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Gobo construction Mixers (Digital)
Old 16th June 2013
Gear nut

Thread Starter
Gobo construction

First of all, I am very new to this.

I don't want to build a "room" here. The space is perfect as is. I record acoustic guitar and voice and I need to knock down the ambient noise that trickles in, especially from my really large window. For now, I want to try gobos.
I just did a test with a very crude gobo (merely a moving blanket hung over a clothes rack) and the mics in their usual position recording the ambience.
When the gobo isn't there the predominant ambient note is C# (approx 140Hz).
When I place the gobo between the window and the mictophones, the predominant ambient note moves down one whole note, to B (approx 123.5Hz).
When I add another moving blanket with space between them, the fundamental frequency is not affected but there is much less higher frequency noise.
That all makes me very happy because it means there might actually be a solution for me.
This is the question: I have decided to make a frame for Ultratouch and use it in the current structure. There's a couple of ways I can approach it:
Hang one 3.5" layer full length to the floor.
Hang two 3.5" layers with an air gap of 3-4" in between them. Not that much harder to do.
Is there any benefit to that?
If I'm stuck with the B I shall change my songwriting to reflect that, with the city of Los Angeles ommmmming along incessantly.

Old 17th June 2013
Gear Guru
Ethan Winer's Avatar

I don't think a gobo is the best solution for noise passing through a window. Usually a "plug" made of a solid material that covers the window without any air leaks is better. Can you post a photo of the window?


The Acoustic Treatment Experts
Old 19th June 2013
Gear nut

Thread Starter
Thanks for the reply Ethan. The window is massive: 190" w x 84" h
Not going to attach a photo since a plug is out of the question, thought about how I could do that but it's more trouble than I am up for.
To clarify I am trying to carve out a space to track acoustic guitar and voice. Nothing bigger than that. Here is a plot of my space:

As you can see it offers some pretty serious challenges (and advantages as well.)
Right now the computer and monitors are just to the right of the kitchen and I am tracking directly across near the concrete wall.
I am actually not that unhappy but would like to just knock down the bass fundamental a little bit more - it's almost down where I would end up hipass filtering it out anyway, but not quite.
Where the mics are placed my place hums at Bb-B on the lowest E string of a guitar, approximately 120Hz. To be honest I am not totally sure that is all coming from the window but to my ear that seems to be the source.
I need the fixes to be impermanent, so I thought gobos might be a good idea. I could easily hang a broadband absorber or 2 on the concrete at the tracking area if that is a good idea.

Old 19th June 2013
Lives for gear

Have you considered FFT noise removal like Izotope RX? All that is required is a noise floor sample from the mic you use to record. It won't help spurious noises like car horns but it will eliminate hums and broadband noise.

Otherwise if you think Gobos are the best solution, you will need a few of them, roughly 4 or 5, placed in a circle around the recording position. The more the better.
Old 19th June 2013
Gear nut

Thread Starter
A HPF is working pretty well right now.
I'd like to explain my expectations. I am already pretty happy with moving blankets, would love to be able to knock down that 120Hz or so just a little lower so I can set the HPF at a slightly lower frequency. I record all mid side. I set the HPF on the side mics high enough so that is not a problem, but I would like to be able to move the HPF on the mid mic down a little bit, dropping the resonant frequency my mics hear 10Hz would be amazing. I don't really understand how that works, hence the question.
This is never going to be an ideal acoustic environment and that is part of it's charm. I have a solid concrete wall that is 69' long and over 11' tall. I have vaulted ceilings that go from over 11' to almost 17'. It's actually a pretty amazing sounding space, but the hum of the city is a bit much.

However, hope springs eternal, what about the bedroom area? Farthest from the window. It is 13'8" x 18'3" with a non-vaulted 16'9" ceiling. Not my first choice aesthetically, but possible in some future iteration.


Last edited by Anna Stoic; 19th June 2013 at 06:16 AM.. Reason: addendum
Old 19th June 2013
Gear interested

It all depends on what kind of room sound you are after. Typically vocals are recorded in booths with a lot of absorption so your bedroom would be more ideal for this as I'm guessing it has better absorption than the living area. Just make sure you have bass traps in the corners! Are you using a room mic aswell as close mics? If so then the living room is definitely the better option for guitar regarding a good room sound. For the lower frequency absorption I'd definitely recommend getting some bass traps to put in the corners of the rooms, and also aim your guitar towards the dry wall, as dry wall absorbs low frequencies a lot better than concrete. Ultimately gobos are good for manipulating reflections, but unless they are fairly thick and located in the corners of the room, they won't help much with low frequency humming. Hope this helps.
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