John Sayers' Recording Studio Design Forum

I'm sure you know ... but ...

GORILLA makes a duct tape that is FANTASTIC !

... just NOT sure you can ever peel it back off. [which may bring tears to the eyes].

Measurements as I promised.

First two pics:
Left speaker measurements before and after cloud.
It got slightly better on 120 Hz.



Right speaker measurements before and after cloud.
No significant imoprovement on 120 Hz dip.. Otherwise a little better.



Left speaker waterfall plot after the cloud.


Right speaker waterfall plot after the cloud.


RT60 plots. Left and right speaker.



Both doors at the back are still untreated. Might cause some reflections.

Still wondering what causes that 110-120Hz dip at the right speaker..
Maybe it's just a curse of the way too small control room

-janne

_________________
http://www.myspace.com/moonwagonfin

http://www.miamiwiseguys.com/

Here's also whole spectrum plots on both speakers.
Octave smoothing is 1/3.



-Janne

_________________
http://www.myspace.com/moonwagonfin

http://www.miamiwiseguys.com/

Hi Janne,
If i compare your measurements I noticed something.
Your left speaker measurement is since begin around 7db better than the right speaker drop at 110hz. In vertical view your room is very symmetric and the horizontal view has one door at the rearwall and one angled part like a small basstrap.

How deep is this angled part and what rockwool did you use in it?

Before you added the cloude there was a 7db difference and i beliefe this angled rockwoolpart at the rearwall is the reason for it.

To get most absorbtion you need to do a calculation, wavelengh/4 = thickness of purous absorber 77cm. Depending on what type of rockwool you used this can be effectively >15db with rockwool 40-50kg.
Comparing your harddoor and there is only 5-10cm insulation between the studs (expected from the pics) that i belief is a reflecting part for 110hz to the right rearwallside were you have insulstion with a wall space of around 30cm that is better but not thick and effective anough for 110hz.. This could be the 7db difference between both speakers. 30cm insulation vs 5cm in this area.

From the pics i see you have build in nice corner traps on the frontcorners but there maybe should be much more deeper space for porouse material in the middle and outer middle part too. This is the opposide of your door that might reflect and theres only the end of the cornertrap that is maybe 5-10cm rockwool on both sides. Maybe this two front and rear areas could be the reason for the standing wave.

Since you added the big cloude everything got some db better. But the mode was shiftet a little up cause of the additional material that makes the room smaller. Since the cloude is angled and deep the front part of the cloude seems to improve the horizontal mode too.

This assumption that the room lengh is the cause is supported by the calculstion of the second room mode freq=343 / roomlengh. On your first site you wrote the room is 3,4m long but you added drywall and additional mass, so it would be interesting what the actual lengh is from the drywall to door. I assume 3m so this seems to be a second room mode 343/3=114hz. The Room width was 2,8 without drywall? So lets say 2,5m would be 135hz that does not fit to your freq problem. Also the heigh can not produce the mode of around 110hz if the measures are correct.

You can do a additional simple test. Put a large thick woodpanel in front of the angled rearwall part faced to the rearwall. The 110hz on the left speaker shouldnmove a bit up and should get more worse. Or put two rockwool bags stacked before the angled part and measure again to see whats happening.

If you open the door and put in the doorway two rockwool bags from floor to ceiling. What happens to the right speaker?


If it is the case you recognize differences you might have the same "probl" like me What i would do and i will test it myself,
Sawing two big holes into the reflecting wall. Near as big as a door. Now you have the option to build in big boxes with a panelabsorber or simply use as much space as much you have for the box and put in rockwool. It is only worth if you can get the deph >40cm for absorbing min 10db of 110hz and if you enlarge the room this way the mode might change a little bit to 105hz. If you have only a wood construction house you could build some nice looking boxes from the inside to the outside of the house. Looking similar like a tool shed or an electric tower. Stuffing it with low dense rockwool.

