Acous-Tickling

PaulBrewer

http://www.gearslutz.com/board/tips-techniques/342843-room-analysis-primer.html

Here's a cool post from an Ex Boarder regarding Acoustics ...

danjokill

PaulBrewer wrote: »

http://www.gearslutz.com/board/tips-techniques/342843-room-analysis-primer.html

Here's a cool post from an Ex Boarder regarding Acoustics ...

Nice one!!! I'm doing some study in this area at the moment, thanks for the link.

PaulBrewer

And I have another cooking!

Chris from www.Munro.com is just finishing what he describes as a 'Long' email on Acoustics for our delectation.

That's if he's still talking to me ....

You may recall me mention he did U2's room. I just heard U2 are in Olympic studio in London mixing (apparently 4 studios!) and I was taking the pizz that they'd moved out of his room (which was just their recording room) as there was a 'horrible pinging noise'.

He didn't catch the joke... and rang them .... Ooops:o

PaulBrewer

Yer man came good .... get yer Geeky Heads around this

"Sound is transmitted from one room to another by airborne transmission
(directly through a partition) and by flanking transmission (through the
building structure). When designing a studio it is important to consider
both of these. Sound insulation relies, predominantly, on mass. To
achieve high levels of sound insulation you need a lot of mass
(particularly at low frequencies). As a rule of thumb you need to double
the mass of a single leaf partition to achieve a 6dB increase in sound
insulation. For high levels of sound insulation this gets very heavy
very quickly. You can increase the efficiency of a partition by using a
number of different materials which create discontinuities in the
acoustic impedance. This is usually done with a double leaf partition
such as a double dense concrete block wall with a cavity between or a
double stud wall. Care must be taken to ensure that the mass-air-mass
resonance of the partition does not adversely affect the sound
insulation performance and this is best done by designing the partition
such that the mass-air-mass resonance frequency is below the frequency
range of interest (i.e. <20Hz). However, this requires either very heavy
partitions or very large air gaps. It is also important that there are
no rigid connections between the two leaves, or if bracing is absolutely
essential (wall ties for double concrete walls for example) these should
be specified and spaced to achieve appropriate tuning.

Flanking transmission is often underestimated. If you continually
increase the mass of a partition you get to a point where the sound
insulation does not improve because the flanking transmission is
limiting the partition performance. Depending on the building
construction this limit can be quite low. The standard 'room-in-a-room'
design seeks to eliminate, or at least greatly reduce, flanking
transmission, however the design of a floating studio requires great
attention to detail.

I always start by looking at what level of sound insulation is required
which involves assessing source noise levels (worst case octave band
Lfmax) and the background noise level you want to achieve in the
adjoining rooms (generally octave band Leq NR curves). Typically in a
high spec professional studio you would aim to keep Lfmax breakthrough
below the target background Leq in all octave bands. That establishes
the magnitude of sound insulation that is required - next you need to
find out what construction will achieve this level of sound insulation
and whether the structure of the building you are putting the studio in
can take the additional load of this construction. It is not always
necessary to build a floating room. If the studio is built directly off
a good solid concrete foundation the level of flanking transmission is
likely to be quite low. It would generally only become necessary when
aiming to achieve very high levels of sound insulation. If a studio is
to be built off a timber joist floor it is generally quite difficult to
achieve very high levels of sound insulation, primarily because the
structural capacity is often quite low so you can only add limited mass.
The structural capacity can be increased by adding steels etc, but this
can be disruptive and costly.

The point of 'floating' a room is to decouple the studio from the main
building structure in order to eliminate flanking. The main component of
a floating room is a floating floor. This is a floor that is built on
anti-vibration mounts such that every connection between the floated
structure and the main building structure is resilient. This can be
achieved with spring AV mounts, neoprene pads or (allegedly) rubber or
neoprene sheet or mineral wool. It is vital that you know the deflection
characteristics of the AV product you use and its load limits etc. A
floating floor is a mass-spring system and so has a resonant frequency
dictated by the deflection characteristics of the AV material and the
mass of floor that rests on it. It is imperative that the system is
designed with a resonance below the frequency range of interest
(typically studios are designed to 10 or 11Hz). Below this resonant
frequency structure-borne noises are amplified (so a poorly designed
floating room can actually make sound insulation worse at certain
frequencies). Above this frequency structure-borne sound is rejected to
some degree. To yield good results it is important that the dead load
(mass of the floor and any permanently installed kit) is much greater
than the live load (people in the studio and non-permanent kit)
otherwise the live load will over-compress the AV pads and force the
resonant frequency higher thus compromising the performance of the
floor.

The walls of the studio can either be built off the floating floor (you
will need a different type or distribution of AV material around the
perimeter of the floor to account for the additional mass of the walls)
or built on a separate AV system outside the floating floor. My
preference is for the former. An isolation ceiling should either be
supported from the floating floor using whatever structural elements are
required, or by suspending it from the structural soffit above on
suitable AV hangers. Again the deflection characteristics must be known
and their spacing carefully calculated. All joints, junctions, openings
and services penetrations should be packed tightly with mineral wool and
sealed with silicone. As mentioned before you must ensure that the only
connections between the studio and the existing structure are resilient.

None of the theory or maths required to design a 'room-in-a-room' is
particularly complicated, but it is crucial that every possible
transmission path is identified and that appropriate steps are taken to
mitigate against them. Some of the construction methods used when
building studios are very different to standard building practices so it
is worth finding a builder that fully understands what to and what not
to do. This is much easier said than done of course...

If anyone is interested enough to ask any questions I'll do my best to
answer them.

Chris Walls"

studiorat

2 excellent articles Paul.

Good to see someone is linking to a correct room mode calculator. There was a wrong one floating around there for a while. A "+" instead of a "x" it was...

I'm all for re-instating dan-dan if he could be bothered to come back...

PaulBrewer

Cool!