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Author Topic: Do humans prefer the sound of comb filtering?  (Read 10975 times)

Laurence Nefzger

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Do humans prefer the sound of comb filtering?
« on: July 31, 2014, 03:25:58 PM »

I have read many of the discussions and seen the ample measured evidence of how comb filtering alters the magnitude response of speakers. Comb filtering is presumed to be bad. However, in my experience I have rarely had anyone prefer the sound of a mono speaker over a spaced pair of speakers even when playing mono material. I admit that this is purely anecdotal and have not performed a controlled experiment.
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Re: Do humans prefer the sound of comb filtering?
« Reply #1 on: July 31, 2014, 03:28:16 PM »

I have read many of the discussions and seen the ample measured evidence of how comb filtering alters the magnitude response of speakers. Comb filtering is presumed to be bad. However, in my experience I have rarely had anyone prefer the sound of a mono speaker over a spaced pair of speakers even when playing mono material. I admit that this is purely anecdotal and have not performed a controlled experiment.

What is the "sound" of comb filtering?

Is it like the sound of one hand clapping?
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Tim McCulloch

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Re: Do humans prefer the sound of comb filtering?
« Reply #2 on: July 31, 2014, 03:33:43 PM »

I have read many of the discussions and seen the ample measured evidence of how comb filtering alters the magnitude response of speakers. Comb filtering is presumed to be bad. However, in my experience I have rarely had anyone prefer the sound of a mono speaker over a spaced pair of speakers even when playing mono material. I admit that this is purely anecdotal and have not performed a controlled experiment.

I don't think most casual listeners will notice any but the most egregious comb filters, particularly in transient settings.  Move into an install where understanding the spoken word is critical, and where many listeners tend to routinely sit in the same seats, then perceptions change.

A good example of combing, though, is the "power alley" of L/R subwoofers.  The folks standing in the 60Hz null will have a very different opinion than the folks in the middle of power alley, and my guess is the former would have a better opinion of a mono sub source than the latter folks.

Dick Rees makes a good point:  that by itself, an acoustic comb filter doesn't have a 'sound', per se.  You are either in a node or null, and you won't know any difference until you move.
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John Roberts {JR}

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Re: Do humans prefer the sound of comb filtering?
« Reply #3 on: July 31, 2014, 03:48:41 PM »

I have read many of the discussions and seen the ample measured evidence of how comb filtering alters the magnitude response of speakers. Comb filtering is presumed to be bad. However, in my experience I have rarely had anyone prefer the sound of a mono speaker over a spaced pair of speakers even when playing mono material. I admit that this is purely anecdotal and have not performed a controlled experiment.

Comb filtering occurs in the human outer ear so hearing combing is natural. We use this natural combing to identify the angle of incidence vertically (above-below) for arriving sounds. Of course we combine these sound cues with other cues.

Stereophony is about far more than simple comb filtering. Our meat computers interpret the different arrival times from the two speakers as spacial information defining the musical instruments in a multi-dimensional space.

About the only way for humans to not experience comb filtering is with ear buds located inside the folds and reflections of the outer ear.

I do not know that humans prefer ear buds to normal audition but that is a question for you to inspect.

Psycho acoustics is a mature science but human audition is somewhat subjective so YMMV.

JR
 
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Ivan Beaver

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Re: Do humans prefer the sound of comb filtering?
« Reply #4 on: July 31, 2014, 07:25:44 PM »

Music and speech are very different things-processed on different sides of the brain.

What we "prefer" with the 2 speaker setup is not combfiltering-but rather the "surrounding or spacious" sound of seperated speakers.

Speech will always sound clearer with a single speaker. 

A single speaker also provides much more localization than separated speakers.

I had the chance to do an interesting experiment last week during a demo.

We were in a VERY WELL behaved room. One of the tests was to play a mono music track through the existing system (no slouch there) and the system we brought in.

I was sitting in the middle (or as close as i could get) and kept being "pulled" to the left side.  So I moved one seat to the right-and now I was pulled to the right.

On the "non house system", it did not matter which seat I sat in-the image was just big and in front of me.

The house system had multiple separated drivers while the "non house" system was a true point source (one source of sound).

Both were measured ahead of time and had the same measured freq response-but yet they sounded completely different.

There is a lot more going on than just one simple measurement can describe.
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Steve M Smith

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Re: Do humans prefer the sound of comb filtering?
« Reply #5 on: July 31, 2014, 07:26:15 PM »

I think comb filtering is something people see rather than hear.

If you look on the PA of the Day FaceBook page, you will notice that as soon as there is a picture of two or more speakers next to each other, someone will post a two word message "comb filtering" (sometimes with a question mark at the end for some reason).

When I started in sound many years ago, we just stacked up horn loaded speakers without any thought of comb filtering and usually we got away with it.

A good antidote to the comb filter commentors is to show them a picture of a large Clair S4 system or a stack of Rat Trap 5s.


Steve.
« Last Edit: August 01, 2014, 01:54:12 AM by Steve M Smith »
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Tim McCulloch

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Re: Do humans prefer the sound of comb filtering?
« Reply #6 on: July 31, 2014, 07:53:59 PM »

I think comb filtering is something people see rather than hear.

