Studio build in Wales, UK...again!

[Paulus87]

I'm considering something along these lines. I'm looking at maintaining as much energy as possible though, so I might leave them solid. I have the option to drill holes afterwards if needed. But they're not very useful locations for helmholtz/membrane traps anyway being in the center of the room. I could treat certain modes slightly if needed, but probably not the most efficient treatment location.

Dan

You could argue that it is the most important area to have sufficient treatment due to it being directly over your mix position, it's also presumably the shortest dimension? And the centres of boundaries are high pressure areas. It will definitely deflect first order reflections in the range of interest though, which is good.

Paul

[Waka]

You could argue that it is the most important area to have sufficient treatment due to it being directly over your mix position, it's also presumably the shortest dimension? And the centres of boundaries are high pressure areas. It will definitely deflect first order reflections in the range of interest though, which is good.

It is the shortest dimension yes. They are high pressure areas, but mainly only for the floor ceiling axials, my (0, 0, 1) is 69Hz or so. I'm not going to be able to fit a pressure based device deep enough over the mix position to treat this, even (0, 0, 3) would need a deep trap centered on 207Hz to be useful .

My aim for the middle of the ceiling is to avoid all pressure based devices and to reflect the first reflections to the rear and fill behind the reflecting panels with additional absorption.
The side walls will have a combination of polys/angled panels and pressure based devices. The rear wall will be mainly absorption with hangers. (I'm considering a diffuser in the center, but we'll have to see.)

Dan

[Paulus87]

You could argue that it is the most important area to have sufficient treatment due to it being directly over your mix position, it's also presumably the shortest dimension? And the centres of boundaries are high pressure areas. It will definitely deflect first order reflections in the range of interest though, which is good.

It is the shortest dimension yes. They are high pressure areas, but mainly only for the floor ceiling axials, my (0, 0, 1) is 69Hz or so. I'm not going to be able to fit a pressure based device deep enough over the mix position to treat this, even (0, 0, 3) would need a deep trap centered on 207Hz to be useful .

My aim for the middle of the ceiling is to avoid all pressure based devices and to reflect the first reflections to the rear and fill behind the reflecting panels with additional absorption.
The side walls will have a combination of polys/angled panels and pressure based devices. The rear wall will be mainly absorption with hangers. (I'm considering a diffuser in the center, but we'll have to see.)

Dan

It sounds like a good plan, it's all trial and error. Just a thought - the reflective panels that you are going to put up there will have a membrane effect, whether wanted or not, especially if you seal them. 69hz should not be too difficult to target in a shallow amount of space (albeit fiddly to tune) with the correct density/materials (roughly 100mm cavity and 5kg/m2 will get you there) so you just might be able to achieve both if you needed to.

Paul

[Waka]

the reflective panels that you are going to put up there will have a membrane effect, whether wanted or not, especially if you seal them.

Indeed. I don't plan to seal them up there, I'll be leaving the sides open and stuffing behind them.

69hz should not be too difficult to target in a shallow amount of space (albeit fiddly to tune) with the correct density/materials (roughly 100mm cavity and 5kg/m2 will get you there) so you just might be able to achieve both if you needed to.

That's true, but I also want to reflect quite a lot of the frequency spectrum, so I'll be using thick mdf/ply nearer to 15kg/m2. Which calculation are you using for your estimate above? Panel absorbers are so difficult to target the right frequency, that I don't think I can get the correct high Q device I need to treat the mode.

Especially considering an angled panel seems to completely change the theory and the calculators just seem to take an average depth and guess.

I'm leaning towards a BAD panel design to scatter the reflected waves a bit too. To try and reduce the specularity in the room.

It's all good fun!

Btw sorry for the thread hijack!

Dan

[Paulus87]

the reflective panels that you are going to put up there will have a membrane effect, whether wanted or not, especially if you seal them.

Indeed. I don't plan to seal them up there, I'll be leaving the sides open and stuffing behind them.

69hz should not be too difficult to target in a shallow amount of space (albeit fiddly to tune) with the correct density/materials (roughly 100mm cavity and 5kg/m2 will get you there) so you just might be able to achieve both if you needed to.

That's true, but I also want to reflect quite a lot of the frequency spectrum, so I'll be using thick mdf/ply nearer to 15kg/m2. Which calculation are you using for your estimate above? Panel absorbers are so difficult to target the right frequency, that I don't think I can get the correct high Q device I need to treat the mode.

Especially considering an angled panel seems to completely change the theory and the calculators just seem to take an average depth and guess.

I'm leaning towards a BAD panel design to scatter the reflected waves a bit too. To try and reduce the specularity in the room.

It's all good fun!

Btw sorry for the thread hijack!

Dan

It's all good Dan, this is all relevant to my build anyway so it all helps.

This is an interesting read:
https://www.acousticsciences.com/art-no ... bass-traps

It gives the formulas for both limp and more rigid panels.

Also the multi-layer absorber calculator online is pretty accurate according to Jens on Gearslutz, so that is a quick and handy way to design some panels.

