Reply To: Quieter Woodworking?
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First, it depends a bit on what hammer you use, a plastic head like Paul uses being the better choice at the high end.
In the sound booth example, the two layers are both decoupled from each other and from the frame of the house. The single leg channel is very flexible and none of the screws or other fasteners form a riuigid connection between the layers of the system. One set of screws connects the rchannnel to the frame, then you use a second set of screws to connect the drywall to the channel. The second isolated layer is the same, except that the second channel connects to the first channel and the second layer of drywall is also free floating with respect to both the frame of the house and to the first layer, so sound isn’t transmitted from layer to layer through the structure.
That leaves 4 air-mass couplings that have to be driven, each with an efficiency loss.
Low frequency sounds energy can’t drive through both layers of mass well and high frequency sound energy is mostly absorbed by the mass of drywall because drywall doesn’t have a natural resonance at high frequencies.
This is particularly so if you use one of the sound deadening drywalls, which is basically two thin layers of rock with an elastomeric isolator between them. That gains you about another 4-6 decibel attenuation, which doesn’t sound like a lot, but remember sound is measured on a log scale.
There are sound clips you can use for the First layer instead of channel, but I’ve never used them, so I can’t comment on ease of installation.
Think of it as trying to shout through concrete block or a cement wall. If you don’t actuall hit the wall, it’s going to be hard for the air to energize the mass.
I can’t emphasize enough that the secret to success to the system is in prevention of paths for sound to travel through cracks. That generally means limiting penetrations through the drywall, separating the penetrations between the layers, and caulking any cracks with a rubberized caulk, including the room perimeter. The goal is to make sure the drywall floats independent of the structure.
There are also sound baffles for ducts. Rather expensive, but they act like a silencer on a firearm and greatly reduce sound traveling through the heating system.
With the added sound insulation in the joists, you can achieve a sound attenuation in the 60 decibel range across the spectrum of sound. That turns a 90-100 decibel Sound ( think train horn or jet engine) into something in the 40-50 decibel range, which translates to a quiet room or a room with a hot air heating system.
That translates to a 80-90% reduction I sound energy, depending on how careful you are in the details.
There are APps for phones and iPads that can measure sound, and the room I’m sitting in measures in the mid 40’s. My basement shop, nearer the furnace has an ambient noise in the low 50’s with my high efficiency furnace fan running continuously. I. Not sure how accurate the APPs are on an absolute scale, but they do well on a relative basis.
And I ran a test last night with the app while I was chopping II 1/4”motrices into softwood. The iPad was set up about 3 feet from the bench at the tail vise end. Chopping directly on my bench, the APP measured 95 dB spikes. ( very short duration) Chopping on the cutting pad reduces the spikes about 5 dB. I didn’t take the vibration pads out from under the bench, but that gives additional sound reduction. Weatherstripping heavy doors ( they make fire doors with gypsum cores) helps also.
Sometime in the 60’s, the Nation Bureau of Standards wrote a tome on all this, which is available online. There are also works by people who build home theaters, that use the quiet board and more modern materials ( the quiet board costs about $50 a 4×8 panel, so it is about 3times what drywall costs. ) we used it as a quantifier you could show to a general partner of the law firm when a discussion on what quiet was came up.
Rather than go on endlessly, here’s a couple links that give options for different levels of attenuation.
First, the more modern one that is geared for home theaters.
http://www.dryco.ca/documents/hometheatre.pdf
And the NBS standards, which is what we used for attourney’s offices and theaters and radio station studios. It used more traditional materials.
http://digicoll.manoa.hawaii.edu/techreports/PDF/NBS77.pdf
The second is public domain government product, so if I knew how to host it here, it would be perfectly legal.
I like the idea of making chopping motrices a family affair…
- This reply was modified 6 years, 11 months ago by Larry Geib.
- This reply was modified 6 years, 11 months ago by Larry Geib.