”Facts”? “Please stop.” …?


Let me explain DanDan:



Look at this zoomed in FFT of the 120 Hz noise and you´ll see that there´s actually two signals there: 120 Hz & about 120,8 Hz. I assume you know about “beats” and how that works? Now calculate the beat frequency for those fc’s and then look at the waterfall in this post: https://gearspace.com/board/8624107-post269.html

Makes sense right?

Yes it does Jens, thank you. Clever investigating. I think you have shown that this is a time variant noise. During the thread various sources have been suggested, from instrument to fridge, directly resulting from tests showing repeated decays, and the effect disappearing due to changes in the test, or just at random. I presume the recording of ambience doesn't reveal it turning on or off which would be further convincing. We could ask Alejandro to deliberately turn on and off the fridge and to make another background noise recording of this happening. Or to go next door and do the same with their appliances. Or to look for a transmitter nearby. We could start to wonder why 19Hz has come and gone seemingly randomly. Etc. Etc.
Or we stop here and celebrate the fact that he is happy that he has a very decent response and that most if not all practical possible improvements have been explored.

DD

Ok, so moving on then.


Some plots of the latest IR’s:



Modal frequencies of interest: 18-19, 23, 34-37, 48 and 67 Hz. Which ones are worth trying to treat is hard to say without being on site but I would personally try to get every modal decay down to about 400 ms (T60) if possible, 500-600 ms tops, depending on frequency (18,5 Hz is low enough to ignore completely but it would be interesting to know what boundaries are in play in order to add to the body of knowledge). Perhaps even more important is to try and regain some energy (in a controlled way naturally) in the frequency range above the modal region, depending on preference naturally, but if one want´s it dry/dead; it should be dry/dead in the entire frequency range and not only in the highs.

In context and given that Alejandro has often professed little knowledge of acoustics, I think his success is quite remarkable. Fairly close to EBU spec for critical listening rooms to my eye.


Alejandro, felicitaciones por tu éxito y que éxito sea tuyo siempre!

Hasta Luego, DD

The main noise (IMO) comes from computer noise... I'm sure. I have to put in some case, don't know (Tips are welcome) . But another sure noise is from electrical web. That room, doesn' t have earth (and don't know if the entire Block has it), so I have a lot of work to do in future.
Great time here folks. I learned a lot, did some mixes and I' m superb glad. hehhehhehhehhehhehheh
Thank you Dan, Jens, everybody. I love you all. Keep in contact!

Sure Jens, I need your help yet. Give me a couple of days to recuperate me and we'll fix next issues, that surely seems easier (I didn't sleep at night thinking about issues). I have sessions overcoming and my whole studio is a trash. Dust where you put any finger or look, engines, screws, etc... NW8 KAOS!!!

ETC’s:



Early reflections I would try and treat (absorb or redirect/diffuse down to below about -20dB or lower) are at; 1.2, 3.9 and 8.7-9.9 ms (relative to direct sound). After that, it´s a matter of personal preference and limitations set by the room (size).

Well Right side has a a panel, in case you don't know...

Hello fellow. I went back into the ring!
This week I was trying some problems related to electricity. I found an outlet had its polarity reversed, therefore no problem meeting the 50 HZ ...(that shows me the REW RTA).
Moreover, some Rockwools installed in early reflections (using the technique of mirror), so new measurements will upload them tomorrow and try to give me their opinion ...

Hallo...

You still haven't fixed your modal resonances!!

Why do you need to install more roxull? Is it cold in your room?

Read the OP's post again ...

What post?

Good, I guess you´re aware of the limitations of the "mirror technique" (only gives a hint on geometric first order reflection paths and not reviling higher order reflections, or the ones caused by diffraction for other obstacles)?

https://gearspace.com/board/studio-b...on-issues.html


The ETC will reveal if you where successful in you guesses as to where the early reflections where coming from.

+1; and almost more importantly, it details the NON-OBVIOUS sources of destructive energies.

No, my room is quite warm and pleasant these days, but if you help me with my problems would be great. What you suggest I do about it? (apart from contact with Matt) see what frequencies they should be treated and how?

It's good that your room is warm and pleasent. My point here was that you have good decaytime above 100Hz so you don't have to concentrate anymore in this region. Let this be and don't install more absorbtion because if you look at your ceiling you have plenty of it. All off a sudden you guys are talking about early reflection when the biggest problem is in your bass region.

It is entierly up to you to contact Matts or not. But, It took him one hours to adjust my Helmholtz resonators in my downstair livingroom as can been seen in my thread.

It is difficult to say to you what you have to do via a forum and not been able to be in site and do your own measurements. I can say this to you, don't build any more boxes because it won't help your problems below 100Hz, you have clearly proven this. All I can see is that from your waterfall measurements you have resonances with boxes or not, you have to adress this first.

I find it very puzzled that despite the experts here in this forum they really can't help you with your problem.

Godd luck

So just because the OP’s boxes (that are probably too small, not tuned right or not placed no a relevant boundary) does not work; your conclusion is that no other treatment option (even if used correctly) will work except Matts' magic boxes … are you sure you´re not Matts …?

And your comment on early reflection treatment just expose your lack of understanding of control room acoustics. Modal control is important but not more than early reflection control; you need both, and if the OP wants an accurate monitoring situation without early reflections and unless he is prepared to start splaying walls to redirect the early energy instead of absorbing it; more absorption at early reflection points is the only way forward.

And regarding the modal issues; It´s usually a good idea to understand the problems before trying to address them.

How to treat nulls

Jens....lägg av!!

As far as I know, Matts don't have a twin brother but I am a brother and a twin to Mctwins. So, now you all know.

Läs några trådar där Mctwins medverkar så förstår du mitt skämt bättre.

There is a simple enough answer Matts.

There are no experts.
There is no problem.

There have been various attempts to fix insignificant or impossible issues, which of course could never succees. Particularly as the measurements kept showing different results apparently at random.
I put some time and effort into sorting this out. Turns out the answers were at the start of the whole thread.
Ciro

I am continuing with Alej via PM. He is currently investigating the closet doors and ceiling as sources of those reflections seen in the ETC. The doors may be removed, replaced with a thick drape, or whatever. The window at the left can be covered with Fibre except when visual is needed.

I will say it again, to all this time. Please stop posting.

DD

?

OP: Is this what you want? No more help exept from DD via PM?

No doubt about it, but as I said before I do not think Matt trip to Buenos Aires to tune my room ... And I could not afford such an expense.
Yep, I began to feel the same.

I did everything you asked me to do. I read hundreds of posts, links. That my boxes were poorly constructed I can attest that it was not. At best, they are useless in the bud. I think I should call someone in my country to take charge of the matter... I want to mix songs, make art. I do not want to be an acoustician.
Godd luck me
Thank you fellows

Jens, my motives here are human rather than technical.
Anyone is free to use PM as they see fit. As you did already with the OP.

This thread is 321 posts long. Ciro came to what I would call a very reasonable and reasoned conclusion in post 21. In the meantime 300 posts? And what result? 10 MLV boxes and hours of work on random measuring excursions.
Further posting (in public, i.e grandstanding) of suggested solutions to non existent, insignificant or insoluble problems, will only create another 300 posts and more frustration for the OP, thinking he has a mysterious problem and is incapable of solving it. There is no problem apart from the early reflections which are easily sorted or ignored.


DD

I stand corrected, were 19

Please note that I have not provided any solutions to your problem yet, and the reason being that I think there´s still uncertainty about the cause of the issues (what boundaries relate to what modal decay) and what theoretical problem actually is an audible real-world problem.

If you find that for example 37 or 48 (isch) Hz to be problematic and you do the investigation necessary to fully understand what boundaries are involved in reproducing these modes (in other words; what surfaces would benefit from treatment in order to reduce the modal decay of these frequencies) , I will give you my suggestions on treatment.

