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Author Topic: QSC K10 tweeter polarity  (Read 17490 times)

Jay Barracato

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Re: QSC K10 tweeter polarity
« Reply #30 on: June 18, 2011, 12:00:04 pm »

You can make it 3, I measured two different boxes. I am in perfect agreement that the stock tweeter has a negative initial impulse.
That is the definition of "reverse polarity." Case closed. This is the point that Bob Lee and others argued incorrectly, and it is the only reason I bothered registering to post here. I posted the same polarity information on the QSC board, but the post was deleted.

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Since then, I see that the tone has gone from "is definitely better" to "is arguably better"
No. That was my original "tone." You apparently did not read the first post in the sticky on the FAS forum. Here's a quote: "First, the speaker comes from the factory with the HF polarity reversed. Although this is a common "feature" of loudspeakers, it trades one set of problems for another, arguably worse, one." That was posted well before this thread was begun.

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1. Please describe the physical setup of your measurement arrangement.
Asked and answered. In these particular measurements, the speaker and mic were elevated above the floor about 2 meters, but the results would be identical with a ground-plane measurement. To make it as clear as possible, there are no environmental reflections in my data.

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2. Please defend your conclusion that reversing the polarity to the positive position is "better" using specific examples from your data.
It is audibly - to me, and to a significant number of other listeners - superior to have all elements in a multiway system respond with the same polarity. Furthermore, it is best when that polarity is positive, IOW a positive-going voltage at the input produces positive-going pressure at the output. Sounds containing transient information - i.e., drums, cymbals, other percussion instruments - are better-defined. It is easier to hear how the drummer has tuned his snare drum and snares, for instance. Additionally, the attack portion of the sounds produced by percussively-excited instruments - acoustic piano and guitar, for example - are better-defined to my ears.

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What in the data shows better "transient response"?.
Positive polarity of both woofer and tweeter are necessary - but not sufficient - conditions for the best transient response. When reversed polarity is correctd, transint response is improved by definition.

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For the record, my conclusions based on both your and my own measurements are:

1. The stock position of the HF has a negative initial impulse (negative polarity).
Again, case closed. That was and remains my point in responding here. You agree. Why argue further?

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changing the HF polarity steepens the phase response.
Having both devices in correct polarity makes the group delay error caused by the crossover transition apparent. That error is there, regardless. Any argument that the speaker's behavior has been "optimized" via strategic use of FIR filters is clearly shown to be false by this fact alone.

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5. Based on your impulse response curve, the amount of time for the initial impulse is the same for both positions, just opposite in direction.
"Direction" matters.

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Since I deploy my speakers with more of the listeners closer to on axis than off axis,
Describe the typical dimensions and geometries of your "deployments," and we'll do the trig. My money says you're mistaken on this one.

1. Your sticky was edited after this thread began.

2. Your conclusion is based on your belief that + is always better, regardless of the measurements. You have still failed to point at anything in your data other than the direction of the polarity.

3. You still have not defined transient response, nor demonstrated how it is revealed in the data. Once again you have simply reported your belief that this factor is somehow better. Saying it is better "by definition" doesn't help when you have not defined the term nor referenced the data.

4. If you want to bet on the angles of my deployment, which you know nothing about, I want to bet on your SIGNIFICANT number of users that have inverted the polarity and found it sounds better. I am using that term statistically, and I am just as sure no where approaching a significant number of users have made the swap.

It is my current interpretation that you possess an opinion that matching the polarity of the two drivers overrides all other design considerations. This bias pre-dates your collection of the data, and you have attempted to use the data to promote this bias, whether the data supports it or not.

Obviously, both the QSC engineers who designed the box and I do not feel that way. Your continued inability to define what is better about the box when matching polarity and defend it using your own data leaves me one thought:

Should I invert the polarity of the HF in my K10's?

