RPG Modex Plates (35Hz) placement question

[audioguy]

PS: if anyone has ideas for fixing the Skylines so that they can be removed without making a complete mess of the wall I'm interested.

Depends on what your definition of a complete mess is



I am using heavy duty Velcro from Home Depot. BUT, do not put the sticky side on the wall or, by any definition, you will have a mess (I know ... I've done that many times and that is how I am currently mounting them).

Leave the protective covering on the side that goes on the wall and use a heavy duty staple gun to hold the Velcro to the wall. But do use the adhesive side on the Skylines. You will still need to touch up the wall when they are removed but nowhere near the extent if you apply the sticky side.

I have not tried this but someone makes wall hangers that can be used on walls and will not remove paint. I would go to Loews and see what they might have that uses a similar approach.

Let me know what you find out as I will be moving into a new house/new room in 5 or 6 months and will need to apply these yet again.

 

[stevekale]

LOL! Thanks for the advice! I wish we had a Loews here in London. I was indeed thinking of affixing the Velcro directly to the wall... After a bit more reading (funnily enough including a thread on AVS which included Rutgar) I'm thinking that tacking with pin nails four (or even just 3) 6ft strips of MDF or Hardboard to the wall will make the most sense. (I want to place them in a solid 3x2 block.) I could then either glue the panels to the (furring) strips or use Velcro to attach the panels to the strips. This way I only have a few fine nail holes to tidy up. I guess the downside, though, is they will sit 3mm off the wall (or more if Velcro). How much Velcro is needed per panel?

 

[DonH50]

Oops, missed the technology, sorry.

Quick hand-waving, Ethan or somebody feel free to correct:

1. Typical absorbers (filled panels) are velocity based. They work by taking the energy from the sound waves and converting to heat in the absorbing material (it's only a little heat, you won't hurt your panels by playing too loudly, just your ears). Velocity is zero (or very close) right as against a wall (sound waves stop and then reverse as they bounce off the wall) so they work better when spaced out from the wall a bit where the velocity is higher. That is the oft-mentioned air gap.

2. Pressure-based absorbers use the pressure differential to absorb sound. Pressure is actually highest where the sound waves hit a wall, so they should normally be flush-mounted for maximum efficacy. As you move off the wall, velocity is higher but pressure reduces, and pressure-based absorbers become less effective.

A loose analogy is water waves. Velocity is highest in the open ocean, slowing and then stopping as they hit a wall. Velocity is 0 right at the wall. Pressure is lowest out in the open, increasing as you approach and then hit a wall.

HTH - Don

 

[Rutgar]

Has anyone used something like Velcro to fix these?

I had a bunch of Skylines years ago, which I had on the ceiling. I used Velcro to place them. Several fell off. Not from the Velcro failing, but from the adhesive on the Velcro failing. The wall might work a little better. Frankly, I didn't like what the Skylines did on the ceiling to my sound, and sold all of them. For the ceiling, I like what 3 to 4 inch thick RPG BAD panels do, better than the skylines. On my back wall, I have a bank of RPG Diffractals across. A friend of mine just installed BAD panels on his back wall (and on some other key points in the room), and it sounds really good. He is also using Modex Plates.

In the photo below, you can see the diffractals. You can also see some of the RealTraps, under the Diffractals. But I have since removed them, and relocated them to a more effective place in the room.

 

[Ethan Winer]

Quick hand-waving, Ethan or somebody feel free to correct:

You got it exactly.

--Ethan

 

[stevekale]

Cheers guys. They'll be on the wall - I just need to figure out which walls given I'm 8cm short on the left side for them to go on the front wall recesses. Aesthetically the very front of the side walls would be next best. I also then don't have a problem with the inward-opening doors. But I will take some measurements with them leaning against the relevant walls to compare acoustic impact.

Any rules of thumb re height of placement of panels such as the Skylines? I have 2x59.5 = 119cm vertical and 3 x 59.5 = 178.5cm of width. Ceiling height of 229cm (i.e. 7.5 ft; w/ wall width of 412cm). I was thinking 80cm off the floor, leaving a gap of 30cm between the tiles and the ceiling (or perhaps a fraction lower). I don't think dead-centred would "look right" but is there any rule of thumb for sound quality?

