Speaker terminals?

[Searing]

I just bought JBL k120's.  I know that these speakers have the reverse where red is neg. and black is positive.  I have a feeling the ones I bought have been reconed, even though the guy says he doesn't think so.  Anyways, how do I test to see wich terminal is + and which is -?  Thanks!

Chris

[FYL]

Use a 9V battery connected + to +, - to -, if the cone moves forward the phase is correct, if not phase is reversed.

[jhadhar65]

It doesn't make any difference as long as you're not mixing them with other speakers and all the JBL's are connected the same way.

[Searing]

Yes all JBL's are connected the same way (at least these older ones)  red is neg. and black is Pos.  I think it does matter which way you hook them up!  I am asking because on the photos I saw of the speakers I am buying, the guy had his white (+) lead going to the red terminal, and his neg lead black going to the black terminal.  This is why I thought they may have been reconed?!?  Here's some pictures.

http://picasaweb.google.com/JPArgueta/Twin#5439621055567475858

[FYL]

JBL initially followed WeCo conventions (polarity was determined with a range of drivers fitted with a motor in front of the diaphgram, hence the inversion) then switched to industry-standard conventions.

All vintage AlNiCo drivers should be inverted, but there are some exceptions such as the 123A-1. Later models can use either system, cf. this JBL's tech note from the early '80s: http://www.jblpro.com/pub/technote/tn_v1n12b.pdf

[jhadhar65]

>I think it does matter which way you hook them up!

Think about it again.  We're dealing with a cyclical wave.  It makes no difference to the wave where it starts or where it ends, as long as it cycles.  It can matter a great deal to a speaker array where one or more speakers (but not all) are not in phase with each other because of frequency cancellation.  As long as all the speakers in an array connected to the same source are all in phase with each other, it doesn't matter whether they push first or pull first.  By "array", I mean a multiple speaker cab, multiple cabs with one or more speakers each, etc.

Take a single speaker cab you're 'sure' is connected right.  Listen to it really good.  Now swap the spade connectors and listen again.  Can you hear a difference?  The answer should be no.

[FYL]

We're dealing with a cyclical wave.  It makes no difference to the wave where it starts or where it ends, as long as it cycles.

Record a kick drum; make two copies, one respecting the original phase, the other reversed; compare them using an AB or ABX gizmo.
Do they sound the same?

Then do the same for guitar or piano.

[Searing]

I always thought the purpose was to get the cone moving forward?  I was under the impression that backwards movement did not sound as good?

Also, So these are original K120's, built between 73 and 79.  Do you guys think the black terminal is positive and th red neg.?  I will test them when I get them either way, but I heard that battery testing them can cause damage?  Thanks!

Chris

[jjasilli]

Something falls somewhere, and I'm there to hear it.  (Or someone beats a drum.)  The soundwave, or that portion of it traveling toward me, may commence as the +portion of the wave; the (-)portion; or somewhere in between.  But this seems to be irrelevant.  The wave has a certain wavelength.  Depending upon my distance form the source, the portion of the wave that first hits my ear is entirely accidental.  So how could it possibly matter whether the wave commmences in its + or (-) phase.

Nevertheless this pertians to the production of sound.  REproduction of sound, and the dynamics of microphones may be governed by other practical considerations, or even mojo.

[FYL]

Also, So these are original K120's, built between 73 and 79.  Do you guys think the black terminal is positive and th red neg.?

Negative (reversed), like most Alnico JBL's.

I heard that battery testing them can cause damage?

A 9V battery a couple of seconds across a big bad 8-ohm 4" VC rated for 200 watts won't do any damage, it translates to a little bit more than 10 watts dissipated in the coil (P = U^2 / R = 9 * 9 / 8 = 10.125 watts). OTOH, the same 9V battery could damage or fry more fragile speakers such as tweeters.

[jhadhar65]

>Record a kick drum...

That's apples and oranges.  A recorded kick is an entire wave form from attack through final decay.  Forward and reverse means much to that.  A single wave - meaning zero crossing to max excursion to zero crossing to max excursion to zero crossing - doesn't care (much) which way it's going...

I mean:

*  Record a kick drum, play it back through a single speaker = a distinctive sound.
*  Reverse the wiring of the speaker and play the same waveform forward through it again = the same distinctive sound you heard the first time.

I'm not saying anything here you don't agree with and I know so based on your position on cap tone.  I'm only saying it doesn't matter if the speaker is initially an out-ee or an in-ee as long as all of them in the stack are the same.  Nobody ever splices tape worrying about positive or negative slopes, do they?

Barring any mechanical requirements of a vintage speaker, he can connect them either way and it won't matter to him as long as they're both the same way.  (I think that's a statement you can support.)

[Searing]

For peace of min (wether it makes any difference or not in the real world)  I want to hook the + to the + and the - to the -.  It's psychological!   So then, JBL Alnico's K120's:  Speaker cable + to black speaker terminal and - to the red terminal, correct?

[FYL]

I'm only saying it doesn't matter if the speaker is initially an out-ee or an in-ee as long as all of them in the stack are the same.

Agreed.

[FYL]

So then, JBL Alnico's K120's:  Speaker cable + to black speaker terminal and - to the red terminal, correct?

If they are original or reconed according to JBL specs, yes.

[sluckey]

So then, JBL Alnico's K120's:  Speaker cable + to black speaker terminal and - to the red terminal, correct?

Just be careful if you ever have to jump-start them!