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#24: Studio Acoustics

By | May 25, 2007

Studio 1AWelcome to the Podcasting Blog, I’m Ken Walker and this week we’re gonna talk about some more how to topics. I wanna deal with studio acoustics and I’m gonna give you some helpful links to some do-it-yourself acoustic solutions and we’ll also review some commercial acoustic treatment from Auralex.


Room acoustics is overlooked a lot, especially in the home recording studio. With podcasting getting so popular though, and people getting much more serious about it, I honestly expect the topic to become more common.

Pretty much every room has its own sound, when you walk in the room, there is an enormous amount of factors that control what that room sounds like. The size of the room, the materials that make up the floor, the walls, any furniture in the room, all these things affect the sound of that particular room.

For the podcaster, believe it or not, room acoustics can play a big role in your sound. For one thing, small rooms generally have a very bad sound for voice work, at least if they’re left alone. So if you have a small bedroom where you do your recording, you’re definitely gonna want to treat it with something. This effect is usually very pronounced in a bathroom, it gives you the “I’m a great singer syndrome” which works great while you’re in the shower, but it doesn’t work so well when you’re doing a voice recording, particularly spoken voice.

Let’s get into some acoustical engineering real quick and then we’ll get down to the treatment. The reason it’s good to know what problems you’ll face is because there are different types of treatments meant specifically for different types of problems. For example, you don’t generally buy a bass trap to treat flutter echo.

Now, if you record in a very large, open room, you’re probably going to be better off then in an untreated, smaller room, but, with the large open room you have the problem of people walking by, doorbells ringing, things like that, plus the small room gives you a little bit of privacy. The kinds of sounds we’re going to be worried about are some low frequency standing waves, excessive reverb or flutter, and a dead, flat sound osta viagra suomessa. The latter is actually the opposite type of problem from the first two, which I’ll deal with shortly.

By the way, what we’re talking about today has very little to do with sound proofing, which keeps outside sounds from coming into your studio, and inside sounds from leaving your studio, that’s not what this is all about. This is strictly about controlling the sound that’s generated inside your studio, mostly you and your co-host or interviewee.

In a small room, especially if it is symmetric, and a square room is much worse than a rectangular room, but both are difficult. In a small room, you have parallel walls. Two walls face each other at parallel, and you have two sets of these walls. The problem is that when sound is generated, albeit a guitar or just you talking, that sound stands a good chance of bouncing off one wall, and hitting its matching parallel wall, and bouncing right back. It can go on and on and of course sound travels very fast so you don’t hear a bouncing, you hear what sounds like a sound just going on and on until it just runs out of energy. It makes things kinda muddy sounding. It’s more prevalent with lower frequency sounds but it can occur at higher frequencies as well.

You have to approach this in three different ways. Absorbtion, diffusion, and absorbtion. The reason I say it like that is because there are really a couple of different kinds of absorption, because there are different kinds of sound. For the sake of making this plain and easy, we’re just gonna say low frequencies and high frequencies. Low frequencies are strong and they can go right through walls and bounce around all over the place, not to mention we can hear them very well most of the time. So for those frequencies, you want what is called a bass trap. You can buy these at music stores or online, but I’m gonna include a link to some great plans on making your own and they work very well and will cost you much less, you can even make them look fairly decent.

Basically you have a container, at least with the do-it-yourself kind, and you fill it with sand or insulation, and the container, which is fairly large, is sealed so it’s air tight. You usually put them in the corner and depending on your room, one or two will probably do you. It’s designed to absorb those low frequency waves that will help you tweak the sound of your room tons. After you get a couple you’ll probably notice a big difference right away, again, depending on your room size and what’s already in it, also depending on what sound sources are in the room. Play your stereo with heavy bass, then drop a couple of these in the room and play again.

The other kind of absorption that we want to do is for the high frequency signals and these cause a lot of reverb or echo. Reverb is actually a very rapid and decaying echo. Echo you would get in a very large room or like if you’re at the Grand Canyon. Reverb you’ll hear in a parking garage, or the bathroom. The reverb you hear is noticeably different depending on the environment. It could be tight and close together, stopping quickly once the sound source stops. Or it could be long and drawn out, making things sound very muddy or unintelligible.

A little tiny bit of reverb is OK for your voice, but if you can actually hear it when you play your recording back, it’s too much. Ideally, for podcasting or radio type voice work, you want a pretty dead sounding room. Incidentally, when recording musical instruments, you probably want a live sounding room, meaning that you can hear reverb. With voice work like this though, it’s better to have the room too dead, than too live, because you can always add a little reverb to sweeten it up, but you can’t take it away once it’s recorded.

You’ve probably got a guitar playing buddy and you’ve heard about egg cartons or carpet on the walls right? Don’t waste your time. Egg cartons do VERY little to control sound and I’ve even read of studies showing that they actually accentuate certain frequencies. That’s not what we want. Carpet has a limited effect, it can tone things down a good bit and in a pinch I’ve even used it. The thicker the better, but carpet has drawbacks.

