Small Room Acoustics

Okay, personal example. I need to set up on the short wall, so one short wall is two 54"x36" windows with corners. the other short wall is two doors IN the corners (no bass trapping allowed.) Should I face the windows, or face the doors? It sounds like facing the windows will eliminate the window reflection problem, but facing the doors will allow bass trapping behind...maybe I'm not getting this exactly.
I'm working with a Primacoustic London 8 set and ceiling cloud and have made the ultimate mistake of wasting $150 on some used gray Auralex foam bass traps. 7'6"H x 9'11 1/2" W x 12' 8 1/2" D. What should I buy for decent bass traps? A link would be great :D
 
Last edited:
Well, scrap all that. If I go to SPI in Greensboro, what should I buy? I am complete newb noob n00b when it comes to acoustic treatment. How much do I need first, then we'll talk about placement. I can still return the Priamacoustic stuff if it's a waste of time/money. Have to keep the Auralex as it was used from GC. But JHB mentioned above that it could be useful placing it over good tile, so maybe all is not lost there either.
 
I've got a similar set up as yours, but only one corner-door, so I chose to set up on that wall, with the windows behind me. Note that you still probably have upper corners (wall-wall-ceiling) above the doors that can be trapped.
 
I made some some small 'chunks' from the 2" thick Roxul, 3"x24", total of 6 of them stacked 3-2-1, wrapped them in leftover burlap, but it was too flimsy to hang up as is. Haven't got around to attaching to a couple of 6" wide 1/4" plywood pieces (V-shaped).
 
user7_pic5272_1314593087.webp

That's the ticket.
 
Sorry for the long absence here. I have been very busy. We are the designers for SAE school here in Jakarta and for the Digital Media Center at Foothill college in San Jose, CA.. not to mention the many studio builds all over, large and small. ;)

dainbramage said:
.... For the back wall, does that count as early reflections as well?
Click to expand...
Any wall in a critical listening room counts. You will always want to control the propagation of sound from the source (speakers) so that there is zero interference at the listening position. Reflections from the operator/listening are treated completely differently.

jim1961 said:
Hello JHB

I see many here that frequent other sites. Anyway, was curious about your RT60 criteria.
Click to expand...
My RT-60 criteria is determined from:
http://tech.ebu.ch/docs/techreview/trev_274-hoeg.pdf
Subjective assessment of audio quality

http://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1116-1-199710-I!!PDF-E.pdf
METHODS FOR THE SUBJECTIVE ASSESSMENT OF SMALL IMPAIRMENTS IN AUDIO SYSTEMS INCLUDING MULTICHANNEL SOUND SYSTEMS

http://www.aes.org/technical/documents/AESTD1001.pdf
Multichannel surround sound systems and operations

http://tech.ebu.ch/docs/tech/tech3276.pdf
Listening conditions for the assessment of sound programme material: monophonic and two–channel stereophonic

This boils down to the following formula: RT60 = 0.25*((room volume in cubic meters/100)^(1/3))
This should be a straight, horizontal line. From 200 Hz down to 63 Hz, the decay (RT60) may rise by 25% maximum.
It is used in BOTH (imperial & metric) of my room mode calculators available for free download from my publications page. This information is seen in cells L57 and N57 of the first tab on the imperial version - L60 and N60 of the metric version.

jim1961 said:
I was especially interested in your comments regarding limp mass or thin walls letting the lower bass (<100hz) escape. My walls are thin, and the room has plenty of places for the bass to escape. Curious why my RT jumps at the lowest reading register.
My decay, IMO, looks good down to about 45hz. Not so great around 40hz :(
Click to expand...

40 Hz is 28 feet long. It could be that you have a heavy partition at 28 or 56 ft.. or even 14 ft, and it could cause the issue. There could also be other resonance issues. That's why testing is always the 'fail-safe'. As much as I would like to say that everything can be calculated, most often it is the factor that is omitted or forgotten that really messes up the equation. :cursing: - you know what I mean...

So it's back to the detective work; as Sherlock Holmes would always say, 'Eliminate the suspects one by one, and then whatever/whoever is left (no matter how unlikely) must be the culprit.'
Jim, Can you run some sweeps with REW and post the MDAT file? One speaker only. I'd like to see what's going on there. And please list the exact construction of your walls.

Cheers,
John
 
Can you tell me if it would be overkill/underkill in my 7'6"Hx10'Wx12'8"L room to use the following:
Facing wall: 10x7'6 w/ 50Hx60W window. First cover the window with cloth vertical blinds. 36x24x6 bass traps with the auralex on top to the ceiling.
Ceiling cloud 24x48 directly over the sitting position (centered at 58" from facing wall) + mirrored on opposite side of the light fixture.) Should I get a soft fixture to replace the hard glass?
Eight 24x24x2" panels for each side of the listening area. Are the back half of the long walls going to require a lot of treatment or just touches?
Eight more on the back wall + 24x6 bass traps above the doors. Replace the door into the room with a solid core with neoprene around the door to seal. (should I keep the hollow core door?
Thanks in advance.
 
Broken H,

Please post a rough drawing of your room with the proposed treatment...

