# Need help with soundproofing



## countryboy (Nov 27, 2009)

Ok. So I just moved a Central Electric Home Furnance to my brothers bedroom closet and its loud in the room. I was wondering how i could like decrease how loud it is so that he can watch tv and all that and not be bothered. i'm new to all this stuff, so i need a good easy way to go, and preferrably cheap because im not made out of money. I hadt to take out a peice of the closest frame to get the heater in so yea. If any 1 can help plz. i'm trying to improve the place i got until im able to get a beter place.


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## slownsteady (Nov 27, 2009)

A double layer of drywall will block a lot of sound. Also try to close any seams or gaps around the closet. I'm not sure about ventilation for an electric unit. You may have to provide some, but if you do, point the vent into a crawlspace or attic.


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## Nestor_Kelebay (Nov 27, 2009)

If I understand an electric furnace, you need to keep the door to the closet open in order to allow the heat to get into the bedroom.  If the electric furnace is making all the noise, and the closet door is open to allow the heat into the bedroom, then I must respectfully disagree with the previous advice about making the walls heavier.

Under normal circumstances, making the walls heavier by adding drywall would be a good gameplan to reduce noise transmission between rooms.  In this case, I presume the door to the closet is open to allow heat to get into the bedroom, and that wide open door pretty well nullifies any other measures you take, including the double drywall thickness on the walls.

Here's why Slownsteady's advice would normally be correct for reducing noise between rooms.  If there's anything you don't understand about the Mass Law, post your question and I'll try to explain it.

http://www.nrc-cnrc.gc.ca/eng/ibp/irc/bsi/85-sound-tranmission.html

The noise is almost certainly being caused by the housing of the electric furnace vibrating due to vibrations caused by the fan and motor inside it.  I would try wrapping foam rubber around the electric furnace to dampen the movement of the metal panels of the machine into compression and expansion of the foam, thereby converting one mechanical motion into another rather than have it produce sound waves.

Just pay a visit to your local landfill and seek out old couches or camping mattresses.  Remove the cushions from the couches and unzip them to liberate the foam rubber inside them.  Also keep your eye out for plywood or any other kind of relatively heavy material that can be used as a new outer surface for the heater.  Sandwich that foam rubber between the external panels of the electric furnace and the much heavier plywood or material you were able to obtain (even drywall), and hold evertything together with tape, rope, bungee cord, whatever.

Now, the vibrations of the light sheet metal panels will be dampened by the foam.  Whatever vibrating the much heavier (plywood or whatever) external panels do will be of much lower frequency, and therefore won't be as audible to human hearing.  The reason why is that if the panels are heavier, they have more inertia and simply cannot change their direction of motion as quickly as the much lighter sheet metal exterior panels of the electric furnace.  It's really the inertia of the new heavy external panels that you provide that results in the sound deadening.  Even if the foam rubber transmits the vibrations of the sheet metal panels through the foam rubber without any dampening, the heavier plywood or drywall panels have more inertia and cannot vibrate as quickly as the sheet metal could, and therefore cannot produce the higher tones that we perceive as being louder than lower frequency vibrations.  But, the foam rubber will dampen the vibrations of the sheet metal exterior of the electric furnace, and therefore the heavier plywood or drywall panels should not move at all (or very little) resulting in little sound being produced by the machine.

Taking advantage of mass (and therefore inertia) to prevent vibrations and therefore reduce noise is one of the basic principles used by vibrations and accoustics engineers to reduce noise and vibration problems in buildings.  The Mass Law of accoustics is explained in the link above.  In a nutshell it says that noise transmission through a wall, floor or ceiling will be reduced by 6 decibels (or to 1/4 of the previous sound energy level) by each doubling of the frequency of the noise OR each doubling of the mass of the wall, floor or ceiling (per square foot).  And, of course, the reason why is that a heavier wall, floor or ceiling simply can't vibrate at the higher frequencies that a lighter wall, floor or ceilng can because of inertia.  If anyone is interested in the Mass Law, post again and I'll explain more completely.

Also, anything you can do to improve the balance of the electric motor and fan impeller to eliminate those vibrations in the first place will help the most.


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## countryboy (Nov 27, 2009)

Well its so much as just the blower, or motor, im not sure exactly wat it is called. what i do know is that the old motor that blows the air into the vents went out and my dad had to get a new one. the new 1 is a 240V if i remember right motor and its like loud. i got my brothers door close and i can barely hear it in the room. i know it needs to have air to go into the blower so that it can work properly. im just not sure about using drywall because of me living in a trailor and the floor is already fallen threw in a couple of areas.


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## Ted White (Nov 30, 2009)

Not sure that laminating old foam to the furnace is the way to go. The foam won't actually damp anything.

