do have my L300 connected the 'normal' way, amp's red to red, etc.

2) What's confusing, though, is the N333 crossover schematic, as shown in the previous post, which illustrates the HF wiring as reversed, compared to the LF and MF. Taking JBL's 'black/black-striped wire goes to black connector' standard, does this mean that for the 077, this should be reversed, i.e. black-striped to red connector on the 077? Or could it be that JBL might have intentionally reversed the wires themselves for this network so that we the end-users won't have to deal with such matters and just connect the wires as one would for the other drivers? I'd appreciate your help in clearing up this confusion to get my L300 wired correctly.

Thanks.
Steve K

[grumpy]

I think you answered your own question:

"JBL... intentionally reversed the wires themselves for this network so that we the end-users won't have to deal with such matters and just connect the wires as one would for the other drivers"

This driver is connected in reverse phase intentionally, so red-red, and black-black
will do this.

-grumpy

[Steve K]

Thanks for the quick response, grumpy.
But I just had to find out for myself by listening for any difference in the sound with reverse connection between the crossover and the 077. So I unscrewed the 136A off, reached behind the 077 from the vent hole with my left arm and hand, and pulled out the tweeters. I found that I had connected them red-to-red, black-to-black when I installed it previously. So, I wired it in reverse this time, red-to-black, black-to-red, and put everything back in. Ditto for the other speaker. It only took less than 15 minutes, surprisingly not as bothersome as I anticipated the task to be.
I then popped in a CD and turned the volume up. The result: the highs seem sweeter, and each instruments' notes are more defined, the bass a bit tighter, and better imaging, too. It led me to think, maybe the LE85 driver covers a lot of bandwidth that I probably didn't feel that much was being missed before. Overall, there is more of that 'being there-ness.'
Well, to be honest, I don't know if this effect of all the drivers being in-phase or out-of-phase. All I know is that for the moment I like the sound I'm hearing now.

Steve K

[grumpy]

All I know is that for the moment I like the sound I'm hearing now.

That's what counts! :-) Would be fun to do some measurements but I'm short
the proper crossover and slant plate... maybe later. -grumpy

FWIW, the owner's manual p15 -would- have this information (wiring diagram), but
the scan available from Harman makes this particular diagram worthless.:(

both schematic and wiring diagram here are useful though:
http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4333B.pdf

[Steve K]

I think I know what the problem was. My ears.

I read the technical paper posted by mech986, which I totally missed somehow on my first perusal. This is what it says in the very last paragraph: If JBL negative convention loudspeaker systems or transducers are used, the required polarity inversion should be made at the system or transducer input terminals themselves. Note carefully: making the polarity inversion anywhere else in the audio chain is an invitation to confusion.
So I took apart the woofer and tweeter out of the box again. Rewired the 077 to red-to-red, etc, according to grumpy's 4333 schematic. Put back everything together. But this time, I reversed the amp-to-terminal connection, as prescribed in the above quoted passage. The sound is fine and not different from what I heard before. My conclusion - schedule a visit to an ear specialist!

[Domino]

Well I have just been through this polarity thing with my L300's before reading these posts. I am using a Dynaco ST70 amp with mine. Any way my speaker internal wiring is as per N333 schematic and I have had my speakers since new. When checking each speaker with a "C" battery, the 136A woofer moves backwards red connection to + battery. This agrees with the 2235 spec in the JBL Tech bulletin 12C as this woofer is listed negative polarity. The 2405/077 is also listed as negative polarity. The LE-85/2420 is positive polarity as far as I can see. Therefore the L300 speaker system is a negative polarity system like the 4333 as listed in Tech Bulletin 12C. The Le-85 seems to be connected positive for the reasons and diagram in Bulletin 12C, page 3 figure 2 because of the length of the horn. I can definately hear the difference upon reversing the red and black at the amp for each channel. The midrange is much more forward hooked up "red to red". I have now settled on "red to black" at the amp after 30 years!! Much less in your face LE85 horn. The differece is very noticeable on recordings with up front vocals.
Try it you'll see. Next I'm gonna try reversing my 4313B's which are also listed as "negative".

[Domino]

I just can't help but mentioning this. I have also noticed going over some of the old "polarity" posts that it has been stated that if you want to correctly reverse the polarity of a speaker system you must change the polarity hookup of each individual driver. That is not true. Reversing the "red and black" at each speaker cabinet does the same thing. It was stated that the signal has to go thru the crossover components first. We're talking complete circuit here! That's like saying if you hook up a light bulb, a battery, and a switch, that the switch has got to be before the light bulb in the + line or the circuit won't work right.