Vent ideas? critique please.

I just had a pretty good gypsum assembly installed for my basement room and while I knew this would be an issue ahead of time, I am actually kinda happy with this weird, metallic echo that I get out of the 5 vents protruding through. I'm intrigued with using it as a makeshift natural reverb chamber, I've tried it with some vocals and acoustic guitar and really have enjoyed the results I get. The obvious problem though is that I won't want EVERYTHING to sound like it was recorded in a boiler room (just SOME :)) First, once the room is finished, I'm going to see how using homemade rigid fiberglass absorbers will affect the rooms sound (which has an astounding, full two seconds of decay presently!) to see how much of it is just the standing waves and the bare drywall. However, if these vents are still sounding offensive, can anyone think of some sort of removable covering to put over them to block most (if not perhaps all) of the echoing that travels through these vents and interfering with some of my more sensitive mics? I thought about building some sort of mini version of the standard rigid fiberglass broadband absorbers that people recommend making so often and making sure it is mounted far enough from the vent to encourage good airflow while blocking most of the direct sound exiting the vents. Would this be very effective? I know for a fact that there are no lower frequencies making their way through there to any great degree , but the upper register definitely needs work. I'm particularly worried about my overhead drum mics which will have to be pretty close to the ceiling since I only have about 7' 2" (2.18meters) to work with. I also don't really want to bother covering the vents up when I record as a couple hours could go by before I unseal them. I'm hoping I can make a difference by taking care of the direct sound coming out of the vents, while not worrying about the weaker reflections that may escape and be harder to hear. Thanks in advance for any suggestions on how to minimize this particular problem or if my idea would work very well. Overall there are 5 vents, 3 on the ceiling evenly spaced across the long way of the room... and two air returns on the floor, on same wall, though on opposite ends lengthwise. Remember that I'm wanting to have the ability to fairly easily pull down/put back up whatever assembly I build to utilize the natural reverb chamber that has been created and dampen the effect when I don't need it. I'm going to have all the electricity and carpet installed by the end of next week and am fast approaching "room treatment" and "recording" time! Super excited!!

Where is your build thread?

I thought about building some sort of mini version of the standard rigid fiberglass broadband absorbers that people recommend making so often and making sure it is mounted far enough from the vent to encourage good airflow while blocking most of the direct sound exiting the vents.

I don't think that will work very well, since fiberglass does not act as a barrier for sound: it isn't anywhere near massive enough or dense enough for that. The sound will just pas right through it, unless you make it extremely thick. But you say that you don't have the space for that, since your ceiling is very low... To me it sounds like the issue is not the vents, but the ducting, and it sounds like your ducting was not done the way it should have been for a recording studio. My guess is that they did not install insulation INSIDE the ducts, like they should have. Duct liners on the inside is what you need, and it sounds like you don't have it. It also sounds like there are no silencers in-line with those ducts, nor multiple 90-degree angles, which is normal practice for studio HVAC ducts. So I dn0t think there is much that can be done to damp your ducts, short of stuffing several feet of mineral wool down each one! But that kind of defeats the purpose, since it would totally block the airflow.

I'm going to see how using homemade rigid fiberglass absorbers will affect the rooms sound (which has an astounding, full two seconds of decay presently!)

Your RT-60 is over 2000 milliseconds? Wow! You sure are going to need some serious acoustic treatment in there!

I'm going to have all the electricity and carpet installed by the end of next week...

Carpet? Is this going to be live room, or a control room? Either way, carpet is not normally recommended. It might be fine for a home theater, but most experts here recommend a live floor (bare concrete, or laminate, etc.) and dead ceiling. In your case more than most, since you will HAVE to have a dead ceiling, due to the need to use overheads on the drums with an already very low reflective ceiling. So putting carpet on the floor would probably be a mistake. I think it would kill the room, acoustically. But that's just my opinion. Others may differ. - Stuart -

I think this is his build thread, Brien: viewtopic.php?f=2&t=11785&p=85958#p85958 Hmmmm... another thought. They are going to install the electrical work next week: But how are they going to do that, if you already had the drywall installed? All power and light circuits should have been installed BEFORE the drywall, unless you are planning to have everything surface mounted, with no penetration of the inner leaf at all? Is that it? I sure hope so! If not, then doing the electrical work now is going to seriously damage or destroy the sound isolation properties of your walls / ceilings. - Stuart -