If the sound is through conduction, you'll have to isolate the base and possibly use flex duct to make the initial connections to the existing rigid duct.

If the sound is airborne, then another layer of drywall will work well, presuming you can seal up flanking paths.

Ted White


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## kok328 (Nov 30, 2009)

Look at a product called "sound rock drywall".  It is designed to build soundproof rooms and has the equivalent sound efficiency of 8 layers of drywall in one application.
This helps meet STC standards.


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## Ted White (Nov 30, 2009)

There isn't a sheet of "soundproof drywall" made that equals eight sheets of standard drywall. That's a well known unsubstantiated piece of marketing hype, I'm afraid.

Much better from a performance and economical standpoint to use standard drywall. In this instance, you're not producing enough noise to warrant exotic damping.


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## Nestor_Kelebay (Nov 30, 2009)

> So I just moved a Central Electric Home Furnance to my brothers bedroom closet and its loud in the room.



Gentlemen:  The problem here is NOT how to prevent noise from traveling through a wall.  The problem is how to prevent noise from traveling through an open doorway.  


If this electric furnace is in a bedroom closet, then the closet door has to be open for the warm air from the furnace to get into the bedroom.  With the closet door open, then it doesn't matter how much of whatever you add on the closet walls, the electric heater, and hence the closet and the bedroom will still be noisy.  Putting extra drywall on the wall between the closet an the neighboring rooms will simply make those neighboring rooms quieter.  The wide open door to the bedroom will ensure the bedroom is just as noisy as before.

You could put a heavier door on the bedroom closet, but it would have to be closed to do any good, and that means the heat from the electric heater will stay in the closet.

The cause of the noise is that the electric motor and fan impeller are causing the machine to vibrate.  It's the vibrations of the exterior panels of the heater that are creating noise.  Those sheet metal or plastic panels are light in weight and don't have very much inertia, so they can change their direction of motion rapidly, and that means that they can produce higher pitch sounds that our ears are more sensitive to (that sound louder to us).

By wrapping the machine in foam rubber, the foam rubber will dampen the motion of the exterior panels.  That's cuz movement of the panel will require compression of the foam rubber, and so any movement of the panel will be converted into the  mechanical energy of compressing the foam, and that produces no noise.  Sound is a wave and it both reflects off surfaces and moves through materials.  Sound is absorbed in foam rubber, and so there's little energy left in the sound wave to move the plywood or drywall on the exterior of the heater.  Also, because those new outer surfaces are heavier, they have more inertia and cannot change their direction of motion rapidly.  The result is that the plywood or drywall will move very little (so the sound wave they produce will have a low amplitude or be "quiet") and can only reproduce lower pitch frequencies that our ears are less sensitive to (that seem quieter to us).  That is, the plywood or drywall on the heater will only produce a quiet low frequency hum.

This is the whole idea behind using heavy weights to dampen the vibrations of machinery.  If you have a machine that vibrates and causes both operator fatigue (cuz of the vibrations in the ground) and noise, you can mount it on a very heavy base, and then have that base supported on springs.  Now, in order for the machine to vibrate, the heavy base it's bolted to has to vibrate with it.  But, that heavy base has too much inertia to move and change direction (or "vibrate") at the frequency the machine could, and so the result is that the heavy base can only move at very low frequencies in response to the machine's vibration.  In order for the operator to feel vibrations in the ground, then the heavy base needs to move (in order to impart force through the springs into the ground).  But, that heavy base moves far less and far slower than the machine does, and so the operator of the machine feels almost no vibration through the ground.

Using mass to prevent vibrations is something that's done all the time, only this time we're using both a vibration absorbing material and mass to stop the vibrations of a machine causing noise.


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## Ted White (Nov 30, 2009)

I think this is an electric furnace, not heater. Still, the door would be a major flanking path as Nestor indicated.


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## Nestor_Kelebay (Nov 30, 2009)

What's the difference between an electric furnace and an electric heater?

Also, a wide open door way isn't a "flanking" path.  Flanking means to go AROUND something.  That's like calling a straight line between your starting point and ending point a "detour".

Sound is a wave and follows the same laws of physics as any other wave.  In order to stop the noise being made by the machine, you need to stop it's exterior surfaces from moving.  Without the exterior surfaces of that machine moving, there could be no sound waves created in the surrounding air.  The fact that the machine is noisy means that something must be causing pressure waves in the air surrounding the machine, and that requires that the exterior surfaces of the machine move.

My solution is to dampen the movement of the exterior surfaces of the machine.


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## Ted White (Nov 30, 2009)

Electric heater is small and heats a room. Electric furnace heats bigger area and had ducts. I guess my point being that if it's a furnace, he needs air to support combustion, but doesn't need the door open to get heat out.

