Need advice for Home Theater / Project Studio

**tmwalke1** · **01-14-07, 01:22 AM**

This is my first post, I'd appreciate any advice I can get....

I am remodeling a room for use as a home theater and simple recording studio. The room is about 19' X 14" by 9" (2438 CF). The listening position for the HT will be just about dead center in the room, the mix position for the studio will be behind that facing the left wall. I have a door dead center in the back wall and doors in both corners of the front wall - the doors in front make it impossible to put bass traps in those two corners.

Because I am going to do recording as well as listening, I am thinking I will go with a reflective floor (hardwood) that I can control with throw rugs as needed, a dead ceiling (build some clouds), and some combination of diffusion / absorbtion / nothing on the walls. I have already added a second layer of sheetrock with Green Glue. Here are a couple of pix:

This is the front - the screen and front speakers will go in the middle between the doors.
P1010018.jpg

The back.
P1010019.jpg

Here's a couple of waterfall plots I snapped with Room EQ Wizard (really cool software!!!). Note the humongous node at 76Hz. The first plot was taken dead center, the second off to the side where I'm planning the project studio mix position. The nodes aren't as bad there. I have also attached a screenshot from ModeCalc that shows the predicted node at 76Hz. I'm wondering if the nodes on the long axis are dampened because I don't have the doors on those walls yet - maybe I'm going to have another big problem at 60Hz as well.

waterfall - center.jpg
waterfall - mix position.jpg
ModeCalc Results.JPG

So, my big questions are:

1. Am I really going to be able to suck a 15dB node out of this room with some traps in the rear corners and maybe the ceiling (I'm thinking maybe a trap along the center line in the ceiling since that's a peak of the 76Hz node, or maybe along the edges of the ceiling long-ways).
2. Can I do this with some 703 straddling the corners, or will I need to build something more elaborate like a membrane trap or Helmholz resonator?
3. Does anybody have any thoughts on a good RT60 target for a multi-use room like this? I'd like to get an idea so I know how much 703 I should buy.

Thanks in advance for any thoughts you may have. I'm planning to capture some "after" waterfall plots when I'm done, which I'll post.

Tim

**Ethan Winer** · **01-14-07, 11:18 AM**

Tim,

> The listening position for the HT will be just about dead center in the room <

If by "dead center" you mean halfway front to back, that's a big mistake. Much better is to be about 38 percent of the way into the room from either the front or rear wall. With a 19 foot length that distance is about 7'3". For nearfield monitoring being 38 percent back from the front wall is best. In a home theater setting with a large screen TV you'll probably be closer to the rear wall than to the front wall.

> doors in both corners of the front wall - the doors in front make it impossible to put bass traps in those two corners. <

Not so! You can put two bass traps adjacent in those corners - one on the wall and one right on the door. There are also corners where the walls meet the ceiling and even where the walls meet the floor. Those are every bit as valid as corners where two walls meet.

> I have also attached a screenshot from ModeCalc <

I recently made a new native Windows version of my ModeCalc program that looks nicer and also gives more information and with a more detailed Help file. Here's the link:

www.realtraps.com/modecalc.htm

> Note the humongous node at 76Hz. <

All rooms have peaks and nulls. Which proves the point that you need as much bass trapping as you can possibly manage. You'll never get that room perfectly flat, but you can definitely get it from "This sucks" to "Wow, this is great!"

> Can I do this with some 703 straddling the corners, or will I need to build something more elaborate like a membrane trap or Helmholz resonator? <

Yes, 703 or equivalent can make a big improvement. I'm not a fan of tuned absorption, though both of those trap types can be made more or less broadband to cover a range of about an octave. In a room that size you can do a fine job with porous absorbers.

> Does anybody have any thoughts on a good RT60 target for a multi-use room like this? I'd like to get an idea so I know how much 703 I should buy. <

Maybe 200 to 300 milliseconds. But that's for all frequencies, not just 1 KHz!