I would recommend facing the window. The light fixture, if centered in the room will be behind you and will most likely not present any reflection issues. The side walls can be minimally treated with 2" panels but you will not absorb the reflections of frequencies much below 400 Hz or so.. (guesstimate).
Overhead, place the 'important' panels at the calculated reflection points. See my ReflectionsBoundariesMass spreadsheet on my pubs page.
Back wall, treat as well as possible.
Door: It depends on your isolation requirements. The use of a massive well sealed door will not improve bass trapping or improve room acoustics, but usually creates the need for more trapping. ;)

Cheers,
John
 
Thanks John, I'll get the drawing done as soon as possible. We're in the process of emptying the room at the moment. Should be done Wed or Thurs. My problem with the door is iso, not acoustic. Have grandkids and I thought I'd use some neoprene seals around the door to better keep their noise out and was wondering if sold core will do better isolation than hollow. I can afford a $200 solid or $700 steel door (if it will make a significant difference, but $2000+ for an iso door is too far out of budget.
Again, thanks for the great reply! I'll check your spreadsheet.
 
The solid-core door will help keep outside noise from getting in, and a neoprene-foam (weatherseal) around it will also dampen vibrations. Hang a couple of your 2'x2' traps on it if it is at a point of reflection.
 
Got through some calcs from John's site (a lot of good math there!) and now know where to set the chair, the speakers, the clouds and how to treat side and back wall. Have to get a couple more traps when I put the solid door in to put on it...Get out the SPL and Spectrum apps and see what I can figure out about cancelling all those nasty 230 Hz and under waveforms. Hopefully the corner traps will do their work...If not, it will be a short while till more $$$ work their way into the studio.
 
jhbrandt said:
Sorry for the long absence here. I have been very busy. We are the designers for SAE school here in Jakarta and for the Digital Media Center at Foothill college in San Jose, CA.. not to mention the many studio builds all over, large and small. ;)


Any wall in a critical listening room counts. You will always want to control the propagation of sound from the source (speakers) so that there is zero interference at the listening position. Reflections from the operator/listening are treated completely differently.


My RT-60 criteria is determined from:
http://tech.ebu.ch/docs/techreview/trev_274-hoeg.pdf
Subjective assessment of audio quality

http://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1116-1-199710-I!!PDF-E.pdf
METHODS FOR THE SUBJECTIVE ASSESSMENT OF SMALL IMPAIRMENTS IN AUDIO SYSTEMS INCLUDING MULTICHANNEL SOUND SYSTEMS

http://www.aes.org/technical/documents/AESTD1001.pdf
Multichannel surround sound systems and operations

http://tech.ebu.ch/docs/tech/tech3276.pdf
Listening conditions for the assessment of sound programme material: monophonic and two–channel stereophonic

This boils down to the following formula: RT60 = 0.25*((room volume in cubic meters/100)^(1/3))
This should be a straight, horizontal line. From 200 Hz down to 63 Hz, the decay (RT60) may rise by 25% maximum.
It is used in BOTH (imperial & metric) of my room mode calculators available for free download from my publications page. This information is seen in cells L57 and N57 of the first tab on the imperial version - L60 and N60 of the metric version.



40 Hz is 28 feet long. It could be that you have a heavy partition at 28 or 56 ft.. or even 14 ft, and it could cause the issue. There could also be other resonance issues. That's why testing is always the 'fail-safe'. As much as I would like to say that everything can be calculated, most often it is the factor that is omitted or forgotten that really messes up the equation. :cursing: - you know what I mean...

So it's back to the detective work; as Sherlock Holmes would always say, 'Eliminate the suspects one by one, and then whatever/whoever is left (no matter how unlikely) must be the culprit.'
Jim, Can you run some sweeps with REW and post the MDAT file? One speaker only. I'd like to see what's going on there. And please list the exact construction of your walls.

Cheers,
John
Click to expand...

My latest mdats can be found on the last post at this link My Listening Room - Page 13 - Gearslutz.com

The interior walls are 3/8" (thin) sheetrock. No insulation in between. :(

On one side of the 185" dimension, to the R of the R speaker, a big section of the wall (which was once an opening) has 2 layers of 3/4 sound board. This measurement corresponds to about 72hz. Right about where the RT60 jumps. If not the cause, further thinking leads me to feel this is contributing.

The floor is 3/4" on 2x6. No slab. Pier house. 10-12" insulation underneath.

Down around 70hz, the RT is allowed some increase, yes? Maybe its not so far out of line in the grand scheme of things being fairly low.

As far as my 41hz decay issue, much of it has to do with my main sub XO being at 40hz and it overlapping the mains. I might be better here if I could adjust the XO to 35hz or so. But I cant.
 
Last edited:
JHB, I guess my real question for you is whether there is anything here to really be concerned about. The right channel (red) doesnt behave as nicely as the left channel. The areas around 63hz and 630hz are a bit off id say. Despite the data, I just dont know whether to put much validly in RT60 for small rooms.

These are derived from my latest mdats Gearslutz.com - View Single Post - My Listening Room


rt 60 l r 07 24 14 mic 30.webp
 
You must log in or register to reply here.
Back
Top