# Where to buy fiberglass duct board?



## dogma (Nov 5, 2017)

I'm considering building removable sound baffles for some of the equipment in my home shop/garage, probably 3 sided with an open top of ventilation.  In particular, the household vacuum system is probably taking about 15 mins off my life expectancy every time it cycles on.  I've done a bit of online research on materials and come to the conclusion that fiberglass or mineral wool are the only real options for a thin walled structure under 3" in thickness.  While there are rigid foams that claim sound dampening properties, I can't seem to find published NRC values, which makes me suspect the claims are dubious. 

The usual big box stores seem to carry both fiberglass and mineral wool.  However, it is unfaced and would need to be enclosed to prevent shedding fibers (supposedly, directly painting the surface will damage the should dampening properties -- I'm suspicious of this claim as well unless it is so loaded with paint the the interior air spaces are filled).  Full sized or even quarter sheets of foil lined fiberglass duct board seem to be hard to come by.  The big box stores don't carry it and its difficult to find online, other than part of a precut air return box.  The sole online HVAC specialty site I've identified that carries it quoted $195 for a full sheet with residential delivery (s&h was "only" $175 if picked up from a courier's terminal).

I'm honestly flabbergasted as this is such a commonly used material.  I would call an HVAC company but its a Sunday.  Assuming it isn't summoned by occult means, where is duct board normally purchased?  Local HVAC supply? Or do you have to go through an industrial supplier such as Granger, Graybar, etc.? (I just checked and Granger will do local pickup for quarter sheets but they have to order it in....)


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## pdentrem (Nov 5, 2017)

You can buy sound absorbing blankets that can either hang on the wall or wrap around the noise maker with the top/bottom open for breathing. 

https://www.mscdirect.com/browse/tn...-Barriers-Dampeners-Insulation?navid=12106348

I simple way to control sound is to make a few sound baffle/absorbers using Safe and Sound by Roxul. Using a 2x2 lumber make a frame that is cloth covered with the Roxul inside and place on the wall(s) to absorb the sound either directly or the reflected sound as it aproaches you. Alot cheaper than the premade stuff.

Here is the site that explains a fair bit on how they work. http://acousticsfreq.com/


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## ezduzit (Nov 5, 2017)

dogma said:


> ...I would call an HVAC company but its a Sunday...



Since I presume this problem has been an ongoing one I really don't see the urgency or necessity of obtaining these materials on a Sunday. And it seems you need to do some more research on reducing sound levels of noisy machinery before spending money on materials. 3-sided with open top isn't going to do much. Look at what others do to contain the noise from their dust collection systems, for example.


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## dogma (Nov 5, 2017)

ezduzit said:


> Since I presume this problem has been an ongoing one I really don't see the urgency or necessity of obtaining these materials on a Sunday. And it seems you need to do some more research on reducing sound levels of noisy machinery before spending money on materials. 3-sided with open top isn't going to do much. Look at what others do to contain the noise from their dust collection systems, for example.



This isn't an urgent project but it would be nice to have a clue before calling up businesses.

A hermetically sealed container isn't practical for my application (I'm not interesting in implementing a cooling system for a vacuum cleaner system). Nor am I ready to invest the effort to try to analyze the power spectrum and trying to engineer some sort of grating system to block the problematic frequencies.   I disagree with your assertion that an open top would largely negate sound dampening abilities.  As sound is essentially isotropically radiated, and reflects easily off many common surfaces, a large faction of the energy forming the wave form at the observes ear has reflected off multiple paths.  Extending a sound attenuating material vertically above the source may have several interactions with the portions of the wave that do not pass completely from the material (attenuated) or radiated directly towards the opening.  Sound energy is converted to heat as the wave as it reflected back and forth between surfaces of the attenuation material.  It should be possible to the tune it adjusting the vertical length before having to modify top or bottom ventilation apertures.  This is why the air ventilation system in your home is much quieter than putting your ear directly over the blower and the same principle that automotive mufflers are based on.


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## ezduzit (Nov 5, 2017)

dogma said:


> ...This is why the air ventilation system in your home is much quieter than putting your ear directly over the blower...



No, it is because the sound path is a labyrinth.


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## dogma (Nov 5, 2017)

pdentrem said:


> You can buy sound absorbing blankets that can either hang on the wall or wrap around the noise maker with the top/bottom open for breathing.
> 
> https://www.mscdirect.com/browse/tn...-Barriers-Dampeners-Insulation?navid=12106348
> 
> ...



Wow - those blankets have an impressively high NRC relative to the thickness.  By any chance have you ever tried to cut one to shape?

I was hoping to avoid the weight of having to create a frame to support the dampening material in order to make it easy to service the air compressor, vacuum, etc.  -- although that would allow fiberglass bats to be used too.  I suppose I could put it on castors so it could be rolled back. Hmm.


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## dogma (Nov 5, 2017)

ezduzit said:


> No, it is because the sound path is a labyrinth.



Steel isn't particularly absorptive of sound energy.  I suspect the internal routing in an automotive muffler is largely to increase the effective length by reflecting the sound waves many times so there are more interactions with the packing material.  As an example,  I believe HVAC duct mufflers are typically a straight tube to minimize the change in static pressure while typically not being heavily contained in total length.


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## Eddyde (Nov 5, 2017)

I have used these batts with great success: https://www.homedepot.com/p/Roxul-C...athing-Board-6-Piece-Pack-RXCB11224/206789748
I made a simple frame out of plywood and covered them with fabric. They are being used in the studios and live performance space of a local radio station (the black squares hanging on the walls).


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## ezduzit (Nov 5, 2017)

dogma said:


> ... I suspect...I believe...





dogma said:


> ...A hermetically sealed container isn't practical for my application (I'm not interesting in implementing a cooling system for a vacuum cleaner system). Nor am I ready to invest the effort to try to analyze the power spectrum and trying to engineer some sort of grating system to block the problematic frequencies.   I disagree with your assertion...



My previous career was in design engineering. One of the projects I worked on was an engine driven generator, in a sound "proof" box. My second career, as a boat builder, also has provided opportunities for using my experience in reducing noise levels from machinery spaces. 

My assertion is that you should research this a bit more before buying materials that won't do the job. 

Unsubscribed.


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## 7milesup (Nov 5, 2017)

We built a complete enclosure around the dust collector with plywood, which was then lined with an inner layer of sheetrock.  The sheetrock is held away from the outer plywood by sound isolation channels.  The exhaust air is ducted through a baffled homemade exhaust port.  The amount of sound deadening this enclosure creates is absolutely incredible.

Sound Proof channel


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## kd4gij (Nov 5, 2017)

I think this is what you are asking for.
https://www.homedepot.com/b/Building-Materials-Insulation-Rigid-Insulation/N-5yc1vZbaxx


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## ACHiPo (Nov 6, 2017)

Sounds like you want Owens Corning 703FRK rigid insulation used for ducts and acoustic treatment:
https://www.acoustimac.com/owens-corning-703-frk-6

Cut with a utility knife or hacksaw and tape together with good duct tape.


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