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How can I tame these wild modes? Studio Monitors
Old 1st September 2011
  #1
Gear Maniac
 

How can I tame these wild modes?

I've been working on this room for more than a month now and still haven't succeeded in flattening the frequency response at the listening spot as I would like to. The problems are mainly in the low frequency area, with the most annoying modes at around 62, 81 and 110 Hz. This room will mainly be a place to do my mixes, but also to rehearse and record music.

So far I've built 2 corner bass traps in the rear wall corners and two huge bass traps in the front wall corners (yet to be covered with cloth). They both consist of rock wool with a density of about 35kg/m3. In addition, I've built a couple of wall absorbers, ceiling absorbers and a big cloud. These are mostly melamine foam in front of rock wool panels. The listening experience in the room has become quite pleasant, even though it clearly lacks some diffusion. But I'd really like to get rid of the most annoying room modes first.

The 62 Hz mode is the loudest at the front wall between the speakers. The 81 Hz mode is the loudest at the side walls. The extreme notch at 110 Hz is a mystery to me. At some places in the room this frequency just disappears.

Looking at the pictures and the measurement graphs, would you

- try adding more absorption to the front wall?
- try to catch the modes with a helmholtz resonator?
- do something else (what)?

I hope the pictures are more or less self-explanatory. I am aware that more info would be needed for a thorough diagnosis. In case this turns out to be really complicated I would also consider spending some $$ on a professional consultation. Just drop me a line if you are interested and keep in mind that this is a very low budget project.
Attached Thumbnails
How can I tame these wild modes?-010911-spl-left-orange-right-green-.jpg   How can I tame these wild modes?-010911-wf-l.jpg   How can I tame these wild modes?-010911-wf-r.jpg   How can I tame these wild modes?-010911-etc-l.jpg   How can I tame these wild modes?-010911-etc-r.jpg  

How can I tame these wild modes?-010911-rt60.jpg   How can I tame these wild modes?-front-wall-view.jpg   How can I tame these wild modes?-rear-wall-view.jpg   How can I tame these wild modes?-studioplan-josefstr.gif  
Old 2nd September 2011
  #2
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boggy's Avatar
Quote:
Originally Posted by bermudaben View Post
........
- try adding more absorption to the front wall?
Yes.
Quote:
Originally Posted by bermudaben View Post
- try to catch the modes with a helmholtz resonator?
No.
Quote:
Originally Posted by bermudaben View Post
- do something else (what)?
.....
Add more absorption to side walls, back wall and ceiling.
Then add binary diffusion over all this.

EDIT1: when I wrote "add more absorption", I mean "add more ("huge") absorption like you have in front part of side walls near your speakers".

EDIT2: Absorbers that you already have on your walls isn't much effective below 200Hz. "Huge" absorbers that you have near your loudspeakers are fairly effective below 200Hz, as you already noted
Old 2nd September 2011
  #3
Gear Maniac
 

Thanks, boggy! Why are you opposed to Helmholtz devices? I myself am also kind of sceptical about them. I tried to build one some time ago but it didn't work, even though I stuck to the formula somebody gave me. But there seem to be lots of formulas out there...

With broadband absorption, on the other hand, you can't really go wrong. If it doesn't work deep enough just make it thicker!

Also I think I haven't seen a helmholtz resonator in a professional studio. The pros seem to work with broadband absorption and diffusion only.

Is there a calculator software that shows me how thick I need to build absorbers made of mineral wool to be effective down to a certain frequency?

When buying mineral wool, what specs should I pay attention to? Is it rather density (kg/m3) or flow resistivity (kPa x s/m2)?

So you think the absorption at the back wall is not effective enough? The diameter of those absorbers is 60cm.

Edit: hey I just found this: Porous Absorber Calculator Is it any good?
Old 2nd September 2011
  #4
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Jens Eklund's Avatar
Quote:
Originally Posted by bermudaben View Post
Also I think I haven't seen a helmholtz resonator in a professional studio. The pros seem to work with broadband absorption and diffusion only.
You either have not been to many "professional studios" or you are blind. Unless NE-design or similar, porous only absorbers are used sparsely and only where needed (early reflection points) and pressure based , membrane or perforated (array of Helmholtz), are used extensively. Overuse of velocity based absorbers results in a dead room and this is usually not the criteria wanted for critical listening rooms.

All of your other questions has been answered in this forum many times over.
Old 2nd September 2011
  #5
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Glenn Kuras's Avatar
I have to disagree, I worked with thousands of professional studios that do not have any kind of tuned traps. Bob Katz place comes to mind. Agreed tuned trapping can be helpful, but not the end all.

bermudaben,
If you would like to send me a PM I can stir you to some of the real pros to help you, if you want to go that route, with your room.
BTW boggy is one of them.
Old 2nd September 2011
  #6
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Jens Eklund's Avatar
Quote:
Originally Posted by Glenn Kuras View Post
I have to disagree, I worked with thousands of professional studios that do not have any kind of tuned traps.
Perhaps it differs in different parts of the world but in Scandinavia you’ll be hard pressed to find a “professional setting” without any form of pressure based absorber.

LEDE/RFZ is among the most common designs of a control room and you cannot build those rooms without using pressure based absorption.
Old 2nd September 2011
  #7
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Glenn Kuras's Avatar
No it does not differ, have worked with places all over the globe. There are a lot of factors that go into design, so there is no rule.
Old 2nd September 2011
  #8
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Quote:
Originally Posted by Jens Eklund View Post
You either have not been to many "professional studios" or you are blind.
You are right. I haven't had the opportunity to work in many high end studios yet. Apologies for that...

I'm still wondering why boggy advised me against working with tuned absorbers.

Quote:
All of your other questions has been answered in this forum many times over.
This is the nature of forums, to a certain extent. Searching old threads for certain information can be very time consuming. But I'm trying to keep redundant questions at a minimum

The Porous Absorber Calculator tells me that 60cm of rock wool absorption is close to the optimum. So the two corner absorbers should be quite effective.

Anyway, I'm beginning to see the dimensions and cost it will take to make this room sound "professional". I really need to think about whether I'm willing and able to spend this kind of money.
Old 2nd September 2011
  #9
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boggy's Avatar
Quote:
Originally Posted by bermudaben View Post
You are right. I haven't had the opportunity to work in many high end studios yet. Apologies for that...
No need to apologize at all...
Quote:
Originally Posted by bermudaben View Post
I'm still wondering why boggy advised me against working with tuned absorbers.
Because you are DIY amateur, as you already said in some thread, you don't know much about acoustics, and you don't like to learn much more, you have some money that you like to spend to your acoustics treatment, then I trying NOT to spend your money to many non working helmholtz prototypes, because my "clever" theoretical advices. heh
More wideband absorption always working. You have room with decent volume, and you really can treat your room well.
Quote:
Originally Posted by bermudaben View Post
This is the nature of forums, to a certain extent. Searching old threads for certain information can be very time consuming. But I'm trying to keep redundant questions at a minimum
Of course, we all learn something new, every day...
Quote:
Originally Posted by bermudaben View Post
.......
Anyway, I'm beginning to see the dimensions and cost it will take to make this room sound "professional". I really need to think about whether I'm willing and able to spend this kind of money.
Wideband LF absorption is most precious in acoustic treatment, something like basic investment.
Also I'm sure that you already know that all people like non-wild bass in his room, not only professionals.


About tuned absorbers:

Using tuned absorbers at "live end" is already recommanded in AES LEDE paper for small rooms, but there aren't much more details other than formula for frequency, below which this tuned absorber must work:

fc=3*c/a

c is speed of sound
a is smallest room dimension
room should became "transparent" for frequencies below fc

How to have diffuser AND (a serious, tuned) absorber at back wall isn't too much clear from this paper... I expect different solutions from different acousticians (if there isn't some sort of recommended treatment)... I believe also, that this problem is solved in many studios, because I don't know anyone that like wild bass in his room.

Tuned absorbers only works at boundaries of room where sound pressure is high, this means that you must keep your tuned absorbers relatively thin if you like to be near to area of high pressure. This became impossible in small rooms where volume of rooms became comparable with volume of ordinary resonant absorber.

Also in small rooms you cannot keep lowest room modes out of your audible frequency range, and treat only next ones that needs no huge absorbers relative to volume of room.

Helmholtz absorbers with openings instead of membrane, needs to have about 30-50% opened area (relative to surface where we have resonance and high pressure) if we need effective and noticeable influence in room acoustics behavior. Huge box with couple of small holes, can really resonate at low frequencies, but, because this type of resonator works only where sound pressure is big, and only in areas near to holes, effectiveness is directly related to surface size of openings. If this surface is small, Helmholtz absorber won't really work, even if it resonate at correct frequency.

30-50% opened surface also decrease Q factor of Helmholtz absorber, then he became more wideband (good thing IMHO).

So, after your money (first reason), I have some other reasons why I use only wideband type of absorbers, pressure or velocity based... or simple explaination, .... I like that things, I try to design, and people spend money of it, really works something, not only "looks like"...

Glenn, thank you very much!

EDIT: I know that (relatively thin) wideband resonant absorber, that works below 100Hz exist, but it is out of reach for most DIY amateurs, at least for now:

Perforated Panel with Porous Absorber trap

Old 2nd September 2011
  #10
Gear Guru
 
Glenn Kuras's Avatar
boggy,
No problem... We need more level headed people like you to do design. No need to recommend something if it is not going to fit in a persons design/budget/skill level.
Old 2nd September 2011
  #11
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anyone else feel that with such massive traps (eg the stacked rockwool) that he should look at a lower GFR material?
Old 2nd September 2011
  #12
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boggy's Avatar
Quote:
Originally Posted by localhost127 View Post
anyone else feel that with such massive traps (eg the stacked rockwool) that he should look at a lower GFR material?
His material isn't too bad... if we looks for density:
Quote:
Originally Posted by bermudaben View Post
........ They both consist of rock wool with a density of about 35kg/m3. ............
I believe that he has read some older posts.
Old 2nd September 2011
  #13
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Jens Eklund's Avatar
Quote:
Originally Posted by boggy View Post
No need to apologize at all...

Because you are DIY amateur, as you already said in some thread, you don't know much about acoustics, and you don't like to learn much more, you have some money that you like to spend to your acoustics treatment, then I trying NOT to spend your money to many non working helmholtz prototypes, because my "clever" theoretical advices. heh
More wideband absorption always working. You have room with decent volume, and you really can treat your room well.

Of course, we all learn something new, every day...

Wideband LF absorption is most precious in acoustic treatment, something like basic investment.
Also I'm sure that you already know that all people like non-wild bass in his room, not only professionals.


About tuned absorbers:

Using tuned absorbers at "live end" is already recommanded in AES LEDE paper for small rooms, but there aren't much more details other than formula for frequency, below which this tuned absorber must work:

fc=3*c/a

c is speed of sound
a is smallest room dimension
room should became "transparent" for frequencies below fc

How to have diffuser AND (a serious, tuned) absorber at back wall isn't too much clear from this paper... I expect different solutions from different acousticians (if there isn't some sort of recommended treatment)... I believe also, that this problem is solved in many studios, because I don't know anyone that like wild bass in his room.

Tuned absorbers only works at boundaries of room where sound pressure is high, this means that you must keep your tuned absorbers relatively thin if you like to be near to area of high pressure. This became impossible in small rooms where volume of rooms became comparable with volume of ordinary resonant absorber.

Also in small rooms you cannot keep lowest room modes out of your audible frequency range, and treat only next ones that needs no huge absorbers relative to volume of room.

Helmholtz absorbers with openings instead of membrane, needs to have about 30-50% opened area (relative to surface where we have resonance and high pressure) if we need effective and noticeable influence in room acoustics behavior. Huge box with couple of small holes, can really resonate at low frequencies, but, because this type of resonator works only where sound pressure is big, and only in areas near to holes, effectiveness is directly related to surface size of openings. If this surface is small, Helmholtz absorber won't really work, even if it resonate at correct frequency.

30-50% opened surface also decrease Q factor of Helmholtz absorber, then he became more wideband (good thing IMHO).

So, after your money (first reason), I have some other reasons why I use only wideband type of absorbers, pressure or velocity based... or simple explaination, .... I like that things, I try to design, and people spend money of it, really works something, not only "looks like"...

Glenn, thank you very much!

EDIT: I know that (relatively thin) wideband resonant absorber, that works below 100Hz exist, but it is out of reach for most DIY amateurs, at least for now:

Perforated Panel with Porous Absorber trap

There are many things in this post that does not correlate well with what can be sourced from the literature on this topic. For example, an open are of 30% or higher will not introduce any significant Helomholtz effect since the open area is simply to large and the panel will act as a broadband absorber (except for maybe the higher range) and will not absorb bass better than a normal porous only absorber of the same depth. To be utilize the extended bass absorption offered due to resonance, the open area needs to be lower than approx 10%. The pressure distribution of lower order modes does not usually represent any problems since most perforated panels rarely exceeds 250 mm depth so there’s still lots of pressure variation before reaching the maximum particle velocity zone.


EDIT:

From Acoustic Absorbers and Diffusers, theory design and application, SE, page 15:

“Too often, many people place porous absorption in corners of rooms thinking this will absorb sound, since all the modes have a ‘contribution’ in the corners. However, while the modes have a maximum pressure in the corners, the particle velocity is very low and so the absorption is ineffective. For these reasons, resonant absorbers are preferred for treating low frequencies.”
Old 2nd September 2011
  #14
Gear Maniac
 

Quote:
Originally Posted by localhost127 View Post
anyone else feel that with such massive traps (eg the stacked rockwool) that he should look at a lower GFR material?
I am using rock wool with a GFR of 6000 rayls/m for all the bass traps and absorbers.

The guy who I hired to help me with building the studio (I sacked him in the meantime ) said not to place any absorbers on the front wall so that the speakers can be placed directly at the wall in order to avoid the SBIR effect. But I reckon if I cover the wall with 40cm rock wool there won't be much of a SBIR effect because the reflections are largely absorbed? Or is the SBIR effect still something to take into consideration when placing that much absorption behind the speakers?
Old 2nd September 2011
  #15
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boggy's Avatar
Quote:
Originally Posted by bermudaben View Post
I am using rock wool with a GFR of 6000 rayls/m for all the bass traps and absorbers.

The guy who I hired to help me with building the studio (I sacked him in the meantime ) said not to place any absorbers on the front wall so that the speakers can be placed directly at the wall in order to avoid the SBIR effect.
EDIT: Placing speakers near to stiff and dense wall will introduce SBIR issues, not avoid it...
Your speakers are designed to freely stand in an untreated room. If you place it near your wall you will have (over all other problems which untreated room has) low frequency boost that you don't need, your speakers are designed to have a flat frequency response without needs of any stiff and dense wall nearby.
Quote:
Originally Posted by bermudaben View Post
But I reckon if I cover the wall with 40cm rock wool there won't be much of a SBIR effect because the reflections are largely absorbed?
Yes.
Quote:
Originally Posted by bermudaben View Post
Or is the SBIR effect still something to take into consideration when placing that much absorption behind the speakers?
No, you really don't need to take this in consideration, after that much absorption you will have a relatively bigger problems than some SBIR residue.
Old 2nd September 2011
  #16
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Glenn Kuras's Avatar
Quote:
EDIT: Placing speakers near to stiff and dense wall will introduce SBIR issues, not avoid it...
Your speakers are designed to freely stand in an untreated room. If you place it near your wall you will have (over all other problems which untreated room has) low frequency boost that you don't need, your speakers are designed to have a flat frequency response without needs of any stiff and dense wall nearby.
"What is SBIR" Acoustic Panels and Bass Traps.
Old 2nd September 2011
  #17
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Jens Eklund's Avatar
Quote:
Originally Posted by boggy View Post
EDIT: Placing speakers near to stiff and dense wall will introduce SBIR issues, not avoid it...
Unless placed a considerable distance away from the front wall, I would say it’s the complete opposite:
https://www.gearslutz.com/board/6124899-post6.html

and most monitor manufacturers (and most acousticians as well for that matter) would probably agree:
I am not getting enough bass?
Old 2nd September 2011
  #18
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boggy's Avatar
Quote:
Originally Posted by Glenn Kuras View Post
Definitely, a commercially available full range loudspeakers (not subwoofers) didn't designed to be placed near stiff and dense boundaries. SBIR possibly can help sometimes, but this method can be moved to ordinary loudspeaker placement... if someone find this placement is best... why not?

BTW, I never have any satisfying measurement result when loudspeakers are close to the back wall...

Also, I found that bermudaben's acoustician mixed causes and consequences:
Quote:
Originally Posted by bermudaben View Post
.............
The guy who I hired to help me with building the studio (I sacked him in the meantime ) said not to place any absorbers on the front wall so that the speakers can be placed directly at the wall in order to avoid the SBIR effect. ......
(bolded by me)

Or... it is not needed to move loudspeaker near to wall to avoid SBIR issues. Actually, moving loudspeakers near to wall will cause SBIR issues (!).
SBIR issue sometimes can help (as you wrote in your SBIR text), but I personally never had luck with this method...

EDIT: To be sure that we understand each other, I mean SBIR = Speaker Boundary Interface Response = "This is a term to describe how the proximity of a speaker to a hard boundary (wall/ceiling/floor) will change the response, especially in the low end." (this definition I found at GIK Acoustics link, which Glenn provide)
Old 3rd September 2011
  #19
Gear Maniac
 

Quote:
Originally Posted by boggy View Post
Actually, moving loudspeakers near to wall will cause SBIR issues (!).
So you don't agree with the text from the Genelec website?

I think if you have an untreated wall behind the speakers what Genelec say is completely plausible: place the speakers as near to the wall as possible (or at least 2.5 m / 7.2 ft. away from it) to minimise SBIR issues. BUT if you have thick absorption on the front wall it's a completely different story. And in my case, having more absorption and moving the speaker away from the wall a bit will certainly be beneficial, because it will help with the room modes.
Old 3rd September 2011
  #20
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boggy's Avatar
Quote:
Originally Posted by bermudaben View Post
So you don't agree with the text from the Genelec website?
No, I don't agree, because we have more near walls in small rooms that are close to our speaker (side walls, ceiling, floor, back wall), and this situation isn't described.
In Genelec text we have a situation with only one boundary in a theoretical half space, even floor SBIR isn't modelled.

With all our boundaries, we have more SBIR issues that can be only solved with basic loudspeaker placement methods, using measurements (easier) or with listening sessions (much more time consuming). And this is a only one way to find a compromise between all real SBIR issues in a small room, not only one that is idealised and isolated.

EDIT: BTW, I also don't know any commercial loudspeaker manufacturer which tell (publicly) to its customers not to buy loudspeakers from it, without a proper room acoustical treatment, but no one complain because this...

Quote:
Originally Posted by bermudaben View Post
I think if you have an untreated wall behind the speakers what Genelec say is completely plausible:
place the speakers as near to the wall as possible (or at least 2.5 m / 7.2 ft. away from it) to minimise SBIR issues.
As I already wrote, I never had a luck with this, I never had a good overall response when loudspeakers are too close to the wall.
When I do loudspeaker placement in some unpredictable room, I always get a better results when speakers have more distance from the front wall.
We don't really need to debate this, you have a measurement microphone, I see that you are skilled with measurements, so try to move your measurement position (independently) and your speaker from wall(s), to (carefully) find the best (overall) frequency response in this, partially treated room, ... when you find it, build your acoustic treatment over this loudspeaker position.
Quote:
Originally Posted by bermudaben View Post
BUT if you have thick absorption on the front wall it's a completely different story. And in my case, having more absorption and moving the speaker away from the wall a bit will certainly be beneficial, because it will help with the room modes.
SBIR issues, room modes... will be better solved with more absorption in room.
Old 3rd September 2011
  #21
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SörenHjalmarsson's Avatar
 

Quote:
Originally Posted by boggy View Post
Or... it is not needed to move loudspeaker near to wall to avoid SBIR issues. Actually, moving loudspeakers near to wall will cause SBIR issues (!).
SBIR issue sometimes can help (as you wrote in your SBIR text), but I personally never had luck with this method...

EDIT: To be sure that we understand each other, I mean SBIR = Speaker Boundary Interface Response = "This is a term to describe how the proximity of a speaker to a hard boundary (wall/ceiling/floor) will change the response, especially in the low end." (this definition I found at GIK Acoustics link, which Glenn provide)
There seems to be some confusion here, perhaps it is in the terminology... SBIR stands for Speaker Boundary Interference Response, and it describes the predictable 1/4 wavelength, 180 deg phase cancellation, frequency issue that is directly related to the distances between the loudspeakers and nearby room boundaries.

There will be SBIR in bigger rooms aswell, the question is at what frequency and if the interfering wave will have been sufficiently attenuated (due to distance) before reaching the listening position. Moving the speakers closer to a boundary won't "cause the SBIR issues", it will only change the frequency at which it occurs. Moving the speakers closer to a boundary, however, will result in a LF shelving boost (proximity effect) which is easily countered with EQ. This also gives your speakers additional output and lower distortion...

Measuring is good, but we still need to be able to tell the difference between the modal and boundary related issues. If we are to apply a treatment that will sufficiently dissipate a problem frequency, caused by superposition, we first need to know what the problem frequency is - and whats causing it...


MVH
Old 3rd September 2011
  #22
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boggy's Avatar
Quote:
Originally Posted by SörenHjalmarsson View Post
.........
Measuring is fine, but we still need to be able to tell the difference between the modal and boundary related issues.......
Peaks and dips in (measured) frequency response caused only by boundary related issues don't introduce resonances in room, which can be displayed when doing "waterfall" or "burst decay" analysis. I only wish to tell that it's easier and faster to decide where to place loudspeaker and listener only with measurements, and that I haven't good experience with placing loudspeakers close to the front wall.
Old 3rd September 2011
  #23
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SörenHjalmarsson's Avatar
 

I mean... you might treat your front wall with 40cm worth of trapping, only to find that (when the speakers are in their optimum positions) you would have needed 45cm - or that it would have sufficed with 10cm...



MVH
Sören
Old 3rd September 2011
  #24
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boggy's Avatar
Quote:
Originally Posted by SörenHjalmarsson View Post
I mean... you might treat your front wall with 40cm worth of trapping, only to find that (when the speakers are in their optimum positions) you would have needed 45cm - or it would have sufficed with 10cm...



MVH
Sören
If I understand.... Yes, its better to find the best loudspeaker and listener position BEFORE you doing any treatment.
Old 3rd September 2011
  #25
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boggy's Avatar
Quote:
Originally Posted by SörenHjalmarsson View Post
.....Moving the speakers closer to a boundary, however, will result in a LF shelving boost (proximity effect) which is easily countered with EQ. This also gives your speakers additional output and lower distortion...
........
(bolded by me)
Yes, but adding a real equalizer to monitoring chain isn't always easy and practical, and must be decided before doing a treatment of some room.

EDIT: I mean, this cannot be a general advice appropriate to anyone (IMHO)
Old 3rd September 2011
  #26
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SörenHjalmarsson's Avatar
 

Quote:
Originally Posted by boggy View Post
Peaks and dips in (measured) frequency response caused only by boundary related issues don't introduce resonances in room, which can be displayed when doing "waterfall" or "burst decay" analysis.
What i was trying to say was that: You First need to localize the individual problems (as you describe boggy) before applying treatment. You don't cover your front wall with a 'certain amount of treatment' before localizing a specific problem, and determined it's cure, that is in relation to that specific area (wall).

Quote:
No, you really don't need to take this in consideration, after that much absorption you will have a relatively bigger problems than some SBIR residue.
That might be so, but that's a generalization... It all depends on the impedance of the boundary structure, aswell as the boundary/speaker relationship. 40cm might have sufficed, it might have not, or it might have been overkill...

Quote:
Originally Posted by boggy View Post
EDIT: Placing speakers near to stiff and dense wall will introduce SBIR issues, not avoid it...
Your speakers are designed to freely stand in an untreated room. If you place it near your wall you will have (over all other problems which untreated room has) low frequency boost that you don't need, your speakers are designed to have a flat frequency response without needs of any stiff and dense wall nearby.
But we can still take advantage of it, like with flush mounting.


Quote:
Originally Posted by boggy View Post
Definitely, a commercially available full range loudspeakers (not subwoofers) didn't designed to be placed near stiff and dense boundaries. SBIR possibly can help sometimes, but this method can be moved to ordinary loudspeaker placement... if someone find this placement is best... why not?

Or... it is not needed to move loudspeaker near to wall to avoid SBIR issues. Actually, moving loudspeakers near to wall will cause SBIR issues (!).
SBIR issue sometimes can help (as you wrote in your SBIR text), but I personally never had luck with this method...
What i was trying to say earlier was that: SBIR can never help, but we can use the proximity effect to our advantage (like with flush mounting).


MVH
Sören
Old 3rd September 2011
  #27
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SörenHjalmarsson's Avatar
 

Quote:
Originally Posted by boggy View Post
(bolded by me)
Yes, but adding a real equalizer to monitoring chain isn't always easy and practical, and must be decided before doing a treatment of some room.

EDIT: I mean, this cannot be a general advice appropriate to anyone (IMHO)
Here's what i meant:
https://www.gearslutz.com/board/6368308-post31.html
https://www.gearslutz.com/board/6360083-post2.html


MVH
Sören
Old 3rd September 2011
  #28
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boggy's Avatar
Quote:
Originally Posted by SörenHjalmarsson View Post
What i was trying to say was that: You First need to localize the individual problems (as you describe boggy) before applying treatment. You don't cover your front wall with a 'certain amount of treatment' before localizing a specific problem, and determined it's cure, that is in relation to that specific area (wall).
It's not easy for a DIY amateur (our bermudaben is one) to "localize a specific problem" without much knowledge of acoustic science. He knows pretty good how to use a measurement microphone, he already know what is "not that flat" and what is "more flat", so why we need to frustrate him more, with details that he already tell us that he doesn't understand?
https://www.gearslutz.com/board/6976708-post30.html

I see that we have well-educated enthusiasts and professionals on this forum but I think that it's better to lower our discussion level a bit, if (not as well acoustically educated) DIY amateur ask for help. I once tried to explain him that he need to learn more, here:
https://www.gearslutz.com/board/6974319-post19.html

After that I decide not to use any method that he cannot reach...

Quote:
Originally Posted by SörenHjalmarsson View Post
That might be so, but that's a generalization... It all depends on the impedance of the boundary structure, aswell as the boundary/speaker relationship. 40cm might have sufficed, it might have not, or it might have been overkill...
To measure (a true) impedance of boundaries you possibly need an impedance probe which is very expensive.... If bermudaben doesn't have impedance probe, and if he doesn't know what to do with measurement results from acoustic impedance measurement system, then we must find a way how to help him to treat his room without an impedance probe and enough knowledge, but with a decent measurement microphone and with enough knowledge how to do a basic acoustical measurements...
Basic advises for loudspeaker placement that may be found at stickies, is really helpful. Solving SBIR issues or non-issues are integrated in a basic loudspeaker placement methods, and people may find a best response, this means, they find the best compromise for all SBIR issues in room in one process, with single target: finding a most flat frequency response... (without any equalizer)
I don't know what is may be easier than this.
Quote:
Originally Posted by SörenHjalmarsson View Post
But we can still take advantage of it, like with flush mounting.
Yes, of course, but I don't like to tell someone, that he need to buy an extra equalizer after acoustical treatment is started, without agreement before start... and I also believe that there are better methods.

Quote:
Originally Posted by SörenHjalmarsson View Post
What i was trying to say earlier was that: SBIR can never be good, but we can use the proximity effect to our advantage (like with flush mounting).
What I was trying to say is that any commercial loudspeaker manufacturer measure (frequency response flatness of) its speakers in an anechoic room where we don't have ANY boundary (at least we are trying hard not to have it). If we move loudspeaker too close to (a stiff and dense) wall, then we need to use an equalizer, so, we begin to build a custom loudspeaker, not an acoustical treatment. I don't have problem, I can do even this, but it's not trivial to extract only a shelving filter shape in an untreated room from measurements. Same situation is with soffit loudspeaker mount. If soffit mount is built from concrete. you must undo a baffle step compensation shelving filter already included in any commercial speaker, or you will have 6dB louder low-end. And as I already said, I don't have a problem with this, but someone may have a problem... and that is a reason why I write in this way, I try to find an easier and more secure path for bermudaben (with more or less success, of course)

Best regards

Bogic
Old 3rd September 2011
  #29
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SörenHjalmarsson's Avatar
 

boggy,

I'm sensing some agitation here, which leads me to believe that we are misinterpreting each other. Let me try and clearify:

I have not suggested any means, methods or solutions that would be out of our OP's budget or knowledge base. In fact, i have not made any suggestions whatsoever as of yet - i've merely been discussing the theory of some different principles and phenomena...

I saw some confusion regarding SBIR (aswell as the 'proximity effect') and so i tried to clearify...

I also noticed some general advice and so i tried to explain that there are no cookie cutter solutions in acoustics, i can't see the harm in that? The whole point of measuring is to confirm problems and to make the solutions as efficient as possible.

These are all pretty basic and undisputed opinions, i'm not sure where we went wrong... or where our proposed solutions and/or opinions differ exactly?


Sincerely
Sören
Old 3rd September 2011
  #30
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boggy's Avatar
Quote:
Originally Posted by SörenHjalmarsson View Post
boggy,

I'm sensing some agitation here..............
I had no intention for any agitation here, I know that we all trying to help bermudaben, and I don't know what is wrong if we don't have identical opinions.
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