Thanks for all the input. I don't really have a studiobuild. I was going to do a fully serious studio design about a year ago, but I decided that I didn't want to get that involved in this basement project since I didn't think I would be living here for many more years. It is just a one room fits all sort of situation, no control/studio split. I'm just going to make some large movable walls to block a decent portion of the noise from my mixing side, while leaving the mobility to change the segments of the room at will. I was going to make isolation good enough not to bug my neighbor (wall design: Ground-> CMU->studs->rockwool->5/8gb ->Green Glue-5/8gb...ceiling the same, but with whisper clips.) I have found the isolation has worked for my purposes now that the construction is done. The ducts a were non-negotiable part of the pre-existing basement. I wasn't about to change the system around. And also one of my considerations was being able to "sell it" to the next buyer as a good home-theater room, which I think it will do just fine at. Electrical stuff has been run through small holes which have been caulked at each layers installation and the boxes will be surface mounted. I do have an electrical box opening to deal with now as well though. That will be fun. :lol: So what's the general reasoning for wanting a reflective floor and not ceiling? My understanding for small rooms (though it may be generalized) is that you want to make it pretty dead since the reverb characteristics won't sound that great in the first place. Thanks again for responding. I know I don't have a studio build, but that will pry happen when I'm willing to shell out some serious cash and have a fresher slate to work with than a pre-existing basement situation. I was just looking to make it possible for me to push my recording sessions into the evening and have a nice, finished looking room to boot (it used to be all dingy...).

I was just bumping this in hopes of getting a response to my question about the reasoning behind a live floor and dead ceiling. Why couldn't it work the other way around? Being that they are parallel walls with the same surface area, it seems to me like they would react much in a similar fashion, with the exception being that if the floor was dead, my feet would in turn live a little longer! :) Also, this carpet is definitely going in one way or the other (land-lords orders, you know), so if this is such a big problem, what are some creative ways of limiting the problem? I have been building those some 6'X3' 703 absorbers for the last 2 days, I have made 8 and already the difference is amazing.

Well, I've read many good, solid reasons for keeping a dead ceiling and a live floor, and you can find an interesting discussion about that on Ethan's web site, but the one that makes the most sense to me is that wherever you go in the world, your ears are always the exact same height above the floor, so your brain is very, very accustomed to hearing reflections off the floor, and uses that as an acoustic clue. The distance to the ceiling varies all the time, as you walk around, so your brain pretty much ignores that. So we, as humans, always expect to hear a certain kind of acoustic clue in our music that indicates the floor is "there", where it should be, and when that sound is absent, the music sounds vaguely strange. That's the argument that makes the most acoustic sense to me. So, I guess the alternative for you, if you have zero choice about carpet, is to build your ceiling at the same distance above your head as the floor normally is, and always keep your mics at the same distance from the ceiling as they normally would be from the floor, but that sure sounds like a complicated way of doing things! I really can't say how important this is, but practically all the good studios I've seen and been in always have live floors and dead ceilings. If that is just ordinary carpet, then the acoustic characteristics are probably unknown and unpublished, so you would basically be on your own trying to figure out what it will do to your room acoustics, and how bad it will make it. Normal house / office carpet is selective absorptive and selectively reflective, at different frequencies, but unless the manufacturer publishes acoustic data (unlikely!), then you really don't have much clue as to what it will do. My guess would be that it will make your room very "cavey" and "dull" and "hollow" sounding, since it will absorb some highs and not others, at varying levels, while not doing anything at all to most bass frequencies. But check out Ethan's site for that discussion on room treatment. - Stuart -

Ah, I see now. That makes sense to me as well. hhhmmm... Well, for a next best shot... what about some thin material or panels that could be dropped on the floor just prior recording to add back some amount of reflectivity, knowing that 'no carpet' is not an option? perhaps some plastics? (the image I have in my head is something like a plastic drop cloth or even something more rigid)

hat about some thin material or panels that could be dropped on the floor just prior recording to add back some amount of reflectivity,

Sure. that would work. I would suggest something like plywood or MDF, though, as it is more massive, and would "hide" the carpet a bit better, in the acoustical sense. It is also more durable than plastic, and gives you a better surface to walk on. You could cut one large sheet of plywood into several smaller pieces that fit together, to make it easier to handle, and shape them to fit around furniture, etc. Once the carpet is in, you might want to experiment a bit with different amounts of plywood coverage, until the room sounds good. For example, start with 25% of the floor covered, maybe in the middle of the floor, and see how that sounds. Then add another piece to get maybe 40%, and see if that improved things. You don't want to go too far the other way, either! You say you already have a strange sounding room, due to those ducts, so you probably don't make it too live. Just play around with coverage until the room sounds as natural as possible, with as little reverberation and resonance as you can get while still getting good sound. Trial and error os what you need, I think! - Stuart -

Excellent, I can't wait to give this a try and experiment with it! The cut up plywood sounds like the best (and cheapest) route, so I think I'm going to take it! I'll report back later with the progress and perhaps even some pictures of the project (I don't know why I didn't think to do that during the earlier phases... just a bit too hectic, I guess) Though just for clarity's sake, what exactly is MDF? I'm intrigued... Thank you once again for your thoughts and assistance. Bryce

Though just for clarity's sake, what exactly is MDF? I'm intrigued...

