NTi Audio Webinar Measuring Sound Insulation NTi Audio English English

NTi Audio Webinar Measuring Sound InsulationYouTube↗ IA↗(long shot)
Science & Technology 1.5K views 16 likes 1 dislikes 30 Oct 2018

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Hello and a very warm welcome on behalf of NTi Audio.

Thank you for joining us for today's webinar.

The topic of this webinar is measuring sound insulation.

My name is Markus Becker, I am moderating this presentation.

I am assisted today by Berno Nigsch, our sales director.

He will take care of the incoming questions

and assist me whenever necessary.

Here you see a list of the topics that we have prepared for you

We will say some words about the required equipment,

about airborne and impact noise measurements,

we will clarify some terms & parameters

and the issue of microphone positioning.

We have a brief statement about the reverberation time measurement,

which is also part of the whole procedure.

And we have prepared a practical presentation for you.

At the very end we will summarize the key issues

and provide some hints and tips

before I will take a look at the questions that have come in

and provide some additional comments.

I expect that the webinar will last about half an hour.

Let us first take a look on the two different ways

we are measuring sound insulation.

The 1st one is the airborne noise insulation.

Here we have a schematic sketch of a person,

who is apparently annoyed by incoming sound

The cause can be outside of the building,

in which he is located, or within.

In both these cases

the sound would be transmitted via the air.

That is why we call it airborne noise.

This can either happen through the facade,

or in-house, which is more frequent.

The 2nd case is the impact noise.

We see that schematically by this dancing couple,

who are stamping on the floor.

This stamping will we result in a noise

that is audible in the room below.

This impact noise also needs to be measured

In this presentation we will focus

on the in-house airborne noise

and on the impact noise.

The facade measurement is a special case,

which is very closely related to the in-house measurement.

Thus we will not say too much about that in this presentation.

What equipment do we need for these measurements?

1) We need an omnidirectional loudspeaker + amplifier.

2) We need a tapping machine for the impact noise measurement.

3) We need one or several sound level meter(s)

(we will come back to that issue later)

4) We need a software that allows us to calculate the results

from the measurement data that we are acquiring.

Let us take a closer look at the airborne noise measurement.

We have a sending room and a receiving room.

To start the procedure,

we would measure the background noise in the receiving room.

It is quite apparent that this value plays a major role,

because when we measure the incoming sound

from the neighboring room in a later stage,

we have to differentiate that incoming sound

from the existing background noise.

For that purpose we have to measure this value first.

Second, we place the omnidirectional sound source in the sending room

and we adjust its sound pressure level

so that the sound transmitted through the wall

is minimum 10 dB higher than the background noise in the receiving room.

If you cannot reach this 10 dB difference, it is not a big problem,

as the software that we will present later in this webinar

can cope with that situation.

But if possible, adjust the volume so that we have this 10 dB difference

between the transmitted sound and the background sound level.

Next, we will measure the noise level in the sending room,

which is called L1,

and then the noise level in the receiving room, which is called L2.

In a third step

we will analyze the reverberation time in the receiving room

and finally calculate the results

from these measurements that have been acquired in the two rooms.

Well, I have mentioned a couple of values and parameters.

Let us take a closer look on them.

I will not go into all the details,

but I have listed here a couple of frequently used

measurement and calculation results,

starting with the two levels I just mentioned: L1 and L2.

These are averaged sound levels.

Very important: these are not broadband levels!

We are always measuring & analyzing the spectrum,

i.e. we want to know the spectra of the corresponding sound levels

With these two levels we can calculate the Noise Reduction NR,

or the Normalized Noise Reduction NNR,

according to this formula.

Here you see the parameter T = reverberation time of the receiving room.

It is quite apparent that when you have a room,

which is exposed to neighboring sound,

then the reverberation time in the receiving room

has an impact on the overall sound level in that room.

That is the reason why we have to acquire the reverbaration time in the receiving room

Here we have the Apparent Transmission Loss ATL,

which is another value that can be calculated,

and here you see the area of the common partition

or the volume of the receiving room,

which play a major role.

By the way, these standards that I have listed here

are all referring to the ASTM,

i.e. the American Standard for noise insulation measurements.

Down here we have a third important formula,

which refers to the impact sound level measurement.

These three formulas are very frequently required for sound insulation measurements.

Some additional hints for the airborne insulation test:

a) How long do you have to measure?

That depends on the frequency range, in which you are interested .

If your measurement range starts at 100 Hz upwards,

then you can restrict yourself to 6 sec. measurement duration

whereas if you want to cover the whole frequency bandwidth

from 20 Hz upwards, then you need 15 sec. measurement duration.

b) You can execute the measurements sequentially or in parallel.

