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the elephant wrote: ↑Mon May 10, 2021 10:55 am The folks who fund a lot of what we do for money tend to sit within 100 feet of the stage. I would measure things from about 75 feet away. In most halls the sound fades unevenly, so this zone is the sweet spot. In places like the Meyerson the sound fades much more evenly. You can hear every instrument as the note fades away. If you played in the Meyerson you could test from anywhere in the room. But you don't. I don't. None of us do. (Except for Matt, of course!) I would confine my measurements to where the spendy seats are located.

Also, measuring pressure waves (db) will not give you the complete story, as the overtones in the sound do as much as the sheer volume in projecting a clear, audible tone at all dynamics and in all ranges. I have done this in the past with several colleagues to locate where the crappy parts of our hall are. (We got some very surprising results, too.) In the end, we all decided that the mouthpiece had about the same amount of effect as the bell (the "horn") in our hall with its problems and that these findings did not hold in *any* other space.

While you could end up chasing your tail, it is fascinating stuff. I encourage you to do this and to share what you decide the numbers tell you. It might be good to have someone sit in the audience at one of these concerts, hold the db meter and take some notes for you. The difference between an empty hall and a hall filled with bags of meat is very telling.

Good luck!

bloke wrote: ↑Mon May 10, 2021 1:22 pm I guess I'm most interested (not in the numbers in some read-out, but...) in how wide-RANGING I can make the numbers (in various ranges, from usable-quietest to usable-loudest).

SIDEBAR: Has THIS ever annoyed anyone else?

> You are asked to play a solo piece (or some sort of audition/sample of your playing) for some group of people in their room, and the room (no...I'm not referring to the amount of time the reverberation lasts, but...) is WAY to resonant...?? (ie. "Pianissimo" comes out "Fortissimo")

peterbas wrote: ↑Mon May 10, 2021 2:11 pm

matt g wrote: ↑Mon May 10, 2021 12:44 pm Doubling the sound intensity adds 3db, as a rule of thumb.

The issue with decibels as a unit is that it requires a reference. As mentioned above, speakers are often measured at one meter. But you also need to know if this is narrowband, spectrum level, etc.

A proper marking would be something like 100db reference 20 micropascals at one meter in a 1Hz band at 100Hz.

The room is an acoustic waveguide, and yes it matters. Reflectivity of the surfaces will be frequency dependent as a function of angle. Attenuation in the room is frequency dependent, and increases as frequency increases, so higher pitches die off a bit faster than lower ones.

Wall construction will matter as well both on the surface and underneath.

Are there people in the seats? They matter also. One, they reflect and absorb sound differently than the chairs. Two, they are a heat source and will cause the sound to bend (refract) differently in large spaces.

Anyhow, all of this stuff would have to be taken in to account to figure out how the sound will propagate.

However, for the purposes you’re seeking, if you consistently measure at the same point, that’s usually good enough. Getting away from the near field effects is a good idea. For ease of thought, 50’ should be sufficient.

3 dB is for non-correlated sound sources. If 2 tubas are playing the same note they would be 6 dB louder. But here again correlated means same frequency and phase and for the higher harmonics the correlation will be lost since they're length is in the neighborhood of the distance between the two tuba players. So more then 3 dB louder but less then 6 dB.

I don't get "the room is an acoustic waveguide" since a waveguide does what it says, it guides the wave. A room reflects in different direction like you said so I don't see the waveguide connection.

For seats, when to design for good acoustics the seats should absorb the sound as good as possible similar to a human body. Otherwise measurements between an empty hall are to far off to use for a fully loaded hall.

the elephant wrote: ↑Mon May 10, 2021 10:55 am Also, measuring pressure waves (db) will not give you the complete story, as the overtones in the sound do as much as the sheer volume in projecting a clear, audible tone at all dynamics and in all ranges. I have done this in the past with several colleagues to locate where the crappy parts of our hall are. (We got some very surprising results, too.) In the end, we all decided that the mouthpiece had about the same amount of effect as the bell (the "horn") in our hall with its problems and that these findings did not hold in *any* other space.