I think they definitely seem easier in theory than in practice to design, but I don't think that should put you off. It seems people struggle to get good results from membranes when they DIY because they either build them too small and too few or they are trying to treat an issue that doesn't exist, and therefore make things worse by introducing large objects in to their space changing the modal behaviour.

BAD panels seem like a great way to go, I was thinking of building some for my reflective angled side panels too. Lots of drilling but pretty straight forward. So I'll either use BAD panels, or slats I can't decide yet.

I am getting quite ambitious but I think I would like to install 3 windows on each side as well, this would enable me to see into the iso booths, corridor and the outside. So the glass panels would follow the same angles as set out in my design, but I wouldn't be able to have absorption directly behind the glass for obvious reasons, but I could still have absorption below and above the glass. The glass would have a slight membrane effect despite not being sealed, but there would be no resonance in the cavity behind since the cavity would be open on the sides with absorption above and below. Each of these windows would have to have another window in the actual walls themselves, so that I could still see through the walls without compromising isolation.

Something a bit like this:

3D1 copy.jpg

What do you think?

Paul

[Waka]

This is an interesting read:
https://www.acousticsciences.com/art-no ... bass-traps

It gives the formulas for both limp and more rigid panels.

That was an excellent read! Thanks.

Also the multi-layer absorber calculator online is pretty accurate according to Jens on Gearslutz, so that is a quick and handy way to design some panels.

Yes I use that tool a lot but mainly for porous absorption calcs.

I think they definitely seem easier in theory than in practice to design, but I don't think that should put you off. It seems people struggle to get good results from membranes when they DIY because they either build them too small and too few or they are trying to treat an issue that doesn't exist, and therefore make things worse by introducing large objects in to their space changing the modal behaviour.

I think the most difficult thing to get right about membrane traps is making them high q at the right frequency! I love them for low frequency lower q abosorption, I'll use the BBC's A10 style membrane traps if necessary. Really you need them to be tune-able in place after taking measurements to get them to hit the right frequencies if highly targeted frequencies are required.
I haven't seen many good suggestions for tuning these device after the fact.

Helmholtz slot resonators are easily tune-able by varying pipe length and fabric resistance in place, so I'm more inclined to those for targeted treatments.

BAD panels seem like a great way to go, I was thinking of building some for my reflective angled side panels too. Lots of drilling but pretty straight forward. So I'll either use BAD panels, or slats I can't decide yet.

I am getting quite ambitious but I think I would like to install 3 windows on each side as well, this would enable me to see into the iso booths, corridor and the outside. So the glass panels would follow the same angles as set out in my design, but I wouldn't be able to have absorption directly behind the glass for obvious reasons, but I could still have absorption below and above the glass. The glass would have a slight membrane effect despite not being sealed, but there would be no resonance in the cavity behind since the cavity would be open on the sides with absorption above and below. Each of these windows would have to have another window in the actual walls themselves, so that I could still see through the walls without compromising isolation.

This design looks awesome! I'm not sure how you plan on constructing these, but would be cool if you can work it out. You might want to design the window modules completely in sketchup first though, to foresee any construction issues. You will have to carefully calculate your glass thickness though.

Dan

[Paulus87]

This is where I'm currently at with my room:

108350614_3102809309836965_377198965538052384_n.jpg

109825258_3102809339836962_3243782301072022394_n.jpg

110024554_3102809416503621_8163528095635583537_n.jpg

I setup the mains just for fun more than anything, but I also wanted to hear how it was sounding so far with this first stage of treatment and run some quick and dirty measurements. So far, sounding excellent and the measurements are not showing any terrible problems so I am quite pleased. I'll post some measurements when I run the tests properly.

(The white rolls of Dacron in the corners are not going to stay there, I just used them as some little bass traps while waiting to be used for fabric frames)

I am going to go ahead and construct my rear wall treatment. I'm going to have 2' of hangers along the wall then splaying out in the corners. I'll also continue the soffits above this treatment which will connect the two side wall soffits, but the rear soffit will be 4' thick instead of 2'. The top of the rear wall framing will connect to the soffit above it.

RearWallDimensions.png

I've attached a plan and a 3D image of the rear wall framing for you to have a look at; the uprights are roughly 4' apart and doubled. The reason for this is it will provide larger open area for the waves to hit the hangers without posts in the way every 2', but also when I build the fabric frames to cover it all I can install 2 frames next to each other and have enough wood behind them so that they are both supported properly.

RearWallFraming3D.png

I may or may not put a slatted poly diffsorber on the front of each corner, I've left enough room for this should I decide to go ahead with it. I also am not sure whether or not I want to install a diffuser on this wall, but it's something that I can add later fairly easily by removing the fabric frames and adding a bit of framing to support it.

Regarding my fabric frames, I am planning on using 2x1 timbers to make the frames and then stretching the fabric over. I may put a Dacron layer over the frame before the fabric, or I may put the Dacron on the structural framing first - I'm not sure yet. I am also debating whether or not to place 1" Rockwool inside each fabric frame to provide a little extra absorption but to also provide a slightly more substantial surface for the walls, which is the reason for the flat horizontal members added to the main framing - it will provide back support to the Rockwool and prevent people pushing through the fabric. I can add some sturdy wire mesh over the entire front face of the framing, and then put the fabric frames filled with the thin Rockwool and it should be quite solid - hopefully. Thoughts?

