40hz problem !!

[KC Blitz]

Originally Posted by blackfinder

hello i need YOUR guru's help !!


testing my room with a mic + 31 bands RTA/EQ i saw what in the display the problem i supposed to be by hearing it by myself !!

doing some measurements with pink noise at the mixing chair and behind from the cough placed near the wall i saw there's a strong peak at 40hz, more than other frequencies. another less strong at 125-160hz range.

i have in use many traps built with "readybags", everyone assembled into a plywood fame with 2x5cm rockwool panels; 120x60cm, 50kg/m3 density.

2 traps for every corner (one above another)
2 traps onto every side wall
2 traps on the rear wall
7 traps distributed all over the ceiling

room's dimensions are:
L 4.05 mt
W 3.75 mt
H 2.70 mt

calculating the modal resonance from the MHSOFT web site it results the nesty fundamentals freqs are 43 46 64....


WHAT i could do to improve the bass response ??

i thought i used too many panels but it seems i have too many peaks at 40 and 120-160 considering the huge traps i using !!!

if needed i can upload some pics of room walls and RTA display !


thanks in advance to all slutz that will try to help me !!

If your only real problem is 40hz I wouldn't worry about it too much as you traps are clearly helping to sort out the rest of the frequency spectrum.

From what people say on here, 40hz is tough to sort out, especially with broadband absorbers.

[Ethan Winer]

Originally Posted by blackfinder

testing my room with a mic + 31 bands RTA/EQ

Third octave measuring is not adequate. You need software like ETF, FuzzMeasure, or Room EQ Wizard.

calculating the modal resonance from the MHSOFT web site it results the nesty fundamentals freqs are 43 46 64....

This too is not useful information because a modal prediction is just that - a prediction. Until you actually measure you don't really know what the response is.

WHAT i could do to improve the bass response ??

The answer is always more bass traps, though as Jamie said it's tough to target frequencies as low as 40 Hz. Most music has little energy that low, so you should be more concerned with frequencies above 60 to 80 Hz or so.

This article explains how I use ETF, but the principles apply to all such programs.

--Ethan

[blackfinder]

thanks guys !

well...i would add some more info to better understand to help me !


i already tried to put another 3 traps in the rear wall: 1 for each corner a 3rd centered, just above the other 2 already there.
so a total of 3 traps per corner: 2 (10+10cm) traps for both corners plus another one up the others.
also 3 traps in the center wall area (2 cuped in the middle of wall and added another one below them)

shitzz !!! this sorted pratically nothing at my ears and looking the rta display it seems nothing changed ! :(

i also tried to move speakers near or far from the wall to check how the bass response
changes...but sincerey the variations appear to be minimal referring the 40hz peak i have.

i would try to exchange the speakers position inverting the placement on the other wall, transforming the actual front wall into rear and viceversa...just curious to check the sound and what the mic will ear !


tomorrow i'll get a measurement with FuzzMeasure or Room EQ Wizard (i'm on mac) and will upload some pics of the room to give you a real idea on how and where i placed the traps, and off course some screenshots of the FFT graphic result at chair and cough positions.


my bigger doubt is: peaks at 40hz and 120-160 as i have could be blame of insufficient density or thickness of the traps i using ? mmmm....

meanwhile thanks a lot for our replies !

[Northward]

You're going to need some more advanced (and tuned) traps to reach that low.

Systems using resistance to flow (rockwool) are absolutely great as broadband traps, but even with a (thin) membrane fitted, they don't work that low. They "cut off" under around 80hz, depending on brand, type etc. So adding more of the same won't help.

I would recommend Helmholtz type / tuned (thick - 2mm) membrane systems. Problem is they have to be calculated pretty accurately.

Treating 40Hz is going to use a lot of room whatever the solution used... Not sure you'll be happy with that. Another pb with those tuned systems is that they can have re-emission issues if not built right.

Let's see some 1/24th measurements first

[Ethan Winer]

Good advice there Northward. I've seen porous traps absorb down to almost 30 Hz, but it takes a lot of them.

Treating 40Hz is going to use a lot of room whatever the solution used.

