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Author Topic: In-ceiling speaker comb filtering  (Read 5703 times)

Kyle Malenfant

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In-ceiling speaker comb filtering
« on: November 15, 2014, 12:43:32 am »

Hi All.  I was at a local Miller's Ale House tonight and noticed a pretty heavy amount of comb filtering between the ceiling speakers as I walked around the restaurant.  No logos on the speakers so not sure the brand/coverage pattern.  Ceiling height is 11' and the speakers were placed at 8' intervals.

I've done a few ceiling speaker installs using JBL products and following (more or less accurately) the layout as designed by their ceiling speaker software dictated and didn't get the interference I heard tonight.

As I understand it, we want the coverage to overlap slightly so the levels are consistent throughout the space. 

Question:  So why would the comb filtering happen in one case but not the other?  If the speakers were placed further apart so coverage is not overlapping, then the volume won't be smooth as one walks around the venue.

Can anyone shed some light on this?
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John Rutirasiri

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Re: In-ceiling speaker comb filtering
« Reply #1 on: November 15, 2014, 12:53:49 am »

Are you sure it was comb filtering and not phase reversal on one of the speakers?

Also, I have seen some 3-way install speakers that has the mid/hi assembly being adjustable.  I suppose one can adjust it too much that it affects the neighboring speaker.

Finally, could it be the speaker processor/zone controller programmed incorrectly?

JR
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Kyle Malenfant

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Re: In-ceiling speaker comb filtering
« Reply #2 on: November 15, 2014, 01:17:39 am »

Are you sure it was comb filtering and not phase reversal on one of the speakers?

Also, I have seen some 3-way install speakers that has the mid/hi assembly being adjustable.  I suppose one can adjust it too much that it affects the neighboring speaker.

Finally, could it be the speaker processor/zone controller programmed incorrectly?

JR

Could have been phase several but I heard the interference between every speaker (in the couple of areas I walked through).

The mid/high adjustments are a possibility..no way to know without knowing the model of speaker.

Same goes for the processing..no clue as I couldn't get any info by glancing at their AV rack by the bar.


I know there are many unknowns here which could affect the performance of the system..just hoping to get some insight.

Thanks for the comments.
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John Rutirasiri

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Re: In-ceiling speaker comb filtering
« Reply #3 on: November 15, 2014, 01:41:56 am »

I suppose a bad/different transformer on one speaker could cause what sounds like comb filtering.

This one I'm not sure...perhaps one of the install experts can chime in:  if a wrong tap was used on the transformer on just ONE of the speakers, would that only result in a different volume on that speaker, or would it have an impact on the freq/phase response that it sounds different than the rest of the speakers?
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Lee Douglas

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Re: In-ceiling speaker comb filtering
« Reply #4 on: November 15, 2014, 08:47:58 am »

If they were running stereo pairs (rather than 70V mono) and one of each pair were wired out of phase, because maybe the wiring convention was misunderstood, you would experience cancellation as you passed the mid-point of each pair.
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Ivan Beaver

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Re: In-ceiling speaker comb filtering
« Reply #5 on: November 15, 2014, 09:34:18 am »

It could be not so much combfiltering but a irregular coverage pattern.

Meaning that the highs are narrower than the mids which are narrower than the lows.

So what you hear is a lot of basic coverage issues.  The end result can sound the same-holes in the freq response.

With any speaker it is important to have the same pattern over as wide a range as possible.  If not, it is going to sound different at different places.

Back in my days of the install world-I have listened to many different ceiling speakers and heard VERY DIFFERENT coverage patterns-despite what the spec sheet simple numbers say.

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Craig Hauber

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Re: In-ceiling speaker comb filtering
« Reply #6 on: November 16, 2014, 12:58:56 am »

Out of polarity plain and simple. 
Ceiling rigs are such a mish-mash of interference, reflections and audio bouncing around everywhere (especially in modern "echo-chamber" style restaurant interior design) that if you heard obvious combing then it was a batch of out of polarity speakers.
It only takes a couple wrong ones to affect everything.

Many of these systems are put in by the electrical contractor using non-standard wiring (i.e. cat 5), and modern speakers use phoenix connectors with no color coding, it's amazing they get connected at all sometimes.

I've watched a master electrician wire "+" to the black wire and "-" to white -as they would normally for outlets and switching, yet an apprentice wiring a different string of speakers who is a car audio hobbiest wires it properly the opposite way!