If you look on the PA of the Day FaceBook page, you will notice that as soon as there is a picture of two or more speakers next to each other, someone will post a two word message "comb filtering" (sometimes with a question mark at the end for some reason).

When I started in sound many years ago, we just stacked up horn loaded speakers without any thought of comb filtering and usually we got away with it.

A good antidote to the comb filter commentors is to show them a picture of a large Clair i-5 system or a stack of Rat Trap 5s.


Steve.

I think you meant Clair S-4.  Flat packed S-4 DO exhibit comb filtering, but remember that the design is older than some of our participants here and reflects the state of the touring industry at the time they were created..  The way Clair deployed them over the last 15 years or so, with a carefully determined amount of splay and some processing, minimized the interaction between boxes but cannot eliminate it at all frequencies.  Much better than when they were flat-packing them 25 years ago.
« Last Edit: July 31, 2014, 09:02:34 PM by Tim McCulloch »
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Ivan Beaver

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Re: Do humans prefer the sound of comb filtering?
« Reply #7 on: July 31, 2014, 08:59:13 PM »

A true story.

in my past life as a PA/lighting provider, I used to provide for a local small arena-2500 seats.

I would always bring in 4 stacks per side to do a show-for all different types of music/acts.

I knew what my rig sounded like in the room.

We got a call to do a wedding-but they could not afford the large system and did not want it.  They just wanted a small system for the dance floor.  The stage remained in the same place it always did.

So we took in 1 stack per side-everything else was the same-same amp racks/processing FOH etc.

My help (also an audio engineer) and myself went "WOW-this sounds soooo much cleaner than our full system".

It was not as loud-but sounded way better-even with canned music.

Comb filtering is not something that people go WOW-that sounds bad.

But RATHER-without it, the sound is just much clearer.

I would argue that most people in our business would not even recognize combfiltering when they hear it.  HOWEVER they can easily hear it when it is not there.

It is not like this big "distortion" or poor freq response.  Although most people would perceive it as a lack of high freq, and then try to boost the treble to make up for it.

That will not fix it-as the dips are still there-but the overall level of the HF will be "louder".  Once you remove the combfiltering-the sound will "pop out" and become much clearer.

A good way to try this on your own is to take a mic and run it into 2 channels of a digital console.

Bypass the tone controls and set gains and levels the same.

Route both channels to the output (headphones or speakers).

Listen.  Now add a little bit of delay (say 1ms) to JUST ONE of the mic channels.  Now listen.  If you can't hear the difference-then the nearest lighting console is calling your name.

Play around with the delay time on ONE of the channels (say between 0.5 and 4 ms0 and listen to what it sounds like.

From time to time put the time at 0 or simply mute one of the channels (it doesn't matter which one) and listen to the channel without the combfiltering.

Have fun and educate yourself :)
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John Chiara

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Re: Do humans prefer the sound of comb filtering?
« Reply #8 on: August 01, 2014, 01:49:26 AM »

I think comb filtering is something people see rather than hear.

If you look on the PA of the Day FaceBook page, you will notice that as soon as there is a picture of two or more speakers next to each other, someone will post a two word message "comb filtering" (sometimes with a question mark at the end for some reason).

When I started in sound many years ago, we just stacked up horn loaded speakers without any thought of comb filtering and usually we got away with it.

A good antidote to the comb filter commentors is to show them a picture of a large Clair i-5 system or a stack of Rat Trap 5s.


Steve.

I read Bob Heil's Sound System book back in the '70's and always stacked vertically and not horizontally.
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Steve M Smith

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Re: Do humans prefer the sound of comb filtering?
« Reply #9 on: August 01, 2014, 01:52:18 AM »

I think you meant Clair S-4.

You're quite right.  I5 is a more modern system. 

I got in late and did a quick image search and messed it up! (post corrected),

I read Bob Heil's Sound System book back in the '70's and always stacked vertically and not horizontally.

I would have loved to have something like that thirty years ago but we didn't know it existed or where to find it.

And as we were the only sound company on the Isle of Wight (a little island hanging off the south coast of England, to quote Frank Zappa) there was no one else to get advice from.

We started off stacking up JBL 4560s, Martin folded W horns and various other non-descript cabs, initially two stacks (one per side) vertically.  But when we got some more, it was two stacks per side in whatever space they would fit.

On top of any horizontal issues, there was also the question of how to align them.  We were aware of a rough rule of thumb to try to align all of the drivers in a straight line vertically, but did that apply to the drivers in the folded W cabs as they were facing the other way?  Or were they wired reverse phase?

I'm sure there were people who knew the answers then, but they weren't us.  We just relied on trial and error.

Today it is much easier to learn as there is the internet, forums like this and some great videos on Youtube - especially those by Dave Rat, some of which have recently made me change my way of thinking.


Steve.
« Last Edit: August 01, 2014, 02:44:21 AM by Steve M Smith »
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Re: Do humans prefer the sound of comb filtering?
« Reply #9 on: August 01, 2014, 01:52:18 AM »


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