CARA - Room Acoustic Software

I just bought a copy of CARA and have started digging into it. After a bit more exposure I plan to post a review on it.

Rather than post a novel at the end, let's take the serial approach. Here's the first installment of the review as promised.

First a little background for reference. While far from being an engineer, working in the software industry for a couple of decades have provided me with a great deal of experience using computers and applications. I build my own systems (they're faster AND cheaper than off the shelf units), can program a bit and know user interfaces pretty well (sold development tools too long not to), but have never worked extensively with a CAD or drawing package. I'm also reasonably new to high-end audio, so please pardon any mangling the lingo.

My current room is rectangular and setup is pretty straight forward. BUT the room where I'm moving this month is complex to say the least. Describing it is a chore. Picture an L-shaped room. One leg is 19.5'x12' with a 13.5'-10.5' cathedral ceiling peaked in the center. A hallway off one end goes to the rest of the house and there is a small room (with double doors) across from the hallway. This end of the room also has a 7' ceiling that is 3' wide and is where the front door is located. The other part of the L is 10'x9' with an 8' ceiling and the kitchen is off to one side of it. The two sections of the L are also divided by a low hanging 10"x10" beam. There's a plethora of materials with lots of windows, tile, carpet and other surfaces of varying reflective/absorbtive properties. Nice place, but acoustically a tough room.

This room is what prompted the purchase of CARA. By no means am I deluded into thinking anything replaces experience, but getting a solid starting point is the desired result. For a rectangular room the various formulae provide that; this room demanded more.

But enough background. The CARA package appeared two days after it was ordered. Very prompt shipment and delivery by Rhinetek which is worth a lot of Brownie points. I loaded the software and dove right in.

There are two main parts to CARA. A CAD package to design the layout of the room and a calculation module. There is also a graphics playback module that is accessed via the calc module.

Installation was simple. Put the disk in and let it install. Suggestion to new users: The help system comes up upon launching the software. Take the time to go through the information being offered as it will save time in the long run. For those like me, it is possible to bull your way through, but you'll eventually read the same material, so do it up front and save yourself the hassle. For instance, the ceiling height is set with the initial room definition and cannot be changed without starting over!

First up was modeling my current room which is rectangular. Very simple and straight forward. Unfortunately, nothing new was discovered. Apparently all the formulae from Cardas, Hales, etc. are good starting points and all CARA did was reinforce what I already knew (the room is too small).

Once the basic room layout is modeled wall materials are defined and windows, doors, curtains, furniture, etc. are added. CARA supplies a library of materials and furniture, plus an editor allows altering them or adding new ones. Finally, speakers are selected and a listener position is defined. A library of speakers is included and an editor is provided for adding others or editing the existing ones. The speaker library contians mostly European manufacturers products. That's no surprise since the package was written in Germany.

While CARA can be used to analyze an existing set up it is also a good tool for selecting a starting point in a new room. When searching for an optimum position both speakers and listener are defined as regions, not finite positions. For instance, in one model the speakers are at one end of the room, the listener at the other. As laid out the listener region covers half the room and each speaker a quarter. When run CARA will find the best position for each within the defined region. This, of course, takes a little time. Depending on the number of variables used (and there are too many to go into here; suffice to say that everything including relative humidity is included) each model takes from 10-30 minuts to run. The greater the number of iterations the better the information, but the longer the run time. Weights can be applied to each of several measures depending on what the user wants to accomplish. At the end a chart is provided that includes SPL at varying frequencies along with direct sound and first wave front, as well as a static charts outlining the results of the location diagram with similar information plotted. The system also extrapolates a set of "quality numbers" for comparisons. Extrapolated as deviations from the target functions defined before running the simulation, included are frequency response, location, clearness/clarity, weighter average value and total optimizitation reference number, all expressed as percentages.

Once an optimal position is determined the sound fields can be computed and played back in an animated mode. This takes considerably longer (30-45 minutes), but the result is an eye opener. Virtual test tones are played in the room and the results are displayed onscreen. This feature alone has already taught me a lot about how waves set up in a room. Watching the waves rise and fall graphically reinforces why a particualar position may be better than one just a foot way.

So, after running a number of scenarios I am close to deciding how to initially setup the room. Next up will be to tweak and measure the results and compare them to CARA's. So far, my recommendation is that CARA is worth the $50 price of admission. Let's see if that opinion holds.

