how to soundproof Studio doors

[Melv]

Hello all. I have just finished building the outer door for my studio (room within a room)but it is not very effective at blocking the sound coming from inside the studio to outside. Obviously I need to also build a door for the inner room too, but I thought I would try a test of the outer one alone just to get a gauge of how well it worked. Unfortunately it isn't very good. I will now explain how the door is made and hopefully you great people can tell me where I went wrong.
I used an oak veneered solid external front door, then I built a 30mm deep frame and attached it all around the edges on one side with a 2mm rubber membrane between door and frame. I then stuffed a layer of 50mm fibreglass to inside of frame and then attached 5mm mdf to the frame to form a flush door. The finished depth of the door is 75mm. This is made up of 38mm door, 2mm rubber, 30mm frame and 5mm mdf. I also stuck a 6mm neoprene sound strip all around the door stop so that when door is closed tight, it compresses against the neoprene strip and hopefully forms an air tight seal.
Any help or advice is much appreciated. I don't even mind if I have to scrap the whole door and start from scratch.

[gullfo]

it would be helpful to understand the wall structure. if you have a wall - air - wall scenario, and there is a gap between the exterior door jamb and the inner wall frame (and you want this gap to avoid coupling) and it's not sealed, you'll get a lot of sound making its way to the exterior wall as well as the door. if, otoh, it is sealed, maybe the door needs some damping - perhaps attaching a heavy absorber unit on the inside of the door will help. unlike a wall unit where the air gap is beneficial, in this case we're using it to damp any resonances.

[Melv]

it would be helpful to understand the wall structure. if you have a wall - air - wall scenario, and there is a gap between the exterior door jamb and the inner wall frame (and you want this gap to avoid coupling) and it's not sealed, you'll get a lot of sound making its way to the exterior wall as well as the door. if, otoh, it is sealed, maybe the door needs some damping - perhaps attaching a heavy absorber unit on the inside of the door will help. unlike a wall unit where the air gap is beneficial, in this case we're using it to damp any resonances.

Hello Glenn. Thanks for your quick response. The wall structure from outside to in is as follows.. 0uter shell/wall is dense concrete paint grade blocks. Then a 50mm air gap (I think this should've been bigger but lack of space dictated this), then 75mm studded wall with fibreglass insulation, a layer of plasterboard a layer of 6mm neoprene and another layer of plasterboard. When I did the quick sound test I didn't use my Db meter but just stood outside while my friend shouted and banged on a tin can in the studio. (It was a quick spur of the moment test just to see what sound insulation one door would do). This was done without the inner door fitted. I suppose it was a pointless test as like you say the air gap would be almost useless in this situation. I just thought the test would be a lot quieter than it was, even with the one door. It was almost as loud as if I just had an ordinary door on there. So do you think the door construction I explained earlier is ok and it's just the fact I haven't fitted the inner door yet?

[gullfo]

if you friend can cover the inner opening with a sheet of plywood to simulate the inner door, you'll be able to determine if that is the main source of the sound leaking.