Sequentially means that you first measure the sending room,

and then the receiving room.

In parallel: if you have e.g. 2 sound level meters available,

then you can connect them to the laptop

and measure the result in one step,

i.e. you are measuring both rooms in parallel

Keep in mind that you don't execute just one measurement per room,

you have to do several ones,

and you have to change the position

of the microphone / test instrument in the room

in order to acquire several results per room.

That applies not only on the measurement,

but also on the position of the sound source.

I.e. you have to repeat the measurement

at different positions of the sound source

Last but not least, keep in mind that

airborne noise measurement is a relative measurement.

If we apply a higher level in the sending room,

we get of course a higher level in receiving room.

Most important is the difference between these two values,

which is the core information that we are getting from thes measurements.

I have been talking about changing microphone positions.

There are 2 ways to achieving that.

A) The microphone boom.

This is an automated, motor driven device

that slowly rotates the microphone in a circular plane.

B) You can do that manually by holding the microphone / sound level meter

There are different patterns that you can follow,

depending on the available space in the room.

The semicircles are e.g. recommended for very narrow conditions

These sketches have been derived from the ISO 16283 standard.

This is probably the easier way to move the microphone.

It takes less efforts to set up a test by doing it manually.

Now let us walk over to the impact noise measurement.

Hereby we start the same way:

we measure the background noise in the receiving room

and then we set up the tapping machine.

This is very important:

when you set up the tapping machine,

you have to do that carefully

this is a precision device that needs precise and accurate installation.

We have recorded an instruction video on this procedure.

You don't need to write down this link here just visit our website

and search for the tapping machine.

There you will find the video that shows you how to do that properly

to make sure that the tapping machine is operating correctly.

Then you run the machine, i.e. you switch it on

and you measure the sound it creates in the room below,

i.e. you measure the sound level L2 in the receiving room.

At the end you calculate the results.

Of course you also have to consider the reverberation time.

What is important in contrast to the airborne noise measurement?

Here we have an absolute measurement.

The tapping machine will always produce a sound

by the impact of these falling hammers in a defined way

so there is no higher or lower level that has been created

it's always standardized.

All you have to do is to measure the receiving room.

That is why it is an absolute measurement.

Now the reverberation time.

We have just published a new website on the topic of RT60.

This is a very nice website with lots of background information

and practical information on how to do the measurement.

When you visit our website you will find it easily.

One more hint: we already had a webinar on RT60 measurements.

You may find the recording of this RT60 webinar on our website.

Normally you execute the RT60 measurement

in building acoustics with the omnidirectional sound source

because you need it anyway.

The test signal is gated Pink noise.

Well I am at the point of the practical presentation.

For that purpose I have here in my room a Dodecahedron speaker.

I have 2 pcs. XL2 connected to my PC,

one XL2 is in my room, where I am sitting,

the other one is next to it.

Thus I can simulate a sound insulation measurement.

And I have the Sound Insulation Reporter software installed on the PC.

and that is what I am going to run right now.

Here you see the startup screen of this software.

When you start with a new analysis,

the first thing to do is to open a new file.

and you select the applicable standard

Here - talking about the United States - we would select the ASTM

You see, there are a couple of other standards implemented in the software.

You just select the one that you need in your country.

Then you decide, whether you want to execute an airborne, impact or facade measurement.

I am going for airborne.

Now I will restrict myself to just one speaker position.

Here you can select the results that the SW shall calculate.

Just a side note: if you are more acquainted with feet,

you can change the unit for the dimensions of the room.

and you see down here in the status bar

the applicable standard for this calculation,

i.e. for the analysis that I am going to do now.

Now you have two options

to import the measurement data into the software.

A) You click here on 'Import..'

and you select the data from the XL2.

Let us assume that you have recorded all the data

and saved it on the XL2.

I have done that before, and transferred this data to my computer.

So here I select these measurement results.

You can see they are dropped & displayed in the graphic.

The issue is now that the software needs to know,

what was the sending room, receiving room or background noise?

Thus you have to manually assign this information

to the corresponding curves.

Well, I know that my first 3 measurements

were executed in the sending room.

That is why I manually assign them to L1.

The second 3 curves I assign by right-clicking to the receiving room L2.

The reverberation time data is detectable by the software,

that is why it already has assigned it,

and the last measurement would be the background noise.

Having made these assignments

I can swap over to the calculations page.

Here I can click on the individual results,

the averages and the additional data.

I could even disable individual curves if they do not fit

e.g. if something went wrong during the measurement.

So here I can get a very nice overview

on the acquired data.

The final step is to customize my measurement report.

I would e.g. enter the name of the client,

the name of the location etc.

I also have to adjust the volume and the dimensions

I will just leave the default values now,

but this is the customization that you have to do.

