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Author Topic: Room acoustics, treatment and sound proofing  (Read 1994 times)

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Offline Glenn

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Room acoustics, treatment and sound proofing
« on: August 29, 2015, 03:44:38 PM »
This topic came up, and I thought I'd share a bit of info on the subject while I was on a roll thinking back to the 'studio days'.  8) 

It would be cool to hear what you've done to solve room acoustic issues, and what you use for sound treatment and sound proofing etc.    :)   :)

Here's what Way2lon did to help tame a bit of room boominess picked up by his mic ...

I replied to his thread there... and the following is a repeat of what I wrote there....  ;D

I have a bit of experience with taming room acoustics and standing waves from recording spaces, and I've tried many approaches, from money saving points of view and from 'quality, get the job done' point of view too.  8)

Over the years, I've researched, designed and built a few studios from scratch, wanting to make sure the investment was going to pay off, I wanted to do it 'right' the first time.

When I first started recording, before I built my own studio, I once made a booth from huge refrigerator boxes... wired two together, cut the inside dividing walls out, put a light in there, lined it with shag carpet inside and out, and cut a small hole through it to put a mic in there, and a stool.   This was VERY confining, and created a very dead sound!  ::)  It served the purpose though.

To catch mids and high end standing waves ....
 I found out I could achieve the same or better results than making a confined booth, using the space of the room itself, and dampening only certain frequencies, (mids and highs) with some soft cushions strategically placed in the corners, and some curtains hung on the walls.  You could also frame a piece of shaggy carpet and hang it on the wall.  But don't expect this to deaden or cancel room boominess! 

I once mounted thick carpet on 2 sheets of plywood 4 X 4 ... and then stood them up against each other in a V shape, placing the mic in the center of the "V" to stop the mids and highs from rolling around and back into the mic.  This works well too. You can make a mini one and place it on a desk where your mic is and have pretty good results that way too.

Forget using egg crates or cardboard...  stapled to ceilings etc ...

the main thing is to break up the hard flat surfaces... that's key. IMO

To dampen room boominess.... 
The soft surfaces will only work on the mid and high end, ... the bass is an entirely different animal, and needs special attention to attenuate the bass freqs from rolling around the room... and indeed from exiting too... especially if you're using a bass amp, or speakers with a sub woofer.
Bass standing waves can be more than 35 Feet wide and high.. 10 meters or more... that means they travel through walls and ceilings like they aren't even there! 

Of course, the boominess from a voice isn't quite so drastic because it's not as loud or as low as a sub woofer, but the principal is the same!   You want to stop the bass freqs from rolling around the room and bouncing back into the mic.

I suggest looking up 'bass baffles' which you can build yourself ... the measurements are most important to catch specific freqs to REALLY dampen the BOOMY Bass standing waves.  You should only need two to four baffles depending on the size of the room.

You don't need a special tent, as I learned years ago. 
Sometimes it's as simple as getting the mic away from all the walls, use soft materials hung on flat surfaces to break up the bouncing sound waves, and you should be good to go.

If room reflections (standing waves) remain an issue, you might try and switch from an Omni directional mic to a more directional model for that room, and stay closer on the mic rather than further away, just use a good pop filter and it should work fine.

You may also simply cut some bass boominess by using EQ, dropping freqs below 100 or 200, as long as it doesn't end up making the voice sound 'thin' as a result.  A little cut at 100Hz can go a long way in taming boominess.   You can also try getting closer to the mic and utilize some mics ability to create what is known as a 'proximinity' effect.. which DJ's use to get the full bassy sound in the voice.


Sound treatment vs. sound proofing.

Some people get these terms mixed up ...
If you want to not only 'treat' the space inside the room - but also stop sound from exiting the room (sound proofing), then you need to study various materials that will help.
You want materials that have a good STC rating (sound transmission class) with good STL (sound transmission loss) characteristics and numbers.  You want high STL numbers, ... sound goes in at say 90dB SPL (sound pressure level) and comes out the other side of the material at say 70 dB SPL, that's an STL of 20dB ....  In sound proofing, it's common practice to use several types of materials to stop unwanted sound from passing through, such as wood panels, insulation, concrete blocks, and the ultimate... LEAD LINED WALLS! lol
You can fill walls with sand too, just make sure they're sealed really really well, or the vibrations over the years will have you in a 'beach setting' before you know it! lol  :P

There's lots of remedies for sound treatment, and some are easier to execute than others.. sometimes it's best to just save up a few bucks and invest in some computer tuned materials like SONEX which I've used in many applications to 'treat' the rooms less than perfect sound characteristics.  You can get sonex acoustical foam that acts on the highs, and mids, and special sonex for BASS and room boominess!  I still have a few panels of sonex from the old studio days ...  You don't need to cover the entire surface, as just a few panels strategically placed can do a great job of taming a room's acoustics. 

If you're planning on building a 'recording space' or studio, from scratch, the most important thing to consider is the exact dimensions of the finished room(s).  The size - length width and height all make the room what it will sound like, .... get one dimension off by a few inches or centimeters, and you can screw the whole design up... get it right, and you can have an awesome sounding room that is balanced and needs no 'room EQ' from the monitor amps.  You want a flat frequency response across the range from low to high.    This is why 'rectangle' or square rooms don't often translate well as a studio... often one or two, or all walls will be built 'splayed' so that no opposing wall is parallel to each other. 
The key is to prevent the standing waves from building up in the first place.

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Offline Musical Bear

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Re: Room acoustics, treatment and sound proofing
« Reply #1 on: August 31, 2015, 01:46:21 PM »
years ago, a friend of mine had a basement and treated the ceiling with those egg cartons, and they seemed to help stop the sound from bouncing around.  He took them down a couple months later when he found tiny fibres on his glass coffee table, and wiped it off, and then had to do it again a week later. 
He said he figured the vibrations from his stereo was causing the cartons to disintegrate and were filling the air with fibre material from the cartons. 

funny, he had a big thick shag carpet on the floor then - weren't the 70's great! lol
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