John Sayers' Recording Studio Design Forum Archive

Thank-you Stuart for your reply.

It's been a little while since I've posted an update so here's a big one for you all.

We have a structure up! without boring you all with a boring story it's been up and down but miraculously we have something that resembles a room.

The short of it is, we unknowingly hired cowboys who should never have taken on the job, even though it is an incredibly simple job that still managed to make a mess of it. The structure is not perfectly square, the ridge beam is made up of two beams with a central truss... the truss is off centre.... ridge is like a slightly bent banana. BUT believe it or not it ended up being a million times better than the first TWO attempts... yes. sigh. I could go on.... but I shan't.

So we now have a frame with 18mm OSB on the outside. Just to remind you I am building this studio in stages due to budget and time restraints, and I've started unusually with my inner leaf rather than outer. I will add the outer leaf at a later stage, but having the inner leaf constructed first will allow me to get a lot of my gear that is either in storage or cluttering up our house or my parents house all setup in one place.

Since the inner leaf is temporarily exposed to the outside world, weather proofing is required though eventually will not be needed once it is all covered with the outer leaf, so the roof is just felted for now with a 1' overhang all around. This will eventually be cut off when the outer leaf goes up.

This week I've been weather proofing the OSB walls with a brush on stain solution. Believe it or not OSB is incredibly resilient to moisture in the short term... it's been untreated like this for over 2 months and within that time we've had almost non stop rain and the worst storm to have hit the UK in over 30 years... so bad that everywhere near rivers was flooded and there has just been an insane amount of rain fall as well as 80mph winds. The studio in its naked state has survived it as if nothing happened. Of course I would not recommend leaving it untreated forever but it's nice to know that 1. it didn't blow down and therefore must be strong enough to cope with the weather here and 2. it has not turned into a soggy mess. I was very surprised about this and I was planning to felt or clad it to protect it, but it appears to be bone dry inside and stain should be enough. so for those of you using OSB and are worried about rain, it seems there is no immediate reason to worry too much. The OSB looks as virgin as the day it was installed.

My next job will be to get the temporary doors on and then get the drywall layers up. I am building this inside out so I will beef up the OSB with 2x 15mm drywall layers backer rodded and caulked and held in with cleats in each bay between the studs. The ceiling I will use 'beef up modules' made from frames and inserted in to the bays.

My only questions for now are:

1. despite it appearing dry inside is there a chance that moisture could soak through the OSB from the outside (even with the weatherproofing stain) and then causing the drywall to get damp? This is my main worry as it would be hidden. If there is a chance of this then I will install a damp proof membrane internally on the OSB before putting the drywall layers.

2. if the answer to the above is no, then should I install a vapour barrier for internal moisture? In the UK we rarely do this on our homes, but if we were to do it then it would go on the warm side of the insulation... now as I am building this inside out does that mean it should go over the insulation facing inside the room or behind the insulation between the insulation and the drywall layers?

Any help on this would be great as I do not want to trap moisture by installing either 1 or 2 in the wrong place.

We have a structure up!

Hooray!

believe it or not it ended up being a million times better than the first TWO attempts... yes. sigh. I could go on.... but I shan't.

This sucks, but I feel your pain.

I've started unusually with my inner leaf rather than outer.

Interesting for sure. Fingers crossed that goes okay.

1. despite it appearing dry inside is there a chance that moisture could soak through the OSB from the outside (even with the weatherproofing stain) and then causing the drywall to get damp? This is my main worry as it would be hidden. If there is a chance of this then I will install a damp proof membrane internally on the OSB before putting the drywall layers.

How long do you expect to leave this current structure exposed to the elements?

2. if the answer to the above is no, then should I install a vapour barrier for internal moisture? In the UK we rarely do this on our homes, but if we were to do it then it would go on the warm side of the insulation... now as I am building this inside out does that mean it should go over the insulation facing inside the room or behind the insulation between the insulation and the drywall layers?

Barrier would go inside your room, covering up the insulation.

Greg

Gregwor wrote:

We have a structure up!

Hooray!

believe it or not it ended up being a million times better than the first TWO attempts... yes. sigh. I could go on.... but I shan't.

This sucks, but I feel your pain.

I've started unusually with my inner leaf rather than outer.

Interesting for sure. Fingers crossed that goes okay.

1. despite it appearing dry inside is there a chance that moisture could soak through the OSB from the outside (even with the weatherproofing stain) and then causing the drywall to get damp? This is my main worry as it would be hidden. If there is a chance of this then I will install a damp proof membrane internally on the OSB before putting the drywall layers.

How long do you expect to leave this current structure exposed to the elements?

2. if the answer to the above is no, then should I install a vapour barrier for internal moisture? In the UK we rarely do this on our homes, but if we were to do it then it would go on the warm side of the insulation... now as I am building this inside out does that mean it should go over the insulation facing inside the room or behind the insulation between the insulation and the drywall layers?

Barrier would go inside your room, covering up the insulation.

Greg

Hey Greg! Good to hear from you, thanks so much for your help all the way through my thread so far it means a lot to me. I haven't checked out your build diary since the last time I posted before last, so I am going to check it out in a minute!

I plan to have the stained OSB exposed for around a year or so, that's the plan though as we all know, plans often don't go to plan...
BUT my father has a structure built from stained OSB which has lasted over 10 years now with zero maintenance... the OSB has not swollen or deteriorated in any way, though he does not have any drywall pressed up against it on the inside so cannot be sure it would not be a problem. What are your thoughts?

