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Reverse Polarity?

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Conanski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2017 at 5:43pm
Originally posted by AJ113 AJ113 wrote:

So if the B400s and the reflex cabs were operating at separate frequencies, presumably the phase problem is reduced to a minimum?
It makes the problem a bit easier to manage but it's still a complicated problem.



Originally posted by AJ113 AJ113 wrote:

As you say, the B400s are only useable down to 60Hz (although you would never believe that when listening to them!), so does it follow that there would be little in the way of phase issues below 60Hz, regardless of anything else?


No... and that gets to one of the big misunderstandings about speaker interactions, the area of influence for any given speaker system extends both above and below it's rated range of operation. Properly aligning these two speaker systems requires several things, delay for gross time alignment, EQ for response shaping both inside and outside the intended range of operation, independent level control for each output, and after all that is applied perhaps some phase adjustment. And figuring out exactly how much of each of those things is needed requires some test equipment, so this is not a trivial exercise if you want it done correctly.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Darkstar Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2017 at 6:39pm
Originally posted by AJ113 AJ113 wrote:

And that somehow gives the member free licence to post snide remarks? I'm a newbie posting in a newbie forum asking for help. If you don't want to help, surely the best option is not to post?

You were not the subject of said snide remark, it was a member who has supposedly been around just as much as him here and I am pretty sure they've had a debate on this kind of topic already. Even if it doesn't change anything, and I'm not Toasty's lawyer, I don't feel like I have the right to judge as telling someone he is wrong doesn't necessarily have to be a source of friction. 

Back to the on topic, I agree it doesn't sound very constructive but he's got a point: phase switching is not to be confused with time delay and moving boxes around can lead to other issues unless previously measured.
You can choose to go by ear, but it can be very misleading and unpractical if you move the boxes around different venues where loudspeaker placement can be subject to change.

Polarity switch in your case seems to be the fastest way to align said subwoofers with reflex boxes, although that doesn't take measurement out of the equation independently of box typology.
Bass =/= Enough
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2017 at 7:06pm
"You were not the subject of said snide remark, it was a member who has supposedly been around just as much as him here"

Yup, that´ll be me. And quite honestly, I couldn´t really give a shite. I know it´s not a simple matter to get cabs running in time and phase, but you have to start somewhere. I shift cabs around with my LMS all the time and also have SMAART to help, but that´s all money and the OP obviously just wanted something rough and ready. Not everyone can afford Lake, SMAART, etc, etc.

This happens so often on here. Someone asks a simple question and within half a dozen posts, they´re being told to buy Powersoft K20´s, BMS coaxials and Lake processing. A bit over the top really.


Earplugs Are For Wimps!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2017 at 9:22am
Originally posted by Earplug Earplug wrote:

"You were not the subject of said snide remark, it was a member who has supposedly been around just as much as him here"

Yup, that´ll be me. And quite honestly, I couldn´t really give a shite. I know it´s not a simple matter to get cabs running in time and phase, but you have to start somewhere. I shift cabs around with my LMS all the time and also have SMAART to help, but that´s all money and the OP obviously just wanted something rough and ready. Not everyone can afford Lake, SMAART, etc, etc.

This happens so often on here. Someone asks a simple question and within half a dozen posts, they´re being told to buy Powersoft K20´s, BMS coaxials and Lake processing. A bit over the top really.


Thank you for that. As you have correctly deduced, my rig is at a lower level and I just want to be somewhere in the ballpark. Anything else would be overkill.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mitchiemasha Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2017 at 7:13pm
Originally posted by AJ113 AJ113 wrote:

Quote

Sure. If you want to be wrong.
So why don't you tell me how to go about doing it right?

Simple... Play a test tone at the cross over frequency, equal volume to both cabs. Phase invert 1 speaker incorrectly, adjust the delay time until you get most cancellation, it's a process of back and forth to get it as fine tuned as possible. Reflip the polarity. Now your cabs will be completely inline.

No need for fancy equipment to measure all you need to align them. 

I suppose the same method could be done by moving the actual cab but it would be awkward. When you match the volumes accurately the cancellation sticks out like a sore thumb. It's clear as day and removes all the guess work. 
MY OTHER DECKS ARE CDJ'S BUT THERE'S NO AUTOMIX FOR WHEN I'M WASTED
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mitchiemasha Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2017 at 7:27pm
Another thing to remember. Inverting polarity doesn't change the time domain. I put some nice diagrams on here some time ago.

Edit: I dug the link out. Was worth a reshare.



Edited by mitchiemasha - 15 October 2017 at 7:33pm
MY OTHER DECKS ARE CDJ'S BUT THERE'S NO AUTOMIX FOR WHEN I'M WASTED
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2017 at 8:30pm
Originally posted by mitchiemasha mitchiemasha wrote:

...Inverting polarity doesn't change the time domain. ..
Well, that's why I asked the question in the first place. Given that it doesn't change the time domain, how does changing the polarity help?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2017 at 8:54pm
Originally posted by mitchiemasha mitchiemasha wrote:

...Play a test tone at the cross over frequency, equal volume to both cabs.
When you say both cabs, you mean one B400 and one BR? (I have two of each)
Originally posted by mitchiemasha mitchiemasha wrote:

Phase invert 1 speaker incorrectly
How do I do that? Do you mean reverse the polarity?
Originally posted by mitchiemasha mitchiemasha wrote:

adjust the delay time until you get most cancellation
Adjust what delay time? Do you mean set up a delay to the B400s?

