UREI 813C Expertise needed

[rusty jefferson]

Drug out a pair of 813C monitors and set them up. Owned them for a while, but never used them do to space limitations. Had OLDMICS put new surrounds on the 2215s, and we tried them out. Heard a little breaking up from one of the tweeters, and figured either the diaphragm or crossover was going. OLDMICS and WIDGET both felt the diaphragm was the likely culprit, so I removed both 801Cs and took them to John (OLDMICS) to evaluate, and replace the diaphragms.

While he was looking them over, he noticed the spring actuated wire attachments on the midrange/woofer (one colored Red, and one Black) were inverse from the + and - signs on the UREI decal located just below them on one spoke of the frame. So he takes out a phase tester and finds that to make the woofer section pull in on a positive charge, as the tweeter and 2215 helper woofer do, we have to follow the color coded spring clips, and ignore the UREI decal. There was some discussion as to whether the crossover might invert phase, but after checking the schematic, he felt it wouldn't.

As I reinstalled the drivers, each cabinet was tested with the phase test from the rear binding posts. All three driver pulling in with the positive charge. In the system I'm using, the preamp inverts phase and the amp doesn't, so we attach the speaker/amp wires red/red and black/black thereby inverting polarity at the speaker cabinet. When we run the phase test through the system, all the drivers are now pushing when given the positive charge.

Everything is now in absolute phase. So........should it be? Is the midrange woofer supposed to be out of phase with the tweeter/helper woofer? Is the UREI decal wrong? Has this been covered in 1000 threads already? Are a lot of people listening to out of phase speakers because they followed the decal? Are my drivers unique? We listened to music, and audible phase tests, with the woofer wired both ways, and there is a difference.

Appreciate any knowledge you can share. Diaphragms cured the breaking up for anyone still interested in that detail.

[Robh3606]

The 801C I have has a UREI label opposite of the standard JBL E-145 terminals. Why would you ignore it?? It's there to make sure you wire it up correctly. Use whatever the original wiring was when you opened them up. The crossover time aligns the woofer and compression driver so there may of may not be a driver phase change. Take a look at the 813C schematic.

http://www.jblproservice.com/pdf/URE...s/813C-L,R.pdf


Rob

[rusty jefferson]

The 801C I have has a UREI label opposite of the standard JBL E-145 terminals. Why would you ignore it?? It's there to make sure you wire it up correctly. Use whatever the original wiring was when you opened them up. The crossover time aligns the woofer and compression driver so there may of may not be a driver phase change. Take a look at the 813C schematic.

http://www.jblproservice.com/pdf/URE...s/813C-L,R.pdf


Rob

If it's wired per the decal, the woofer is pushing, as opposed to pulling, when bench tested, as well as through the crossover, with the phase tester. I.E. out of phase with the other two drivers. My main question was, should it be?

I can't tell from your photo, if the connectors on your driver are color coded in reverse, as mine are.

Several of the drivers appeared to be improperly wired per the schematic. That's why we took the time to be sure all were in phase on reassembly. I just don't know if they all should be. The 2425Hs and the 2215s had been serviced previously.

[Robh3606]

If it's wired per the decal, the woofer is pushing, as opposed to pulling, when bench tested, as well as through the crossover, with the phase tester. I.E. out of phase with the other two drivers. My main question was, should it be?

From what I am seeing that's the way it looks using the Urei Label. I would assume the schematic to be correct. This is not a simple design between the delay in the woofers crossover and the helper woofer. Do you have any measurement capability? Why are you asking?? Do they sound right??

Rob

[Eaulive]

Go as shown on the schematic, it's common to reverse the polarity on drivers due to crossovers and driver positions, using a phase tester to check the phase of individual drivers is a mistake, since they can purposefully be wired backwards in a given setup.

To test the phase relationships of a whole system use a RTA and a pink noise, many times you'll see that the driver that was wired backwards is actually blending at the crossover points with the adjacent drivers.

"Absolute phase" ??? by definition phase is relative, it's important when it's taken against something else.

I would really like to meet somebody that hears a difference when ALL the drivers in a listening room are inverted

More audiophool propaganda.

[subwoof]

All older JBL transducers are polarity noted by this:

when placed facedown on a surface, the red terminal is on the right ( right on red ).

This convention means that the "outward displacement / positive" terminal is the black ( left ).