So barrier goes over the insulation, so in effect it will be the very last thing to go on before the fabric. In that case, could I just wrap my insulation in plastic like John and others have done? Would that be as effective as a vapour barrier?

Now, if I install a damp proof membrane on the OSB inside (before the drywall goes on) and then wrap the plastic/vapour barrier over the insulation, will that risk trapping moisture in and make the drywall damp? Or does it not work like that? I'm really sorry for my noob ness on this issue and beg for your guidance.

Many thanks and happy thanksgiving!

Hey Greg! Good to hear from you, thanks so much for your help all the way through my thread so far it means a lot to me. I haven't checked out your build diary since the last time I posted before last, so I am going to check it out in a minute!

I'm doing my best to help people out where I can!

I haven't updated my thread in a while. I just updated it.

What are your thoughts?

My brother had his subfloor exposed for about a month of heavy rain and it is all swollen and screwed up.

So barrier goes over the insulation, so in effect it will be the very last thing to go on before the fabric.

This is tricky because the warmest side would be your insulation when you're building an inside out inner leaf. However, if I were you, before you build your outer leaf, I would wrap the outside of your inner leaf with barrier. That's where I would put it.

In that case, could I just wrap my insulation in plastic like John and others have done? Would that be as effective as a vapour barrier?

I believe you are referring to what these guys have done in terms of acoustic treatment, not in terms of building code stuff.

Now, if I install a damp proof membrane on the OSB inside (before the drywall goes on) and then wrap the plastic/vapour barrier over the insulation, will that risk trapping moisture in and make the drywall damp? Or does it not work like that? I'm really sorry for my noob ness on this issue and beg for your guidance.

Since you're building your room the opposite of normal, this does pose an issue. You might have to put up a barrier inside (in front of your insulation) for now, and then tear it down once you build your outer leaf.

Greg

Gregwor wrote:

Hey Greg! Good to hear from you, thanks so much for your help all the way through my thread so far it means a lot to me. I haven't checked out your build diary since the last time I posted before last, so I am going to check it out in a minute!

I'm doing my best to help people out where I can!

I haven't updated my thread in a while. I just updated it.

What are your thoughts?

My brother had his subfloor exposed for about a month of heavy rain and it is all swollen and screwed up.

So barrier goes over the insulation, so in effect it will be the very last thing to go on before the fabric.

This is tricky because the warmest side would be your insulation when you're building an inside out inner leaf. However, if I were you, before you build your outer leaf, I would wrap the outside of your inner leaf with barrier. That's where I would put it.

In that case, could I just wrap my insulation in plastic like John and others have done? Would that be as effective as a vapour barrier?

I believe you are referring to what these guys have done in terms of acoustic treatment, not in terms of building code stuff.

Now, if I install a damp proof membrane on the OSB inside (before the drywall goes on) and then wrap the plastic/vapour barrier over the insulation, will that risk trapping moisture in and make the drywall damp? Or does it not work like that? I'm really sorry for my noob ness on this issue and beg for your guidance.

Since you're building your room the opposite of normal, this does pose an issue. You might have to put up a barrier inside (in front of your insulation) for now, and then tear it down once you build your outer leaf.

Greg

Thanks Greg, some good ideas there. While I continue my research on preventing moisture build up I have another question regarding the new concrete slab that will be poured in the new year.

We didn't get a chance to pour the new slab before the frame was constructed for various reasons, but it's not a big deal as it can be poured after and it will shield it from getting rain dimples. So the structure is built on blocks, which are built up on the original slab on grade. All covered with a damp proof membrane and then 100mm celotex rigid insulation is on top of that. This is for thermal purposes.

My question is: Should I line the sides with celotex insulation as well and pour the new slab into the middle or should the new slab connect to the blocks at the edges? I've attached 2 images to illustrate what I mean. If I line the sides then it will reduce thermal bridging, but it may create a flanking path for sound... though the sound will just be met by more concrete, so perhaps it doesn't matter?

Your images illustrate you trying to float a new slab inside your building. You should just leave it as is. Your outer leaf should have it's own decoupled slab poured. Sorry if I'm not properly understanding your idea here. I hope I've made my response clear enough!

Greg

Gregwor wrote:Your images illustrate you trying to float a new slab inside your building. You should just leave it as is. Your outer leaf should have it's own decoupled slab poured. Sorry if I'm not properly understanding your idea here. I hope I've made my response clear enough!

Greg

You’ve understood correctly, and the reason for this is because as I explained earlier in my thread the original slab is very rough, it was never done properly as the building was original just a farm building, it was never insulated and it was not level at all. This new slab is just to have a nice level and smooth floor. I know the ideal is to completely redo the slab but that was not an option.

Yes my outer walls will be built on their own slab and foundation.

So with that in mind I’m wondering whether to pour the slab to the edge or leave a gap so that I can avoid thermal bridging.

Hope that clears things up? Thanks again

So with that in mind I’m wondering whether to pour the slab to the edge or leave a gap so that I can avoid thermal bridging.

Acoustically speaking, I doubt leaving the gap would negatively affect things. I think you should be asking a structural engineer their opinion. Also, realize that you're going to be losing height in your room. Are you sure you don't want to just use some thin leveling compound?

Greg

it was never insulated and it was not level at all.

Does it need to be insulated? I'm not familiar with the climate where you live, but if you don't have a problem with extreme cold such that the ground freezes deep down in winter, then I'm not sure you need to have it insulated. Yes, it should save on energy costs if you do that, but is that a big issue?

This new slab is just to have a nice level and smooth floor.

