Question: Bob Golds room calculator

[Shellacattack]

Has anyone used this calculator?

http://www.bobgolds.com/Mode/RoomModes.htm

I'm trying to understand what it's telling me about my room dimensions, but it's fairly technical. Near the bottom of the page, it shows this (I've added the X in place of numbers):

"Frequency Regions:
- No modal boost: Xhz to Xhz
- Room Modes dominate: Xhz to Xhz
- Diffraction and Diffusion dominate: Xhz to Xhz
- Specular reflections and ray accoustics prevail: Xhz to Xhz"

Can anyone explain this to me? I interpret "room modes dominate" as meaning this is the frequency range that my room accentuates.

Basically, I'm trying to turn the calculations into a way to understand my mixes better, and determine what my room requires in terms of treatment.

Thanks for your help!

[GIK Acoustics]

Hello!

If your main cause is to find out what problems your room is having, I highly suggest testing as opposed to calculating. Calculation is useful before a room is built, but testing is the only way to get concrete details about the space you're in. You can usually correlate what the calculators give you with what your response looks like - this can help differentiate whether problems you measure are due to room modes or other phenomena like SBIR, so they can be helpful. But they really don't give you an idea of what exactly is happening at mixing position.

You can use the following (free) program to test your room: http://gikacoustics.com/room-eq-wizard-tutorial/

[Shellacattack]

Thanks for the tutorial link! I've had REW for awhile now, but hadn't used it yet because I kept having issues when calibrating it. Your tutorial helped a lot in that regard!

However, I may have calibrated something incorrectly. My graph doesn't look too strange, but the dB reading on the left side seems much higher than any pics I've seen on this forum or others. It also differs from the dB reading for the graph examples shown in the GIK tutorial. Is this an issue?

Here's a link to the pic...

https://plus.google.com/photos/11164461 ... 9889209761

[fossiltooth]

Alexander's advice is pretty spot-on. The best thing to do is measure with a microphone at this point.

For the record, you're thinking of "nodes". That's a point of complete (or nearly complete) attenuation. "Modes" are often bandied about as being synonymous with "resonances." But I believe that the correct distinction is actually between "nodes" (a null point of no vibration) and anti-nodes (resonant points). Technically, both are part of the room's "mode". That's niddlely technical distinction though.

Anyway, here's my stab at translating this stuff. These are wild guesses at what this person means to convey, but they are somewhat educated ones, I think:

- No modal boost: Xhz to Xhz

"Extreme low frequencies where the room should be somewhat immune to developing resonant standing waves."

- Room Modes dominate: Xhz to Xhz

"Low frequencies where you may have significant build-up in one place or another"

- Diffraction and Diffusion dominate: Xhz to Xhz

"Frequencies that should be dispersed fairly evenly and randomly throughout the room as they bounce off of reflective surfaces"

- Specular reflections and ray accoustics prevail: Xhz to Xhz"

"Frequencies that are not dispersed evenly and randomly, but rather remain concentrated and bonk around from one reflective surface to another creating imaging issues and flutter echo."

It's hard to say, as this was not written for easy reading. But if you want to better understand the difference between specular reflections and diffusive ones, try this. The wikipedia pages on nodes and room modes are pretty good too.

[JWL]

Shellac,

Your graph looks pretty typical. Don't worry about the dB values; that's only necessary if you need very precise measurements relative to different measurements, ie, if you need 85dB to really be 85dB. The shape of the curve is really what you are interested in.

Room mode calculators in general are useful when you are planning to build rooms, as they predict where the modal frequencies will be based on the rooms dimensions. If you are already in a room then measuring the space is much more useful.

But at the end of the day, no matter where the peaks and nulls are in your room, the first steps (and possibly the only needed steps) of treatment are always the same.

[GIK Acoustics]

Thanks for the tutorial link! I've had REW for awhile now, but hadn't used it yet because I kept having issues when calibrating it. Your tutorial helped a lot in that regard!

However, I may have calibrated something incorrectly. My graph doesn't look too strange, but the dB reading on the left side seems much higher than any pics I've seen on this forum or others. It also differs from the dB reading for the graph examples shown in the GIK tutorial. Is this an issue?

Here's a link to the pic...

https://plus.google.com/photos/11164461 ... 9889209761

I'm glad our tutorial was helpful!
The actual level shown doesn't matter so long as it's not above the visible portion in REW! Haha! As long as your noise floor is sufficiently low, you should be quite okay!

Feel free to ask any other questions. You can post any questions here, PM me, or fill out our acoustical advice form on our site if you'd like help interpreting the measurements! We also just published an article on our website that I wrote about decay times and waterfall graphs, describing what it shows and how to treat the room based on what it shows. Here's a link to the article: http://gikacoustics.com/understanding-decay-times/

[GIK Acoustics]

Fossiltooth, you've done a good job explaining them. Allow me to expand a bit further on the first point:

- No modal boost: Xhz to Xhz

"Extreme low frequencies where the room should be somewhat immune to developing resonant standing waves."

Yes - but moreso, under the first axial mode - we simply can't predict how it will behave. Resonance could still happen, but it simply won't be a byproduct of room modes. So it doesn't imply that there will be good response under that frequency. Room modes actually are beneficial as they help give us a predictable behavior and can actually help a room's response as well. Though we must dampen these resonances, the actual support for bass they provide is welcome.