Originally posted by mitchiemasha mitchiemasha wrote:

...When you match the volumes accurately the cancellation sticks out like a sore thumb. It's clear as day and removes all the guess work. 
How do you go about accurately matching the volume? Do you mean measure the spl at a given distance?

Presumably, once the optimum delay time has been established, this could be translated into physical distance for any future operations?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mitchiemasha Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2017 at 11:28pm
That's a lot of questions... 

How does changing the polarity help?
Good question. I have my theories and beliefs to why this is said but it's outside my knowledge to be sure.

When you say both cabs, you mean one B400 and one BR? (I have two of each)?
You do the 2 cabs you are trying to align with each other. Lows with the Mids. Then do the other 2. Which will likely be the same setting.

How do I do that? Do you mean reverse the polarity?
Yes, you'd have to experiment to see which way was actually incorrect.

Adjust what delay time? Do you mean set up a delay to the B400s?
You should buy a DSP, Driverack/Ultradrive etc! If not... doing the test tone at cross over frequency will still work with physically moving the speaker.

How do you go about accurately matching the volume? Do you mean measure the spl at a given distance?
You could do that but I find i don't need too, even if the volume isn't matched perfectly, the point of most cancellation will still be the correct delay time. Setting the test tone to the same volume by ear is enough. You can even adjust the volumes at most cancellation, to get more crenelation, this will result in a better matched volume. Experiment with the method and everything will become clear, you'd have no need to ask these questions.

Presumably, once the optimum delay time has been established, this could be translated into physical distance for any future operations?
No. if you set your speakers up in a different position, you'd need to do it again. If it's mid tops on bins, mark out where they sit, that will be the same every time.
MY OTHER DECKS ARE CDJ'S BUT THERE'S NO AUTOMIX FOR WHEN I'M WASTED
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 20 hours 34 minutes ago at 8:19am
Originally posted by mitchiemasha mitchiemasha wrote:

That's a lot of questions... 

How does changing the polarity help?
Good question. I have my theories and beliefs to why this is said but it's outside my knowledge to be sure.

When you say both cabs, you mean one B400 and one BR? (I have two of each)?
You do the 2 cabs you are trying to align with each other. Lows with the Mids. Then do the other 2. Which will likely be the same setting.

How do I do that? Do you mean reverse the polarity?
Yes, you'd have to experiment to see which way was actually incorrect.

Adjust what delay time? Do you mean set up a delay to the B400s?
You should buy a DSP, Driverack/Ultradrive etc! If not... doing the test tone at cross over frequency will still work with physically moving the speaker.

How do you go about accurately matching the volume? Do you mean measure the spl at a given distance?
You could do that but I find i don't need too, even if the volume isn't matched perfectly, the point of most cancellation will still be the correct delay time. Setting the test tone to the same volume by ear is enough. You can even adjust the volumes at most cancellation, to get more crenelation, this will result in a better matched volume. Experiment with the method and everything will become clear, you'd have no need to ask these questions.

Presumably, once the optimum delay time has been established, this could be translated into physical distance for any future operations?
No. if you set your speakers up in a different position, you'd need to do it again. If it's mid tops on bins, mark out where they sit, that will be the same every time.
OK thank you very much, that was very helpful.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 19 minutes ago at 4:34am
Originally posted by Earplug Earplug wrote:


"You were not the subject of said snide remark, it was a member who has supposedly been around just as much as him here"

Yup,
that´ll be me. And quite honestly, I couldn´t really give a shite. I
know it´s not a simple matter to get cabs running in time and phase, but
you have to start somewhere. I shift cabs around with my LMS all the
time and also have SMAART to help, but that´s all money and the OP
obviously just wanted something rough and ready. Not everyone can afford
Lake, SMAART, etc, etc.

This happens so often on here. Someone
asks a simple question and within half a dozen posts, they´re being told
to buy Powersoft K20´s, BMS coaxials and Lake processing. A bit over
the top really.




Room EQ Wizard is free, the manual is excellent and there’s a ton of resources online for free. Hell, there’s even a guide on how to setup with REW and the soundcard in any PC on this very forum by odc40r. Timo Beckman also has a ton of videos. As do Meyer. Or Nathan Lively has articles, podcasts, and a cheap as chips PDF with that process and more.

Mic wise, even an SM58 would do better than a bloody tape measure.

If you can’t manage that then the invert polarity / cancellation method can get you in the right ballpark but you should use ‘warbles’ not a single sine wave. Google them. Again, free.

By the way, a POLARITY flip does cause a shift in the phase response of a speaker, it’s more complex than that diagram makes out. You can see that easily in - you guessed it- REW.

You don’t have to spend megabucks to do something better than guesswork at best and flat out lies at worst. Telling someone an answer that stops them learning further is just ridiculous, sound is a science that allows for art to be practised, and any time you tell somebody a process that seems super simple - because the simple answers are often the wrong ones - rob somebody of the agency to follow a scientific method and get the best results.


Edited by toastyghost - 13 minutes ago at 4:40am
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