HOWEVER it is very important to wire the cabinets as designed ( and as pictured on the schematic ) for proper performance. And yes it is COMMON to find HF or MF components wired " out of phase " on certain systems.

Absolute phase integrity is not a prerequisite to correct sound.

sub

[Robh3606]

Hello Sub

Did they put a URIE polarity sticker on the helper woofer?? They used a marker to blacken the Red terminal on the 801c I have.

[rusty jefferson]

Apologies for not having a photo of the terminals, as I didn't have have my camera the last time we had the drivers out.

The helper woofers have one Red and one Black terminal each. No Urei decal.

The 2425Hs have one Red and one black terminal each. No Urei decal.

The mid woofers have one Red and one Black terminal each, plus the Urei decal. The (+) sign on the Urei decals are located under the Black terminals. The (-) sign on the Urei decals are located under the Red terminals.

If I attach the green wire (+) to the Red terminal (- sign on decal) the mid woofer is in phase with the other two drivers.

If I attach the green wire (+) to the Black terminal (+ sign on the decal) the mid woofer is out of phase with the other two drivers.

I know some speaker systems have one driver out of phase with the others. My question is, was the Urei 813C designed to have the mid woofer in or out of phase with the other two drivers? Do I follow the decal, or the color coded terminals?

[Robh3606]

Do I follow the decal, or the color coded terminals?

Wire them to the decal. This should match how the +/- as shown in the schematic. Also wire the helper as per the schematic using Subs comment about Red on right as the a key element of this. Don't get hung up in the polarity of the driver terminals. Wiring exactly as it is shown on the drivers in the schematic. IE face down with the correct collored wires to the correct terminals as they are laid out.

Rob

[subwoof]

UREI ( and then UREI/JBL ) must of used a dozen different brands ( and model numbers of each to make it more fun ) of helper woofers ( and the mids too ) over the many years of production.

Altec, Emminence, P+S, EV, JBL and others. In addition the raw assemblies were sold to others for their custom monitors ( big reds for example ) and their crossovers might of used different wiring conventions.

Each of the 813 versions used way over-packed insulation to mimic larger volumes and minimize the variation in the LF outputs. Either way it's not the same performance as a carefully tuned cone / box combination but it did sound very nice.

But they were BASTARDS to lift up and put into those soffitts...

sub

[1audiohack]

"Absolute phase" ??? by definition phase is relative, it's important when it's taken against something else..

True, phase and polarity have been used through out this thread as if they were interchangable, and they are not.

I would really like to meet somebody that hears a difference when ALL the drivers in a listening room are inverted .

I can. Really. Only on a system that behaves very well in the time domain and most don't, and it must be a system I am very familliar with.

More audiophool propaganda.

I can not agree, if you have not experienced it, that does not mean it can not be.

As one example that I can hear, try this, listen to a suprano sax on a 2" driver with a decent horn, that driver can just about cover that instruments full range by itself and that helps to get the crossover out of the way. If you switch the polarity back and forth, when reversed the sax sounds more like a clarinet. I don't want to dilute this thread as this discussion should be in the General Audio Discussion Forum. If you want to continue it there I would be happy to go along.

Absolute phase integrity is not a prerequisite to correct sound.

I can't buy that either, good sound, bad sound, OK sound maybe,, correct or great sound requires all the accuracy you can muster.

[rusty jefferson]

Wire them to the decal. Rob

Thanks, Robh. Easy enough done

They used a marker to blacken the Red terminal on the 801c I have.

This could be the most telling piece of info on the subject.

HOWEVER it is very important to wire the cabinets as designed ( and as pictured on the schematic ) for proper performance. And yes it is COMMON to find HF or MF components wired " out of phase " on certain systems.

Absolute phase integrity is not a prerequisite to correct sound.

sub

This is why I started the thread. I couldn't find any information about the Urei 813C being designed with the mid woofer out of phase, which it will be when I wire per the decal. I know some systems are this way and wanted confirmation this system was designed this way.

I assume you meant absolute phase integrity is not a prerequisite in a particular speaker cabinet, as we're discussing here.

Go as shown on the schematic, it's common to reverse the polarity on drivers due to crossovers and driver positions, using a phase tester to check the phase of individual drivers is a mistake, since they can purposefully be wired backwards in a given setup.

I don't think it's a mistake to have the knowledge of what the drivers are doing individually, relative to phase, both on the bench, and through the crossover. I just need to know what the drivers should be doing by design. The guy I bought these from was making records with the tweeters out of phase of one another.

