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post #33091 of 62250
11/23/10 at 9:30am
Quote:
Originally Posted by audyssey View Post

How did the EBU come up with this? BTW, they're not the only ones. ITU has very similar recommendations.

Yes but they don't do better in explaining the "why". But all of this is not really relevant because domestic listening spaces show a similar low RT. What makes these spaces sound good or bad is modal ringing and first reflections. RT doesn't reveal any of this.
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post #33092 of 62250
11/23/10 at 9:31am
Quote:
Originally Posted by audyssey View Post

Which is quite low (lower than what is found in most home listening rooms) and hence the discussion. How did the EBU come up with this? BTW, they're not the only ones. ITU has very similar recommendations.

Quote:
Originally Posted by SpotcheckBilly View Post

That looks pretty close to the EBU's 0.24 recommendation, doesn't it.

Cheers,
SB

The room (21x16x8 ft) is what I would say, rather normal in size, I know there are quite a few much smaller spaces in use, but I wouldn't say this room size is unusually large though...

So with a RT of 0.228 looks to be good as it compares to ITU and EBU recommendations?
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post #33093 of 62250
11/23/10 at 9:51am
Quote:
Originally Posted by SpotcheckBilly View Post

That looks pretty close to the EBU's 0.24 recommendation, doesn't it.

Cheers,
SB

It is exactly the EBU recommendation for Al's room volume. The 0.24 s mentioned in the paper was for the average room volume of 95 cu. m. in the database presented. 0.24 is not an absolute recommendation. It depends on the room volume as per the formula posted above.
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post #33094 of 62250
11/23/10 at 9:57am
I am of two minds on this line of talk. On one hand it is good to push our knowledge of how to achieve the best performance possible from our rooms/systems, but on the other hand it causes many to think that there may be something wrong that needs to be corrected before they can enjoy their theaters again.

Just tossing that out there.

Jeff
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post #33095 of 62250
11/23/10 at 9:58am
Quote:
Originally Posted by Al Sherwood View Post

The room (21x16x8 ft) is what I would say, rather normal in size, I know there are quite a few much smaller spaces in use, but I wouldn't say this room size is unusually large though...

So with a RT of 0.228 looks to be good as it compares to ITU and EBU recommendations?

Maybe some confusion here.. The value that you found is the EBU recommendation for what they think your RT should be given your room volume. We have no idea what the actual RT of your room is. It's likely significantly higher.
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post #33096 of 62250
11/23/10 at 10:00am
Quote:
Originally Posted by markus767 View Post

Yes but they don't do better in explaining the "why". But all of this is not really relevant because domestic listening spaces show a similar low RT. What makes these spaces sound good or bad is modal ringing and first reflections. RT doesn't reveal any of this.

True. And unfortunately many try to "reduce" RT by adding a bunch of fiberglass absorption that ends up reducing only a certain range of frequencies while having no effect on modal ringing. This can often make things worse because it exposes the lower octave problems even more.
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post #33097 of 62250
11/23/10 at 11:01am
Quote:
Originally Posted by audyssey View Post

True. And unfortunately many try to "reduce" RT by adding a bunch of fiberglass absorption that ends up reducing only a certain range of frequencies while having no effect on modal ringing. This can often make things worse because it exposes the lower octave problems even more.

Very true. It depends where fiberglass is added. Straddling all 12 corners of a rectangular room is pretty effective in reducing modal ringing.
Adding broadband absorption (15 cm fiberglass + 15 cm air gap) to the front wall is also a very good idea. It reduces very early reflections and significantly reduces the amount of reflected sound coming from the back of the room before it gets reflected onto the listening position for a second time.
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post #33098 of 62250
11/23/10 at 12:44pm
Quote:
Originally Posted by markus767 View Post

... Straddling all 12 corners of a rectangular room is pretty effective...

Ya probably gotta be a smartypants to find those extra 4 corners.
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post #33099 of 62250
11/23/10 at 12:46pm
Quote:
Originally Posted by SoundofMind View Post

Ya probably gotta be a smartypants to find those extra 4 corners.

