Big Door Problem!! - Ideas please!!

[JohnGardner]

I finally got the windows installed and managed to do some very unscientific (boombox) tests between the control room and live room which to be honest were a little disappointing.

The strange thing is that from live room to control room the isolation is far far better than control room to live room with the same sound source being played in both rooms at the same volume.

I presumme that this is because the live room walls are all exposed rigid insulation where as the control room walls, at the moment, are just bare drywall (very reflective).

Anyways - my door system seems to be the biggest cause of the leaking sound which is surprising as most of my research here indicated it should be atleast as as good as my walls and others had used similar systems with great sucess. Bottom line is I am going to have to upgrade them soumehow.

Both doors are 33mm (approx 1.5 inches) solid core but the sound seems to just go straight through them

I can't work out if the doors are just to light weight or the seals (12mmx12mm stick on neopreane) are just not up to the job. I have however light tested all the seals and they seam fine but there are place where only a small amount of the seal is touching the door due to gaps between the frame and the actual door and the fact the seals are hard up on the frame.

My walls should be about STC 55 and construction from the live room out is:

50mm rigid insulation in cavity
13mm soundline drywall (5/8th equiv)
75mm fluffy insulation
100mm airgap including frame stuffed with high density fibreglass
2 x layers 13mm soundline drywall (5/8th equiv)
All seams well sealed.

The strange thing about my doors is that when I drilled some small ball catch holes they seem to be filled with this green sawdust like substance, I was told that it's something they pour into the door frames to make them solid core rather than using timber. Maybe this is some of the problem?

My plan is to take the control room door off it's hinges and laminate a layer of 18mm MDF on to the inside face then re-swing it and re seal it with bigger seals that actually cover more of the door. Do you think this will make a big difference? There is also no insulation in the door cavity at the moment, will adding a layer of 50mm rigid insulation to the back of each door make a difference as well? I thought I would start with the control room door first seeing it is in line with the "thicker wall" and then do the same with the live room door if I need to.

Any thoughts would be appreciated.

JohnG

[Dan Fitzpatrick]

one thing to check, does the iso get better when people lean on the door to push it against the seals, then you would know you need the door to close more firmly.

yes, adding insulation to the inside face of each door will help. insulation will decrease the effect of the mass-air-mass resonance. and in general, insulation is good between doors just like it is good inside walls. so that should help.

i hope that green stuff is very dense. how heavy is your door, is it as heavy as you would expect a solid door to be?

adding mass to one or both sides is also a very good idea, if your seal checks out good.

when you add the MDF or whatever, see if it would be possible to add a second jamb with a second seal. the original door and jamb would have one seal. then the layer of MDF would close into a secondary jamb with its own seal. this is i think how paul woodlock did his doors? i think that's where i saw this.

[JohnGardner]

Thanks Dan,

No, the isolation does not seem any better when I push the doors shut.

I guess I will have to try is beefing up one of the doors with a thick layer MDF and then adding insulation to this door and see where we are with it.

It just seems strange that the isolation is so much better one way than going the other way.

Any other ideas would be appreciated.

Thanks

JohnG

[SonicClang]

My first thought was the doors. If your walls are massive, and your doors are thin... well, you know the answer to that equation. I haven't actually installed my doors yet, but here's what I'm planning on doing. Solid core wood doors, two for each doorway. That means between my live room and control room, since there are two doorways, I'll have 4 solid core doors. For sealing them against the jambs I'm going to use magnetic weather strip and a threshold at the floor... don't forget the floor. Then between each pair of doors I plan on putting the thickets studio foam I can afford.

Just curious, what is your ceiling made out of?

[JohnGardner]

Hi there,
live room ceiling is two layers of 5/8th board hung from hat channels with 1" semi rigid insulation inbetween hat channels. The hat channels are attached to the same joists the live room uses.
You can see photos on my site below.
I am sure it's not the ceiling and I still think its really strange the isolation is so much better going one way, not the other. I no nothing about physics but I would have thought the transfer should be the same either way?
Thanks
JohnG

[JohnGardner]

Just as a side note i borrowed a sound level meter from work today and was wondering if someone could let me know what these results mean in wall performance to the STC and TL levels we talk about here.

I had the meter set on FAST and the 30-80db reading range.

Control room music 85.7db, live room 32.3db these were the max and min readings and varied up a few db at the low end ocassionally.

is this a STC / TL of 53 or am I reading it wrong - if so then thats about what the wall performance for my type of build was meant to be and I still need to either beef up and/or insulate the door cavitys

Thanks

JohnG

[SonicClang]

What are your walls made out of?

So sound from the control room to the live room only has to travel through two layers of 5/8" drywall, through a few feet of insulation, and back down through two layers of 5/8" drywall? Well, I can't say what kind of STC that offers, but I can say I made my ceiling beefier than that.

Just as a side question, where did you buy the box that goes in the wall that you plug the mics into? This picture http://www.peelproductions.net.nz/Studio28.jpg I've been meaning to look around as to what those are called. It's like the end of a snake, but it's on the wall. I need to buy some of those for the next phase of my build.

