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Forum index » Science and Technology » Physics » Acoustics
Floating floor efficiency vs impact force
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CSL
science forum beginner


Joined: 05 Jul 2005
Posts: 14

PostPosted: Mon Jul 10, 2006 3:32 am    Post subject: Floating floor efficiency vs impact force Reply with quote

As read from textbooks, isolation pads are commonly used in constructing
floating floors. This isolation problem is then analyzed as a simple
spring-mass system under a sinusoidal disturbing force. The isolation
efficiency can be calculated straightforwardly based on the ratio of
spring-mass system resonance freq and distrusting frequency.



- What's the calculation method if the load is an impact (e.g. a drop of a
heavy mass on the floor) ??

In most of the typical floating floor system, the isolation efficiency is
not 100% for sure. There is still certain percentage of "impact force"
being transferred directly to the floor slab and indirectly to other
structure walls throught flanking.

- How to assess the final sound radiation from these floor slabs and
structure walls due to the original impact force ?

Thanks.

CSL
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Noral Stewart
science forum addict


Joined: 23 May 2005
Posts: 77

PostPosted: Mon Jul 10, 2006 10:46 am    Post subject: Re: Floating floor efficiency vs impact force Reply with quote

Get hold of one of the two most recent editions of the series of books on
noise and vibration control edited by Beranek and Ver, the 1992 or 2005
versions,
http://www.powells.com/cgi-bin/biblio?inkey=65-0471449423-1

The chapter on interaction of sound with solid structures has some brief
discussion of the problem that will get you started.



"CSL" <csll@163.com> wrote in message news:44b1ca39@127.0.0.1...
Quote:
As read from textbooks, isolation pads are commonly used in constructing
floating floors. This isolation problem is then analyzed as a simple
spring-mass system under a sinusoidal disturbing force. The isolation
efficiency can be calculated straightforwardly based on the ratio of
spring-mass system resonance freq and distrusting frequency.



- What's the calculation method if the load is an impact (e.g. a drop of a
heavy mass on the floor) ??

In most of the typical floating floor system, the isolation efficiency is
not 100% for sure. There is still certain percentage of "impact force"
being transferred directly to the floor slab and indirectly to other
structure walls throught flanking.

- How to assess the final sound radiation from these floor slabs and
structure walls due to the original impact force ?

Thanks.

CSL


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Angelo Campanella
science forum Guru Wannabe


Joined: 08 May 2005
Posts: 226

PostPosted: Tue Jul 11, 2006 8:17 am    Post subject: Re: Floating floor efficiency vs impact force Reply with quote

CSL wrote:
Quote:
As read from textbooks, isolation pads are commonly used in constructing
floating floors. This isolation problem is then analyzed as a simple
spring-mass system under a sinusoidal disturbing force. The isolation
efficiency can be calculated straightforwardly based on the ratio of
spring-mass system resonance freq and distrusting frequency.

Extreme self-delusion at work!
Many "floating floor" materials manufacturers practice this.

Quote:
- What's the calculation method if the load is an impact (e.g. a drop of a
heavy mass on the floor) ??

True, you can calculate the resonance frequency, but all this does is
verify that you have troubles. The formula, approximately is :

f=170/SQRT(WD),

where W is the weight of the sprung panel in pounds per square foot,
and D is the spacing. Thus, a floor weighing 2 pounds per square foot
over a 1/2" air gap will resonate at 170 Hz. This is the MO of many
lightweight, low cost floating floor materials, e.g. "Enkasonic".

Quote:
In most of the typical floating floor system, the isolation efficiency is
not 100% for sure. There is still certain percentage of "impact force"
being transferred directly to the floor slab and indirectly to other
structure walls throught flanking.

The glaring problem is that the impact force-vs-time of an adult foot,
be it male or female, excite frequencies down to 20 Hz or less. The
isolation of any mass-spring filter is effective only for frequencies at
and greater than one octave above this resonance frequency. At the
resonance frequency, AMPLIFICATION occurs, giving rise to a "hollow"
resounding sound; very annoying to occupants below.

The only "plus", if you dare call it such, is that the technicality of
producing a better IIC rating in that it filters out higher
frequencies.. When compared to bare concrete, those thin floating floor
treatments do provide a technical increase in reported IIC values (a
"numbers" game).

Since, by various wrangling strategies in recent decades, the average
community minimum requirement for multifamily occupancy has been held to
be IIC 50. In this time frame (since 1980) several "floating floor"
concoctions have been devised that technically meet IIC 50. For
corresponding field testing results, FIIC, acceptability has often been
gratuitously as low as FIIC 45. My experience is that FIIC 45 is suited
only for rental apartments; those where occupants fully expect to move
to better residences in a few short years.

Little imagination is needed to envision what happens when one of these
aforementioned "floating floor" designs finds its way into middle price
and "luxury" condo's.

Quote:
- How to assess the final sound radiation from these floor slabs and
structure walls due to the original impact force ?

The only halfway decent evaluation criteria I know of is the FTS-24
Federal Standards assembled in the late 1960's by then-NBS where values
of STC and IIC were recommended ranging from 48 (Grade III spaces) to 62
(luxury spaces). Assigned values were keyed to room type (living room,
bedroom, kitchen, etc.). And even these values should NOT be taken as
targets, but as MINIMA.

That specific criterion set is only recently being revived quietly (I
have been using it since 1980).

I advise prospective condo buyers and developers that if FTS-24 can't be
fully met, don't buy it. It's a very ticklish subject... fraught with
difficult feelings..developers have a lot of money riding on the
outcome. There are no economical designs available so far. The only way
to get high 50 and low 60 IIC's is to add a drop-ceiling where the
filter resonance frequency can be moved to be below 20 Hz; where the gap
is one to two feet. Tell that to a developer, and you will have lost a
client one way or another. But for me, I sleep better when I take that
position...


Finally, for concrete floors (NOT wood joist floors), carpet provides a
wonderful alternative, since virtually all the impact force frequency
components that transfer easily through concrete (above 200 Hz) are
diminished. The heel "thump" still is produced, but a level less than
for wood joist floor because the mass ratio (weight of foot and lower
leg vs the weight of the floor panel being impacted) is more favorable
for thick concrete floors. But still, to get past IIC 60, the rug may
not be enough; a drop-ceiling should be added.


Angelo Campanella
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