If that is the MAIN goal, then as Greg said, just get it leveled! A layer of leveling cement correctly applied would do the trick of getting it smooth, flat, and level, at lower cost, and faster. Putting down laminate flooring on to of that, over a suitable thermal and acoustic underlay, would give you an excellent floor.

I know the ideal is to completely redo the slab but that was not an option.

But you ARE completely re-doing the slab! You are pouring a totally new slab with all the same issues involved as in pouring any slab. The only difference is that you are not taking out the old slab first... A few hours with a jack hammer and a few guys with shovels and wheelbarrows would solve that problem. The you could, indeed, insulate properly, and lay a proper slab, without losing ceiling height...

Yes my outer walls will be built on their own slab and foundation.

And where will your INNER walls be built??? I hope you were not intending to build them on the slab as shown in your diagram! You can't just build load-bearing walls on the edge of any old thin floated slab, without having the slab properly designed for that purpose! You need a structural engineer to tell you how thick to make the slab edges such that the can support the load of the entire inner-leaf rooms... where to put the rebar, what type of rebar, how many pieces. how to tie it together, whether or not you need mesh as well, what grade of concrete to use... Designing and pouring a floated structural slab is not something you should attempt on your own: hire a structural engineer.

So with that in mind I’m wondering whether to pour the slab to the edge or leave a gap so that I can avoid thermal bridging.

... and acoustic bridging, too! If you are going to all the complexity and expense of laying a separate structural slab for your inner-leaf, then you might as well make the extra effort to make sure that it is a true isolated, floated slab, to maximize your acoustic isolation.

- Stuart -

Soundman2020 wrote:

it was never insulated and it was not level at all.

Does it need to be insulated? I'm not familiar with the climate where you live, but if you don't have a problem with extreme cold such that the ground freezes deep down in winter, then I'm not sure you need to have it insulated. Yes, it should save on energy costs if you do that, but is that a big issue?

This new slab is just to have a nice level and smooth floor.

If that is the MAIN goal, then as Greg said, just get it leveled! A layer of leveling cement correctly applied would do the trick of getting it smooth, flat, and level, at lower cost, and faster. Putting down laminate flooring on to of that, over a suitable thermal and acoustic underlay, would give you an excellent floor.

I know the ideal is to completely redo the slab but that was not an option.

But you ARE completely re-doing the slab! You are pouring a totally new slab with all the same issues involved as in pouring any slab. The only difference is that you are not taking out the old slab first... A few hours with a jack hammer and a few guys with shovels and wheelbarrows would solve that problem. The you could, indeed, insulate properly, and lay a proper slab, without losing ceiling height...

Yes my outer walls will be built on their own slab and foundation.

And where will your INNER walls be built??? I hope you were not intending to build them on the slab as shown in your diagram! You can't just build load-bearing walls on the edge of any old thin floated slab, without having the slab properly designed for that purpose! You need a structural engineer to tell you how thick to make the slab edges such that the can support the load of the entire inner-leaf rooms... where to put the rebar, what type of rebar, how many pieces. how to tie it together, whether or not you need mesh as well, what grade of concrete to use... Designing and pouring a floated structural slab is not something you should attempt on your own: hire a structural engineer.

So with that in mind I’m wondering whether to pour the slab to the edge or leave a gap so that I can avoid thermal bridging.

... and acoustic bridging, too! If you are going to all the complexity and expense of laying a separate structural slab for your inner-leaf, then you might as well make the extra effort to make sure that it is a true isolated, floated slab, to maximize your acoustic isolation.

- Stuart -

Thank-you Greg and Stuart, really appreciate your replies. Sorry for my rubbish quoting skills in this forum, I haven't quite put the time in to learning how to do it properly yet!

I did think about just screeding the floor, but I decided purely for thermal reasons that I want to insulate as best as I can, and the screed would not work well over the insulation as it would probably crack due to how thin it is. Typically in the UK on new builds you actually have to insulate it to meet code. Plus, we do indeed have very very cold winters here and having first hand experience of walking on un-insulated slabs even in mild weather it has convinced me even more of wanting nice cosy feet. I think it'll be more comfortable for artists that come in as well as a lot of them I have worked with previously love to walk around in just socks or bare feet.

The insulation we use for slabs is called celotex, its a very thick and rigid insulation almost like a spray foam but in slab form. This is for structural purposes more than anything else as it gives a nice flat and stable surface for the concrete to be poured on to. Of course it will compress, but not as much as Rockwool etc. As I say, it is designed for this purpose and is used on all new builds all over the country.

Stuart, I hate to scare you but yes the new INNER walls are built on the pre-existing slab. I had the slab checked over by a friend who is a structural engineer, and it was found fit for purpose. The old slab had a previous timber frame building on it, which was a little smaller. When we took this building down I extended the foundations and existing slab on the side. Around the perimeter I cemented a row of 9" hollow blocks and filled the blocks with a little sand and then concrete. The new structure is bolted to these blocks which sit on the slab.

When I build the outer walls they will be built on their own separate foundation and perimeter slab. This was why I am asking the question about the 'new inner' slab. To gap or not to gap? You answered by saying it would be better to leave a gap to avoid acoustic bridging, but was this answered knowing that my inner walls will not be sitting on this new slab?

BTW, when I designed the control room I already accounted for the new slab and ceiling height, so I am not concerned with that as the height will be correct once the new slab is in place.

Thanks again!