I am unconvinced that there is any improvement over the factory design.
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Jay Barracato

Jay Barracato

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Re: Playing with some trig
« Reply #31 on: June 18, 2011, 02:34:55 pm »


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Since I deploy my speakers with more of the listeners closer to on axis than off axis,
Describe the typical dimensions and geometries of your "deployments," and we'll do the trig. My money says you're mistaken on this one.

Lets see...

Start basic... place the speaker on stand 6 feet above the floor with the vertical on-axis line parallel to the floor:

Lets assume the listener wants to be with in plus or minus 20 degrees of that line.

At 10 feet from the speaker the 20 degree line would be at 3.6 feet. So anyone with their ears less than 2.2 feet from the floor or more than 9.6 feet from the floor would be outside of 20 degrees.

At 20 feet from the speaker the 20 degree line would be 7.3 feet. Impossible to achieve in the negative direction. 13.3 feet in the positive direction.

At 30 feet from the speaker the 20 degree line would be 10.9 feet. A listener would have to have their ears 16.9 feet in the air to get more than 20 degrees off axis in the vertical.

Lets back down to 10 degrees off axis as our limit

At 10 feet the listening area is getting smaller but is still plus of minus 1.8 feet. I guess it would be possible to have a seated patron at 10 feet be slightly more than 10 degrees off axis.

At 20 feet the area is plus or minus 3.5 feet. A seated patron is still less than 10 degrees off axis.

At 30 feet the area of interest is now plus or minus 5.3 feet. Someone with their head on the floor could be outside of 10 degrees. Actually at 30 feet the floor is 11 degrees.

In all of these I would be more concerned with energy off of the ceiling rather than a patron being under the angle of interest so lets introduce the 7.5 degree downward tilt of the k10.

At 10 feet, the patron has 0.8 feet at the floor to squeeze their ears into in order to be more than 20 degrees off axis. They would still have to be over 8 feet tall in order to be outside of the 20 degree vertical above this new plane.

At 20 feet from the speaker, even tilted down the listener would have to be over 10 feet in the air, and at 30 feet over 12 feet in the air.

With the downward tilt, at only 10 feet from the speaker as long as the listener is more than 3 feet from the ground, they are less than 10 degrees off axis. With the downward tilt it is still impossible to be more than 10 degrees off axis in the negative vertical direction. At 30 feet anyone standing and shorter than 7.5 feet is still less than 10 degrees off axis.

It is probably not worth starting to recalculate for adding in my infinitely variable balanced tilters, that combined with the 7.5 degrees built into the box give me a 19.5 degree range for the vertical aiming of these boxes.

I will pay attention at my next couple of small shows where these get used for any patrons sneaking in with backhoes or ladders, but it does look to me like most of the ears will be within plus or minus 10 degrees of the on axis plane.
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Jay Barracato

Jay Mitchell

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Re: QSC K10 tweeter polarity
« Reply #32 on: June 18, 2011, 02:37:46 pm »

1. Your sticky was edited after this thread began.
Not the OP, which contains the statement I quoted. The statement I quoted - along with the entire rest of that post - has been there since I put it up on June 6, eight days before this thread was begun. From your behavior, it would appear that your primary purpose is to argue, when the one possible issue has been completely settled. Have you actually tried correcting the tweeter polarity on one of your K10s and listening to it? You could even do a quick A/B with an unmodified one. If you don't like it, you can change it back.

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2. Your conclusion is based on your belief that + is always better, regardless of the measurements.
No. That is your spin. Positive polarity is better in general because of more accurate reproduction - audibly so - of transients in a signal. The data simply establish that the effect on the amplitude response of this particular design is to shift the location of a notch - which is present in either case - at the crossover frequency.

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3. You still have not defined transient response,
Don't you know what it is? I'll help you out, then: it is the response of a two-port system to signals which contain transient information. Examples of signals that contain transient information are:

1. An impulse (Dirac delta function).
2. A square wave.
3. Any sound that has an attack and a decay.
4. Speech.

In short, most of the program material for which sound reinforcement loudspeakers are used.