Yes, and this is my main objection to tuned traps, in smaller rooms anyway. By the time you have enough trap surface to make a real improvement, you don't have any places left to put traps that target the much more important range above 80 Hz or so. In all honesty, once you get down to 40 Hz I think a modest amount of EQ cut is not a terrible solution. Especially in a small room like the OP has.

--Ethan

[blackfinder]

Originally Posted by Ethan Winer

In all honesty, once you get down to 40 Hz I think a modest amount of EQ cut is not a terrible solution. Especially in a small room like the OP has.

--Ethan

it's just i was thinking this afternoon !!!

note that at chair position my ears (and what is measured by EQ/ARC) don't get the 40hz peak yet... instead i have big attenuation under 100hz and a peak in the 100-200hz range referring to EQ/ARC detections.
the resonation at 40hz starts to be subtle audible if you move backward from your listeing position, let's say around 50cm.

anyway the peak at 40hz is really HUGE as you will see in my pics, around an average of 12db !

and looks like is very narrowed cause the behringer EQ and also ARC system showing it by a very similar shape.

anyway FFT response will give us more details... tomorrow we'l see...

stay tuned

[Glenn Kuras]

Originally Posted by Northward

You're going to need some more advanced (and tuned) traps to reach that low.

Systems using resistance to flow (rockwool) are absolutely great as broadband traps, but even with a (thin) membrane fitted, they don't work that low. They "cut off" under around 80hz, depending on brand, type etc. So adding more of the same won't help.

I would recommend Helmholtz type / tuned (thick - 2mm) membrane systems. Problem is they have to be calculated pretty accurately.

Treating 40Hz is going to use a lot of room whatever the solution used... Not sure you'll be happy with that. Another pb with those tuned systems is that they can have re-emission issues if not built right.

Let's see some 1/24th measurements first

If you don't want to go with a tuned trap but broad band an want to hit 40 hz then I would go with filling the corner. Something like our Tri Trap. Cut rigid fiberglass or mineral wool into 17x17x24 triangles and stack floor to ceiling. Just straddling a 4" piece of 703 will start to fall off around 100hz and really not do much at 40 hz.

Glenn

[blackfinder]

thanx for the advice Glenn!

would be great if the 100-200hz peak could be limited by doing something different on the side walls or it's all related to corners damping... let's see after adding pics & graphs what you GURUS will suggest me!!

nowjust recharging my digitalcam, battery finished just when i going to get some pictures of my room


asap i'll upload pics and screenshots from what "heard" fuzzmeasure... i did measurements in chair position with mic in front of speakers and pointed up the ceiling, then i also did a take from the couch (mic in front of speakers) placed near the rear wall as u'll see in the photos.


really thanks to all of you replying and following my problem

PS:
if anyone would check i can also upload the complete files from FUZZMEASURE, so you can open and menage by yourself with all the parameters... I HOPE I DID THE MEASUREMENTS IN THE RIGHT WAY AND SETTINGS !!!

[blackfinder]

ok here below all the pics & graphs....


room's walls:


















to be countinued...

[blackfinder]

AND HERE WE HAVE THE FUZZMEASURE GRAPHS...
please tell me if the settings are good !!
i did measurements for chair position with mic oriented to ceiling and direct to speakers, and from couch with mic oriented to speakers

















THIS IS WHAT THE BEHRINGER 31bands EQ SHOWS IN CHAIR AND COUCH POSITION:











NOW i'm in your guru's hands...
ALL SUGGESTIONS ARE WELLCOME !!

[andrebrito]

Use EQ or membrane absorption... RPG MODEX CORNER is one of the solutions !

[Glenn Kuras]

I would vote against EQ. That spike is at the couch so correction would mess the mix spot up. Also I HATE EQ as it does nothing for the ringing in the room.
More bass trapping but also if you want to help that couch spot (going to be really hard) I would put 6" panels on the back wall, spaced 4" off the wall.

Glenn

[blackfinder]

Originally Posted by Glenn Kuras

I would vote against EQ. That spike is at the couch so correction would mess the mix spot up. Also I HATE EQ as it does nothing for the ringing in the room.
More bass trapping but also if you want to help that couch spot (going to be really hard) I would put 6" panels on the back wall, spaced 4" off the wall.

