Angled walls to be made of sheetrock or burlap

[Andy Brook]

Hi everyone

I already posted about this in the design forum but I think it may be of more relevance here:

http://www.johnlsayers.com/phpBB2/viewt ... 28#p132728

Basically I need to make a decision as to whether my frame work is lined with plasterboard or with burlap - with the the cavity filled with rockwool.

studio speaker new wall angles plan.jpg

If the walls use sheetrock - will this create a 3 leaf system? (outer wall/inner wall/sheetrock) If they are burlap - will the room modes be governed by the internal concrete walls (meaning the framing has no real effect)

[stevev]

hi andy,

If the walls use sheetrock - will this create a 3 leaf system? (outer wall/inner wall/sheetrock) If they are burlap - will the room modes be governed by the internal concrete walls (meaning the framing has no real effect)

Yep, you'll create a 3 leaf system. thou shalt not build a 3 leaf system (although I had to on my ceiling construction for various reasons so I'll probably go to hell for eternity)

Yep, your room modes will be governed by the internal concrete walls.

you'll want the surface that your monitors are soffit mounted in to be hard and dense. Plasterboard probably wont do the trick unless it's perhaps two layers of 16mm. The wall between the two soffit faces needs to be soft faced and insulated. There's plenty of detailed info on soffit mounting on the forum.

That desk built right up to the walls will probably cause you some grief with 1st reflections and possibly bass build up in the adjoing corners. Possibly a free standing desk a little further back and slightly more toe-out on your monitor angle, with the bottem of the soffits built the way John describes in the manual.

Your splayed walls want to be permeable with insulation to stop the first reflections. Again, you'll find everything you need about creating an RFZ on the forum, but the basic gist is that you don't want a hard surface at your points of first reflection. (the floor being the only exception)

Looking at the size of that room you'll need some serious bass trapping in the back corners and wall. Not sure if that's possible if those windows are already in place, but it would be worth not having windows there if it's a choice between them or bass trapping.

cheers,

steve

[Andy Brook]

Hi Steve - thanks for your response

That desk built right up to the walls will probably cause you some grief with 1st reflections and possibly bass build up in the adjoining corners.

I didn't consider any issues from having the desk right into the soffits/wall but that makes a lot of sense. The desk isn't built yet and the mackie can be placed further from the front wall - I just don't want to lose the critical listening position as its worked out very well in terms of the 38% ratio and speaker triangulation.

Possibly a free standing desk a little further back and slightly more toe-out on your monitor angle,

Sorry but I didn't understand what toe-out means - would you mind explaining?

Your splayed walls want to be permeable with insulation to stop the first reflections. Again, you'll find everything you need about creating an RFZ on the forum, but the basic gist is that you don't want a hard surface at your points of first reflection. (the floor being the only exception)

Thank you! That really helps - I'll dig further but the basics helps a lot

Looking at the size of that room you'll need some serious bass trapping in the back corners and wall. Not sure if that's possible if those windows are already in place, but it would be worth not having windows there if it's a choice between them or bass trapping.

The openings are doors and unfortunately they are already there. There was physically nowhere else they could be placed. I was hoping to use the ceiling above the sofa to put in some serious bass trapping.

I ran the figures through the online calculator at http://www.bobgolds.com. The spacing between modes look quite promising and the bonello graph yields a smooth curve. In all honesty should I be worried about tangential and oblique modes as much as the axial ones?

bonello curve.jpg

I've been trying to find software to perform a ray trace too but had no success. I've taken the trial download of Odeon and though it is supposed to support sketchup models it won't support the skp format. Can anyone suggest any better options to use?


Andy

[andy_eade]

Hey Andy,

Stuart kindly gave me some great instruction on Ray Tracing in Sketchup (typically what most folks around here use to do this). It actually didn't too long - especially once I added the raytracer plugin.

The class begins towards the bottom of page 3:

http://www.johnlsayers.com/phpBB2/viewt ... 7&start=30
Cheers for now,

Andy

[stevev]

Sorry but I didn't understand what toe-out means - would you mind explaining?

monitor angle.jpg

If you set your monitors and yourself up as an equilateral triangle, then 'toeing out' is aiming the focal point of the monitors behind the listening position. So you physically turn the monitors to create a slightly wider angle than your equilateral triangle.

I think I went through this in a bit more detail in my build thread, 'dog and bear studio' under 'other studios', with Stuart and others. Actually I think there might be a fair bit there about monitor placement and not getting too hung up about the 38% rule

The openings are doors and unfortunately they are already there. There was physically nowhere else they could be placed. I was hoping to use the ceiling above the sofa to put in some serious bass trapping.

Yep anywhere you can get bass trapping on that back wall is going to help you. You can probably get some on the back wall itself behind and above the sofa.

In all honesty should I be worried about tangential and oblique modes as much as the axial ones?

This is the point at which my knowledge gets a little thin You'll need John or Stuart (Soundman2020) or someone with the same kind of knowledge to help out on this question.

My view on it with out being able to give you the maths, is that in that size room the more bass trapping you can get on the back wall and corners the better. Make sure you use the right density product for fiberglass or mineral wool.

cheers,

steve