Paul

[Paulus87]

Hi guys,

This is going to be a long post, but hopefully many of you will find the following information very interesting and useful.

While contemplating my room and going through different options for my design I started tallying up the pros and cons for such things as hard flush vs soft flush and different finishing options for the surface treatments.

I wanted to explore the option of a fully hard flush, and get into the details. I needed to find the answer to these questions:
1. Should a hard flush be fully sealed in order to function as intended?
2. Is there any benefit to putting bass trapping behind a hard flush if it is fully sealed?
3. If it is not fully sealed, does the area behind the baffle benefit from LF absorption?
4. How do openings for rack units/ventilation in the front baffle affect the performance of the baffle?
5. If the front baffle should be a continuous and smooth extension of the loudspeaker baffles then why is irregular stone often used on the face of the baffle? And how does such a surface produce edge diffraction effects?
6. If I decide on a hard flush then how should I treat the transition between the front baffle and my dual pitched ceiling?

After searching and reading every book on acoustics, loudspeaker design I could get my hands on as well as looking on every thread here and else where on many different forums online, I still could not find the answers. I had many discussions with a lot of intelligent people all telling me different things.

So I decided to ask Philip Newell a couple of very specific questions and I sent him an e-mail:

"Hi Philip,

I am a big fan of your work and have two of your books, which I am reading over and over.

I have a question regarding your use of stone for the front monitor wall in your control rooms, for which I haven’t been able to find an answer in your books.

From what I have read in your book, suitable baffle extensions should be smooth. So, why your choice of irregular stone for such a task? I understand that the irregularities found in the stone are far too shallow to diffuse much below very high frequency, and do not effect low frequency as it appears flat to those waves, but could the stone not cause other problems such as edge diffraction etc at mid and high frequencies?

I have implemented many of your techniques into my own control room including large waveguide absorbers at the rear and on the ceiling; I have monitors with HF and MF soft dome drivers. Would a stone monitor wall be suitable for such monitors?

One other question; does the monitor wall need to be completely sealed air tight from top to bottom and side to side or can there be openings in the wall and the cavity behind the monitor wall be filled with more LF absorption?

Many thanks for your time,
Paul"

To my delight, he replied the next day:

"Hi Paul,

I am glad you find the books useful.

The stone front-wall cannot cause edge diffraction because, above about 300 Hz, the output from the loudspeakers is beginning to radiate forwards into less than 180º. The frequencies that are susceptible to diffraction from that degree of irregularity never come into contact with the stone. In any case, there are no actual corners around which the sound waves can turn 90º, so they don't actually diffract in any way that could send an opposite-phase interference-wave back to the source.

So, yes, a stone front wall is suitable for any type of loudspeaker. Domes will not radiate sideways above about 300 Hz.

The benefit of the irregularity of the stone is to help give more diffuse reflexions to the sounds made within the room, such as of people speaking.

Sometimes we have ventilation openings in the front walls, for example, but not so large that they would allow low frequencies to enter. You really don't want any frequency-selective absorption on the front wall because it needs to give equal 'push' to all frequencies. Anyhow, we usually do hang some absorbent material in the spaces behind the walls, to deter any significant resonances inside them.

If I still haven't completely answered your questions, then by all means let me know.


Best wishes, Philip"


His reply answered my specific questions perfectly. Since he had been so accommodating I thought I'd ask him about some more details:

"Thank you Philip, you answered the questions perfectly. I have to say you are one of very few well known acousticians who has actually taken the time to respond in detail to me, so I very much appreciate that.

My control room has an open beam cathedral ceiling, in to which I have hung large wave guide absorbers much like you describe in your book. Of course, since the ceiling is pitched the hangers are directly under the peak of the ceiling. Underneath the hangers will be a false ceiling covered in fabric stretched over frames.

Now I need to decide how to handle the transition between the front wall baffle and the ceiling. In my original plan I was thinking of building the front wall framing up to the heigh of the eaves (around 2.7m) and leaving the top of the framing open to the hangers above it. This would be a discontinuity in the baffle, which I am not sure is desirable?

I could continue the baffle all the way up to connect to the cathedral ceiling, if this would result in a better low end response. My feelings are the space behind the front wall baffle could be used for extra bass trapping, as well as expanding the internal room volume, which will hopefully result in a better modal response.

Or if the rear wall, and ceiling are both heavily trapped, do you find it unnecessary to implement more low frequency trapping at the front?

I have attached a few diagrams, one with questions to help illustrate my point. I hope, if you do not mind, you could help me with my dilemma.

Many thanks again,
Paul"

With this attachment:

Questions.png

This was his reply:

"Hi Paul,

Regarding the questions on your drawing, first, I would continue the wall straight up, almost to the ceiling, but leave a ventilation gap if you are going to mount rack gear in the wall. Second, I would also continue the front wall to the side walls. Third, the openings for rac gear are OK as long as they are almost full and the equipment doesn't rattle with the bass from the loudspeakers.