Glenn

glenn,
thanks for watching all !

the 2 panels you see on the rear wall are 4" (10cm) thick and are spaced just 4" (10cm) from wall... i also tried to add one more panel for each corner (so a total of 20cm) but they had no real effect on the 40hz peak

you think that just increase back wall's panels from 4" to 6" (10 to 15cm) could be effective ? ...mmm... just 5cm more i'm afraid won't make a real difference

i starting to think the problem is the density of the rockwool i used (around 50kg/m3), that can't absorb at that so low range in effective manner.

what you all think, i could change the response replacing actual panels (also in the corners) with some 70-90 kg fiberglass panels ?

[Glenn Kuras]

Originally Posted by blackfinder

glenn,
thanks for watching all !

the 2 panels you see on the rear wall are 4" (10cm) thick and are spaced just 4" (10cm) from wall... i also tried to add one more panel for each corner (so a total of 20cm) but they had no real effect on the 40hz peak

you think that just increase back wall's panels from 4" to 6" (10 to 15cm) could be effective ? ...mmm... just 5cm more i'm afraid won't make a real difference

i starting to think the problem is the density of the rockwool i used (around 50kg/m3), that can't absorb at that so low range in effective manner.

what you all think, i could change the response replacing actual panels (also in the corners) with some 70-90 kg fiberglass panels ?

Getting the couch area is going to hard and honestly I would add more and just live with it. For myself all I have to do is tell the guys in the back to make me some up and I am done. For you it is a bit of a pain in butt and not sure it would totally get it to the point you want. The good news is the more you add the better the mix spot will be.


Glenn

[blackfinder]

Originally Posted by Glenn Kuras

Getting the couch area is going to hard and honestly I would add more and just live with it. For myself all I have to do is tell the guys in the back to make me some up and I am done. For you it is a bit of a pain in butt and not sure it would totally get it to the point you want. The good news is the more you add the better the mix spot will be.


Glenn

and for the 120hz range peak ? what u would suggest me ?

i could menage with it increasing thick or density on the side walls or it's also related to the real wall reflections too ?

[Weasel9992]

Originally Posted by blackfinder

and for the 120hz range peak ? what u would suggest me ?

i could menage with it increasing thick or density on the side walls or it's also related to the real wall reflections too ?

The answer is the same...more bass trapping. The measurements are great to have, especially when you're setting the room up for the first time, but once you're set up then you're somewhat limited with respect to how you can solve the resonance problems. With low end peaks and valleys pretty much the only thing you can do is add more bass traps...unless you want to move things around in the room.

Increasing thickness at all points is probably not a bad idea...assuming that the density is right to begin with. Are you using 2" panels on your back wall? Looks like 2" at the side reflection points too, right?

Frank

[blackfinder]

Originally Posted by Weasel9992

Increasing thickness at all points is probably not a bad idea...assuming that the density is right to begin with. Are you using 2" panels on your back wall? Looks like 2" at the side reflection points too, right?

Frank

hello Frank, thanx for reading...
i using 2x2" coupled panels (total 10cm) for all the traps you see in the room, those on the side and rear are spaced 4" (10cm) from the wall, density for every 2" rockwool panel is 50kg/m3 (around 3lbs).

as i said i already tried to coupling 3 and 4 panels together to increase thickness, but it seems no real absorbtion gain in the critical measured area !

i'm afraid it's not only question of thickness but also density, now i trying to find some high density fiberglass panels, but here in Italy it's a bit hard to get something like Owens Corning 703 or 705 !

i would try to use 2 or 3 coupled panels of fiberglass, each one 2" thick, with 65-80kg desity (4-5 lbs).
checking around it seems that fiberglass, at the same density value, is more effective than rockwool...

what about this point ?

[eirikur]

I am a total newbie to measuring room response etc, but I thought that the measurement mic should always be pointed at the ceiling? Makes sense to me since you want to measure the room and not the monitors. I saw from your pictures that it aims straight at the monitors.... On the other hand, your ears WILL be facing towards the monitors (hopefully most of the time, anyway) and not the ceiling..

