Help with Acoustic Treatment

Hi all, Im new to this thing of acoustic treatment and i hope someone can help me. The first thing ive done was to calculate the room modes for my room with all the dimensions in meters: Luckly or not (ill find out) i have a friend who gave me 16 ROCKWOOL E-225 panels with the dimensions 135 x 60 x 5 (cm) and with vol. density of 60 Kgm-3. After searching the net from more specific information about these panels i´ve found its absorption variation with frequency.One problem is that this chart is for panels with the same dimensions except depth ( mine are 5 cm).I think that will be small variations in the chart (am i right :?: ) My questions about the panels : What can i achieve with this panels in terms of getting the best low end possible ? Until 500 Hz much of the energy is reflected.Should i put two panels in each of the sides of the RFZ ( to double its depth) and move them from the wall, or is sufficient to just move them from the wall and use only one panel ? Are they useful to make corner traps ? Now, heres a rough plant of my bedroom: As you can see the point where to put absorption to create a RFZ, is in front of the window on the right side of the mixing position. My questions :) ? Can i mount the absorvers of the RFZ on stands ? What else do i need besides creating a RFZ and corner traps ? Also, the window makes a 90 degree angle with a plan wich is perpendicular to the right sidewall.Ive made a quick sketch in paint. So here it is: How to treat the areas marked in red ? I hope im making any sense. Can anyone give me a hand here ? Any sugestions are very welcome :) axe

First, do not worry yourself with absorption coefficients, graphs, and such. It is very difficult or impossible to relate this information to the treatemnt of a small control room. To get the most low end performance out of these panels they should be mounted with as much airspace behind them as possible. You can use them as corner traps, but with the traditional 45 degrees across the floor to ceiling corners, modal resonance below 100 Hz will still be a problem. You can absolutely mount the RFZ absorbers on stands, and this may be best for you since it will allow you to maximize airspace.

David French wrote:

You can use them as corner traps, but with the traditional 45 degrees across the floor to ceiling corners, modal resonance below 100 Hz will still be a problem.

David, First of all thank u very much for you quick reply and help :) When you say if i use the traditional prism design for corner traps ill get modal ringing bellow 100 Hz, are you saying that the modal ringing is due to that design and if i use another type of corner trap leaving a generous air gap that maximizes absorption that problem is minimized ? If the answer is no to the previous question what else can i do to minimize the problem.Ive got to have bass :). axe

Modes are the resonant frequencies of your room. When you play one of these frequencies in the room, it will be unnaturally loud at one place in the room and almost non-existant at others. Also, when you play one of these frequencies in the room, it will persist in the room longer than it should; this is called ringing, like the ringing of a bell. In a commonly sized room such as yours, there will be about 20 or so such freqencies below 200 Hz, the area where it matters. Using 5 cm panels across the corners of your room will be effective at neutralizing the modal ringing above about 100 Hz, but will not be very effective at reducing the modal ringing below 100 Hz. Thicker material will perform better, so perhaps you should double up the panels in the corners. Really, you do not have enough material to completely treat the room, but you do have enough to make a significant improvement. If you have a very small budget for additional treatment, I would buy bales of rolled insulation and stack them in the corners, then cover them with 5 cm thick panels, then use the remaining panels as an RFZ. If you have no budget, I would be happy with the panels you do have and use them in the way I outlined above. I hope this makes things clear.

David, I have a small budget around 200 Euro, so what do you recommend to treat the modes below 100 Hz ? I want to start by the corners, then the RFZ... So ive choosen a design: The corner panels will be mounted on stands to make the air gap variable. Then i will buy more 32 of these panels to make the RFZ, and possibly treat a little bit the ceiling. Is that enough to treat the modes below 100 Hz ? If not, what more do i need ? The corner traps need to go from the floor to ceiling ?The reason that im asking is that i saw some corner panels that where at equal distance from the floor and ceiling. Thanks, axe

David, I have a small budget around 200 Euro, so what do you recommend to treat the modes below 100 Hz ? I want to start by the corners, then the RFZ... So ive choosen a design: The corner panels will be mounted on stands to make the air gap variable. Then i will buy more 32 of these panels to make the RFZ, and possibly treat a little bit the ceiling. Is that enough to treat the modes below 100 Hz ? If not, what more do i need ? The corner traps need to go from the floor to ceiling ?The reason that im asking is that i saw some corner panels that where at equal distance from the floor and ceiling. Thanks, axe

These 10 cm traps will get you down to about 50-60 Hz, which leaves about two modes that could be a problem. They will not be eliminated by the 10 cm traps, but they will ring out for onal about half as long. The room will sound very nice, but will not necessarily measure flawlessly. I wouldn't worry about it. You will be thrilled with what this does. Get rid of the MDF along the edge; this will only hurt performance. Mount the m floor to ceiling. A single panel performs much better when it's all the way up or all the way down vs. in the middle.

Thanks David.I´ll do that. What you recommend as frame material for the panels ? axe

Drywalling corner bead works well. I'm not sure hwat kind of materials you Portugese guys have, but just try to get something with lots of holes in it.

Thanks David. Ill try to find something with lots of holes in it :) axe