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[Bill McIntosh]

OK, this is prompted by a video posted of my friend's marching band.  The video showed a whole platoon of trombones, and most of the instruments have duplicates as well.

So, when a noob like me tries to get louder by adding boxes, comb filtering results.  Do the actual instruments exhibit the same behavior?

Outside in a 100,000 seat football stadium it not likely to be noticed, but I am curious about how sound works.  Probably irrelevant or at least unresolvable in live sound, I guess it could be a factor in mic positioning for recording??

[g'bye, Dick Rees]

Think of a marching band as one very large loudspeaker.

[John Roberts {JR}]

If they played very accurately perhaps, but as it is they are incoherent sources so combine incoherently.

JR

[Jeff Carter]

OK, this is prompted by a video posted of my friend's marching band.  The video showed a whole platoon of trombones, and most of the instruments have duplicates as well.

So, when a noob like me tries to get louder by adding boxes, comb filtering results.  Do the actual instruments exhibit the same behavior?

Outside in a 100,000 seat football stadium it not likely to be noticed, but I am curious about how sound works.  Probably irrelevant or at least unresolvable in live sound, I guess it could be a factor in mic positioning for recording??

Comb filtering happens when you have identical sources that combine coherently so the signals add at some frequencies and destructively interfere at others.

I don't think that's what you get in an actual band or orchestra since the sound from each instrument is different. If you record a single trombone and play it back through 10 loudspeakers, it's not going to sound like 10 trombones, is it?

edit: I got ninja'd by two people more knowledgeable than I am...

[Jamin Lynch]

Comb filtering happens when you have identical sources that combine coherently so the signals add at some frequencies and destructively interfere at others.

I don't think that's what you get in an actual band or orchestra since the sound from each instrument is different. If you record a single trombone and play it back through 10 loudspeakers, it's not going to sound like 10 trombones, is it?

edit: I got ninja'd by two people more knowledgeable than I am...

But wouldn't you have some comb filtering if you have ten trombones playing the same note? Which is often the case in a marching band. Plus all those trombones are moving across the field.

Seems like that would be the same as walking across the horn pattern of 10 speaker cabs.

[Pete Erskine]

But wouldn't you have some comb filtering if you have ten trombones?

Only if the trombone players lips were exactly in sync which couldn't happen.  Even if they are playing the same note the vibration of their lips in not in phase just in sync.

[Chris Hindle]

But wouldn't you have some comb filtering if you have ten trombones?

Sure, if they were all capable of playing the EXACT same note/pitch simultanously.
(Not gonna happen.) back in the 70's, I was in a Drum & Bugle corps. Every mouth / embouchement is a little different. Little sharp here, little flat there. I would think that the subtly difference in each horn gives "bulk" to the performance. A little like chorusing thickens a vocal.

[Jamin Lynch]

Sure, if they were all capable of playing the EXACT same note/pitch simultanously.
(Not gonna happen.) back in the 70's, I was in a Drum & Bugle corps. Every mouth / embouchement is a little different. Little sharp here, little flat there. I would think that the subtly difference in each horn gives "bulk" to the performance. A little like chorusing thickens a vocal.

I'll have to test that theory out when I go see Texas beat West Virginia in a couple of weeks. 

[Bill McIntosh]

I'll have to test that theory out when I go see Texas beat West Virginia in a couple of weeks. 

Hook 'em Horns!   

I am a fan of Charlie Strong  -- excellent coach, excellent person IMHO.  I really hated to see him leave U of Louisville.     

PS:  Thanks for the explanation, it does make sense that the interference occurs for identical signals.

[John Roberts {JR}]

Sure, if they were all capable of playing the EXACT same note/pitch simultanously.
(Not gonna happen.) back in the 70's, I was in a Drum & Bugle corps. Every mouth / embouchement is a little different. Little sharp here, little flat there. I would think that the subtly difference in each horn gives "bulk" to the performance. A little like chorusing thickens a vocal.

Exactly... For combing you need coherence and roughly equal volume. If two horns played the same note you might hear a very low frequency beat, more like an amplitude modulation, but with 10 trombones the sound will be diffuse enough that it just sounds thicker (?).

JR

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