Flanking refers to sound escaping a room. Doors, windows, ventilation, ceiling can lights, outlets would all be examples of flanking.

You'll find that stopping surface movement isn't possible. You can't make anthing infinately stiff, so better pursuing other means.

For isolating mechanical noise, see post #5 of this thread.


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## Nestor_Kelebay (Nov 30, 2009)

OK, cuz I remember seeing these commercials for "Aprilaire" electric furnaces, and what it was was heat lamps inside large diameter copper tubes.  The light from the lamp would heat the copper tubes, and air from a fan blew over the outside of those copper tubes and into the room.  And, they called that nonsense an electric furnace.

The way I look at it is that you can have a tempest in a teapot.  And that teapot floating in a pond.  As long as the exterior walls of the teapot don't move, there won't be any ripples in the pond.  And that's true regardless of what's going on inside the tea pot.


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## Ted White (Nov 30, 2009)

Not sure on the furnace. The OP will have to say what he's got going on there.

In practical terms, regardless of the mental imagery, you can't make something stiff enough so as not to re-create a sound wave.


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## countryboy (Nov 30, 2009)

I am not sure if every 1 is quite clear on a certain point of my problem. I am kind of getting lost. The electric Furnace, that I have in my brothers up goes into a duck ventilation. The ventilation runs in a straight line from one end of the trailer to the other. So The Heater is heating the Master bedroom, the bathroom, brothers bedroom, the spare bedroom, the living room, and the kitchen. I understand about putting up the plywood, drywall, and foam to help reduce the noise, and all that. but my question is that if i go with drywall, would a trailer that has been up for over 20+ years be able to support it? and like I said in an eariler post i had to take part of the frame to the closest out to make it fit right, so he doesnt have a door, and like 2 feet of frame left on his closest.


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## Nestor_Kelebay (Nov 30, 2009)

Countryboy:
So you're saying that the electric furnace occupies most of the closet (all but 2 feet of the closet space).  Is that right?

Ted:
     I don't think the goal is to have NO reproduced sound wave eminating from the external panels of the heater (since it's likely the bottom panel of the heater is gonna make noise and even the warm air ducts themselves will likely vibrate.  I think the goal is to reduce the movement of the exterior panels of the heater as much as practical to reduce the noise in the bedroom as much as is practical.


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## countryboy (Nov 30, 2009)

I took some pics I do not know exactly how much help it would be, but I figure that it might help a little.


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## countryboy (Nov 30, 2009)

Thats after I took the frame out. The front of the heater(the peice that has the little black thing that has something dealing with the manufactured. is where I have to take the panel off to fix it if it breaks down. like the top peice is where the blower is at. the bottom panel is where the thermadisks and where you connect the wiring from the circuit breaker to. The blower/fan/etc blows the air under the unit through the base into the duck system where it gets air to every room.


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## Nestor_Kelebay (Dec 1, 2009)

Does warm air also come out the top of that thing to heat the bedroom, or only out through the bottom into the ductwork?


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## countryboy (Dec 1, 2009)

just threw the bottom, like the pics, the black thing is where the panel comes off so i can get to the blower, and the little vent thing on the top is where the air filter is that sucks the air into the heater to go to the blower


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## Nestor_Kelebay (Dec 1, 2009)

Well, what we need to do is prevent those panels from vibrating.  The problem is that if you cover them with foam rubber, then you're not going to be able to easily get at the blower through the front panel.  Also, you can't cover that top panel (where air gets in to the blower).

If it were me, I'd try wrapping some sort of foam rubber around the side panels, putting plywood or drywall outside of that and holding everything together with bungee cord, rope, twine or whatever.

Doing anything to the closet walls will cut down the noise in the next room, but won't do anything for the bedroom.

You can't cover the top panel because that's the air intake for the electric furnace.

Following the game plan (foam rubber and then drywall or plywood on the outside) will help cut down the noise created by the panels you don't need to remove.  However human hearing isn't linear, so covering 4 or the 5 exposed sides WON'T reduce the noise level by 80 percent.  It'll reduce the noise level, but the percieved reduction will be much less than 80 percent.

If you can remove the blower from the electric furnace, you best option might be to remove the impeller and clean it.  If there is an accumulation of dirt on the impeller, the impeller will be heavier, and is likely to produce stronger vibrations than a clean impeller will.

So, there's not a heck of a lot I can recommend here.  You have a noisy machine, and you can't cover some of it without preventing air from getting into it.

Apart from building a heavy enclosure around it, I'm at a loss to find any truly effective way of cutting down the amount of noise it makes.  And, building a heavy enclosure around would require that the heat can get out to warm the bedroom, and that's going to allow noise out as well.