Then a few weeks later the chain-wide AV vendor shows up with the rack and slams it into place, checks that it makes noise and leaves without ever knowing anything about polarity, let alone any EQ and limiting!

Not complaining too much as it keeps me gainfully employed "fixing" things!


And as far as I have ever experienced, different taps don't affect polarity, if there's any phase differences they are too subtle to hear -especially when you notice the volume difference first and are focused on that.



Hi All.  I was at a local Miller's Ale House tonight and noticed a pretty heavy amount of comb filtering between the ceiling speakers as I walked around the restaurant.  No logos on the speakers so not sure the brand/coverage pattern.  Ceiling height is 11' and the speakers were placed at 8' intervals.

I've done a few ceiling speaker installs using JBL products and following (more or less accurately) the layout as designed by their ceiling speaker software dictated and didn't get the interference I heard tonight.

As I understand it, we want the coverage to overlap slightly so the levels are consistent throughout the space. 

Question:  So why would the comb filtering happen in one case but not the other?  If the speakers were placed further apart so coverage is not overlapping, then the volume won't be smooth as one walks around the venue.

Can anyone shed some light on this?
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Craig Hauber
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Ivan Beaver

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Re: In-ceiling speaker comb filtering
« Reply #7 on: November 16, 2014, 08:13:55 am »

Out of polarity plain and simple. 

And you know this without listening to the particular system? And just going on a simple description?

WOW-that's pretty good.

And they just happened to get enough of the right ones out of polarity to give the same impression around the room?  That would take some thought/planning.

You might be right-and you might be completely wrong.

There is no way to know without more investigation.

I would not be so quick to jump to conclusions-sorry.
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Craig Hauber

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Re: In-ceiling speaker comb filtering
« Reply #8 on: November 17, 2014, 01:17:58 am »

And you know this without listening to the particular system? And just going on a simple description?

WOW-that's pretty good.

And they just happened to get enough of the right ones out of polarity to give the same impression around the room? 

That would take some thought/planning.

You might be right-and you might be completely wrong.

There is no way to know without more investigation.

I would not be so quick to jump to conclusions-sorry.

Not trolling (even though I'm laid-up off work, it's 12-below outside and there's nothing else to do today.)
I've fixed these types of systems enough to know the odds are so high for a polarity issue that I don't bother with "maybe" and just state it definitely in hopes that something can just get fixed faster.

I also went with my answer because the only way to actually get such a clear and obvious example of combing out of the nasty audio-soup that is modern restaurant sound is to have a polarity difference.  Can't imagine any other failure that would stand out as that obvious to an experienced audio guy who is used to hearing ceiling rigs.

No by "polarity" I wasn't just thinking a single speaker, but I guess I wasn't clear beyond describing how entire strings of speakers in a system can be opposite ofothers just because of installer/electrician misconception, but there is also another common occurrence that could be at play also....
Do you realize how many people attempt to wire these systems in "stereo" (however misguided they may be it still happens way too often) Every other speaker L&R!
Gets even worse when there's series-parallel wiring involved instead of 70V.
-And what if the chopped 1/8" cable from the Muzak/DMX/Spotify/Pandora box was not corrected right to the phoenix connector on the back of the Zonepro? (not hard to do, even I've done it wrong in haste)
So if a channel is reversed before even entering the system?
Voila, instant consistent comb filtering over the entire venue!

Not trying to be a prick -even if that's how you interpreted my last post.  (I did disparage the whole modern restaurant sound concept so maybe I was asking for it.)

But I will still stand behind "blatant polarity issue" and Ivan, I'll buy all the rounds at whatever restaurant bar I'm installing in your neighborhood if I'm wrong (got some near Atlanta next spring, last one was Savannah)
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Craig Hauber
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Tim McCulloch

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Re: In-ceiling speaker comb filtering
« Reply #9 on: November 18, 2014, 09:47:26 am »

(I did disparage the whole modern restaurant sound concept so maybe I was asking for it.)

"...modern restaurant sound concept...." deserves all the disparagement you can muster.  I absolutely hate having to shout and scream over the music and overall din of the noize.  I will take my dining dollars where my companions and I can converse without vocal strain.

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Re: In-ceiling speaker comb filtering
« Reply #9 on: November 18, 2014, 09:47:26 am »


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