CARA - anyone use it?

When you say it models all those things to determine the best speaker placement, in what way does it model them? Do you mean it uses them to give you an RT60 curve?

Or do you mean it can actually model all the specular reflections time of arrival and amplitude at the listener position? That might be interesting, but IME the modal behavior is more important and the two rarely co-inside with regards to best speaker position.

Something like this - http://www.hunecke.de/en/calculators/loudspeakers.html

...will allow you to model speaker and listener position with regards to modal behavior. So you can get the best speaker position from that, then maybe tweak a little by ear.

From there you might want to know the RT60 curve, so you write down the main materials in the room and the surface area of each. Do a few quick calculations on a bit of paper and you have your answer. From that you can work out what amount of absorption you need to achieve your RT60 target curve.

The last port of call might be the reflections and their time of arrival. That is easy as you can work out where the first reflection points are and treat them.

You now have ideal speaker position wrt modal behavior, a good RT60 curve and a well defined initial-delay-gap free from first order reflections.

What else do you need to know for getting your system and room set-up?

 

That's exactly what it does. Cara is a finite-element/ ray-tracing engine., and you have control over the number of iterations* and many other aspects if desired. As a result, it can give you a complete 3d plot of SPL levels for the room across the bandwidth you set, at the spatial resolution you set, at any frequency - animated if you like. Very, very powerful, esp for demonstrating to people the ways in which splayed walls don't necessarily help matters at all in control rooms... Yes modal behaviour dominates, but only up to the Schroeder criterion frequency (maybe 300Hz depending on room size); after that decent modelling of the effect of finishes can be very illuminating (esp. as a designer of spaces).

So - the RT60 curving is lot faster and more refined than doing it by hand - for a start you get an RT60 curve vs frequency. This is invaluable for balancing finishes/ getting RT60 even across the specturm and a helluva lot more accurate/ faster than doing it by hand - even including making the model sufficient to show the effects.

*each extra level one takes 10x longer, which is why I suggest you start at 3!

 

Thanks for the detailed reply Martin. That sounds pretty cool. Can you see a gated frequency response in the model?

I ask because IME after the first 10ms or so, its not the specular reflections effect on FR thats important, its how diffuse they are and how long the decay rate is vs. frequency. So also an ETC graph would be good.

Can you model a room shape as complex as a RFZ control room? The sort that is kinda an odd octagon shape to avoid first reflections without need for absorption. I only ask because I was whistfully thinking about how I would design my ideal listening room the other day!

P.S. I would do RT60 vs Frequency by hand. But accepted its still not going to be quite as detailed.

 

<goes digging> No, I can't seem to derive an ETC graph. But you can view the early decay curve in detail, or it will take a music file and impose the calculated effect(s) on it, the idea being an 'auralisation' of the room as modelled (I havent; played with this at all...)

Sure, even model a QRD if you like - might take you a while though!

 

Now that IS cool! So you can turn it into a DSP mastering reverb with fully customisable spaces. Any limit to the size of room you can play with? Like.. an auditorium?

It might be quite a nice idea to model a room with and without acoustic treatment. I could put it on my website to help people understand what sort of difference to expect with my SoundSpace stuff. Sounds worth £50 from a curiosity point of view at very least.

 

Drop me a PM Simon if you have an example in mind and I'll have a bash at a 'before and after'

 

Kind offer. PM sent!

 

Simon - If you get to Model your panels/ treatments in cara could i have a set to add in my own room model ?

I would happily buy a set of panels from you. If I knew accurately the effect they would bring.


regards
Andy

 

My copy CARA has arrived and I will be using it over Xmas I have also borrowed a sound level meter from work. My first obstacle is that I need to wrestle a PC off my son to get started.
Andy

 

Have fun with that...

I'll be getting to the sample model over the next few days - will update then.

 

Odeon

I was a bit dubious of CARA (like Tenson) and have never really looked at what it actually does. I have just had a quick look and if it does what it says on the website - it appears to be extremely cheap.

We use this package http://www.odeon.dk/ which is one of the "standards" among acoustic consultants. You don't want to know how much ODEON costs though

Having said that, I'm not sure how useful this level of analysis is for the the acoustcially "small" listening rooms most of us have. This stuff is normally used for much larger listening spaces, i.e. right up to concert halls.

The basic methods required to treat small rooms are well known and I agree with Tenson that in reality your speaker/listener positions are generally not very flexible. It's interesting as a teaching exercise and sounds like a load of (cheap) fun though.

I'm following this thread with interest. Can someone post some outputs of CARA here?

 

Bloody hell, I bet that needs a powerful computer!

 

It used to in the 90's but now everythings fine.

I think the whole CARA thing just shows how some powerful tools are now accessible to all. Having siad that, there's no still excuse for good old experience..

I am old enough to remember the days of TECRON machines to measure TEF and it cost about as much as a new car. http://svconline.com/mag/avinstall_years_ago_sound_6/

Now you can do it with a laptop and about £700 worth of soundcard + software + mic.

 

CARA installed and tried out

I was a little concerned that my lack understanding of sound would hinder sucessfull use of CARA so I was very pleased to have loaded cara on my PC and modelled my basic room and furniture and got my first results in less than 2 hours (speaker positioning and reverb times) - I didnt watch any instruction vids. I am no PC expert the basic functions seem very intuative.

As I suspected my room is far from ideal. Next up - Auralisation a simulation of sound reproduction However for this I will need to read up. This package is brilliant.

Andy

 

Andy - can you post a few screenshots of the outputs?

Can this package output EDT (early decay time) as well as Reverb Time?

If so, that's very powerful. A comparison of the EDT and RT values tell you a lot more about how a room actually sounds with music than RT alone. EDT is an indication of the "running reverberance" in a room (rate of decay over first 10ms) and relates more to what you actually hear when playing music. You don't really get to hear the full RT decay (60ms) with music sources.

 

Hi andyoz Yep Early Decay Time is output

screen dumps are too large to add on to ZG please pm you email address

there some info about the tool here.

http://www.cara.de/ENU/index.html

Andy

 

Just upload the pictures to imageshack and link to them.

 

I will post info from CARA as soon as I can reduce the file sizes of the screen dumps and get my wifes xmas pressie going - a new "hassle free" PC that failed to start on switch on.

I have been adding acoustic foam panels into my modelled room
and now listened to all of the training vids I have run a sound field calculation of my room and animated it you can even spin the resulting 3d map around with the mouse I dont understand what is telling me but wow it is certainly very very impressive.

I agree that CARA is a great way to learn about room effects

I draw a very rough helmholz absorber in the room just to see what would happen. When I ran the acoustic ambiance calculator - cara told me "you have an helmholtz absorber in the room remove it"
Andy

 

What UK dealers sell Cara?

 

Hi Guys...

Very very interesting thread this one.

As I'm going to build a completely new listening studio this year of 100 m2, I was bothered a lot on how I should treat the room getting most for the buck doing that.

I didn't know of this product.

Thanks now I do.

Gerner