Okay, what they measure is 0.7 seconds,

but I roughly estimate this 0.9 second, I think.

You see what I did is,

I didn't spend any money and the total amount of

money for having this kind of instrumentation,

I can estimate this would be about $5,000.

And so, it's way above I think roughly, $6,000 or $7,000.

I didn't spend any money.

So, there are some small error,

I don't know which one is correct,

but it is very close.

So, I encourage you guys to estimate the reverberation period for your room by roughly

calculating the 0.161 multiply by the volume and divide by open area window,

and you do not know very precisely what it means by absorption coefficient,

and we'll continue to talk about how to measure absorption coefficient next lecture.

Okay? So, let me summarize what we've learned today,

and we introduced the actually what Sabine did in a long time ago.

The father of architecture acoustics,

and room acoustics, the founder of room acoustics,

and assumption behind the Sabine's lecture is that he regard

the sound field that can be assumed to be reverberant or diffused.

And you learned about what it means by diffuse sound field,

and direct sound field,

and a reverberant sound field,

and those will be depending on the surface in periods discontinuity.

And that discontinuity will absorb sound energy,

and reverberation period he argued

that ought to determine the quality of a room that is proportionate,

that is equal to 0.161 multiplied by the volume of a room divided by open area window.

And we demonstrated how to use that formula very,

very roughly, extremely roughly,

to calculate the reverberation period.

Okay. This summarizes today's lecture.