Natural Science Forum / Physics / Acoustics / January 2004

Andrew,

I'm not much help on this one.  I thought I should offer a thought though...

We've seen (at least in Australia) some pretty high test results for lab
tests - around STC 50.
The only problem is that we don't usually see it perform in the field any
better than about FSTC 40.

Has anyone had similar issues with operable walls? - by all means answer
andrew's original question too! :)

Cheers,

Matt Terlich

Here you can find a contact for your country:

http://www.dorma-hueppe.com/

Thomas

Looks like the product is sold through Modernfold in the US.  This may be a
high-end partition that will do better than the Modernfold.  However, normal
experience with the Modernfold and their direct competitors is that you are
doing good to get an NIC value in the field that is within 10 of the
laboratory STC value, even though your field room may have a lot of
absorption that should theoretically yield an NIC greater than the STC.
This seems to be the case even when flanking is not strong.  In that case,
with strong absorption in the receiving room, it means that the actual FSTC
of the partition is less than the NIC and possibly more than 10 points below
the laboratory STC.  This inability of the manufacturers to achieve their
laboratory performance in the field has never been fully explained.  Often
of course, you also have strong flanking.  One common problem is the
partition resting on a carpet.

My experience of on site tests for operable walls has been
similar to others in that the "theory" and lab figures are always
very impressive BUT the practice is usually very poor.
Typical on site values being in the region of 35dB R'w !
Given the very high cost of these walls compared to their
static counterparts it can quite a shock to the client when these
50dB+ walls fail at such low levels.

There are 3 main reasons:
1.
The main culprit is the detailing around the head.
Architects tend to specify some kind of Gypsum margin panel
around these structures and never show and form of barrier
above the sliding/folding screen in the ceiling void.
2.
When architects do show some kind of acoustic treatment in the
ceiing void the problem then moves down to the head mechanisim
itself. There is a physical problem of maintaining an aritight seal at the
head, especially after several operations of the wall. Seals compress
(and then stay that way !) becuase they tend be left in the "closed" state
for the majority of their working life.
3. Quality of on site fixing cna be very poor and lead to quite a number of
direct
leakage paths around the head of the operable wall.
What to do ?
A.
I would recommend a degree of absorption material over and around the
head of the wall as it can at least help to negate the leakage issues.
B.
Use foam.lead.foam or mineral wool/lead/foil barriers in the ceiling void.
C.
Replace brushseals with bubble seals and flipper seals that do not become
compressed over time.

I also think the static acoustic tests for operable walls is misleading and
that the procedure for this kind of wall should include at least 50 closing
and
opening cycles PRIOR to the test.

The above list os not the only issues that lead to poor sound performance.
The floor seal can also be a problem as can the interpanel vertical seals

Kind Regards

Lee A Roth
Technical Consultant