Atmospheric pressure

[Mickthemiller]

I've seem a lot about humidity and it's effect on guitars but never seem anything about atmospheric pressure. Last week here in the uk it was low (very low) and all my guitars sounded great. Over the last few days it's risen to around 1030 and the guitars really sound gross. Humidity indoors has remained around 50-60%. Has anyone else notice this effect or is it my ears that react to air pressure?

[Murph]

or is it my ears that react to air pressure?

 

Brilliant.

 

I have some ear issues with popping and such, yawning can pop them, high altitudes when on trips, and some tinnitus from decades of gigging but have never considered this.

 

I'd bet money you are on to something !

[duluthdan]

If i remember my high school physics class correctly, I seem to recall that sound actually travels slower at higher altitude and low pressure because there is actually less air. So, perhaps sound also "decays" a micro fraction slower, and what you describe as better tone may actually be due to a teeny wee bit more sustain ? I dunno. Questions like this used to keep me up at night.

[capmaster]

The speed of sound within air depends on composition and temperature, not pressure. However, air pressure indirectly affects air composition because the vapour pressure of water depends on temperature only, not air pressure.

 

Relative humidity means the percentage of the actual vapour pressure in air compared to its absolute vapour pressure at the given temperature. Given constant composition, the effective relative humidity rises when the air pressure drops. Humidity gauges usually won't show the effect.

 

There is another point of sound propagation in a given medium called dispersion. Within air high audio frequencies travel faster than low, and this effect increases with relative humidity. The more humid the air is, the "fresher" will sounds appear due to the earlier transients. Completely dry air will make anything sound darker and blurry. Moreover, the dissipation of higher frequencies grows with dropping humidity, and this additionally dampens the higher frequencies.

 

Since the attack noise and very high order overtones from acoustic guitars are radiated by the strings only, the effects described above may change tone significantly.

 

Having said that all, it is very likely that your ears don't fool you.