DIY Home Improvement, Remodeling & Repair Forum

DIY Home Improvement, Remodeling & Repair Forum (
-   General Home Improvement Discussion (
-   -   Need help with soundproofing (

countryboy 11-26-2009 10:56 PM

Need help with soundproofing
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.

slownsteady 11-27-2009 09:12 AM

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.

Nestor_Kelebay 11-27-2009 10:31 AM

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.

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.

countryboy 11-27-2009 06:23 PM

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.

Ted White 11-30-2009 09:10 AM

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

kok328 11-30-2009 09:38 AM

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.

Ted White 11-30-2009 09:45 AM

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.

Nestor_Kelebay 11-30-2009 10:08 AM


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.

Ted White 11-30-2009 10:45 AM

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

Nestor_Kelebay 11-30-2009 12:58 PM

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.

All times are GMT -6. The time now is 09:19 PM.