So no, I don't think you will need additional LF absorption at the front. The front wall just needs to be as solid, rigid and non-resonant as possible.


Best wishes, Philip"

Fantastic. Now I know exactly how to proceed with a hard flush in my room if I decide to go that route. To illustrate how it would look I have drawn this up in SU so I can see the transition between the baffle and ceiling:

Screenshot 2020-08-07 at 11.32.55.png

The main point I got from this, and I'm putting it into my own words, is: providing there is sufficient trapping elsewhere in the room then there is no need to have extra trapping at the front behind the baffle, and since this baffle should be sealed up as well as possible no sound will actually get in behind there anyway, in fact the main benefit of the heavy front baffle is to project all sound forward, particularly low frequency, and by allowing the low frequency to get in behind the baffle defeats the purpose.

In an ideal world, the front baffle wall is really just another isolation wall, like all the other walls that make up the control room. Often on this forum people are building partial baffles, which for sure will help, but I feel there has been no distinction made between a true, infinite baffle and a partial baffle, they are often treated as the same thing. This has led to much confusion, at least for me.

The front corners actually still can have bass trapping, and should have bass trapping there, but the front corners are no longer the corners behind the speakers, they are at the junction between the front baffle and the side walls. That is where bass trapping can be installed. In fact, the whole wall behind the speakers is no longer part of the room, the new front baffle extension has moved in front of the speakers, and that is the new boundary of the room.

Of course, with a partial baffle/flush the above is not relevant. But I am still trying to work out why one who wants to go the hard flush route would build a partial baffle instead of a proper, fully sealed front wall. It is almost the same amount of effort.

Now, after having said all of this, I still believe there are some advantages of a soft flush over a completely hard flush. Mainly being:
- Helps to reduces SBIR from near fields, which a hard flush does not.
- Can take up less floor space
- Easier to modify/Less commitment
- Easier to build/cheaper
- Retains maximum room volume
- Still has a lot of the benefits of a hard flush

There's three main disadvantages as far as I can see, those being:
- Doesn't necessarily completely eliminate SBIR since one cannot easily build a large enough trap around the monitors in order to absorb all low frequencies.
- No LF boost
- Baffle step frequency is no longer lowered

So am I any closer to making a decision regarding hard/soft flush? No, not really! But I am wiser, I now understand what each option entails.

I think, I may at first go with a soft flush approach, with slats but design it in such a way that I could easily convert it to a fully fledged hard flush if I feel it's not enough. The slats would be just for the operator, to provide self noise cues and would not interact with the direct sound from the speakers, so the periodicity is not an issue and as we have learnt from Philip Newell the HF and MF drivers do not radiate 180 degrees and so edge diffraction from the slats won't be a problem, especially since the slats will not be close to those drivers. This is the approach John Brandt uses.

Screenshot 2020-08-07 at 11.33.51.png

Please let me know if you have any thoughts or anything to add to this knowledge, it's all greatly appreciated and massively useful.

Paul

[Waka]

What an awesome post Paul, thanks!

Good thinking in reaching out to Phillip Newell! He sounds like a really nice guy, he responded quickly to a question from a reader of his books without being condescending or short.

I have a few thoughts about his answers and would love your opinion. I really respect Newell and these aren't in any way intended to detract from the info he gave.

The stone front-wall cannot cause edge diffraction because, above about 300 Hz, the output from the loudspeakers is beginning to radiate forwards into less than 180º. The frequencies that are susceptible to diffraction from that degree of irregularity never come into contact with the stone. In any case, there are no actual corners around which the sound waves can turn 90º, so they don't actually diffract in any way that could send an opposite-phase interference-wave back to the source.

This information is exactly what I was thinking! Good to have it confirmed. Stuart was always very picky about front wall baffles being completely smooth. I trusted that it would be safer just in case, but had a sneaky feeling it would matter very little in the end.

Although, I'm not sure I'm completely clear on his point about edge diffraction though:

The frequencies that are susceptible to diffraction from that degree of irregularity never come into contact with the stone.

A first reflection would not need to radiate 180º (or 90º off-axis)from a speaker to interact with the front wall. For example in my own room, the angled baffle extensions around the other speaker would interact with any sound that was 40º - 70º off axis. I appreciate that the baffle surrounding the speaker wouldn't diffract any sound from that speaker, but with the angles involved, the other speaker's baffle could interact with it, no?

Having said that, I doubt an irregular stone surface would cause any destructive early reflections of any appreciable energy anyway though, the majority of the energy would still be directed into the room behind you.

I find this statement a little contradictory also:

Sometimes we have ventilation openings in the front walls, for example, but not so large that they would allow low frequencies to enter. You really don't want any frequency-selective absorption on the front wall because it needs to give equal 'push' to all frequencies.

If the energy above 300Hz does not ever come into contact with the stone, how can it give equal "push" to all frequencies? A hard flush mounted front wall logically can only add "push" to low frequencies. The angled baffle extensions over first reflection points, would (as I understand) also affect the mids and some higher frequencies.

