ASTM E336 Field STC Test Question

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Mark B - 23 May 2008 22:07 GMT

When doing an FSTC test of a partition in an existing building, is it
recommended to keep the sound source off the floor to reduce flanking
through the floor structure from one room to another? We are using
the Norsonic 260 speaker system.

This is a new hotel with insulated, staggered stud (wood) walls
between rooms. NIC measured out about 10 points worse than textbook
rating for partion (47). I would expect the field test to be worse,
but maybe not this much worse. I am now wondering if having the
speaker resting on the floor effected the results by exciting the
floor directly.

M Bagdon

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Asbjørn - 24 May 2008 11:13 GMT

That may matter if the floor boards are continous under the partition wall,
but that would also ruin the sound insulation.
I am not familiar with your ASTM methods but if they resemble the ISO
standards:
Have you evaluated the flanking sound transmission (via doors-corridor,
windows, ceiling, ventilation, power installations, etc)?
That usually matters far more than the loudspeaker mounting.
And the practical determination of the other parameters like the Test
Specimen Area, the Receiving Room Volume and Absorption also has a great
influence on the result.

- Asbjørn

> When doing an FSTC test of a partition in an existing building, is it
> recommended to keep the sound source off the floor to reduce flanking
[quoted text clipped - 9 lines]
>
> M Bagdon

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Angelo Campanella - 25 May 2008 06:01 GMT

> When doing an FSTC test of a partition in an existing building, is it
> recommended to keep the sound source off the floor to reduce flanking
> through the floor structure from one room to another? We are using
> the Norsonic 260 speaker system.

I have performed many of those tests, and yes, the speaker placed on
the floor surface above will indeed make a one to two point difference
in the result; for the worse. The reason is simple; the speaker sound
level at the floor surface will be quite intense as compared to its
level in the rest of the room. My procedure is to set the speaker on a
table or between two A-frames, ladders or saw horses with a board
spanning between as a raised platform.

Procedurally, the excess insonification can be avoided by always making
the room below tbe the Source Room, whence the speaker ia quite remote.
When this is not prcrical, then the speaker must be in a raised
position, nominally a meter or more above he floor.

> This is a new hotel with insulated, staggered stud (wood) walls
> between rooms. NIC measured out about 10 points worse than textbook
> rating for partion (47). I would expect the field test to be worse,
> but maybe not this much worse. I am now wondering if having the
> speaker resting on the floor effected the results by exciting the
> floor directly.

    Figure two points offset for the worse.

    If you have not had much experience in analyzing faulty dtrucures you
may be missing some vital facts.

    Two factors give rise to the shortfall:

    First, prctical structures, unlike laboratory test rooms, have sound
flanking paths of several sorts around the floors and walls. Secondly,
the practicality of common construction practices will deteriorate the
isolation possible with basic building materials as are used in lab
tests without outlet boxes or without leaky seams at the floor and ceiling.

    In general, experience is the best techer. Just get a lot of
experience. I often run extra tests, also useful to the client, on
consulting jobs to broaden my knowledge...

        Angelo Campanella

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Natural Science Forum / Physics / Acoustics / May 2008

ASTM E336 Field STC Test Question