Removing Air Conditioner Hum from building

I have a 4000 sq.ft facilty located in a relatively new building - less than 6 yrs old. I lease the entire second floor and am above a liquor store (The owner of whom -also owns the entire building) On the second floor I have a control room and a live room, as well as some other rooms for storage, etc. The live room is 19'6" w x 21' deep - ceilings are 10' The ceiling is standard drop ceiling, although we added 2x4 sheets of rockwool above each panel. Above the ceiling grid is apprx another 10'-12' of height before the actual roof of the building. Things have been relatively quiet in the live room - very suitable for tracking vocals, etc. At the time of construction, I did not have the budget to build isolation rooms, vocal booths etc. - so I just utilized a drum shield located in a corner / the panels of the shield were treated with standard auralex 2x4 and the surrounding walls in the "vocal area" were treated as well. On the roof of the building are located 4 commerical grade AC units // 2 for the first floor and 2 for the second floor (my location) I have been noticing recently that the when recording vocals, I am picking up a terrible hum from the AC units - granted I usually turn my units and fans off while tracking; however one of the AC units from the first floor unit appears to be gaining some noise with age. In the interim - I have been using Wave's Z-noise to cut out what it can - and obviously understand that this can't be a long term solution I have called the HVAC team and they checked out all the units on the roof and said that all is well - despite the noise. So I believe that I will need to construct some sort of booth or room to "keep the noise out" If anyone can offer some solutions - most likely DIY, due to budget. I am not familiar with the best ways to keep "building noise" out and I want to make sure that I follow the best plan of action - I have several string octet sessions coming in Jan and this could prove to be a real problem. Thanks so much for any assistance. Regards Kevin Johnston Abingdon, MD

Hi Kevin, and Welcome! :) There's a few things you should check for on the HVAC system before thinking about booths, since the booths will need air from the HVAC anyway! But first: What type of "hum"? Is this a mechanical hum, coming through the building structure? Or is it air humming as it moves past something? Does the same HVAC that feeds your live room also feed another area of the building that might have some type of humming machinery in it? You HVAC guys might not be aware of how to isolate the HVAC system for studios: they might just be ordinary HVAC folks, that know about offices and houses, but not about studios, so I'd suggest that you might want to find an HVAC company that has experience with studios, ang get tehm to come check out the system. There are several things that should be done on an HVAC system for a studio. First, the "noise bit" must be mechanically isolated from the building structure, using proper isolation mounts that are dimensioned correctly for the equipment. Next, the HVAC ducts need to be decoupled (isolated) from the machinery with flexible sleeves where they connect to the equipment, and those also need to be dimensioned correctly for your specific equipment. Third, the ducts need to be lined on the INSIDE, not just the outside, using proper duct liner. Fourth, the ducts need to be mounted on isolation brackets, to keep structure-borne noise out of them. Fifth, the duct runs need to be long, and have at least two 90° bends in them, and/or proper silencer boxes need to be installed in-line with the ducts. Sixth, the ducts going to your studio should not go anywhere else in the building, and should be split for the individual rooms long before they get there, and silenced separately. Seventh, all the ducts should be over-sized (have a larger cross section than would normally be used), so that you get a larger volume of air moving more slowly, instead of a small volume of air moving fast. There's other things that can be done too, but I'd check that all of the above have been done correctly first. Maybe you could post a recording of the "hum" here, and also some photos of the HVAC system. - Stuart -

Stuart, thanks for the quick reply -I'll try and answer some of your questions - 1. - What type of hum - this is a mechanical hum that is coming through the building. As I mentioned the building I am in has 4 units on the ceiling (2 for the studio (second floor) // and 2 for the first floor liquor store. - There are two units for the second floor / One unit, covers my lounge, hallway areas, kitchen and control room (in essence one half of the second floor) The second unit covers the live room, and two smaller rooms that I sometimes use for tracking, amps, storage, etc.) I have control over the second floor units -as I can turn them off // incl the fans - but interestingly enough, when unit 1 is on - though the ac is blowing in the control room / its effect on tracking in the live room is minimal, if noticeable at all. Both of these units are located - pretty much about 12 feet above the control room (on the roof) // The units for the lower floor (which are larger units) are located at the far end of the building (not directly above the live room (but basically the next room over) - It is the mechanical hum that is generating from those units - it equates to a low rumble at best - What makes the situation a bit tricky - the owner of the building also owns the liquor store - and certainly is not sensitive to the plights of his upstairs tenant - or more likely - not sensitive to forking over the costs to adjust his HVAC unit. I may call the HVAC folks again myself and mention some of your suggestions. I thought that perhaps building some sort of isolation enclosure, might be the lesser of two evils // but I aso dont want to invest time and money to find out that the hum still is rearing its ugly head. I certainly could post an example -as I recorded dead air through the SM7-B / distressor from the "vocal area" to use as a basis for the waves Z-noise profile. looking forwrad to your thoughts kj

I thought that perhaps building some sort of isolation enclosure, might be the lesser of two evils // but I aso dont want to invest time and money to find out that the hum still is rearing its ugly head.

Well, you certainly could do that. It is an option. But if the sound is flanking through the building structure and HVAC system, which seems to be the case from what you say, I'm not sure how well that will work, unless you take special precautions: you still need to hook up the HVAC to the isolation booth, if you plan to have people staying alive in there for very long, or amps and speakers running inside without overheating. So the hum would still get in through the HVAC, unless you also build large silencers. And you'd also need to decouple the booth from the building structure, to keep the hum from flanking on. So an iso booth is an option, but needs to be thought through carefully, and designed with the above in mind to make sure it actually does isolate that specific hum, as well as everything else. Sure, please do post a sample of the noise, so we can hear what you are dealing with.

not sensitive to forking over the costs to adjust his HVAC unit.

Time for a cost-benefit analysis! Get a quote from HVAC guys that actually do understand studios on how much it would cost to correctly isolate that unit (hopefully just suitable vibration mounts and duct decoupling: shouldn't be too much), and compare that to the cost of designing/building the isolation booth, with all the details and accessories. If there's a huge difference in cost, your choice is easy, even if it means forking over your cash to fix his building! But if the costs are similar, I'd go with the booth: at least you'll bu building something that you own, for your own benefit! That would be my approach: others might not agree... :) - Stuart -