Updated Reverberation Time Calculator

[John Sayers]

I've created a new reverb calc adding Owens Corning 2" and 4" - 703 and 705 as options.

you can either add them as full wall covering or use the right hand side option and add the area per wall.

HERE

Enjoy

Cheers
john

[z60611]

John Sayers:

I remember that page!

Concrete unpainted: (0.36,0.44,0.31,0.29,0.39,0.25);
Concrete with Paint: (0.10,0.05,0.06,0.07,0.09,0.08);
What a difference paint makes.

I don't see the air correction at 4000hz.

I thought the Sabine equation was only to be used if the absorption coefficient is less than 0.3, otherwise the Millington-Sette is to be used instead (because to get from Norris-Eyring and Millington-Sette's, to get to Sabine's equation you have to use an approximation that's only valid for small absorption values).

I've been playing around with a new spreadsheet for RT60, conditionally changing equations based on average absorption for the frequency. I haven't decided what to do with absorption coefficients > 0.99 yet.

[John Sayers]

Yeah - it's just a guide to give people and idea of the absorption effect.
I just thought it worthwhile to update it to include 703 and 705.

BTW - I 've fixed the concrete figures.


cheers
john

[msikio]

thanks John, that's a great tool.

What about adding double layer (1") of plasterboard as an option for walls/ceiling ?

[Young Shoota]

how do i use the calculator?

walls i built or walls that was there first. and how do i interpret the numbers that are at the bottom when i click on the frequency

[gullfo]

base it on the walls you plan to build.

[horseman]

So what can we work out with this calaculator?

Let's start with a room with the following dimensions.

Length 6 metres
Width 5 metres
Height 2.4 metres.
and with all the walls and ceiling in painted concrete and the floor in unpainted concrete. (i.e. we are going to treat the garage) We are then going to add the typical treatment (you know, get out the egg cartons, heavy drapes and curtains etc)

Carpet on the floor
Heavy drapes on the rear wall
Heavy drapes on the front wall
Light drapes (egg cartons) on the side walls
Light drapes (egg cartons) on the ceiling.


The original room has a relatively flat response (Bright Blue), albeit a bit long all over and especially in the top end, and would sound very bright and live with reverb times around .8 sec. When the typical treatment is applied we land up with a room that has a long reverb time at 125Hz and short at 4kHz. Because the high end reverb is shorter people will say the room is dead but in fact it's not really, it's only dead in the top end and too dead at that. The frequencies below 500Hz are the real concern.

This is the mistake everyone seems to make. All the treatment added only effects the high frequencies. You must consider all the frequencies when you treat a room. The shorter reverberation time in the high end is reasonable at 0.3 sec (around 0.4 -0.5sec is desirable) but you must take down the low end as well. The reverb time at 125Hz is around 2 sec, at 250 it's 0.92 sec,at 500 it's down to 0.49 sec and it reaches 0.3 sec at 1000Hz and is right down to 0.21 sec at 4kHz. The low mid and lows need correct treatment. See the low-mid and low frequency absorber pages.

Excuse me if i have missed something, this demonstration is a little confusing for me, how does using heavy drapes, eggs and carpet double the reverb time in the lower end? Where "before" shows 0.5sec at 125hz, and "after" shows 2sec at 125hz

Please Enlighten me!


Regardds

Luke

[horseman]

NOTE:
The quote in my previous reply did not include the graph found in this link

http://johnlsayers.com/Recmanual/Pages/ ... ulator.htm

[John Sayers]

Yes Luke - that's the updated one.

[horseman]

Yes,



What i am an unsure about is the example given half way down the page regarding the room (length 6 width 5 height 2.4m).


It shows that before any treatment, the reverb time at 125 hz is approx 0.5 sec,

It then shows that after treatment, the reverb time at 125 hz is 2 sec


I dont understand how this is possible, how does adding minimal treatment like drapes and egg cartons quadruple the reverb time at low frequencies


Cheers

http://johnlsayers.com/Recmanual/Pages/ ... ulator.htm

[John Sayers]

I have no idea why that occurs - as I say on the page I got the calculator from http://pages.nyu.edu/~pf207/acoustics/rt60.html which no longer exists. It was 1998 BTW!

[DiMarco]

Hi, The RT 60 looks like a super useful tool. Thank-you!
Does "Ac. tile suspended" mean acoustic tile in a drop ceiling grid or suspended in some other way?

Trying to decide if I should add a drop ceiling when the only frequencies being recorded will be human voice. Or concentrate on the walls instead. With this tool, I think I can just try different options and see the impact. Nice!