May be out of place here, but I have a question about HOME THEATER acoustics

[pepar]

I apologize if I am completely out of place here on this STUDIO forum with my home theater question, but I'm looking for opinions from people familiar with small room acoustics. A possible flaw in my thinking is that the target environment is different for a studio than for a home theater. Fingers crossed here! :-)

My sense is that my room is over-dampened. From asking on some other forums, I get the impression that there is a range of decay times that is appropriate for its size depending on preference and that mine falls at the bottom end of the range. That I *think* it is a bit too dead suggests to me that my preference would be for a bit more, umm ... air.

Hopefully, I can get some feedback on my room. TIA!

(note: I have two electronic correction devices and that is what the label denotes)

[avare]

The graph shows an RT60 around 200 ms. On the low side low. What is the size of the room? Recording 5.1 room specs use 3500 ft3 as a nominal with an RT60 of 250 ms, adjusted by the cube root of the actual to reference room volume (smaller rooms having lower RT60 times).

Well sized,
Andre

EDIT: I misread the graph initially. DanDan caught later in the thread, thanks. The post has been corrected

[Ethan Winer]

Originally Posted by pepar

I'm looking for opinions from people familiar with small room acoustics.

Nice to see you here.

A possible flaw in my thinking is that the target environment is different for a studio than for a home theater.

A common goal for all listening rooms is to remove the sound of the room so you hear the direct sound as clearly as possible. I don't think your room is too dead, but switching to the RT60 display in REW will help confirm that. As I read your graph, the decay time is about 100 ms for the top 30 or 35 dB, which means the RT60 is twice as long. If the room is small that's not really a problem IMO.

What are the dimensions?

The graph below shows the RT60 in the small room used for my Hearing is Believing video. That room sounded amazing with the full treatment, and you can see that the RT60 is not only uniform, but fairly short.

--Ethan

[pepar]

Thanks, avare and Ethan. The plastered and hardwood floored room is nominally 13 x 21 x 8 for a volume of ~2184cu ft. I say nominal on the dims because the left and rear walls, and the ceiling is angled about 1°. There is a false wall in front (AT screen, LCR behind the screen) and the "cavity" is lined (front, left and right walls floor to ceiliing) with 2" J-M Linacoustic. And there are OC703 17x17x24 superchunk bass traps at the wall/wall corners and the wall/ceiling corner. The area just in front of the false wall is covered floor to ceiling with thin black carpet for light control. There are 48x48 absorbers (2" OC SelectSound Black) mounted on those sections. From seated ear level down the rest of the room has the same carpet. There are the 2" OC SelectSound Black absorbers on the front ceiling area (48x96) and the rear wall (24x96). And there are six comfy recliners. All of this can be seen on the site linked in my sig.

I feel like I have acoustical whiplash from all of the different opinions from people who make a living in acoustics. Because there seems to be some disagreement on RT60 for small rooms, here are also RT30 and RT20.

To your comment, Ethan, I believe that I have removed the room from my theater listening; the second row - the main seating positions - is just barely within the critical distance/nearfield. I think that is A Good Thing, but to my ears it just sounds like I have over-dampened the room.

[DanDan]

+1 to you are welcome here. A much nicer crowd here than those home theater types you will find...
Big enough room, nice I would say. From the graphs I see an issue at 1.5K. Something ringing? Metalwork, heating rads? Looks like you could use some more Bass also.
Are those graphs an average of various listening (mic) positions?
Take a look at the room over at Ethans with his new diffusors. Not a topic I can expound on, but he can. Some of those bad boys at the back, maybe on the ceiling perhaps. Space Couplers are another interesting product. For a quick and inexpensive fix, I am pretty sure you could simply remove some of the treatment in there to restore a bit of life. If that is a possibility let us know and we can suggest which ones to go.
I work in mix rooms. I like a dead acoustic, I know where I stand in terms of how much reverb to apply, because I am used to it, and the deadness does not obscure the rev. However, many think otherwise, and for listening pleasure a sense of envelopment is good particularly in a cinema.
As a complete aside, many recent recordings, particularly the young folks ones :-) use little or no rev. There is a taste issue.
DD

[pepar]

Originally Posted by DanDan

Big enough room, nice I would say. From the graphs I see an issue at 1.5K. Something ringing? Metalwork, heating rads? Looks like you could use some more Bass also.

I will investigate the 1.5KHz issue. I do plan on adding more bass traps.

Are those graphs an average of various listening (mic) positions?

It is a single position measurement taken at the main listening position.

