Splaying Walls and Ceilings

[davecfraser]

Hey,

Long Time Reader, first time poster. I'm a professional singer / songwriter and I record my own stuff for independent self-release

I'm building a small basement room that will function as my live room AND listening room. I know this is LESS than ideal, but this is my space constraint.

My first priority is making a decent sounding live room, I can always have stuff mixed elsewhere, or just learn to compensate for a less than ideal room.

It is currently walled in on 3 sides (one interior wall and 2 exterior walls) and I will be building a 4th wall (interior) and installing a door.

The dimensions of the room are 11'6" wide and 7' 5" high.

My plan is to gut the ceiling, put in Roxul RHT-40 3" insulation between the floor joists, and hang the ceiling with genie clips and then 5/8" drywall and another layer of 5/8" drywall attached with Green Glue. I'm hoping this will soundproof this from the room above decently well.

I will also do the same thing for the interior wall, and leave the 2 exterior walls alone.

Building the 4th wall straight across the width would make the room 15' long, BUT I could also angle this and make one end longer than 15' and get a splayed angle. I understand this would help reduce flutter echo, but will make modes more complex and impossible to calculate? People have said building this 4th wall at an angle won't give a positive benefit with such a small room, is this true?

Would splaying the ceiling (like having it go up to a peak which is offset from the floor by 8-10 degrees help?

The Acoustigard people also told me modes wouldn't be an issue due to the green glue, which doesn't make sense to me.

I plan on constructing the wall the same way as the ceiling, stuffed with Roxul RHT-40 3"

I've constructed 15 bass traps that work awesome out of 4" Roxul RHT-40 and some fabricland fabric and small wood frames. I am willing to add more.

I want to know if splaying the walls and possibly ceiling will have any positive effect and if so, why or why not?

THANKS!

[Rod Gervais]

Originally Posted by davecfraser

My plan is to gut the ceiling, put in Roxul RHT-40 3" insulation between the floor joists, and hang the ceiling with genie clips and then 5/8" drywall and another layer of 5/8" drywall attached with Green Glue. I'm hoping this will soundproof this from the room above decently well. I will also do the same thing for the interior wall, and leave the 2 exterior walls alone.

First (and foremost) unless you don't really like your head - you do not want to fasten drywall to drywall with green glue. It must be mechanically fastened - which means screws (my preference over drywall nails).

The same goes for walls.

Next, without seeing some details I have no way of knowing to what extent this might help you......... I would also point out that "decently well" is a relative term - nothing that anyone here can quantify.

Building the 4th wall straight across the width would make the room 15' long, BUT I could also angle this and make one end longer than 15' and get a splayed angle. I understand this would help reduce flutter echo, but will make modes more complex and impossible to calculate? People have said building this 4th wall at an angle won't give a positive benefit with such a small room, is this true?

I don't know which people you refer to, but I can see 2 benefits right off the bat..... the first you mentioned - dealing with potential for flutter echo in at least one direction........ the 2nd is added room volume.

Both of which are always beneficial.

Next - Splayed walls do not make modes more complex..... nor impossible to calculate - they only make the calculations more complex.

However - you have a very small space to begin with - this is what you have to work with, I would opt for the greatest amount of volume possible.

In addition - this is a tracking room - not a control room - asymmetrical spaces are a benefit in tracking spaces...

That having been said - with your (restricted) height and width - if you could push that 15' dimension out to 15'-7 3/4" you would be in better shape acoustically.

Would splaying the ceiling (like having it go up to a peak which is offset from the floor by 8-10 degrees help?

Absolutely not - you have no real ceiling height to begin with - lowering it is not going to benefit you any way shape or manner......

The Acoustigard people also told me modes wouldn't be an issue due to the green glue, which doesn't make sense to me.

Which is good because it would not make sense to anyone in their right mind.

Not only will it not solve modal issues - it will add to them - this because any increase in isolation adds to modal issues. If all of the sound escaped from the room there would be no modes.
Rod

[avare]

Rod said it all. +1.

Andre

[Glenn Kuras]

The Acoustigard people also told me modes wouldn't be an issue due to the green glue, which doesn't make sense to me

I have to ask. Did they say why it would not be a problem? Totally wrong as Rod pointed out..

[davecfraser]

Originally Posted by Rod Gervais

First (and foremost) unless you don't really like your head - you do not want to fasten drywall to drywall with green glue. It must be mechanically fastened - which means screws (my preference over drywall nails).

Sorry thought that was implied, what I meant to say was "attached with drywall-to-drywall screws and screwed in with a phillips screwdriver bit and electric drill in a clockwise motion with green glue in between"

Originally Posted by Rod Gervais

Next, without seeing some details I have no way of knowing to what extent this might help you.........

What details do you need?

Originally Posted by Rod Gervais

I would also point out that "decently well" is a relative term - nothing that anyone here can quantify.

Ok, I'd like to be able to have someone play drums in this room and not hear anything in other rooms but perhaps the kick drum, and to have that diminished by 80%
I'd like to be able to yell and bang on an acoustic guitar and have it silent for the folks in the rest of the house.

Originally Posted by Rod Gervais

I don't know which people you refer to, but I can see 2 benefits right off the bat..... the first you mentioned - dealing with potential for flutter echo in at least one direction........ the 2nd is added room volume.

Both of which are always beneficial.

Ok so build a splayed wall for the wall i have to build anyways.

Originally Posted by Rod Gervais

Next - Splayed walls do not make modes more complex..... nor impossible to calculate - they only make the calculations more complex.

A pair of parallel walls have one fundamental mode, correct?

Does it reason that each cross section of the walls has a different mode? (IE the section where the gap is closest has a mode, the section where the gap is largest has a different mode (lower frequency), and all sections in between have modes in between, in other words there are an infinite number of modes between the two ends (and between the two frequencies correspding to those two ends' modes_?

Originally Posted by Rod Gervais

However - you have a very small space to begin with - this is what you have to work with, I would opt for the greatest amount of volume possible.

In addition - this is a tracking room - not a control room - asymmetrical spaces are a benefit in tracking spaces...

Why are asymmetrical rooms a benefit in tracking spaces? No flutter echo?

Originally Posted by Rod Gervais

That having been said - with your (restricted) height and width - if you could push that 15' dimension out to 15'-7 3/4" you would be in better shape acoustically.

Absolutely not - you have no real ceiling height to begin with - lowering it is not going to benefit you any way shape or manner......

Thanks, I'll take your advice on this.


I do appreciate your input, I just want to fully understand the WHY of what I'm doing.

[Rod Gervais]

Originally Posted by davecfraser

Sorry thought that was implied, what I meant to say was "attached with drywall screws and screwed in with a phillips screwdriver bit and electric drill in a clockwise motion with green glue in between"

You would be amazed at the number of people who intend on doing exactly what I cautioned about...... I've learned (over the years) that nothing should be assumed...... especially here (meaning the Internet)

What details do you need?

Building sections, floor plans - large scale details indicating how you plan on assembling the structure while maintaining isolation. With isolated construction "the devil is in the details"

Ok, I'd like to be able to have someone play drums in this room and not hear anything in other rooms but perhaps the kick drum, and to have that diminished by 80% - I'd like to be able to yell and bang on an acoustic guitar and have it silent for the folks in the rest of the house.

Well, you will not achieve that using the construction methods you describe - in order to reach that level of isolation you really need to build a complete "room within the room" - as well as adding some mass to the floor above.

This is no small task.

Ok so build a splayed wall for the wall i have to build anyways.

You can if you wish - although I did not say you should - I simply explained that what you heard was incorrect....... if you opt for the most room volume then the wall would have to be parallel.

A pair of parallel walls have one fundamental mode, correct?

Does it reason that each cross section of the walls has a different mode? (IE the section where the gap is closest has a mode, the section where the gap is largest has a different mode (lower frequency), and all sections in between have modes in between, in other words there are an infinite number of modes between the two ends (and between the two frequencies corresponding to those two ends' modes?)

In the strictest of terms - an asymmetrical room would do a heck of a lot more than just deal with flutter echo - it would also remove axial modes...... although you would not tend to appreciate this in a small room..... especially a small room with 2 pairs of surfaces which are still parallel.

There would (indeed) still be modal activity, and there would be (as you surmise) an increase in the number of modes involved..... however the level of the modes would be lessened - and thus easier to treat......

When it comes to low frequencies it is not as if you would have to treat them individually. With the exception of tuned traps - when you treat for one you treat for all.

Achieving this, however, is not (necessarily) as easy as it might seem on the surface. It is not just having asymmetrical surfaces - it is having them in the right geometric combinations....

Why are asymmetrical rooms a benefit in tracking spaces? No flutter echo?

In critical listening spaces you're looking for acoustical symmetry.. you design for a (relatively) small listening space in order to create a stereophonic mix. The sound source and the listening positions are "fixed" positions within the space.

In a tracking room the sound source could be anywhere - the listening position could be anywhere - in both the sense of ears and microphones.....

Also - sounds can be produced from an (almost) infinite number of sources combinations of those sources - different tunings of those sources, etc., etc., etc.

While it is (relatively) easy to deal with early reflections in a control room - where you have a fairly small area you're concerned with - and speakers that never move - doing that in a tracking room is much more challenging.

A well thought out and designed asymmetrical tracking room, coupled with absorption/diffusion gets the job done quite well.

However - in combination tracking/mixing rooms - or small tracking rooms - I would always opt for symmetry and maximum room volume over asymmetry any day of the week.

The loss in room volume (in this case) hurts you much more than any small benefit you might see using an asymmetrical design.

This is not nearly as simple as it might seem on the surface......

Rod

[davecfraser]

Rod, in this case, making the wall I'm building assymetrical will INCREASE my overall room volume (this is due to the placement of a door on the already built interior wall which leads to a basement apartment). In other words if I build it straight I will actually be losing potential studio volume and be adding volume to the adjacent room which will be a hall-way which needs to be a hallway (it's my basement boarder's entrance)

[Rod Gervais]

Originally Posted by davecfraser

Rod, in this case, making the wall I'm building assymetrical will INCREASE my overall room volume (this is due to the placement of a door on the already built interior wall which leads to a basement apartment). In other words if I build it straight I will actually be losing potential studio volume and be adding volume to the adjacent room which will be a hall-way which needs to be a hallway (it's my basement boarder's entrance)

Then make the long side as long as you can possibly make it for the purpose of volume.

Benefits for flutter echo begin around 12 degrees out of parallel, in the case of your 11'-6" width that would translate to one 15' wall and one 17'-4 3/4" wall.

The dimension I mentioned in my earlier post (15'-7 3/4") was for a rectangular room....

Rod

[davecfraser]

Rod, awesome, thanks a lot.

[davecfraser]

Hey Guys

Just wanted to say thanks again for the help, I've almost finished the room (without interior treatment)

The ceiling is 88" tall, the width is 11.5 feet and I built the 4th wall at an angle so the short side is 15' 2" and the longest side goes to about 18'

I've already got 15 bass traps (2 x 4 x 4") so my plan is to put them around the room in the corners and as a cloud above the listening position. I will provide readings as soon as I get the room finished.