I see you only angled one piece of glass in the CR window. Why is that? Limited width of the wall? Maybe you can answer my question about setting the glass on the sill. Is it ok for the glass to sit on an angle on its own corner? Or do I have to either have the glass cut so it sits flat on an angle, or should I adjust the sill?

[kendale]

Aloha John,

Just curious...what frequencies are you hearing leaking through the most of: lows, mids or highs? Is it the same frequencies leaking both ways?

Aloha

[JohnGardner]

Hi There,

The wall unit is just called a "wall box/plate". Try a search for on the net. There are a few places that make them online.

The window has two layers of glass - it's just hard to see the other one.

Hi Kendale, well I have only really tried one way - that is control room to live room. The frequencies seem across the board - that is, I can hear the song clearly the boombox is playing, just at a much lower volume.

I need to do some tests the other way once I get the power hooked up.

Thanks

JohnG

[Dan Fitzpatrick]

John,

that should be a rough estimate of STC ... did you use A weighting or C weighting? it may not matter much, but i think A weight more closely matches the way STC is calculated.

to do a more accurate STC measurement, measure the TL at as many different frequencies as possible, then use the STC methodology to derive STC from the resulting frequency curve. here you would use C weighting.

the methodology should be out on the net somewhere. it involves trying to fit the standard STC curve to the curve you come up with.

but it sounds like beefing up the doors and adding insulation to the door insides will help, if you are sure the sound is coming from the door and not through the walls.

i'm glad to hear that it is not the closing pressure of the door that is the problem, because i've always thought that would be an issue with doors, and wondered how to get a forceful close. but it sounds like it's not that big a deal.

[kendale]

Aloha John,

Any luck, progress, updates?

Aloha

[Johnrg]

I whipped up an insulation baffle for the inside cavity of the live room door but still need to upgrade the control room door with a layer of MDF and an insulation baffle. Probally next week at this stage.
I'll get a photo of the door baffle up tonight, looks very smart.
JohnG

[WiseMindsRecordingStudios]

MDF-Hollowcore-MDF

That's all I can say. IMHO you just can't beat the triple layer.

There are a ton of issues that need to be addressed here. Having just finished this phase of my build I think I can help you. We open on the 20th of February so please be patient, I will try to post a more comprehensive post later this evening.

[WiseMindsRecordingStudios]

John,

Got a look at your studios site. Looks great. Do you have updated pix? The pix there say May 2005.

I see that you are using double doors so my MDF-Hollowcore-MDF doors would probably either not work or be overkill.

I guess my question (unless I missed it) is what are you using to close the doors? Or keep the doors closed? Have you done a light test? Put a light between the doors and turn the lights off...look for light leaks. The smallest of leaks will let a LOT of sound through. When I first set my door up I did this test and found several places I could see light getting through... a few adjustments and the doors came to life.

Just some thoughts, just in case you haven't tried yet.

[Johnrg]

Hi Andy,

Thanks for the reply.

The photo's are up to date - May2005... was when I started the whole thing. I might change that to "ongoing" I think.

I am using 1/2inch x 1/2inch neopreane rubber seals attached to timber cleats right around the door. The doors close with ball catches top and bottom and stay really well in place.

I have tried the light test several times and all looks OK. When you pull the door really hard shut to double make sure of no leaks the isolation does not get any better so the seals seem fine.

I have a funny feeling that part of the problem with the doors might be actually be the size of the seals and the fact that 1/2 x 1/2 is actually really hard to compress very far.

My seals are not really "compressed", more like the door just sits up flush against them enough to block out light but is this enough to block sound - I am not sure.

I was thinking about ripping the seals off one door and moving the cleats much closer to the door and getting smaller/wider seals that I can compress well when the door shuts into place. Maybe something like 7mm thick x 12mm wide as apposed to the 12mm thick I am using now. This way I could really compress the seals to ensure a tight fit. I am also going to beef one of the doors up with another layer of 18mm MDF.

I am also starting to think that some of the sound maybe coming down through the ceiling. The problem is when you are standing in the room it's really hard to tell where it's coming from. Most of the time I think it's the doors but now and then I thnk it's the ceiling/walls/floor. It's just so hard to tell.

When we designed the room John said it would probally be a STC of about 50-55 and the ceiling would be the weak link. My noise meter tests show about 53db reduction so I suppose that's basically spot on. I guess I just thought STC50-55 would be better than it actually is. As thing's stand at the moment a vocal condensor mic in the live room would easliy pick up the monitors in the control room even at really low levels. This is not quite what I had in mind!!.

The strange thing is that the isolation from the live room to the control room seems much much better. I can't really test it because I have no power in there at the moment and my drums are in peices but I had a friend in there last night yelling at the top of his voice and he was basically impossible to hear. But if he stood in the control room and did the same thing when I was in the live room he was really easy to hear. I no nothing about physics but I would have thought that the sound transfer should have been the same both ways even if one room is treated with absorbtion and one is not.

All I can really do is beef up the door, install the new more "compressable" seals and hope it makes a big difference.

If it's not the doors but the walls/ceiling/floor or a combination of the above that are the problem I'm kinda stuffed.

JG