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Sound Proofing
3

Sound Proofing

Sound Proofing

(OP)
My 10-year-old granddaughter had a school project to build a containment that will completely block the sound from an I-phone (V5). Her father said to take in a bucket full of water, drop the phone in and it won't be heard. I thought that there must be a less destructive way to do it.

The sound from the closest thing we had to an I-phone (Galaxy S3) was 75 dba (with a background of 30 dba). The steps I took were
  • Build a small box out of 3/4 inch particle board. Top and bottom were two layers (1.5 inch) thick (second layer fit inside the sides). Sides were 3/4 inch thick. Inside of the box was 8" X 8" X 3". That cut the sound to 68 dba
  • Put high density foam pad on bottom and sides of box. Sound 65 dba.
  • Got a 16" X 24" X 8" plastic box and put high density foam mat in the bottom. Then a layer of minimally expanding spray foam, then the wooden box, finally filled the plastic box with spray foam. Sound 55 dba with the lid off.
  • Put a 10" X 10" high density foam mat on top of the wooden box then another mat over the inside of the plastic box and put the lid on. Sound 44 dba.
  • Put 2-1/2 inches of minimally expanding spray foam on top of the plastic box lid. Sound 35 dba.
I seem to be unable to get rid of the last 5 dba. People have paid me to design sound enclosures (for compressors), after this experience I don't think I'll take another of those jobs, I seem to suck at it.

I don't have instrumentation to evaluate sound frequency, just magnitude. I could not determine a specific part of the box that was leaking (the 5 dba over ambient was consistent wherever I held the meter (always about 6-inches from the box). Anyone have any ideas?

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

I'd create an enclosure with a vacuum (or as close to one as you can get). The sound will have a hard time making it out if there is no medium for transfer.

Maui

RE: Sound Proofing

2
What was your granddaughters idea?

RE: Sound Proofing

I assume weight is not an issue. I've had success in the past using Mass Loaded Vinyl (2 lbs spec) with sound absorbing foam on top of the vinyl (towards sound source) to insulate sound while the vinyl blocked. You are likely accomplishing the same task with the thick wood which wasn't an option for me. One of the biggest issues is the frequency. High frequencies are easy to block/insulate while lower frequencies can be very tricky. Do you have access to a good sound chamber? Our rule of thumb was that the sound chamber needed to be rated for 10 dba lower than the device being tested as to prevent the environment from not contributing. I wouldn't be surprised if you took your "soundbox" somewhere quieter and you got better results.

Good luck.

RE: Sound Proofing

(OP)
Her idea was cardboard and egg crates. She couldn't get the egg crates to stick to the cardboard and got frustrated.

Weight is an issue, she has to be able to carry it on the bus to school. Size is also an issue, it can't be bigger than 30 inches in any dimension (so size pushes a vacuum chamber out of consideration.

I've always relied on changes in material to filter different frequencies, but it isn't working to get the last 5 dba here.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

"so size pushes a vacuum chamber out of consideration"

http://en.wikipedia.org/wiki/Vacuum_flask

How much money do you want to spend Zdas? We use the opposite of what you're describing with our precision instruments - i.e. we put them in enclosures to keep sound out.

We've had some success with alternating layers of dampers and absorbers plus mass loaded vinyl or similar. However, we're concerned not just with audible noise but lower frequency vibration too.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Sound Proofing

Harbor freight has "vacuum pack" bags for clothes that are pretty cheap, use a shop vac to remove air. Would be interesting to see what happens if you just put your entire box in one.

Or if you want to bend the rules, is the sound coming from the ringer? Completely shielded box, no reception, no ring, no sound.

RE: Sound Proofing

My gut instinct says an approach might be to alternate high and low density layers. The "impedance bumps" (yes, yes, I know...) at the interfaces would make transmission of acoustic energy difficult.

RE: Sound Proofing

Kenat, that's exactly what I was thinking. Just buy one of those Thermos vacuum containers, and place the cell phone inside of it. It you want to be even more conservative, wrap the phone in some sound deadening material when you place it inside the thermos. It's easy, simply, cost effective, and should work surprisingly well. And she can easily carry it on the school bus.

Maui

RE: Sound Proofing

Is there anything in the "rules" to stop you adding a noise generator (transistor radio?) to the outside of the box to alter the ambient noise level and make the sound containment part of the task a few dB less demanding?

A.

RE: Sound Proofing

(OP)
Kenat and Maui,
My wife and granddaughter are on the way to the store with my son's i-phone to buy a thermos. I can't believe I wasted $100 and 20 hours work if this works (it wasn't a waste I spent the time with my granddaughter and that was fun).

I'll let you know how that works.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

Turn off the ringer? winky smile

RE: Sound Proofing

(OP)
Both a sound generator and turning off the ringer have been proposed by other groups and have been shot down by the teacher. She also rejected the bucket of water idea.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

The mass loaded foam works well on generator enclosures.

The commercial product usually comprises a ~1/8" thick sheet of PVC-ish plastic that is apparently compounded with lead dust or something similarly dense, bonded to 3/4" or more of polyurethane foam on both sides. It can be cut with a circular saw and bonded with contact cement. Soundown is one source. They don't usually give it away.

