Wall/slot

The rockwool on the opposite wall will take care of pretty much all flutter problems, so if the angles are too difficult you could make the slats just straight; this will probably make the absorbers a bit more "peaky", though; if you want them to stay wider range, pick whichever angle method is easier for you... Steve

Steve, maby this is a stupid question but what if I make the angles top to bottom instead of left to right? is it the same? Thank you!

NO, it might actually be BETTER that way; more bass buildup in corners (including wall/ceiling corners) so if you were to make the depth MORE at top and bottom, LESS at center, it may improve low end absorption a bit... Steve

Thats nice! here is my thought slot W 5mm slat W 200mm D from wall 150mm slat depth 20 mm Absorption freq=111hz 1) What is the bandwidth of the helmholz? 2)Will it be effective in such a low freq or it is better to use membrane absorption? 3) If I use many 3mm slots at top ,where the maximun depth will take place, will I have better absorpion in that range?

Helmholtz's usually have about 2 octave usable range more or less, but don't work very well at that low a frequency. You've still not explained (or I missed it) what you're trying to do here - if you're happy with the room, why mess it up? And wny 111 hZ? Have you run tests that show that particular frequency to be a problem? I'm thinking I'm sorta just "pissing in the wind" here... Steve

knightfly wrote:

I'm thinking I'm sorta just "pissing in the wind" here... Steve

And the meaning is....????? yes I am happy with the room! I have put a speaker in the room playing pink noise and took measurements using an omni mic. In spectrafoo I see dips not just ±5db but more in the range of 100-160hz! Why that happends? I dont know. I am just trying to tame those dips Any suggestions Steve? Cheers

What do you think? Finally I finish these monsters!:lol: Cheers

Looks pretty cool Yiannis - have you done the bottom seals yet, or will you? Sorry, the "pissing in the wind" comment was my frustration talking; here it means "getting nowhere, and badly"... You talk in one case about dB, then change to hZ; how many dB at what frequency are you concerned with, and where was it measured in the room, where was the speaker, the mic, etc - this can mean everything or NOTHING, so EXACT details are important... Steve

Thank you Steve. I haven't done the bottom seals because the MDF goes all the way down at the back and the side panels. There is only a small gap around about 2-3mm to let the castors scroll. Should I put rubber there or something else?

Forgot to mention, the foam-lined board is something you push up against the bottom of the panel after it's in place, just to seal around the bottom.

I don't undertand this well when I am recording acoustic string instruments I always here a peak at around 100hz and at around 125hz. The problem is that I was hearing those freq also before put all the absorpion in the room. It doesn't make sense,does it? i am very carefull when I am recording so for sure is not the sound hole. i also hear it thru headphones. I have done some measurements but before I say something stupid would you please guide me how to take correct measurements in the tracking room? Thanks

To measure JUST THE ROOM, regardless of the positions of mics/instruments/speakers/instrument natural resonances, etc, place a single speaker's woofer (facing into the corner) at one corner of the room as close to the corner as you can get it; then place the mic in the exact OPPOSITE corner (example - speaker @ bottom right rear corner, mic at top left front corner) - Run the tests again (no instruments or other resonant devices in the room) and see what they look like. This will be as close to getting just the room's natural responses. Anything else you see in subsequent tests is a result of things like speaker, head, mic, and instrument placement; it can also be (usually is) instrument RESONANCE. If you've not already found out, moving ANYTHING (including your body) will change the results at some point in the frequency band - Doing the above test will tell you whether your 100-125 hZ is really the room, or just what's in it (and where) - if the peak is still there, it's the room... Steve

Steve when you say:

place a single speaker's woofer

could I put the 1031 genelecs and turn the tweeter off? I will do the tests and post again The picture below is both the resonators in place but not completely painted and sealed. :wink:

Its looking good!! With the casters along the bottom, how are you going to "bandaid" this for TL?

