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Old 24th February 2011, 07:11 PM   #10131
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Originally Posted by bentoronto View Post

4. GET A GRIP... there are only some many ways halls vary from one another and/or that conductors can fool with. Maybe just: reverb time, high-and-lows, city noise level..... Maybe more. Basic stuff. So let's not attribute a whole texture of control to them. Yes, in a stone cathedral, you have to let the racket from the trombones die down before something else starts up and Berlioz' massive Marche Funebre et Triumphal has to be played slow. Duh. I say as something of connoisseur of conductors, at least when I was young - yes, good one's are wonnerful, but they aren't doing a whole lot apropos the hall characteristics.... the multi-mic recording engineer is.
there is control of reverb time at each frequency and initial time delay from first sound to the beginning of the reverberation time.
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Old 24th February 2011, 07:14 PM   #10132
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Anyway, there was a dispute. The managers controlled the money and as the golden rule has it, he who has the gold makes the rule.
i remember a dome project i worked on. the opinion of the owners was: regardless of the sound, the dome will sell out.
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Old 24th February 2011, 07:49 PM   #10133
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i remember a dome project i worked on. the opinion of the owners was: regardless of the sound, the dome will sell out.
Gee,

My favorite dome project was profitable and educational. They had a budget of 250K. Cost was around 90. I knew they would throw out too low a price so I quoted 225. Low guy at 85 was thrown out, the brand name folks they wanted were 750, so I got it.

Everything worked well except the woofers, rolled like a rock at 300. No bass, classic two zero curve. Checked everything in the electronic circuits, power was there. Blown speakers? Hit the down button on the speaker cluster winch, music was still playing. As it dropped 15 feet, all the low end showed up! Raise the cluster... gone. Down... back on! A slight realignment of the mids and highs allowed for the new operating position.

I placed a piece of tape on one of the wire ropes to clearly mark the correct operating height. Worked well until the house electricians got tired of climbing to the hoist platform and put on a remote control so they could operate the winch from the control room. "Yeah that looks about the same."

So there were two important lessons to be learned.
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Old 24th February 2011, 08:36 PM   #10134
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The idea is the same as using water at an appropriate speed for scale aircraft models.

You want the model to map 1KHz, but you have a 10:1 model, then you either have to use 10KHz or pressurise the model.

Wrinkle
I don't follow you, your only choice with air is 10kHz pressurizing to 10ATM will not change the speed of sound 10X. Same is true of water, sonar?

MJL21193 help, it's back.
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Old 24th February 2011, 09:22 PM   #10135
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I don't follow you, your only choice with air is 10kHz pressurizing to 10ATM will not change the speed of sound 10X. Same is true of water, sonar?

MJL21193 help, it's back.
They may have been pressure for absorption coefficients to scale the material, or my recall may be foggy.

Yes everyone knows that the velocity of propagation is almost a constant for a gas. It is explained that the difference when measured at different altitudes is due to temperature (10 degrees F is about a 1% change). Of course PV=NRT has nothing to do with it? Then there is the difference between compression and rarefaction.
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Old 24th February 2011, 09:30 PM   #10136
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??? The speed of sound in air varies as temperature not pressure. I can just see the doll house violins and microphones.

>For an ideal gas the speed of sound depends only on the temperature and
is independent of gas pressure.<

Yes, but what about modelling dissipation with respect to frequency?
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Old 24th February 2011, 09:42 PM   #10137
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Originally Posted by simon7000 View Post
They may have been pressure for absorption coefficients to scale the material, or my recall may be foggy.

Yes everyone knows that the velocity of propagation is almost a constant for a gas. It is explained that the difference when measured at different altitudes is due to temperature (10 degrees F is about a 1% change). Of course PV=NRT has nothing to do with it? Then there is the difference between compression and rarefaction.
My recall is that they also had to change the pressure to get all parts of the scaling right.
And PV=nRT**gamma, and gamma is not one, but that effect is quite small over the range of pressures we are dealing with here.

Also Scott
What is the bit about "MJL21193 help, it's back." to do with?

Wrinkle
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Old 24th February 2011, 09:48 PM   #10138
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BBC RD 1970/13: Acoustic scaling: General outline. H.D. Harwood, A.N. Burd

The reason to enclose the model would be to ensure a very low %RH can be maintained locally to avoid excess in-air losses at the very high frequencies used - the Beeb used a zeolite trap in the setup. I can't see that high pressures per se help in any way.
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Old 24th February 2011, 10:35 PM   #10139
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I think they use gas other than air. Not pressure, temp, or etc.

Another technique is light beams to eyeball bounce angles.

I worked on Roy Thomson Hall in Toronto, a BBN product around 1980. Turned out to be a very poor sound.

Funny, I sat with the development team during the first orchestra rehearsals. I said to the construction manager, "Hey, this is just the way I like it, really dead." Boy, did he give me a dirty look.

At the staff and friends open-house concert before opening, the acoustician did some testing with a full house (starter pistol, etc.). Tuning the reflector clouds is fine-tuning for the sound the players hear versus shared with the audience.

My end of things involves "user friendly" issues such as seating, womens toilets, access, etc. Some of these halls are interesting for seating. Check out the aisles!
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Last edited by bentoronto; 24th February 2011 at 10:44 PM.
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Old 24th February 2011, 11:36 PM   #10140
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Originally Posted by wrinkle View Post
My recall is that they also had to change the pressure to get all parts of the scaling right.
And PV=nRT**gamma, and gamma is not one, but that effect is quite small over the range of pressures we are dealing with here.

Also Scott
What is the bit about "MJL21193 help, it's back." to do with?

Wrinkle
An old thread that should be let lie, it all ended in a big laugh let's keep it that way.

Gamma IIRC is due to the degrees of freedom for the gas molecules. Degrees of freedom is the neatest fudge factor that I have come across.
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