Foam/plywood/foam may work.
Foam/metal/foam may work better.
It isn't necessary that the mass layer be completely contiguous. A cardboard box, covered with a layer of flexible foam, with flat metal plates bonded to the faces, and with more flexible foam covering all, should work fairly well.

The self-expanding canned foam is probably too rigid when it sets up. Weatherstrip type foam is about right.

Mike Halloran
Pembroke Pines, FL, USA

RE: Sound Proofing

(OP)
We bought a Pelican waterproof plastic phone case (foam back), pulled the foam out of the wooden box, put the Pelican case in the wooden box, used a real iPhone (what a crappy default ringtone, it is only one frequency range, the Galaxy S3 cycled between very low and very high and was a challenge to mitigate), radiated sound is now zero (just the Pelican case by itself took the phone from 79 dba to 55 dba, at that point the wood, spray foam, and plastic seemed adequate.

We were looking for a vacuum bottle, but everything in this town had a bottle mouth that the phone (or an ice cube) would not fit through. I still want to try that. We put the phone in a FoodSaver jar (used paper towels to keep the phone off the walls) and sucked the most vacuum our FoodSaver could do (probably 15 inHg. Sound went from 79 dba to 65 dba.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

Take a roll of glass fibre loft insulation from Home Depot. Jam the phone right down into the centre of the roll. It just about meets the 30" dimension, and is low cost and more-or-less manageable on a bus.

RE: Sound Proofing

Increase the mass of the enclosure by using say, concrete. Make a small wood box as an inner concrete form. Make a larger wood box to be the outer concrete form. Size the boxes so that the concrete will be, say 2" or 3" thick on all sides and the bottom. Use Quikrete, or a similar packaged concrete mix, to fill the space between the to boxes. After the concrete sets leave both the inner and outer forms in place. Place the phone on a soft cushion, with the cushion sitting on a concrete slab (not a table or wood floor). Place the concrete box over the phone. Doubt if you will hear much.

Mass is the best sound attenuator, not many applications where mass may increased without practical limits, but this project sounds like one of them.

Good Luck

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Sound Proofing

In order of priority for A weighted noise problems

1) leakproof enclosure

2) physical isolation of vibration source from external enclosure

3) some acoustic damping in the cavity (ie foam or rockwool

4) suppress any thin panel resonances with bitumen sheet or equivalent

5) increase surface density (kg m-2) of enclosure

6) frequency analysis

But frankly if you've pulled >30 dBA out then you might as well jump to (6)

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Sound Proofing

(OP)
Thanks for the input everyone. The near perfect air seal on the Pelican case, coupled with the very good seal on the wooden box, and several inches of various foam products did the job. Didn't need any concrete or steel at all.

All of the sound work I've ever done has been to get big, low frequency point sources down to around 20 dba above ambient at 100 m. I never thought about exactly how difficult it is to get to zero dba at enclosure contact. That last 5 dba turns out to be a real challenge.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

Being able to hear 14 dB of attenuation cut in as you pumped air out of a FoodSaver jar while the phone was still ringing would make an epic bit of show and tell.

But showing that, with good engineering, you can meet a spec completely is a valuable lesson too.

So many teaching opportunities, so little time.......

Hope your grandaughter has had a good time with all this.

A.

RE: Sound Proofing

(OP)
We both had a blast trying to come up just a little more. When she showed it to her dad last night she was pretty proud of it. I was proud of her.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

(OP)
More like a lucky grandpa. I just don't get to see them as much as I want to. Having them with us last week was way fun.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

Damn, I wish I had that much time to spend with the kids on fun things like this as a parent!

RE: Sound Proofing

I wish my kid had had any interest in 'science fair' stuff.

Food sealer bag/vac storage bag was much more practical than my thermos solution, nice one 1 gibson & Zdas.

As Gregs list points out, still need to isolate direct mechanical transference for the vacuum to work. Again working the other way round but one vibration isolation approach we used to do was put a small microscope on a big block on 'concrete' then suspend that from some long bungee chord. Replicate this inside a good partial vacuum and I'd be interested to see how it works.

(Greg, I may have to print off your list and post to my cube. Sound & Vibration is one area I feel grossly deficient in given what I work on. Then again it's not clear some of our acoustic enclosure vendors are much better.)

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Sound Proofing

(OP)
I have found acoustic mitigation suppliers to be a pretty spotty lot. They'll all tell you that their gee-whiz technology is the best way to do it--all but one of them is wrong or lying.

For compressors we've found that mass and layers with changes in material are the key to getting to the sound down. In this project I've found that there is an enormous difference between "down" and "gone".

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Sound Proofing

I've usually found the machine vibration guys to be bearable, the architectural acoustics ones are all care and no responsibility. They'll recommend a treatment package for a room, but will not sign up to its performance.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Sound Proofing

If it's the ringtone you need to block a Faraday cage would work as effectively as the bucket of water and be less destructive.

RE: Sound Proofing

Surestick is right. Put it in a metal lunchbox and it won't get a signal thus won't ring.

RE: Sound Proofing

It might be interesting to put the phone inside a couple layers of ziplock bags and then inside a bucket of water.
non-destructive, aside from a little pressure on buttons.

Jay Maechtlen
http://www.laserpubs.com/techcomm

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