Soundproofed grow cabinet

[kaljukajakas]

Hi,

this thread is for all who have grown tired of their noisy cabinet...

Mine was humming at a good 64 decibel (C-weighted) or the sound level of an average conversation. Pretty obvious at nighttime when it's quiet outside. The fan hung on bungee cords but that was about it when it came to noise insulation.

So I decided to add some sound insulation. The cabinet, BTW, is 24" by 44" by 6' for a 400W light.



The entire inside, the bottom, the top, the doors - everything is covered with 3/5" thick dense (almost like drywall, it will break instead of bending) mineral wool ceiling tiles:

http://www.amfceilings.co.uk/product.asp?productid=9&section=13

The tiles are attached with drywall screws and double-sided tape, so there's a small air gap between the insulation and the particle board. The 120 cfm fan has a two piece muffler: 16" of 4" inner diameter fiberglass pipe insulation inside the cabinet and a 24" long muffler just outside the cabinet (not visible in any pics) at a 90 deg. angle to the first one:




The tiles made it easy to lightproof the box as well as there's now a "lip" inside the cabinet:



Here's the air intake, the tubing takes a twisty path starting from the bottom of the cabinet:



Water will damage these tiles so the entire floor and 2" of the walls had to be completely waterproofed. I built a tray from 1/24" polystyrene sheet that does the job nicely and catches any runoff from pots when watering as well so no need for separate trays anymore. There's a rubber mat ontop of the polystyrene as my pots have rather flat bottoms.



The result: the cabinet is now at about 55 decibel or half as loud (decibels are logarithmic) as it was. The mufflers worked wonderfully for quieting the ducting outside the cabinet as well, from a very noticeable mechanical hum to a whispery breeze.

Any ideas as to further soundproof the cabinet? I've gone over it with the decibel meter and there doesn't seem to be any places where it's louder than the rest. The top used to be the loudest part as it's closest to the fan and ballast but I added a second layer of rockwool on the outside of the cabinet and covered that with a 24" by 44" piece of particle board and it's as quiet as the rest now. Even at night time, you have to get within foot or two from the cabinet before it becomes noticeable as a source of noise. Otherwise it sounds like backround noise and you have to concentrate to notice it.

 

[Guest]

How far are you away taking your sound measurements? 1 Meter?

First off I would go with insulated ducting. Most of the noise I would think comes from rushing air either in or out of the cab or the hood.

Maybe Dynamat? There is also a material for soundproofing recording studios. It's not foam though. (I know these threads are about silencing fans but it carries to quieting a cabinet.)

Used in this thread

http://www.icmag.com/ic/showthread.php?t=87456&highlight=fan+box

Another with underlayment

http://www.icmag.com/ic/showthread.php?t=34939&highlight=fan+box

 

[kaljukajakas]

The sound was measured from about 1 meter or 3 feet away. The C-weighted reading is much higher than the A-weighted (more human response). A-weighted was about 54 dB before and my meter shows pretty much nothing after the conversion since it only has a 50-130 dB range.

I've already applied dynamat strips to the fan body and I'll probably encase it in fiberglass as well but that won't do much good as the small oscillating fan makes nearly as much noise as the extractor fan. Doing the entire interior with dynamat would be very expensive, asphalt or SBS roofing is something I've considered but it would add quite a bit of weight to the doors. Should work well though! The ceiling tiles I used are pretty dense and have very good sound insulation properties (thick dense fiberglass matt with extra long fibers would be ideal), the roofing should hopefully cut out those low frequencies the tile and the particle board don't absorb. But it's not easy to absorb low frequencies without adding a lot of mass...

The air rushing into the cab is actually suprisingly quiet, the mechanical noise of the fans is much more noticeable. The entire cabinet hums a bit with the noise. Even when I suspend it from a bungee (it's sitting on cushy foam blocks at the moment)The ducting is not a problem yet. All of the ducting outside the cabinet is well insulated and there's no point in insulating the internal ducting due to the oscillating fan noise.

Anyway, I'm quite happy with it as it is now. But I'm sure one day the urge to tinker will strike again

 

[Guest]

BTW my desktop PC is 58 db c weighted at 1 meter.... just checked.

Totally understand where you're coming from. I think when people talk about "quiet" on these forums they're either delusional or deaf because silence isn't something I've ever witnessed in a grow.

I believe when you get to a certain point the job is to mask the noise....... ask freezerboy about that. lol.... People talk about about aquariums, fans etc. I have a fan running in the hall of my house and no one has ever said anything about the fan. It's a Stanley and it covers any sound from the grow. If anyone asks I'll say it's to move fireplace heat to the bedrooms etc.

 

[kaljukajakas]

50 dB - whereabouts I'm at now according to the A-weighting - is an average value for background noise, 40 db would probably be "quiet" for all intents and purposes if you live in an apartment in a city.

The ducting I have in my apartment is perfectly legitimate so that noise isn't a security issue, more of an annoyance, but a humming cabinet can look out of place. Right now you might notice it if you wander close and stand quietly.

 

[FreezerBoy]

The result: the cabinet is now at about 55 decibel or half as loud (decibels are logarithmic) as it was.

So, just how many points does it take to drop noise by Half? I've heard 3, I've heard 10 ...

 

[catman]

So, just how many points does it take to drop noise by Half? I've heard 3, I've heard 10 ...

A reduction of 3 dB is half the noise.

