RPG Modex Plates (35Hz) placement question

stevekale · Apr 21, 2013

Hi

I have recently purchased 2 of these panels to deal with low-end reverb/accentuation. See room setup below (my equipment rack is in the recess on the right side of the front wall):

The panels are 1m wide (by 1.5m tall) and so there isn't quite enough room to place both panels on the recesses of the front wall. Therefore I was planning on placing them on the very front of the side walls behind the main speakers (as suggested by the supplier). I'm now wondering if they would be better placed on the lower corners of the rear wall. I could run some tests with them leaning against the wall but they're not the easiest of things to move around.

A couple more graphics from REW in case they're helpful (with the first also showing room modes):

Thoughts? (The REW measurements above were before the new heavier and larger carpet went in. This has already made a difference to the sound of the room. On the rear wall I going to place 6 RPG Skyline panels for diffusion. I will then see how all this sounds/measures before looking at additional absorption on the side walls.)

Thanks in advance for the advice

Regards

Steve

PS: the front speakers are Egglestonworks Andra III (isobaric). I do not use the sub for 2-channel audio, only for LFE in video applications although I can use my Theta Casablanca to send LF to the sub and front speakers together. I've not played with this configuration yet but it would effectively be similar to a 3 sub setup. The Andra IIIs are good to 18Hz or so.)

Rutgar · Apr 21, 2013

Hi Steve. I think the front recesses would be the best place for them (placed close to the ceiling). With that said, since you don't have the space there, then I would have to agree with the manufacturer that the next best spot would be behind the speakers on the side walls. It's been my experience that a room has far more bass build up on the speaker end, than on the non-speaker end. And I have found that by placing all of my available bass traps at the front of the room, that I have better results. That's not to say you should ignore the back half of the room. It still requires attention. But I would put the two heavy-hitter modex plates up front.

dallasjustice · Apr 21, 2013

50 hz null is your biggest problem, IMO. I would find out where the 50hz null is coming from. I would guess its length axial mode related but I don't understand your room dimensions from the diagram. If the 50hz null is length related and you can't move your speakers or seat, you must use the modex plates on either the front or back walls.

stevekale · Apr 21, 2013

Rather than thinking of the 50Hz "null", I have been focused on the room modes that are boosting 35/42Hz and 70-100Hz (in particular). All room dimensions are on the diagramme in centimetres. (Ceiling height is 2.3m.) You can see the room modes in the REW chart, colour-coded by type and weighted for strength. But, yes, your point about length-related modes is why I was thinking the rear wall may be better (given the front wall is not an option).

From Bob Gold's calculator:

dallasjustice · Apr 21, 2013

Looks like front or back wall then. What other treatments do you have in your room? Can you move your seat or speakers? I wouldn't dismiss the so called null (SBIR) it will be far more audible and easier to treat than ringing at 35hz.

stevekale said:
Rather than thinking of the 50Hz "null", I have been focused on the room modes that are boosting 35/42Hz and 70-100Hz (in particular). All room dimensions are on the diagramme in centimetres. (Ceiling height is 2.3m.) You can see the room modes in the REW chart, colour-coded by type and weighted for strength. But, yes, your point about length-related modes is why I was thinking the rear wall may be better (given the front wall is not an option).

From Bob Gold's calculator:

stevekale · Apr 21, 2013

These are the first treatments to go in (other than the heavier and larger rug). It's interesting, of the axial modes, as I understand it, 35Hz and 70Hz are length related, 42Hz and 84Hz width related and 74.9Hz height related. It would seem a bit of a crap shoot as to whether front side corner is better than rear corner. Maybe I will have to get out the microphone and run some tests with them idling in each spot. Yes, I can move the seating.

PS: I have 6 150mm RPG Skylines waiting to go on the rear wall once I figure out how to affix them in a way that will allow them to be removed....

Ethan Winer · Apr 21, 2013

I think the rear wall behind you is a better place, but the only way to know for sure is to measure the LF response and ringing with the traps in both locations.

stevekale said:
From Bob Gold's calculator

Mode calculations are useless for this, mainly because they can vary from reality by quite a lot. Again, the correct way to assess an improvement from room treatment is to measure.

Also, nulls are caused by the same reflections as peaks, and often nulls are more damaging. Your waterfall graph is too congested to see what's happening at low frequencies. Better to display only the bass range.

--Ethan

Bruce B · Apr 21, 2013

One thing that I see is your sitting position is supposed to be in the center of the circle that your speakers form. In other words, the distance to your listening position is supposed to be exact for each of the L/C/R/LS/RS

stevekale · Apr 21, 2013

Bruce B said:
One thing that I see is your sitting position is supposed to be in the center of the circle that your speakers form. In other words, the distance to your listening position is supposed to be exact for each of the L/C/R/LS/RS

Unfortunately, often the real world forces some compromises... In this case, there are two inward-swinging doors that cause a problem for the LS/RS. (The distances to the L/R/C are the same, 2m.) If I move the seating forward to provide room for the rears, I approach sitting in the very centre of the room. For the surrounds, I decided to let my Theta Casablanca manage the timing implications of the shorter distance (1.2m instead of 2m).

Ethan Winer said:
I think the rear wall behind you is a better place, but the only way to know for sure is to measure the LF response and ringing with the traps in both locations.

Yes, I suspect there's no shortcut here. Now to find the time to do so...

Here's a closer look at the waterfall below 300Hz. (If there is another cut that would be useful, please let me know.)