--Ethan

**Scott R. Foster** · **01-14-07, 01:20 PM**

Tim:

There is no RT60 in a small room - just a relative notion of reverb field strength that will vary enormously depending on where you measure from [you are already working this out for yourself with your measurements - but its important to understand - so I mention it].

The 38% rule Ethan mentions is a good guess on a starting place for the listening position, but keep in mind that in a small room using length axis expression for LP designation per single digit % is kind of silly once you take into account that your head moves through few % points of this axis just sipping a cup of coffee. Speaker placement and console early reflection control are susceptible to fine degrees of placement yielding significant benefit - your head placement is not, as it will move around too much for such precision to remain sensible once a real person sits down in a real chair and starts working twiddling knobs, leaning back to listen, sipping coffee, etcetera. Unless your chair gets bolted to the floor and you work with your head in a clamp, when working at 38%, your are also working at 34% or 42% or more likely, all three. The LP is a zone not a point in space.

I suggest you optimize you speaker positions and mix desk layout with precision - let the chips fall where they may on LP, just get in front of the mid room and behind the 1/4 depth and you'll be fine.

Or use this number:

37.51%

Then do corner bass trapping as Ethan suggests - add some early reflection control and you'll be in great shape.

For mode calcs, here's a nice graphic online mode calc tool [works for Mac as well as PC] that includes all the modes [not just axial] - also it has lots of useful calcs / notes / links at the bottom:

bobgolds.com/Mode/RoomModes.htm

More here:

forum.studiotips.com/viewforum.php?f=27

I like this one:

forum.studiotips.com/large_files/RoomModeCalculator.zip

Good Luck!

**Ethan Winer** · **01-15-07, 01:48 PM**

Scott,

> your head moves through few % points of this axis just sipping a cup of coffee. <

No kidding. Not sure if you ever saw my "Believe" article, but the graphs below show the low frequency and broadband response at two locations only four inches apart in the RealTraps lab room.

Conventional wisdom holds that the bass response in a room cannot change much over small distances because the wavelengths are very long. (A 40 Hz sound wave is more than 28 feet long.) Yet you can see in the top graph that the peak at 42 Hz varies by 3 dB for these two nearby locations, and there's still a 1 dB difference even as low as 27 Hz. The reason the frequency response changes so much even at low frequencies is because many reflections, each having different time and phase delays, combine in different amounts at each point in the room. In small rooms the reflections are strong because the reflecting boundaries are all nearby, so that further increases the contribution from each reflection. Also, nulls tend to occupy a relatively narrow physical space, which is why the nulls on either side of the 92 Hz marker have very different depths. Indeed, the null at 71 Hz in one location becomes a peak at the other.

The two responses in the lower graph are so totally different you'd never guess this is even the same room and loudspeakers!

At the risk of starting a flame war among the audiophiles in attendance

here's the full article:

www.ethanwiner.com/believe.html

--Ethan

**Glenn Kuras** · **01-15-07, 03:02 PM**

Ethan wrote:

"I recently made a new native Windows version of my ModeCalc program that looks nicer and also gives more information and with a more detailed Help file. Here's the link:

www.realtraps.com/modecalc.htm"

And you did a fine job sir. Hats off to you!!

tmwalke1:
At this point I would not even worry to much about a room mode calculation. You are already shooting the room so you know bad it is. Start in the right spot (as Ethan said 38%) and get as many bass traps in that room as you can. I would start with the front corners if nothing else and don't forget about the first reflection points in your room!! Last but not least ENJOY YOUR SPACE!!!

Glenn

**Ethan Winer** · **01-15-07, 03:35 PM**

Glenn,

> And you did a fine job sir. Hats off to you!! <

Thank you Sir!

> At this point I would not even worry to much about a room mode calculation. <

Good point. Unless someone is willing and able to add new walls or change existing walls, anything a mode calculator tells you is moot. Further, even measuring is not usually necessary since the solution is exactly the same no matter what is measured: Treatment at all the first reflection points, and as much bass trapping as you can possibly manage.