 

[audioguy]

I had a bunch of Skylines years ago, which I had on the ceiling. I used Velcro to place them. Several fell off. Not from the Velcro failing, but from the adhesive on the Velcro failing.

I had the same issue until I stapled them (hand stapler purchased at hardware store) in all four corners to the ceiling. I used pieces of Velcro about 2' x 2'.

In my next room I don't know what I will be using but given I have used these Skylines in 4 different theaters and painted 5 different colors, I sure got my use out of them.

 

[stevekale]

I should mention this wall is solid plaster (main load-bearing wall of an old Victorian house). A staple gun may struggle/chip the hell out of the plaster.

2 feet x 2 feet?

 

[Rutgar]

Steve, these pics may interest you.

Here are some photos of my friend Scott's room (a Jeff Hedback design):

In the first photo, all 5 treatments on the front and side walls are Modex Plates. The treatments on the ceiling are RPG BAD panels.


This photo show the back wall. All treatments are RPG BAD panels of varying sizes and thicknesses.

 

[stevekale]

In the first photo, all 5 treatments on the front and side walls are Modex Plates.

Wow! That's a lot of Modex plates. Interesting he went high rather than as low as possible.

 

[stevekale]

These pics may help illustrate my front wall... If I owned the place it wouldn't look this way at all... The centre speaker is currently at Eggworks getting upgraded to Andra III spec.

And the rear corners/doors:

Left

Right

 

[DonH50]

Unfortunately those alcoves are nice little resonant chambers. But, too short for 35 Hz from what I can tell, so I would place the panels along the back aide wall corner, back wall, or front side wall (nearly beside the speakers, beyond the alcoves). In that order. If the back wall is not treated you might consider adding broadband treatment there (absorbers or diffusors).

 

[Roger Dressler]

But I don't see my challenge as a lack of bass - rather too much and a lack of decay. I also don't have the challenge of multiple seating positions

Hi Steve,
My suggestion had nothing to do with adding more bass, but to deal with the dramatic response swings for which you are seeking relief with traps. Adding a 2nd sub could have a significant effect on that. Have you seen the Welti papers on this subject?

Your sub's response looks much as mine did when I used a single sub. I went for 4 but that was probably not necessary. It's a low-commitment thing if you can do the experiment with a borrowed sub.

 

[stevekale]

Hi Steve,
My suggestion had nothing to do with adding more bass, but to deal with the dramatic response swings for which you are seeking relief with traps. Adding a 2nd sub could have a significant effect on that. Have you seen the Welti papers on this subject?

Your sub's response looks much as mine did when I used a single sub. I went for 4 but that was probably not necessary. It's a low-commitment thing if you can do the experiment with a borrowed sub.

Understood Roger. Just for clarification, for the measurements posted above, there is no sub operating - just the two Andras. Your arguments are why I was thinking of sending a crossed-over LF signal (via the CB) to the sub as well. I would then have LF coming from 3 points instead of two. It was papers posted by Amir that made me move the sub to where it is shown in prep for this experiment (albeit those papers had the third sub elevated to the ceiling which I'm not about to do with a 50kg brick).

 

[stevekale]

Unfortunately those alcoves are nice little resonant chambers. But, too short for 35 Hz from what I can tell, so I would place the panels along the back aide wall corner, back wall, or front side wall (nearly beside the speakers, beyond the alcoves). In that order. If the back wall is not treated you might consider adding broadband treatment there (absorbers or diffusors).

The problem with "back ide wall corner" is the two doors into the room. With the front side walls, surely the pressure will be greatest right in the alcove, right up against the front wall. (On the right side wall near the speaker is a window.) I took a closer look last night at the rear wall and I have another problem there - the right side (4th pic) door is not inset very far from the corner. (Both doors have their hinges in the corner.) So placing the Modex Plate in this corner will impair the door. On the other side (3rd pic) the door is set away from the corner enough that this isn't a problem. The bulk of the rear wall will be covered by the Skylines.

These old houses are a mish-mash of haphazardly placed objects. Sigh...

 

[Rutgar]

The problem with "back ide wall corner" is the two doors into the room. With the front side walls, surely the pressure will be greatest right in the alcove, right up against the front wall. (On the right side wall near the speaker is a window.) I took a closer look last night at the rear wall and I have another problem there - the right side (4th pic) door is not inset very far from the corner. (Both doors have their hinges in the corner.) So placing the Modex Plate in this corner will impair the door. On the other side (3rd pic) the door is set away from the corner enough that this isn't a problem. The bulk of the rear wall will be covered by the Skylines.