Maybe he was talking about adding equal "push" to all relevant frequencies (aka. low end). I can understand if he meant putting a membrane or helmholtz absorber in the front wall centered on a room mode, for example 65Hz, might negatively affect the ability to "push" frequencies in that region. But then I have to ask, isn't that desirable? The room is adding too much energy to that mode anyway? I want "pull" not "push"

His points about the baffle continuing across the whole front wall make sense. If you're going full infinite baffle, you might as well go all the way.
Although he mentioned that you could:

leave a ventilation gap if you are going to mount rack gear in the wall.

This highlights that the key is not to have it sealed, only that it is massive. Is a timber framed structure even suitable in Newell's eyes? Were you planning on hanging stone cladding on the baffle or something?

Also if a ventilation gap at the top is needed and acceptable for your active rack gear, wouldn't you also require a lower ventilation port for the "chimney" to function?

The main point I got from this, and I'm putting it into my own words, is: providing there is sufficient trapping elsewhere in the room then there is no need to have extra trapping at the front behind the baffle

I took the same point from what he was saying. I think in your case, you have enough ceiling height and rear wall depth to implement the trapping required for this to work. I think in a smaller room, especially one with a low ceiling, you would struggle to get the the necessary trapping without utilising the space behind the speakers.

My studio's ceiling height is just 2.51m and the bottom of my inside out ceiling is 2.31m, So I have 200mm to play with, and maybe a little more along the wall/ceiling corners. I think I would be severely limited without my two front corner helmholtz resonators and fully-filled speaker baffles having ports to open it to the room.

The front corners actually still can have bass trapping, and should have bass trapping there, but the front corners are no longer the corners behind the speakers, they are at the junction between the front baffle and the side walls. That is where bass trapping can be installed. In fact, the whole wall behind the speakers is no longer part of the room, the new front baffle extension has moved in front of the speakers, and that is the new boundary of the room.

This is a good point. Although for room modes to terminate at this point instead of behind the speakers it would truly have to be a massive baffle, with a construction as rigid and solid as the room walls themselves.
By pushing the front wall corners in front of the speakers you still do limit the bass trapping here to a degree though. In order to preserve the energy and direct it behind your head to your diffuser etc. instead of absorbing it you have to maintain the baffle's hard surface. If you fill where the baffle extension meets the side walls with a super chunk for example, it's going to cover a lot of the hard surface and work counter to the design goal of preserving energy at first reflection points.

Of course, with a partial baffle/flush the above is not relevant. But I am still trying to work out why one who wants to go the hard flush route would build a partial baffle instead of a proper, fully sealed front wall. It is almost the same amount of effort.

I've explained a little bit about my reasons above. I believe that a full sized hard front wall flush mount (I'm still not convinced sealing it is necessary for it to function in the same way), is excellent for improved low end response, and will be better at this than a "partial" hard flush mount, but I also feel that it's not the best solution for small rooms. I think the sacrifice of the room volume and usable absorption in the front corners is too high a price.
My current opinion is this:
A hard faced partial flush-mount has 90% (made up number) of the benefits of a full flush-mount (assuming the same construction methods/materials used), but has less energy preserved in the very low end. When floor space is at a premium and ceiling height is limited, the front wall is simply too valuable to spend almost entirely on added bass boost.

Now, after having said all of this, I still believe there are some advantages of a soft flush over a completely hard flush. Mainly being:
- Helps to reduces SBIR from near fields, which a hard flush does not.

What do you mean here? As in additional monitors on the desk/stands aside from your mains?

A soft front wall could absorb energy radiating out of the back of the near-fields, but it won't eliminate it completely if you're desk is less than 3m or so from the front wall anyway.
Have you considered ray tracing the near field SBIR to see how a massive baffle behind might redirect that energy anyway? Maybe the angles will negate this problem. If we're talking about frequencies so low as to be pretty much omnidirectional and are not really directed by your baffle angles, then can you even absorb them sufficiently? And will the reflected energy be significant enough to be destructive?

Thanks again for passing on the your conversation with Phillip Newell and your thoughts Paul, it's really appreciated! I've bookmarked the info. i'm looking forward to more of your build progress!

Dan

[Paulus87]

What an awesome post Paul, thanks!

Good thinking in reaching out to Phillip Newell! He sounds like a really nice guy, he responded quickly to a question from a reader of his books without being condescending or short.

I have a few thoughts about his answers and would love your opinion. I really respect Newell and these aren't in any way intended to detract from the info he gave.

The stone front-wall cannot cause edge diffraction because, above about 300 Hz, the output from the loudspeakers is beginning to radiate forwards into less than 180º. The frequencies that are susceptible to diffraction from that degree of irregularity never come into contact with the stone. In any case, there are no actual corners around which the sound waves can turn 90º, so they don't actually diffract in any way that could send an opposite-phase interference-wave back to the source.

This information is exactly what I was thinking! Good to have it confirmed. Stuart was always very picky about front wall baffles being completely smooth. I trusted that it would be safer just in case, but had a sneaky feeling it would matter very little in the end.

Although, I'm not sure I'm completely clear on his point about edge diffraction though:

The frequencies that are susceptible to diffraction from that degree of irregularity never come into contact with the stone.

A first reflection would not need to radiate 180º (or 90º off-axis)from a speaker to interact with the front wall. For example in my own room, the angled baffle extensions around the other speaker would interact with any sound that was 40º - 70º off axis. I appreciate that the baffle surrounding the speaker wouldn't diffract any sound from that speaker, but with the angles involved, the other speaker's baffle could interact with it, no?

Having said that, I doubt an irregular stone surface would cause any destructive early reflections of any appreciable energy anyway though, the majority of the energy would still be directed into the room behind you.

I find this statement a little contradictory also:

Sometimes we have ventilation openings in the front walls, for example, but not so large that they would allow low frequencies to enter. You really don't want any frequency-selective absorption on the front wall because it needs to give equal 'push' to all frequencies.

If the energy above 300Hz does not ever come into contact with the stone, how can it give equal "push" to all frequencies? A hard flush mounted front wall logically can only add "push" to low frequencies. The angled baffle extensions over first reflection points, would (as I understand) also affect the mids and some higher frequencies.

Maybe he was talking about adding equal "push" to all relevant frequencies (aka. low end). I can understand if he meant putting a membrane or helmholtz absorber in the front wall centered on a room mode, for example 65Hz, might negatively affect the ability to "push" frequencies in that region. But then I have to ask, isn't that desirable? The room is adding too much energy to that mode anyway? I want "pull" not "push"

His points about the baffle continuing across the whole front wall make sense. If you're going full infinite baffle, you might as well go all the way.
Although he mentioned that you could:

leave a ventilation gap if you are going to mount rack gear in the wall.

This highlights that the key is not to have it sealed, only that it is massive. Is a timber framed structure even suitable in Newell's eyes? Were you planning on hanging stone cladding on the baffle or something?

Also if a ventilation gap at the top is needed and acceptable for your active rack gear, wouldn't you also require a lower ventilation port for the "chimney" to function?

The main point I got from this, and I'm putting it into my own words, is: providing there is sufficient trapping elsewhere in the room then there is no need to have extra trapping at the front behind the baffle

I took the same point from what he was saying. I think in your case, you have enough ceiling height and rear wall depth to implement the trapping required for this to work. I think in a smaller room, especially one with a low ceiling, you would struggle to get the the necessary trapping without utilising the space behind the speakers.

My studio's ceiling height is just 2.51m and the bottom of my inside out ceiling is 2.31m, So I have 200mm to play with, and maybe a little more along the wall/ceiling corners. I think I would be severely limited without my two front corner helmholtz resonators and fully-filled speaker baffles having ports to open it to the room.

The front corners actually still can have bass trapping, and should have bass trapping there, but the front corners are no longer the corners behind the speakers, they are at the junction between the front baffle and the side walls. That is where bass trapping can be installed. In fact, the whole wall behind the speakers is no longer part of the room, the new front baffle extension has moved in front of the speakers, and that is the new boundary of the room.

This is a good point. Although for room modes to terminate at this point instead of behind the speakers it would truly have to be a massive baffle, with a construction as rigid and solid as the room walls themselves.
By pushing the front wall corners in front of the speakers you still do limit the bass trapping here to a degree though. In order to preserve the energy and direct it behind your head to your diffuser etc. instead of absorbing it you have to maintain the baffle's hard surface. If you fill where the baffle extension meets the side walls with a super chunk for example, it's going to cover a lot of the hard surface and work counter to the design goal of preserving energy at first reflection points.

Of course, with a partial baffle/flush the above is not relevant. But I am still trying to work out why one who wants to go the hard flush route would build a partial baffle instead of a proper, fully sealed front wall. It is almost the same amount of effort.

I've explained a little bit about my reasons above. I believe that a full sized hard front wall flush mount (I'm still not convinced sealing it is necessary for it to function in the same way), is excellent for improved low end response, and will be better at this than a "partial" hard flush mount, but I also feel that it's not the best solution for small rooms. I think the sacrifice of the room volume and usable absorption in the front corners is too high a price.
My current opinion is this:
A hard faced partial flush-mount has 90% (made up number) of the benefits of a full flush-mount (assuming the same construction methods/materials used), but has less energy preserved in the very low end. When floor space is at a premium and ceiling height is limited, the front wall is simply too valuable to spend almost entirely on added bass boost.

Now, after having said all of this, I still believe there are some advantages of a soft flush over a completely hard flush. Mainly being:
- Helps to reduces SBIR from near fields, which a hard flush does not.

What do you mean here? As in additional monitors on the desk/stands aside from your mains?

A soft front wall could absorb energy radiating out of the back of the near-fields, but it won't eliminate it completely if you're desk is less than 3m or so from the front wall anyway.
Have you considered ray tracing the near field SBIR to see how a massive baffle behind might redirect that energy anyway? Maybe the angles will negate this problem. If we're talking about frequencies so low as to be pretty much omnidirectional and are not really directed by your baffle angles, then can you even absorb them sufficiently? And will the reflected energy be significant enough to be destructive?

Thanks again for passing on the your conversation with Phillip Newell and your thoughts Paul, it's really appreciated! I've bookmarked the info. i'm looking forward to more of your build progress!

Dan

You're welcome Dan, I thought it'd be good to share and I'm glad you found it useful.

Regarding the ventilation gaps - he stated that those were only needed if mounting rack gear in the baffle. In other words, ideally it would be sealed all the way to the ceiling.

Here's my thoughts about it being sealed or not: We're talking about ideals here, in a perfect world...The reasons for it being sealed to the ceiling, floor and side walls is because those surfaces also extend the baffle. In effect, all of the boundaries in the room are the baffle! That's why the front baffle should be massive, and the same mass as all the other walls because that baffle becomes your new front wall. To have an optimum baffle of great mass, all the other walls should match it. The baffle should achieve the at least same TL as all the other inner walls/ceiling/floor, unless we start talking about invisible alpha...

If it cannot be sealed completely then you do the best you can, and ANY baffle extension is better than none.

Philip more often than not uses timber frames front baffles. The framing is sturdy, boarded with several layers of plasterboard, chipboard and dead sheet (bitumen) in between each one. There's usually 4-6 layers of boards, with the dead sheet between. If I was going to go this hard flush route then I would do something very similar and yes, clad it with synthetic rock. This is also what Philip does quite often.

Hidley was famous for using poured concrete front baffles, which is ideal, but of course much more complicated and a lot more effort.


Regarding your other thoughts: We're comparing a non environment concept with a RFZ concept. NE does not have baffle wings and there is no need for first order reflections to be deflected behind the listener to a diffuser for return. The energy hits the side walls, ceiling, rear wall and never comes out again, it's obliterated to oblivion by the wave guide absorbers and the membranes behind. Interestingly, these membranes are usually the inner actual walls themselves, tuned to target whatever LF required by the room. Again, invisible alpha. In fact Newell refers to these inner walls as "acoustic control walls".

In my room I am not going full NE, as I think I would find it too dead. I am taking elements from NE & Jensen and combining them to come up with something a little unusual, but not unique.

I completely agree with your points regarding smaller rooms; they need all the help they can get and utilising that space behind the front wall is definitely a brilliant way of doing that.

To your last point regarding near fields; "A soft front wall could absorb energy radiating out of the back of the near-fields, but it won't eliminate it completely if you're desk is less than 3m or so from the front wall anyway. " I'm not sure I follow here. If the desk is 3m or so away then any returning reflections from the front wall to the listening position are already likely to be down -20dB and after 20ms, and not likely to cause comb filtering so no need for absorption unless you are trying to fulfil a higher standard than that.

Near fields typically do not go below 50hz, which can easily be absorbed by deep trapping around the main monitors.

Paul

[Paulus87]

What do you mean here? As in additional monitors on the desk/stands aside from your mains?

A soft front wall could absorb energy radiating out of the back of the near-fields, but it won't eliminate it completely if you're desk is less than 3m or so from the front wall anyway.

Dan

Dan, I re-read this and realised I had misread you the first time.... for some reason I missed the word less and now it makes sense.

But, I am still unclear as to why the absorption won't eliminate it (providing it is sufficiently deep). Would you mind expanding on this point as it would be a good learning opportunity for me?

Paul

[Waka]

Hi Paul,

Regarding your other thoughts: We're comparing a non environment concept with a RFZ concept. NE does not have baffle wings and there is no need for first order reflections to be deflected behind the listener to a diffuser for return. The energy hits the side walls, ceiling, rear wall and never comes out again, it's obliterated to oblivion by the wave guide absorbers and the membranes behind. Interestingly, these membranes are usually the inner actual walls themselves, tuned to target whatever LF required by the room. Again, invisible alpha. In fact Newell refers to these inner walls as "acoustic control walls".

In my room I am not going full NE, as I think I would find it too dead. I am taking elements from NE & Jensen and combining them to come up with something a little unusual, but not unique.

You're right, I saw the angles on your front wall and thought of RFZ.
In this case I understand completely what he means. Newell is the NE room man, so I should have clicked!

I agree with you about not being comfortable with NE rooms. After adding my rear wall treatment to my own room, I consider the rear wall too dead. It's very peaceful in there, but I also find it a little stifling. I love the clarity, but the rear wall feels like a bottomless pit . But of course, each to their own!

I'm warming to the idea of letting some diffused reflections arrive (obviously very difficult and not possible completely in a small room) after a 20ms ITDG, so I'm aiming to bump up the energy of these later reflections without destructive interference, to add some spaciousness in the room. In my most recent measurements I have a nice ETC curve, (minus a floor bounce and sadly some ceiling reflections) but there is no real termination of the ITDG. After the direct sound it immediately drops to -20dBFS and then steadily declines from there never returning. At 20ms I'm at -25dBFS, but I would like that to be above -15dBFS, if I can get it. Only time will tell!

I'm really excited about the results of your side wall treatments, they look to be an optimum solution for a control room.

Dan, I re-read this and realised I had misread you the first time.... for some reason I missed the word less and now it makes sense.

But, I am still unclear as to why the absorption won't eliminate it (providing it is sufficiently deep). Would you mind expanding on this point as it would be a good learning opportunity for me?

