Film-Tech Forum ARCHIVE: JBL Horns

This is topic JBL Horns in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=010474

Posted by Michael Voiland (Member # 5386) on 05-20-2010, 02:26 AM:

Ok so we have a single 15 for the middle of our theater. The horn on top of the cabinet is a jbl compression driver 16 ohms i am not sure about the model i didn't think to look. It has to have a diameter on the back of the horn about 4 inches but i am going to assume its a 2 inch compression driver.
The connectors on the back of it suck and they are not holding a good connection speaker vibration has caused it not to say connected. It looked almost like it was threaded into a socket and i gave it a slight turn well its loose now. Is their a way to tighten this connection on these stupid push button connectors up so they don't rattle loose and keep a good connection. This is on our center channel.

Posted by Sean McKinnon (Member # 612) on 05-20-2010, 10:48 AM:

There is a way to tightn the push in plugs down but I would be more concerned about the excessive vibration. Is this horn properly mounted to the LF cabinet?

Posted by Michael Voiland (Member # 5386) on 05-20-2010, 06:22 PM:

Yes its just that it has come loose over the past 6 years and since no one ever sees it they never worry about it. I found it out after their were complains about sound being muffled.

Posted by Demetris Thoupis (Member # 833) on 05-21-2010, 01:10 AM:

Three solutions,
Remove the binding post and solder the cables directly! Make sure that you have a secure point so as not to have the inner cable being forced by the input cable. Do not solder directly the binding posts!

Replace the binding posts (if you can find a replacement)

Buy new speaker [Big Grin]

Posted by Tony Bandiera Jr (Member # 2365) on 05-21-2010, 12:07 PM:

LOL good ones Demetris [Big Grin]

Fourth solution:

Remove the cover that the posts are mounted on, on the backside will be pigtail leads and nuts holding the binding posts on. Tighten your nuts and it'll be good to go. [Smile]

Posted by Michael Voiland (Member # 5386) on 05-22-2010, 02:09 AM:

I did the forth solution tonight before i got a chance to read it. Whoever put these things in had half of them wired backwards to the crossovers aka pos to neg and neg to pos so my 3 screen channels are now all in phase to each other. Now to check the rest of the theaters.

Posted by Mark Gulbrandsen (Member # 72) on 05-22-2010, 04:54 PM:

Be careful... Some of them should be wired backwards or out of phase. Depends on model... You may want to ask Steve Guttag. He can tell you which models off the top of his head
Mark

Posted by Jeremy Weigel (Member # 4208) on 05-22-2010, 05:11 PM:

I have a pair of JBL subs that were out of phase. After checking numerous times that the polarity was connected correctly from the amp to speakers and removing the drivers to check the connections between the drivers and push terminals (all of which were correct based on color coding) I ended up reversing one of them inside the cabinet and leaving a note for future reference.

Posted by Gordon McLeod (Member # 33) on 05-22-2010, 05:33 PM:

On should always verify speaker phaseing with a tick box like the easy phase that smart used to sell

Posted by Dave Macaulay (Member # 813) on 05-22-2010, 05:59 PM:

As I recall JBL coded all drivers so a positive voltage on the red terminal moves the voice coil out of the magnet assembly. Since the horn diaphragm is mounted opposite to cone drivers, the horn sound waves will be "out of phase" with the bass bin's if you connect both with amp + to the red terminal.

Posted by Monte L Fullmer (Member # 2797) on 05-22-2010, 07:36 PM:

What would be the reasoning over this from JBL to have each driver to "pull" opposite if the positives were tied together?

Seems a bit confusing and kinda goes against logical wire terminations..

-Monte

Posted by Steve Guttag (Member # 268) on 05-22-2010, 09:51 PM:

Positive voltage on red or "+" terminal having a cone driver move out of the magnet is the convention of most.

JBL did it in reverse in a "retaliation" to Altec convention since James B Lansing was the father of both.

As for what drivers are in "normal" phase versus reverse...if a JBL driver is a legacy driver (can be a direct replacement of an earlier driver) then it will follow the traditional JBL convention of reverse phase. If it is a NEW JBL driver that does NOT DIRECTLY REPLACE a legacy driver, then it will follow normal phase.

Thus 2225, 2226 drivers will follow reverse phase. 2425, 2426, 2445, 2446, 2450 drivers will also follow reverse phase.

Subwoofers is where it gets tricky. The 4645 (original) used the 2245H, it is reverse phase. The 4645B and 4645C use the 2242...this is NOT a direct replacement of an earlier driver so it follows NORMAL phase. The 4642A subwoofer uses 2241 drivers...the 2241 IS a replacement of the 2240 driver so it follows REVERSE phase! JBL states that the 4141 and the 4642A follow NORMAL phase...which means the cabinets have to be wired reverse internally. I can and have found them wired wrong and, in the case of the 2242A, with each driver wired opposite (to the terminals on the cabinet)!

As Gord says...use a phase checker to ensure you are wired in-phase. The CP650 and CP750 even give you the "thump" for the phase checker to work from.

Steve

Posted by Michael Voiland (Member # 5386) on 05-22-2010, 09:57 PM:

I will go back up their and get the model of each but only the center and left were wired backwards only for the horn. The right was wired correctly.