In my case everything on the rightspeaker measurement was better when the door was on the right side. It was a very light and thin door that i think worked like a panel absorber and let the mode freq pass. This was the idea integrating a new doorlike light and vibrating material in the rearwall but as a real panelabsorber, maybe 4mm plywood. I can paint it on the floorside and can make it look really nice AND do not have to deconstruct anything in the inside as i can do the whole box from the outside of the room.

I will upload some skizzes today in my thread to hopefully get more opinions on it.

Stay tuned to fix it.

Regards
Aaron

Thanks Aaron!

It's nice to get other aspects to the problem

I'm suspecting the same thing as you are.
Angled absorber is only 250mm deep at the middle. It's stuffed allmost full with rockwool. (density is about 40-50kg/m3).

Right corner I've super chunk bass trap as you noticed.
But in the left corner (where the right speaker points at) I've got nothing as the door have to be there...
And that corner might be my problem.

Front corners are stuffed full with insulation (upper boxes) and bottom ones I've hangers.
In the middle part is 100mm rockwool.

I'm not going to do any major changes in the room as I'm nearly finished
but I'm definitely doing the tests that you suggested.

I should have measured the room more earlier...

I'm waiting your skizzes and your next update! Good luck with that

And thanks again!

-Janne

_________________
http://www.myspace.com/moonwagonfin

http://www.miamiwiseguys.com/

Hi Janne,
I have found a measuring graph on your thread and did an additional room mode calculation with the
room width and the room lengh The room width has a mode in the center of 120hz and the Room lengh of 100hz. Both modes are first standing room modes and become a problem in the center of the room. In the graph is also shown a thicker outer wall of the right side and a thick wall on the front. I guess these are massive walls. Can you recognize with a sine generator on 100hz a maximum at the front of the room? There should be a second maximum at the rearwall but depending on the wallthickness behind your absorber not as loud as the front section.
the same with the 120hz mode - do you recognize a maximum on the right side where the massive wall is? The second mode should also be at the opposite but as it is an inner wall not as loud as on the massive side. This could be the reason for your different measures on left and right speaker. The wall-mode is triggered more or less depending on the space of the speaker to the wall and weight/stiffness of the wall itself. I did a large research and only two layer drywall on the opposite wall can create a mode even if there are no massive walls only drywall.
Another question what frequency did you tune your slot wall?

Usually if this is the case, the most effective would be to put a big superchunk on the front maxima and
focussing the right slot wall to 120 hz. OR lean back one meter for mixing


Regards
Aaron

Hi Aaron and thanks again

My house is an old wooden house so the walls are not very massive. Front wall and right wall, yes those are more massive than the back wall and the left wall. I suppose there are 150mm wood studs with insulation between the wall cavity, then 12mm Particle board. I attached also 15mm firerated gypsum for extra sound isolation layer.
Back wall and the left wall is only 2x4" wood studs with gypsum layer on both sides. Outer side is a layer (maybe two layers) of 12mm gypsum and inside layer is 15mm gypsum board.
I didn't build this house so I don't know the actual materials which the builder had used. Only visible ones..

I made the test as you were adviced. Firstly tested with 100Hz sinewave.
And yes the maximum was at the front wall. 10 dB louder than the mixing position. At the back wall it was only 3 dB louder than the mixing position. Both speakers allmost the same measurements +/- 1dB.

Second test. 120Hz sinewave.
Right speaker: At the mixing position 3dB louder than at the left wall and 3dB quieter than at the right wall.
(Mp 65dB, Lw 62dB, Rw 68dB)

Left speaker: At the mixing position 1dB louder than at the left wall and 5 dB louder than at the right wall.
(Mp 64dB, Lw 65dB, Rw 60dB)

I also made the following tests as you earlier suggested. Here are some graphs and test fotos:
First test:
Rock wool sag and additional corner bass traps stacked in front of the angled back wall part.

Left speaker measurement at the mixing position:

Right speaker measurement at the mixing position:


Second test:
Same setup but in the corner where the entry door is.

Left speaker measurement: some reason the problem frequency turned around between the speakers?? Now the 110Hz dip is more deeper at the left speaker measurement...

Right speaker measurement: actually quite good +/- 5dB


Third test:
Same setup as second test but the door is now open and the absorbition stack is in the hall.

Left speaker measurement:

Right speaker measurement:


As the problem frequency spikes are quite sharp. Could I build panel trap or traps tuned on 100-120 Hz and place them on problem spots? Could it be the cure?

Many thanks again Aaron
-Janne

_________________
http://www.myspace.com/moonwagonfin

http://www.miamiwiseguys.com/

Hi Jane,
Very interesting! So much is going on there so here are my thoughts.
Pic1:
rockwool placed in the center of the rear wall.
The 110 mode is looking 7db better for the left speaker. No big changes for the right speaker at 110hz.

Theres also a second mode at around 190hz that looks around 10db better for both speakers. I assume that this mode has been before but hard to see cause your old measuries show a small dip at 190hzA too and maybe the intense in the new measuries is different caused by a different mic position just some cm...
Wow. The right speaker has not the 190 drop anymore too. Looks good. This frequency is a candidat that can be absorbt with > 45cm rockwool very fine instead the 110 mode. I can not guarantee that a thinner absorber can be as effective for 190hz but you might try 15cm of 60kg rockwool as a kind of big additional hanger bags in the center of the rearwall, close to the slot wall.

Pic2:
Rockwool at the left corner.
Both corners must be mode maximas for the 110hz cause it looks much better if you place the rockwool bag there.
8db better on the right speaker and what is going on with the left speaker? I guess it does not have a big effect for the left speaker placing the bag there. it seems to have something to do with the wall mounted speakers that they push the sound pressure more to the diagonal corners. Testing this could be tuning a sinus wave 110hz out of the left speaker and listen at the diagonal right corner if there is a louder max than at the left corner.

Pic3:
Rockwool at left corner.
Hey, here you hit the bulls eye again i think. This is looking good on both speakers.
Funny to see that the 190 hz drop is there again on the left speaker but not even as much on the right. So i think the 190 hz must be a mode coming from the center-right part of the rear-wall. The 110db are only 6-7db on both speakers. Nice.

But as i wrote i think you have an additional room mode at 2,85m width that makes your peaks on the measures wider, nice to see on lspkr_3 pic.


Yes, this is what i actually going to do in my room. Our problem is the space and that we have to fight with modes that absorbers usually need alot of space so in theory panel absorbers and helmolz kind resonators should be the way to go to save space and getting the room response nearly flat.
As slot walls are some kind of helholz resonators i think it is not bad going with it but they also reflect a lot and need to be deeper than Johns standard slot wall.

Thats the reason i asked about the frequency you tuned yours.
If you did not tune the rearwall slot wall to your mode you may should consider using this space for a new slot wall around 20cm deph from wall and 15cm slats 3mm slots 22mm thick slats. Maybe a mix for 110hz and 190hz.
I still think the 120hz is a mode of the room width. You can see on your actual measuries there is a low dip at around -9db that does not even change on the graphs. So usually you should add a 120hz slat to your sidewall slotabsorbers. Hard to check but try to put a big bag on the sidewall and we will see if there is a change on 120hz then.

Panel absorbers are not easy to build and they are big reflecting surfaces. I think it would be more effective to build a Heavy-weight-foil absorber. This is the same like the vibrating plate but with a 5-6kg /qm foil instead.

You might wait till i am done with my 100hz tuned slot wall that i can tell you if it makes sense to overwork yours

It would also be interesting now making a measuring with two or three bags placed at the corner between the door and center part of the rearwall. If the theory is right the 190drop must be away on both speakers and the 110drop must be similar to your last measuring

Best regards
Aaron

"Panel absorbers are not easy to build and they are big reflecting surfaces. I think it would be more effective to build a Heavy-weight-foil absorber. This is the same like the vibrating plate but with a 5-6kg /qm foil instead."

