HyperboLine ™ new Player in the Old Game

Re: HyperboLine ™ new Player in the Old Game

Bennett Prescott said:
I suspect this is due to different limitations. In the phone network, higher frequencies require more bandwidth. Digital phone switching equipment operates at a sample rate of 8kHz, which means the maximum usable frequency response is 4kHz.
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It is my understanding (and I could be wrong about this) that the telephone bandwidth was determined long before any digital stuff got put into use and was the result of speech intelligibility research. I think that 8khz sampling was chosen to support the already established spectrum.

btw, your 4.5db attenuation appears to me to be a better case example. For instance, at 85 deg F temp and 20% humidity the absorption is almost 13db. I'm not sure how often it gets that dry at 85 but even at 50% humidity at 85 deg it's over 10db of attenuation. The calculator that Art linked to in the first post is pretty cool and shows that the air absorption is a pretty strong variable. It seems to make sense to tilt the response towards the top end for outdoor and long throw applications as compared to the telephone receiver where the sound travels mere millimeters.
 
Re: HyperboLine ™ new Player in the Old Game

Hey Drew,

The effects of atmosphere on long throw audio are what make long throw audio tough, but humidity is a much stronger driver than temperature at the types of pressures that we humans are likely to exist in. Temperature largely affects time of flight. If you're finding a 5+ dB change in gain for a 15°F change in temperature something is wrong (I used 70° in my calculation).
 
Re: HyperboLine ™ new Player in the Old Game

Bennett Prescott said:
Hey Drew,

The effects of atmosphere on long throw audio are what make long throw audio tough, but humidity is a much stronger driver than temperature at the types of pressures that we humans are likely to exist in.
Click to expand...

The HF attenuation from the dry air in the high desert is specifically what drove my interest in a more efficient means of making HF travel further.

Being was used to the Land of 10,000 Swamps, 50% humidity 85 degree weather outdoor shows were typical, with HF attenuation of 7.3 dB per 100 feet at 15 kHz (23.8 dB at 100 meters) in addition to the usual inverse distance losses.

Reduce the humidity to 20% ("a dry heat" (^;), and the attenuation nearly doubles, 14.4 dB per 100 feet, 47 dB at 100 meters- when I first started doing shows in New Mexico with different equipment than I was used to, I thought the gear was the problem, it was several years later that I found out it was the dry air that was killing the HF.

Art
 
Re: HyperboLine ™ new Player in the Old Game

drew gandy said:
It is my understanding (and I could be wrong about this) that the telephone bandwidth was determined long before any digital stuff got put into use and was the result of speech intelligibility research. I think that 8khz sampling was chosen to support the already established spectrum.
Click to expand...

I suspect you are both right. The telcos have been dealing with electronic amplification for a long long time, with crude transducers on either end so were happy just to deliver intelligible speech. The telephone company was also a very early player in digital audio, and that 8kHz sample rate no doubt was established with a sharp pencil for how low could they get away with. In addition to that low sample rate, the original telephone codec conversions used a low word length (bit depth?) with non-linear quantization step size. There was more resolution around zero crossings, for less perceived distortion with speech. The old telephone conversions made MP3 sound good, but has gotten better over time as technology gets cheaper. Some of the codecs used in modern cell phones don't suck, while not up to audiophoolery standards.

JR
 
Re: HyperboLine ™ new Player in the Old Game

Bennett Prescott said:
If you're finding a 5+ dB change in gain for a 15°F change in temperature something is wrong (I used 70° in my calculation).
Click to expand...

Perhaps. I was playing with the calculator and noticed that some changes didn't seem to correspond with the graph on the same page. But I'm not completely clear on relative humidity vs absolute humidity for this equation.
 
Re: HyperboLine ™ new Player in the Old Game

drew gandy said:
Perhaps. I was playing with the calculator and noticed that some changes didn't seem to correspond with the graph on the same page. But I'm not completely clear on relative humidity vs absolute humidity for this equation.
Click to expand...

Absolute humidity is a measure of the amount of moisture in the air, regardless of the air's temperature.
Warm air can hold more moisture than cold air, so air will have a higher relative humidity if the air is cooler, and lower relative humidity if the air is warmer.
Relative humidity is expressed as a percent of moisture in the air relative to the temperature of the air.

The calculator allows you to set RH from 10 to 100% and temperature −20 °C to +50 °C separately.
At low temperatures, since the air can hold less moisture, the differences in RH values affect HF attenuation less, and the thicker cold air attenuates less.
 
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