Should a speaker system ever?

[Ken Pachkowsky]

"Be out of phase" on any pair of drivers...?

For example a 3 way system. Something tells me I read somewhere that its possible?

Thanks

[Robh3606]

Hello Ken

You meen a woofer out of phase with the other woofer as an example. Normally no. You wouldn't run the mids or the tweeters in a stereo pair out of phase with each other. Normally the phase of the drivers are all matched between the two cabinets.

Rob

[hjames]

"Be out of phase" on any pair of drivers...?

For example a 3 way system. Something tells me I read somewhere that its possible?

Thanks

In some of the JBL 434x systems the woofer is out of phase with the other drivers

[grumpy]

within a system? sure, it's done all the time.

[Ken Pachkowsky]

Hello Ken

You meen a woofer out of phase with the other woofer as an example. Normally no. You wouldn't run the mids or the tweeters in a stereo pair out of phase with each other. Normally the phase of the drivers are all matched between the two cabinets.

Rob

Sorry Rob, NO

What I mean is:

In a 4345 for example, would the 2421B's left and right be out of phase with the 2405's left and right?

The reason I ask is my HR-7's are out of phase on the mid bass 2122H and the horns or 2426's.

Ken

Ken

[Robh3606]

The reason I ask is my HR-7's are out of phase on the mid bass 2122H and the horns or 2426's.

Ken

Oh well what Grumpy said then.

Rob

[Ian Mackenzie]

If the system uses 12 db network slopes in the crossover its usual to have the mid and woofer polarity reversed but not always the case with the woofer to horn systems where the horn is displaced behind the woofer 1/2 a wave length at the crossover point.

3rd order and higher odd order slopes can be either polarity.

24 db LR slopes requires the drivers are nearly always in phase.

In designs like the 4430/4435 the crossover frequencies and LC component values were shifted so the drivers could be in phase (12 db slopes).

That system has a 15 degree upward tilt of the crossover region to benefit inverted placement in control rooms

The phase response of a driver can vary considerably over its operating range ..particularly and the low end where it acts as a high pass filter.

Its not a simple yes no answer.

[grumpy]

if you leave the Left and Right business out, as it just confuses the issue,
the +/- sense at the input terminals can be different at the various drivers
within one cabinet... e.g. a midrange may appear to be intentionally wired
with the + terminal of the driver to the - terminal on the input to the cab.

Why? at crossover a 12dB/oct slope will cause a 90 deg phase shift (one way
with a low pass filter, the other way with a high pass filter)... if you hooked
up such a crossover/driver pairing in-phase, they would cancel each other
at/near the crossover frequency (being 180 deg out of phase). Swapping
the polarity of one of the drivers takes care of this, in terms of frequency]
response.

This is a simplified explanation, as there are consequences.

(some of which Ian, aka flitter fingers, has hinted at)

[Ken Pachkowsky]

Oh well what Grumpy said then.

Rob

Sorry for the confusion.

No, should a pair of drivers within a system be out of phase with another pair of different drivers within the same system. Apparently the answer is yes, its done all the time...

Can someone explain the reason that its done in some systems?

Ken

[Ken Pachkowsky]

Thanks for the input guys.

[Robh3606]

Can someone explain the reason that its done in some systems?

Hello Ken

So the drivers are in phase through the crossover region. That way the drivers sum properly where they overlap.

Rob

[boputnam]

Oh well what Grumpy said then.

As is typically the case.

Apparently the answer is yes, its done all the time...

Oh, yes.

I suspect you are deploying your xta DP448 (or did you go another route...?). In any event, you should start with the OEM configuration (if Westlake will share that with you) - using their crossover points, slopes, group delays and inversions.

Then, if you have measurement gear to run impulse responses, magnitude trace (transfer function) and RTA, you should run some of your own iterations, watching the effect(s) on the phase trace and frequency response. It is very informative. And, no doubt, you will run into non-trivial decisions about whether a certain filter is really needed if it imparts an undesirable phase anomaly. Decisions, decisions, decisions...

As example, here are some OEM tunings for a 15" two-way coaxial, biamped. These are for deploying as a full-range support (no sub). Not my useage, but it gives an idea of the inputs...

[Audiobeer]

Now how did I know you were going to be here on the Phase or Polarity issue Bo!

[Steve Schell]

Hi Ken! I wish you were still close enough to visit. Say hi to Julie for me.

As mentioned, 3 way 12dB/octave crossovers often invert the mid driver to maintain even power response, though to me this is a B.S. solution. To attempt to put Humpty Dumpty back together again and reassemble a complex waveform, the individual components need to be both time aligned and in proper polarity. Real recorded waveforms are highly asymmetric. With most consumer systems past and present, non-aligned with jillions of crossover parts the subtleties can get lost, but in a really sorted out system ( the kind you like, I know), running drivers in opposite polarity just doesn't make it. This is one reason many hobbyists like simple 6dB/octave passive networks. The driver protection is minimal, but the drivers can be connected in proper polarity and The Sound Is Good.

With the Lansing Iconic and probably lots of later Altec two way systems, the stock configuration is a 12db/octave passive network with compression driver connected 180 degrees out of phase with the woofer. I have listened to the Iconics both ways; one either has a muddled sound stage and a smooth frequency response (stock connection), or a vivid sound stage and a response hole at the crossover frequency (drivers in same polarity). I haven't tried the Iconics with a 6db/octave network for fear of blowing the unobtanium 801 field coil drivers, but I have used this type of network with many other two way systems (like A7s) with great results. These days the results with charge coupled networks would be even better. I am running charge coupled 6dB crossovers on my all horn system at present (mid and bass compression drivers time aligned) and there is no going back.

In Jim Lansing's two way D-1000 system design, some of his last work, he used a third order 18dB/octave network. He had a great ear, and my guess is that he was well aware of the above dilemma with the 12dB network. As I understand it, with a third order passive network one can have the drivers in proper polarity as with the first order network, and with a high level of protection for the high frequency driver.

Wait a minute Ken... I just remembered... we were checking driver polarity on your Westlakes way back when with your PAA2 RTA. I scooped up a PAA3 shortly after and have used it for polarity checks for years now. You are already on top of this stuff!

[Ken Pachkowsky]

As is typically the case.

Oh, yes.

I suspect you are deploying your xta DP448 (or did you go another route...?).

Nope, I am using the dual deqx units.

I was messing around and discovered the mid bass drivers and mid horns were out of phase. Without this system having an internal network....I could not understand why they would be wired out of phase?

Ken