 

[kaljukajakas]

Wasn't it 3 dB half/twice the power and 10 dB half/twice the noise? Because the human ear response is also logarithmic.

 

[hyposomniac]

3dB is a doubling (or halving) of energy, 10dB is approximately a PERCEIVED doubling (or halving) of sound.


1 sone = 40 phons = the loudness of a 1kHz pure tone at 40dBSPL = 20 micropascals of pressure

http://www.phys.unsw.edu.au/jw/dB.html

What kind of meter are you guys using?

 

[kaljukajakas]

I got my cheap (but ok quality) sound meter from dealextreme:

http://www.dealextreme.com/details.dx/sku.3085

22.75$ + free shipping anywhere in the world is hard to beat

 

[kaljukajakas]

Some progress: I built an oscillating fan by mounting a 120mm computer fan with green LEDs (nightlight) on the base of an old oscillating centrifugal fan. The cabinet isn't much quieter overall but the sound blends in better as the old fan used to make a different noise depending on where it was pointed (I guess they are not meant to be mounted upside down). Takes a lot less power too while still moving air at about 30 cfm.

 

[Pipedream]

"3dB is a doubling (or halving) of energy, 10dB is approximately a PERCEIVED doubling (or halving) of sound."

Ahhhh, someone that stated it correctly. You have no idea how many techs I tried to drill this into. They could learn to do an RTA with a Audio Spectrum Analyzer and still miss this basic point.

Bravo! :smile:

 

[ZinksInk]

""3dB is a doubling (or halving) of energy, 10dB is approximately a PERCEIVED doubling (or halving) of sound."

I can expand on this a little for those that are interested.
As we know dB is a logarithmatic unit that describes a ratio.

Below I have given a partial explination as to how one arrives
at a number that expresses a ratio.

First its important to note

Depending on your unit of measurement you will use one of two
different formulas. This depends on Power [watts] or Voltage [Volts].

Sound pressure level is auctually measured in DBspl whos reference uses the formula for volts.

For Volts:
Adding +6db gives us 2x energy in volts, and adding +20db gives us 10x energy in volts.

Remeber this is a logarithmatic function so these relationships are not linear.

For Power which is measured in watts:
[Denoted by dbm]
Adding +3db gives you watts x 2
Adding +10db gives you watts x 10

Standard References:
0 dbv = 1V [semi pro unit of measure]
0 dbu = .775 volts [reference for pro gear]
0 dbm = .001 watts
0 DBspl = 20µ micropascals

To calculate DB select one of the two equasions below

Power = Log (M/R)x10 = DB
Voltage = Log (M/R)x20 = DB

where R = standard reference point or known starting volume
and M = Measure, a known or unknown output.

For example:

Measure AMP Reference
2watts--------|>-------4watts

db Gain = 3db

DB SPL is what we are most concerned with.
dBspl = 20 log (p1/p0)
where P0 and p1 are the sound pressures in dynes per square centimeter or newtons per square meter.

This equasion says that if 1 SPL is twice another, it is then 6db greater;
If it is 10 times another it is 20db greater.

As hyposomniac and pipedream pointed out a sound which is 3dB higher in level than another is barley perceived to be louder and a sound which is 10dB higher in lv is perceived to be about twice as loud.

0 db SPL is defined as the threshold of hearing of a young undamaged ear in the ears most sensitive range between 1kHz-4kHz It represents a pressure lv of .002 dynes/cm sq.

If we relate SPL to other various pressure levels we could make a chart as follows:

140 db .45 ACP Colt Pistol (25' away)
130 db 50 HP Siren (100 feet away)
120 db Threshold of Pain
110 db Typical recording studio control room Rock music 10 feet away
100 db Film Scoring 20 feet away
90 db Loud Classical Music / Heavy Street Trafic (5 ft)
80 db Cabin of Jet Aircraft (cruise configuration)
70 db
60 db Average Conversation (3ft away)
50 db Average suburban Home (night)
40 db Quiet Auditorium / Recording Studio
30 db Quiet Whisper (5ft away)
20 db Extremely Quiet Recording Studio
10 db Rustling of leaves
0 db Threshold of Hearing (youths, 1kHz to 4kHz)

This chart was taken from the Yamaha Sound Reinforcement Hand Book, Page 26

Let me know if i missed any thing.

 

[kaljukajakas]

A little update. I found this ~2mm thick aluminium backed bitumen sealing tape at a hardware store. I looks and feels alot like dynamat and is easy to apply. So I stuck a roll on my doors. Then at another hardware store I found some fiber reinforced mylar that has a 3mm thick closed cell foam backing.



I applied the stuff to my doors, they now have 4 layers:



And a layer of aluminium tape on the edges for a nice finish:



If I put my hand or ear to the doors they definitely vibrate and hum less, but of course since I applied the stuff only to the doors the overall sound level hasn't changed much. Have to get some more tape...

 

[Pipedream]

Keep in mind that as you build up those walls and doors, you are also insulating in the heat that would otherwise be lost to the outside. Do enough of it and the cooling load on your ventilation system will also increase.

 

[tequila_sunrise]

What kind of fan are you using? I just switched to a td100x and it is much quieter than my vortex. It is made of plastic, so it is lighter and also doesn't make as much noise.

 

[kaljukajakas]

I had a S&P td100 fan but switched to one of those inline metal fans that bulge to about 10" in the middle. It uses about as much power as S&P fans but has better pressure and is about as loud.