My only advise so far regarding treatment is:
https://gearspace.com/board/8524842-post19.html

And so far, I still feel that the first point (“Identify areas related to each mode”) is not fully taken care of.


I really don´t feel that it´s fair to blame me for the partially unsuccessful treatment applied to your room.

So now we just forget about all this and leave it?

Why not learn from the mistakes made here so that others don’t need to repeat them again and again.

Why not try to help the OP getting it right (and not via PM, but in public so that others also can learn something)? Isn’t this what this forum is all about?

Ok, I will on Monday. Thank you Jens.

OK Jens...
Sorry for the delay but I have my mother admitted to intensive care. It was just a scare.

Well I hope I have found the resonance points.

19 Hz = A + B UP 3 Corners
36 Hz = Inside the closet. Perhaps the entire wall echoes.
46 Hz = Also inside the closet + A & B Corners.
54 Hz = B to D (ceiling + wall 2 corner). It also echoes the door of the room, and something out of it.
64 Hz = B to D (ceiling + wall 2 corners)
114 HZ = A + B at half height. Below Monitors line, between the floor and wall.

I hope this serves to something.

Thank you very much for your time.

How to confirm room modes:


In a hypothetical room with the dimensions (X) 5 x (Y) 4 x (Z) 3 meters (and assuming rigid boundaries and no openings), you would expect to find these modal frequencies below 100 Hz:

Freq. - Mode
34,30 - 1,0,0
42,88 - 0,1,0
54,91 - 1,1,0
57,17 - 0,0,1
66,67 - 1,0,1
68,60 - 2,0,0
71,46 - 0,1,1
79,26 - 1,1,1
80,90 - 2,1,0
85,75 - 0,2,0
89,30 - 2,0,1
92,36 - 1,2,0
99,06 - 2,1,1

These can be confirmed by placing a speaker in one corner (in order to excite all modes *) and then playing each frequency whilst walking around and identifying the nodes and anti-nodes (dips and peaks) for each mode. Taking the first axial mode related to the length (X 5 m) 1.0.0 for instance; you would hear the tone loud at the entire area of the two short walls (the 4 x 3 m areas) and a null in the middle of the room. You will not hear any significant change in amplitude as you move in the Y or Z axis (from long wall to long wall, or up and down). If you play for example the frequency corresponding to the 2,1,0 mode (81 Hz assuming the theoretical model is spot on; not the case in real life naturally but often not that far off assuming rectangular room and solid walls), you´ll find two nodes (nulls) along the X axis (length) and one node in the Y axis. Etc etc.

So; why do we need to know this?

Suppose that you´ve manage to build a couple of highly efficient (high Q) membrane absorbers that you want to use to tame the long decay of 34 Hz seen in our hypothetical measurements. If you only care about the areas of high pressure variation, you could mistakenly assume that placing these panels along the long walls (but close to the short walls) might be a good place since you heard the 34 Hz mode loud in these areas, but since 34 Hz is due to the axial mode related to the short walls (4x3 m areas): 1.0.0, the panels will have little or no effect on the 1.0.0 mode if not placed on these areas.

Finally; what about if your measurement shows a resonant frequency lower that the theoretical first mode of your room? If one or more of your walls are not solid and heavy, they will let some low frequencies through. Exactly which once depends on the complex acoustic impedance of the wall. If you play this low frequency and discover that you have a high pressure variation (high amplitude) at the front wall, but little pressure at the rear wall; you might find that if you continue outside of your room, you might find the other high pressure zone (assuming axial mode) at a solid boundary located behind your rooms rear wall. If you´ve discovered the first axial mode using the front wall of your room and an external solid wall outside of your room, trying to combat this mode by placing panels on the rear wall (of the 5x4x3 room) might be a pointless exercise since there’s no or little pressure variation close to this surface for this mode.


EDIT:
* Exception might be if the speaker is placed against one or two lossy walls and there´s modes caused by coupled spaces.

How beautiful lecture!
I think I read it about 1000 times.
Now would be good to put it into practice in my room. So, the following would be ...