# Forum Home Renovation Home Theatres  Measuring sound penetration

## phild01

I have been wanting a simple way of determining sound penetration through a wall, door or window without the need for specialised equipment, so subjective evaluation. This is to determine what measures to take to minimise outside noise coming into a room. Appreciate any ideas!

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## John2b

If it were easy, there would be no need for specialised equipment, which in any case still can't accommodate personal preferences based on such things as expectations, and even physiology (personal hearing acuity, for example). Your best bet is to get a couple of decades of experience in modelling, design, build and evaluation. Then you would at least have a chance of having a reasonable fist at 'gut feelings', though based on my encounters as a professional electro-acoustic engineer, even that is not guaranteed.

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## phild01

Well, not sure a couple of decades helps me now. I am thinking of setting up a petrol motor outside and try and measure the sound penetrations close to each wall and see if anything I do would give an appreciable difference. I suspect some areas but I could spend a few thousand with no great outcome..

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## Marc

Phil, do you need to reduce noise from a motor, or is the motor just an experimental source of noise to achieve reduction from ambient noise? 
Reducing noise from a motor is easy. Good luck with ambient noise.

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## John2b

It would help a lot to know what the source of noise is that you are trying to abate, and is the requirement to block outside noise getting in or inside noise getting out. What is the barrier (wall, floor, ceiling, roof, door and window) construction and what penetrations are there through the barrier for ventilation and other services?

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## phild01

The noise I wish to minimise is variable like Woolworths home deliveries (their engine noise, basket crashing, dropped trolleys, reversing beeping), garbage collection, paper deliveries. a shift worker etc. I only have one wall and glass door (6.5 laminated with noise seals) of concern and *not* asking how to treat these areas. I just want to determine if the structure of the room is propagating most of the noise. Treating the wall and door will bring about a reduction but it may not be great so I want to have an idea what the other surfaces are doing.

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## Marc

Sounds like a case for moving to a quieter location to me ...  :Smilie:

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## phild01

Unfortunately Marc, those intrusions are atypical. Cul-de-sac and driveway serving several properties. Woolworths use noisy trucks and a delivery here is around 15 minutes up a steep driveway. Anyway this is not what I wish to go on about.

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## johnc

There is a lot you can read about sound. Double glazing makes a big difference so does hanging something like a blanket/rug off a wall. Anything outside that can act as a baffle such as plants or slats etc. You aren't so much blocking the sound a baffle just turns it into something else. Noise can pass through solid material but a series of slats with material behind them can block the noise. I don't know much about it other than masking noise in an office enviroment, in a shed and reducing noise transmission in the home

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## phild01

> There is a lot you can read about sound. Double glazing makes a big difference so does hanging something like a blanket/rug off a wall. Anything outside that can act as a baffle such as plants or slats etc. You aren't so much blocking the sound a baffle just turns it into something else. Noise can pass through solid material but a series of slats with material behind them can block the noise. I don't know much about it other than masking noise in an office enviroment, in a shed and reducing noise transmission in the home

  Yes, I know all of what can be done but is not my question. Sure you can make a wall resilient to sound penetration but the noise also travels in the structure of the room and other walls add to the problem. I would like to find what levels other surfaces are contributing. The offending wall might be at 60% and the total of remaining surfaces might be even greater or not much different, this is what I would like to discover. 
I am not sure your standard microphone could do this. Maybe there is a way of focusing the microphone but I really didn't want to go to this much trouble. Sort of thinking of using a long cardboard tube to my ear and directing it to each surface as a convenient way of quick analysis.

