Posted by: "Rob Danielson"
> I obtained the attenuation range by recording inside (with my body
> between the door and the mics) and outside by the door and comparing
> the files.
Just seemed awfully little for the structure you were describing.
> The low frequencies are the rub. I could stand in the booth 150 yards
> from a city blvd and hear nothing but a faint, very low (>50Hz)
> presence coming from the direction of the street and from the floor.
> A telling moment came when a bus passed and I found that not only
> could I tell it was a bus, but that I could "point" to it as it
> passed. (So much for low frequencies not playing a role in source
> localization).
Those army soundproof booths stopped low frequencies well. Our building
was right next to a road that carried lots of truck traffic and it did
not penetrate the booths. Don't know if they would have been enough to
stop tank noise, but we did not have to deal with that.
I've made the point for some time that low frequencies are directional,
even if it's maybe a problem to reproduce that directionality.
The manufacturers of sound systems just wanted to save money by
promoting the idea of one centrally located sub. From that has grown the
idea that low frequency is not directional.
> What kind of structure could absorb that much low Hz energy? I've
> only built three projects with sound abatement priorities, but my
> guess is that it should be almost free of ground transmission and
> require a LOT of mass on all sides. If there's a way to do it without
> mass/material, I'd love to know more about it. Of course, if the
> chamber is constructed in a remote location away from local traffic
> and one can work between commercial jet fly-overs, -40 from 40 =3D 0.
>
Low frequency can be cut the same way as the others, layering is more
effective than thick massive setups. I'm sure the literature can give
info on this.
Indeed a lot of this sort of work is done in the quietest part of the night=
.
Walt
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