Author Archives: Russ

Sound Dampening

The Goal:

I want to be able to play guitar, or do some only moderately loud woodworking tasks in the garage without waking up the wife in the bedroom, which is 1 floor up and 1 room over from the garage, but with a bunch of HVAC ducts in the garage ceiling.

First, a little nomenclature:

  • STC: Sound Transmission Class

    “The STC number is derived from sound attenuation values tested at sixteen standard frequencies from 125 Hz to 4000 Hz. … The measurement is accurate for speech sounds, but much less so for amplified music, mechanical equipment noise, transportation noise, or any sound with substantial low-frequency energy below 125 Hz.”

  • dB: decibel
    • dBA:

      “dB(A), dB(B), and dB(C) These symbols are often used to denote the use of different weighting filters, used to approximate the human ear’s response to sound, although the measurement is still in dB. These measurements usually refer to noise and noisome effects on humans and animals, and are in widespread use in the industry with regard to noise control issues, regulations and environmental standards. Other variations that may be seen are dBA or dBA. According to ANSI standards, the preferred usage is to write LA = x dB. Nevertheless, the units dBA and dB(A) are still commonly used as a shorthand for A-weighted measurements. Compare dBc, used in telecommunications.”

  • dB = 10 * log10( Power ratio ): Loudness Reference: http://www.sengpielaudio.com/calculator-levelchange.htm
  • Note: for x power ration = n dB, 1/x ratio = – n dB. So, for example -50dB of attenuation means 0.00001 th of the original power, or 1/32nd as “loud”.
  • You’ll often hear people (I’m certainly guilty) say “10 dB of attenuation”, which would be equivalent to “-10 dB of gain (amplification)”.
  • We get a sound level drop of 6 dB per doubling of distance ref
    dB Power Ratio How much louder it sounds Effective distance change (Inverse Square of Power)
    50 10^5 32x ~312x
    30 10^3 8x ~32x
    10 10^1 2x ~3x
    6 ~4 ~1.5x ~2x
    3 ~2 ~1.23x ~1.4x
    0 1 ~1x 1x
  • OITC
  • NIC: Noise Insulation Class. Similar to STC, but without modifications based on the reverberation time, the size of the room and the size of the test partition

Some Overview Stuff:

Some Product options:

  • resilient clips or resilient channel drywall
  • green glue: a sound dampening glue. From the website:

    “The rigidity and low damping of conventional adhesives works to worsen sound isolation by lowering the coincidence dip and raising low frequency resonances. Green Glue has a positive effect on sound isolation, making the performance difference between Green Glue and conven- tional adhesives considerable.”

  • batting/insulation
  • butyl rubber
  • Mass loaded Vinyl:
    • via isostore

      “Mass loaded vinyl tests show little to no gain when included in assemblies using resilient clips or resilient channel. The gains achieved with the MLV in basic walls, floors, and ceilings are created by resolving resonance issues and not from the actual mass of the MLV. The standalone rating is only relevant when the material is exposed, i.e. around pipes, duct, hung from fences, in curtains over windows or doors, etc.”

    • via isostore

      “The goal of wrapping pipes and ducts is to minimize surface vibration
      resonance. Installation is simple by cutting the MLV to fit, overlapping
      slightly, and taping the seam with a basic duct or foil tape. Both tape
      products can be purchased from any local hardware store.”

    • 1lb MLV ~= 4dB Attenuation.

Standard construction = 2×4 studs, insulation (pink stuff?) 1 sheet of 5/8″ drywall on each side

dBA STC Configuration/Product
33 Standard wall construction, minus insulation
38 40 Standard wall construction
45 Standard wall construction, w/ 2 sheets of 5/8″ drywall on each side
42 44-45 Standard wall construction, 1lb MLV on one side
47 52 Standard wall construction, 1 layer green glue between 2 sheets 5/8″ drywall one side
49 55 Standard wall construction, resilient channel assembly on 1 side
55 Double layer of 1/2″ drywall on each side, on staggered wood stud wall, batt insulation in wall
51 56 Standard wall construction, 1 layer green glue between 2 sheets 5/8″ drywall both sides
72 8″ concrete block wall, painted, with 1/2″ drywall on independent steel stud walls, each side, insulation in cavities

References: * http://www.greengluecompany.com/download/file/fid/817 * http://www.greengluecompany.com/test-data

Some Sound levels:

STC What can be heard
25 Normal speech can be understood quite easily and distinctly through wall
30 Loud speech can be understood fairly well, normal speech heard but not understood
35 Loud speech audible but not intelligible
40 Onset of “privacy”
42 Loud speech audible as a murmur
45 Loud speech not audible; 90% of statistical population not annoyed
50 Very loud sounds such as musical instruments or a stereo can be faintly heard; 99% of population not annoyed.
60+ Superior soundproofing; most sounds inaudible
  • Quiet bedroom at night, = 30 dB (SPL)
  • Conversational speech, 1 m = 60 dB (SPL)
  • Hammer stroke on brass tubing or steel plate at 1 m distance = 160 dBA
  • Hammer stroke in a smithy at 5 m distance (greatest level) = 150 dBA
  • Angle grinder outside at 1 m distance = 90 dBA
  • Hammer on Nail 104 dB
  • Hand Saw 80-90 dB
  • vacuum cleaner 70 dB
  • washing machine dishwaser 65 dB
  • http://physics.info/intensity/

Ok, so now some math:


 90dB Hand Saw (assume 1m?)
-20dB ~30ft = ~10m from workbench to bedroom = 1/10 distance
------ -------------------------------------------------------
 70dB ~30ft = ~10m from workbench to bedroom = 1/10 distance
-30dB "quiet bedroom"
------ -------------------------------------------------------
 40dB Attenuation needed in ceiling and walls

So, according to that math, I should already be have a “quiet bedroom”. Which means that either:

  • The sound is coupling much better into the HVAC ductwork than calculated (I haven’t been able to find any data on coupling to ductwork).
  • The garage is creating echos, or in other words, the 1/r^2 loss doesn’t apply because of the extra echos.
  • Most likely, because one of the walls had about a 3″ gap in the dry wall along the bottom edge, I wasn’t even getting the ~33dB attenuation from “Standard wall construction”.

