I just installed a new dishwasher, and its a little noisier than I had hoped. The motor itself is pretty quiet, it's just the sound of water splashing around in the plastic tub that I'd like to address. It's not installed with its back to a real wall, it's built into sort of a peninsula. There's just a 1/4" panel that covers the back side, and there's not a lot of space in there.
I was thinking about using a few scraps of Dynamat on the back of the tub to quiet it down. Is that the best thing to use, or is there a cheaper, home store grade of self adhesive insulation that I don't know about?
02Pilot
SuperDork
5/20/19 3:10 p.m.
If it's sloshing and not vibration, I'd think you'd have better results with a sheet of mass-loaded vinyl.
Good old fashioned fiberglass works great. Dynamat is more or less a viscous weight-adding technique that changes the resonance frequency of the panel and converts some of the sound energy to heat. It works so-so on high frequencies. It is also very expensive. Fiberglass or something like grey carpet padding works by the millions of fibers doing the same basic thing. They absorb and diffuse tiny bits of sound energy as friction/heat.
The fibrous types of things tend to work better on high frequencies. That is why when you go into a sound booth, it is lined with foam or fiber stuff, and it is why the room "sounds" like it is closing in on your ears. It destroys high frequencies. I think you're better off using a fibrous mat instead of dynamat.
Killing high frequencies = diffusion. Killing low frequencies = restriction. Bass will pass through things more easily because it just moves the panel sympathetically. That's why when you hear a boom-boom car go by your living room, you can't hear the voices or the music, just the boom. Wimpy materials like foam and fibers don't stop bass. That is why dynamat works so well with bass. It uses its viscous properties to prevent panels from moving sympathetically with the sound energy. Treble on the other hand (like the spraying water in your machine) doesn't respond well to dynamat. There isn't much movement of the panel with treble, so dynamat won't shine here. What you need is something fibrous to diffuse the sound
When I installed my used dishwasher, it didn't come with the blanket. On the way home I picked up some fiberglass that had blown off a double-wide in transit and made my own blanket.
In reply to 02Pilot and Curtis:
Very interesting. I'm learning stuff here! I wish I had grabbed the blanket off of the old machine before they hauled it away.
I also want to make sure that I use something that can handle 200+ degree heat from the high temp drying feature, and not absorb any moisture from condensation.
Curtis said:
The fibrous types of things tend to work better on high frequencies.
This ^^
If not fiberglass, some sort of batt-type material. The blankey that came with my dishwasher was polyester fiber. Fiberglass will likely do a better job, but itches like crazy (don't get it on your hootus).
02Pilot
SuperDork
5/20/19 4:10 p.m.
In reply to Woody :
That stuff looks like it might be decent for stuffing behind and under the rear seat in my 2002 to kill some road noise. Let us know how it works out - if it's effective I may have to order a couple rolls.
slefain
PowerDork
5/20/19 4:12 p.m.
This is timely. Our newly renovated house has the dishwasher in the kitchen island. If the dishwasher ends up being too loud to watch TV in the other side of the room, I'm going to line the cabinet with sound deadener. The countertops are all granite, which I hope cuts down on some of the noise.
i was just gonna ask what happened to the blanket on your dishwasher...
Our new one did not come with a blanket so I transferred it from one to the other. Between a stainless tub with its own sound deadener and the blanket, the machine is quiet as a churchmouse.
JakeOG
New Reader
5/20/19 5:02 p.m.
I put a carpet scrap in during the remodel. Works well. Cost nothing.
A lot of dishwashers don't come with rear insulation, A) because they can get another inch of depth to the tub, and B) most dishwashers install toward a wall.
Easy to add though.
I've never known condensation to be an issue. Many of the factory blankets are a mixture of whatever shreds of fabric they can get cheap including cotton, poly, acrylic, etc.
The lowest melting temp of those materials is the acrylic which doesn't melt until 320F, then the next is poly which is nearly 500F. Cotton is IFR, so it will neither melt nor flame.
Woody said:
In reply to 02Pilot and Curtis:
Very interesting. I'm learning stuff here!
My music degree included a heavy concentration on physics. It fascinates me.
In reply to Woody :
You really should post up a .wav file of the noise before and after. 
In reply to Curtis :
If the noise disturbs you, you need to change it! If you just bought it, you can return it. Because if it irritates you from the beginning what will be in the future? I had such a situation with [my canoe paddle].
SVreX
MegaDork
3/13/20 7:39 p.m.
In reply to Woody :
Not done. Insulate that bottom section too.
I just installed a new dishwasher in my house which is so quiet we can't tell when it is running. I noticed the effort they put into the insulation- the toe kick was insulted, the removeable panels, even the electrical knockouts.
Fill EVERY gap.
In reply to SVreX :
Well...that was a long time ago and it's all closed up now. Besides, I ran out of material. But it's so quiet that I can't even tell that it's on when I'm sitting in the same room.
On a related note, I hate this berkeleying dishwasher. The controls are on a vertical surface that is even with the edge of the countertop, and every time you gently brush against it, it turns itself on. Like a dozen times per day, every day.
My wife says that hate is a very strong word, but I hate this berkeleying dishwasher.
so, obviously this is a canoeing... just a matter of time, and yes I've added them to my 'watchlist'...
but, it's intersting to see how these threads that get dragged up tend to get a "oh yeah, this is how that worked out" feedback, lessons learned thing. So, in a way, the jokes on them... in a way, they're actually making this place better. even if it is a frelling pain in rear to trackdown and take care of.