Take a look at the room over at Ethans with his new diffusors. Not a topic I can expound on, but he can. Some of those bad boys at the back, maybe on the ceiling perhaps. Space Couplers are another interesting product.

So, you are of the opinion that my room is a bit too dead? :-)

For a quick and inexpensive fix, I am pretty sure you could simply remove some of the treatment in there to restore a bit of life. If that is a possibility let us know and we can suggest which ones to go.

I have a section of Linacoustic on the front wall (behind the false wall) that I have been eying as a candidate for removal. Beyond that there is no more absorption to remove except for ripping glued carpet off the wall, something which I am loathe to do for obvious reasons. Diffusors are an option if I can sort through the conflicting advice on whether I need them or not. ;-)

Thanks to everyone who's commented so far!

Jeff

[Ethan Winer]

Originally Posted by pepar

I feel like I have acoustical whiplash from all of the different opinions from people who make a living in acoustics.

But far better than all the opinions in the "Acoustics Master Thread" over at AVS!

there seems to be some disagreement on RT60 for small rooms, here are also RT30 and RT20.

Those are all the same thing. I'm pretty sure that RT30 and RT20 report the same RT60 time, just that only the top 30 or 20 dB is actually measured to avoid low-level noises from influencing the results. The rest is extrapolated, which works perfectly well because decay times are linear.

--Ethan

[DanDan]

Andre misread the Waterfall initially. 100mS. So did I. Ethan is clearly more correct with the 200mS. Those Txx figures are confusing. Topt in REW is IMHO the best shot at getting decay measurement.
I would measure a few more positions. Frequency Response drive one speaker. For Waterfalls etc. drive them all. It will at least inform you how things change quite a lot even with small movements. You may change your listening position as as result (if possible).
I don't have an opinion regarding deadness. I generally prefer it.
In this case I am only responding to your feelings that it is a bit dead and you want more air and so on.
21 feet seems like a decent length to me. I don't think there would be any disagreement or confusion about recommending diffusion on that back wall, and or ceiling.
DD

[pepar]

Originally Posted by DanDan

Andre misread the Waterfall initially. 100mS. So did I. Ethan is clearly more correct with the 200mS. Those Txx figures are confusing. Topt in REW is IMHO the best shot at getting decay measurement.
I would measure a few more positions. Frequency Response drive one speaker. For Waterfalls etc. drive them all. It will at least inform you how things change quite a lot even with small movements. You may change your listening position as as result (if possible).
I don't have an opinion regarding deadness. I generally prefer it.
In this case I am only responding to your feelings that it is a bit dead and you want more air and so on.
21 feet seems like a decent length to me. I don't think there would be any disagreement or confusion about recommending diffusion on that back wall, and or ceiling.
DD

I noticed that my waterfall did not represent a 60dB drop, so I picked up on the mis-reads. The comments are all appreciated though.

I will try some more measurements with L&R driven; I wouldn't know how to drive L, R and Center and still have the Audyssey room correction inline.

I am close to being talked down from my "room is too dead" thinking. ;-) Still, I am going to add twenty-four additional lineal feet of ssc bass trap and do not want to lose ground RT-wise. And I'd like for the front lobe of my (side) surrounds to not collapse as it does now with my completely deadened front end. I posted some questions on diffusors here if anyone cares to chime in.

Jeff

Jeff

[avare]

Just looking at the RT plots, you have an unbalanced graph. By too dead do mean somewhat boomy,or the highs have little life? Ethan has a line for that: All rooms need low end absorption.

The EBU nominal for that room works out to ~230 ms. Your room is definitely on the low side.

Andre

[DanDan]

Jeff, it hasn't been tested to my knowledge, but how about FRK or plastic film fronts on all that SSC acreage? It should enhance LF trapping, improving your bass level and evenness. However the FRK maintain some liveness.
Doesn't Ethan have an article concerning the Audity ;-) on his site?
In any case I would measure and tweak without any such device in line. When your organic work is done, then try the electronic assistance.
DD

[pepar]

Originally Posted by DanDan

Jeff, it hasn't been tested to my knowledge, but how about FRK or plastic film fronts on all that SSC acreage? It should enhance LF trapping, improving your bass level and evenness. However the FRK maintain some liveness.
Doesn't Ethan have an article concerning the Audity ;-) on his site?
In any case I would measure and tweak without any such device in line. When your organic work is done, then try the electronic assistance.
DD

To drive LCR, I'd need a 1x3 unbalanced line level splitter to drive the multichannel analog inputs. Can't I get away with just front left and right?

