experiments in acoustics

Jake: Do you have any favorite songs or albums?

Paul: Sure I know lots of favorite songs and albums.

Jake: Anything in particular?

Paul: Alright, the most played album in my collection is Kenny Burrell and Jimmy Smith – Blue Bash. I’ve worn out one copy on vinyl and I’m in the enjoyable process of wearing out my second. I have it on CD also but it doesn’t sound nearly as good as the vinyl. Recorded by Van Gelder. Recorded in his home, his personal studio… actually his parents home.

Jake: How would you define the field you’re working in?

Paul: The field I’m working in, I help musicians get their music out so that it can be heard at its best.

Jake: I understand you have more than a working knowledge of acoustics because of your interest in sound production. More broadly though, how does acoustical knowledge help you do what you do?

Paul: The biggest way is it allowed me to design a room for careful listening, which is what we’re sitting in right now and its a very important tool in what I do. So over the years having worked in a few studios and having built several I’d learned enough that when I built these two new rooms I had a lot better idea what I was doing than previously and so I was able to build very workable tools, that’s the main thing that counts. Additionally, when I have to listen in other rooms, I have a better idea of what I’m listening around. And I do listen in other rooms, I check my work in a variety of other rooms including cars, and so that’s helpful. That’s the main thing.

Jake: So if I have a small studio apartment, approximately 2000 cubic feet, and I’d like to use if, for example: for mixing, single track recording and mastering; and I can afford maybe $1000 to improve the acoustics, what should I do?

Paul: Well it depends whether you can spend all that money on the listening acoustics or if you have to spend some of that money isolating things. Isolating is expensive, generally speaking. So if you have that issue, then you’re going to decide how much you have to spend there and how much is left over to improve your listening acoustics. If you’re asking what you can get for a thousand dollars to improve the listening acoustics (lets say you’re lucky and you don’t have to worry about isolation), then not knowing what your layout is, I’d say what I would look for first is a place that you can create a situation where you have symmetry, left to right symmetry in your monitoring and in the acoustics of the monitoring. That’s a huge thing. If you can achieve it, it gives you a huge advantage in mixing and mastering. So first I would look at what’s available. And see what where you can put together something where the side walls are not too close yet not too far and that there would be… that you’d be able to achieve symmetry. Symmetry, meaning that the speakers are equal distances for their respective side walls and that the treatment that you wind up with is equivalent on left side and the right side. It may be that you only have to treat one, maybe one side already has big windows but they have big curtains and the other side has a blank wall; then you treat the blank wall and then you have symmetry because you’ve got absorption on both sides.

Then the next thing I would do once discovering where that is and making a plan to put the monitoring there, is determine how smooth you can get the bass response before treatment and that means that you try driving the room from different locations, moving the woofer around, and either by measuring if you’re lucky or by listening if you’re not find the spot that gives the smoothest response, and again, you want symmetry so if your left channel you can find one spot that gives you a smooth response but the symmetrical position on the other side does not give you a smooth response, then you haven’t finished yet, you haven’t found it. So keep moving it around until you can find locations that give you a smooth low end response in the room at the listening position, or as smooth as you can, and still are symmetrical.

So you haven’t really spent any money yet, you’ve just started identifying stuff And that’ll tell you what you have to spend money on. As I said, you may have to… once you’ve found that much, then you want to pay attention to you’re early reflections. You want to identify what surfaces will give you one bounce reflections you’re only concerned with one bounce at the moment. Which, you know, you can use the mirror technique¹ to find that. So you’re going to spend a little money dampening those. So that you don’t have any one bounce reflections from your monitors to your ear. Then I would say the next thing is, once you’ve taken care of that, is how smooth did you get the low end response, and if you still have big problems, then you’re going to want to start building bass treatments to try and deal with them.

Jake: You mentioned measurement if you’re lucky enough, what things would you be measuring for?

Paul: Well I was talking about the first stage where you’re trying to find a location that’ll give you the smoothest low end response so you’re just measuring low end response, and looking for resonances, particularly that are poking out (they’re actually more of a problem then the holes in the response (although they’re both bad)) so you’re trying to find the smoothest and once you get to the third stage, after you’ve got your symmetry your smoothest low end response and your first reflections dealt with, then you’re looking for overall power response in the room. We hear, from loud speakers, a combination of power response in the entire room and the direct sounds coming to our ears. And in the low end its all power response. Our ear do not discriminate between the direct sound coming off the front of the speaker right to our ear and the sound that went out to the side walls and reached our ear later. At the very low frequencies, there is no difference because it doesn’t behave like ray tracing at low frequencies, but even through the low-mids, the way it adds up, the overall power response is what we hear. As you get higher and higher in frequency, the ear discriminates more and more and you’re hearing more of the frequency response of the direct signal but the power in the room still has an effect. So that’s the other place you start to get benefit from measurement is when you start to figure out how to smooth our the power response.

Jake: Ok, now some time has passed, I’ve earned some money mixing my friends’ demos, so I can afford another thousand to improve the same space; what should I do?
Paul: Well, after that, the question is how good are your speakers and amps; I think they’re about equally important If you’ve got the first three, four things we talked about acoustically pretty much under control, then the quality is determined pretty much by how good the speakers are… speakers and amps.

Jake: Alright, that’s all I’ve got, is there anything we haven’t covered you’d like to add?

Paul: Well lets see, if we are talking about listening quality, acoustics for listening quality, I would mention we talked a lot about absorption, I should mention there is such a thing as too much absorption. So we definitely want to control those early reflections, but its good if the rest of those surfaces in the room are a little live, particularly if you can get them diffusing, any way you can get them diffusing. So that you have some liveness in the room, its just late enough its not in the real early arrival window so its not confusing the sound its just giving it some acoustic support.

Jake: Thank you very much, that’s all.