Polarity issues again

[boputnam]

If you are miking a kick drum and the initial attack is forward, but the signal transmitted to your drivers is backward, you lose the initial punch in the chest. Not to mention the actual drum will be out of phase with your sound system.

Be careful not to confuse electrical polarity with acoustic (time) phase.

Merely by position of the subs, they are typically out-of-phase with the kick drum and bass (and with the Mains, too, if physical separation is sufficient).

Know your λ (lambda)...

[DavidF]

"This is great information... I was bewildered by this reverse polarity thing and vulnerable to any explanation..."

Compression drivers had to "pull" on the voice coil. I can easily see a small engineering group establishing a standard that positive going current pulls in all drivers, woofers or horn drivers. JBL chose to go all coils the same, Altec chose to have woofers different from their compression drivers. Ain't it that simple, after all?

I still hold that since I can't be sure that every one of my vinyl and digital disks, and each and every cut on same, are outputting absolute polarity, then I can't also pretend it makes a difference if my woofers Woof or Moof.

[boputnam]

I still hold that since I can't be sure that every one of my vinyl and digital disks, and each and every cut on same, are outputting absolute polarity, then I can't also pretend it makes a difference if my woofers Woof or Moof.

I really like that...



Well done.

[indycraft]

To woof or to moof........that is the question?

Compression drivers had to "pull" on the voice coil. I can easily see a small engineering group establishing a standard that positive going current pulls in all drivers, woofers or horn drivers. JBL chose to go all coils the same, Altec chose to have woofers different from their compression drivers. Ain't it that simple, after all?

I still hold that since I can't be sure that every one of my vinyl and digital disks, and each and every cut on same, are outputting absolute polarity, then I can't also pretend it makes a difference if my woofers Woof or Moof.

[grumpy]

... or foow/foom, ... fwiw.

[spaulcox]

Okay, I now have a personal theory about why the old JBL speakers had negative polarity, but I'll need some of you speaker rebuild guys to confirm it. I just thought about it today. Here goes:

On the old JBL speakers, there was very little voice coil overhang; i.e., the voice coil height was basically similar to the gap length. I had speakers come into the repair department that actually had the voice coil popped out of the gap. It was a rare occurrence, but I saw several examples of that during my days at JBL.

So, my theory is that good old Jim Lansing understood that a loud positive pop coming through an amp could push the speaker cone forward, clean out of the gap, while that same pop to a negative polarity speaker would slam the coil back into the basket, but that negative slam would cause less damage to the speaker than an outgoing pop would.

You'd hit the voice coil to cone glue joint, and that would absorb some of the shock.

Anyway, that's my personal theory as to why the original JBL speakers had reverse polarity. In all the years I spent at JBL, I never thought to ask anybody why we did it that way. I'm sure George Martin or Howard Wieser probably knew the real reason.

Speaker Guy:

The only twist on all that is that JBL knew the RED post was negative, so when they used their drivers in their own enclosures they wired them accordingly so that a positive charge moved the speakers forward. I like the first story I heard about this, in that it was simply a mistake in initial production. They had shipped large quantities in the beginning before they even realized they were wired backwards, then decided to keep it that way so that the next batch would be in sync with the previous ones.

[spaulcox]

Be careful not to confuse electrical polarity with acoustic (time) phase.

Merely by position of the subs, they are typically out-of-phase with the kick drum and bass (and with the Mains, too, if physical separation is sufficient).

Know your λ (lambda)...

Speaker Guy;

Good graph, so you want your subs in phase with your kick drum, unless you have your mains 87 feet out front of the stage. At this point you want to reverse the polarity of your subs 180 degrees.

[Harvey Gerst]

Speaker Guy:

The only twist on all that is that JBL knew the RED post was negative, so when they used their drivers in their own enclosures they wired them accordingly so that a positive charge moved the speakers forward.

Except, the positive signal from an amp went to the Red terminal on the x-over, and the black terminal of the Crossover went to the black of all the drivers. So, after exiting the network, the positive signal out of the x-over went to the speakers Red terminal, which resulted in the speakers moving backward, into the gap. At least, that's how I remember it on the N500, N1200, N2500, etc..

Again, this is as I recall, from 40+ years ago.

[spaulcox]

Except, the positive signal from an amp went to the Red terminal on the x-over, and the black terminal of the Crossover went to the black of all the drivers. So, after exiting the network, the positive signal out of the x-over went to the speakers Red terminal, which resulted in the speakers moving backward, into the gap. At least, that's how I remember it on the N500, N1200, N2500, etc..

Again, this is as I recall, from 40+ years ago.

Speaker Guy;

I'm not sure why this is so interesting to me... but it is. The old 4560 and those Scoop bass bins from the seventies (they had the single and duel 15 design) were wired so that positive (tip) of the phone plug advanced the speakers forward. Also a 12dB per octave passive crossover network flops the phase 180 degrees. The more recent SR4715 with two 2226H, which I own 4 of, also move forward with positive.

I still think they just made a mistake in the beginning??? I have worked with Altec, Utah, Jensen, Peavey, McCaulley, Eminence, Celestion, Yamaha, Carvin, EV, Community, Cerwin Vega, Oxford, Rola, Community, Grundig, Olson, Weber, Cleveland, Heppner, and several more. JBL is the only speaker I've seen with RED negative.

PS Don't get me wrong... out of all of those... JBL drivers are my favorites. I also really miss the D, K, & E series. I understand the alnico shortage, but liked the "E" series too. JBL should really bring them back!

[Domino]

I just got my Cricket yesterday for Phase checking. What a great unit!!
http://www.musiciansfriend.com/produ...5&src=3SOSWXXA