--Ethan

**Scott R. Foster** · **01-15-07, 04:18 PM**

I disagree - modal calcs can be useful even if you will not be moving walls.

For example, if you get into actually measuring the room with anything beyond your ears, knowing the "theoretical" modal content of room can help a great deal in analysis. In doing such as that - its nice to have ability to look at the entire calculable modal content - thus calculators that go beyond simply the structure of the axials should be used.

This one is web based so its works on Macs too - which is nice.

http://www.bobgolds.com/Mode/RoomModes.htm

and the piano keyboard reference scale is a neat twist.

But if you are literally doing it all by ear - then I agree, calculating the modes is pointless - and frankly, that method works pretty **** good if you know what you are doing. Arguably, in a small room, all you need is a little common sense, and a good set of ears [maybe bringing along a couple sets of good ears would be smart].

**Ethan Winer** · **01-15-07, 05:15 PM**

Scott,

> knowing the "theoretical" modal content of room can help a great deal in analysis. <

How so? What would someone do differently in treating their room knowing the predicted modes versus simply measuring the response and ringing? I'm not convinced measuring is all that useful either since as I said earlier the solution is the same regardless. And I measure rooms for a living!

I'm sure you recall the thread at RO where I showed that the measured mode frequencies were off by as much as 20 percent from what was predicted for the RealTraps lab. So I don't see a whole lot of value in running a mode calculation on a room whose dimensions won't be changed. But if you'd care to elaborate on how someone could use those calculations - specifically - I'll be glad to listen and learn. BTW, my showing the extreme disparity between predicted versus measured modes is yet another example of "theory" often missing the forest for the trees. Indeed, if knowing the room's state ahead of time is valuable at all, it's the measured response I care about, not a prediction that may or may not even be close to reality.

> In doing such as that - its nice to have ability to look at the entire calculable modal content - thus calculators that go beyond simply the structure of the axials should be used ... http://www.bobgolds.com/Mode/RoomModes.htm <

I agree - Bob made a neat program there. But I find all that data very confusing. I just entered the dimensions for the RealTraps test lab, and Bob's program spit out 80 modes! (Listed in the table below.) What the heck is someone who is not a professional acoustician supposed to do with all that data? Heck, what is a professional acoustician supposed to do with all that data? Build 80 different tuned bass traps? I am serious! What do you do with all that data? How do you distinguish which modes matter a lot and which modes don't matter as much or even at all?

More to the point, how do you get from that list of modes to an effective treatment solution for a basement home theater or bedroom project studio?

--Ethan

Quote:

