Please Help - Hole at 105 Hz

liax1975 · Post by **liax1975** » Fri Dec 15, 2006 5:37 am

Hello to all,

hope that anybody can help me.

I tuned my control room:

http://www.liax.de/studiobau_2006/Schraeg-links-1.jpg

and i bought a sound-level-meter to measure my results,
directly on the position where i sit when I am mixing I have a hole

105 db [edit I meant "Hz"]

and a peak at

120db [edit I meant "Hz"]

How can I solve this problem ?

I don´t want to change the position where I sit, also then there are other holes in the frequence spectrum.

Should I built a Helmholzt for the 120Hz and will this solve also the hole at 105Hz ??

And where should I place it ? Normally there where the Peak is, but this is my sitting position !

PLEASE HELP !

Thanks in advance

Holger

Post by **kendale** » Fri Dec 15, 2006 6:15 am

Aloha and welcome to the forum, Holger

If you could provide some of the following info, please:

- What are the measurements of your room (L x W x H)
- How far from the front wall are you positioned?
- How from from the floor are your ears when seated?

Here are a few threads that might prove helpful.
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=2441
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5801
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=610
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5930
http://www.johnlsayers.com/phpBB2/searc ... de=results

Hope this helps,

Aloha

liax1975 · Post by **liax1975** » Fri Dec 15, 2006 7:18 am

Thanks for your reply.

The Dimensions are a little bit hard to write down, because it´s not a straight room, the front walls are 30° and 60° angled. Also the rear wall is filled with material.

I uploaded some pictures and here are some more:

http://www.liax.de/index_old.asp

The sealing is also filles with absorbation material.

where should I place an Absorber (Helmholtz?) and which frequencies should it absorb ?

liax1975 · Post by **liax1975** » Fri Dec 15, 2006 7:20 am

Ouh, sorry .. One pic is too largeeee ...

Post by **kendale** » Fri Dec 15, 2006 8:56 am

Woah!

Any chance you could resize that puppy, please? It makes reading this thread really hard, much less wanting to respond.

By the way, what is your ceiling height?

Thanks!

Aloha

liax1975 · Post by **liax1975** » Fri Dec 15, 2006 9:26 am

Ah, i found the edit button

Now thie pictures should fit to 1024x768 !

The ceiling height is 2,43m ..

Post by **John Sayers** » Fri Dec 15, 2006 9:55 am

Holger - db = decibels = level.

Hz = Hertz = frequency.

You have a 4 db boost at 120hz and a dip of -3db at 105 hz giving you a general response of +4/-3 - which really is not bad at a frequency like 110hz. a 7db variation.

Looking at your graph it appears that the lowmids - 300hz are generally higher than the low end. - what setting do you have on the low end adjust on the rear of the 20/20s??

cheers
john

sillybird · Post by **sillybird** » Fri Dec 15, 2006 10:01 am

Hi Holger

Even if I can't help you, just wanted to say, nice work! just clicked through your building pics, well done!

Greez
Roman

Post by **kendale** » Fri Dec 15, 2006 10:09 am

Aloha,

Thanks for resizing!

At first glance this is what I think I'm seeing:
- there is a null @ 3' 3" Feet = 0.9144 Metre(s) (Room Length)
- the mix position is just inside of the null

It is much more effective and much less expensive to move the mix position forward to about 38% of the room length than it is to try (if it is even possible) to compensate for the null. (Mix Position @ 38% - 4' 9" Feet = 1.4478 Metre(s)

It is also helpful to avoid the nulls from floor to ceiling as well. Position seating higher or lower as necessary.

Hope this helps,

Aloha

liax1975 · Post by **liax1975** » Fri Dec 15, 2006 10:17 am

Thanks !!

Sorry, I meant "Hz"

Better to show it in pictures.
I put two hangers into each corner in the back of the room and also one below the 20/20 !

It is not exactly as explained here in the forum, but I had only a small space around the 20/20 so I tried it this way !

Maybe this cuts the lower frequency down too much ??

Just saw that another answer arrives !

liax1975 · Post by **liax1975** » Fri Dec 15, 2006 10:32 am

@ kendale

Thanks ... I just moved my mixing position including table approx 40cm more to the front but

mysterious:

The dip at 105 db is still there. But what I mentioned, if I put my head over the table the 105 db are back , this was also the fact at the "old" position.

I putted my hands on the stands that I built for the table and they vibrated at 105db a lot !!

I posted a picture of my stands for the table, well, they are black now, but they are still hollow inside !

Could it be that these stands are the reason for the 105 db dip ?

Should I drill somme holes into them ??

liax1975 · Post by **liax1975** » Fri Dec 15, 2006 10:37 am

I measured again, table and mixing position at the new position:

Now the dip is -6db !!

Larger than before ..

Mysterious ........

I assume I build some great 105 Hz Helmholzt Resonators when I built the stands for the table !

Could this be ????

Post by **gullfo** » Sat Dec 16, 2006 4:18 am

maybe stuff the legs with some insulation to dampen them and perhaps cut some holes (after trying insulation) to alter their resonate frequency.

I think the mode calculations were a bit off since I don't think your room is 97,000 cubic feet...

the room mode calculator has a column for feet and a separate column for inches... the inches column looks off...

Post by **kendale** » Sat Dec 16, 2006 7:13 am

Aloha,

My thanks to Glenn, and my apologies to all,

Redid the calculations on metric to feet converter http://convert.french-property.co.uk/
Holger’s Room - L x W x H
L 4,40 Metre(s) = 13.1233595801 Feet (13’ 1”)
W 3,60 Metre(s) = 9.842519685 Feet (9’ 10”)
H 2,43 Metre(s) = 6.56167979 Feet (6’ 6”)
Room Volume 836 cu. ft.
Ear Level 1,3 Metre(s) = 3.280839895 Feet (3’ 3”)
Current Mix Position 1,60 Metre(s) = 3.280839895 Feet (3’ 3”)
Proposed New Mix Position @ 38% from front wall 1.4478 Metre(s) = 4’ 9” Feet

While there is a change in room volume and some of the modes, the mix position is still roughly the same.

I posted a picture of my stands for the table, well, they are black now, but they are still hollow inside! Could it be that these stands are the reason for the 105 db dip?

I don't think they would cause a dip in response, especially if they are hollow and vibrating.

If, as a process of elimination, you were to to indeed stuff them with insulation, say mineral wool @ 3pfc density (before drilling holes) and see what difference (if any) that makes, and then move on to another option you might be able to at least eliminate them as a possible cause in the equation.

There are several threads that suggest that stiffness/mass/density is applicable when trying to eliminate unwanted resonances in floor/wall/speaker mounting assemblies. Drilling holes into your desk stand would seem to compromise the abilty to dampen its ability to not resonate. If anything, insulation and perhaps another layer of mdf would add more mass & stiffness to your stand.

I did notice what looks to be a sub located beneath the table in your pic link attachment. Is that correct? if so, have you tried taking a reading without it? At different level settings? At a different location?

Will continue to ponder the posibilities....

Aloha

Post by **kendale** » Sat Dec 16, 2006 9:12 am

Aloha Holger,

I just moved my mixing position including table approx 40cm more to the front but...

Found another miscalculation. Try moving your mix position (your chair at least) 38% of the length of your room from front wall This would put your chair about 1.4478 Metre(s) = 4’ 9” Feet

Let us know how that sounds...

Aloha