How to determine mode vs SBIR issue?

[studiogenocide]

I'm glad your back Fitz. You helped me a lot- and we are doing some very sweet tracks these days. I know it doesn't pertain to this thread, but I upgraded to a new mic pre and DAW that I just love. Holla back if you get a minute in a PM. Cya

 

[1tonio]

Tonio,

understand - there is no such animal as the "38% rule" - it is not a rule - it is a suggested starting point only - it is intended to give put you in the ball park of where your sweet spot will be- but once there it is up to you to make the effort to do extensive testing to find the actual sweet spot - which would include testing multiple speaker locations as well as the locations for your ears.

The 38% location was a suggestion made by studio designer (who I believe we can now refer to as "world renowned" seeing as he is designing studios in Europe as well as the States) Wes Lachot - who has made it quite clear that this was never intended to be viewed as a rule.

Just telling you this so you can keep the proper perspective......

Rod

Hi Rod,
Understood. I just wanted to let Ethan know that I used the 38% mixing position in mind as a start. Before making rear wall treatment decisions I wanted to see how to figure out what was the modal issues for rear wall (treatment) and SBIR issues (moving the mix position/speakers).

On my waterfall plot, is it safe to say 45, 60 an 90 hz peaks are modal, and
70 ish, and 120 hz nulls are SBIR?

Trying to determine how SBIR is effecting my situation. Based on Ethans freq/distance calculator 70 hz is @ 48 " at 1/4 wavelength, and I am sitting at about 50 " from the speakers and 58" from the front wall. I could just randomly move the speakers around and find a sweet spot, but I want learn the maths.

I don't want to take the : just put more BB panels in there approach. I realize for this small square room, it probably will take enough sabins to the point of being dead. With the coupled openings I'm wondering even if I add a bunch of BB traps etc will not be worth it or my time or budget. I see a RT60 about 1 sec in the low end, and the mudd area (200-300hz) or so is only .2 ms. Not sure if getting RT60 in T30 mode is even something to consider in a small room, however.

T

 

[Rod Gervais]

Hi Rod,
Understood. I just wanted to let Ethan know that I used the 38% mixing position in mind as a start. Before making rear wall treatment decisions I wanted to see how to figure out what was the modal issues for rear wall (treatment) and SBIR issues (moving the mix position/speakers).

OK


On my waterfall plot, is it safe to say 45, 60 an 90 hz peaks are modal, and
70 ish, and 120 hz nulls are SBIR?

I cannot determine from a waterfall plot what the source problem is - this because it does not really give me a time indicator. The value of a waterfall plot has to do with indications of ringing more than anything else. I do not place as high a value on their use as some do.

But they are pretty.........

Trying to determine how SBIR is effecting my situation. Based on Ethans freq/distance calculator 70 hz is @ 48 " at 1/4 wavelength, and I am sitting at about 50 " from the speakers and 58" from the front wall. I could just randomly move the speakers around and find a sweet spot, but I want learn the maths.

SBIR effect take place before they reach you - and thus your location has little to do with them - just for visual purposes - picture a reflection from a wall that affects a tone as it is traveling towards you - you only receive the effect -

If moving your small distances drastically changes the level of those frequencies then my first guess would be room modes - if they are relatively stable - then SBIR would be the more likely source.

Rod

 

[1tonio]

Rod,
Based on : The way to tell if a given peak is modal or due to SBIR is to look at a waterfall plot. Modal peaks have extended decay times called ringing, and non-modal peaks do not.

Can we conclude that the waterfall plot shows ringing at 45,60& 90hz?

I cannot determine from a waterfall plot what the source problem is - this because it does not really give me a time indicator.

Is the impulse response graph or ETC graph the appropriate time indicator for SBIR?



T