Frequency hz Spacing % Wavelength 1/2 Wavelength 1/4 Wavelength p q r Mode
34.9 32'5" 16'2" 8'1" 1 0 0 Axial
49.0 28.7 23'1" 11'6" 5'9" 0 1 0 Axial
60.1 18.4 18'10" 9'5" 4'8" 1 1 0 Tangential
69.9 14 16'2" 8'1" 4'0" 2 0 0 Axial
70.6 0.9 16'0" 8'0" 4'0" 0 0 1 Axial
78.8 10.4 14'4" 7'2" 3'7" 1 0 1 Tangential
85.3 7.6 13'3" 6'7" 3'4" 2 1 0 Tangential
85.9 0.6 13'2" 6'7" 3'3" 0 1 1 Tangential
92.8 7.4 12'2" 6'1" 3'1" 1 1 1 Oblique
97.9 5.2 11'7" 5'9" 2'11" 0 2 0 Axial
99.4 1.5 11'4" 5'8" 2'10" 2 0 1 Tangential
104.0 4.4 10'10" 5'5" 2'9" 1 2 0 Tangential
104.8 0.7 10'9" 5'5" 2'8" 3 0 0 Axial
110.8 5.4 10'2" 5'1" 2'7" 2 1 1 Oblique
115.7 4.2 9'9" 4'11" 2'5" 3 1 0 Tangential
120.3 3.8 9'5" 4'8" 2'4" 2 2 0 Tangential
120.7 0.3 9'4" 4'8" 2'4" 0 2 1 Tangential
125.7 3.9 8'12" 4'6" 2'3" 1 2 1 Oblique
126.4 0.5 8'11" 4'6" 2'3" 3 0 1 Tangential
135.5 6.7 8'4" 4'2" 2'1" 3 1 1 Oblique
139.5 2.8 8'1" 4'1" 2'0" 2 2 1 Oblique
139.8 0.2 8'1" 4'0" 2'0" 4 0 0 Axial
141.3 1 7'12" 3'12" 1'12" 0 0 2 Axial
143.4 1.4 7'11" 3'11" 1'12" 3 2 0 Tangential
145.5 1.4 7'9" 3'11" 1'11" 1 0 2 Tangential
146.9 0.9 7'8" 3'10" 1'11" 0 3 0 Axial
148.1 0.8 7'8" 3'10" 1'11" 4 1 0 Tangential
149.5 0.9 7'7" 3'9" 1'11" 0 1 2 Tangential
151.0 0.9 7'6" 3'9" 1'10" 1 3 0 Tangential
153.5 1.6 7'4" 3'8" 1'10" 1 1 2 Oblique
156.6 1.9 7'3" 3'7" 1'10" 4 0 1 Tangential
157.6 0.6 7'2" 3'7" 1'10" 2 0 2 Tangential
159.9 1.4 7'1" 3'6" 1'9" 3 2 1 Oblique
162.7 1.7 6'11" 3'6" 1'9" 2 3 0 Tangential
163.0 0.1 6'11" 3'6" 1'9" 0 3 1 Tangential
164.1 0.6 6'11" 3'5" 1'9" 4 1 1 Oblique
165.0 0.5 6'10" 3'5" 1'9" 2 1 2 Oblique
166.7 1 6'9" 3'5" 1'8" 1 3 1 Oblique
170.7 2.3 6'7" 3'4" 1'8" 4 2 0 Tangential
171.9 0.6 6'7" 3'3" 1'8" 0 2 2 Tangential
174.7 1.6 6'6" 3'3" 1'7" 5 0 0 Axial
175.4 0.3 6'5" 3'3" 1'7" 1 2 2 Oblique
175.9 0.2 6'5" 3'3" 1'7" 3 0 2 Tangential
177.3 0.7 6'4" 3'2" 1'7" 2 3 1 Oblique
180.4 1.7 6'3" 3'2" 1'7" 3 3 0 Tangential
181.4 0.5 6'3" 3'1" 1'7" 5 1 0 Tangential
182.6 0.6 6'2" 3'1" 1'7" 3 1 2 Oblique
184.7 1.1 6'1" 3'1" 1'6" 4 2 1 Oblique
185.5 0.4 6'1" 3'1" 1'6" 2 2 2 Oblique
188.4 1.5 5'12" 2'12" 1'6" 5 0 1 Tangential
193.8 2.7 5'10" 2'11" 1'5" 3 3 1 Oblique
194.7 0.4 5'10" 2'11" 1'5" 5 1 1 Oblique
195.8 0.5 5'9" 2'11" 1'5" 0 4 0 Axial
198.7 1.4 5'8" 2'10" 1'5" 4 0 2 Tangential
198.9 0.1 5'8" 2'10" 1'5" 1 4 0 Tangential
200.3 0.6 5'8" 2'10" 1'5" 5 2 0 Tangential
201.3 0.4 5'7" 2'10" 1'5" 3 2 2 Oblique
202.8 0.7 5'7" 2'9" 1'5" 4 3 0 Tangential
203.8 0.4 5'7" 2'9" 1'5" 0 3 2 Tangential
204.7 0.4 5'6" 2'9" 1'5" 4 1 2 Oblique
206.8 1 5'6" 2'9" 1'4" 1 3 2 Oblique
207.9 0.5 5'5" 2'9" 1'4" 2 4 0 Tangential
208.2 0.1 5'5" 2'9" 1'4" 0 4 1 Tangential
209.6 0.6 5'5" 2'8" 1'4" 6 0 0 Axial
211.1 0.7 5'4" 2'8" 1'4" 1 4 1 Oblique
211.9 0.3 5'4" 2'8" 1'4" 0 0 3 Axial
212.4 0.2 5'4" 2'8" 1'4" 5 2 1 Oblique
214.7 1 5'3" 2'8" 1'4" 1 0 3 Tangential
214.7 0 5'3" 2'8" 1'4" 4 3 1 Oblique
215.3 0.2 5'3" 2'7" 1'4" 6 1 0 Tangential
215.4 0 5'3" 2'7" 1'4" 2 3 2 Oblique
217.5 0.9 5'2" 2'7" 1'4" 0 1 3 Tangential
219.6 0.9 5'2" 2'7" 1'3" 2 4 1 Oblique
220.2 0.2 5'2" 2'7" 1'3" 1 1 3 Oblique
221.2 0.4 5'1" 2'7" 1'3" 6 0 1 Tangential
221.5 0.1 5'1" 2'7" 1'3" 4 2 2 Oblique
222.1 0.2 5'1" 2'7" 1'3" 3 4 0 Tangential
223.1 0.4 5'1" 2'6" 1'3" 2 0 3 Tangential