The next step after the new slab goes in will be beefing up the walls and framing out the treatment walls, ceiling, and front wall. I've attached an image of my monitors that I will install in the front wall; they measure 33" wide, 24" high and 14" deep. The two LF drivers are 10". These monitors are incredibly heavy, like trying to lift 4 concrete blocks at once.

Anyway, this got me thinking that not only would it be a good idea to increase the strength of the front wall for obvious reasons but it might also be worth trying to increase the width of the baffles. In my current design, the baffles are 5' wide, which gives only gives 28" baffle extension shared either side of the speaker cabinets.

I was thinking logically that even though it would be impossible to build a truly infinite baffle perhaps the next best thing given the restrictions of the size of my room would be to make the baffles at least as wide as the 1/4 wavelength of the lowest frequency that the speakers can generate. Of course, they will go down to 20hz and perhaps beyond, but they are rated at 38hz - 20khz +-2db, so I'll aim for 38hz. This means the baffles should be about 7.5 feet wide, which is doable with a little tweaking.

My question for you guys is, do you think it's worth it or would my original 5' baffles be more than wide enough? I am aiming for the best that I can achieve, and I know bigger baffles are better, so my gut tells me to go for it, what do you think?

My question for you guys is, do you think it's worth it or would my original 5' baffles be more than wide enough? I am aiming for the best that I can achieve, and I know bigger baffles are better, so my gut tells me to go for it, what do you think?

To answer your question, here is a copy/paste from a post Stuart replied to at one point:

1) The speakers should not go in the corner, nor on the line that divides the corner. In other words, if your walls intersect at 90°, then draw a line out from each corner at 45°, and stay away from that: don't put your speaker exactly on that line, since it implies that you'll be getting the same artifacts from the side walls as from the front wall. Put your speakers either outside or inside of those lines. More commonly you'll want your speakers "inside" those lines (more towards the center line of the room).

2) The "38% of room depth rule" is not a rule, but it is a useful guideline for a starting point. You'll generally want to have your listening position a bit closer to the front wall than that location, but do be aware that you might be getting into problematic SBIR territory there. (You can treat that, to a certain extent).

3) Keep the mix position away from 25% and 50% of room depth, and try to stay between about 32% and 44%

4) You can angle your speakers differently than the "textbook" 30° angle: Anything in the range 25° to about 35° will work well under most circumstances.

5) Keep the speakers as far apart as possible, while not violating rules 1 and 4.

6) Keep the mix position at a good distance from the speakers, within the range of about 1m to about 5m. Further away is usually better.

7) Don't put the speakers at 25% of the room width: that's a modal null for some frequencies, and a peak for others. Try something more like 28% to 34%.

8 ) Make the front baffle of your soffit as wide and tall as you can, within reason. The width should be at least three times the diameter of your low frequency driver. In other words, if you have a speaker with an 8" woofer, then you want the soffit baffle to be at least 24" (60cm) wide. Wider is better.

9) Do not put your speaker in the middle of the soffit baffle: Offset in both directions. In other words, the distances from the acoustic center of the speaker to each edge of the baffle should be very different, by at least 20%. So for example if your speaker axis is 30cm from one side of the baffle, it should be more than 36cm from the other side, less than 24cm from the bottom edge, and more than 44cm from the top edge. (Rough distances, for illustration only...). Larger differences are generally better.

10) Make the baffle as massively heavy as you can, and as rigid as you can.

11) Make the structure inside the soffit (the framing that holds the baffle and speaker in place) as rigid and massive as you can.

12) Mount the speaker inside an enclosure box that is either a very tight fit, in order to keep the speaker rigidly fixed in place, or mount it on suitable rubber pads, to completely decouple it from the the box. Carefully choose the properties and dimensions of that rubber, to make sure the speaker is still decoupled down to at least one octave below the speaker's low cut-off frequency.

13) Take into account that speakers need a lot of space behind them for cooling, and a path through the soffit for cooling air to flow.

14) Rear-ported speakers need special attention: Do not overload the rear port, acoustically, with an enclosure box that is too small, or un-ventilated, or un-damped.

15) Damp the hell out of the soffit interior! Fill it entirely with suitable damping if you want, except for the cooling path.


-------

Here are a few questions for you:
- what brand and model are those speakers?
- what do the dispersion charts look like for them? --> can they be mounted vertically and can that center module be flipped upside down?
- are you SURE you want those speakers? I know Stuart hates the NS10's, but with a sub woofer, I love mine. It might be easier to design around and mount those with a removable baffle allowing you to easily change your speakers out in the future.

Greg

Gregwor wrote:

My question for you guys is, do you think it's worth it or would my original 5' baffles be more than wide enough? I am aiming for the best that I can achieve, and I know bigger baffles are better, so my gut tells me to go for it, what do you think?

To answer your question, here is a copy/paste from a post Stuart replied to at one point:

1) The speakers should not go in the corner, nor on the line that divides the corner. In other words, if your walls intersect at 90°, then draw a line out from each corner at 45°, and stay away from that: don't put your speaker exactly on that line, since it implies that you'll be getting the same artifacts from the side walls as from the front wall. Put your speakers either outside or inside of those lines. More commonly you'll want your speakers "inside" those lines (more towards the center line of the room).

2) The "38% of room depth rule" is not a rule, but it is a useful guideline for a starting point. You'll generally want to have your listening position a bit closer to the front wall than that location, but do be aware that you might be getting into problematic SBIR territory there. (You can treat that, to a certain extent).

3) Keep the mix position away from 25% and 50% of room depth, and try to stay between about 32% and 44%

4) You can angle your speakers differently than the "textbook" 30° angle: Anything in the range 25° to about 35° will work well under most circumstances.

