Predicting the sound at the listening position

Hi, I'm in the early design phase of a studio to be built within the ground floor of an existing structure. The control room could potentially be a Louden room (19'L x 14'W x 10'H) with angled slot walls in front to create a RFZ. These dimensions look very good in Bob Gold's room mode calculator. So let's assume a good starting point for room dimensions and correct studio construction (layered stiff walls etc). My priority is to nail the sound specifically at the listening position. How do I do this? Is there modeling software or an acoustics consulting company that can run the numbers and predict the acoustics at a specific location of a room? Thanks, I'll be posting more as design and construction moves along.

It can be done, to a certain extent. There is even some software that can "auralize" for you, so you can hear how it would probably sound. But it isn't just the room dimensions that matter: You also need to know the treatment on each of the walls, the exact location of the speakers and the listening position, and some parameters of the sub. REW can do some basic room simulation, but only for the low end of the spectrum. However, it's the low end that is the most important! It predicts roughly what the response will be like. Here's what it would be for those dimensions, up to 200 Hz, assuming typical home-studio speakers, locations and treatment, and sub crossover at 150 Hz. Assuming you wanted more of a full-range speaker prediction (not just the sub), it would look more like this: Got that by setting the sub crossover to 15kHz, instead of 150 Hz. Of course, that's for a purely rectangular room: It would be a bit different for an RFZ design, and different again if your speakers are soffited: You'd need to adjust that for the lack of SBIR on the front wall, and suchlike. And also, that's purely theoretical! An actual room built like that would not necessarily match that exactly, although it would be reasonably close. - Stuart -

Thanks for the info, and graphs, Staurt! Looks like there's a big dip at 70hz which is exactly the kind of thing I want to address in software rather than by moving a wall after the fact. I'll download REW and experiment. In researching REW I came across other software such as Cara and ABEC. Do you have any thoughts on these? I'm primarily interested in modeling low frequencies as the rest can be treated post construction. It would be interesting to experiment with splaying walls to see how that effects the listening frequencies too (which REW can't do), but if necessary I'm fine with modeling only rectangles with REW until I nail it. One other question if I may. Is Sketchup (free version) the standard for DIY studio design these days?

Looks like there's a big dip at 70hz which is exactly the kind of thing I want to address in software rather than by moving a wall after the fact.

Right! It's a lot cheaper to do it in the design stage, too: moving the mouse definitely costs less than moving a wall! :) However, that 70Hz dip is associated more with the treatment than with the room dimensions. I just there in some pretty much common treatment parameters there, and that dip turns out to be associate greatly with the ceiling: it is, after all, the tangential mode associated with width/height, and also the tangential associated with length/height. So increased damping on the ceiling and a throw rug on the floor would help there, and so would an angled, hard-backed cloud. Lowering the ceiling to 9'7" also helps quite a bit, as does increasing the width by 8", moving the sub a few inches more into the room, and also decreasing the length to 18'2". Doing all of the above, you get this: That's probably about as good as you are going to get it, for a room with roughly those dimensions. The ratio is 1 : 1.53 : 1.89, which is close enough to Louden's best ratio. The modal spread is quite decent like that.

In researching REW I came across other software such as Cara and ABEC.

I played around with Cara a bit, and found it reasonable but frustrating. It's not very intuitive, and setting things up is a bit of a pain, I was actually planning to buy it last year, but found that buying it is even harder than using it! Nobody wanted to take my money and e-mail it to me, believe it or not... :shock: On the other hand, you probably don't need t go crazy on trying to predict your room acoustics: Reality seldom matches even the best software predictions, since relatively minor difference during the actual construction can have much bigger effects than you'd expect. So the general advice around here is to stay build then measure, then treat. Of course, stay away from bad ratios with your design and get close to a good one, but there's also no need to try to nudge things around by 64ths of an inch or tenths of a degree to try to get a "perfect" ratio: there is no such thing. There are "better" ratios and "worse" ratios, and that's about it. You'll find that SBIR due to speaker placement, good layout and geometry, and good treatment are far more important than having the best possible ratio under the sun. I can build you a room with a perfect Sepmeyer #1 ratio that sounds terrible, and I can also build you a room with a ratio rated way down towards the bottom of the list, but that sounds rather good. There's a lot more to studio design than just ratios! :)

I'm primarily interested in modeling low frequencies as the rest can be treated post construction.

Low frequencies can also be treated post-construction, actually... :) Provided that the treatment is done right. But yes, low frequencies is where you need to concentrate your efforts most, since they are non-directional, harder to isolate, and harder to treat in general, in addition to the modes being few and far between, and the wavelengths being very large, with respect to the size of the room and the things in it.

One other question if I may. Is Sketchup (free version) the standard for DIY studio design these days?

Pretty much, yes. At least, it's what most people here use. It's a very useful tool, very powerful once you get the hang of it. The learning curve is a bit steep to start with, but it all starts to make sense after a while. - Stuart -

Hey Stuart, Thanks so much for the information! Damn, that's a mighty fine frequency plot you came up with. You should patent that shape (but let me use it first)! Sorry for the delayed response. I got buried this week mixing and mastering, so I'm just getting back to this. So, FYI, two different acoustics modeling software makers confirmed for me that unless the room is a simple shape (rectangle) they can't predict the bass response accurately. I had assumed that since we put a man on the moon 50 years ago, there would be software to tell me how much bass I'd get in my mixing position by now. :roll: My plan is evolving for this studio -maybe doing it inside a barn, but the control room shape will be carried over into whatever design I end up with. Once I get further along I'll post a floor plan to get people's feedback. Mucho Regards! Angelo Angelo