Wow, the faux FRK sounds intriguing. Any suggestions on what paper/plastic to use?

Jeff

[DanDan]

Great, I was going to ask Andre for two links. The EBU control room spec is one, I have lost mine.
The other has been referred to elsewhere. A BBC paper testing plastic films facing absorption, 1-6mm. Something like that. For modal work it is probably best to drive the room from as many different spots as possible. In building acoustics we place the speaker on the floor in a corner for maximum modal drive. Do your best, do leave out the corrections though. I presume your bass system is being driven?
For frequency response it is best to drive one speaker at a time, including the sub all the time though. I am a bit lost when it comes to LCR, the combing issues are scary. Best to do each individually I guess. There is a great detailed workout of sub integration using measurement over at ETF home Acoustisoft.
DD

[pepar]

Originally Posted by avare

The EBU nominal for that room works out to ~230 ms. Your room is definitely on the low side.

Andre

I thought "nominal" meant "OK?" :-)

[pepar]

Originally Posted by DanDan

Great, I was going to ask Andre for two links. The EBU control room spec is one, I have lost mine.
The other has been referred to elsewhere. A BBC paper testing plastic films facing absorption, 1-6mm. Something like that. For modal work it is probably best to drive the room from as many different spots as possible. In building acoustics we place the speaker on the floor in a corner for maximum modal drive. Do your best, do leave out the corrections though. I presume your bass system is being driven?
For frequency response it is best to drive one speaker at a time, including the sub all the time though. I am a bit lost when it comes to LCR, the combing issues are scary. Best to do each individually I guess. There is a great detailed workout of sub integration using measurement over at ETF home Acoustisoft.
DD

I've used 3-mil/4-mil poly as a vapor barrier, so that is commercially available. Could it really as simple as spray adhesive-ing *that* onto the ssc face?

Yes, my test measurement was with a "1.1" configuration - full sweep from 10Hz to 20KHz. The waterfall showed it all, but for some reason the RTs did not.

FWIW, my sub/main integration is ... tits. For that, my best test material is Between The Sheets by Fourplay. Nathan East and Harvey Mason are my assistants on that test. And the other demo is the opening battle sequence of Master and Commander: Far Side of the World. That battle has cannonade of varying depths and timbre that absolutely is jaw-dropping.

Jeff

[Glenn Kuras]

Originally Posted by Ethan Winer

But far better than all the opinions in the "Acoustics Master Thread" over at AVS!





--Ethan

Yea that thread is like reading a Chinese manual.

[avare]

Originally Posted by DanDan

Great, I was going to ask Andre for two links. The EBU control room spec is one, I have lost mine.

Here is the EBU document for stereo listening. Tech. 3276 second edition, May 1998. Related is the spec for muiltichannel sound Tech. 3276-E. Just to keep things simple, it also known as 3276E.

Well specified,
Andre

[avare]

Originally Posted by pepar

I thought "nominal" meant "OK?" :-)

Yes and your graphs showed highs under 200 ms.

Nominally,
Andre

[Ethan Winer]

Originally Posted by Glenn Kuras

Yea that thread is like reading a Chinese manual.

It's much worse than that. It's way too long for anyone to read it all, and it's full of contradictory opinions including much outright wrong information. Did I mention it's way too long?

--Ethan

[DanDan]

Thanks Andre,

Gratefully, DD

[gremmy]

Originally Posted by Ethan Winer

It's much worse than that. It's way too long for anyone to read it all, and it's full of contradictory opinions including much outright wrong information. Did I mention it's way too long?

--Ethan

Do you have any idea why they keep that thing as a sticky? There is no way a person could read it and come away with a fundamental understanding of basic acoustics (which IMO would be the main reason why a thread like that should be stickied in a forum where DIY types are building their own theaters). I tried learning something from that thread once and just gave up. It would be a lot more helpful if someone actually maintained a summary post at the top of the thread with an inventory of the stuff that most everyone agreed on.

[pepar]

Originally Posted by gremmy

Do you have any idea why they keep that thing as a sticky? There is no way a person could read it and come away with a fundamental understanding of basic acoustics (which IMO would be the main reason why a thread like that should be stickied in a forum where DIY types are building their own theaters). I tried learning something from that thread once and just gave up. It would be a lot more helpful if someone actually maintained a summary post at the top of the thread with an inventory of the stuff that most everyone agreed on.

Very few people search or, for that matter, read. They post ... and get replies usually, but the process extends the thread ... making it dauntingly long... so people don't search or read ... they just post. Rinse and repeat.