John Sayers' Recording Studio Design Forum Archive

DanDan wrote:Soffit or Flush Mounting is common in the higher echelon of studios. It completely eliminates Front Wall BIR and Speaker Cabinet Edge Diffraction. It creates an up to 6dB LF boost, which is benign, often welcome, and easily controlled by the simplest Eq. Result more and extended LF, headroom.
Downside- the modes are driven most efficiently at this pressure zone.

For less than full boundary flush, I suggest googling loudspeakers and open baffle, infinite baffle, etc. etc.

Respectfully DanDan,we are not communicating very well today. If you were to poke back a few posts, you'd see I am not talking about soffit mounting. Glen did a drawing that would visually explain what but it did leave me full of questions.

My questions were pretty specific. I appreciate you taking the time but not sure I'm not being led down a rabbit hole that won't have those answers. Trust me, I've some expertise in rabbit holes.

DanDan wrote:Soffit or Flush Mounting is common in the higher echelon of studios. It completely eliminates Front Wall BIR and Speaker Cabinet Edge Diffraction. It creates an up to 6dB LF boost, which is benign, often welcome, and easily controlled by the simplest Eq. Result more and extended LF, headroom.
Downside- the modes are driven most efficiently at this pressure zone.

For less than full boundary flush, I suggest googling loudspeakers and open baffle, infinite baffle, etc. etc.

Alright, look that the problem this way.

This is the front of the control room. Still a work in progress for treatment as everything got torn out. Sounds 150% better already with the bass traps and ceiling cloud. Now imagine if it looked like this. Now my real wall is two feet away from the back of the monitors. Ok, create a new boundary. What rules apply? My first thought, bass is omni directional. Too small a boundary and bass just goes around? Mass, how much? Its not a real wall nor is it really a baffle. Something in between maybe but to understand how the parameters apply, where to start? Is the answer really go back to my teenage years of speaker building 101?

bass is pretty much omni directional, and SBIR is effectively the "LF comb filtering" effect - distance to wall/ceiling and distance to listening position all determine how much of an effect you experience. so no simple rule or even equation can fully solve it - only suggest starting points. so having a solid surface behind the speakers causes a slight shift in how the particle wave energy actually hits a boundary - or returns from one. hence - "infinite baffles" provide the longest path, and simple porous absorption the shortest (ignoring the angular aspects of wave propagation for the moment). so a set of membranes and porous absorption can be set up to "torture" the wave propagation resulting in attenuation which balances the time and frequency response of the space. size of the space matters because the room "harmonics" define the modes and subsets of modes. and the ideal room has a nice even distribution of modes and related sub-modes for the lowest possible frequency the room supports above being simply "pressurized"...

so - to the chase - you'll want to plat around with the positions and absorption placement to find a good enough balance. that nice large cloud you put up will definitely help. i'm surprised more people don't realize the benefits of quality acoustic tiles in the pursuit of better acoustics on a budget. granted they're somewhat institutional in appearance, but if you're spending all your time staring at the ceiling and feeling sad about them, maybe there's something else you (the royal you) could be doing

cheers!

gullfo wrote:bass is pretty much omni directional, and SBIR is effectively the "LF comb filtering" effect - distance to wall/ceiling and distance to listening position all determine how much of an effect you experience. so no simple rule or even equation can fully solve it - only suggest starting points. so having a solid surface behind the speakers causes a slight shift in how the particle wave energy actually hits a boundary - or returns from one. hence - "infinite baffles" provide the longest path, and simple porous absorption the shortest (ignoring the angular aspects of wave propagation for the moment). so a set of membranes and porous absorption can be set up to "torture" the wave propagation resulting in attenuation which balances the time and frequency response of the space. size of the space matters because the room "harmonics" define the modes and subsets of modes. and the ideal room has a nice even distribution of modes and related sub-modes for the lowest possible frequency the room supports above being simply "pressurized"...

so - to the chase - you'll want to plat around with the positions and absorption placement to find a good enough balance. that nice large cloud you put up will definitely help. i'm surprised more people don't realize the benefits of quality acoustic tiles in the pursuit of better acoustics on a budget. granted they're somewhat institutional in appearance, but if you're spending all your time staring at the ceiling and feeling sad about them, maybe there's something else you (the royal you) could be doing

cheers!

