Hum/Whistle from Pressure Difference between Rooms

[ianda]

Hi all. The college I attend has a smallish recital hall attached to its performing arts building. There are two entrances into the hall: one on stage and one for the audience.

When both of those doors are shut, there is a HORRIBLE hum/whistle that is very loud ... loud enough to make its way onto recordings and, in my opinion, deem them unacceptable. (Try removing a hum like that without taking out some of the highs of the actual piece). However, when one of those doors is open, even as little as two inches, the hum/whistle is gone.

My guess is that the hum/whistle comes from a pressure difference between the recital hall and the lobby area. We've talked to the custodial staff, and there's really no way to equalize the pressure with the current air vent setup.

Is there anything we can install on the doors to create a seal to keep out this hum/whistle? We'd need to install it on both sets of doors, most likely on all of the door edges (i.e. top, sides, and bottom).

Any suggestions will be GREATLY appreciated.

Sincerely,
ianda

 

[knightfly]

Hey, Ianda - you didn't mention which side of which pond you're on, so don't know about convenience - still, here's a little info that may help- First of all, doors are generally the biggest pain to fix if you're wanting good sound isolation - for just stopping the whistles, it may be slightly easier. Still, most likely not a cheap fix.

There is some good basic info here - these guys are commercial, but have a very informative site for acoustic problems as well. In this first link, pay particular attention to their comments on the way most doors are hung - you may need to first get some caulking material and remove some trim to get at the doorjamb mounting. Check it out...

http://www.customaudio.freeserve.co.uk/articles/doors.htm

When you're done there, go here -

http://www.customaudio.freeserve.co.uk/seals.htm

this may help with some ideas - one or two of these may be adaptable to your existing doors, or at least give you an idea for a DIY solution.

These next people are where serious studio builders go for their doors, if you look around their site there is some good info on seals, etc - +, Im pretty sure they also sell just seal kits, including drop thresholds (the bottom of doors is the hardest part to do right)

http://www.overly.com/doorCo/Products/Acoustical/acsWoodDoors.cfm

Here's some good looking bottom seals - however, I couldn't find any info on pricing - guess you could email them, but they're in Australia...

http://www.arach.net.au/~watno/raven.htm

Another possibility -

http://www.solderworld.com/plastics/company/ct_23748.htm

Follow your nose on this one - click on BBC tab for sure...

Go here, and click on the installation directions links for more info on how/what to do.

http://www.silentsource.com/adoors-overly.htm

I hope some of this helps you decide what to do - I've no idea of your budget, location, carpentry skills, or other resources so can't really get much more specific - if you want to expand on this, post back and be more specific on details... Steve

 

[Sennheiser]

I'd probably get the custodial staff turn turn off the HVAC while recording. At least until it gets too cold.

Either that, or try opening one door or the other enough to equalize the pressure until the whistling stops.

Those are the cheap fixes. I sure wouldn't be spending money on a facility that I didn't own.

 

[ianda]

I forgot to mention...

I forgot to mention some small specifics about the hall.

The recital hall is part of the arts building, which also houses the drama department, as well as other academic classes. As you can imagine, some folks think it is OH so funny to be loud and obnoxious in the lobby of the building, which is - of course - just outside the recital hall doors. So, propping one of the doors open a bit isn't an option. Then we'd have laughter, talking, and yelling to contend with, rather than a (fairly) consistently pitched whistle that can be removed (somewhat cleanly) through a noise reduction feature in audio programs.

And, as you'll agree, winters in Minnesota make turning the vents off a very bad idea. (When I got up this morning, it was 18 degrees!)

I was hoping for a simple solution that doesn't necessarily make the doors soundproof (which would cost way too much).

Keep the ideas coming. This will help us (and our faculty) out a lot.

Much Appreciated,
ianda

 

[knightfly]

Ianda - sorry for the delay getting back to you - this board must be located near you, and the 18 degree weather doesn't help the molasses, January or any other month...

Am I to assume (hate that) from your comments that you are on your own as far as resources go, or will the school kick in anything like help or money?

As I mentioned in my earlier post, doors are one of the biggest pains in quieting a studio recording area. The top and sides are relatively easy, most times some soft foam sticky tape can take care of leakage.

It's the bottom of the door that's the biggest problem, since few people will lift their feet walking thru a door. This makes it necessary to use higher tech methods of sealing. that's why I pointed you to some of those links, so you could see what's involved.

The only way I can think of to take care of the bottom of your doors that's reasonably priced, would be to custom cut a piece of lumber, perhaps 2x6, so that it conforms to the door frame and door bottom as close as possible when laid flat on the floor, then use soft foam glued to the bottom and front edge (the one in contact with the door) and place this board up against the door bottom from the inside ONLY while recording.

The downside of this method for any PUBLIC building, is that it's ILLEGAL. Firecodes don't allow any exit to be blocked during business hours.

I think that with one of the drop thresholds retrofitted to your doors and some inexpensive foam tape around the other three sides, you could get rid of the "phantom teapot" - If that's not an option due to lack of support from the school, it would seem to me that you're back to the noise reduction scheme.

If that's what you end up doing, it would help to know what software you're using to record with. I use Samplitude and Sound Forge, mostly Samplitude. I think most software that even offers noise reduction uses similar methods - personally, the best method I've found as far as clarity of finished product is concerned, is to leave some dead air either before or after each take, recording just the background noise, then wait until final mixdown and try both individual track NR (non-destructively) AND a complete mix WITH noise, processing the NR only AFTER the mix. Listen to BOTH methods and decide which works best for YOU. Depending on your Software, you may decide that the mix sounds more open when you only run it thru the NR algorithm ONCE. (You would have left a tail on the mix, where ALL channels of NOISE are present, giving you a SUM of the noise to get your noise sample from, which you then use to subtract from the overall mix.

There is a "cast in concrete" axiom that goes something like this: "GOOD, FAST, CHEAP - Pick any TWO - you can't EVER have all three..." Sooo, if I'm correct in assuming (yuck) that you're pretty much on your own here, I hope I've given you something that can help... Steve