To test the phase relationships of a whole system use a RTA and a pink noise, many times you'll see that the driver that was wired backwards is actually blending at the crossover points with the adjacent drivers.

I'll see if I can get OLDMICS to help with this, as I don't have the tools.

"Absolute phase" ??? by definition phase is relative, it's important when it's taken against something else.

I would really like to meet somebody that hears a difference when ALL the drivers in a listening room are inverted

More audiophool propaganda.

I believe it is critical that proper phase be maintained, from the microphones in the studio to the speakers we listen to the music through.

I had an experience just a few weeks ago listening to a piece of music I am very familiar with on someone else system that sounded incoherent. The vocalist was beaming from both speakers instead of imaging between them, and guitar and horns were much further left and right on the sound stage then they should have been. A quick internet check told us his preamp inverts phase (news to him). Switched the speaker leads, and it sounded as it should.


Rohb, would you mind doing a phase/battery test on your 801s (per the decal) and let me know if the mid woofer is out of phase with the tweeter? Thanks

[Eaulive]

I don't think it's a mistake to have the knowledge of what the drivers are doing individually, relative to phase, both on the bench, and through the crossover. I just need to know what the drivers should be doing by design. The guy I bought these from was making records with the tweeters out of phase of one another.

When I said "mistake" I meant that if you're using this method to connect your independent drivers in your speaker cabinet, you will maybe wire them wrong. Now if you talk about knowledge of course "wanting to know how" is not a mistake

I believe it is critical that proper phase be maintained, from the microphones in the studio to the speakers we listen to the music through.

Then you should be talking about "polarity", not phase, meaning that a positive sound pressure in the studio creates a positive sound pressure in your listening room.
This polarity thing is debatable, I don't hear any difference and I know nobody who can, but then again, I don't know everybody
1audioshack claims he can and theorically the claim that there is a difference can be logically supported so I can not say it's impossible, only very unliky IMHO.

I had an experience just a few weeks ago listening to a piece of music I am very familiar with on someone else system that sounded incoherent. The vocalist was beaming from both speakers instead of imaging between them, and guitar and horns were much further left and right on the sound stage then they should have been. A quick internet check told us his preamp inverts phase (news to him). Switched the speaker leads, and it sounded as it should.

This sounds more like a phase problem than a polarity problem, like when you have one of the channels with inverted polarity (one channel 180º out of phase with the other), the sound stage is completely out of wack so as the LF response.
If you tell me you reversed both speakers polarity and everything came back to normal, then I find it very strange.

[Eaulive]

As one example that I can hear, try this, listen to a suprano sax on a 2" driver with a decent horn, that driver can just about cover that instruments full range by itself and that helps to get the crossover out of the way. If you switch the polarity back and forth, when reversed the sax sounds more like a clarinet. I don't want to dilute this thread as this discussion should be in the General Audio Discussion Forum. If you want to continue it there I would be happy to go along.

I really have nothing to add, I will try and make some honests test with what you describe, I don't doubt your word if you say you can hear the difference, like I said, it is theorically possible.

Absolute phase integrity is not a prerequisite to correct sound
I can't buy that either, good sound, bad sound, OK sound maybe,, correct or great sound requires all the accuracy you can muster.

I don't know what's more noticeable, the reversed polarity of a driver or the interference that is created at the crossover points because the driver is out of phase with its neighbour ?
Like I said sometimes a driver can have the correct polarity but due to the crossover or the position it's suitable (and common) to purposefully reverse one to preserve the phase of the signal of two overlapping drivers

[Earl K]

Rusty,


- As RobH pointed out ( as well as subwoof ) / wire the 3 drivers according to what you see in that schematic .

- As to reconciling the wiring in the posted schematic, to what you and Oldmics have observed / here's what you both need to know ;

"Polarity Checkers are very unreliable devices when used on ( passive or electronic ) "all-pass" networks ( & thats what that Urei network is ) .
- ie; They can give a false reading .

- The delay derived from an all-pass network is frequency dependent ( so all the phase changes go through multiple 360 deg. rotations ) .
- This makes "polarity" a moving target over the operating range of the transducer .

- One typically doesn't encounter this when dialing in a delay on a digital speaker management system ( such as Oldmics typically uses ) .
- One always encounters this phenomenon when using older analog crossovers that offer a simple "delay" adjustment on only the woofer section ( such as I continue to use ) .

<> EarlK