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## John2b

Phil, you are correct - there are several pathways that sound will enter your building, and all of them need to be addressed to minimise their contribution if that contribution is significant. Your situation sounds very similar to my place in the city where we were near a factory, a carpark and a busy street and a main road with pub and restaurants. The noise would start at 6am with the factory rubbish collection and diesel driven compaction which would go on for 20-30 minutes. Then the factory's clearers came with an army of vacuums and blowers to clear the footpaths. Next the vehicular traffic as the shift workers arrived, and then the neighbour who would blow back all the stuff blown over his way from the factory. Then there was the wave of Jim's Gardeners with an army for 2-stroke mowers, trimmers, blowers and suckers attending to each of the houses in our street. And every day there'd be someone using a chains-saw within earshot. I am amazed there were any trees left anywhere. Later the traffic would reverse and then the restaurants would crank up with noisy extraction fans and patrons arguing in the car park. It's probably what sent me nuts! 
Using an external noise source like you suggested is a standard method of investigation, but you need to identify all of the transmission paths so you are able to asses the contribution of each. 
Some of the things to think about**: 
Can you install a boundary acoustic barrier between your property and any of the noise sources? A barrier on the boundary needs to be at least a couple of metres high, solid, essentially airtight, and continuous to be effective. 
The room which you want to isolate needs to be effectively airtight (a 1% gap will let 90% of the noise through). That means all windows and doors need to seal shut. If water can seep through the gaps, so can sound energy. 
Double glazing is effective. For high frequency noise such as steam escaping it is best to have different thicknesses of glass, say 6mm and 10mm. For low frequency noise such as engine throbbing it is best to have a large gap between panes (100mm or more) and heavy (thick) glass. If you have existing timber framed windows it is often possible to add a second pane of glass to the existing frame, which is cheaper than replacing the entire window. This is commonly known as secondary glazing and we did several large windows this way. Where there was an existing double hung sash window, we installed a second sash window on the inside. Sealing of the sashes is critical and the window needs to be made specifically for noise reduction. Replacing panes with thick laminated glass may be all that's needed for small windows. 
External doors need to be solid and heavy. Wall vents and powerpoint penetrations can let sound through. If the external walls are stud walls, the studs will conduct external noise through the studs and noggins to the interior walls. In this case you can add an additional internal or external wall on its own studs not connected to the existing and put heavy insulation in between. 
The ceiling will also contribute significantly to noise intrusion. This can be improved by sarking under the cladding, heavy bulk insulation on the ceiling, and a building blanket type insulation layer over the bulk insulation. In worst cases a second ceiling can be hung on resilient mounts under the original. 
Low frequency noise may also be coupled through the ground, but is uncommon and more expensive to deal with as that noise source will couple into the whole building. The solution is the support the entire building on resilient mounts tuned for the purpose. 
As I mentioned above, an external noise generator is a standard way to measure sound intrusion, however it can be quite annoying during the process for neighbours. in the case of my own house, I took advantage of the everyday noise sources as test signals, i.e. the noises I was trying to eliminate. That means being prepared to do investigations while those random, external noises were being generated. 
Unfortunately our ears are not particularly discriminating and don't make good test devices for all noise sources and pathways. For leakage tests I have an open stethoscope which I can hold in close proximity to potential noise sources. For surfaces I have a mechanics' conduction stethoscope that can be held against surfaces that might be vibrating to see how much noise they are generating. With these two devices you can check every nook and cranny for leaks, flanking and conduction sources of noise.

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## johnc

I doubt there is a simple test, sound tends to bounce around off hard surfaces. It also finds its way through gaps and openings. It comes through solid walls, it is also highly variable so one engine for example could be inaudible inside while another might drive you nuts. Good luck, hopefully you find something that helps

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## Moondog55

If you want my old Tandy SPL metre I'm happy to post it to you. Rough as guts but it gives a broad indication

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## phild01

> Double glazing is effective. For high frequency noise such as steam escaping it is best to have different thicknesses of glass, say 6mm and 10mm. For low frequency noise such as engine throbbing it is best to have a large gap between panes (100mm or more) and heavy (thick) glass. If you have existing timber framed windows it is often possible to add a second pane of glass to the existing frame, which is cheaper than replacing the entire window. This is commonly known as secondary glazing and we did several large windows this way. Where there was an existing double hung sash window, we installed a second sash window on the inside. Sealing of the sashes is critical and the window needs to be made specifically for noise reduction. Replacing panes with thick laminated glass may be all that's needed for small windows.

  Yes this was the first thing I am considering. A secondary internal sliding door, either double glazed 4mm glass or a single 4mm tempered glass, being different to the main glass, also the 100mm gap. Next step would be the external facing wall with 16mm fyrchk and green glue. But this may all be somewhat futile if the ceiling and structure are emitting similar levels. Floor is slab on rock and there is a room above. Your points about air gaps are correct and the bedroom door may need to be solid core.
It is not as though there is constant noise, it's just that the area is so quiet that any noise is an issue for me, probably wouldn't concern 99% of others. Already playing white noise through the night but it is annoying knowing it's 'artificial' nature.