**Scott R. Foster** · **01-15-07, 05:52 PM**

Yes it is all rather complicated.

**Glenn Kuras** · **01-15-07, 07:16 PM**

"Frequency hz Spacing % Wavelength 1/2 Wavelength 1/4 Wavelength p q r Mode
34.9 32'5" 16'2" 8'1" 1 0 0 Axial
49.0 28.7 23'1" 11'6" 5'9" 0 1 0 Axial
60.1 18.4 18'10" 9'5" 4'8" 1 1 0 Tangential
69.9 14 16'2" 8'1" 4'0" 2 0 0 Axial
70.6 0.9 16'0" 8'0" 4'0" 0 0 1 Axial
78.8 10.4 14'4" 7'2" 3'7" 1 0 1 Tangential
85.3 7.6 13'3" 6'7" 3'4" 2 1 0 Tangential
85.9 0.6 13'2" 6'7" 3'3" 0 1 1 Tangential
92.8 7.4 12'2" 6'1" 3'1" 1 1 1 Oblique
97.9 5.2 11'7" 5'9" 2'11" 0 2 0 Axial
99.4 1.5 11'4" 5'8" 2'10" 2 0 1 Tangential
104.0 4.4 10'10" 5'5" 2'9" 1 2 0 Tangential
104.8 0.7 10'9" 5'5" 2'8" 3 0 0 Axial
110.8 5.4 10'2" 5'1" 2'7" 2 1 1 Oblique
115.7 4.2 9'9" 4'11" 2'5" 3 1 0 Tangential
120.3 3.8 9'5" 4'8" 2'4" 2 2 0 Tangential
120.7 0.3 9'4" 4'8" 2'4" 0 2 1 Tangential
125.7 3.9 8'12" 4'6" 2'3" 1 2 1 Oblique
126.4 0.5 8'11" 4'6" 2'3" 3 0 1 Tangential
135.5 6.7 8'4" 4'2" 2'1" 3 1 1 Oblique
139.5 2.8 8'1" 4'1" 2'0" 2 2 1 Oblique
139.8 0.2 8'1" 4'0" 2'0" 4 0 0 Axial
141.3 1 7'12" 3'12" 1'12" 0 0 2 Axial
143.4 1.4 7'11" 3'11" 1'12" 3 2 0 Tangential
145.5 1.4 7'9" 3'11" 1'11" 1 0 2 Tangential
146.9 0.9 7'8" 3'10" 1'11" 0 3 0 Axial
148.1 0.8 7'8" 3'10" 1'11" 4 1 0 Tangential
149.5 0.9 7'7" 3'9" 1'11" 0 1 2 Tangential
151.0 0.9 7'6" 3'9" 1'10" 1 3 0 Tangential
153.5 1.6 7'4" 3'8" 1'10" 1 1 2 Oblique
156.6 1.9 7'3" 3'7" 1'10" 4 0 1 Tangential
157.6 0.6 7'2" 3'7" 1'10" 2 0 2 Tangential
159.9 1.4 7'1" 3'6" 1'9" 3 2 1 Oblique
162.7 1.7 6'11" 3'6" 1'9" 2 3 0 Tangential
163.0 0.1 6'11" 3'6" 1'9" 0 3 1 Tangential
164.1 0.6 6'11" 3'5" 1'9" 4 1 1 Oblique
165.0 0.5 6'10" 3'5" 1'9" 2 1 2 Oblique
