Design of white noise generator for bathroom??

[MichiganMark]

My wife doesn't like to hear bathroom sounds, and has asked me to mask them.  We have an ERV (energy recovery ventilation) system in our house, thus putting in a traditional bathroom fan isn't an option.  I've tried manufactured noise generators, but they can't be turned on with just an external switch.  Here's what I'm looking for:

1.  Can be permanently installed in the wall or in the ceiling.
2.  Generates white noise at sufficient volume to mask normal bathroom sounds.
3.  Comes on automatically when it receives power.  (None of the off-the-shelf noise generators come on automatically when they get power - you still have to hit a button on the units for them to come on.  I don't have enough knowledge of electronics to modify one of the commercial units so that it will come on automatically.)
4.  Ideally 120V, but 12V, 24V or other voltage is acceptable; I'll just add a step-down transformer if needed.  I plan to provide power using an everyday 120V motion-activated switch.
5.  I don't care about appearance or size - I'll build a box around it or put the unit in a box in the ceiling.

If someone knows of an existing unit that will work, excellent!  If someone wants to invent one, I think they would sell.  If someone knows of a simple design that I can build myself, that'll also work.

Above all, my wife thanks you greatly.  I'm hard-of-hearing, so bathroom sounds don't bother me!

[donlisms]

I'm not afraid to respond.  Harrumph.

You would probably be better off with pink noise than white noise. When measured in "real world" terms that are more realistic for the way we create and respond to sound, on a log scale, white noise gets louder as the frequency goes up.  Wimpy midrange, and no lows.

Pink noise, on the other hand, is nicely balance compared to most sounds.  It's how we tune sound systems in a room sometimes; more musically representative. 

The main point is that for audio masking to work, the frequency spectrum and the amplitudes of the source and the masking have to be at least in the same ballpark.

Now... I don't even want to speculate about the particular sounds you'd like to mask, but to do it well enough to actually work, you should probably start with spectral analysis of, eh, uh... the actual sounds.  Uhm.

Then you need to generate something like that spectrum at that amplitude.

The simple approach is just to shotgun it - a pink noise generator, an appropriate amp and speaker, a little experimenting, and hope for the best. 

It occurs to me that the levels will be lower and more representative at the, eh, uhm, listening end, after the source has been filtered and attenuated to some degree, rather than in the little room.  If that's an option at all.  In other words, less total volume from the masking device.

Uhm.

[shabaz]

A quick/ugly hack could be to use an MP3 player board. Admittedly over-the-top in terms of the underlying tech!, but cheap(ish) and easy to try different sounds etc. Or maybe just a bathroom/shower radio, tuned on AM to no station.

[MarkF]

When I built my house, I had the bathroom walls filled with fiberglass insulation.
The builder thought I was nuts until I told him why.  No more bathroom sounds.

It would mean tearing into the walls though...

Or.  Just turn on the exhaust fan.

[Geoff-AU]

Maybe reading this book would help the wife

https://en.m.wikipedia.org/wiki/Everyone_Poops

Then again, maybe OP really gives the thunderbox its name.

In either case it would be remiss of me not to say that you definitely want brown noise to mask it

We have a Dohm Classic (for assisting with sleep, not household peace at pooping time), these units are good for masking sounds, and they have a real fan in them not some awful speaker making a jarringly useless attempt at producing broad spectrum masking.

http://thedohm.com/

[Circlotron]

Or maybe just a bathroom/shower radio, tuned on AM to no station.

FM radio between stations has a more predictable and uniform hiss.

[SiliconWizard]

Really install just any audio system that can play digital audio at a couple Watts, you'll find hundreds of ready-made files with "white noise" content (which is not white, but we know what this is about), pick the one that your wife likes best, and call it a day. Designing something from scratch for this is not worth it.

[jfet]

A little humor, it might be easier to replace the wife

[Gyro]

Really install just any audio system that can play digital audio at a couple Watts, you'll find hundreds of ready-made files with "white noise" content (which is not white, but we know what this is about), pick the one that your wife likes best, and call it a day. Designing something from scratch for this is not worth it.

White (or better, pink) noise seems to be a very poor use of such technology. Why not something more relaxing like waves crashing on a beach or a trickling stream! There must be much better masking sounds than a 'constant' amplitude noise.

[BILLPOD]

Good Morning MichiganMark, All of my ideas have already been suggested by others, but thinking ahead, since you can't install a fan, how does your Wife handle the smells produced by the 'bathroom noises'.

[Gyro]

Mostly Hydrogen and Hydrogen Sulphur compounds so (hopefully silent!) combustion comes to mind. 

[donlisms]

Audio masking, one sound hiding another, works when the instantaneous amplitude and frequencies are in alignment.  The sounds can get confused. Otherwise, what you get is a fairly clear mix of both sounds.

The advantages of continuous pink noise are that it solves the time alignment problem, it covers all frequencies, and the amplitude can be easily set across the whole spectrum, rather than trying to deal with specifics of the spectral response. The continuity also makes it ignorable - it is transients that tend to attract your attention. You just kinda stop thinking about it.

Waves (as in oceans!) have a limited spectrum and somewhat random amplitude over time.

Rain has a nice continuity, unless they throw in thunder just to be cute and distract you. But it still has a very limited bandwidth.

There may be natural sound that work, but I think we would find they have characteristics quite similar to pink noise!

The example I like to give when I'm teaching sound engineers is that two guitars of similar character smush together; you can't tell which is playing what. But if you have a bass, as loud as you want, and a triangle, as gentle as you want, you can clearly hear it.

I do tend to think in this case, having the noise at the... listening end... would be more effective.