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## Moondog55

There are also rules about truck noise and perhaps a quiet email to Woolworths letting them know their truck is in need of a new muffler or word will be sent to the EPA and the RTA.
Subbies are loath to spend money on stuff like that so sometimes do need a little forcing/encouragement.
We have spent quite a bit on money here on insulation and noise abatement and now we are hearing all the bits we haven't done yet because everything matters and Harleys with no mufflers are damned loud

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## phild01

> Harleys with no mufflers are damned loud

  Too right, and the new Mustang is not far behind.

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## John2b

Sounds like you are on the right track. I would be inclined to have at least 6mm laminated glass in the secondary door, preferably thicker. Heavier glass will work much better on engine noises.  In the previous house which was on a road that was busy at shift end at 2am, I used 10mm glass on the french doors facing the road, and that worked well. Don't forget to silicone the doorframe to eliminate any airspaces. If there is a room above, I would think it unlikely that much sound will come down through the ceiling (unless there is a big window open in that room). That is an easy one to check with a conduction stethoscope with the probe held to a few different spots on the ceiling. A cardboard tube will work as an open stethoscope if you can come up with some sort of sealing cup over your ear, but won't give you any idea of the energy in a wall or ceiling panel because open stethoscopes pick up airborne noise, not structural noise. Mechanics' stethoscopes pickup structural noise and start around $20 at car parts stores. Make sure the ear-tips are sealing to exclude air-born noise from your ears when you are using either kind of stethoscope to evaluate sound ingress pathways.

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## phild01

> I would be inclined to have at least 6mm laminated glass in the secondary door, preferably thicker.

   I would choose that but the existing glass is already that so I have to use a different glass thickness. 
I once bought a cheap stethoscope but it never really worked but interested in what you say about a conduction stethoscope. Is that different to a doctor's one?

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## phild01

Is this of use then: https://www.repco.com.au/en/tools-eq...009/p/A9503440

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## Marc

Street traffic noise is perhaps the hardest to stop because it is so variable. I suppose that a sign stating delivery trucks will be shot at the end of the street, is not a consideration?
Bst solution was offered by JohnC. Deflection of sound is the best way. Not sure what a hedge of particle boards at an angle will do to your resale value though  :Smilie:

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## phild01

> Bst solution was offered by JohnC. Deflection of sound is the best way.

  Yes,meant to mention I had the idea to attempt that. But unfortunately I am elevated and it might need to be a 10m high keystone wall.

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## Moondog55

While vegetation isn't a 100% block, some mitigation will take place. Bamboo in pots perhaps. One of the fast growing tall varieties.
The mitigation panels along the freeway here are pretty good but they are tall and heavy, a bit too heavy to "Fall off the back of a truck and follow you home"

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## John2b

> I would choose that but the existing glass is already that so I have to use a different glass thickness.
> I once bought a cheap stethoscope but it never really worked but interested in what you say about a conduction stethoscope. Is that different to a doctor's one?

   It is a myth that the glass has to be a different thickness. For any thickness of glass there is a critical frequency where conduction peaks. The critical frequency range for glass in the 4-10mm range is not important in your described circumstances because your problem is not in that frequency range. If you already have a 10 door, you could use 6 for the secondary door, and used laminated glass, not toughened. I think 4mm will be too light add a useful amount of attenuation to what your existing 10mm door is giving. 
Doctors stethoscopes often have an open side and a conduction side, but the conduction side is different to a mechanics' stethoscope in that the diaphragm is designed for skin contact. In a mechanics' conduction stethoscope the diaphragm is in a small cavity. There is a rod or contact point connected to the diaphragm that you can touch onto a hard surface you want to listen to. The vibrations on the surface are conducted to the diaphragm, which acts like a loudspeaker to create sound that you can hear. The fancy way to do it if you want to spend at least 100 times as much, is to use an accelerometer (mechanical microphone) connected to a preamplifier, amplifier and loudspeaker with analysis software.  https://www.ebay.com.au/i/3329291138...SABEgLzp_D_BwE 
Edit: Yes the Repco one is the go. I've got three because they aren't all equal - some work better than others depending on what you are trying to do so I can pick the one that gives me the most information for the job in hand.

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## phild01

> I think 4mm will be too light add a useful amount of attenuation to what your existing 10mm door is giving.

  My existing door is 6.4mm not 10. I don't really want to have a heavy door to open and 10 might blow the budget. I would have thought that 4mm toughened would be effective keeping in mind the slide seals will be less than ideal at stopping sound.
I did see that ebay stetho. Do you think this type would be sensitive enough to pick up the very light sound emitted at such a small point of contact, after all it is plasterboard not metal.