Some need to be smartied up to find more than four corners.
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post #33100 of 62250
11/23/10 at 1:10pm
Quote:
Originally Posted by SoundofMind View Post

Ya probably gotta be a smartypants to find those extra 4 corners.



Best, Markus
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post #33101 of 62250
11/23/10 at 1:19pm
I don't think SoM is saying that you're wrong about there being twelve corners in a rectangular room, only that most people don't think of all of the corners as, well ... corners. Nevermind thinking "outside the box" most haven't completely thought out the inside of the box.

Jeff
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post #33102 of 62250
11/23/10 at 1:45pm
There are two in every room and one in every corner. What is it?
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post #33103 of 62250
11/23/10 at 2:22pm
Quote:
Originally Posted by SoundofMind View Post

There are two in every room and one in every corner. What is it?

The letter o ?

Quote:
Originally Posted by pepar View Post

... only that most people don't think of all of the corners as, well ... corners. ...

Yes, when I read corners, I immediately thought vertices. It took me a moment to figure out that "12 corners" was referring to edges.
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post #33104 of 62250
11/23/10 at 2:59pm
It's hard to imagine any but the fanatical actually doing that.

Quote:
Originally Posted by markus767 View Post

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post #33105 of 62250
11/23/10 at 3:43pm
Quote:
Originally Posted by noah katz View Post

It's hard to imagine any but the fanatical actually doing that.

Then we've come to the right place
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post #33106 of 62250
11/23/10 at 4:44pm
What would be the over/under on WAF for fiberglassing all of that?
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post #33107 of 62250
11/23/10 at 5:23pm
Quote:
Originally Posted by Bill Mitchell View Post

The letter o ?

O yeah. Vertices, dang, I remember those...I knew we had lots of smartypantses around here.
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post #33108 of 62250
11/23/10 at 5:42pm
Quote:
Originally Posted by Bill Mitchell View Post

Yes, when I read corners, I immediately thought vertices. It took me a moment to figure out that "12 corners" was referring to edges.

Sort of makes me wish that when teacher told me to go sit in the corner I did so in the one formed by the ceiling and the front wall ...
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post #33109 of 62250
11/23/10 at 5:52pm
Quote:
Originally Posted by noah katz View Post

It's hard to imagine any but the fanatical actually doing that.

I've done 7 of the 12.

Can't do it in the front wall and ceiling. No space because the screen is there.

Kinda hard to do it between the walls and floors ... I'm not that fanatical ... yet.

Mark
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post #33110 of 62250
11/23/10 at 7:24pm
Quote:
Originally Posted by streetsmart88 View Post

I've done 7 of the 12.

Can't do it in the front wall and ceiling. No space because the screen is there.

Kinda hard to do it between the walls and floors ... I'm not that fanatical ... yet.

Mark

There are so many ways to interpret this post . I pity the fool that jumps into this thread and reads this first!
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post #33111 of 62250
11/23/10 at 11:43pm
Quote:
Originally Posted by markus767 View Post
Adding broadband absorption (15 cm fiberglass + 15 cm air gap) to the front wall is also a very good idea. It reduces very early reflections and significantly reduces the amount of reflected sound coming from the back of the room before it gets reflected onto the listening position for a second time.
Uh, that is 30 cm... too thick for the local management... any way to do
it thinner with another material?
And what about adding it to the back wall instead of the front wall? Or both.
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post #33112 of 62250
11/24/10 at 2:55am
Quote:
Originally Posted by rickardl View Post
Uh, that is 30 cm... too thick for the local management... any way to do
it thinner with another material?
And what about adding it to the back wall instead of the front wall? Or both.
"Difficulties of development" are always and immediately followed by "development of difficulties", eh?!! For the time being I will rely on Audyssey algorithms and available memory to store and compensate the responses of my living room, ...after all I don't live in a church!
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post #33113 of 62250
11/24/10 at 5:03am
Quote:
Originally Posted by rickardl View Post
Uh, that is 30 cm... too thick for the local management... any way to do
it thinner with another material?
Well, if you want fiberglass to have a significant effect at lower frequencies then it has to be thick.