These old houses are a mish-mash of haphazardly placed objects. Sigh...

When we installed some Modex Plates at another friend's house (who is also a member here, and may chime in... you know who you are Michael!), he had a similar situation with his door right to the corner where he wanted to place the Modex Plate. To make matters worse, he had the light switch to room, just on the other side of where the Modex Plate needed to go. We ended up squeezing the Modex Plate up to the light switch, as close as possible (the lip of the plate actually overlaps the light switch). This left only a few inches between the corner and the plate. But, those few inches were enough to allow the door to open almost all of the way. In your case, your door looks like the main door to the house. So you probably don't want to impede that door at all. But I would think you could still place the Modex Plate there, as long as you allowed maybe 6 inches or so from the corner where the door is. You might try just placing one on the floor (having someone holding the plate as flush as he can against the wall) and testing the swing of the door. Keep in mind the base board will probably kick the plate out just a bit, so the clearance will be even better once the plate is mounted on the wall. If you like that, the other suggestion I would have, would be place a long door stop on the base board so the door doesn't swing open, hit the Modex Plate, and damage it.

 

[dallasjustice]

Bill is ths world record holder for most modex plates installaed in one weekend. Was it 9 total (3 type 2)? They all look great too!

When we installed some Modex Plates at another friend's house (who is also a member here, and may chime in... you know who you are Michael!), he had a similar situation with his door right to the corner where he wanted to place the Modex Plate. To make matters worse, he had the light switch to room, just on the other side of where the Modex Plate needed to go. We ended up squeezing the Modex Plate up to the light switch, as close as possible (the lip of the plate actually overlaps the light switch). This left only a few inches between the corner and the plate. But, those few inches were enough to allow the door to open almost all of the way. In your case, your door looks like the main door to the house. So you probably don't want to impede that door at all. But I would think you could still place the Modex Plate there, as long as you allowed maybe 6 inches or so from the corner where the door is. You might try just placing one on the floor (having someone holding the plate as flush as he can against the wall) and testing the swing of the door. Keep in mind the base board will probably kick the plate out just a bit, so the clearance will be even better once the plate is mounted on the wall. If you like that, the other suggestion I would have, would be place a long door stop on the base board so the door doesn't swing open, hit the Modex Plate, and damage it.

 

[microstrip]

Although I am not an expert, I will risk an opinion - if I am completely wrong we will learn from the experts corrections!

Looking at your dimensions and graphs it looks that most of your ringing is due to the second order modes of 4,12 (84Hz) , 4,9 (70Hz) and 4,4m (78Hz) (4.9 minus the chimney depth). As the 70 Hz looks to be the worst I would put the Modex plates in the back wall near the corners.
I would not place them in the alcoves wall - the front area of the chimney is larger than the area of the alcove and the chimney can't be ignored in the overall problem. Putting them in the back will help for all front wall reflections.

In order to compensate the null at 50 Hz you don't need a large subwoofer - it will have to work mainly between 40 and 60Hz. But it must be placed far from the main speakers. Perhaps moving the existing sub or just putting an good DSP based equalizer can help.

All IMAO (in my amateur opinion).

 

[Roger Dressler]

Understood Roger. Just for clarification, for the measurements posted above, there is no sub operating - just the two Andras.

Ahh! Ok, then please proceed. Will await your results.

 

[stevekale]

Ahh! Ok, then please proceed. Will await your results.

A quick play around this evening with xover to sub. Modex Plates unboxed in front corners on side walls - leaning against rather than properly installed. Skyline panels not installed. New larger rug in place (versus previous measurements.)

Three measurements below. One, just the Andras running full range (green). Two, sending a low frequency pass to the sub (positioned as shown in diagramme) with Butterworth xover @ 100Hz, slope 24 (i.e. aggressive). Three, same as two but xover set at 160Hz. All 1/3 octave smoothing.

I thought the effect of using the sub on the very low end was rather interesting...which would you prefer?

1/6th octave smoothing:

A few other charts, all without the sub.

Full range SPL:

Waterfall is improved:

RT60 seems to be much better than before:

Same with spectrogram: