Wall/slot

Yiannis · Post by **Yiannis** » Fri May 27, 2005 7:48 am

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

Yiannis · Post by **Yiannis** » Tue May 31, 2005 5:04 am

What do you think?

Finally I finish these monsters!:lol:

Cheers

knightfly · Post by **knightfly** » Tue May 31, 2005 3:19 pm

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

Yiannis · Post by **Yiannis** » Tue May 31, 2005 6:36 pm

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

knightfly · Post by **knightfly** » Thu Jun 02, 2005 7:08 am

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

Yiannis · Post by **Yiannis** » Thu Jun 02, 2005 11:34 pm

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.

VSpaceBoy · Post by **VSpaceBoy** » Fri Jun 03, 2005 4:46 am

Its looking good!!

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

Yiannis · Post by **Yiannis** » Fri Jun 03, 2005 5:21 am

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

knightfly · Post by **knightfly** » Fri Jun 03, 2005 10:26 am

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

Yiannis · Post by **Yiannis** » Fri Jun 03, 2005 3:18 pm

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?

Yiannis · Post by **Yiannis** » Mon Jun 06, 2005 11:54 pm

These are the results from two room corners.

i don't like what I see at all.

Steve any comments?

Yiannis

knightfly · Post by **knightfly** » Tue Jun 07, 2005 3:51 am

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

Yiannis · Post by **Yiannis** » Tue Jun 07, 2005 3:58 am

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

Yiannis · Post by **Yiannis** » Tue Jun 07, 2005 5:27 am

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

knightfly · Post by **knightfly** » Wed Jun 08, 2005 4:10 am

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