166.7 1 6'9" 3'5" 1'8" 1 3 1 Oblique
170.7 2.3 6'7" 3'4" 1'8" 4 2 0 Tangential
171.9 0.6 6'7" 3'3" 1'8" 0 2 2 Tangential
174.7 1.6 6'6" 3'3" 1'7" 5 0 0 Axial
175.4 0.3 6'5" 3'3" 1'7" 1 2 2 Oblique
175.9 0.2 6'5" 3'3" 1'7" 3 0 2 Tangential
177.3 0.7 6'4" 3'2" 1'7" 2 3 1 Oblique
180.4 1.7 6'3" 3'2" 1'7" 3 3 0 Tangential
181.4 0.5 6'3" 3'1" 1'7" 5 1 0 Tangential
182.6 0.6 6'2" 3'1" 1'7" 3 1 2 Oblique
184.7 1.1 6'1" 3'1" 1'6" 4 2 1 Oblique
185.5 0.4 6'1" 3'1" 1'6" 2 2 2 Oblique
188.4 1.5 5'12" 2'12" 1'6" 5 0 1 Tangential
193.8 2.7 5'10" 2'11" 1'5" 3 3 1 Oblique
194.7 0.4 5'10" 2'11" 1'5" 5 1 1 Oblique
195.8 0.5 5'9" 2'11" 1'5" 0 4 0 Axial
198.7 1.4 5'8" 2'10" 1'5" 4 0 2 Tangential
198.9 0.1 5'8" 2'10" 1'5" 1 4 0 Tangential
200.3 0.6 5'8" 2'10" 1'5" 5 2 0 Tangential
201.3 0.4 5'7" 2'10" 1'5" 3 2 2 Oblique
202.8 0.7 5'7" 2'9" 1'5" 4 3 0 Tangential
203.8 0.4 5'7" 2'9" 1'5" 0 3 2 Tangential
204.7 0.4 5'6" 2'9" 1'5" 4 1 2 Oblique
206.8 1 5'6" 2'9" 1'4" 1 3 2 Oblique
207.9 0.5 5'5" 2'9" 1'4" 2 4 0 Tangential
208.2 0.1 5'5" 2'9" 1'4" 0 4 1 Tangential
209.6 0.6 5'5" 2'8" 1'4" 6 0 0 Axial
211.1 0.7 5'4" 2'8" 1'4" 1 4 1 Oblique
211.9 0.3 5'4" 2'8" 1'4" 0 0 3 Axial
212.4 0.2 5'4" 2'8" 1'4" 5 2 1 Oblique
214.7 1 5'3" 2'8" 1'4" 1 0 3 Tangential
214.7 0 5'3" 2'8" 1'4" 4 3 1 Oblique
215.3 0.2 5'3" 2'7" 1'4" 6 1 0 Tangential
215.4 0 5'3" 2'7" 1'4" 2 3 2 Oblique
217.5 0.9 5'2" 2'7" 1'4" 0 1 3 Tangential
219.6 0.9 5'2" 2'7" 1'3" 2 4 1 Oblique
220.2 0.2 5'2" 2'7" 1'3" 1 1 3 Oblique
221.2 0.4 5'1" 2'7" 1'3" 6 0 1 Tangential
221.5 0.1 5'1" 2'7" 1'3" 4 2 2 Oblique
222.1 0.2 5'1" 2'7" 1'3" 3 4 0 Tangential
223.1 0.4 5'1" 2'6" 1'3" 2 0 3 Tangential "

Oh wait if that is all there is then

I think I will stick with shooting the room.

