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Reverse Polarity?

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AJ113 View Drop Down
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    Posted: 12 October 2017 at 7:58am
I was lazily reading through my Tannoy B400 user's manual when I came across this little gem hidden away in a small corner:

Important : always invert the B400 polarity if used with standard reflex loaded
loudspeakers


1. So if I use my B400s (folded horns) in combination with reflex boxes I have to switch the polarity? Does this include the mids/tops if they are reflex? Or is it only referring to bass units?

2. Can anyone explain in layman's terms why this is so? I'm guessing it's beause they are horn loaded from the back of the loudspeakers, and therefore would effectively be out of phase with front loaded cabinets?

3. What is the easiest way of reversing the polarity? Swap the connections around at one end of a Speakon cable?


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Post Options Post Options   Thanks (1) Thanks(1)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 13 October 2017 at 12:59am
The idea was that with reversed polarity the horns would "better" sum with reflex boxes but the reality is horns need a lot more processing than a simple polarity flip to properly sum with reflex boxes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 13 October 2017 at 3:27pm
Would I be right in thinking the simplest way is to set the reflex boxes further back from the horns?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 13 October 2017 at 3:44pm
Originally posted by AJ113 AJ113 wrote:

Would I be right in thinking the simplest way is to set the reflex boxes further back from the horns?


Yes, that´s more or less it. You need to measure the horn length and place the relex cabs back that amount.


Earplugs Are For Wimps!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 13 October 2017 at 5:28pm
Originally posted by Earplug Earplug wrote:

Originally posted by AJ113 AJ113 wrote:

Would I be right in thinking the simplest way is to set the reflex boxes further back from the horns?


Yes, that´s more or less it. You need to measure the horn length and place the relex cabs back that amount.




Sure. If you want to be wrong.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 13 October 2017 at 5:39pm
Just playing devil's advocate here a bit:

If I had say, two horns and two reflex cabs, and I set them up as a centre cluster, reflex cabs side by side and a horn either side of them, would that create a line/array, without the need to actually physically line them up in an arc?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 13 October 2017 at 6:48pm
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Sure. If you want to be wrong.
So why don't you tell me how to go about doing it right?


Edited by AJ113 - 13 October 2017 at 6:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 13 October 2017 at 11:28pm
What reflex boxes do you have and what kind of processing(EQ, crossover) do you have available?

According to the specs the B400 is only usable down to 60hz so it's entirely possible your reflex boxes could go significantly lower. If that is the case then using the b400s as kick bins crossed higher than the reflex subs may be the way to go.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote corell Quote  Post ReplyReply Direct Link To This Post Posted: 13 October 2017 at 11:31pm
Measure Group Delay (or phase) around the x-over frequency. You will most probably notice that a BR enclosure is far from 0ms group delay.
Actually, in some cases where i had to mix FLH and BR (because customer wanted me to), i had to delay the FLH to the BR for the best solution, because it was a BR with a very high Q tuning.
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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 5:20am
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?

Because he always does and repeating the same things over and over can be tiresome, there's plenty of threads with this topic in which he pointed out how to do it right.
Problem is the search function on this forum is a mess, just tried finding a link for you and I can bet I wouldn't find it after a full day of searching.

In short you need equipment that can measure all you need to align your speakers, going the rough way can only help mitigate cancellation but will likely mess up other things.

Edited by Darkstar - 14 October 2017 at 5:22am
Bass =/= Enough
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2017 at 8:44am
Originally posted by Darkstar Darkstar wrote:

...Because he always does and repeating the same things over and over can be tiresome...
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?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2017 at 9:22am
Originally posted by Conanski Conanski wrote:

What reflex boxes do you have and what kind of processing(EQ, crossover) do you have available?

According to the specs the B400 is only usable down to 60hz so it's entirely possible your reflex boxes could go significantly lower. If that is the case then using the b400s as kick bins crossed higher than the reflex subs may be the way to go.
That is a very good suggestion. Currently I only have a two-way crossover but it wouldn't involve too much to upgrade to three.

So if the B400s and the reflex cabs were operating at separate frequencies, presumably the phase problem is reduced to a minimum?

And thinking on...

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?
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