L300 phasing issue

[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/Stu...ries/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.