If by panel you mean membrane, what is the difference between a panel and a foil membrane?
Either one can be difficult to figure...but you still have to figure either one and you still have to build it.

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

Hi xSpace, good question. I also did not see people build foil resonators here... in german forums they are compared and discussed more often ...instead of other more importand things like very nice people you might better find here
membrane and foil works the same principLe in theory but for a 0,3-0,4 thick heavy-foil you need less deph for the resonator. The front is also not as flat and stiff like a plywood 4mm panel and wood panels tend to post vibrate some ms. Mdf more than pressboard or plywood.

http://62.75.219.232/safranedriver-p18h ... 2db97e34a0

This foil is not a pond foil. It is most times heavier and commonly used for cars to avoid vibrating of the thin metals.

I often read people build panel resonators they are not effective. There are also VPR resonators with a thin steel sheet onto a basotec that could be considered for this low frequency range but i most often readed people have had good sucess with these foil resonators. As you say we must try it at least. Maybe a panel resonator is just good as a foil resonator if it is build well and good in place but with a wood panel there will still be the big flat reflecting zone that may could bother in context to the small room size.

Again, all theory. I did not build this foil absorber myself yet but reading good things about it.

Best regards
Aaron

Sorry I forgot to answer that tuning question..
Actually rearwall angled absorber is not hemholtz type resonator at all. I didn't seal it's cavity. It's just an absorber and I added slats in front of it to keep a little high frequency energy in the room.
Whereas side wall absorbers are hemholtz slot resonators. I didn't tune them any specific frequencies. I should have calculate room modes before I cutted those slats
Slats sizes are 120mm, 70mm and 30mm, slots are 2,5mm, 5mm and 10mm. Cavity behind it changes from 70mm to 250mm.
I'm thinking that my side wall resonators don't go low enough to handle that problematic frequency 120 Hz...

I'm gonna test it like you said. Putting a rockwool bag against the right wall and taking new measurement.
If there's a remarkable improvement then I could tune half of the right wall to handle 120 Hz? Let's say hight of the speaker soffit starts to the ceiling.
How's that sounds to you?

I was wondering the same thing as Brien but at the meanwhile I wrote this post you already answered us
But yeah! I've got no rush. I'm waiting that you finish your slot wall. Then we both are wiser about this subject

I'll also do this other measurment as you said at the end of your post. Let's see what happens. This is definitely getting interesting

Thanks!
-Janne

_________________
http://www.myspace.com/moonwagonfin

http://www.miamiwiseguys.com/

Hmm yes and i guess the measures would look much better if there were tuned. Maybe you have to take use of your great carpener skills again and put in just tuned slot walls.


Do you think or did you a calculation? Your slat panels are looking really thin but if they are 2cm thick you have 111hz on the deepest side and 200hz on the small angle. This is not as bad... Or how thick ware your slat panels?


Maybe this could improve something but you really need to re calculate your slot wall if it really can be modified to hit this frequency and check if the mode comes from the width but i still guess it. Everything makes sense so far that 120hz comes from the room width.


those foil resonators seems to be interesting for small rooms even not as nice looking as slot walls


yes this is a good idea. I finished the border yet and tomorrow i will cut the slats.


I'm curious too and am looking forward to see the measures. You might do one reference measure next time without rockwool that we can compare more easily

Best regards
Aaron

Have you tried swapping L and R speakers?

_________________
Bill
www.billpillmore.com

Hi Bill, what do you think should happen then?
Best regards
Aaron

I guess I am saying this. In order for a membrane to work it has to be tuned from the start.

So if you use a steel plate or an aluminum veneered product or plywood, you still require the numbers on either of these materials to make an accurate panel, right?

So, rather than deviate with unknown properties, stick with what you can verify.

Unless you can verify the properties from the start, it's all guess work. And aluminum is highly, highly reflective in the high end, so while you could get lucky and produce a panel that actually resonates at the low frequency desired, the high end reflection might introduce more treatment issues than typical measures would produce.

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.