Booth Ventilation: REALITY CHECK

Greetings all, I’ve learned a lot pouring over this site. Unfortunately, I didn’t discover it until I built my booth and ran out of oxygen. (yes, the dreaded ventilation issue). I’m posting this to get my thoughts straight and to put it out there in case anyone with more experience can warn me that I’ve completely lost my mind (thanks in advance) I’ve converted the rear of a walk-in closet into a voiceover booth for me and my Neumann. It’s been acoustically treated but not soundproofed (acceptably quiet for my needs). There are no windows or central HVAC ducts to tap into. AND we live in a condo, so I can only punch through one wall. So I’m forced to do basic fan intake/exhaust ports into the adjacent bedroom (not ideal -- but it is what it is: adding a snorkel to a woodshed) The booth is only 198 cubic feet. Rod Gervais mentioned an airflow of 15 cfm per person. Another site recommended a minimum room air change per hour of 12 (ACH). 198 x 12 = 2376 2376 ÷ 60min = 39.6 It seems a 40 cfm fan would do the trick. I ordered a Silenx 120mm computer case fan rated at 90cfm with a supposed dba of 18. I’m skeptical of these numbers, but I plan to power it at 7V instead of 12V, so I’m hoping it works out. I’m also, based on the wise words of Mr. Gervais, going to use this sole fan as an EXHAUST, with a PASSIVE intake vent. I plan to mount the fan on neoprene pads. Both vents would be routed through home-made, lined mdf ducts. (Miniature versions of what most of you guys are doing -- remember the cubic footage!) These would be very short runs of only a foot or two -- so I would be constructing them only to dampen noise leakage from outside. I’m imagining them as duct muffler boxes of the kind I’ve seen on this site -- with dual internal opposing baffles -- just enough to absorb the spill. The exhaust will be mounted HIGH, and the intake low -- about five feet apart on the same wall (max in my little room). I’m still fishing for the exact dimensions and design of the baffle boxes. AND I’d prefer not to use mineral wool or fiberglass. I don’t want to add a filter to the system and diminish airflow. I have a lot of Auralex Foam left over -- it seems like I could use that in some way inside the muffler boxes. If I flipped the pointy-triangle stuff over and stapled it flat, it would be more compressed and less absorbent, but it would still be pretty good - wouldn’t it? Like I said -- I’m posting this as a Hail-Mary Reality-Check before I start hacking drywall. So any general advice or admonitions are greatly appreciated. I attach the pix out of superstition - maybe someone will think of SOMETHING I've overlooked... The red numbers were for another purpose (trying to determine vent locations)

These fans are designed to move air through computer cases - they are not room fans, and will not operate properly as room fans - I.E.: - you will never pull that much fresh air (not anywhere near to it) through your room with that, Damn, if you could - they would be putting all of the commercial fan companies out of business - Try checking out Dayton , yu need a real fan that will overcome the static pressure issues this will include. Rod

Thanks, Rod. I kept reading about case fans in small booths -- I guesss it's a crock. Obviously this fan question determines the design of everything else. That's my first major concern now -- what fan do I get?

got to Broan Fans and look for an in-line fan that's capable of producing your 90 cfm at 1" of static pressure........ Rod

Many thanks for the tip, Rod. Checking out the broans now. I'm kind of new to this static pressure concept, but you said 1" and that seems to be off the charts -- did you mean 0.1"? This is the one I'm thinking about: http://www.drillspot.com/products/47101 ... Losone_Fan I'm also new to noise ratings in sones rather than dba. This one's rated at 0.7 -- I know they're different animals but is that comparable to (what?) 28 to 30 dba? Just trying to anticipate how rigorous my baffling box design will need to be -- I'd love to have the sucker running even while recording. Thanks again

Recieved my new inline fan and deliberating installation. The fan is for exhaust. The intake would be passive. As short runs and low fan speed seem to be reccommended I am considering building plenum boxes for both ends. Or else, wondering if anyone's tried the Suncourt Duct Mufflers. 1. Can anyone point me to a post with a good DIY plenum design? (I've been searching the site) 2. The "muffler" on the passive intake -- should I design that differently from the one on the fan/exhaust end? As it exists mainly to dampen noise from neighboring room. 3. What is the most absorbtive acoutical lining material (and if fiberglass, do I need filters? Is basic duct board good enough?) 5. I'm worried about transmitting fan vibration noise through metal ducts in short runs. Is it enough to buffer/warp with neoprene or foam wherever ducts meet walls or ceiling brackets? Thanks in advance. JR

Jack Russell wrote:

I'm also new to noise ratings in sones rather than dba. This one's rated at 0.7 -- I know they're different animals but is that comparable to (what?) 28 to 30 dba?