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## John2b

Well if it were my problem to solve I would not bother with a 4mm door. I just don't think 4mm is heavy or stiff enough to add a useful amount of attenuation at low frequencies where you need it. I would not use toughened glass - the lamination layer in lamininated glass also helps, and the price difference is negligible. 
A mechanics' stethoscope will work, espcially if you eliminate anmbient noise on your eardrums with good sealing of the ear tips, so that you are listening only to the sound you are trying to isolate. Your own hearing acuity* and experience or ability to think analytically will be significant unknowns, and some stethoscopes seem to work better than others for a particular case. The strongest signals may be picked up when you put the probe under the span of a beam or joist, rather than in the middle of lightweight sheeting, because of the extra weight behind the contact point. A point that is fixed in three planes (e.g north-south / east-west / up-down) will conversely produce a weak signal. The same applies for a "high tech" accelerometer of course. 
*Whilst hearing ability generally decreases with age and occupational noise exposure, hearing acuity generally increases with age and experience, and often outweighs the effect of hearing loss. Think of it like developing a taste for wine - taste buds and smell generally decline with age, but appreciation of flavour increases with age despite the sensory loss.

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## phild01

> *Whilst hearing ability generally decreases with age and occupational noise exposure, hearing acuity generally increases with age and experience, and often outweighs the effect of hearing loss. Think of it like developing a taste for wine - taste buds and smell generally decline with age, but appreciation of flavour increases with age despite the sensory loss.

  Wish that was the case for me, half the time I need to rewind and use subtitles (but I do feel better when the subtitles miss it as well  :Smilie:  ).

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## John2b

> Wish that was the case for me, half the time I need to rewind and use subtitles (but I do feel better when the subtitles miss it as well  ).

   That is the case for most men over 40. Why men? Because men use drills and mow lawns. (To be sure women who have lived in noisy environments also suffer.) NIL (noise induced hearing loss) or more correctly EXPOSURE induced hearing loss causes a widening and deepening notch centred on ~3kHz. This is partly why different thicknesses of glass don't add much - they attenuate better in a frequency band where your hearing is already poor (and where there is heaps of attenuation already). 
Human hearing starts with the most sensitivity at ~3kHz and the species has evolved to take advantage of that in speech. The sibilant sounds that distinguish consonants (t, s, k, etc) rely heavily on this frequency range. When you suffer EIHL (exposure induced hearing loss) speech becomes difficult for the ear/brain to process. (Note: EIHL or NIL is unrelated to age hearing loss, which starts at 22kHz and drops about 2kHz per decade, thus not becoming a problem for speech comprehension until people are typically in their 90s.) When noise is added to the signal (e.g. Restaurants and pubs) it can become intractable. 
When a sound system or television is added into the mix, thing go from bad to worse. Added on to an artificial reproduction to start with, by far the most common approach to loudspeaker design almost always results in a room sound power deficit at ~3kHz, just where it cases the greatest problem with speech processing! There are some loudspeaker designers who understand this issue (very, very few world-wide unfortunately) and it is possible to buy loudspeakers that make speech easier to 'hear' in a room, and ease marital friction at the same time by reducing the incidence of "turn down the TV!" exclamations from the better half. 
Rest assured that whilst you have got older and wiser, you are better able to think about and appreciate what you can actually hear, even though you can't hear as much.

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## phild01

> A mechanics' stethoscope will work, espcially if you eliminate anmbient noise on your eardrums with good sealing of the ear tips, so that you are listening only to the sound you are trying to isolate.

  Well I got the mechanics stethoscope but the idea seems like a dud. Could not hear a thing with it maybe because it just ain't possible to isolate the far louder in room noise. Even a good set of hearing protection can't block out sound absolutely, I should have realised that I guess.

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## John2b

I often use a mechanics stethoscope for identifying noise sources, but I guess experience helps and I know what to expect and what to listen for. I've got four stethoscopes and one might work better for one application than another, so I can pick and choose. I originally bought one to listen to bearing noise in turntables (record players) which typically is extremely low level noise. I did use them for identifying noise ingress into our city unit, along with open stethoscopes for leakage around doors and windows. What was the louder noise in the room? Explain what you were trying to do and I might have some suggestions.

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