REW cntrl room test plus video tour. Advice?

Merry Christmas to you to, Ale! And a Happy New Year! I'll keep my open for when you bump the thread... I'm enjoying this one! :) :thu: - Stuart -

Soundman2020 wrote:

Merry Christmas to you to, Ale! And a Happy New Year! I'll keep my open for when you bump the thread... I'm enjoying this one! :) :thu: - Stuart -

Hi Stuart! Turns out I can,t stop thinking about all of this, I am trying!!! Hahahaha I was doing some research on the hard backed cloud but I couldn't find much informations. I just can't wrap my head around how it would work. Would the hard back vibrate as a membrane at a specific freq? Also does all of the insulation go under the hard backing? Would 703 be fine? Just trying to plan it for when I am back... Also I started looking at the etc graph and saw a strong reflection within the first 20 milliseconds. I guess I can find out at what distance from the speakers the reflection is taking place and it looks like it's the desk. anyhow! No pressure on any of this, I just wanted to put it on "paper" so I don't forget or go too crazy thinking about this heheh Ale

I was doing some research on the hard backed cloud but I couldn't find much informations. I just can't wrap my head around how it would work.

It does many things at once. Two of those are creating the RFZ in the vertical plane, and helping to break up modal issues in the vertical plane. "Reflection" is the easier to understand: any sound hitting the hard back of the cloud, from either above or below, will "bounce off", and it will "bounce" in a different direction from the one it arrived... simple "mirror" rule: Angle of reflection = angle of incidence, flipped about the surface normal". So if a sound arrive at an angle of 30°, it will also be reflected at an angle of 30°. The second one "modal" is not so obvious. Modes are standing waves, yes, and some people seem to think that because it is a "standing" wave, then it isn't "moving". Wrong. The wave only "stands" in the sense that the peaks and valleys always form at the same locations in the room, but the wave still moves. The energy still moves. There is still a wave front that progresses in the normal manner, by air molecules bumping into each other and passing on the energy. If you put a solid, massive, hard surface in the way, then those collisions happen with the surface, and some of the energy is not transferred through to the other side. But low frequency sound waves also act like pressure changes, not just like particle movement, so this isn't 100% effective in braking up modes, but it does help. At the very least, it can "smear" the mode to be lower, broader Q, which is good. Best case, it does that as well as re-directing part of the energy in a different direction, which basically converts part of the mode from axial to tangential, and that's another good thing. Yes, it can also act like a membrane, flexing along with the pressure changes around it, but it is not a membrane trap, since there is no sealed cavity behind it. However, since it is damped on both sides, it can still absorb some of that energy.

Also does all of the insulation go under the hard backing?

Some below, some on top. I normally do a 2x4 frame with the hard back on top, and fill the 2x4 with insulation, then very thin plastic, then mesh, then black cloth, then the final finish fabric. I also put more insulation in top, since there's stil acoustic stuff happening above the hardback, and porous absorption up there helps.

Would 703 be fine?

Yup!

Also I started looking at the etc graph and saw a strong reflection within the first 20 milliseconds. I guess I can find out at what distance from the speakers the reflection is taking place and it looks like it's the desk.

String test! Zoom in on that problem, and use the tools in REW to measure the distance,rather than the time. That will tell you how much further that specific reflection traveled than the direct path from speaker to mic. So mark a piece of string with that length, tape it to the speaker and to the mic, then move the middle "slack" part around the room to see what surface it touches. Whatever that is, that's where the reflection came from. For example, if you find out from REW that the reflection took a path that is 18" longer than the direct path, and the direct path is 64" (for example!), then the total path is 64+16=82, so get a piece of string, mark it at two points 82" apart, tape one point to the speaker and the other point to the tip of the mic, and there will be 18" of slack string hanging down. Use your finger or a pen to make a "peak" in that string leaving it taught on either side, and move the peak around all over, up and down, side to side, and along the string, to see what it touches. As soon as the peak touches a surface in the room, you have found your culprit. Of course, I don't mean that you tape the string to the speaker cone and the actual mic! :shock: Set up the mic stand without the mic in it, at the same point the mic would have been, and tape it to that. For the speaker, cut a piece of cardboard to the same size as the front baffle of the speaker, poke a hole in the cardboard at the location of the acoustic axis, tie the string through the hole, and tape the cardboard over the entire speaker front. - Stuart -

Soundman2020 wrote:

I was doing some research on the hard backed cloud but I couldn't find much informations. I just can't wrap my head around how it would work.

It does many things at once. Two of those are creating the RFZ in the vertical plane, and helping to break up modal issues in the vertical plane. "Reflection" is the easier to understand: any sound hitting the hard back of the cloud, from either above or below, will "bounce off", and it will "bounce" in a different direction from the one it arrived... simple "mirror" rule: Angle of reflection = angle of incidence, flipped about the surface normal". So if a sound arrive at an angle of 30°, it will also be reflected at an angle of 30°. The second one "modal" is not so obvious. Modes are standing waves, yes, and some people seem to think that because it is a "standing" wave, then it isn't "moving". Wrong. The wave only "stands" in the sense that the peaks and valleys always form at the same locations in the room, but the wave still moves. The energy still moves. There is still a wave front that progresses in the normal manner, by air molecules bumping into each other and passing on the energy. If you put a solid, massive, hard surface in the way, then those collisions happen with the surface, and some of the energy is not transferred through to the other side. But low frequency sound waves also act like pressure changes, not just like particle movement, so this isn't 100% effective in braking up modes, but it does help. At the very least, it can "smear" the mode to be lower, broader Q, which is good. Best case, it does that as well as re-directing part of the energy in a different direction, which basically converts part of the mode from axial to tangential, and that's another good thing. Yes, it can also act like a membrane, flexing along with the pressure changes around it, but it is not a membrane trap, since there is no sealed cavity behind it. However, since it is damped on both sides, it can still absorb some of that energy.

Also does all of the insulation go under the hard backing?

Some below, some on top. I normally do a 2x4 frame with the hard back on top, and fill the 2x4 with insulation, then very thin plastic, then mesh, then black cloth, then the final finish fabric. I also put more insulation in top, since there's stil acoustic stuff happening above the hardback, and porous absorption up there helps.

Would 703 be fine?

Yup!

Also I started looking at the etc graph and saw a strong reflection within the first 20 milliseconds. I guess I can find out at what distance from the speakers the reflection is taking place and it looks like it's the desk.

String test! Zoom in on that problem, and use the tools in REW to measure the distance,rather than the time. That will tell you how much further that specific reflection traveled than the direct path from speaker to mic. So mark a piece of string with that length, tape it to the speaker and to the mic, then move the middle "slack" part around the room to see what surface it touches. Whatever that is, that's where the reflection came from. For example, if you find out from REW that the reflection took a path that is 18" longer than the direct path, and the direct path is 64" (for example!), then the total path is 64+16=82, so get a piece of string, mark it at two points 82" apart, tape one point to the speaker and the other point to the tip of the mic, and there will be 18" of slack string hanging down. Use your finger or a pen to make a "peak" in that string leaving it taught on either side, and move the peak around all over, up and down, side to side, and along the string, to see what it touches. As soon as the peak touches a surface in the room, you have found your culprit. Of course, I don't mean that you tape the string to the speaker cone and the actual mic! :shock: Set up the mic stand without the mic in it, at the same point the mic would have been, and tape it to that. For the speaker, cut a piece of cardboard to the same size as the front baffle of the speaker, poke a hole in the cardboard at the location of the acoustic axis, tie the string through the hole, and tape the cardboard over the entire speaker front. - Stuart -

Stuart! Hope you had a good break with friends and family! Happy new year!! I just got back from home depot... gearing up for the cloud project! Picked up a 4x8 which i cut into a 4x7 for transportation purposes.. I want to have recessed lights and already have the philips hue downlights with cans, I was about to make the 3 holes for the lights when, I STOPPED and thought.... Let's ask Stuart! So, in order to have to 3 downlights i would have to make 3 pretty big holes into the plywood... Is that ok? is there another way? I am not sure if it is safe or possible to enclose those lights.. Let me know what you think! The cloud will be built this week and hung the next one! Cheers Ale

I was about to make the 3 holes for the lights when, I STOPPED and thought.... Let's ask Stuart!

:thu: Very smart move! :) Anything you are unsure about, you should always ask. As one of my teachers used to say, way back when... "The only dumb question, is the one you DON'T ask!".

So, in order to have to 3 downlights i would have to make 3 pretty big holes into the plywood... Is that ok?