5) Keep the speakers as far apart as possible, while not violating rules 1 and 4.

6) Keep the mix position at a good distance from the speakers, within the range of about 1m to about 5m. Further away is usually better.

7) Don't put the speakers at 25% of the room width: that's a modal null for some frequencies, and a peak for others. Try something more like 28% to 34%.

8 ) Make the front baffle of your soffit as wide and tall as you can, within reason. The width should be at least three times the diameter of your low frequency driver. In other words, if you have a speaker with an 8" woofer, then you want the soffit baffle to be at least 24" (60cm) wide. Wider is better.

9) Do not put your speaker in the middle of the soffit baffle: Offset in both directions. In other words, the distances from the acoustic center of the speaker to each edge of the baffle should be very different, by at least 20%. So for example if your speaker axis is 30cm from one side of the baffle, it should be more than 36cm from the other side, less than 24cm from the bottom edge, and more than 44cm from the top edge. (Rough distances, for illustration only...). Larger differences are generally better.

10) Make the baffle as massively heavy as you can, and as rigid as you can.

11) Make the structure inside the soffit (the framing that holds the baffle and speaker in place) as rigid and massive as you can.

12) Mount the speaker inside an enclosure box that is either a very tight fit, in order to keep the speaker rigidly fixed in place, or mount it on suitable rubber pads, to completely decouple it from the the box. Carefully choose the properties and dimensions of that rubber, to make sure the speaker is still decoupled down to at least one octave below the speaker's low cut-off frequency.

13) Take into account that speakers need a lot of space behind them for cooling, and a path through the soffit for cooling air to flow.

14) Rear-ported speakers need special attention: Do not overload the rear port, acoustically, with an enclosure box that is too small, or un-ventilated, or un-damped.

15) Damp the hell out of the soffit interior! Fill it entirely with suitable damping if you want, except for the cooling path.


-------

Here are a few questions for you:
- what brand and model are those speakers?
- what do the dispersion charts look like for them? --> can they be mounted vertically and can that center module be flipped upside down?
- are you SURE you want those speakers? I know Stuart hates the NS10's, but with a sub woofer, I love mine. It might be easier to design around and mount those with a removable baffle allowing you to easily change your speakers out in the future.

Greg

Hi Greg thanks for your reply.

The speakers are made by Quested, they are custom made and yes I will definitely be using them. For what it's worth, I also enjoy using the NS10Ms! But I will not be flush mounting them instead of the Questeds - The Questeds are incredibly honest, clear and flat within +-2db throughout the frequency range. I don't know if you've ever used ATC100SCMs? I've used them extensively and almost got some instead, they are similar to Quested, but the I prefer the Quested. Yes the HF & MF baffle can be rotated, but only 180 degrees, so these speakers need to be installed horizontally. The dispersion is wide, but I do not have charts, off the top of my head the full dispersion is 120 degrees. They also recommend the ears be 80 - 100cm from the tip of the axis crossing, but I may struggle to manage that unless I compromise my RFZ, so I'm aiming for about 60cm.

I actually used the same quote from Stuart earlier on in this thread and that is the criteria I've been using throughout my design. I originally decided on 60" for the width of my front baffles based on the 3x LF driver guideline based on Stuart's advice, since I have 2 LF drivers per speaker that would be 60" or 5'. However, Stuart also mentioned that on speakers that have 2 LF drivers far apart (such as mine) the width should be greater, if possible. He also mentions in other threads that he prefers to use the total width of the monitor including the cabinet x3 as a guide, so that would mean my baffles should be 8.25' wide. Now, I could manage that if it was essential, it would just make it a little more challenging. While consulting with another studio designer he mentioned I could base the width of my front baffles on the length of the quarter wavelength of the lowest frequency rated for the monitor, so this is why I am now considering front baffles of 7.5' in length. I know that bigger is better, I am just wondering will it be substantially better if I use a 7.5' (or larger) compared with 5' (or smaller) baffle design?

If you look at some rooms designed by John, or Wes, or Tom Hidley you can see that they use baffle designs which are definitely smaller than they should be based on the above criteria. Now, this could be due to room restraints or cost, or other aspects that I don't know about. However, it seems that a lot of them are purposely designed with a smaller baffle, so this leads me to wonder why? These guys all know what they are doing and so they wouldn't have simply overlooked this seemingly vital aspect of the design.

Take Wes for example, he's a perfectionist and yet his baffles are more often than not too narrow based on the above criteria even when the rooms are designed from the ground up. Wes uses very large 30-degree soffit wings which are actually side walls, they extend all the way from the edge of the baffles to beyond the ears in the mix position. This is to create a true RFZ design, and if you ray trace one of his rooms you will see how far back the RFZ extends. Perhaps this is the reason the baffles are narrower so that he can accommodate these long, angled side walls, and perhaps that is more important in the overall sound than a wider baffle would be? Thoughts?

So I am weighing up larger baffles and a smaller RFZ vs smaller RFZ and larger baffles.

Related to this point - are soffit wings considered counting towards the overall width of the baffle extension?

What you are actually battling with here, is the baffle step response issue. The "baffle step" refers to the point in the spectrum where the front baffle of your speaker or soffit stops being large with respect to the wavelength. That's the point where the "power imbalance" starts. Above that frequency, all of the energy is projected forwards, "beaming" out in a cone, while below that frequency the wave "wraps around" behind the speaker as well, in a sphere, so half of the energy goes backwards while the other half goes forward. In other words, above the baffle step, all of the POWER goes forward, while below it, only half of the POWER goes forward while the other half goes backward. Thus, there is a power imbalance of 6 dB: the level going forward drops by 6 dB below the baffle step response frequency.