In the end you click here on the result view

and this is the standardized display.

You can print that out, it completely conforms to the standard.

It shows you the corresponding results:

the Noise Reduction NR,

the Normalized Noise Reduction NNR

or the Apparent Transmission Loss ATL.

One more hint: down here you see the ASTC

(according to the new standard)

the Apparent Sound Transmission Class

is also displayed here on the result screen,

which you can print out.

There is a second way of executing a measurement

and I want to show you that in practice.

For that purpose I have here a webcam in my room.

This is one of the two XL2 devices,

here I have the amplifier for the omnidirectional sound source

Now I will now create a new file.

Same settings: ASTM standard airborne noise, one position.

But now I will let the software guide me through this measurement.

For that purpose I connect my PC to the two XL2 analyzers,

you see here I have already assigned them

to the source room and to the receiving room,

I have selected the measurement duration: 15 sec.

I could also connect the software to the power amplifier

in order to remote control the sound

that is generated by the omnidirectional loudspeaker

But I will renounce on that in my presentation,

I will rather witch On/Off the amplifier via remote control.

Before I start the measurement

I have to put on my hearing protection,

as it will get quite loud in this room.

As soon as I click here on the start button

you will see down here a countdown timer,

which shows me the 15 sec. duration

that need to expire before the final result has been acquired.

I will now put down my headset for a moment

and start the measurement.

I will actually execute two measurement cycles.

Maybe you have seen the countdown timer down here,

you have seen how these data have been acquired

and, what is very comfortable with this solution,

the software directly assigns the acquired results from the two XL2 devices

to the list of measurements.

Quite obviously the PC knows,

which analyzer is doing which measurement,

so it can directly assign the corresponding data.

The next step will be to measure the background noise.

So now I need a silent room and I start again

Third step is the RT60 reverberation time.

For this purpose I am going to put on my headset again

and switch On & Off the loudspeaker

while the instrument will trigger to turning Off the loudspeaker

and measure the reverberation time.

Maybe you have noticed here on the screen of the XL2

the decay of the sound that was created

and here you see the corresponding results.

Now I have all the data I was looking for.

I can double-check them on this screen,

and go to the result screen,

where I have the standard-conform printout of my measurement results.

Let me get back to the webinar presentation

and provide additional hints.

1) When you want to measure these different steps

by using the XL2 manually, i.e. by holding it in your hand

to execute these measurements,

then we recommend that you use the so-called

"Sound Insulation" profile.

This is a file that we are providing free of charge

on our website from where you can download it.

Then you can install it on the XL2

and it will simplify the operation of the XL2 on-site

because it just supports the sound level measurement

and the RT60 measurement in the way

that is needed for this sound insulation analysis.

2) When you think about buying an omnidirectional loudspeaker

keep in mind that sound insulation measurements usually take quite a long time.

You have to repeatedly change the position,

i.e. pretty long measurement periods at several locations

Thus you are usually running this loudspeaker for a long period of time,

e.g. one hour at a very high level.

Therefore it is very important that the created sound level is stable.

Of course the loudspeaker will get hot over time

and normally it then loses efficiency.

But a good Dodecahedron loudspeaker

has a lowl power compression,

which means the generated sound pressure level remains high

despite that you are using it at high volume for a long period of time.

Power compression, the weight of the loudspeaker

and the maximum level it can create

are the most important parameters

when you want to buy such a device.

What are the targets values you are looking for?

Airborne sound insulation is the higher the better.

A high airborne sound insulation result indicates

that you have a good insulation between the two rooms.

With impact noise it is just the opposite,

here a low result is what you are looking for,

because a low impact noise result

means a good insulation between the upper and the lower room.

Last but not least, if you have results that are not satisfactory,

if you have to improve the situation, what can you do?

Talking about airborne noise you can improve the wall structure,

you should watch out for leakages,

leakages are always bad as they reduce the sound insulation

So you should fill them up.

Sound absorbers would be another option

to improve the situation regarding airborne noise.

When we talk about impact noise, the building structure plays a key role.

Maybe a floating floor would be a solution,

or laying carpets could help to improve the situation

if it is not acceptable.

Here ares some actual limits from England and Ireland,

the corresponding National Building Regulations.

You can see here that for airborne noise

there is a minimum result that needs to be achieved

in England 45 dB and in Ireland even 53 dB

for new-built dwelling houses or flats,

whereas impact noise should be low:

for that reason you have a maximum value that must not be exceeded

for England and for Ireland

with the corresponding definition of the results

Good, I am at the end of my presentation.

I want to thank you for your attention

and I would be happy to welcome you again in one of our future webinars.

You will be informed via email as usual.

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