We are talking about the hard-back for your cloud, right? The piece of plywood or MDF or OSB that goes on the top side of the cloud framing? If that's it, then no problem: you can cut holes in that. It's mainly there to deal with two things: mid-range reflections, and low frequency modal issues. That's why it is so big, because it is dealing with long wavelengths, many feet long. The size of the hole that you'd cut for a typical light fitting, is just a couple if inches across. It will have a negligible effect on the purpose of the cloud. You should never cut holes in your walls or ceiling, of course! Nor in any treatment surface that relies on resonance or sealed cavities. But it is OK to cut holes in your cloud. If you are going to use a light fitting that gets hot, make sure that you leave plenty of space around it on top: don't put insulation right next to it, not anything else. Leave a gap of a few inches, for safety. Also make sure that all of your wiring is sized correctly to carry the current, and that all your connections are tight and safe. Get an electrician to check it before you turn the power on! - Stuart -

Soundman2020 wrote:

I was about to make the 3 holes for the lights when, I STOPPED and thought.... Let's ask Stuart!

:thu: Very smart move! :) Anything you are unsure about, you should always ask. As one of my teachers used to say, way back when... "The only dumb question, is the one you DON'T ask!".

So, in order to have to 3 downlights i would have to make 3 pretty big holes into the plywood... Is that ok?

We are talking about the hard-back for your cloud, right? The piece of plywood or MDF or OSB that goes on the top side of the cloud framing? If that's it, then no problem: you can cut holes in that. It's mainly there to deal with two things: mid-range reflections, and low frequency modal issues. That's why it is so big, because it is dealing with long wavelengths, many feet long. The size of the hole that you'd cut for a typical light fitting, is just a couple if inches across. It will have a negligible effect on the purpose of the cloud. You should never cut holes in your walls or ceiling, of course! Nor in any treatment surface that relies on resonance or sealed cavities. But it is OK to cut holes in your cloud. If you are going to use a light fitting that gets hot, make sure that you leave plenty of space around it on top: don't put insulation right next to it, not anything else. Leave a gap of a few inches, for safety. Also make sure that all of your wiring is sized correctly to carry the current, and that all your connections are tight and safe. Get an electrician to check it before you turn the power on! - Stuart -

Hi Stuart ! yes correct, hard backed cloud ! here attached a picture of the work in progress. My one question now is: what tipe of hardware should i install on the plywood ? some kind of hook ? do you have a specific suggestion? thank you!

My one question now is: what tipe of hardware should i install on the plywood ? some kind of hook ?

Yes-but-no! :) Keep it all steel, definitely, and use chains, definitely, but nothing "open", such as a hook, which could come loose and dump the whole thing on your head! Use only hardware that can be closed, such as hooks that have a spring-loaded, or sliding, or threaded closure on them, that creates a solid closed circle after it is attached. Also, each attachment should be rated for at least ten times the weight it will carry. So for example, of your cloud weighs 120 pounds, and you have six chains on it, then each chain will be carrying 20 pounds, so each one should be rated to carry at least 200 pounds. Every piece of hardware on each chain should be rated for 200 pounds, minimum. That's the general rule for rigging, stagecraft, gaffers, etc. But there's more to it than that. Look into the best practices for stage rigging, theater rigging, TV studio rigging, etc. and follow those. Hanging heavy stuff above your head needs careful consideration, and careful planning for safety, ... if you value your head! :) - Stuart -

Soundman2020 wrote:

My one question now is: what tipe of hardware should i install on the plywood ? some kind of hook ?

Yes-but-no! :) Keep it all steel, definitely, and use chains, definitely, but nothing "open", such as a hook, which could come loose and dump the whole thing on your head! Use only hardware that can be closed, such as hooks that have a spring-loaded, or sliding, or threaded closure on them, that creates a solid closed circle after it is attached. Also, each attachment should be rated for at least ten times the weight it will carry. So for example, of your cloud weighs 120 pounds, and you have six chains on it, then each chain will be carrying 20 pounds, so each one should be rated to carry at least 200 pounds. Every piece of hardware on each chain should be rated for 200 pounds, minimum. That's the general rule for rigging, stagecraft, gaffers, etc. But there's more to it than that. Look into the best practices for stage rigging, theater rigging, TV studio rigging, etc. and follow those. Hanging heavy stuff above your head needs careful consideration, and careful planning for safety, ... if you value your head! :) - Stuart -

thanks Stuart! sorry i wasnt specific enough, I was wondering on what tipe of attachment my closed hook should have in order to keep it secured on the plywood surface, i imagine i would need as much surface contact as i can with the ply, with, thinking of the same concept of when you hang heavy things off of drywall, where the attachment used expands to hold the weight more securely. Not sure i am able to explain it better.. thaaanks

Attachments can either screw into the wood, or be bolted all the way through it. Same applies to the mounting points on the ceiling. As long as each attachment has three or four screw holes, and you use suitable screws that penetrate deeply into the wood, and they are capable of holding ten times their fraction of the weight, then you should be fine. - Stuart -