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If you want to bet on the angles of my deployment, which you know nothing about, I want to bet on your SIGNIFICANT number of users that have inverted the polarity and found it sounds better.
You've got a real talent for reading things that are not there into my statements. My experience with listener preferences in this exact situation - inverting the polarity of one of the two elements involved in a crossover transition - goes back more than 20 years. It includes some very expensive studio monitors and some high-level cinema speakers (ever seen an IMAX movie?), as well as various levels of sound reinforcement speakers. In more than one instance, there were controlled comparisons in neutral listening environments, with other variables eliminated. FYI, it is always possible to design a crossover that does not produce an on-axis amplitude notch with correct driver polarities.

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I am using that term statistically, and I am just as sure no where approaching a significant number of users have made the swap.
See above. The term I used was "listeners," and there are quite a few speakers with which the comparison has been made.

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It is my current interpretation that you possess an opinion that matching the polarity of the two drivers overrides all other design considerations.
Your "current interpretation" is wrong, then. In this case, it is my opinion that correcting the polarity of the HF driver corrects an audible issue without creating any new ones.

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This bias pre-dates your collection of the data,
There is a huge difference between bias and learning from experience. I strongly recommend the latter. It has always worked for me.

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Should I invert the polarity of the HF in my K10's?
Have you listened to the difference? Isn't that the final arbiter?

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I am unconvinced that there is any improvement over the factory design.
Apparently with no listening experience to support your opinion. I'd say that could serve as a textbook definition of "bias." But that's just my opinion.
« Last Edit: June 18, 2011, 02:45:48 pm by Jay Mitchell »
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Jay Mitchell

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Re: Playing with some trig
« Reply #33 on: June 18, 2011, 02:43:26 pm »

Start basic... place the speaker on stand 6 feet above the floor with the vertical on-axis line parallel to the floor:
Good. Now, consider the corrected-polarity scenario: the notch is on axis, aimed parallel to the floor, at a height of roughly seven feet. Exactly how many listeners would you say can possibly be exposed to the amplitude notch? Dirk Novitzki might. Most folks won't.
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Jay Barracato

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Re: Playing with some trig
« Reply #34 on: June 18, 2011, 03:03:36 pm »

Start basic... place the speaker on stand 6 feet above the floor with the vertical on-axis line parallel to the floor:
Good. Now, consider the corrected-polarity scenario: the notch is on axis, aimed parallel to the floor, at a height of roughly seven feet. Exactly how many listeners would you say can possibly be exposed to the amplitude notch? Dirk Novitzki might. Most folks won't.

Okay restate that: Put the on axis line at 6 feet from the floor, and then look at the angles. The math clearly tells me that any listener from 10 feet to 30 feet is definitely less than 20 degrees off axis and in most cases less than 10.

I am done. Anyone with an actual interest can look at both of our arguments and decide for themselves.

The simple fact that no one else has responded tells you how much this community really cares.
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Jay Barracato

Jay Mitchell

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Re: Playing with some trig
« Reply #35 on: June 18, 2011, 03:10:55 pm »

Okay restate that: Put the on axis line at 6 feet from the floor, and then look at the angles. The math clearly tells me that any listener from 10 feet to 30 feet is definitely less than 20 degrees off axis and in most cases less than 10.
Right. Think about what you just said: most listeners will be within the angular range of flattest response with the tweeter polarity corrected. The notch is completely gone from the amplitude response at -10 degrees vertical.

Have you tried correcting the polarity and listening? You seem to have ignored my question the first time I asked.
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Jay Mitchell

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Re: QSC K10 tweeter polarity
« Reply #36 on: June 18, 2011, 03:44:13 pm »

http://srforums.prosoundweb.com/index.php/m/579762/0/#msg_579762

It seems not everyone got the same results as you did !!!! .Hmmmm
It seems "not everyone"' knows how to test loudspeakers. That photo has a couple of very serious "what's wrong with this picture" screwups. It is a textbook example of how not to test loudspeakers. The data is of no value.
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Re: QSC K10 tweeter polarity
« Reply #36 on: June 18, 2011, 03:44:13 pm »


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