MDF="Medium Density Fiberboard". It's a type of manufactured wood, made from wood particles in a resin base, and pressed into shape to form large sheets. A lot of cheap furniture is made from that kind of manufactured wood these days. It might be slightly cheaper than plywood in your area, or more expensive. It varies from place to place, I think. It probably won't hold up as well as plywood in relation to wear over the years, but it will still work. One thing I forgot to mention: don't forget to treat your ceiling! If you have a live floor, you should have a "dead" ceiling. It will give your room a more "spacious" sound, acoustically (making it sound as though the ceiling were much higher than it actually is), and also helps to control flutter echo and comb filtering. A few inches of fiberglass or mineral wool should do the trick. - Stuart -

Ah yes, I plan to. I was making some of these broadband absorbers in frames to hang from the ceiling once I find some proper way to fasten them! Is this any better than just painting some 703 and gluing it to the ceiling?

Pretty much the same, I'd say. But you do not want to paint or glue insulation! That will kill the acoustic properties if the painted / glued part. It works because it is porous, and the fibers can vibrate along with the sound to absorb the sound and turn it into low-grade heat. If you paint it / glue it, then the fibers cannot move, air cannot penetrate, and it loses acoustical characteristics. What you can do in the ceiling is to put it between the joists, if you build the ceiling inside-out, and use something like string, package strapping, or wire mesh stapled across the joists, with acoustic cloth below that to hide the "ugly factor". - Stuart -

Ah. That would have been so much easier, but there wasn't much I could do with the ceiling due to the already low height and the finished living room above it! I have built about 10 of those panels now and hung the ceiling ones, 6 in all. I still have to make some odd shaped ones due to the random locations of vents, doors, windows... etc. I apologize for not having posted pictures yet, I work and go to school full time as well so it's really been a stretch trying to get this project done. I will try to get that done here in a day or two to give a sense of what's going on a little better. I have a new question though, Stuart. Near the corners where I want to put bass traps, I think there may be an issue.... The surface mount outlets (metal 4 plex boxes) are about 1 ft 5" (about 47 meters) from the corner, though only on one side from each corner. Is it going to be worthwhile to make bass traps in that corner with only 2 ft wide (60.96 cm) to work with? I plan to take it to the ceiling if I need to, but this puny width and the not very impressive height of 7ft 2 in (2.18 m) doesn't leave much overall real-estate for what I would think an effective bass trap would be. I could maybe add more space by making the triangle lopsided giving it a longer base, but would that in anyway effect it's ability to absorb bass for the worse? The other idea I'm thinking of staring at it here is that maybe I could just make another absorber like I have been, with the height from floor to ceiling and with the 4" of 703 in it. and either fasten it to the wall or have a base on it. Actually, as I typed this, the square one seems to me the easiest since I have square frame building on the mind right now :shock: . Do square bass traps work the same as ones straddled across a corner? I may try this tonight, I can always reuse the lumber and materials for smaller absorbers I still need to make if it doesn't work. It's kinda funny all these little things you don't think about until it's all installed in front of your face and you are working on a later phase of the project. I wasn't thinking bass traps when I was talking with the electricians, haha.

Is it going to be worthwhile to make bass traps in that corner with only 2 ft wide (60.96 cm) to work with?

Well, 60 cm is better than nothing! It should still get you a decent amount of bass trapping.

I could maybe add more space by making the triangle lopsided giving it a longer base, but would that in anyway effect it's ability to absorb bass for the worse?

I don't think it would have a negative effect. If it will increase the surface area and depth of the trap, then it can only help, as far as I can see.

Do square bass traps work the same as ones straddled across a corner?

Do you mean "square" as in "up against the wall" instead of straddling the corner? That will still work, but it won't be as effective. Room modes are concentrated in the corners, so you get a free boost in effectiveness by straddling corners. A wall gives you a 6 db Boost, the corner between two walls gives a 12 dB boost, and the "tri-corners" (where two walls and the ceiling meet, or two walls and the floor) give you an 18 dB boost, theoretically. So straddling tri-corners should be your first priority, followed by normal corners, and last of all just up against a wall. - Stuart -