Posted by Cameron Glendinning (Member # 3516) on 05-23-2010, 12:16 AM:

I was under the impression that the positioning of the horn and the miss allignment of the magnets for both the woofers and mid horns could also effect the phasing.
Also some if not all 12db per octive crossovers reversed or introduce a 180 shift the phasing as well?

If one looks at the eq one can see the effect of either the peak or dip in response created by the miss match! I remember reading an altec manual that discribed the sound effect of a miss matched phasing.

Is it possible that the person who wired it up also eqed it? If so perhaps you have now made it out of phase? At least a new eq would probably be required as the wiring does effect the frequency response of the system, as it has probably been eqed in its last configeration?

Posted by Louis Bornwasser (Member # 3063) on 05-23-2010, 01:19 PM:

Also: on Legacy JBL units, it was necessary to reverse the phase in order for explosions to be "positive" phase. See the original THX drawings for reference. Louis

Posted by Richard Hamilton (Member # 321) on 05-23-2010, 04:24 PM:

When I took a sound reinforcement course, I was taught that phase was the alignment of the drivers. Polarity is the connections. The instructor demonstrated the phasing by stacking 2 bookshelf speakers and running pink noise. He slowly slid the top speaker back and there was an immediate dip on the analyzer screen. As he moved the speaker further back, the dip moved along with it.

Posted by Michael Voiland (Member # 5386) on 05-24-2010, 01:32 AM:

Interesting that is true. Polarity would be the correct term to use I guess. It doesn't matter the theaters have all been so botched and haven't been eqed in 6 years at least. This is including the new screen some new curtains more decorations (yuck)
I am just trying to keep this stuff from breaking because everything at the place i work is run into the ground then fixed sort of.

Posted by Steve Guttag (Member # 268) on 05-24-2010, 09:25 AM:

The flaw in just changing the polarity is that it presumes a periodic wave form and that you are out only for 1/2 of a cycle. Mechanical time alignment is best but failing that, electrically delaying the component furthest forward is best.

In Rane analog crossovers, like the AC22, you can adjust the delay continuously. Thus, play a tone at the crossover frequency and adjust the delay until the output is maximum...it is very fast to do.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 05-24-2010, 09:32 AM:

Rick,

Your teacher demonstrated time alignment... not phasing! He probably didn't realize or know what he was doing. If drivers are too close to each other you can experience phase cancellation and you will see that dip where the frequencies cancel out. But you also want drivers in the correct plane so the signals all arrive to you at exactly the same time.

When you reverse the polarity of a driver you are causing it to operate 180 degrees out of phase. Like Gord says... use a phase checker and before hand know which way your system's components are supposed to be connected. You haul the ladder around considerably less and make less trips up to the screen speakers if you do.

Mark

Posted by Robert Minichino (Member # 3495) on 05-24-2010, 10:16 AM:

A polarity change is effectively the same as a frequency-dependent delay line that delays by 1/2f seconds. Consider an all-pass filter, which has a transfer function H(s) = (sRC-1)/(sRC+1), i.e. a pole-zero pair on the real axis, mirrored across the imaginary axis. At low frequencies, the phase shift of the transfer function is 180 degrees, is 90 at 1/2piRC, and 0 at high frequencies. If we keep moving the quadrature frequency higher, RC approaches zero, and more frequencies experience the 180 degree phase shift. At RC=0, H(s) = -1, or a simple polarity reversal.

Hocus-pocus aside, a polarity reversal is genuinely useful in crossovers where the effective phase of the driver outputs in the crossover region causes cancellation, but is not useful for fixing the drivers' physical alignment. In the crossover situation, there is only a small region of frequencies where both drivers play, so you don't end up with comb filtering. If you had two identical drivers playing the same signal, you would get comb filtering if they were physically offset, and switching the polarity on one would only move the comb, whereas a real time delay (by moving drivers or electrically with an all-pass filter of some sort) would eliminate it.

Posted by Richard Hamilton (Member # 321) on 05-24-2010, 10:36 AM:

Syn-aud-con

Mark, I think they know what they're teaching. It's possible I'm remembering wrong.

Mark, this is a good page to read.
phasing and polarity

Posted by Robert Minichino (Member # 3495) on 05-24-2010, 11:08 AM:

Time-delay, physical shifting of sources, the effect of crossovers on signals, and polarity all relate to phase. The confusion comes in because phase is the positional relationship between two pure tones. Complex signals don't have a single phase, but their pure tone components do. You can look at a plot of phase versus frequency just as you would a plot of magnitude versus frequency on a spectrum analyzer, although it wouldn't be terribly useful in practice. So when you're talking about phase, you're talking about an abstract overarching concept.

A time delay or physical shift has a phase response that is proportional to the frequency, so it would show up as a sloped straight line on our hypothetical phase spectrum analyzer. The polarity reversal would be a straight line at 180 degrees. And a real crossover would have a curve of some sort (the same you'd see in a Bode plot).

Posted by Tony Bandiera Jr (Member # 2365) on 05-24-2010, 12:50 PM:

Markertek sells a great tester for only $100, check it out HERE.

It is well-made in metal cases and is about the only one around anymore.

Pulse unit can drive line level or a speaker directly and the receiver has a built-in mic, and it also has built-in cable testers for 1/4" as well as XLR.

A great value and a MUST for setting up any sound system and checking speaker polarity.

Posted by Gordon McLeod (Member # 33) on 05-24-2010, 03:01 PM:

I beleive it was a german firm that made the one smart sold