I was simply highlighting the front wall SBIR, that I'm sure you're already aware of. I think the key here is it has to be "sufficiently deep". If your near-fields are 2m from the front wall for example you will get a cancellation at roughly 43Hz. You would need very thick absorption to negate the deep null this causes. How deep were you planning in your "soft" flush mount?

Dan

[Paulus87]

I'm really excited about the results of your side wall treatments, they look to be an optimum solution for a control room.

Well, they look like they're going to achieve what I hope to achieve, but who knows... I am wondering how the width of each panel will affect which frequencies are reflected and which will be ignored, and what will happen to the ignored ones... at lower frequencies the panel will appear like a flat wall, frequencies whose wavelengths are longer than the panels are wide will go around them into the absorption I suppose, will the absorption be enough to effectively attenuate them etc etc, these are all thoughts I have but haven't taken the time to work out. The good thing about them is they're easy to take down and replace with something else if they have any strange effects, but I do hope they work.

I was simply highlighting the front wall SBIR, that I'm sure you're already aware of. I think the key here is it has to be "sufficiently deep". If your near-fields are 2m from the front wall for example you will get a cancellation at roughly 43Hz. You would need very thick absorption to negate the deep null this causes. How deep were you planning in your "soft" flush mount?

Yeah it's a good point, all dependant on type of near field and distance etc.

Since my near fields are a pair of NS10M they don't go much lower than 50hz. The treatment surrounding the mains will be up to 4' at its thickest and 1' at its shallowest. With an average depth of 2.5' it should have an absorption coefficient of at least 0.6@50hz, but more likely a lot more since it'll be wave guide absorbers (hangers) with their increased surface area and redirection effects.

Also, the near fields could have their backs pushed up against the soft flush wall, which I am pretty confident would completely negate the problem, although they may get in the way of the mains. I think it would be cool to have them on motorised stands which can be raised and lowered on demand.

SBIR and LBIR are interesting, the more I try to understand it the more complicated it gets. SBIR seems to be irrespective of listening position, and obviously LBIR is effected directly by SBIR, and it is the sum of both of these effects that dictates the destructive and constructive interference. Although I understand it to a degree, and the principles behind it, I am yet to find an easy to understand article on the effect.

Paul

[Paulus87]

Any one have any insight into how a particular sound reacts to objects smaller/larger than its wavelength?

I assume, in simple terms, (and, ruling out any absorption by the object) sound reflects off of an object which is larger than its wavelength, and if the wavelength is longer than the objects dimensions it diffracts around it?

So then, how effective are my side wall panel reflectors - if they're roughly 2' wide then they will only reflect sound waves of 560hz and above, everything else will diffract around it. And then, how does the splay angle affect things? How about the height?

This is something that I think is overlooked due to how complicated it is. I could only find these threads on GS regarding this:

https://www.gearslutz.com/board/studio- ... p-pls.html (post no.34 onwards)

https://www.gearslutz.com/board/studio- ... ption.html (Sorry, it's 4 pages long but a very interesting read)

Anyone have any definitive info on this?

Paul

[Waka]

Any one have any insight into how a particular sound reacts to objects smaller/larger than its wavelength?

MHOA chapter 7 is a great source of info about this (Do you have the book?)

I assume, in simple terms, (and, ruling out any absorption by the object) sound reflects off of an object which is larger than its wavelength, and if the wavelength is longer than the objects dimensions it diffracts around it?

Kind of, but it's not a simple cut off point. MHOA uses the term "acoustically small" or "large". If the object is smaller than the wavelength virtually all of the sound will be diffracted and wrap around, very little will reflect. But as you get larger than the wavelength, less and less diffracts until it's almost perfect reflection.

So then, how effective are my side wall panel reflectors - if they're roughly 2' wide then they will only reflect sound waves of 560hz and above, everything else will diffract around it. And then, how does the splay angle affect things? How about the height?

This is something that I think is overlooked due to how complicated it is.

When the reflector is not perpendicular to the wavefront things would get complicated!

If your reflectors have only one free edge (attached to ceiling floor, and wall) then that's the only edge sound can diffract around. That's seems like a good thing though because this edge will diffract the sound into the absorption, that's a key feature of waveguides.

Height behaves exactly the same as width, if the height is acoustically small, then the sound will wrap right over it, or if it's acoustically large, then less will diffract over the top edge.

Remember that lower frequencies reflect over a wide dispersion area anyway, until almost completely omni-directional at very low frequencies. So attempting to reflect them in certain directions does not seem useful. Specular reflections at higher frequencies are the destructive ones that you need to watch out for.

With your current design your reflectors will work at mid-high to high frequencies and the lower frequencies will diffract around act similarly to a flat surface.

Looking at your rear wall design I see you plan to put a diffuser in, could the effectiveness of this be reduced by you having reflectors all pointing to the rear on your side walls? Much of the diffuse energy will reflect from the diffuser to a side reflector, across the room to the other side wall reflector and back to the rear wall again. Will these reflections reach the mix position?

Maybe ray tracing some reflections from the diffuser will shed light on this.

Dan