Hi chaps,
just wanted to follow up on this now that I've installed the door and taken measurements. I'm pretty happy overall.
In the end I decided against making my door from scratch as I wasn't sure I could get it looking great and I had a spare door after replacing the other doors in the house. That is a Shaker Evolution from Todd Doors which is solid construction using chipboard and oak veneers. The interior panels are quite thin so I chose to fix a constrained damping layer on the back side. I'm not very skilled or knowledgeable in this area so I did a bit of reading and asked a few questions. The result was a sandwich of 18mm MRMDF and 9mm ply glued together using a 1mm layer of an MS polymer, in this case, Sticks Like **** Adhesive. The idea is that any sound hitting the front panel generates vibrations which are converted to heat in the flexible polymer and not passed through to the back panel. Meh, I had to add some mass and some extra layers so thought why not. I've got no measurements of just the standard door so can't compare before and after. I applied the polymer by covering the door and then using a mosaic tile adhesive trowel to create small ridges. Seemed to work well. The final layer was edged in iroko that I had lying around and glued to the back of the door.
Anyway, the result was a 60Kg door that took a bit of lifting into place but seems to work well. I've used the Lorrient products mentioned on this thread, the 15mm batwing for now and I have the fir tree's to put on the door at a time when I can be bothered to take it off its hinges again (but given the performance it may not be needed). On the base of the door I'd planned to use one of the Lorrient drop seals but realised that because it's a cupboard I don't need the floor threshold to be flush. So I continued my door stop all the way round and used a basic foam draft excluder across the bottom.
Here are some pics that show the door in place and the network rack on the wall. As well as the measurements I took.
pics
The SPL readings were taken with REW and a UMIK-1 sat on a chest of drawers just next to the door. I took the readings over two days so the setup must have changed slightly as the baseline silence reading is louder than my final reading with the door closed. But you get an idea of the performance.
The SPL plots have labels of 'startup' and 'idle'. Startup is just after power on when all the fans come on max speed during boot. The switches and the 1U server are bloody loud here. Idle is taken when everything has booted and calmed down to its idle state. I've taken readings with the door open, with the door closed and with the door closed plus all the seals fitted.
The final two plots are perhaps the easiest to read. The two comparison plots show the idle and startup SPL with the door open and with the door closed with the seals. It's quite a difference. At idle, I can only just hear the fans with no other sounds in the house. At startup it's fairly clear that there are servers in the cupboard but it's a vast improvement to before.
The Lorrient Batwing products seem to be fantastic at cutting the higher frequencies. If you look at 400Hz up on the startup plots with the door closed, with and without seals, it's impressive.
On the idle comparison there are still some peaks at 50/120/180Hz that I need to investigate and they might be vibration in the rack itself as I haven't added any damping yet. They could also be spurious as below 400Hz, a car going past completely upsets the lower frequencies.
Anyway, thanks for the help. Hope that might be useful for anyone else trying it. The Batwing product is one of the best for sound reduction in their catalogue and was pretty easy to fit aside from a few swear words emitted when trying to get something that is sticky on two sides tight into the corner.