But I may be wrong, or this has minimal effect on the results...?
Educate me!

[Tomer1]

Indeed,
You want to capture the room as a whole and not emphesize a certein area of the room.
So Flat against the ceiling,At mix\sitting point and ear hight\level.

About the low bass freq peak,
Your room is small- according to Porous Absorber Calculator ,
It will be unpractical to build a broadband design that will absorb down to 40hz.
Even 20cm with 20cm air gap will not result in considerable reduction around that peak.

I would look into tuned devices.

[blackfinder]

eirikur and Tomer1,

i did measurements with mic placed UP the ceiling and DIRECT to monitor from chair mix position.

i also did same thing for the couch, but i saw that positioning the mic UP results in virtually the same response...so i added just the direct to monitors response.

unlike the couch area, in the mix sitting area the UP and DIRECT placing gave me noticable differences so i added both analisys.


Tomer1,

that's just my fear...no way to menage with so deep low waves !!
i did some counts and with tuned resonators i should have sacrify too much big space in order to use a couples of them tuned at around 40hz !


THANKS A LOT TO ALL FOR WATCHING MY TREAD !

[eirikur]

Ah... I see.. note to self: read more carefully next time..
My bad..

[blackfinder]

Originally Posted by eirikur

Ah... I see.. note to self: read more carefully next time..
My bad..

no prob

any other suggestions from acoustics Gurus here at GS ??

[Tomer1]

Here is an alternative,
I saw that in some BBC studios they used tuned panels droped from the ceiling,
Its not the optimal spot to possition a helmotz (I think you usualy use itat maximum velocity spots such as rear wall) but will work.

Im sure you could spair 30-35cm of ceiling since yours is releativly high and build a trap which will be effective in that range.

[blackfinder]

Originally Posted by Tomer1

Here is an alternative,
I saw that in some BBC studios they used tuned panels droped from the ceiling,
Its not the optimal spot to possition a helmotz (I think you usualy use itat maximum velocity spots such as rear wall) but will work.

Im sure you could spair 30-35cm of ceiling since yours is releativly high and build a trap which will be effective in that range.

mmm.... here is where ? you can provide a link ?

[Tomer1]

I meant as in... here is an idea.
I'm almost sure I saw it in the BBC R&D reports regarding studio design.

Cant seem to find it,
I'l go threw my book collection, maybe I've seen it there...

[Tomer1]

Found it!
Chapter 20 in Alton Everest's master handbook of acoustics.
Perforated Vinyl front , The entire ceiling of this small recording room is made of Helmotz reasonators, looks very much like conventional
"cieling clouds" only tuned.

You should consider this.

[blackfinder]

Originally Posted by Tomer1

Found it!
Chapter 20 in Alton Everest's master handbook of acoustics.
Perforated Vinyl front , The entire ceiling of this small recording room is made of Helmotz reasonators, looks very much like conventional
"cieling clouds" only tuned.

You should consider this.

thanks a lot !!

i should have that in PDF, will check it out tomorrow

[laddie.music2]

have you tried using the BAGEND AUDIO E-Trap???

It's a subwoofer type thing with a transformer which changes the ballistics of the subwoofer speaker cone,
it's a tunable hermo type absorber.

I've seen it in action, i've seen minimum of 6db's all the way down to 20hz, and up to 12db's depending on the room.

They are amazing, check them out, and they are pretty small ;-)

Untitled Document

[elan]

Originally Posted by Ethan Winer

Good advice there Northward. I've seen porous traps absorb down to almost 30 Hz, but it takes a lot of them.



Yes, and this is my main objection to tuned traps, in smaller rooms anyway. By the time you have enough trap surface to make a real improvement, you don't have any places left to put traps that target the much more important range above 80 Hz or so. In all honesty, once you get down to 40 Hz I think a modest amount of EQ cut is not a terrible solution. Especially in a small room like the OP has.

--Ethan

great point, how to cut at 40/50 hz? i mean how you would do? with a plug in? or with a hardware eq? with which plug in? with which hw eq?

thanks!!