The MDF at the sides and back panels goes all the way down. Only 2-3mm space left for the casters to scroll. With a close cell foam at those gaps I hope to have good isolation

Yiannis, the foam you just referred to is what I meant by using the foam boards. as long as you have that crack sealed well, it doesn't matter HOW you do it. By "woofer", I just meant that the woofer part of the speaker should be as close to the actual corner as possible. Place the 1031 on the floor, woofer toward the corner (not into the room), and don't worry about the tweeter one way or the other; all you're looking at here is stuff below around 400 hZ, so it won't matter. As long as your mic is OMNI, it can go as close to the diagonally OPPOSITE corner from the speaker as you can get it.... Steve

Thanks Steve, what will happen in a slot resonator if the gap between two slats varies? Lets say it stars a 5mm and goes up to 10mm? Will the frequency varies too gradually?

These are the results from two room corners. :shock: i don't like what I see at all.:cry: Steve any comments? Yiannis

Not enough info to say; below about 45 hZ it's speaker fall-off, above about 400 hZ it's anybody's guess (reflections from nearly anything), and the peak at the lower end could be nearly anything. Can you describe EXACTLY, mic position vs. speaker position for each test, what's the red line/green line, what mic was used, + any OTHER details of the tests? It's typical for nearly any room to show variations up to 20 dB, some times MORE - smoothing those out is the name of the game, played with types/placements/amounts of various materials. Don't expect miracles, or quick fixes; but we WILL work on this, and probably both LEARN something in the process... Steve

Hi Steve, 1) the top line is peak and the bottom average. 2)mic used ECM 8000 3)Speaker was at bottom corners faced to supeclunks and mic was exactly to the oposite corner.High 4)Pink noise used 5)no instruments or chairs in the room. 6) floor is laminating Anything else that I could post? PS:would it be better to use a better quality LD condenser mic? PS2:could you please answer my question in the previous post about the slots? thank you

these are new tests. As the two photos show(previous post mic+speaker)EXACTLY the same speaker placement, mic placement and pink noise volume. Here are the results 1st LEFT corner 2nd RIGHT corner :wink:

http://www.genelec.com/pdf/OM1031a.pdf What position was your bass tilt and bass roll-off switch in for the test? I'm asking, because that close proximity to corners would (I think) produce a "hyped" bass response, and the Genny's have (looking at their freq response charts) about 12 dB of range @ 60 hZ - Other than that, I'm not seeing any big nasty peaks/dips in the response. Can you re-scale to just show about 40-300 hZ full width so we can see the modal/proximity effects? All the higher freq stuff isn't relevant here... Steve

Hi Steve, Bass tilt :off Bass rolloff: off. Pictures below L-corner R-corner 40-305hz Thank you

Steve any comments?

Yiannis, sorry for the delay (I only need 36 more hours a day and I might be able to keep up :=) I'm thinking from your pix, etc, that the mic was sitting too close to all that absorption and not at the very peak of the room corner - that could place the mic in an anti-node, as well as cause more absorption of the highs, which would cause your graph to look like it does - the positioning I mentioned is normally used BEFORE any treatment, so you can get an idea of what the room needs; where you were forced to put mic and speaker is quite a ways away from the boundaries of the room so results won't be the same. On the slat question - down around 150 hZ, a 1 meter wide helmholtz presents its ENTIRE FACE to about a HALF wave length; so nearly anything you do from one side of the slat to the other, will likely be AVERAGED as far as response goes. For higher frequencies, this tends to be LESS true but still enters into the results. About the only way I know of to get much "averaging" out of varied slot width and depth, is to build "separators" into the device while assembling so that each slat (or pair of slats maybe) has its OWN SEPARATE cavity to work against - this makes the unit into several separate resonators each with its own characteristic frequency. For your room, maybe try LOTS of measurements while moving the speaker away from the wall(s) about 2" at a time (50mm) - make note of where it is the most even, then place it there and start moving the mic around your potential recording position until the curve smooths out some more; this includes HEIGHT changes for each, as well. It's very time consuming, but hard to do any other way with a room like yours because there are too many things getting in the way of calculations (plus, calculations are only a starting point anyway :=) This type of measurement is where ETF software really helps; you can set it to "machine gun" mode, so it "fires" about once a second - then you just watch the screen and move things slowly til it gets better or worse... Steve