Glenn

**tmwalke1** · **01-15-07, 10:03 PM**

Thanks, guys. My first exposure to studio design was an article Ethan co-wrote in EQ Magazine (September 2004), so this dialog is like sitting and listening at the grown-up table for me!

I actually have laid out the surround speaker wire drops in the room for a listening/viewing position just forward of center in the long axis of the room. I wired for 7.1 even though that's probably overkill, at least for now. Getting to 38% may be tough because of min viewing distance, but I should be able to get in the neighborhood.

So, based on what you've told me, I'm thinking of something like this:

1. 703 straddling the rear corners (the two vertical corners plus the rear wall/ceiling corner), 2' wide, 4" thick, kraft paper out. I'll probably use some of the space in the middle of the vertical traps for small cabinets (maybe use some 703 in the cabinet doors as well).
2. 703 around the remaining ceiling corners, 4" thick, kraft paper out, maybe at a shallower angle.
3. A ceiling cloud about 6" below the ceiling, alternating 2" and 4" 703, about 200 square feet.
4. About 180 square feet of 703, 2" thick, mounted directly on the walls.
5. Maybe a couple of panel traps adjacent to the front vertical corners, if I can make it work aesthetically.
6. Some diffusion panels on the walls interspersed with the absorption, particularly in the back.

Any additional thoughts before I get the credit card out for the next materials purchase?

Thanks,

Tim

**Scott R. Foster** · **01-15-07, 10:30 PM**

Tim:

Shop for other brands too - not just 703. CertainTeed and Johns Mannville for instance also make 3 lbs. denisty semi-rigid insulation boards. Also take a look around at rockwool prices - a lot of folks find big savings by switching to rockwool - prices vary by location - look at denser stuff in rockwool though... its has lower gas flow reisitance per unit density than the FG boards and is flakey and kind of hard to handle at low densities. 60 kg/m3 or about 5 lbs. RW is said to be roughly = to 703 acoustically but stuff up to 8 lbs. is used with good results in well known commercial devices and the denser stuff has better handling properties than the floppy RW.

And get the naked stuff - the paper or scrim will just put a big fat peak in what would otherwise be a fairly smooth absorption curve.

In a room under 5.000 cubic feet I would typically use all thick panels [at least 4"] and treat fewer SF - focus the reflection point treatments to right where needed and leave more bare wall/ceiling - you get a boost on the LF control that way as the thicker panels work low in the band whereas the thin do not - also teh highs sparkle a bit more that way - YMMV.

I wouldn't bother with panel traps - or any resonate devices unless and unti I had to. You'll get more absorption across the band with a porous broadband device [thus the name - eh?].

Good Luck!

PS: why not post a rough sketch of the room with your proposed treatments and major furniishings - after all, you know what they say about the worth of a a picture.

**Glenn Kuras** · **01-16-07, 09:31 AM**

>1. 703 straddling the rear corners (the two vertical corners plus the rear wall/ceiling corner), 2' wide, 4" thick, kraft paper out. I'll probably use some of the space in the middle of the vertical traps for small cabinets (maybe use some 703 in the cabinet doors as well).<

As many corners as you can cover is always a good thing. Yes you want to have the kraft paper to the front. This should be only used for the bass traps within the room. And YES use the kraft paper it will help pick up more low end and keep the highs alive in the room. To much absorption on the highs can leave a room with no life in it.

