Subs with reversed polarity (surprise!)

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My point is that ONE accidentally chosen mic location hardly tells the story about other locations, such as my chair. ... And that is exactly what i prove in the other thread. The FR for my chair is about as nice as I can make it with my poor powers and yet it bears just minor resemblance to the accidental location .......... the chair FR is pretty good and I am certain that nobody would want to see the inverted polarity subwoofer curve which has to be a lot worse. But, the inverted curve does kind of look better in the accidental location. Gosh, I hope somebody will insist I post the inverted polarity chair curve.
Ben, could you please post a little diagram showing the room, its size including height and where the speakers are positioned as well as your chair AND the 'accidental' position.

I assume from what you've said that AT YOUR CHAIR, the out-of-phase response is much worse. Please let us know if this is not the case.

The relative position of 'chair' & 'accidental' has bearing on my assertion about consistency of response over an area .. for which I only have senile memories from 40 yrs ago. :eek:

I'm tempted to ask you for a series of measurements within a 3' radius of your chair, both in and out of phase, but I realise that's asking a lot.

I'm sorry I can't provide my own measurements cos this Millenium, I'm a REAL beach bum and live in a shed. :) But a diagram of your setup/room/positions etc may be sufficient to get me off my **** and try some of my simpler room simulations. I am no longer in a position to do full PAFEC FEA/BEA of rooms. :mad:

BTW, the 'simple' simulations use 'method of images'. This is much more accurate (both pedantically & in real-life) than claiming "It is the results of bouncing off the walls and the irregular distances and phase irregularities that have an impact on the bass in a dipole." or "The rear sound bounces around and the phases get messed up a lot"

Also https://www.diyaudio.com/forums/subwoofers/339164-moved-mic-omg.html#post5823532 comes up with 'no thread specified'.
 
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You really need other people to post graphs to prove that running 2 subs out of phase loses all the bass ?

Only if there right beside each other. At a half wave length they add. At 40hz thats 7 ft. at 80hz 3.5 ft or not much. So the position of the sub affects the phase between drivers and theres always peaks and throughs and they change with freq. ( and this is all before room modes). Thus the phase reversal switch on most better subs. And part of the reason many sugest multiple subs in vary different locations. Flat bass thru the whole room is very difficult to achieve, lots of room treatment and experimenting with sub positions AND phase is the only way to get close. If your only worried about the sweet spot thats a lot easier and EQ is your best friend but if you have a large dip ther you may still have to expirement wth location/phase.

Where does all the energy go, a hot wind? ;)

I believe the drivers burn it up because they have to push harder. The acoustic (air) coupling causes them to push against each other. As one pushes forward it has to push air thats moving in the opposite direction, from the other driver. Just a guess.
 
In a perfectly symmetric room, including geometry, furniture, and absorptive/reflective materials, with symmetric sub placement and a listening position on the centerline, I find it hard to imagine that subs out of phase wouldn't almost completely cancel each other out in the low end. Every path pair (L-sub & R-sub) to the listener should be identical length, making the arrival times identical. If one sub is 180 deg out of phase with the other but the same amplitude, they should cancel.

That's a pretty unusual room, but plenty of listening rooms are "largely symmetric".
 
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Inwas talking about multiple subs alla Gedes, not 2 subs at speaker locations. But even than room modes are more important than refletions. And furniture can make a room unsymetric. Try changing the phase of one stereo speaker with low end and see what it sounds like. The bass doesnt completely dissapear.
 
In a perfectly symmetric room, including geometry, furniture, and absorptive/reflective materials, with symmetric sub placement and a listening position on the centerline, I find it hard to imagine that subs out of phase wouldn't almost completely cancel each other out in the low end. Every path pair (L-sub & R-sub) to the listener should be identical length, making the arrival times identical. If one sub is 180 deg out of phase with the other but the same amplitude, they should cancel.
All I can reply to that abstract logical argument is:

"When the toilet paper of experience is depleted, the **** of reason goes unwiped"

BTW, are you talking only about one-eared listeners? Perhaps with their single ear (with symmetrical pinna, of course) centred on the top of their skulls?

By contrast, can't recall reading as much concentrated good sense as the recent posts of cbdb. Thanks.

Ben
 
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Of course not. Normal humans with a pair of ears would suffice just fine. You seem to be looking for reasons to dismiss the limit cases, which is foolish. I fully acknowledged the vagaries of real world rooms in my post.