Thanks Glenn,

I mainly was looking to confirm what my intuition was telling me with this. I'm trying to add to my knowledge base for when I can afford other monitors. Even dug out my old Master Handbook of Acoustics 3rd Edition. Did a lot of reading over the weekend. It gels slowly at my age. Wish I was better at asking the questions. Would make it easier for everyone.

Next step after I complete the filling in middle is going to be working out a long series of REW measurements with 3 different pairs of monitors and see what orientation and listening position yields the best results for at low bass response. Lengthwise with the angled ceilings may not be the right position as I've had trouble as I move out into the room. The waterfall graph shows the problem. I can even out the bass but it is substantially lower than the rest of the bandwidth. I may try the other direction but would have to face away from the live room to keep it symmetrical.

As to the cloud, it is super light and was cheap and easy. 8ftx8ft barely over 40lbs.

A quick update. Got my listening and speaker placement settled. Took a lot of measurements but I've got what I hope is a workable baseline given the odd shape of the room.

The room has a flat ceiling that is 12'6" x 8ft in which I placed an 8x8 cloud. That left me some flexibility on the side walls where the ceiling joins. Decided on 12 inch of R38 beginning flush at the top of the front bass traps and across the flat ceiling. This maintains a decent ceiling height in the middle of the room and hopefully enough low end absorption at the sides.

Here is the baseline measurements. With the angled ceiling, it is hard to figure out all the variables but some RTA testing and mock up has me thinking this will help enough with the 120Hz dip to get +/- 2db across the pressure region. Hoping it helps somewhat with the huge null at around 400Hz but still have a lot of untreated surface area left still. I'm a fix the tough issues first kind of guy.

More open framed traps. Z-clips arrive today and fabric later this week. Then hope to measure and re-evaluate.

Now my real wall is two feet away from the back of the monitors. Ok, create a new boundary. What rules apply? My first thought, bass is omni directional. Too small a boundary and bass just goes around? Mass, how much? Its not a real wall nor is it really a baffle. Something in between maybe but to understand how the parameters apply, where to start? Is the answer really go back to my teenage years of speaker building 101?

Many of us wonder about this. I frequently opine that I do not think a small area, e.g one trap, behind a speaker is enough to do mitigate the lower frequency SBIR caused by it's thickness.
But if I understand you correctly you are suggesting a whole boundary of 2' treatment.
It would be great to see the results before and after if you actually do this.
I do note that the late great Boggy achieved great LF results with 2' treatment.
There is an option. Speakers almost touching the real boundary, sunk into deep fibre treatment. On might say Soft Soffit or Pseudo Soffit.

DanDan wrote:

Now my real wall is two feet away from the back of the monitors. Ok, create a new boundary. What rules apply? My first thought, bass is omni directional. Too small a boundary and bass just goes around? Mass, how much? Its not a real wall nor is it really a baffle. Something in between maybe but to understand how the parameters apply, where to start? Is the answer really go back to my teenage years of speaker building 101?

Many of us wonder about this. I frequently opine that I do not think a small area, e.g one trap, behind a speaker is enough to do mitigate the lower frequency SBIR caused by it's thickness.

But if I understand you correctly you are suggesting a whole boundary of 2' treatment.

I have this in the back wall already. I had asked for insight into possibly doing this for the entire front. I did end up mocking it up both with and without a boundary in front of the monitor. Perhaps because the side walls still need to be done but it did not measure well when I tested it.

It would be great to see the results before and after if you actually do this.
So if you look at the picture, you'll note the monitor hugs up against the front bass trap. Move it towards the center and I get a even bigger dip at 120Hz. I even tried moving the bass trap out and was even worse. I mocked up a 12inch trap and moved the monitors outward but that was a no go either. I am pretty sure it is a combination of that front angle at the knee wall/ceiling junction and sidewall interaction along with two sets of corners on the way up to the flat ceiling.

I do note that the late great Boggy achieved great LF results with 2' treatment.
There is an option. Speakers almost touching the real boundary, sunk into deep fibre treatment. On might say Soft Soffit or Pseudo Soffit.

These are temp monitors I am using for figuring out the room. I have a measured curve for them as a reference. Not ideal but am learning a lot about how to tune the room.