Roger Dressler · Apr 21, 2013

Steve,

I think you will get much further toward a bass solution by adding at least one more subwoofer than with any manner of practical bass treatments. Any chance of borrowing one for a while? Does not have to be the same model. Stick it under the center speaker, aiming into the fireplace.

DonH50 · Apr 21, 2013

I would try mounting them across the corners (at an angle so each panel makes a triangle with the corner), either back or rear.

Rutgar · Apr 21, 2013

DonH50 said:
I would try mounting them across the corners (at an angle so each panel makes a triangle with the corner), either back or rear.

I believe Modex Plates do not work like that, and must be flat on the wall.

dallasjustice · Apr 21, 2013

You are on the right track as far as RPG Modex Plates. I have 4 of them in my room. My dealer Scotty Warren and Rutgar (Bill) installed them today. They are by far the most effective and least offensive bass trap ive had in my room, and ive had many. We hung 2 type 2 on front wall and 2 type 1on back wall.
Having said that, you really wont be happy with just 2 modex plate. You should take a much more comprehensive approach.

dallasjustice · Apr 21, 2013

That's right. They are pressure based traps.

Rutgar said:
I believe Modex Plates do not work like that, and must be flat on the wall.

stevekale · Apr 22, 2013

Bruce B said:
One thing that I see is your sitting position is supposed to be in the center of the circle that your speakers form. In other words, the distance to your listening position is supposed to be exact for each of the L/C/R/LS/RS

Thanks for adding the graphic, Bruce. I'm familiar with this. I have made a couple of adjustments to this and a few compromises. My front L/R speakers are spaced more widely but still on the same arc. Eggleston advise a minimum spacing for the Andra III of 7.5 feet. As noted, I had to bring the rear speakers in closer but they're set at the right angle. They're also floor-standing, full-range Eggleston Rosa and so don't tilt downwards. (Under-utilised as surround speakers!) At any rate, for room acoustics I'm focused on 2-channel performance. The Andras do better alone without the Rel Stentor sub, although as I note I may send LF to all three (and surround LF to the two surround and the Stentor).

stevekale · Apr 22, 2013

Roger Dressler said:
Steve,

I think you will get much further toward a bass solution by adding at least one more subwoofer than with any manner of practical bass treatments. Any chance of borrowing one for a while? Does not have to be the same model. Stick it under the center speaker, aiming into the fireplace.

Hi Roger. My wife would happily have someone collect for free my entire audio gear. Adding another speaker would be a challenging exercise. At the moment, my main Krell FPB 200 amp is sitting in the fireplace cavity on a set of Wave Kinetics A10-U8. But I don't see my challenge as a lack of base - rather too much and a lack of decay. I also don't have the challenge of multiple seating positions - my diagramme shows 3 seats but in reality it's 2 armchairs side-by-side which I will exchange for a 2.5 seater couch so I can sit in the middle for audio listening.

stevekale · Apr 22, 2013

dallasjustice said:
You are on the right track as far as RPG Modex Plates. I have 4 of them in my room. My dealer Scotty Warren and Rutgar (Bill) installed them today. They are by far the most effective and least offensive bass trap ive had in my room, and ive had many. We hung 2 type 2 on front wall and 2 type 1on back wall.
Having said that, you really wont be happy with just 2 modex plate. You should take a much more comprehensive approach.

4 - nice! I bet there was a lot of huffing and puffing when they were installed. Mine are Type 2 (effective down to 35Hz). I will start with these and the Skyline diffusers on the rear wall and see how things are from there. If I owned the house I might be more aggressive. You didn't go for the broadband plates in combination with the Type 2?

What did you pay for the plates in the US? The pricing I have seen seems very expensive versus here which is unusual. In USD I paid about $750 per plate (including 20% sales tax). (The Type 1 are a bit cheaper.)

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.

stevekale · Apr 22, 2013

dallasjustice said:
That's right. They are pressure based traps.

They're certainly designed to hang on the wall. That said, I don't see anything in their construction (other than sheer dimensions) which would restrict another implementation. A cavity behind the panel would likely aid absorption. RPG used to make (and, I understand, are presently redesigning) a floor stand for the plates so that they didn't need to be affixed to the wall. But the panels are huge and heavy - 1.5m x 1m and circa 40+kgs - and are designed so as not to need to consume a lot of a room's interior by sitting flat on the wall. (It was the risk of toppling that led to the withdrawal of the floor mount stand.)

Rutgar · Apr 22, 2013

stevekale said:
They're certainly designed to hang on the wall. That said, I don't see anything in their construction (other than sheer dimensions) which would restrict another implementation. A cavity behind the panel would likely aid absorption. RPG used to make (and, I understand, are presently redesigning) a floor stand for the plates so that they didn't need to be affixed to the wall. But the panels are huge and heavy - 1.5m x 1m and circa 40+kgs - and are designed so as not to need to consume a lot of a room's interior by sitting flat on the wall. (It was the risk of toppling that led to the withdrawal of the floor mount stand.)

Someone else here, more knowledgeable then me may want to chime in... but from my understanding, Modex Plates will work best mounted directly on the wall. Because of the way they work, you want them in the highest pressure zone (right off the wall). They were designed with this intent. So standing them out away from a wall would most likely lesson their effect.

It is interesting though, that you mentioned RPG is working on a stand for these. Not for purposes of getting them away from the wall, but it would make them an option to use when there is no wall to attach them to (such as a window, etc.)

stevekale · Apr 22, 2013

stevekale said:
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.

Has anyone used something like Velcro to fix these?

RPG Modex Plates (35Hz) placement question

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