Concert Hall Acoustics

[Art Hovey]

Here's a serious article. (Boneheads won't be interested.)

http://scitation.aip.org/content/aip/ma ... ip-live-06

What might happen if similar techniques were applied to our favorite instruments?

[Kevin Hendrick]

Here's a serious article. (Boneheads won't be interested.)

Then why did you bother to post it here?

Most likely for the rest of us ...

(thanks, Art!)

[Kevin Hendrick]

Sciences where high-tech equipment and statistics are gathered to an end of (not a direct quote) "people will perceive the results in different ways" are fascinating.

As is often said of school elections, "your millage may vary" ...

[robcat2075]

I recall in high school our physics teacher said that if you were to place a trumpeter at each side of the stage playing the same note and you stood exactly between them you would hear nothing because the two sounds waves would cancel each other out.

Since then I've always been a bit skeptical about the things physics people say about this, that or the other music thing.

[eutubabone]

well now, that's because they are trumpets. Tubas are much bigger and therefore their sound waves are much more robust, hence their sound waves would not cancel out each other. However, even if they did, playing louder would fix it.

[eupher61]

Actually, the trumpet thing is not that far off reality. Try point two stereo speakers to the same point at identical distance. If exact, there is a dead spot--a nodal point as it were.

The problem with the teachers assertion is that if you were standing directly between them, you would eliminate the impact of the wave against each other. So you'd be hit by two trumpet sounds.

The other problem is....frequency and amplitude would have to be identical. Volume wouldn't be much of a problem with trumpeters. Pitch...well...

[gwwilk]

I recall in high school our physics teacher said that if you were to place a trumpeter at each side of the stage playing the same note and you stood exactly between them you would hear nothing because the two sounds waves would cancel each other out.

Since then I've always been a bit skeptical about the things physics people say about this, that or the other music thing.

Your high school physics teacher was a pinhead, because that's the only way his ears could both be in the same plane.

[robcat2075]

Your high school physics teacher was a pinhead, because that's the only way his ears could both be in the same plane.

That is the most accurate explanation.

[robcat2075]

The problem with the teachers assertion is ...

What was suspicious to me at the time was the absurd oversimplification he was trying to present.

Even IF you got two human trumpeters to produce the exact same pitch and volume and somehow one was the exact inverse of the other and you managed to listen at the exact midpoint... there is still the fact that the sound is radiating 360° from their bells and bouncing back off an infinite number of points in the room and there is just never going to be any convenient listening place to cancel that out.

And.. rather later i thought... since the waves won't be the inverse of each other shouldn't they be doubling the heard volume instead of canceling each other out?

[NCSUSousa]

What was suspicious to me at the time was the absurd oversimplification he was trying to present.

Even IF you got two human trumpeters to produce the exact same pitch and volume and somehow one was the exact inverse of the other and you managed to listen at the exact midpoint... there is still the fact that the sound is radiating 360° from their bells and bouncing back off an infinite number of points in the room and there is just never going to be any convenient listening place to cancel that out.

And.. rather later i thought... since the waves won't be the inverse of each other shouldn't they be doubling the heard volume instead of canceling each other out?

You're correct on this. It is WAY oversimplified and can't be done reliably with 2 human players in a normal room for the reasons listed above.

The only reliable way to create this effect is to use a recorded mono-track sound source, like a trumpet player to stick with the example. Play it in an acoustically 'dead' room using 2 matched speakers on the same amp. If the speakers are wired to match (+ wire to + terminal on both speakers), then the sound amplitude is doubled (3db more) at the central line through the room that is equidistant between the 2 speakers. If ONLY one speaker of the pair is reversed (+ wire to - terminal), then that line will be a 'dead' where the sound cancels. If they're both reversed, it's the same as having them wired correctly as long as the amplified source is producing a balanced signal.
You can measure this sound cancellation effect with a small microphone, or if you're using your ear, you can hear it with 1 ear at a time. You'll always be able to hear the sound with your other ear.
This setup also works with more complex sound sources (like a music CD) if you isolate either the right or left sound channel and run it to both speakers.
It's really an odd experience. And Yes, I've done this in a less than perfect room. It can also be done in your car to change the 'node' points if you think you're getting too much sound at one seat location vs another. It's actually a common practice for car audio tuners when they're adjusting a multi-speaker system to try things like this to improve the stereo imaging at the driver's position.

There is way more in the wave propogation theory that will also explain other points in the room where the sound is amplified regardless of the wiring swap. Add sound reflections from a normal room and the whole thing just gets more complicated. Of course, the microphone or other listening device ruins the whole thing according to Heisenberg's uncertainty principle so there's never really a completely 'dead' spot.

It is theoretically possible for 2 expert players to create this effect in a regular room, but it will vary over time between amplifying and canceling because they will always be some amount out of tune with each other. The more in-tune they are with each other, the more pronounced the effect will be. For 2 beginners, you'll never notice the difference other than to know that one is slightly out of tune with the other. If they aren't at exactly the same volume (even if they are in tune), then the cancellation point moves toward the player who is softer rather than being in the exact middle.

[joh_tuba]

This is probably the closest anyone has gotten to applying the sorts of methods used in the article to tuba design: http://www.bias.at/?page_id=8&sprache=2

I suspect some of the newer instruments(particularly the reinvented 2155 bugle turned into a Thor) are in part a product of such a process but I have no insider knowledge to prove it.. Clearly someone figured something out.

This link references the same food and wine research as the acoustic article and does an excellent job of explaining why this line of reasoning isn't wasted energy:http://www.ted.com/talks/malcolm_gladwe ... sauce.html
Not having a clear cut singular definition of best doesn't mean there are not multiple bests or patterns of taste that can be observed and maximized.

What's interesting to me about the article is that they seem to be focused on the sorts of halls that have a 'box' in which the sound is 'packaged' and then projected into the larger room next door. An audience, by design(and as observed in the article) is made to feel separated from the performer. As a tuba player, we are often sitting at the back of that box with our bells pointed into a curtain or rafters or both.

If there is a shell it often makes our multi-directional sound very directional. To build on the article's wine metaphor: I believe that the modern audience, accustomed to listening to pristine recordings turned up to '11' want to feel immersed in the music. They want to be able to swim in the wine and take it all in. This is what has driven the 6/4 York style instrument craze. They are horns perfectly adapted to produce a surround sound affect out in the hall. It's often been observed certain horns just sound better in certain halls. This article points at a reason why this might be the case and why we might like it!

The new Disney Hall in LA and the Kauffman in KC are a stark departure from the 'band in a box' concert hall. Both place the ensemble in the middle of the room and are acoustically engineered to create a much more intimate chamber music listening experience. The most striking thing about playing in Kauffman is how much just playing 'nice' is actually rewarded. It's very much a hall in which what you hear is what the audience hears.


The article, as I'm reading it, seems to point to proximity as THE primary factor that maximizes audience enjoyment. As I read it, really, the more 'intimate' the acoustic the more you feel enveloped(reverb) AND the more clarity. I kind of feel like the article simultaneously argues for multiple 'bests' while discovering commonalities among those 'bests' that point toward just keeping the audience close. Halls like Disney and Kauffman go a long way toward satisfying that objective.

Soo... assuming I'm drawing the right conclusions.. a tuba that is simultaneously very clear and 'fills the room' would satisfy the largest percentage of the audience.

Am I on the right path with this?