I’m gonna sound like an acoustical foam salesmen here but, carpet is generally more flammable, plus it deteriorates fairly quickly, not to mention it won’t look very nice on your walls. I have no idea how you’d get it on the ceiling, which actually will need to be treated a bit as well.

This week I’m gonna be reviewing a product by Auralex which is an acoustical treatment manufacturer, one of many. Studio foam generally excels in all these areas where carpet isn’t so good, plus the foam works better than carpet as in it absorbs more sound. Aside from Auralex though, there are tons of other places where you can get foam, and even a bulk supplier that I know of.

True acoustical foam IS NOT the same as like what you’d get for doing cushions or something for a chair, it’s a different animal. The cells are made differently and the material is much more rigid, so don’t run out to an upholstery shop and staple a bunch of 1 inch foam on your walls. Studio foam usually applies with contact adhesive or something similar to liquid nails, although it is a special formula since the regular liquid nails will eat foam.

So you stick the stuff to the wall, and you don’t completely cover the wall, instead on parallel walls you want to try to stagger the placement of the foam so that you don’t have one foam pad directly across from another foam pad. That way, you really cut down on standing waves because when a wave does hit the wall, it will run into a foam pad on the parallel wall.

Believe it or not, I actually do have a do-it-yourself solution for this, but to be honest, I don’t really know if it’s worth it because I don’t think it’s much cheaper and the studio foam generally looks better. However, in all fairness, I will throw in a link because I think the gentleman did a great job on his tutorial and I respect people that make things themselves.

Our last problem is that of diffusion. We actually don’t want to totally absorb all the sound in your room because that might cause you to go crazy. You know those commercials they used to have where they’re testing the phone line and they have this black room with foam all around it and they drop a pin on the table next to the receiver? Well, they really have rooms like that. But people don’t realize what quiet is until they go in there. It’s very eerie and people get nauseous if they’re not used to it.

Instead, what we want to do is absorb lots of sound, and then diffuse the rest of it, meaning that we’re spreading the sound out and breaking it up into little pieces, scattering it all around the room. That way no one sound is focused on a particular part of the room. To do this we can use diffuser panels, which are just squares, mostly hollow, with real weird patterns on them that look very, random. Sound hits them and gets split up, bouncing in all kinds of different directions. It’s a good idea to put them on the ceiling, in general. Your room will not sound quite as dead, but the reverb in the room will die very quickly.

And of course, I’ve got a do-it-yourself link for a diffuser project that I highly recommend. I suffer from ‘tiny studioitis’ as I have an 8’x8’ room inside a room for my studio and the sound was initially terrible. I built a bass trap which helped a lot, and then treated the walls, that helped too, and I also found this diffuser panel idea on the net and that helped even more.

Sometimes, it’s not an ‘one’ thing that does it all, but it’s the combination of several treatments together that make your studio sound great for voice narration, which is what podcasting is. Studio foam will make a big difference, but the other treatments are just as necessary.

Product Review
I was doing an installation of sound equipment in a very large venue and the architects didn’t know much about sound, and didn’t ask anyone, so they built a huge square. After the fact, I was asked to fix the ever present reverb that totally muddied up the sound. I had installed very high end audio equipment but you can not fix reverb with EQ. People couldn’t understand the speaker and they were always asking the front of house engineer to turn the volume up, which only made things worse.

Given the extremely high ceilings, the only option was about $5,000 worth of foam. I called up Auralex and they were extremely helpful, suggesting models of their foam. I happened to be about 2 hours from their warehouse so I sent a driver over to pickup the load.

As soon as a third of one wall was covered, BIG difference. I mean this place had a good 4 seconds of reverb. After the foam was on the walls (which were about 25 feet high) it was amazing. You could hear reverb in your left ear, which was facing the center of the room, and no reverb in your right ear, which was facing the foam on the wall! I finished the install, which went fairly nice, just spray some adhesive on the wall, some on the foam, and stick.

The only downside to this was that the carpet in the place was grayish and on the phone the salesman told me the foam was ‘charcoal’. Their brochure photo showed charcoal as well, but this charcoal was more brown, and even plumish. They said that the foam process yielded less than consistent results, and that it truly was the correct ‘charcoal’ foam.

I’ve since found that they have a more cosmetically appealing line which is covered with an acoustically transparent fabric, which I would probably use the next time the need arose.

All in all, I cut the reverb time by more than half, which considering the room size and ceiling height, was pretty good. They didn’t want the front of the room covered, where the stage was, so that area would have helped a lot more. They could have also used some diffusion on the ceiling, but that was out of budget for the time being. The foam itself was a good product, it worked well, it was a little costly in my opinion, but you get some great support and a lot of selection.

That’s it for this week, you’ve been listening to the Podcasting Blog, I’m Ken Walker. You can contact me at podcasting@seocompany.ca or just leave a comment on the blog. Until next week, happy podcasting.

 
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