This is why bi-amped speakers generally have much larger amps on the woofer: to make up for the "lost" 6 dB that doesn't go where the power from the tweeter goes. In simpler active, as well as passive, speakers, there's a cross-over that attenuates the highs by 6 dB, to "correct" the power imbalance, and in both cases the amount of power correction can usually be adjusted by a switch or knob, based on the location of the speaker in the room: seldom is the actual final power imbalance as big as the 6dB theoretical, once you take the room into account.

But the "baffle step" is still there in other ways too! It's not just power imbalance (which can be corrected). There's also the issue of edge diffraction, SBIR and other problems, all of which are related to the dimensions of the speaker cabinet or the soffit. And therefore are also related to the "baffle step response".

Given the "baffle STEP" name, you'd think that if you look at a graph of the speaker response, there's a sudden sharp "step" in the power curve, exactly where the wavelength coincides with the width of the cabinet. But that's far from the truth! In reality, there's a gentle curve that covers the 6 dB range, with the center point of that curve being at the "baffle step" frequency. The range of the curve covers two octaves each way (so four octaves in total). The frequency at the center point of that curve is at 115824/W, where W is the width of the baffle in millimeters (or f=4560/W where the width is in inches). That's the point where it is 3 dB down from the pure "beaming" level, and 3 dB up from the pure "wrap around" behavior.

But that equation only applies to the speaker when it is tested in a true free field! In other words, no room around it, or in an anechoic chamber. the REAL response in a real-world room will never be a perfect "6dB-drop-over-four-octaves" curve, since the room itself affects the response. However, what's important about that equation is that it still does mark the center frequency of the region where all of the baffle-related problems occur! It's not important to know if the power imbalance is 2dB or 6 dB, or 3.78516 dB, or whatever. What's important is WHERE the change takes place, because that also marks the point where all the other problems occur too.

And that brings us to the purpose of the soffit: it isn't magic. All it does is to move that dreaded "baffle step" point down to a lower frequency: Ideally, it would move it off the bottom end of the scale completely, so low that it is totally outside of the audible range. But in reality, you'd need a HUGE room to do that... so big that it would sound bad in numerous other ways, and also be absolutely impractical. Do the math: to get the baffle step response mid point down to 5 Hz (two octaves below 20 Hz, so no part of the curve is in the audible spectrum), you'd need a baffle that is 1140 inches wide! So, each of your baffles would need to be 95 feet wide, plus a decent area between them... implying a room about 250 feet wide, and therefore about 400 feet long, and maybe 300 feet high... just a little large for a typical home studio, perhaps! Doesn't quite fit in the average garage or basement... or 747 hanger, either!

In other words, no matter what we do in room design, it will be a big compromise with respect to theoretical perfection. But it's not as bad as you'd think. Your current speakers are 33" wide, implying a baffle step response of 138 Hz, so the effect extends upwards to 552 Hz and downwards to 34 Hz. If you make your soffit baffles 6 feet wide, then the baffle step point would be at 63 Hz, with the curve rising up to 250 Hz, and falling down to 16 Hz. So it would still be twice as good as it is at present, since it lower the point by more than an octave.

If you did go to 7' 6", then you'd get the mid point at 51 Hz, top end at 202 Hz, bottom point at 13 Hz.

If you go to 8' 3" wide, then you'd have 46 Hz mid point, 184 Hz top, 12 Hz bottom.

But, as I've said before, it's not just the power imbalance that we are interested in! That can easily be adjusted electronically, so it isn't even an issue, really. What matters a lot more, is the other effects: SBIR, edge diffraction, etc. You are ALSO driving those down the spectrum, and in fact eliminating some of them entirely, if you design your baffle correctly.

The reason I recommend 3x speaker width (plus speaker), is because it will drop the baffle step by two octaves! That's all. Plain and simple. It's not a magic number. Nothing esoteric here. For most small speakers, that puts the baffle step end point way below the bottom end anyway, and the mid point far down. If you can only go 2x speaker width, that doesn't mean it wont work! It just means your baffle step only went down a bit more htan one octave which is still pretty good, and very useful.

While consulting with another studio designer he mentioned I could base the width of my front baffles on the length of the quarter wavelength of the lowest frequency rated for the monitor,

Well... that's another approach, a different "rule of thumb", but I prefer to use the actual equation for baffle step response.

If you look at some rooms designed by John, or Wes, or Tom Hidley you can see that they use baffle designs which are definitely smaller than they should be based on the above criteria.

Like I said: there's no way that you could possibly build a truly complete baffle that pushes the entire curve off the low end, so anything that anyone does is compromise! It really is that simple.

Now, this could be due to room restraints or cost, or other aspects that I don't know about.

Right! Studio design is nothing more than juggling an never-ending series of compromises, to compromise the compromises with the other compromises, and arrive at the best compromise of compromises, ... hopefully.

However, it seems that a lot of them are purposely designed with a smaller baffle, so this leads me to wonder why?

See above: it is impossible to make it "big enough", ever, no matter what you do, so make it as big as practical, then do other things to the room to reduce the effects of the "imperfect compromises".

and yet his baffles are more often than not too narrow based on the above criteria

Not really! you missed out on the key point here...

uses very large 30-degree soffit wings which are actually side walls, they extend all the way from the edge of the baffles to beyond the ears in the mix position.