Hopefully someone else, perhaps Ted White, may think of something I haven't thought of.


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## Ted White (Dec 2, 2009)

I'd be inclined to seal the door first and see what happens. Thin 3/8" foam applied to the door stops. Try testing a big towel for that gap under the door. If the reduction is noticeable you can look at more thorough and permanent seals. If the door is hollow core, change out for solid core.

If the door sealing helps, the next level would be to apply drywall inside the closet. The added mass will likely be all that's needed.


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## Launchpad (Dec 2, 2009)

At this point, I'd be inclined to hand my bro a sleeping bag, a cup of coffee and tell him there's only six more weeks of winter (To keep his morale up). 

Sounds like you don't have a lot of money to dump into the project, and all of the ideas sound great so far. BUT, for cost effectivness- I like the idea of scrounging for old sofa cushions at the dump (has a survivalist element to it) and the solid core door sounds good but can tie up more cash. 

So, what about building an access wall where the door is? Cut the vent and foam pad the inside of the closet as best as possible. Don't know if it will work, it just sounds plausible in my small mind and I'm having a hard time keeping up with all the talk of "flanking manuevers" and tea kettles floating in a Zen like pond that make no sound vibrations if no one is there to hear it.


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## Nestor_Kelebay (Dec 4, 2009)

Ted White said:


> There isn't a sheet of "soundproof drywall" made that equals eight sheets of standard drywall. That's a well known unsubstantiated piece of marketing hype, I'm afraid.
> 
> Much better from a performance and economical standpoint to use standard drywall. In this instance, you're not producing enough noise to warrant exotic damping.



Ted:

     My understanding is that when they make drywall, they stir the gypsum slurry rapidly in order to introduce air bubbles into it to make it lighter.  And, in fact, when I cut drywall, I often see small voids in the gypsum core.

I've heard of "Fire Stop" drywall and now "Soundproof" drywall, and it seems to me that the blindingly obvious way to make both is to NOT stir the gypsum slurry, and thereby keep those air bubbles out of the gypsum core.  The result would be more gypsum between the fire and the studs and more mass between the noise and the listener.

Are you aware if this in fact how they make "Soundproof" and "Fire Stop" drywalls?  It would seem to me to be the simplest way to make drywall do both jobs better without changing the production process much.


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## Mikeman (Dec 18, 2009)

Easiest way to muffle the noise is to blanket the furnace or the closet with leaded foam of the type used to muffle engine compartments on boats. It is fire proof and very effective at muffling noise so long as the noise is not coming through the ducting from the motor which is often the case. 

Most of the sound is probably traveling through the door so it can be improved by adding a layer of sheetrock adhered with Green Glue which is designed for use with home theater setups to dampen noise being transmitted to other rooms of the house. 

Don't know about your furnace but variable speed fans make less noise on startup. After I replace my furnace with one using a variable speed motor the noise of it starting up was barely audible.


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## slownsteady (Dec 18, 2009)

Countryboy;

The short answer is you have to box it in, man. If it's sticking out into the room like the picture seems to show, you'll just be spinning your wheels. 

Turn off the stereo & the TV and really LISTEN to find out where the sound is coming from. Remove some of the panels to see if that reduces noise. If the panels are the culprit then Nestor's idea may help. If it's the motor buzzing, try cleaning it. If there is vibration throught the floor, you may be able to get some cushioning under it. You might even consider putting some support under the trailer if you need to build a wall.

Good luck on this one.


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## DavidLuke (Apr 22, 2010)

Ted, 

regarding this statement There isn't a sheet of "soundproof drywall" made that equals eight sheets of standard drywall. That's a well known unsubstantiated piece of marketing hype, I'm afraid.
I would say the soundproof drywall will be better than few layers of drywall if not 8.


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## Ted White (Apr 22, 2010)

That's what you'd say, eh?


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## Ted White (May 7, 2010)

Nestor_Kelebay said:


> Ted:
> 
> My understanding is that when they make drywall, they stir the gypsum slurry rapidly in order to introduce air bubbles into it to make it lighter.  And, in fact, when I cut drywall, I often see small voids in the gypsum core.
> 
> ...



Nestor my apologies for not seeing this post earlier. Im the past I have consulted with 3 of the 4 manufacturers of this factory-damped drywall. For years, drywall manufacturers have looked at ways to make drywall lighter. Incorporating air is one means. This happens to be counter to what we need for sound isolation, exactly as you have stated. In fact, if they pursued avenues to "mass-load" the board to make denser, sound isolation would improve furher.

Currently, the 5/8" TypeX fire-rated board you referenced is the best readily available board to start an isolation wall with. It's cheap and heavy.


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