>2. 703 around the remaining ceiling corners, 4" thick, kraft paper out, maybe at a shallower angle.<

That will help also

>3. A ceiling cloud about 6" below the ceiling, alternating 2" and 4" 703, about 200 square feet.<

If you treat the low end enough then 2" panels should be fine.

>4. About 180 square feet of 703, 2" thick, mounted directly on the walls.<

Focus on the first reflections of the room.

>5. Maybe a couple of panel traps adjacent to the front vertical corners, if I can make it work aesthetically.<

These can work GREAT, but this would be more like icing on the cake if you are still having trouble frequencies. Most small rooms do just fine with broad band absorption in it. I would treat the room first with broad band and see how good it sounds.

Glenn

**Ethan Winer** · **01-16-07, 03:00 PM**

Glenn,

LOL, I popped in early this morning and saw the need to correct a few things, but by the time I got here I see you addressed it all.

--Ethan

**Ethan Winer** · **01-16-07, 03:13 PM**

Scott,

> Yes it is all rather complicated. <

I don't mean to put you on the spot, but even you have to admit that's not much of an answer. I've seen you and a few others state repeatedly around the various forums that a "full" mode calculation is necessary, and any mode calculation that doesn't include non-axials modes is incomplete and misleading.

Since you stated above that knowing all the modes is useful not only when establishing dimensions for a new room not yet built, I'm hoping you can elaborate and tell us specifically how one gets from that list of 80 modes to knowing what panels are needed and where to put them. I'm especially interested in knowing how you'd handle the uncertainty of knowing if the modes as predicted even align with how the room responds. That is, the disparity of up to 20 percent I once measured versus what was predicted.

--Ethan

**Glenn Kuras** · **01-16-07, 03:38 PM**

Thanks Ethan,

BTW I do have a question for you.

Scott wrote:

"And get the naked stuff - the paper or scrim will just put a big fat peak in what would otherwise be a fairly smooth absorption curve."

I would think that a "big fat peak" on the low end would be a good thing. Lets say that a panel has a "big fat peak" at 100 hz but the room has problems at say 80hz. That "big fat peak panel" at 100hz is not going to mess up your room or hammer a null into it. So what gives with the "The peak is a bad thing"? Granted it would help more if some ones room peak (or null) was at the same place as the panels "big fat peak", but the "big fat peak" at 100hz panel will not do damage either. right?

Now if a panel has a "big fat peak" at say 1k now that might be something to worry about.

Sorry for the “BIG FAT PEAK” statement so many times. Just found it funny.

**Ethan Winer** · **01-16-07, 04:40 PM**

Glenn,

> I would think that a "big fat peak" on the low end would be a good thing. <

Yeah, no kidding - it's not like the curve of absorption is the curve of frequency response you'll end up with!

What Scott Foster might be concerned about is that a peak in absorption at one place implies lower absorption somewhere else. But I see the exact same behavior in the data for Scott's company's products, with a large peak around 100 Hz followed by a huge dip at 200 Hz. So I really don't understand Scott's point or his objection. Indeed, that peak is more related to the corner placement than to the amount of absorption from the trap!

> Lets say that a panel has a "big fat peak" at 100 hz but the room has problems at say 80hz. That "big fat peak panel" at 100hz is not going to mess up your room or hammer a null into it. So what gives with the "The peak is a bad thing"? <

You are absolutely correct. Too much absorption at a bass frequency that doesn't need absorption will harm nothing. This is different from higher frequencies where a balanced reverb time versus frequency is desirable. Moreover, even if one measurement shows no problem at your 100 Hz example frequency, I guarantee you that somewhere else in the room that extra absorption at 100 Hz will be valuable.

As we all know, one of the biggest bass problems in all rooms is comb filtering that occurs in front of the rear wall. Even in a large room where the rear wall is many feet back, that is still one very important source of bass peaks and nulls. Probably the most important. These peaks and nulls are 100 percent positional, meaning there will be a big null at 100 Hz 34 inches in front of that wall, and likewise for all other distances related to 1/4 wavelength. So

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