Bingo! There you have your answer.... Those wings ARE the baffle! They extend the baffle. There's no law that says the baffle has to be flat forever, out to infinity...

This is to create a true RFZ design,

Partly, yes, but they are ALSO integral to the soffits... and therefore are part of the baffle. Measure those TOGETHER WITH the actual "baffle", then do the above calculations, to see why those rooms sound so good. I do the exact same thing in all of my rooms: Take a look at the corner control room thread, and you'll see that, in reality, the soffits extend all the way to the rear walls! The sliding glass doors on each side of his room are part of the baffle too!... it's not just the actual baffle that you see around the speaker itself. That's a small room, so I used every trick in the book to force the response to where I wanted it. If you check that thread soon, over the next few days, we'll be posting the final REW graphs, showing the end outcome after everything we did, and I'll challenge you to find any trace of the baffle step response, or SBIR, or edge difraction on those graphs!

Perhaps this is the reason the baffles are narrower so that he can accommodate these long, angled side walls,

That's part of it, sort of, but the baffles are not really "narrower" at all, when you consider that the wings ARE the baffle as well...

Make the actual speaker baffle as big as it can be, reasonably, then AT THE SAME TIME shape the RFZ with the wings to be as big as it can be.... the resolve the conflict that these two approaches will create, by blending the soffit into the wings, even if that means reducing the apparent width of the "baffle" itself.

But do be careful with all this: you are also creating an inverse wave-guide shape like that, so you need to take care with that too...

And don't forget vertical: your ceiling is also part of this whole deal, and so is your cloud... assuming it is hard-backed....


(I seem to be giving away all my secrets today... it must be Christmas or something! )



- Stuart -

Soundman2020 wrote:What you are actually battling with here, is the baffle step response issue. The "baffle step" refers to the point in the spectrum where the front baffle of your speaker or soffit stops being large with respect to the wavelength. That's the point where the "power imbalance" starts. Above that frequency, all of the energy is projected forwards, "beaming" out in a cone, while below that frequency the wave "wraps around" behind the speaker as well, in a sphere, so half of the energy goes backwards while the other half goes forward. In other words, above the baffle step, all of the POWER goes forward, while below it, only half of the POWER goes forward while the other half goes backward. Thus, there is a power imbalance of 6 dB: the level going forward drops by 6 dB below the baffle step response frequency.

This is why bi-amped speakers generally have much larger amps on the woofer: to make up for the "lost" 6 dB that doesn't go where the power from the tweeter goes. In simpler active, as well as passive, speakers, there's a cross-over that attenuates the highs by 6 dB, to "correct" the power imbalance, and in both cases the amount of power correction can usually be adjusted by a switch or knob, based on the location of the speaker in the room: seldom is the actual final power imbalance as big as the 6dB theoretical, once you take the room into account.

But the "baffle step" is still there in other ways too! It's not just power imbalance (which can be corrected). There's also the issue of edge diffraction, SBIR and other problems, all of which are related to the dimensions of the speaker cabinet or the soffit. And therefore are also related to the "baffle step response".

Given the "baffle STEP" name, you'd think that if you look at a graph of the speaker response, there's a sudden sharp "step" in the power curve, exactly where the wavelength coincides with the width of the cabinet. But that's far from the truth! In reality, there's a gentle curve that covers the 6 dB range, with the center point of that curve being at the "baffle step" frequency. The range of the curve covers two octaves each way (so four octaves in total). The frequency at the center point of that curve is at 115824/W, where W is the width of the baffle in millimeters (or f=4560/W where the width is in inches). That's the point where it is 3 dB down from the pure "beaming" level, and 3 dB up from the pure "wrap around" behavior.

But that equation only applies to the speaker when it is tested in a true free field! In other words, no room around it, or in an anechoic chamber. the REAL response in a real-world room will never be a perfect "6dB-drop-over-four-octaves" curve, since the room itself affects the response. However, what's important about that equation is that it still does mark the center frequency of the region where all of the baffle-related problems occur! It's not important to know if the power imbalance is 2dB or 6 dB, or 3.78516 dB, or whatever. What's important is WHERE the change takes place, because that also marks the point where all the other problems occur too.

And that brings us to the purpose of the soffit: it isn't magic. All it does is to move that dreaded "baffle step" point down to a lower frequency: Ideally, it would move it off the bottom end of the scale completely, so low that it is totally outside of the audible range. But in reality, you'd need a HUGE room to do that... so big that it would sound bad in numerous other ways, and also be absolutely impractical. Do the math: to get the baffle step response mid point down to 5 Hz (two octaves below 20 Hz, so no part of the curve is in the audible spectrum), you'd need a baffle that is 1140 inches wide! So, each of your baffles would need to be 95 feet wide, plus a decent area between them... implying a room about 250 feet wide, and therefore about 400 feet long, and maybe 300 feet high... just a little large for a typical home studio, perhaps! Doesn't quite fit in the average garage or basement... or 747 hanger, either!

In other words, no matter what we do in room design, it will be a big compromise with respect to theoretical perfection. But it's not as bad as you'd think. Your current speakers are 33" wide, implying a baffle step response of 138 Hz, so the effect extends upwards to 552 Hz and downwards to 34 Hz. If you make your soffit baffles 6 feet wide, then the baffle step point would be at 63 Hz, with the curve rising up to 250 Hz, and falling down to 16 Hz. So it would still be twice as good as it is at present, since it lower the point by more than an octave.

If you did go to 7' 6", then you'd get the mid point at 51 Hz, top end at 202 Hz, bottom point at 13 Hz.

If you go to 8' 3" wide, then you'd have 46 Hz mid point, 184 Hz top, 12 Hz bottom.

But, as I've said before, it's not just the power imbalance that we are interested in! That can easily be adjusted electronically, so it isn't even an issue, really. What matters a lot more, is the other effects: SBIR, edge diffraction, etc. You are ALSO driving those down the spectrum, and in fact eliminating some of them entirely, if you design your baffle correctly.

The reason I recommend 3x speaker width (plus speaker), is because it will drop the baffle step by two octaves! That's all. Plain and simple. It's not a magic number. Nothing esoteric here. For most small speakers, that puts the baffle step end point way below the bottom end anyway, and the mid point far down. If you can only go 2x speaker width, that doesn't mean it wont work! It just means your baffle step only went down a bit more htan one octave which is still pretty good, and very useful.

While consulting with another studio designer he mentioned I could base the width of my front baffles on the length of the quarter wavelength of the lowest frequency rated for the monitor,

Well... that's another approach, a different "rule of thumb", but I prefer to use the actual equation for baffle step response.

If you look at some rooms designed by John, or Wes, or Tom Hidley you can see that they use baffle designs which are definitely smaller than they should be based on the above criteria.

Like I said: there's no way that you could possibly build a truly complete baffle that pushes the entire curve off the low end, so anything that anyone does is compromise! It really is that simple.

Now, this could be due to room restraints or cost, or other aspects that I don't know about.

Right! Studio design is nothing more than juggling an never-ending series of compromises, to compromise the compromises with the other compromises, and arrive at the best compromise of compromises, ... hopefully.

However, it seems that a lot of them are purposely designed with a smaller baffle, so this leads me to wonder why?

See above: it is impossible to make it "big enough", ever, no matter what you do, so make it as big as practical, then do other things to the room to reduce the effects of the "imperfect compromises".

and yet his baffles are more often than not too narrow based on the above criteria

Not really! you missed out on the key point here...

uses very large 30-degree soffit wings which are actually side walls, they extend all the way from the edge of the baffles to beyond the ears in the mix position.

Bingo! There you have your answer.... Those wings ARE the baffle! They extend the baffle. There's no law that says the baffle has to be flat forever, out to infinity...

This is to create a true RFZ design,

Partly, yes, but they are ALSO integral to the soffits... and therefore are part of the baffle. Measure those TOGETHER WITH the actual "baffle", then do the above calculations, to see why those rooms sound so good. I do the exact same thing in all of my rooms: Take a look at the corner control room thread, and you'll see that, in reality, the soffits extend all the way to the rear walls! The sliding glass doors on each side of his room are part of the baffle too!... it's not just the actual baffle that you see around the speaker itself. That's a small room, so I used every trick in the book to force the response to where I wanted it. If you check that thread soon, over the next few days, we'll be posting the final REW graphs, showing the end outcome after everything we did, and I'll challenge you to find any trace of the baffle step response, or SBIR, or edge difraction on those graphs!

Perhaps this is the reason the baffles are narrower so that he can accommodate these long, angled side walls,

That's part of it, sort of, but the baffles are not really "narrower" at all, when you consider that the wings ARE the baffle as well...

Make the actual speaker baffle as big as it can be, reasonably, then AT THE SAME TIME shape the RFZ with the wings to be as big as it can be.... the resolve the conflict that these two approaches will create, by blending the soffit into the wings, even if that means reducing the apparent width of the "baffle" itself.

But do be careful with all this: you are also creating an inverse wave-guide shape like that, so you need to take care with that too...

And don't forget vertical: your ceiling is also part of this whole deal, and so is your cloud... assuming it is hard-backed....


(I seem to be giving away all my secrets today... it must be Christmas or something! )



- Stuart -

Wow, that's what I call an answer to a question! Thank-you for my early Christmas present Stuart, very generous of you

I now know not only the 'how' but also the 'why' behind determining the widths of baffles, which is something I had found...well, baffling... for a while.

If you don't mind, I am in need of a couple of clarifications...

- In regards to the soffit wings also being part of the baffle, surely the middle section between the two 'actual baffles' would also be considered part of the baffle? So, really half of the middle section, the part around the speaker itself plus the wing would all make up one 'infinite' baffle per speaker? In that case, the baffle could end up being very wide indeed, thus lowering that baffle step considerably.

I must ask then, at what point does a baffle stop being a baffle and simply a side wall? What I mean is, if there's nothing to say a baffle must be continuously flat forever then surely a side wall should be considered part of the baffle?...if it were hard and rigid...but then I suppose that may cause unwanted reflections depending on the angle of those side walls.

- Regarding offsetting the speaker in the baffle by at least 5/8 or 2/5 or 20% I am assuming this applies only to the 'actual' baffle around the speaker itself? Otherwise, surely the soffit wing would induce this offset automatically?

Now, assuming it does only apply to the 'actual' baffle, is there a preferred wider and narrower side or is it not important? For example, should the speaker be offset closer to the soffit wing, or closer to the middle section? I see most of the time the speaker is closer to the middle section as opposed to the soffit wing, is there a reason for this? The only reason I can think of is if a wider and longer spread is wanted then the speaker should be closer to the soffit wing, and vice versa, but is there a more important reason for doing so that I am not aware of?

- Lastly, I think it's important to mention that my monitors are actually tri-amped. I have an active crossover unit and 3 power amps, the HF and MF drivers have their own channels and the LF drivers share a channel per monitor. So that will help to balance the power once I figure out how to set it properly.

Paul