I should note that the wavelengths involved can be so long as to swamp minor variances from symmetry, but hey, I don't want to get pedantic or anything. Keep on keeping on.
 
For those who are following this thread, I would like to point out that Ben used two very different "subs" in each corner. See POST #1 for details.

If this was repeated with two identical my guess is that the results might not be the same...

The key is the phase response of the subs, which can be quite different for various types of enclosure (sealed box, vented, TL, etc) and they can have very different group delay (which is the same thing as phase rotation).

So, what the phase differences are, who knows? But this is likely not really two sources "in phase" and "180deg out of phase". At least I strongly suspect they are not. If the phase just happened to be 90 degrees different across the low frequencies, "reversing" the phase to one of them would have absolutely no effect at all. That wouldn't' be all that much of a "surprise", eh?

These kind of details need to be clearly established when doing this kind of "experiment" or you risk findings that are just rubbish.
 
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Yes, CharlieLaub, I completely agree. It's not always easy to conceive experiments that generate results which are reliable. Lots of things matter. Everything must be accounted for. Your phase response example (even if amplitude response is identical) could throw all kinds of things out of whack. Thanks.
 
Ben, please post a pic showing your room dimensions and where your speakers, chair & 'accidental position' are.

Posting curves where these are not specified isn't data ... especially if the subject is as in the title.

It's, "OMG, I threw the ball in the air and it landed in a pile of ****. Fortunately, I had loadsa toilet paper."

And yes. Charlie is right to point out your **** is certainly affected by the different piles of **** in each corner.
 
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It takes a whole 5 minutes for somebody to do the two runs and show that their left and right sub annihilate one another when they reverse the wires to one, assuming you are leaving the subs and all else in the system and in your room unchanged from before the test.

How about some data instead of endless jaw-jaw?

Yes of course there is substantial cancellation and modified FR when in reversed polarity. Let's see how much in the rooms of these critics.

B.
 
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You're arguing a point that hasn't been made. Everything -- EVERYTHING -- depends on the details. No one test makes a definitive statement without a clear accounting for those details. You seem resistant to this idea. The very fact that your original test utilized 2 subs of radically different design makes it extraordinarily difficult to draw broad conclusions from your results.
 

ICG

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You are absolutely right, it's wasted time, energy and effort. Everyone then has to read up to the last post. Multiplied with all the users who tried to help so far, that's even more, a huge ammount of time wasted. I hate it if someone asks such questions, doesn't give informations and puts up unfounded conclusions and 'measured facts'.
 
I use two RYTHMIK 15 subs in the back of my room - 0nly place I could put them. Only from 20 to 50 hz.

There is no question I get greater output and a smoother phase plot with them out of phase.

One is about 9 feet up and the other side is on the floor. I have adjusted for delay for all but the woofer 9 feet up This makes a very big difference. Since the woofers are in the rear I have delayed the main speakers and the woofer on the floor sounded best not all the way in the back so I have delayed it, also

Using a xilica box and REW and thousands of measurements and adjustments. Still the best those drivers perform is when they are out of phase. Measurements taken at the listening chair at ear height.
 
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rickmcinnis, I have no problem believing that. I would ask, and no offense, but are they both wired with the same polarity? Does a 9V battery make both drivers move out (or both in)?

Regardless, two identical subs in different placements, one advanced in phase ahead of the mains, the other not . . . not surprising that flipping phase on the other makes a difference (one way better than the other).
 
I use two RYTHMIK 15 subs in the back of my room - 0nly place I could put them. Only from 20 to 50 hz... Using a xilica box and REW and thousands of measurements and adjustments. Still the best those drivers perform is when they are out of phase. Measurements taken at the listening chair at ear height.

Well rickmcinnis, I guess it is just you and me, people with experience, versus the Theoreticians.

When I had a giant OB sub along a side wall, I just could never decide if I (and my many REW plots) preferred the orthogonal or the reversed polarity. For sure, I am not favouring generally reverse polarity. Just saying, systems need to be tested.

And if you are smart enough to have a DSP, you should wiggle the phase a bit. Below are shown two curves with my subs and my large ESL panels. In one of the plots one of the subs has a mere 45-degrees added (or subtracted, not sure).

I leave it to all the perceptive readers to guess which is the one that looks a whole lot better (OK, mostly in one dramatic place near the crossover point*). Let me add, after a long time of listening to my speakers, I certainly couldn't guess which curve I was listening to without looking at my Behringer DSP.

B.
* beats me how the heck anybody with a passive crossover could ever get their system right
 

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