OK, that's the happy side. Here are the frustrations so far: a) CARA is metric only! I had to convert all measures before plugging them in. Minor, but it's a hassle. That cost them in the useability assessment. b) Whereas CARACALC can be started multiple times so that multiple models can be computed simultaneously, it would often times crash when the computation was halted. If one module crashed the others would continue to run, but only until they were halted. THEN they would crash. Again, kind of frustrating, but no show stopper. The good news is 2-3 models will run on my machine at the same time with no problems. YMMV as my system has 384 megs of fast RAM, though it didn't seem to be a memory issue.

Next installment: Was the setup info valid?

Was the set up info CARA provided valid?

Having modeled the room with reasonable care, including speaker position/toe-in, furniture, wall hangings, etc. CARA was set to determine the optimum speaker position. What was quickly learned was that in this room it was better to put some constraints on the software. Given too much lattitude the outcome was a "speakers-in-the-face" result. But this is a very complex room with angles, peaked ceiling, etc. In a simple, rectangular room the results were predictable as they were very close to those provided by the Cardas method. Being somewhat limited by the usuable space, CARA was run with those limitations considered. The end results are surprisingly good. After considerable tweaking the speakers are now within 1-2 inches from the positions defined by CARA for distance from front, side wall and each other. The model used, BTW, was to optimize for three listening positions side-by-side on a sofa. In this scenario CARA takes an average of the three. The variances may well come from my having made adjustments from the center position only.

Next, the calculation module, CARA Calc, was run to computing the sound fields of the room. The results were quite interesting. When CARA calculates sound fields it is as though virtual test tones ranging from below up to above the audible range (5Hz to 20.48kHz) were being generated within the modeled space. The effects are display in a 3-D animation using color variances to indicate changes in sound pressure in dbs. The animation can be started, stopped, and stepped backwards and forwards via a VCR-style control. This makes it quite easy to visually locate probable problem areas in a room.

Two observations derived from actually listening to my system and room were supported by CARA's sound field calculations. The first, and worst, is a bad bass problem in the left front corner. In CARA this shows up as a large red region. In reality simply putting one's head in the corner quantifies that the problem exists. The other was more telling of CARA's usefulness. A friend noted there was a shifting image in the mid-bass on the right side. The sound field visualization in CARA shows a small peak at exactly that position.

One downside to CARA Calc is the time necessary to run a complex model. My room has 150 visible polygons. This is high and it may be possible with further experience to bring this number down. The maximum reflection for this calculation was set to 5. According to the online documention "The maximum reflection order describes the highest number of reflections from any surface of a sound ray passing from a loudspeaker to the listening place. In a rectangular room, a reflection order of 1 yields 6 possibilities, one reflection for each wall surface. The order 2 yields 18 possibilities. For a realistic result of the sound field calculations a reflection order of at least 10 should be used. Increasing the maximum reflection order increases the calculation time, order 20 may take hours to complete."

Even though my model was run at a low maximum reflection order, the calculations took three days to complete. Thus, this is probably a step best taken when the user is satisfied with the model's completeness unless the number of visible polygons is low. Unfortunately, this limitation (actually a function of the machine as much as the product; mine is an AMD 850 with 384 megs of RAM) also renders CARA less useable for "what if" scenarios such as determining optimum placement of acoustic treatments.

All in all I have found CARA to be an interesting, useful tool. A side benefit is that now, as my system and room set up evolves, I will have a visual record of the changes for comparison.

Two things I would change in CARA are: 1) Add support for inches and feet 2) Make all fields, such as speaker placement, editable so the values can be edited instead of static displays. Dragging icons around works, but for accuracy nothing beats numeric input.

Next up: Long range impressions.

Fpeel, Thanks for the great review. I'm going to call for CARA RIGHT NOW!

Couldn't tell from your post: Were you able to make a model of your funky room?

My system is located along the long wall toward one side of a very large room. Is this something it seem CARA will be able to help? I know you're not tech support, but I'd appreciate a users impression.

Thanks,
Meta

Though not previously experienced with any CAD products, I was able to model everything in this room including a couple of odd corners and the two exposed beams on the ceiling. Not the most complete CAD package according to a buddy who would know, but definitely workable with some diligence.
BR>BTW, my system is set up along the 19.5' wall. A neat feature is the ability to do a 3-D walk through of the modeled space. Mine looks alarmingly like my room. Except my speakers aren't blue. ;-0 Which reminds me of a bugaboo in CARA. Be careful when defining the regions in which speakers or listeners can be moved during optimizations. If these overlay a 3-D object (sofa, rack, TV, etc.) the speaker or listener will be raised above that object. To avoid this I always do a 3-D walk through before running any calculations.

Ran the calculations once without realizing this had happened and got great reference numbers. Turns out the speakers and listener were suspended about six feet in the air! Haven't figured out how to make stuff float in the air quite yet...