Reverse Polarity? |
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Conanski
Old Croc Joined: 26 January 2006 Location: Ottawa, Canada Status: Offline Points: 2515 |
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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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Darkstar
Registered User Joined: 08 October 2014 Location: Italy Status: Offline Points: 326 |
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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. |
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Bass =/= Enough
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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"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. |
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Earplugs Are For Wimps!
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AJ113
Registered User Joined: 11 March 2016 Location: Hull UK Status: Offline Points: 123 |
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mitchiemasha
Registered User Joined: 27 August 2009 Status: Offline Points: 466 |
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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. |
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mitchiemasha
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AJ113
Registered User Joined: 11 March 2016 Location: Hull UK Status: Offline Points: 123 |
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AJ113
Registered User Joined: 11 March 2016 Location: Hull UK Status: Offline Points: 123 |
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Presumably, once the optimum delay time has been established, this could be translated into physical distance for any future operations? |
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mitchiemasha
Registered User Joined: 27 August 2009 Status: Offline Points: 466 |
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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. |
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AJ113
Registered User Joined: 11 March 2016 Location: Hull UK Status: Offline Points: 123 |
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toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10920 |
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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 - 17 October 2017 at 4:40am |
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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Ok, yes, plenty of free resourses out there - although Timo Beckman´s videos are far from simple to understand, as is a lot of the time/phase stuff. It can be difficult to get your head around what is actually happening. People will learn as they go along and at their own pace. Not everyone running a system is that technically minded, nor interested in getting into the physics of sound propagation. They just want some simple advice.
The original question was about switching polarity on the B400´s when used with reflex cabs. As you say yourself, that is not the answer - there are many other factors to consider. Time delay - either physically or electronically - is far better. |
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Earplugs Are For Wimps!
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