This is a simulation with 150 mm fiberglass (5000 rayls/m); significant absorption is > 0,8:



Fraunhofer has developed absorbers that are only 100 mm thick but they are expensive and heavy. Basically those absorbers are a sheet of metal glued to a layer of foam. They work at lower frequencies. So if you want to make them broadband a second layer of foam needs to be glued on top which makes them thick again.

Quote:
Originally Posted by rickardl View Post
And what about adding it to the back wall instead of the front wall? Or both.
Depends on what kind of sound field you're trying to create. My speakers have narrow directivity to minimize very early reflections. The delayed reflections from the back wall help in preserving some "liveliness".
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post #33114 of 62250
11/24/10 at 8:44am
I have a "modest" 7.1 system, using the Onkyo TX-SR606 and Onkyo's SKS-HT540 Speakers. Samsung LN40A550 LCD, & a Sammy Blu-ray C6500...Here's my "newbie" question...Would mounting my center speaker behind my LCD be foolish or would it add to "centering" the dialog? My LCD is on top of an entertainment center.

Ghpr13
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post #33115 of 62250
11/24/10 at 9:02am
Quote:
Originally Posted by Ghpr13 View Post
Would mounting my center speaker behind my LCD be foolish or would it add to "centering" the dialog?
That would be ...unwise. To simulate what that would sound like, put your hand over your mouth and start talking. Placing the speaker above or below the TV and pointing it down (or up) to the ears is the way to go.
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post #33116 of 62250
11/24/10 at 9:07am
Quote:
Originally Posted by markus767 View Post

Fraunhofer has developed absorbers that are only 100 mm thick but they are expensive and heavy. Basically those absorbers are a sheet of metal glued to a layer of foam. They work at lower frequencies. So if you want to make them broadband a second layer of foam needs to be glued on top which makes them thick again.
Another equally effective (but also expensive) solution is the Modex Broadband by RPG. Spec sheet here: http://www.rpginc.com/products/modex...-Broadband.pdf

Very similar characteristics to the data that Markus posted. We have used these with great results in the research labs at USC.
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post #33117 of 62250
11/24/10 at 10:10am
Quote:
Originally Posted by audyssey View Post
That would be ...unwise. To simulate what that would sound like, put your hand over your mouth and start talking. Placing the speaker above or below the TV and pointing it down (or up) to the ears is the way to go.
audyssey,
Thanks. I figured it was rather stupid, but I had wanted to ask. I am thinking about mounting it above the LCD and aiming it downward. It would be above the LCD but attached to the wall behind the entertainment center. Would that be an OK spot for it? (My TV room is about 12' X 9')

Ghpr13
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post #33118 of 62250
11/24/10 at 10:20am
Quote:
Originally Posted by Al Sherwood View Post
The room (21x16x8 ft) is what I would say, rather normal in size, I know there are quite a few much smaller spaces in use, but I wouldn't say this room size is unusually large though...

So with a RT of 0.228 looks to be good as it compares to ITU and EBU recommendations?
Quote:
Originally Posted by audyssey View Post
Maybe some confusion here.. The value that you found is the EBU recommendation for what they think your RT should be given your room volume. We have no idea what the actual RT of your room is. It's likely significantly higher.
I understand, the mathematical model only gives information back based on size not treatments or surfaces.

Determining that would take some careful measurements I am sure...
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post #33119 of 62250
11/24/10 at 1:24pm
Quote:
Originally Posted by Al Sherwood View Post

I understand, the mathematical model only gives information back based on size not treatments or surfaces.

I would even claim that the mathematical model is plain wrong for acoustically small rooms like living rooms and home theaters.

Quote:
Originally Posted by Al Sherwood View Post

Determining that would take some careful measurements I am sure...

Careful measurements will show that reverberation time doesn't correlate to what is perceived by a listener.
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post #33120 of 62250
11/24/10 at 1:36pm
Quote:
Originally Posted by markus767 View Post

I would even claim that the mathematical model is plain wrong for acoustically small rooms like living rooms and home theaters.



Careful measurements will show that reverberation time doesn't correlate to what is perceived by a listener.

Hi Markus, don't stop here. Give reason by expanding your statements, please. Thx!
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