OK - seeing as DB ratings are in sound pressure levels- but have really little to do with how loud sounds appear to be to a human being....... Phons were developed to create an equation relating to the volume perceived by the human ear. Thus - A tone is "X" phons if it sounds as loud as a 1000 Hertz sine wave of "X" decibles or dB. 40 phons equals 40dB at 1000 Hz. Phons are logrithmic and thus 50 phons are twice as loud as 40 phons. Sones (on the other hand) are a method of taking this from the log to linear - which is much easier for most people to understand. The calculation is "a tone of x phons is 2(x-40)/10 sones. So one sone is 1000 Hz @ 40dB 2 sones are 1000 Hz @ 50 dB 3 sones are 1000 Hz @ 60 dB 4 sones are 1000 Hz @ 70 dB or the equivilent perceived volumes for different frequencies. To adjust for this - you have to use the Fletcher/Munson Curves. Just so you understand - on the Fletcher/Munson curves - a 60Hz signal @ 69dB sounds slightly less loud than a 1000 Hz signal @ 40dB. So if you were buying a piece of equipment with a frequency range of 60Hz and it measured (with your radio shack meter) 60dB - then its sone rating would be around .97 sones. And, if the equipment was running in the frequency range of 5K @ 40 dB (measured) then it would be almost 50 phons and would be roughly 1.8 sones. So all if all 3 frequencies were measure @ 40dB - the 1K signal would be the base - then the 60 hZ signal is almost at the threshold of a human's ability to hear - and the 5 k signal would seem almost tqice as loud. I hope that helped,.......... Oh - one other thing - that .7 sones is measured @ 5' from the unit - - @10' you should not be able to really hear it witout fighting to - and with masking probably not at all. Rod

Jack Russell wrote:

Recieved my new inline fan and deliberating installation.

Kewl

The fan is for exhaust. The intake would be passive.

Good choise - that puts the fan sending it's noise away from the room.

As short runs and low fan speed seem to be reccommended I am considering building plenum boxes for both ends. Or else, wondering if anyone's tried the Suncourt Duct Mufflers.

Well - I went and looked at their site - and I left them a message letting them kow that I was dissapointed to see them deliberately misleading the public. They claim a 3dB reduction is a cutting in 1/2 of the perceived violume - and this is a lie. 3dB is a doubling of wattage - 6 db is a doubling of sound pressure - 10 dB is a doubling of perceived amplitude (on a weighted scale). I let them know I would blacklist their site and product with anyone who inquired about them unless (until) they cleaned up their act. Including (of course) the person whose ijnquiry of their product sent me there in the first place. So no - I wold not recommend them for your project. what exactly is this going to be dumping into? What are the noise levels there (ambient)? It is very possible that you can just make the duct lined (or use super duct) with at least 2 90 degree bends - and not have any noise problems at all in your room with the fan running full.

3. What is the most absorbtive acoutical lining material (and if fiberglass, do I need filters? Is basic duct board good enough?)

Polymer coated duct lining is recommended so as to not allow fibers to become loose over time.

5. I'm worried about transmitting fan vibration noise through metal ducts in short runs. Is it enough to buffer/warp with neoprene or foam wherever ducts meet walls or ceiling brackets?

Nope - if you use metal ducts - then use fully llined ducts. Where the ducts meet walls - nothing special will be required if you use duct board - and I would recommend a canvas boot just before the wall to decouple the transmitting duct from the receiving duct. There is almost no fan noise with this duct - I would not be overly concerned with fan noise itself - once again - ambient noise is my biggest concern here. Rod