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Subs with reversed polarity (surprise!)
Subs with reversed polarity (surprise!)
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Old 19th June 2019, 07:00 AM   #71
kgrlee is offline kgrlee
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Join Date: Nov 2011
Location: Cooktown, Oz
Quote:
Originally Posted by bentoronto View Post
First of all, anybody can see that I've posted pairs of FRs. Tell me, kgrlee, which do you suppose is the same-polarity pair and which the funny one? ............... loadsa stuff which I'm sure is unnerstanabel to wun hu wen 2 skul
Thanks for all the clarification Ben. I have pored over your pic in #46 in the light of these new explanations and am now certain that I have extracted all the data that my small brain can possibly use. I shall not ask for more.

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Of course the signals are for all practical purposes of the crude demo identical. Duh. What is the exercise all about?
What I was trying to establish was if you system uses 2 subwoofers 'IN PHASE', or more correctly 'WITH THE SAME POLARITY', below 130Hz.

In your original post, you show response curves and suggest the 'OUT OF PHASE', or more correctly 'WITH DIFFERENT POLARITY', version is preferable.

What is not clear is if your usual system has these 'DIFFERENT POLARITY' subs below 130Hz.

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At 80 Hz (about 14 inches wavelength) one wave has traveled 10.0 times 360 degrees and the other 10.3. ...

My purpose was to illustrate that even a drastic phase adjustment like polarity reversal in real rooms does not result in the textbook wave arithmetic.
May I suggest you re-visit your textbooks. You might start with the chapter on the speed of sound. I have crossed swords with various acousticians in the past on this subject but even I haven't the nerve to suggest variations as large as you show.

Of course, you might be on a different planet ... where your wavelengths might be entirely appropriate.
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Old 19th June 2019, 12:33 PM   #72
bentoronto is offline bentoronto  Canada
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Subs with reversed polarity (surprise!)
Quote:
Originally Posted by kgrlee View Post
In your original post, you show response curves and suggest the 'OUT OF PHASE', or more correctly 'WITH DIFFERENT POLARITY', version is preferable.
See post #39
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Old 19th June 2019, 09:29 PM   #73
kgrlee is offline kgrlee
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Join Date: Nov 2011
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Originally Posted by bentoronto View Post
See post #39
Thanks for this Ben.

I see that your actually listening position has the subs with 'SIMILAR POLARITY' with some added 'PHASE tweaking'. The curves in your original post were at some position you are reluctant to specify. This allows us to put the correct significance and importance to your posts in this thread.

Incidentally, you say a lot about "textbooks" and "phase annihilation diagram for woofer frequencies", ".. results of bouncing off the walls and the irregular distances and phase irregularities that have an impact on the bass in a dipole...", ".. rear sound bounces around and the phases get messed up a lot".

Which textbooks say these things or similar?

I have a small collection of textbooks which I use mainly for toilet paper as i kunt reed en rite. But none of them say anything of the sort.

I don't think even the tomes written for the unwashed masses claim anything like this. In fact, your claims are the first I've seen of this kind.
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Old 19th June 2019, 09:40 PM   #74
kgrlee is offline kgrlee
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Originally Posted by bentoronto View Post
beats me how the heck anybody with a passive crossover could ever get their system right
Incidentally, AES E-Library >> Is Linear Phase Worthwhile? explains just that though many speaker designers are often unaware of exactly what they are doing.

The most common high quality treble crossover is the Arthur-Smyth third order (AS3) which I helped Robert Arthur-Smyth to formalise at Celestion.

Among other things, it incorporates your 'Phase Tweaking' though the technique was old by the late 70s for passive crossovers.

I just pretended to do the maths to tell the speaker designers what they were actually doing.
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