[magic]

noise source -> power amp -> speaker

The source could be as simple as LM324 configured as a cascade of four 10x noninverting amplifiers, the first input shorted to ground. This POS is noisy enough

[donlisms]

But... maybe it's white noise?  I suppose it could be approximately filtered, easily enough. 

[Perkele]

Build a separate toilet/bathroom.
The problem is not smell or the noises.

[reboots]

Why not a fan that's ducted back into the bathroom?

I once had to install a bathroom fan in a rental property. The tenants had requested the loudest fan possible, possibly for similar reasons. I could have budgeted for a high-end fan, but rated noise is inversely proportional to price. I had to use the cheapest, noisiest Broan-NuTone model. The tenants were pleased.

[Bud]

Maybe watching what to eat and practicing some changes in using the utilities can help mitigate the issue.
Is the concern with the noises experienced outside or inside the bathroom? Installing a noise masking tool inside the bathroom may not be efficient for the outside because of sound propagation attenuation through the wall.

[Retirednerd2020]

I suggest noise cancelling headphones, for her.

[pqass]

Claim plausible deniability.

[MichiganMark]

I'm getting great pleasure out of the suggestions I'm getting.  Here are a few responses:

1.  Get rid of the wife.  Probably not a good idea since she is a retired divorce attorney, and she'd end up with the house.  My wife has extremely good hearing and perfect pitch.  Joking aside, this is a real problem that I need to solve.  What ever solution I find, I'll probably need to apply it to three bathrooms.

2. Thanks for the comments I've received about white versus pink versus brown noise.  I have no expertise in acoustics.  Not to offend, and because I'm not afraid to use the common words for the sounds I'm trying to mask:  urine hitting the toilet when I'm standing up while urinating and farting.  Unfortunately, I don't have access to the equipment needed to measure the frequency of these two different sounds, and can only guess that they generally fall at either end of the audible sound spectrum.  If someone has this equipment, it would be helpful to me and probably entertaining for others to learn the general range of frequencies for these two sounds.  I searched the Internet, and didn't find any information.

3.  My wife and have always used separate bathrooms, which is one reason we've stayed married for 37 years.  When we renovated the house we're in now, we put in two master bathrooms.  I highly recommend it.

4. I'm not concerned about sound transmission through the bathroom walls.  The wall between the bath and bedroom excluding the doorway is only about 2 feet wide.  The adjoining spaces on the other walls are another bathroom and a laundry room. I actually considered insulating this segment of the wall with sound-absorbing mineral wool insulation, but didn't think it would have much effect in the end.  My bath has a hollow-core door, thus I might try to replace it with a solid-core door to better absorb the sound.

5.  I'm guessing that I'll need to find a dual solution:  sound masking and better sound dampening by installing solid-core doors. The second I can handle.  The first is much more challenging.

[MichiganMark]

You clearly have significant expertise in acoustics, and I very much appreciate your help.  I just put up a general response to everyone, and am hoping you can provide me with more technical information about using white versus pink versus brown noise to mask bathroom sounds.  As I see hear it, there are two nuisance sounds to mask:  urine hitting water or the toilet bowl, and flatulence.  Do you have any information about the frequencies of these two sounds, and thoughts about whether pink noise would mask both.

I enjoy getting both the fun and serious responses I'm getting to my post, but this really is a problem I need to solve.  I'm currently using a small portable white noise generator in my bathroom. Kt's ok, but requires me to turn it on manually each time I use the bathroom.

My wife wants to also have noise generators in two other bathrooms that guests use to ensure they aren't embarrassed if they generate nuisance bathroom sounds.  We don't want to give our guests instruction on how to use little bathroom noise generators, thus a noise generator that comes on automatically would be the best solution.  I'm very good with electrical circuitry, and want to put a noise generator in the ceiling controlled by a motion detector set to run for 10 to 15 minutes.
,
Also, based on what you know, how much better sound absorption is there with a solid-core door versus a hollow door?

I've found several schematics on the Internet for building low-voltage white noise generators, but they don't provide me with much information about the frequency or decibels of the sound they create.  There are also hobby kits available on the Internet for low cost, but again they don't identify the sound generated.

[IDEngineer]

Masking sound (really, any signal) almost always has to be at the receiving end. Just because it masks what the transmitter (you) can hear does NOT mean it masks what a receiver (she) can hear. There are too many secondary paths, acoustic and conducted and otherwise. Two sound sources at the same point rarely mask each other, as has been noted herein.

If this is really an issue, you're probably headed for a combination of suppression (via absorptive insulation in the walls and ceiling) and sound generators *outside* the bathroom, between you and the listener.

If you're truly serious, the best approach to starting the soundproofing process is to build the walls like a sound studio. Presume an existing wall with studs on 16in centers. You add another set of studs also on 16in centers but offset from the existing studs, and also offset by an inch or so along the width axis of the wall. This is often done using 2x6's for the floor and ceiling plates, with each set of 2x4's flush to opposite sides of the 2x6's. Then one side's sheetrock lays on one set of studs, and the other side of sheetrock lies on the other set of studs. This removes the conductive path between the two "transducers" (layers of sheetrock). We've done this with TV rooms in our houses and it's amazing how much attenuation you can achieve.

It is possible to retrofit this into existing walls but obviously you'll lose an inch or so of floorspace on each wall.

[magic]

As far as I understand, the purpose of the system is to be heard by the wife inside, so that she thinks that her farts aren't heard outside.

Just make it loud inside, no point overengineering any further

[MichiganMark]

Thanks for the input.  When the house was being renovated and the wall was open, I considered this, and would have used sound-absorbing mineral wool.  I think most of the sound transmission is through the door.  I'll probably replace the bathroom door, but don't think that will be enough for my wife's very sensitive ears.

[MarkF]

Go old school.
Build an 'out house' in the back yard with a half moon cut in the door.