So I figured out what I think is a workable listening position (shown in the measurements) but still have a lot of treatment left. Good news is I am reasonably out of the pressure region. I'll get this round of bass traps up starting at the front bass trap on both sides and up and around to the back. These are only 12inches thick and the cloud is 10 covering the rest of the flat ceiling. I am hoping this gets me to +/- 2db at the bottom end. I am close except that dip at 120Hz. Then of course I hope that big null between 300-500Hz isn't a monster to deal with. Room already sounds a whole lot better and I am not even nearly close to done.

DanDan wrote:

Now my real wall is two feet away from the back of the monitors. Ok, create a new boundary. What rules apply? My first thought, bass is omni directional. Too small a boundary and bass just goes around? Mass, how much? Its not a real wall nor is it really a baffle. Something in between maybe but to understand how the parameters apply, where to start? Is the answer really go back to my teenage years of speaker building 101?

Many of us wonder about this. I frequently opine that I do not think a small area, e.g one trap, behind a speaker is enough to do mitigate the lower frequency SBIR caused by it's thickness.
But if I understand you correctly you are suggesting a whole boundary of 2' treatment.
It would be great to see the results before and after if you actually do this.
I do note that the late great Boggy achieved great LF results with 2' treatment.
There is an option. Speakers almost touching the real boundary, sunk into deep fibre treatment. On might say Soft Soffit or Pseudo Soffit.

A quick image of filling in the middle. I also tried 1 inch of plywood and even placing the monitors between the two frames, stuffing insulation above and below the monitors. The room has an odd interaction going on with the slope and knee wall along with the extra corners they bring.

because it's an odd shape, it won't respond like a rectangular box when trying to assess calculated modes versus measured. so empirical testing is really the only way to go besides simply moving things around and deciding what sounds best to you.

so the plywood behind each monitor did not effect the response?

gullfo wrote:because it's an odd shape, it won't respond like a rectangular box when trying to assess calculated modes versus measured. so empirical testing is really the only way to go besides simply moving things around and deciding what sounds best to you.

so the plywood behind each monitor did not effect the response?

Oddly enough, the room modes checked out with a sub in the corner and then taking the measurements upside down (center and floor vs center and ceiling). All but one tracked pretty close to model which I attribute to an odd measurement position.

Plywood had an effect, just not exactly positive. Also didn't do enough extensive testing of various position options.

I really just think I need to work my way up from low frequency and work out the rest of the room before tackling the front for soffit, soft soffit or hybrid. I can build what ever is needed cheaply enough and change it around without high costs. So I want to get the room to a good starting position first.

Z-clips arrived, still waiting on fabric and I can start placing and testing. I ordered nearly 100 yards of fabric so I'll have enough for the live room. Part of this testing and analysis is to also understand how the ceiling is affecting room response. I need to make the live room work with mics.

When I see the words 120Hz dip, my mind goes straight to floor bounce.
Try move the mic towards such a suspected bounce, i.e. a spot on the floor half way between mic and speaker. If the frequency of the dip increases......

DanDan wrote:When I see the words 120Hz dip, my mind goes straight to floor bounce.
Try move the mic towards such a suspected bounce, i.e. a spot on the floor half way between mic and speaker. If the frequency of the dip increases......

Yes, I've confirmed floor bounce but the measurements lead me to think it is more complicated than that. I have taken hundreds of measurements. These include monitor height, lateral and forward placement along the wall, multiple room orientations and listening positions. There appears to be a number of equal related distances between the floor and ceiling along with angled ceiling and side wall. I can influence this dip in nearly any direction.

The dip at this point is 1db down from my goal of +/-2db and there is still a lot of untreated wall space. I finished up one side of the ceiling traps last night and will do the other this evening. Then will measure to see what if any impact treating these corners have. I'll be out of corners by that point and will move on to wall treatment with hopes I'll be dealing with just 500Hz and above.

Fabric arrived this week and I finally started getting some up. Back wall will get some stained trim around the edges and seams. but good to see some color.

nicely done! are you going to add a strip of adhesive backed cloth over the staples? (like an iron-on or steam-on type?)

gullfo wrote:nicely done! are you going to add a strip of adhesive backed cloth over the staples? (like an iron-on or steam-on type?)

I have some rough sawn pine boards I'll cut into trim pieces and stain with a slate grey color. Same with a baseboard and thin strip for the top edge to give it a unified look.