Cost Estimates

2lb MLV $4.86/sqft
1lb MLV $2-$6.50/sqft
Green Glue (2 tubes per 4×8=32sqft) $1.25/sqft
OSB 7/16″ $0.47/sqft
Drywall 5/8″ $0.43/sqft

Dry Air in the Winter House

So, a while back we replaced an old furnace with a heat exchanger heated by a tankless hot water system. Becky noticed that the air seemed not quite as dry as with the old furnace.

My initial thought, was that the heat exchanger in the old furnace would get hotter, and therefore burn off more moisture, while the hot water powered solution would limit how much the heat exchanger would heat the air. However, during today’s hike, Peter pointed out that the moisture would presumably find its way to the rest of the house. Grrrrr.

The straight dope forum mostly blames the air expansion for the drop in humidity, and this affect alone can be extreme – see the psychrometric chart. For example, 30ºF at 10% RH which is heated to 70ºF will be at 2% RH. With the new system, we did tend to keep the house a little cooler. To continue the example, if we only heated the 30ºF at 10% RH air to 60ºF (probably an exaggerated delta), shows essentially the same 2% RH result on the psychrometric chart. So, I doubt that was the difference. Grr.

There is another potential cause described in a post by Allison Bailes PhD – dry outside air entering the house. According to the post, either a leaky house, or a leaky return vent on a furnace in an unconditioned space can be the culprit according to the article, and this article that describes how the cold dry air mixing with the interior air is the problem. While we likely have both of these problems, I doubt either changed in the transition to the newer heating system. Following the reasoning in the article, if your furnace runs more, with a leaky system, then the air will get drier. However, our newer system would typically run the blower (but not necessarily the tankless hot water) much longer than the older system, but provided moister home air. Hmmm.

I’m not sure I buy the mixing argument of the 2nd Dr Bailes article, since where did the air in the house come from – outside, and got heated up. So, wouldn’t the outside air actually be moister? Mike Rodgers makes a better case for the leaky house argument by saying that houses provide plenty of moister through occupant perspiration, showers, boiling water on the stove, etc; and that a leaky house essentially looses this moisture, to be replaced by dry winter air. This explanation I understand better. It still doesn’t explain what we’ve observed.

Maybe the years with the new system were just moister? The newer system is almost 8 years old at this point. So, doubtful.

Comments and thoughts welcome on FB or via email.

 

MultiCam Editing

A co-worker recently asked me about how to merge multiple camera shots of the same event into one video. I didn’t know the answer. Turns out to be not such a simple thing. However, it sounds like the available software is rapidly catching up with this feature/need.

So, I thought I’d share what I’ve found so far:

The best thing seems to be to output an SMPTE time code to an audio track on each camera. There is a free android app to do this, then I think you just wire the output of your phone to the various camera microphone inputs. This technique is called “jam coding”. Here is an article on the process. Then, there is software, like JamSync (~$250) to automatically sync things up. I think some of the fancier paid applications might have this built-in – not sure.

The advantage of Jam Syncing is that if the cameras are at different frame rates, or they turn off/on at multiple different times (i.e. camera A got lost power for 5 minutes while a battery was swapped, etc), then the software can often recover.
Otherwise the best thing seems to be syncing via the audio. Numerous blog posts say that doing it manually with the video yields worse results and is more time consuming than doing it with the waveforms in the audio.
The good news is that things like adobe premier ($700-800) (not elements) or final cut pro (the link has a bunch of audi footage) (mac only, $300) will do this for you. Also there are 3rd party tools, like plural eyes ($200) that supposedly do it faster and better.
There is a website, called switchcam that will do it, but it is pretty expensive to export your video back out of the website.
There are open source, multi platform non-linear editors (NLE’s) freely available, like openshot, nova cut (funded on kickstarted, but not available yet) and pitivi, but they don’t really seem to do the multi-cam thing well – yet (link also has more links on howto’s for various paid software packages). Here’s a good post on what open source NLE’s (mostly don’t) support multi cam.

3 Reasons to skip the Samsung 4.3 update

Ok, so there are lots of posts around the web about why you should not update your Samsung Galaxy/Note XX phone to 4.3, which Verizon pushed on me a few weeks ago.

  • Battery life now sucks.
  • Touchscreen response is much worse.
  • As of Android 4.3, USB Mass Storage device mode is no longer supported. You have to use some wierd Microsoft MTP or PTP – basically music device or picture device, that is slower, and requres extra software to be install on many (older or linux) computers.This part aparently has a a little bit of a technical explanaintion, relating to licensing fees on the FAT filesystem. Doesn’t matter. I still don’t like it.
  • If you ever want to go back to the stock (or older) versions, you can’t without a JTAG programmer (ie a piece of specialized hardware), or else you’ll “brick” your phone. And depending on the sources that you read, you might even “brick” your phone by rooting it (seems like it depends on if you change the OS version at the same time or not).