So now, combing isnt a problem in an array? - diyAudio
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Old 28th August 2006, 10:06 PM   #1
amt is offline amt  United States
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Default So now, combing isnt a problem in an array?

I stubbled upon this new speaker which is designed by Roger Russell, the designer of the Mac LAs, and his new speaker just uses 25 fullrange 3.5" drivers with EQ (901 like).

http://www.roger-russell.com/columns/columns.htm#single


He claims that combing in columns a myth. So whats the deal. How can so many people claim that combing effects are audible and detract from the performance and now a gentleman with lots of LA experience says its ill effects are corrected in our brains and not a concern. Can simple wiring techique and electronic manipulation eliminate it?


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Old 28th August 2006, 10:46 PM   #2
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He's right to an extent. Again, it depends upon the specific circumstances.

Does lobing exist? Yes. It's inescapable unless you invent a new form of physics. Is is a problem? Usually. The drivers need to be closer together than 1 wavelength of the highest frequency they produce to avoid it in the audio band. The attenuation of HF when using FR or WB drivers alone is both audible and measureable, and has been shown innumerable times in both cases. You can (sometimes) bring it back into line with hefty Eq. Is the ripple, i.e. the peaks and dips in the response also audible? Depends how close together they are packed I suspect for psychoacoustic masking to kick in. Our hearing is amplitude based, so we will tend to focus on the peaks. If they're close together, and out of our most sensitive band, you might get away with it. But I wouldn't bet on it either 99.9% of the time. Jim Griffin, or resident line array guru can give some better views than I can thoughm so I'll leave the rest up to him, when he finds the thread, and any of our other array experts.
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Old 28th August 2006, 10:56 PM   #3
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It was neat to see the other designs he has worked on. Certainly he has experience building speakers. But to me, this new column just looks like another design that will have advantages and disadvantages like all the rest.

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Old 28th August 2006, 11:50 PM   #4
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He claims that precedence effect would counteract any combing. I'm not buying it, but then again I haven't heard his system.

I am curious, however, what sort of EQ he is using with those towers.
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Old 29th August 2006, 06:43 AM   #5
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Till now, I was thinking that it is the direct radiation of identical drivers spaced apart on the same baffle which caused "combing".
Now after reading the subject article, "combing" occurs due to interference between a sound(direct radiation) and its delayed component.
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Old 29th August 2006, 07:15 AM   #6
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His definition of comb filtering is right. It is the generalised definition for it. Your definition is then one possible variant of it.

But I don't buy his arguments on importance (or lack thereof) of comb-filtering. No one would say that room-reflections and the associated response aberrations are unimportant. Even though our ears are able to correct for some of these aberrations it reproduction is bettewr in some rooms than in others - period.
And just because these aberrations happen in a listening room anyway doesn't mean that they have to be produced at the source already.

Just like selling new cars with rust: "Ahhh .... don't care about it every car will start to rust one day ........ !"


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Old 29th August 2006, 08:24 AM   #7
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Quote:
His definition of comb filtering is right. It is the generalised definition for it. Your definition is then one possible variant of it.
In which case "combing" would also occur for a single driver.
I feel My definition is at odds with his and not a variant.
I have read our own guru Jim Griffins paper, so it appears to me a bit different.
Since both gentlemen have good credentials, it is must be that I have not fully grasped the line array fundamentals.
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Old 29th August 2006, 06:27 PM   #8
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This is how I feel too. I must not really see the big picture. The problem is that the lure of a FR array is great - no crossovers with great efficiency and dynamics. Jim Griffin has done such indepth research, which is published, that I tend to regard him as the word on LAs. But designing products for McIntosh are pretty reasonable credentials too. Could it really be to just make a buck the easy way? Doesnt seem likely but I dont know. I sure would like to hear them.

A PE project used smaller drivers and HF problems were evident but apparently not a huge problem. Maybe electronic correction of some sort is the key.

http://www.partsexpress.com/projects.../Kuze3201.html


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Old 29th August 2006, 07:08 PM   #9
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I had a bit of a discussion with this guy in the letters pages of aXp... as much as i can figure from what he says, he belives that the comb filtering can be EQed out and he hears whatever his FR plot tells him to hear.

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Old 29th August 2006, 09:16 PM   #10
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He is correct, room influences can cause comb filtering, but general usage is to describe the effects of interfering point sources like speaker arrays. He needs to define his terminology better.

Quote:
Originally posted by planet10
... as much as i can figure from what he says, he belives that the comb filtering can be EQed out and he hears whatever his FR plot tells him to hear.
I agree, I really don't go with the principle that you can cure time domain problems by tweaking frequency response.
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